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- Front Matter: Volume 11170
- 14th National Conference on Laser Technology and Optoelectronics (LTO 2019)
Front Matter: Volume 11170
Front Matter: Volume 11170
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This PDF file contains the front matter associated with SPIE Proceedings Volume 11170, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.
14th National Conference on Laser Technology and Optoelectronics (LTO 2019)
Structural parameters optimization of lens hood based on a kind of surrogate model
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With the wide use of earth-based laser communication system, more and more engineers like to pursue the design of lightweight structure. Nowadays, engineers often firstly depend on the project experience to design the lens hood, then make analysis based on finite element method to verify its feasibility, but it costs too much time. The paper attempts to give a new optimization design method. Surrogate model are widely used in the fields of aerodynamics parameters optimization, but barely used in design of optical structure. The paper makes an optimal design about lens hood with wide aperture based on surrogate model. First of all, the paper generates some samples by finite element method; secondly, uses the samples to get the surrogate model by surface interpolation; then finds the optimal solution by surrogate model and constraint conditions. The aperture of the lens hood in this paper is 450 mm. One end of the lens hood is attached to main structure, and the other end is free. Middle part of the lens hood is supported by rods which are made of carbon fiber. The optimization variables in this paper is the thickness of the lens hood and the location of the supports robs. The purpose of the optimization is to find the case that the weight is light and displacement of the free end is small. It will not let the miscellaneous light make a negative effect on incident or outgoing path of light. In other words, it will ensure the quality of imagining or effect of detection. The appropriate solution is found by the method proposed in this paper.
Effect of salt content on the photoacoustic detection of glucose solutions
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In this paper, the effect of salt content on the photoacoustic detection and the concentration prediction of glucose was experimentally investigated. The photoacoustic detection system of glucose based on optical parameters oscillator (OPO) pulsed laser and the non-focused ultrasonic transducer in the lateral model was established. The test phantom aqueous solutions combined different salt contents and the different concentrations of glucose were prepared. The test solutions were divided into two types according to the different salt contents, i.e., the lower salt contents (100-500mg/dl) and the higher salt contents (1-4g/dl). Based on the established experimental system, the time-resolved photoacoustic signals and peak-to-peak values of test solutions with different salt contents and different glucose concentrations were all obtained. The linear fitting models for each salt content were established to predict the glucose concentration. Experimental results show that, with the increase of the salt content and glucose concentration, the photoacoustic amplitude increases with the salt content and glucose concentration. The root-mean-square error (RMSE) values of the predicted glucose for the test solutions with lower salt contents are less than that of the higher salt contents. The RMSE value of glucose concentration for the test solutions with the salt content of 100mg/dl is about 13.61mg/dl, its correction coefficient reaches 0.99211. For the test solutions with the salt content of 3g/dl, the RMSE value of glucose concentration is about 62.36mg/dl, its correction coefficient is about 0.85294. Therefore, the influences of higher salt contents on the photoacoustic detection and glucose concentration prediction are more serious than that of the lower salt contents.
Study on EM wave guiding performance of the femtosecond laser plasma filament
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As a kind of special electromagnetic medium, femtosecond laser plasma has the potential of transmitting the electromagnetic wave. In this paper, a theoretical study on 6 GHz EM wave guiding performance of the plasma filament is carried out with the software XFDTD. Then, an experimental setup for the interaction between the EM wave and the plasma filaments is established. Based on the data measured by oscilloscope, the transmission properties of the EM wave along the filament are obtained. The results show the electric field is enhanced out of the waveguide with the plasma filament. The guiding performance of the plasma filament on the TE polarization wave is better than that on the TM one, which is consistent with the experimental results. For TE polarization wave, the plasma filament can reduce the transmission pulse energy greatly and the attenuation is up to 3.5 dB in the experiment. The research results show that the laser plasma filament can provide efficient transmission of the EM wave energy.
Transmission characteristics of long-period fiber gratings via radiation of femtosecond laser
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The effects of pulse power, filling ratio, number of period and period on the long-period fiber gratings (LPFGs) by using radiation of femtosecond laser. The results show that the strong resonance peaks of LPFGs can be induced and the resonant peaks have different degrees of offset. When the parameters of the LPFG are set to be number of grating period of 70, filling ratio of 0.5, pulse power of 2.0 mW and period of 500 μm, the first resonance peak of LPFG has a blue-shift of 147.3 nm. Furthermore, the size of first resonance peak of LPFG is -19.4 dB. These characteristics of LPFGs provide a favorable opportunity for in-depth research of late-model sensing devices.
Effect of C6H12N4 on infrared radiation performance of Pb3O4 / Mg / PTFE infrared decoy
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In order to study the effect of adding hexamethylenetetramine (C6H12N4) on the infrared radiation properties of a mixture decoy of Pb3O4/PTFE/Mg, a formula of Pb3O4/PTFE /Mg = 10: 3: 7 was taken as a basic formula, and different content of C6H12N4 was added in the basic formula to design seven different pharmaceutical formulations. The Combustion process of samples was recorded using a 3-5 micron mid-infrared thermal imager, and the burning time, mass burning rate, radiation area, radiance, as well as the radiation intensity of each sample were calculated. The experimental results show that with the continuous addition of C6H12N4, the combustion temperature of the samples increased firstly and then decreased, besides, the combustion time became longer while the mass burning rate became smaller, when the proportion of additives reached 6%, the temperature came to its maximum of 916.76°C and the radiant brightness was increased from 10956.50 W/m2/Sr to 13517 W/m2/Sr. The longest combustion time was 9.32s with the lowest mass burning rate of 1.72g/s when the proportion of additives reached 15%. And the radiation intensity was increased from 1079.05W/Sr to 1254.1W/Sr when the proportion of additives reached 9%. This showed that the appropriate addition of 6% to 9% of C6H12N4 in the basic formulation contributes to the improvement of the combustion performance and radiation performance of the Pb3O4/Mg/PTFE decoy.
Analysis of heat dissipation characteristics of selective low emissivity materials
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In order to verify the heat dissipation characteristics of selective low emissivity materials, the traditional low emissivity materials and selective low emissivity materials were coated on the oxidized steel surface, and the heat transfer model between the target and the dark room was established. Finally, the heat dissipation characteristics of selective low emissivity materials were simulated, and the effects of the emissivity and the darkroom temperature on the heat dissipation characteristics of selective low emissivity materials were analyzed. The results showed that for high temperature targets, selective low emissivity materials had better heat dissipation characteristics than traditional low emissivity materials. The lower the emissivity in mid-far infrared bands, the better the heat dissipation characteristics of selective low emissivity materials. When the ambient temperature of the dark room fell from 30°C to -30°C, the lower the temperature, the better heat dissipation characteristics of selective low emissivity materials.
3-D measurement based on phase-shifting using calibration of light plane
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Based on the phase-shifting fringe scanning projection technique using MEMS galvanometer, the threedimensional shape measurement of the object can be realized. However, we found that the experimental results were more sensitive to some experimental parameters. To avoid it, we introduced a light plane calibration model in the threedimensional measurement system. This calibration model avoids the physical measurement of some experimental parameters, and at the same time makes the operation more convenient and faster, and improves the stability and operability of the experiment. Through the detection experiment of the plane, the relative root mean square relative error of the obtained result is 9.155mm, which is greatly improved compared with the previous experimental results, but the result is still not ideal. We discuss some factors affecting the accuracy of the system which can be improved in the future. The experiment proved its feasibility and potential, and the Powell prism and MEMS galvanometer selected are small in size. The dimensions of Powell prism and MEMS galvanometer are 9.0mm 8.0mm and 2.5mm 3.0mm respectively. The miniaturization of equipment is very advantageous for achieving integration and maintenance of the device.
Research of in-phase supermode in 16-core Ho3+-doped fluorotellurite photonic crystal fiber lasers
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16-core photonic crystal fiber (PCF) was designed. In order to obtain spatially flat in-phase modes, the super-mode near- field properties were studied through method of numerical simulation calculation and according to coupled mode theory. On the based of the scalar Fraunhofer Diffraction, a far- field in-phase super-mode theoretical modeling was presented. According to the modeling, one discussed the influence of the random phase perturbation, the random amplitude perturbation and the polarization direction perturbation on the far-filed intensity distribution, in detail. The results show that both phase perturbation and amplitude perturbation sharply impact the far-filed distribution of interference intensity and contrast. However, the influence of the polarization direction perturbation is not obvious. When the parameterδ, μ and ▵ increases, the field center intensity decreases and the power of the central spot also does, which means the profile of the spot will blur and the beam quality drop.
Study on transmission attenuation of 10.6μm laser in different weather
Xuan He,
Bing Zhou,
HeXiong Kiu,
et al.
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The 10.6μm laser has a wide range of applications in the military field. The various phenomena occurring during the atmospheric transmission of the laser are highly random, and the factors causing the energy dissipation are complex and variable, so it is difficult to obtain an accurate attenuation coefficient. At present, in this field, the research in sunny weather conditions is relatively mature, and the attenuation studies under three special weather conditions of fog, rain and sandstorm are rare. In order to meet the actual needs, this paper derives a simple calculation method for the attenuation coefficient of 10.6μm laser atmospheric transmission on the basis of summarizing the existing research, which can meet certain accuracy requirements in three weather conditions: fog, rain and sandstorm.
Research on the effect of picosecond laser surface texturing on metal surface properties
Xuanjun Zhang
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The picosecond laser is used to form six different regular morphology microstructures on the surface of the stainless steel. These microstructures have micro-scale corrugated protrusions, and the surface of the protrusions is distributed with small micro-pits of nanometer scale. The elements composition of the processing area is basically the same as that of the substrate, and the content is also close. The content of C element increases and the content of Fe element decreases. The results show that the friction coefficient of the original surface is between 0.8 and 0.9, and the friction coefficient of the textured surface is reduced to between 0.1 and 0.2. The friction coefficient shows a stable change after climbing first, but the time when the textured surface reaches the steady state relative to the original surface is shorter. The wear scars of textured surface are wider than that of the original surface. It has better wear resistance when the rubbing direction is perpendicular to the texture. The wetting angle of the original surface is <90°, and the surface is hydrophilic. The wetting angle of the textured surfaces are >90°, most of which are 110°~120°, and the surfaces are hydrophobicity. The surface friction coefficient is inversely related to the surface wetting angle.
High sensitive detection of atmospheric methane using infrared laser absorption spectroscopy
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Methane (CH4), a key greenhouse by influencing tropospheric ozone (O3) and stratospheric water vapor (H2O), plays an important role on the process of global warming and climate change. In this paper, we report on the development of a gas sensing technique based on high sensitive tunable diode laser absorption spectroscopy (TDLAS). A room-temperature distributed-feedback (DFB) diode laser near 1653 nm is used to excite the rotational-vibrational absorption line of CH4 molecule. Direct absorption spectroscopy and wavelength modulation spectroscopy were used for investigating methane molecular line parameters and sensing gas concentration, respectively. Moreover, potential strategies for sensitivity improvement are also discussed.
Evaluation of free radical scavenging and anti-oxidative capacity of Guigan longmu Decoction
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Guigan longmu Decoction(GL), take in Zhong-jing Zhang’s Treatise on Exogenous of Febrile Diseases, composed of Cinnamomum cassia Presl(Guizhi), Glycyrrhiza uralensis Fisch.(Gancao), Fossil fragments(Longgu) and Oyster shell(Muli), is a traditional Chinese medicine(TCM) formula and is widely used as a clinically medication formula for its efficiency in improving sleep. But the underlying mechanisms by which it exerts therapeutic function have not been thoroughly studied. Cellular damage induced by free-radicals like reactive oxygen species has been implicated in several diseases. Hence naturally anti-oxidant play a vital role in combating these conditions. In this study, The effects of GL on free radical scavenging and anti-oxidative capacity is investigated. By free radical scavenging assays, the IC50 values of GL were 46.03±1.26, 51.45±0.74 μg/ml with DPPH, ABTS assay respectively, and 0.611 mg ferrous sulfate/1 mg GL with FRAP assay. These results indicated that the antioxidant properties of GL hold great potential used as an alternative to more toxic synthetic anti-oxidants as an additive in food, cosmetic and pharmaceutical preparations for the oxidative diseases treatment.
Evaluation of free radical scavenging and anti-oxidative capacity of vespae nidus-epimedii folium formula
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Vespae nidus has been used in traditional Chinese medicine for thousands of years to treat a variety of diseases, including malignant tumors, rheumatoid arthritis, lung diseases, skin disease, digestive and urinary disorders, and dental diseases. As the same, Epimedii folium used to treat kidney-Yang deficiency,impotence and seminal emission, limp wilting sinews and bones, rheumatic arthralgia, Numbness and paralysis, osteoporosis. Vespae nidus-Epimedii folium formula used to treat chronic arthralgia due to Yang deficiency, and painful joints. But the underlying mechanisms by which it exerts therapeutic function have not been thoroughly studied. Cellular damage induced by free-radicals like reactive oxygen species has been implicated in several diseases. Hence naturally anti-oxidant play a vital role in combating these conditions. In this study, The effects of Vespae Nidus nidus-Epimedii folium formula aqueous extract (VEF) on free radical scavenging and anti-oxidative capacity is investigated. By free radical scavenging assays, the IC50 value of VEF were 71.33, 54.07 μg/mL with DPPH, ABTS assay respectively, and 0.161mg ferrous sulfate/1 mg VEF with FRAP assay. These results indicated that the antioxidant properties of VEF hold great potential used as an alternative to more toxic synthetic anti-oxidants as an additive in food, cosmetic and pharmaceutical preparations for the oxidative diseases treatment.
1kHz single-frequency Q-switched Er:YAG laser
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A single-frequency injection-seeded Er:YAG ceramic laser with a pulse repetition frequency (PRF) running at 1645 nm is demonstrated. The Er:YAG ceramic laser is seeded with a Er:YAG non-planar ring oscillator (NPRO) laser. Pulse energy of 5.19 mJ, pulse width of 571 ns at a PRF of 1 kHz is obtained. The fluctuation of the average power is measured to be less than 1.1% in 30 min. The M2 factors are 1.23 and 1.39 in x and y directions, respectively.
Performance improvement method for large aperture frequency conversion crystal
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In huge-scale high peak power laser facility, the frequency conversion unit is responsible for the conversion of fundamental infrared wave at 1053nm into ultraviolet wave at 351nm. In this paper, the mechanism of service performance degradation of frequency doubling crystal is revealed by combining field experiments and numerical simulations. Moreover, we propose a flexure support method that can effectively reduce crystal surface distortion. Further, an experiment platform for offline mounting of frequency conversion crystal is built, and the mechanical and optical characteristics are verified by the experimental results. Finally, online verification is carried out in China’s high peak power laser facility. The results show that the proposed mounting method can significantly modify the crystal surface figure, improve its online performance and increase the highest efficient output power of high peak power laser facility.
Determination of the 87Rb atomic number density in thin rubidium vapors
He Xu,
Yitong Song,
Wei Li,
et al.
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In recent years, the research in the fields of quantum computing, quantum communication and quantum precision measurement has set off the "second quantum revolution" and become an international hotspot. Background cold atomic vapor density is an important parameter in the vacuum systems. At present, the methods of measuring atomic vapor density include absorption line method and fluorescence method. However, for the negative exponential relation between the atomic vapor density and the measurement results of the existing methods, it is impossible to accurately measure the lowdensity atomic vapor. Therefore, based on the principle of magneto-optical Effect and coherence detection, we propose a method to measure the atomic vapor density of rarefied alkali metals. Taking 87Rb atom as an example, under different temperature and pressure conditions, the final measured atomic vapor density range is 1.47 x 1012~5.66 × 1013 m-3. The accuracy of this method is about 3~4 orders of magnitude higher than the existing method. The method effectively solves the measurement problem of low-density atomic vapor.
Photodetector array target calibration technology
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In order to achieve quantitative measurement of the spatial and temporal distribution of far-field laser spot, it is necessary to solve the calibration problem of the photodetector array target measurement system. For the photodetector array target calibration system, the unit detector is scanned one by one, and the unit detector is regarded as a black box. Its input and output correspond to the voltage pulse amplitude and the energy density of the laser beam respectively, in order to meet the energy density. The measured value of the measured value and the actual value of the project indicator, the segmentation relationship between the energy density of the photodetector and the amplitude of the voltage pulse is derived. The verification test shows that the error of the energy density measurement and the calibration true value of the verification test is less than 15% at a small energy density, and the error is less than 10% at a larger energy density. This calibration method has the advantages of simple operation and high calibration accuracy, and has guiding significance for future photodetector array target calibration technology.
Object recognition through scattering media using convolutional neural network
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When coherent light propagates through scattering media, it is scattered by the uneven particles in scattering media, resulting in a seemingly random speckle pattern. However, researchers have demonstrated that the information of the object is still preserved in the speckle pattern. In this paper, the convolutional neural network (CNN), which has a powerful ability to automatically extract nonlinear features, was used to recognize phase objects displayed on the spatial light modulator through scattering media. The experimental results showed that the CNN architecture can recognize faces images hidden by ground glass with a recognition accuracy of 97%. In addition to applying CNN to binary classification problems, we also verified that CNN could be effectively applied to multi-classification tasks, and the classification accuracy of handwritten digital data sets reached 95%.
Research on generating Laguerre-Gaussian beam using spatial light modulator
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High-order Laguerre-Gaussian beams are widely used for the high-precision interferometry, atomic capture and focal volume reduction. The LGp0 beam can produce a small focus and thereby be applied in the super-resolution technology. The phase-only liquid crystal spatial light modulator is able to realize high-efficiency phase modulation of the spatial light with the help of the computer. Based on the angular spectrum method and the Gerchberg-Saxton algorithm, two phase maps for different diffraction distances are designed to shape the Gaussian beam into the Laguerre-Gaussian beam LG10 mode. Through the simulation calculations, the influences of the diffraction distance and the iterations number on the imaging quality evaluated by the mean square error SSE are discussed and verified by experiments. In this paper, the Gaussian beam produced by the He-Ne laser was transformed into LG10 mode with the assistant of the phase-only modulation of spatial light modulator. The experimental results are consistent with the simulation results.
Reflectivity enhancement of silver-based mirror in the wavelength range 400nm-450nm
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With the development of remote sensing technology, the short working wavelength has been extended to 400nm in many current international spatial optical remote sensors. However, the reflectance in the wavelength range from 400nm to 450nm cannot meet the requirement for silver-based mirror. In order to solve this issue, SiO2 and Ta2O5 used as reflectivity enhancement layers are deposited on the silver layer. Simultaneously, the two dielectric films also protect the metallic silver film to from corroding in complicated environment. During the deposition process of Ta2O5 dielectric coating material, oxygen partial pressure, anode voltage and current of the ion source are optimized to get higher refractive index. The values of stress of the SiO2 layer and theTa2O5 layer are analyzed to get the adhesive coatings by the Stony formula and the process parameters of SiO2 dielectric coating material are obtained. The optical constants of these two dielectric films are established by using the Cauchy dispersion formula and the incoherent reflective theory, and then the thicknesses of them are optimized by simplex algorithm. SiO2 layer and Ta2O5 layer are sequentially deposited on the silver layer. The measurement results show that the average reflectivity of the wavelength ranges 400nm-450nm and 400nm-900nm reaches over 95% and 98%, respectively. The reflectivity enhanced silver-based mirror also passes the adhesion test according to relevant technique requirements.
Narrow linewidth high beam quality long pulse solid-state yellow laser at 589 nm by intra-cavity sum-frequency generation
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We demonstrate a compact narrow linewidth high beam quality diode pumped solid-state microsecond (μs) pulse yellow laser at 589 nm by intra-cavity sum-frequency generation (SFG). The resonators are based on a symmetrical co-folding-arm plane-plane structure with a two-rod configuration for birefringence compensation, working in a thermally near-unstable range of the cavity. A twisted-mode cavity for spatial hole-burning elimination and an etalon in 1319 and 1064 nm resonators are employed to realize the narrow linewidth laser output. Moreover, in order to improve the SFG efficiency, the laser spiking due to relaxation oscillations is suppressed by inserting frequency doublers in both 1319 and 1064 nm oscillators. By carefully designing the cavity, a 4.8 W quasi-continuous wave yellow laser source at 589 nm is generated with a beam quality factor of M2 = 1.63 and a linewidth of ~ 0.44 pm. The 589 nm laser is operated at a repetition rate of 500 Hz with pulse duration of ~ 115 μs.
Research on terahertz image compound denoising based on non-local means
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A composite denoising method based on non-local means filter, Lucy-Richard algorithm and adaptive histogram equalization is proposed for terahertz reflection scanning images. Firstly, adaptive histogram equalization is used to adjust the brightness of the image based on Lucy-Richard restoration to improve the image definition, and finally the quality of the reconstructed image is further improved by using the non-local means algorithm based on bisquare weighting function. The experimental results of terahertz image denoising show that the proposed method can preserve the details of the image, effectively remove the background noise caused by the laser output fluctuation in the imaging system, and restore the blurred image, which has a good denoising effect on terahertz image.
Investigation on the methods to extend the transverse relaxation time of polarized alkali atoms
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In order to improve the sensitivity of radio-frequency atomic magnetometer, two methods to extend the transverse relaxation time of polarized alkali atoms are investigated. One way is the application of a non-relaxing coating, another way is the introduction of buffer gas into cell. A theory relaxation model is built, and the dependences of transverse relaxation time on buffer gas pressure, laser power, cell temperature, and magnetic-field gradient are obtained. The measurements of transverse relaxation time are carried out in a cesium atomic radio-frequency magnetometer. The optical experiment conditions which yield the highest sensitivity are determined in experiments. Experiments results indicate that the optimal pressure for neon is 200 Torr. The experimental results are in agreement with the theoretical ones. An ultimate sensitivity of 100 fT/Hz1/2 of the cesium atomic radio-frequency magnetometer has been achieved. This study helps further optimization of the cell performance and the sensitivity of radio-frequency atomic magnetometer.
Dynamic behavior of a short cavity single-mode erbium-doped fiber laser
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Erbium-doped fiber laser as a novel light source and optical amplifier has been widely used in optical fiber communications and optical fiber sensors. Erbium-doped fiber lasers have attracted much attentions for their unique dynamic behaviors and applications. The nonlinear dynamic behavior of a short cavity erbium-doped fiber laser is studied in this paper. The idea of additional degrees of freedom is used to simplify the laser mode to study the dynamics of erbium-doped fiber laser. The three-level mode of the laser is simplified to a two-level mode, and a dynamic physical model of erbium-doped fiber laser is established by using pump periodic excitation. The laser can generate periodic pulses and chaotic pulses when a periodic signal of square wave as a periodic pulse is exciting the pump. The periodic pulsation, quasi-periodic behavior and chaotic behavior of laser under the various conditions are analyzed. It is found that the pump excitation level and its frequency are the main factors that determines the nonlinear dynamics of the laser, and the changes of pump excitation level and frequency will change the dynamic behavior of the laser. The effects of pump intensity, erbium doping concentration and photon lifetime on the dynamics behavior of laser are also discussed. When a large number of numerical calculations and simulations are operated, it is found that the quasi-periodic region and chaotic region are determined by the pump excitation level and frequency. The results have important reference value for erbium-doped fiber laser and laser technology and laser chaos application.
Micro-stripe broad-area infrared diode lasers without deterioration of output power
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We demonstrated high power semiconductor diode lasers emitting around 2.1 μm with the micro-stripe broad area (MSBA) structure which was proposed to improve the broad area (BA) lasers’ lateral beam quality. 1.28W output power at 7A at continuous wave (CW) operation was achieved from the uncoated MSBA laser. It is shown that the micro-stripe structure would lead to worse threshold current and slope efficiency of the lasers because of the less-pumped lossy regions. However, the MSBA lasers would have better heat dissipation system with proper micro-stripe structure and gain advantages on power performance at high currents.
Design and simulation of decoupling control for attitude angle stabilization device of helicopter-borne LiDAR
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The attitude angle disturbance of helicopter payload platform can significantly reduce the density distribution and imaging accuracy of laser point cloud measured by airborne LiDAR, so an attitude angle stabilization device is designed to compensate the attitude angle disturbance in real time. In order to eliminate strong coupling effect of the control system of the attitude angle stabilization device, decoupling control based on neural network inverse system is designed. Firstly, the dynamic model of the control system is established; secondly, the neural network inverse dynamic model is built, and a compound control strategy with PID feedback controller and neural network inverse system feed-forward controller is adopted to realize real-time decoupling control and improve the static and dynamic control performance; finally, simulation experiment for the decoupling control is carried out, and results show that the control system has fine static and dynamic performance. The designed compound decoupling control strategy can effectively improve the control accuracy and has excellent anti-jamming robustness against random error disturbance.
Ultra-high repetition-rate (tens of MHz) nanosecond all-fiber amplifier based on a SESAM passively mode-locking fiber oscillator at 1064 nm
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We report on a nanosecond all-fiber MOPA with ultra-high repetition rate (tens of MHz), which is seeded by a semiconductor saturable absorber mirror (SESAM) mode-locking fiber oscillator at 1064 nm. Ultra-high repetition rate of tens of MHz is realized by reducing fiber length in laser cavity. By using single-mode fiber stretcher with total length of 16 km, pulse width of mode locking laser pulse can be broadened from 28 ps to 1~7 ns. The maximum average power is achieved to be 54 W with pulse duration of 1.3 ns and repetition rate of 27.7 MHz. To the best of our knowledge, this is the first demonstration on an ultra-high repetition-rate (tens of MHz) nanosecond all-fiber MOPA based on a SESAM passively mode-locking fiber oscillator.
Detection of optical vortex using the fractional Fourier system
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The optical vortex (OV) is one type of optical singularity which has a spiral wavefront around a point where the intensity of light is zero and phase is undefined. Exact determination of the OV properties, involving location and sign, are very significant. In this paper, a novel OV detection method using the fractional Fourier system is presented. The fractional Fourier system is employed to provide high-sampling density phase gradient data. The closed form formula for the Hertz potential in terms of phase gradient measurement is given. It is shown that the presence of optical vortices could be visualized as the peaks and valleys of the Hertz potential where peaks correspond to the positive optical vortices and valleys correspond to the negative ones. Therefore it allows the determination of the OV location and sign in a very straightforward way. The validity and reliability are demonstrated through several numerical examples including noisy signals with different signal-to-noise ratio (SNR) levels. The outstanding merits possessed by the proposed technique are its low experiment effort and high detection precision.
Temperature-tuned solid-etalon filter for the space-borne lidar receiver
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Cloud-Aerosol plays a very important role in the Earth's atmospheric system,so accurate data of global Cloud-Aerosol detection are of great importance to the climate.The 532nm detection channel of the Space-borne Lidar for Cloud- Aerosol has a low signal-to-noise ratio during the daytime,so it cannot be effectively detected during the daytime.In order to improve the signal-to-noise ratio of the 532nm detection channel,a high-stability"sandwich solid-etalon" structure is used in series with a narrow-band interference filter.A filter is designed with a high-precision thermal control structure,it's optical performance is detected.The results show that the performance parameters of the filter meet the design requirements: the mechanical structure is compact and reliable; the temperature control accuracy can reach 0.1 °C;the temperature tuning coefficient is 3.49pm/°C,that is, the temperature tuning range of +/-2.3 °C, which satisfies the central wavelength tuning range of 16pm; the incident angle should be controlled within +/-4.2mrad to meet the peak transmittance of more than 75%
Optimum growth parameters of InAs/AlSb superlattices for interband cascade lasers
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We report the optimum growth parameters of InAs/AlSb superlattices (SLs) for interband cascade lasers (ICL) grown by the solid-source molecular beam epitaxy(MBE). The InAs/AlSb superlattices samples were grown on GaSb substrate at different temperatures and characterized by high resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM) and photoluminescence (PL). By changing the group-Ⅴ flux ratio during the SLs growth, the InAs/AlSb superlattices matched to GaSb substrate were obtained. Subsequently, the SLs were grown at different growth temperature. By photoluminescence we found the highest PL intensity was obtained when the SLs samples were grown at 458°C and the PL wavelength is at 1730 nm. From 10 × 10 μm2 AFM image, we found the root mean square (RMS) of the sample grown at 458°C was 1.96 Å which indicates the low surface roughness and god surface morphology.
Detection of optical fringes parameters with global direction metric
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A global direction metric method based on Fourier-polar transform is proposed in this paper, which calculates the global fringe direction according to the directional distribution of intensity from the power spectrum of fringe pattern. By introducing polar coordinate transform, the rotation of power spectrum is transformed into translation component, which can make the calculation process simple and fast. Then the original image is projected along the global fringe direction and the mean value of pixel gray is calculated. Also, the fringe pitch can be calculated from the projection curve close to cosine distribution. This detection method of optical fringe parameters uses overall information of the image, and holds good adaptability and robustness to noise and degraded image. Moreover, without any pre-processing operations such as smoothing filter and threshold segmentation is required in this method. It can directly detect two parameters of global fringe direction and fringe spacing, which is of great significance for quantitative analysis of fringe image.
Amplitude optimization of wavefront shaping using adaptive binary harmony search algorithm
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Focusing light through scattering media using wavefront shaping technique has drawn numerous interests, and shown great potential in various applications including super-resolution imaging, deep tissue microscopy and polarization control. The high speed of amplitude optimization based on digital micromirror devices has the potential to focus light through living biological materials. In this paper, we introduce an adjust binary harmony search (ABHS) algorithm to optimize the amplitude of the incident light. To test the performance and effectiveness of the ABHS algorithm, we establish a numerical simulation model based on random matrix theory. The linear relationship between intensity enhancement and controlled number of segments indicates the validity of our numerical simulation model. Furthermore, we compare the performance of ABHS algorithm with continuous sequential algorithm (CSA) and genetic algorithm (GA) in noisy and fluctuating environments. The simulation results show that ABHS reaches a larger overall enhancement than CSA and GA algorithm in noisy and fluctuating circumstances.
Microfiber/SiC-nanowire coupler for all-optical photodetection
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Semiconductor-based photodetectors have received wide attention. Traditional photodetectors are based on electrical test methods, which inevitably disturbed by dark current noise. In order to overcome this problem, this paper proposes an all-optical photodetection scheme based on a microfiber/SiC-nanowire directional coupling structure, which directly utilizes the refractive index change of SiC nanowire caused by photogenerated carriers instead of the change of photocurrent. The device is fabricated by transferring a single SiC nanowire to a microfiber with diameter of about 1 μm by microscopic operating system. When the device is irradiated by a 266 nm deep ultraviolet laser, its light detection sensitivity reaches up to 103 pm/(W/cm2).
Application of femtosecond frequency combs in the measurement of film thickness
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In this paper, a method to measure the thickness of TiO2 is developed based on the Micklson interferometer. Through a spectral domain analysis of multiple interferograms obtained using a femtosecond pulse laser, accroding to the interferance signals appear in the interferograms the thickness of film can be measured at high speed. we developed a simple method to measure the film thickness and for a sample we use the silicon wafer and coated TiO2 silicon wafer. Thickness of silicon wafer and coated TiO2 silicon wafer were measured respectivly, then from the thickness of coated TiO2 silicon wafer minus the thickness of silicon wafer. Result shows that the avarege thickness of TiO2 is 75.00μm.
A judgement method for mosaic grating error based on diffraction wavefront measured under multiple incident angles
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Holographic exposure mosaic technology is a feasible solution to fabricate large-area pulse compression gratings, where the mosaic grating method of developing region by region is one of the mosaic approaches. In this method, an exposed area of the substrate is firstly developed, and then the developed photoresist grating mask is put back into the previous exposure system. The next area grating mask is fabricated by aligning the interference fringes formed by the exposure beam and the developed real grating. However, since the unequal exposure and inconsistent development, the groove shapes of grating masks in two areas, including groove depth and duty cycle, will be different. When detecting the mosaic grating error, the differences of the groove shapes will cause the dislocation in the -1-order reflected diffraction wavefront at gap of the mosaic grating. It will be superimposed on the phase change caused by the lateral displacement error, so that the judgement of lateral displacement error will be seriously interfered. To solve this problem, the measurement method of the 0-order diffraction wavefront under multiple incident angles is proposed to precisely judge the lateral displacement error in the mosaic grating. In this paper, the grating diffraction analysis program based on the rigorous coupled-wave analysis is firstly written, and then the initial phase of 0-order reflected diffraction wavefront of mosaic grating mask is calculated. Subsequently, the sample is tested by atomic force microscopy and interferometer. By importing the measurement data into the searching program, the groove parameters of grating masks are obtained by the library matching method. Then, the lateral displacement error of the mosaic grating is further deduced. Finally, the feasibility of the proposed judgment method is confirmed by the experiment.
The study of optical statistical properties and coherence for XFEL
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A X-ray free-electron laser (XFEL) facility is based on RF superconducting accelerator at China Academy of Engineering Physics (CAEP) has been planed. The facility will be designed in a radiation range of 0.3-4 angstrom and the electron beam energy will be 12GeV. The main work focuses on the optimization of different parameters through physical analysis such as the undulator peak field strength and electron beam energy selected. A detailed simulation of start up and statistical properties of the radiation from a SASE FEL operating has been performed by time dependent FEL code.
Experiment research of high-power, high-repetition picosecond pulse amplifier
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A high power, high-repetition picosecond amplifier with an all-fiber picoseconds seed source, Nd:YVO4 and Nd:YAG gain medium was designed and experimentally studied. For a injected seeder laser with a repetition rate of 1 MHz and an average power of 2.34 W, a 55 W laser power output was obtained by the two-stage solid-state amplification, and the measured pulse width was 9.2 ps, and the laser wavelength was 1064.5 nm. The laser output characteristics of different repetitive modes were experimentally studied, and the laser output power was 18.4 W in the (1 × 4) MHz burst mode. Since the spectrum of the fiber picosecond seed light is much larger than the gain spectrum width of the amplifying medium, the output power of the entire system does not reach the design index. Next, the fiber seed source parameters need to be optimized to achieve a larger amplification power output.
Optimization design of space mirror support based on topology optimization method
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An optimal design method for lateral support structure of space telescope based on topology optimization theory and substructure method is presented in this paper. Introduced how to simplify the finite element model by substructure method in the process of analysis. Topology optimization is performed on the reduced model. Based on the variable density method (SIMP method), a mathematical model of continuum structure topology optimization is created to achieve efficient use of materials. Design a new type of mirror support structure. Consider the shape of the mirror which under axial gravity, radial gravity and temperature load conditions. The fundamental frequency of the mirror and the displacement of the rigid body are constrained, and the manufacturability of the topological results are also considered. The static and modal analysis of the structure using finite element method shows that the basic frequency and the shape precision of the mirror can meet the design requirements (the fundamental frequency f >120Hz, the surface accuracy is better than λ/60 RMS, λ/10 PV). This shows the feasibility of the method proposed in this paper in the design.
1.2-um InAs/GaAs high-density quantum dot laser
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Here we report the growth method of InGa/GaAs quantum dot (QD) with differnet QD density by manipulating InAs deposition rate from 0.065 ML/s to 0.1 ML/s. Chose the highest density QD as the active region and grow multilayer InAs/GaAs QD with high uniform. Then fabricate a narrow ridge waveguide laser by semiconductor process. The rigid waveguide is 1.8 um high and 5 um wide, and the cavity length is 1mm. The output power of this narrow-rigid laser is 164 mW and central wavelength is 1204.6 nm when the injection current is 0.5 A at 15°C. The threshold current is as low as 35 mA, and threshold current density is 1939 A/cm2.
Design and experimental investigation of nano-structured optical polarizing elements based on two-photon photopolymerization
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In this paper, a nano-polarization device based on two-photon polymerization reduction was designed and experimentally investigated. A broadband near-infrared (3-5 μ m) linear polarizer doped with metal particles was designed. Different from the fabrication methods of lithography and ion etching used in traditional metallic gratings or nanostructures, a two-photon absorption-based photo-reduction and photopolymerization process was adopted. The mixed solution composed by gold salt and photoresist is exposed by a femtosecend laser at a wavelength of 780 nm, at which the reduction reaction of the gold ions and the polymerization reaction of the resin are completed simultaneously, and thereby metal particles in the polymerized material can be obtained. The clusters of the reduced gold particles were observed by scanning electron microscopy, and the peak of gold was found in the energy dispersive X-ray spectrometer, which demonstrated the feasibility of the experiment and laid the foundation for the subsequent functional device fabrication.
Enhanced circular dichroism by all-dielectric multi-size combined chiral structure
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We propose and present a high-efficiency circular dichroism device formed by an array of multi-size chiral slits etched in a silicon layer that is on a silicon dioxide substrate. Numerical results show that the all-dielectric chiral metasurface exhibits a high circular dichroism in the range of 1500-1550 nm. At the resonance wavelength of 1540 nm, the highest circular dichroism (CD = TRCP-TLCP) reaches 97%, and the extinction ratio (ER = TRCP/TLCP) is up to 1999:1. It is also found that multiple wavebands operation can be implemented by manipulating the relative positions of multi-size slits in the structure. The proposed 2D all-dielectric chiral metasurface has the advantages of high circular dichroism, easy-fabrication and high compatibility with linear polarized components, which provides a solution for pixelated full-Stokes polarization imaging.
Influence of energy parameters in Laser-MIG hybrid welding on weld formation of 304 stainless steel
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Laser-MIG hybrid welding was carried out on 304 stainless steel in order to study the hybrid effect of two heat sources of laser and MIG. The influence of energy parameters including laser and MIG power and their line energy of hybrid welding on weld formation was investigated and the optimal energy ratio between laser and MIG arc was got in this study. The results show that the increase of laser power has a dominant effect on the increase of weld penetration, while the increase of MIG arc power has a small effect on the increase of weld penetration which is mainly used to improve forming stability and welding bridging ability. Hybrid effect of laser power and arc power on formation was investigated and processing window diagram was obtained which is of great guiding significance.
Local structure and optical property of GeTe@Cu composite thin film
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Nano particle embedded thin film has great potential application in tuning the optical properties of phase change material. In this paper, we prepared GeTe nano particle embedded Cu composite thin film (GeTe@Cu) by magnetic co-sputtering GeTe and Cu targets. High-resolution transmission electron microscopy (HR-TEM) was used to characterize the local structure of the composite thin film and the GeTe nano particles. It was found that the composite thin film was constituted of net-like Cu-Cu bonds, Ge (Te)-Cu bonds as well as GeTe nano particles. Optical reflectivity of the composite thin film was also measured. Ab initio molecular dynamics (AIMD) simulations was employed to investigate the forming mechanism of GeTe nano particles and the local features in detail. Simulation results revealed that Ge-Te-Ge-Te four-fold ring promote the formation of GeTe atom cluster and large amount of free electrons from Cu atoms make the Ge-Te bonds stronger, in further leading to the formation of GeTe nano particles. These results in this paper paved the way for further research about multi-level optical storage of nano particles embedded phase change composite thin film.
Research on short pulse laser detection method for "cat's eye" target based on spectral features
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A long-distance, high-efficiency "cat’s-eye" target laser active detection method based on the characteristics of target echo spectral segments was proposed. Considering the target echo generation condition, multiple sets of different wavebands, high-frequency and short-pulse detection lasers are used to obtain the high-precision distance value of the detection target, and simultaneously record the echo intensity information of the detection signal for different spectral segments. Analyze the relationship between the target distance, the target feature, the probe band and the beam quality, correlate the distance with the spectrum information, calculate and identify whether the target is a "cat’s eye" target. In the experiment, 1064nm and 1550nm laser sources are used to detect and analyze different types of targets. The test results show that the detection method can quickly and effectively obtain the multi-spectral echo reflection characteristics of the target, and achieve the "Cat’s Eye" target detection in the kilometer range. Effectively reducing the number required for target identifies feature points, improves the recognition efficiency and accuracy, and reduces false alarms.
Fabrication of GaSb-based distributed Bragg reflector semiconductor lasers
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We report on the fabrication of GaSb-based type-I quantum well distributed Bragg reflector (DBR) lasers operating in the 2-μm region. Second-order metallic gratings of chromium are patterned by electron beam lithography. The fabricated DBR lasers emit a single-mode continuous wave at 2.04 μm. The side mode suppression ratio (SMSR) is as high as 35dB with a narrow line-width of 37MHz. The devices show a stable single mode operation with current tuning rate of 0.006nm/mA.
A segmentation algorithm on terahertz digital holographic image
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It is necessary to study the image segmentation of terahertz digital holographic reconstructed images because of the boundary blurring problem. In this paper, a segmentation algorithm based on the region growth is proposed for terahertz digital holographic images. Firstly, the original image is bilaterally filtered and the morphological erosion operation is carried out to obtain the seeds of region growing. Secondly, the genetic algorithm is used to optimize threshold for restricting region growth. Finally, the segmentation results are obtained, and the average structural similarity (MSSIM) is used as an objective evaluation to measure effectiveness of the algorithm. The segmentation results show that the algorithm has a good segmentation effect, and the MSSIM can reach above 0.9.
Point spread function measurement and analysis of three dimensional optical imaging system
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Optical coherence tomography (OCT) and confocal scanning microscopes can perform three dimensional (3D) optical imaging of target objects. They are widely used in many fields because of their non-contact measurement, real-time fast imaging and high resolution. This paper is dedicated to evaluating the resolution of 3D optical imaging systems, enabling third-party metrology assessment, assuring periodic quality, and comparing different systems. An improved standard test method based on the system 3D point spread function (PSF) is proposed in this paper. The standard diameter microspheres were embedded in the robust PSF phantoms as scattering particles. An OCT and a confocal scanning microscope were used to acquire the 3D PSF images. Different from previous studies, this paper proposes a new preparation process for PSF phantoms. In addition, new mathematical model was built based on statistical methods to analyze the PSF that includes hundreds of scattered data. Combining the imaging principles of OCT and confocal microscopy, the imaging resolution of the two optical systems was compared. Finally, a stability experiment was performed to further verify the feasibility of using the PSF to evaluate the resolution performance of the imaging system. The results showed that the resolution based on PSF analysis is in good agreement with the theoretically calculated value, and this method can be used to reliably evaluate the resolution of 3D optical imaging system in the future.
Influence of structural parameters of high-power fiber lasers on stimulated Raman scattering and the suppression methods
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In high-power fiber lasers, stimulated Raman scattering (SRS) is a major factor limiting its power increase. In order to analyze the influence of the SRS effect on high-power fiber lasers, based on the traditional SRS model, we propose a theoretical model of multimode fiber lasers and fiber amplifiers containing the SRS effect. Then, the theoretical model is used to analyze the influence of various structural parameters of the fiber laser on the SRS effect. According to the simulation analysis results, we constructed a fiber laser system based on a master oscillator power amplifier configuration to carry out verification experiments for various structural parameters. The experimental results show that shortening the length of the gain fiber and the transmitting fiber, choosing a signal light of longer wavelength, and increasing the fiber core diameter can suppress the influence of the SRS effect on the fiber laser. And we apply the analysis results to 3 kW fiber laser system, and successfully achieve the suppression of SRS effect in the highpower fiber laser.
Influence of Sn dopant on the crystallization of amorphous Ge2Sb2Te5 by a picosecond pulsed laser irradiation
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Phase-change materials were highly promising for next-generation nonvolatile data storage technology and their properties were usually improved by doping. In this paper, the pronounced effects of Sn doping (0%, 10%, 30%) on crystallization behaviors of Ge2Sb2Te5 (GST) film induced by a picosecond pulsed laser were investigated in detail. The TEM observations presented the crystallization threshold, melting threshold and ablation threshold all decreased with the increasing of Sn doping while the crystal structure and crystallization behavior has not been changed. After single pulse Gaussian laser irradiation, the morphology of crystallized films for GST and Sn-doped GST all presented an ingot-like microstructure at higher laser fluence and equiaxed crystal microstructure at lower laser fluence, which was mainly caused by the temperature gradient. The local grain refinement was found in GSTSn30% films because weaker Sn-Te bond (359.8 kJ/mol) replaced the stronger Ge-Te bond (456 kJ/mol), which was also proved by X-ray photoelectron spectroscopy (XPS). This eventually led to a decline in nucleation energy barrier and increased nucleation rate.
Simulation of the effect of noise on terahertz digital holography reconstructed image
Ping Lin,
Qi Li,
Zuochun Shen
Show abstract
In the terahertz imaging experiments, target is often embedded in a support plate (such as PTFE, etc.). Background noise will be caused by many factors, such as uneven material and non-smoothness of support plate. In this paper, the impacts of noise on terahertz in-line digital holography single-exposure, support-domain constrained phase retrieval algorithm and its reconstructed results are simulated. The support domain is determined by the combination of the Otsu algorithm and the opening and closing operation. Firstly, the influences of noise on 2.52 terahertz in-line digital holographic reconstruction are studied when the transmittance of support plate is 0.93. The mean value of Gaussian noise of the support plate is 0, and the standard deviation range is between 0 and 0.1, and the interval is 0.005. Mean square error (MSE) and peak signal-to-noise ratio (PSNR) are used as the evaluation criteria. Finally, the Gaussian noise with mean value of 0 and standard deviation of 0.04 is selected to simulate and analyze the effect of the reconstructed image with different transmittances. The results show that, when the transmittance of the support plate is 0.93 and the noise standard deviation is 0-0.04, the peak signal-to-noise ratio is less than 6% lower than of the ideal support plate reconstruction.
Temperature characteristics of Faraday anomalous dispersion optical filter at Cs 852 nm transition
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Known as a unique optical filter, Faraday anomalous dispersion optical filter has prior advantages to provide high transmission and high background noise rejection with excellent image quality. In this paper, we studied the temperature characteristics of Faraday anomalous dispersion optical filter at Cs 852 nm transition. The transmitted spectrum is carefully measured under different Cs cell temperatures (39°C–57°C) and environment temperatures (23°C–26°C). The results could provide important reference for further research on Faraday laser, lidar remote sensing systems and imaging systems.
Research about new light source on LARP technology
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Laser has the advantage of high energy density, good directivity and so on. Laser headlamp which using laser as the light source of automobile headlamp also has the merits one of the research hotspots in solid-state lighting lighting. This paper studies the laser actived automotive lighting. This paper introduces analyzes the characteristics and advantages of laser the laser lighting of vehicles. Semiconductor lasers and different types of Ce:YAG fluorescent ceramic sheets Remote static excitation is systematically research with an illumination of 5277lx and a color temperature of 4500K automotive laser lighting.
Relativistic self-focusing in interaction of intense laser beam and exponential decay underdense inhomogeneous plasma
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In the laser and plasma interaction, Wong et al. (2018) and Fuchs et al. (2000) have found that the plasmas present the approximate exponential or exponential decay variation of density in experiments. In the paper, based on their researched results, we investigated beam relativistic self-focusing in interaction of intense laser beam and axially exponential decay underdense inhomogeneous plasma. The results show that the relativistic nonlinear effect gives rise to obvious self-focusing in homogeneous plasma and inhomogeneous plasma, comparing with beam self-focusing in homogeneous plasma, exponential decay inhomogeneous plasma is more benefit to form relatively steady self-focusing. Moreover, plasma inhomogeneity promotes self-focusing. In addition, when the amplitude of plasma inhomogeneity increases, beam self-focusing would obviously strengthen, while with the increase of the degree of exponential decay, self-focusing would slightly decrease.
Control of saturable absorption of topological insulator Bi2Se3 by electron and hole doping
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In this work, few layers of Bi2Se3 is chemically treated, in which the AuCl3 solution is used for oxidation reaction to form p-doping, and BV solution (benzyl dichloride) is put to form n-doping to change material properties. We used pumpprobe system to verify the effect of doping on Bi2Se3 materials. In addition, the nonlinear saturable absorption of the material is also controlled. Through the I-scan test, we found that the saturable absorption has diverse responses to different wavelengths and doping conditions. By doping, the Fermi level of the material can be adjusted to control the saturable absorption of the material, which can be applied to the mode-locked laser. The weakened saturable light intensity can make the mode-locked pulse easier to generate.
Investigation on pulsed laser damage resistance of high-absorption ceramic coatings
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The damage mechanism and application between intense pulsed laser and non-metallic materials have been regarded as the research hotspot in recent years. The ceramic materials have the advantages of high temperature resistance, corrosion resistance, good chemical stability and high temperature mechanical properties, and insensitivity of bonding strength to high temperature. Therefore, ceramics are considered to be a good choice for laser-resistant materials. In this paper, the damage topography and anti-damage properties of high absorption ceramic coatings induced by pulsed laser at different energy densities are investigated from macro and micro levels. Then, combined with the experimental results of absorptivity, the lower limit of damage threshold (better than 8J/cm2) for the ceramic coatings is obtained. Finally, the main factors affecting the pulsed laser resistance of ceramic coatings are discussed. The results of this study can lay an important experimental foundation for the further research on the damage mechanism of intense pulsed laser and ceramic coating materials.
Preparation of low-resistance tunnel junction for high efficiency multi-junction semiconductor laser diodes
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Low reverse-bias series resistance tunnel junctions (TJs) are the key to improving the performances of high efficiency multi-junction semiconductor laser diodes (MJLDs). In this paper, InGaAs QW TJ and InGaAs DQW TJ with single InGaAs layer and double InGaAs layers inserted into GaAs TJs separately, are proposed. TJ chips were fabricated by metal organic chemical vapor deposition (MOCVD) technology and semiconductor process. The measurement results of the devices display that the operating voltage of the InGaAs QW TJ and the InGaAs DQW TJ is lower than that of the GaAs TJ under the same injection current, whether it is a small current or a large current, and the InGaAs DQW TJ operating voltage is lower than that of the InGaAs QW TJ. Both GaAs TJ and InGaAs DQW TJ were applied to 1060 nm dual active region semiconductor laser diode. The ridge lasers with a strip width of 100μm and a cavity length of 2 mm were fabricated. The working voltage is reduced from 3.81 V to 3.38 V at 1 A drive current. Further experimental results indicate that the reverse-bias series resistance of InGaAs QW TJ and InGaAs DQW TJ is lower than that of GaAs TJ, and the performances of InGaAs DQW TJ are the best. This is of great significance to reduce the heat loss of MJLDs and improve its performances.
Generation of an arbitrary order Bessel beam in FDTD for time domain calculation
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An arbitrary order Bessel beam with arbitrary incidence is generated numerically in finite-difference time-domain (FDTD) method using a total-field/scattered-field (TF/SF) approach. This is implemented by decomposition of Bessel beam into a series of plane waves, which are projected into the FDTD simulation domain. The off-axis incidence case is realized by tuning the arrival time when the elementary plane wave gets to the center area of simulation domain, and the oblique incidence case is implemented by rotating the plane waves through Euler angles. Numerical examples concerning backscattering radar cross-sections (RCS) are presented to demonstrate the validity, accuracy, and capability of the proposed method. The results in this paper provide an efficient way to investigate the interactions of Bessel beams and particles with complex shape and composition using FDTD.
Preparation of reflection-type MoS2 saturable absorber and application in 2μm waveband
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The reflection-type MoS2 saturable absorber was prepared by the spin coating method. The silver plated reflector was made by plating the sliver reflective film on a Hydrophilic treated quartz sheet. The Tm,Ho:LiLuF4 all solid-state laser with MoS2 reflective saturable absorber is realized in Q-switched mode-locking operation. The laser maximum output power is 156 mW, typical Q-switched pulse envelope repetition frequency is 10KHz and the pulse width about 200μs. The repetition frequency of the mode-locked pulse sequence is 100 MHz and the modulation depth is close to 100%. The results show that the reflective MoS2 material can be used as a saturable absorber for all solid-state lasers in 2μm band.
Research on common aperture optical device for high energy laser system
Gang Zhao,
Wantao Deng,
Huijun Xia,
et al.
Show abstract
The main working mode of high energy laser system is to focus the transmitting laser beam on target under the condition that the target is tracked in closed loop by fine tracking module, so that it can be damaged or invalidated. Therefore, in order to achieve this effect, an optical device of common aperture is designed for high energy laser system. The emitting system of this device consists of an off-axis two-trans primary telescope module, a Galileo transmission telescope module used in focusing and a beam feeding module composed of dichroic mirror, fast mirror and other optical elements; at the same time, the receiving system of this device consists of the same off-axis two-trans primary telescope module, an imaging module used in fine tracking and the same beam feeding module. Taking incoherent combination laser in space as incident ray, we use optical design software in both sequential mode and non-sequential mode to design and simulate this device. The simulation results show that the distribution of spot at 0.5km~5km is obtained after the laser is modulated by different focusing quantities in the focusing telescope module, and the RMS value of laser wave front is better than λ/20 for emitting system. In addition, the performance of an imaging optical system composed of the primary telescope module and the fine tracking imaging module approach the diffraction limit after optimizing, and the system transfer function is greater than 0.6 at 70lp/mm. Such results in this paper confirm that the structure of this optical transceiver possesses reasonable structure and reliable performance, which meets the requirements of engineering application for high energy laser system.
Continuous-wave mid-infrared GaSb-based optically pumped semiconductor disk laser operating at 2 μm
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The growth conditions and lasing characteristics of the optically barrier-pumped GaSb - based semiconductor disk laser (SDL) emitting near 2 μm in an external cavity configuration are reported. It is made of a GaSb/AlAsSb Bragg reflector, a Ga0.8In0.2Sb/GaSb multi quantum-well active region and an Al0.8Ga0.2As0.03Sb0.97 window layer. Using an intracavity SiC heat spreader, a cw output power in excess of 1.12 W has been achieved at a heat sink temperature of 0 °C.
Micro-ring resonator optical sensor based on silicon and silicon nitride waveguide
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In this paper, we compare the sensing sensitivity, the stability and the temperature sensitivity of the micro-ring resonator optical sensor based on silicon waveguide and silicon nitride waveguide. For the silicon waveguide and silicon nitride waveguide single ring, the sensing sensitivities are 1113nm/RIU and 182.64nm/RIU, the resonance wavelength variations are ±12.5pm and ±7.5pm in an hour testing at the ambient temperature and the temperature sensitivities are 0.038nm/K and 0.018nm/K, respectively. . The sensing sensitivity can be improved to 6080.6nm/RIU by cascaded double silicon nitride waveguide rings to produce Vernier effect.
Influence of haze on pulse and FMCW laser ranging accuracy
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When the concentration of smog is large, the transmission process of laser signal will be greatly disturbed. In order to study the mechanism of this interference and reduce the ranging error, this paper focuses on the accuracy of smog and pulsed FMCW laser ranging. Firstly, based on the Mie scattering theory, the parameters such as scattering, extinction coefficient and asymmetry factor of haze under different conditions are calculated. Then Monte Carlo method is used to simulate the transmission process of pulse and FMCW laser signals. Finally, combined with ranging The principle analyzes the influence of haze on laser ranging accuracy. It is found that the smog will attenuate the amplitude of the pulsed laser signal, and as the transmission distance increases, this attenuation is significantly enhanced, reducing the signal-to-noise ratio of the ranging system. In addition, the delay and broadening of the pulse signal will also become larger due to the increase of the thickness of the haze, causing the waveform distortion of the echo signal, affecting the time discrimination accuracy of the pulse ranging, thereby affecting the ranging accuracy. The amplitude of the intermediate frequency signal of the FMCW laser ranging also decreases with the increase of the extinction coefficient. The amplitude of the echo signal decreases with increasing frequency because the attenuation of the high frequency signal by the haze is more pronounced. At the same time, the increase of the haze extinction coefficient will also reduce the signal-to-noise ratio of the echo signal, affecting the accuracy of the FMCW ranging.
Principle of PWC method application in ZEMAX
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The mathematical forms of Seidel coefficients are different in ZEMAX and PWC method. They are bridged by the wavefront aberration coefficients. The relationship between the wavefront aberration coefficients and Seidel coefficients in PWC method is derived in detail. The basis of PWC method application in ZEMAX is established.
Design of high precision digital phase detector in LDDM system
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The LDDM system is a measurement system mainly used for medium and short-range precision displacement data, especially in the field of practical engineering. In the LDDM system, the accuracy and speed of measurement system depend directly on the design of phase discriminator system. This article introduces a new high-precision digital phase detector based on FPGA hardware platform. It uses improved CIC filter and CORDIC function to design the module. Firstly two orthogonal local oscillator signals are generated, and multiply the two signals separately by the signal to be measured. After the modified CIC filter, the phase difference between the local oscillator signal and the signal containing only DC information is calculated by the CORDIC algorithm solving module. Finally, the phase difference of the signal to be measured is obtained by subtracting the phase difference between the two channels. The results of Matlab and Modelsim simulation and hardware platform experiments show that the high-precision digital phase detector designed in this article achieves a good level of measurement speed and measurement accuracy. The experimental phase error is only 1.03×10-4 rad, and the accuracy reached 0.0515%.With the addition of 30dB noise, the average phase discrimination error of 20 times is 1.02×10-4 rad, which achieve a high accuracy. It is important to achieve a higher accuracy displacement measurement for the LDDM system.
Generation of stretched pulse in dispersion-managed Tm-doped fiber laser
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The stretched pulse has narrower pulse duration and high pulse energy than conventional soliton, so that the stretched pulse can improve the potential application values of 2 μm mode-locked fiber laser in remote sensing, mid-infrared source, material processing and other applications. In this paper, the dispersion management method is adopted to accurately manage the dispersion in the cavity using a commercial ultra-high numerical aperture fiber and a common single-mode fiber. Based on the nonlinear polarization rotation technology to achieve mode-locking, when the pump power is set to 645 mW, the polarization controller is adjusted to achieve stretched pulse output with a de-chirped pulse duration of 581 fs. The center wavelength is 1939.26 nm and the 3-dB bandwidth is 21.8 nm. The repetition rate is 28.9 MHz and the signal to noise ratio is 54.21 dB. At the maximum pump power, the direct output power of the resonant cavity is 9.98 mW, and the corresponding single pulse energy is 0.34 nJ.
212W, Nd:YAG Innoslab nanosecond laser amplifier
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A high-average-power, laser-diode, end-pumped nanosecond multi-pass Innoslab Nd:YAG amplifier was demonstrated. With effective shaping of the electro-optically Q-switched Nd:YVO4 seed laser, a 45W seed laser at the pulse repetition frequency of 50 kHz was amplified to 212W with the pump power of 1145W, and the corresponding optical-to-optical efficiency was 14.6% and the slope efficiency was 17.8%.
Spectral polarization spreading effect of stimulated Brillouin scattering in fibers
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Based on the polarization vector propagation equation of stimulated Brillouin scattering (SBS) nonlinear effects in fibers, we find the spectral polarization spreading behavior in SBS. As a signal light propagates along a fiber, the state of polarization of different frequency components of the signal light will experience different polarization pulling forces from the counter propagating pump light, resulting in a nearly circular symmetry of spectral spreading of the polarization state at the output end of fiber. Through theoretical analysis and simulation, this paper studies the SBS spectrum polarization spreading effects in the cases of ideal single mode fiber(SMF), practical SMF, and polarization maintaining fiber (PMF). Finally, we demonstrate the SBS spectrum polarization spreading effect in a 200m SMF and a 140m PMF experimentally and good agreement with theory is found.
The MOCVD overgrowth studies of III-Nitride on Bragg grating for distributed feedback lasers
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The AlGaN film was overgrowth on the GaN grating substrates by a metal organic chemical vapor deposition method. The gratings were fabricated with fine step shape structure by nanoimprint and inductively coupled plasma (ICP) dry etching. The overgrowth epi-layer acts as the up-cladding layer within the distributed feed-back (DFB) laser diodes, which is the kernel process for the embedded grating DFB. The high quality AlGaN could obtain within the limited space in the DFB structure. It is found that the grating shape changes from rectangle to zigzag with reduced threading dislocation density (TDD), leading to better quality crystalline. The optimized overgrowth contributes to bending the TDs originating from the GaN/sapphire interface by image force during the film coalescence over the zigzag grating. The COMSOL model was built to simulate the effect for shape changing of the grating caused by overgrowth on the grating. The shape changing also affects the resonant wavelength of the DFB via effective refractivity index distribution. And the zigzag grating could achieve a higher Q factor than that of rectangle grating with optimized grating depth, which would contribute to improving the ability of mode selection for DFB laser diodes.
The formation simulation of laser disturbing effect image
Y. Wang,
Q. Chen,
H. Lei,
et al.
Show abstract
Laser active suppressing jamming is one of the most important technologies in the domain of electro-optical countermeasures. In order to obtain the all-around assessment of laser disturbing effect, we must get the laser disturbing effect image. It is very difficult or impossible to collect the hostile laser disturbing effect image in fact. We proposed a method of laser disturbing effect image’s formation simulation in this paper. For the first time, the simulation flow was introduced on laser disturbing effect image. We respectively simulated the laser energy distribution of diffraction effect, interference effect, scattering effect based on laser propagation theory, and then added to get the total laser energy distribution on the optoelectronic detector. Secondly, laser energy distribution can be converted into image grey distribution according to the operation principle of optoelectronic detector. Laser disturbing effect image was thirdly achieved by fusing image grey distribution of target and background. The consistency of simulation image and experimental result proved that our method was effective and feasible. The research achievement can provide the technical reference for carrying out laser disturbing experiment and the all-around assessment of laser jamming effect.
The influence of detector’s integration time on the laser disturbing effect
Y. Wang,
Q. Chen,
G. Xu,
et al.
Show abstract
For the first time, the influence of optoelectronic detector’s integration time on laser disturbing effect has been comparatively investigated under the low repetition rate laser, the high repetition rate laser and the continuous-wave laser in the experiment. In the low repetition rate laser disturbing, the correlation coefficients of laser disturbing effect are all above 0.96 under the different integration time, however, the pixel numbers of the different grey levels gradually increase with the extension of integration time. In the high repetition rate laser or continuous-wave laser disturbing, there are two different phases that both the correlation coefficients and the pixel numbers of different grey levels change with the increase of integration time: the correlation coefficients rapidly decrease and the pixel numbers quickly increase when the integration time is below 10ms in the first phase; the correlation coefficients linearly decrease and the pixel numbers increase when the integration time is above 10ms in the second phase.
Characteristics of return photons from the polychromatic laser guide star excited by a long pulse laser with 330 nm wavelength
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Based on the solution to the rate equations of interactions between laser and sodium atoms, the excitation probability of sodium atoms is achieved. The return photons at 330 nm are numerically calculated for the 1 W laser power at the sodium layer in the mesosphere. Results show that a long pulse laser with a few microsecond durations and 1000 Hz repetition rates can well excite the polychromatic laser guide star to obtain no less return photons at 330 nm than that by the continuous-wave laser in a given condition. In order to obtain enough return photons to satisfy the requirement of tip-tilt detection, the parameters of linewidth, durations, repetition rates, polarization and launch diameters of the laser should be properly chosen. And effects of the laser launch diameters and the atmospheric turbulence on the return photons are slight. For the wonderful vertical atmospheric transmittance T0=0.5 at the Starfire Optical Range, Mauna Kea and Paranal, considering the effects of geomagnetic field, when the power of launch laser varies from 10 W to 25 W with the zenith angles from 0° to 40°, the return photons at 330 nm reach 104 ph/m2/s.
Propagation characteristics of vortex beam passing cube-corner prism
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The light field distribution of the vortex beam propagating through the cube-corner prism is studied, considering the existence of the dihedral angle error and the flatness error in the process of the cube-corner prism, based on vector form of reflection-refraction law. The reflection-refraction mode of the cube-corner prism is established, and the phase distributions of the emitted light field and the diffraction light field are given when the dihedral angle error and the flatness error are considered. As for the cube-corner prism with circular section, the diffraction distribution of the vortex beam on the dihedral angle error and the flatness error is calculated. Meanwhile, the effects of diffraction distribution are analyzed. Simulation results show that, the divergence of diffraction intensity distribution increases with dihedral angle error increases. Also, the output diffraction pattern of the cube-corner prism with the three equal dihedral angle processing errors has six symmetrically distributed symmetrical petal structures. The quality of the output diffraction mode is significantly reduced at the existence of flatness error.
Single acousto-optic tunable filter based double filtering imaging system
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The double filtering system based on single crystal acousto-optic tunable filter (AOTF) in order to improve spectral resolution and reduce side lobe is designed and demonstrated. The effects of single filtering and double filtering on AOTF performance are analyzed. Furthermore, the proposed double filtering technology has the characteristics of high speed, strong stability, flexible tuning, narrow bandwidth and multi-wavelength selection. In this experiment, the spectral bandwidth, side lobe and diffraction efficiency of single filtering and single crystal double filtering in visible range are measured. A double optical wedge compensator is set up at the exit of the double filtering experiment system to compensate the diffracted light drift caused by chromatic aberration. In conclusion, the experimental method of double filtering based on single crystal of tellurium dioxide is better than that of single filtering in spectral resolution and side lobe suppression.
Laser-induced focused ultrasound for noninvasive sonothrombolysis using candle soot polymer nanocomposite-coated photoacoustic lens
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In this paper, a concave carbon-based polymer nanocomposite film was developed for high-amplitude focused ultrasound. The composite films consisting of candle soot nanoparticles (CSNPs) and elastomeric polymers were used as the high-frequency optoacoustic sources. To generated focused ultrasound, these composite films were formed on concave optical lens. A focal waveform with peak to peak pressure of ~45 MPa was achieved at the focal point. The prototyped laser-induced focused ultrasound (LIFU) was applied with noninvasive sonothrombolysis in vitro. For enhanced cavitation effect, we demonstrated a spatio-temporal superposition approach of LIFU treatment in conjunction with low-frequency focused ultrasound from a piezoelectric ultrasound transducer. The in vitro results showed that dualfrequency excitation ultrasound treatment can achieve the sonothrombolysis efficiency of approximately 28% in half of an hour (2 mg/min), suggesting that LIFU generated from composite films may be promising in precision sonothrombolysis.
Research on calibrating the deviation introduced by dispersion in multi-point time dissemination system via ring fiber network
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The relationship between the time deviation introduced by dispersion and the location of remote stations in ring fiber network is studied in this paper. A method is proposed that the location of remote stations in ring fiber network can be sensed by the remote stations, and compensation can be calculated to adjust the convergence position of the recovered 1PPS signal. We demonstrate a time dissemination experiment via 100km ring fiber network to study the correction method of asymmetry deviation introduced by dispersion. After the calibration of the deviation, time synchronization accuracy of 100ps is realized. Synchronized remote stations can be accessed at anywhere in the ring fiber network.
Hyperspectral microscopic imaging of skin squamous cell carcinoma
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Acousto-optic tunable filter (AOTF) is a new type of light splitter with fast tuning, stable structure and portability. In this paper, a hyperspectral microscopic imaging system is constructed by combining non-collinear AOTF with optical inverted microscopy. The feasibility of data augmentation based on hyperspectral images for object detection of skin squamous cell carcinoma is studied. The hyperspectral images collected from unstained sections of skin squamous cell carcinoma are processed into dataset. At the same time, the mature open source object detection model is selected and trained for 20,000 times. Using the trained model to detect the lesion area of other unstained sections, it is found that the model trained by hyperspectral image dataset has a good ability to distinguish the non-lesion area, and there is no false detection. And the model has a relatively accurate detection ability for large lesion area, but the results of the model for small lesion area are not ideal. After analysis, it is considered that the number of samples can be increased firstly, especially in small lesions, and the same to the hyperspectral images. In addition, the model for lesion detection can be further optimized. By increasing the complexity of the model, the model can learn more details and information in the image during the training process. The preliminary results of the experiment prove that hyperspectral imaging is feasible for data augmentation of lesion object detection dataset. This paper provides a new method for the object detection data augmentation of skin squamous cell carcinoma.
Research on iterative method of wavefront reconstruction for imaging through turbid medium
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The problem of the imaging through turbid medium such as fog, haze and human tissue has always been the focus of attention. The turbid medium destroys the wavefront of the incident beam, so the key to the recovery of the image is the reconstruction process of the wavefront. The spatial light modulator (SLM) is employed to reconstructs the wavefront digitally. In order to realize imaging through the turbid medium, a prior image is restored at the target location in the simulation, and the phase modulation of the SLM is obtained by the advanced genetic algorithm. Then the priori image is replaced with the new image to be restored. According to the optical memory effect, the new image can be imaging at the target location. The optical memory effect was tested using a series of circular spots of different sizes, and the results showed that the recovery ability gradually decreased with the increased image size. Finally, the curve of the cost function with the number of iterations in 7 different population is analyzed. The results show that the convergence value increases first and then stops with the increase of the group, and the convergence rate is not positively correlated with the group size. So choosing the right group size makes a lot of sense for image restoration.
Graphene-MoS2 heterostructure transistor
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In order to simplify the preparation process of Graphene and molybdenum disulfide (MoS2) heterostructure transistors, a sessile drop method was proposed for sample preparation. In this paper, few-layers MoS2 and monolayer Graphene liquid were prepared by liquid-phase exfoliation. Then the liquid was successively used to form a film on the Si substrate, which covered with 300nm SiO2, by using spin-coater method. The Graphene/MoS2 transistor was prepared by electron beam evaporation with a metal mask plate. The K4200 semiconductor analyzer and probe platform were used to characterize the transistor. We also see that Graphene/MoS2 transistor is more sensitive to light from same wavelength. This fully demonstrates that the Graphene/MoS2 transistor combines the selective absorption of light of MoS2 and the characteristics of high carrier mobility of Graphene. And it greatly optimizes the performance of MoS2 transistor and Graphene transistor. Thus, Graphene/ MoS2 transistors, which produced by sessile drop method, will have more potential application in the electric and optoelectronic industry.
Impact of quantum capacitance on the characteristics of MoS2 field effect transistor
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MoS2 transistors with SiO2 gate insulators were fabricated from the experiment. The Raman and Photoluminescence of monolayer MoS2 and the electrical and photoelectric properties of prepared MoS2 transistors were investigated. Notably, the electrical performance model MoS2 transistor was carried out by considering the quantum effect of capacity building of MoS2 channel, and comparison analysis according to the result of simulation and experiment results, the model is suitable for the system study of MoS2 transistor. These results suggest that MoS2 transistors are suitable for nanoelectronics and optoelectronics devices.
Algorithms for focusing characteristic of laser beam through scattering media
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The ability to control the propagation of light through scattering media has great research significance in biomedical treatment and laser material processing. How to achieve effective focusing by modulating the laser beam passing through the highly scattering media is extremely important. In this paper, based on the traditional continuous sequence algorithm, improved scanning methods are used to modulate the phase of incident light wave-front, thus achieving effective focusing of the laser beam through the scattering media and increasing the convergency speed of the algorithm to nearly 1.5 times. Similarly, using continuous sequences and their optimization algorithms can focus the light into the desired pattern and the performance of three different scanning methods of continuous sequence algorithm are discussed.
Characteristics of array Gaussian-Schell mode beam propagating through oceanic turbulence
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Based on the generalized Huygens-Fresnel principle, the quadratic approximation and integral transformation techniques of the Rytov phase structure function are used to derive the expression of the turbulence distance and the M2 -factor of array Gaussian-Schell mode beam propagating through oceanic turbulence. The simulation methods of beam superposition are cross-spectral density function superposition and intensity superposition. The simulation results show that the turbulence distance and M2 -factor of the linear array Gaussian-Schell mode beam in oceanic turbulence are related to the coherence length, the number of array beam and the separation distance. The turbulence distance and the M2 -factor for superimposition of the cross-spectral density function are always smaller than for the superposition of intensity. For superimposition of the cross-spectral density function, when the propagation distance is less than 30 m and beam number is 3, the M2 -factor is the smallest curve. Also, the propagation distance is less than 700 m and beam number is 1, the M2 -factor is the minimum curve. When the propagating distance is more than 700 m and beam number is 3, the M2 -factor is the minimum curve. The optimization of beam parameters and superposition methods can obtain the better beam quality.
Research of laser-induced underwater communication zoom optical system
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Based on the loss of laser-induced acoustic signal caused by the undulation of sea level, which affects the communication quality of laser-induced underwater communication system, a laser-induced underwater communication zoom optical system with a focusing position of 10km and a focusing position variation range of ±500m is designed. The theoretical relationship between the adjustment distance and the focusing position is established and the far-field distribution of the Gaussian beam focusing system is simulated. The results show that the energy density of the far-field spot is concentrated, and the spot energy is the highest at the focusing position. The sea level condition was simulated, and the indoor pool experiment was carried out to verify the communication performance of the laser-induced acoustic communication system. The experimental results show that the waveform of the laser-induced acoustic signal and the rising edge of the electrical signal are completely consistent, there is no loss of the laser-induced acoustic signal, and the underwater communication quality is good. It provides a viable reference for laser-induced underwater communication systems with adaptive zoom.
Single zeptosecond pulse generation by scattering of a relativistic electron with an intense circularly polarized laser pulse
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The spatial, temporal and spectral emission characteristics of radiation generated from electron oscillations driven by an intense circularly polarized laser pulse have been investigated theoretically and numerically using a single electron model. The motion of an electron is highly relativistic and head-on (180° ) collision of a single counter streaming electron and an intense circularly polarized laser pulse can produce a single ultrashort zeptosecond pulse along θ = 90° by merely using a few-cycle laser pulse with fixed carrier-envelope phase offset Φ0 = 0 without controlling phase φin [5] which is defined as the phase of the laser pulse when the electron enters it. An interesting modulated structure of the spatial characteristic is observed and analyzed.
Propagation properties of radially polarized partially coherent beam in the oceanic turbulence
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Based on the extended Huygens–Fresnel principle and the second-order moments of the Wigner distribution function, propagation properties of radially polarized partially coherent beam in the oceanic turbulence are investigated. An analytical formula for the propagation factors (M2 -factors) of partially coherent one-dimensional radially polarized beams in turbulent ocean is derived. The intensity distribution, degree of polarization and beam characteristic parameters of radially polarized partially coherent beam in turbulent ocean are numerically described in detail. It is shown that the oceanic turbulence parameters and the initial coherence length have significant influence on the degree of polarization and coherence for radially polarized partially coherent beams, and such beam is depolarized on propagation. As the value of the oceanic turbulence parameters (χT or w) increases and the coherence length of the beam decreases, the normalized M2 -factor increases more rapidly. The results will be useful in long-distance free-space optical communications.
Quasi-continuous-wave long-pulsed, all-solid-state Nd:YAG modeless laser
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We demonstrate the quasi-continuous-wave long-pulsed operation of a compact all-solid-state modeless laser based on intracavity frequency-shifted feedback by an acousto-optic modulator. The laser active medium is an Nd:YAG crystal rod, side-pumped by high-brightness laser diodes of 808 nm. When the pump repetition and duration are 200 Hz and 250 μs, the maximum single pulse energy of 85 mJ is produced at an optical conversion efficiency of ~34%, and also a good beam quality of M2 X = 1.80 and M2 Y = 1.78 is obtained in the horizontal and vertical directions respectively. Moreover, a narrow continuous spectrum is achieved with the 3-dB linewidth of 75 pm (i.e. 20 GHz) and the center wavelength of 1064.16 nm. Via the sum frequency generation, such a long-pulse (several hundred μs), narrow-linewidth modeless laser source is preferred for solving the major problem of saturation of the mesospheric sodium atoms and can create a much brighter sodium guide star to meet the needs of adaptive imaging applications in astronomy.
Study on flat-top shaping technology in picosecond laser micro-machining
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In order to achieve the uniform picosecond laser micro-machining effect, this study carries out the research of shaping the original incident Gaussian beam into a micron-level flat-top beam at the focal position. Based on the principle of diffractive optics, the phase distribution of the shaping element is calculated which meets the micron-level flat-top beam output requirements and the verification of the shaping effect after transforming through the phase distribution is simulated. When the simulated output beam distribution meets the design requirements, the shaping elements is manufactured. Finally, the shaping element is used in a picosecond laser micro-scribing experiment and the scribing effect is analyzed. The final experimental results show that the picosecond laser micro-scribing test is carried out with the shaped flat-top beam, and the uniform scribing effect is obtained which satisfies the design requirements.
Theoretical and experimental study on nonlinear effects of mode-locked and extracavity modulation nanosecond pulsed laser
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Through simulation calculations and experiments, the two popular methods of generating nanosecond (ns) pulsed laser were studied respectively. A new method for generating a ns pulsed laser with high power and ultra-high repetition frequency by using dispersive fiber after SESAM mode-locked oscillator was proposed. In the simulation calculation of the mode-locked ns pulsed laser, the time-frequency evolution characteristics of the laser formation process were analyzed. The variation process of the stimulated Raman scattering (SRS) effect was obtained at different injection powers. In the simulation calculation of the extracavity modulation ns pulsed laser, the threshold of the stimulated Brillouin scattering (SBS) effect was obtained in the 4-stage fiber amplification experiment. Then, the nonlinear dynamics model of the ns pulsed fiber laser was established by considering various nonlinear effects. The results showed the theoretical models were consistent with the experimental investigations. This provided a new way to further optimize the parameter of ns pulsed fiber lasers and also contribute to solve nonlinear damage problems in such lasers.
Engineering the chromatic dispersion in dual-wavelength metalenses for unpolarized visible light
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Chromatic dispersion represents the wavelength-dependent behavior of optical devices and limits their operation bandwidth. Due to the material dispersion restriction of refractive elements, dispersion engineering remains a challenge to imaging technology and optical communication. Recently, metalens offers an attractive approach to engineer the dispersion by introducing the additional degree of freedom with only a single layer of nanostructures. Here, we propose a method to design the dual-wavelength metalenses with controllable dispersion characteristic in transmission mode in the visible region. Three kinds of polarization-independent metalenses are demonstrated, including those with zero dispersion, positive axial dispersion, and negative axial dispersion. All the metalenses show high resolution with nearly diffraction-limited focusing. Our findings may provide an alternative way to design dual-wavelength functional devices in the fields of optical information processing, imaging technologies and complex fluorescence techniques.
Experimental study on the effect of Coptis chinensis-Scutellaria baicalensis on prevention and treatment of ulcerative colitis and antioxidant capacity
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To explore the effect of Coptis chinensis-Scutellaria baicalensis on ulcerative colitis in mice and its antioxidant and anti-inflammatory effects in vitro. Sodium dextran sulfate (DSS) was used to induce acute ulcerative colitis in mice, lipopolysaccharide (LPS) was used to induce cell inflammation model, and ABTS and DPPH models were used to evaluate antioxidant capacity. The results showed that the drug had no significant effect on colitis, but cell experiments in vitro showed that the drug had significant anti-inflammatory effect and could scavenge ABTS and DPPH free radicals. Coptis chinensis-scutellaria baicalensis has anti-inflammatory and anti-oxidative effects.
Study on the prevention and treatment of ulcerative colitis and antioxidant activity of allium macrostemon powder
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To study the preventive and therapeutic effects of Allium Macrostemon Powder (AP) on experimental ulcerative colitis and its antioxidant and anti-inflammatory effects in vitro. Sodium dextran sulfate (DSS) was used to establish the model of ulcerative colitis in mice. Lipopolysaccharide (LPS) was used to induce cell inflammation. The scavenging capacity of AP on ABTS and DPPH free radicals was measured in vitro. The results showed that the drug had no significant effect on colitis, but cell experiments in vitro showed that it had obvious anti-inflammatory effect, and had good scavenging ability on ABTS and DPPH free radicals. AP has anti-inflammatory and antioxidant effects.
Mechanism analysis of influence of shafting error on laser tracker
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The shafting error has a great influence on the measurement accuracy of the laser tracker. Based on the error expression form, a mathematical model is established for the eccentricity error of the shafting system, and the simulation analysis is carried out. The tilting error of the shafting system is obtained from the angle of the geometric angle and the moiré fringe respectively. A specific analysis was carried out. A laser tracker angle measuring system was built to analyze the shafting error in the system and correct the shafting error. The experimental results show that the original error of the laser tracker angle measurement is 189.31", and the corrected angle error is 127.13", which provides a theoretical basis for the highprecision measurement of the laser tracker.
High sensitivity angle-sensing photodetector
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In this paper, a high sensitivity angle-sensing photodetector at the nanoscale is proposed, which mainly consists of SiO2 substrate and two columns of separate silicon nano-blocks and four gold electrodes. When the light in the incident plane perpendicular to the columns is obliquely incident on the silicon nano-blocks, they will absorb different light energy. Then the concentration of electron hole pairs in nano-blocks is also different, which will affect the photocurrent detected by the detector. Simulation results further show that the detection accuracy of the photodetector in the range of 0-45° can reach 0.152° when irradiated with TM polarized light. This angle sensing photodetector has many advantages, such as high sensitivity, low cost, easy integration. It can be used in the fields of information acquisition of light field, automatic driving scene perception and machine vision.
The performance of mid-wave infrared HgCdTe e-avalanche photodiodes at SITP
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HgCdTe has been shown to be the first semiconductor exhibiting single-carrier multiplication in avalanche photodiodes (APDs) up to gain values larger than 1000 and with close to zero excess noise. These results have opened a new windows for low-flux and versatile imaging. In this paper, we report the latest results on MWIR HgCdTe APDs manufactured at SITP. These APDs display a gain of 1000 around 10V reverse bias. The excess noise factor is between 1.2 to 1.45 up to gain of 100, and the quantum efficiency is more than 60% from 1μm wavelength to peak wavelength 4.2 μm. These results show that the technological processes used at SITP are well adapted to APD manufacturing. However, at present, the dark current starts increasing significantly faster than the gain at high bias, and then the device becomes dark current noise limited. APD gain performance was successfully modeled by the simulation of electrical characteristics used Synopsys Sentaurus based on Okuto-Crowell ionizaition coefficient model. Therefore, Sentaurus would be used as a powerful predictive tool for SITP technology and stress its reproducibility and optimize the devices .
Magnetohydrodynamics-based microfluidic optical switch
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As one of the core devices in all-optical networks, optical switches can convert optical signal physically and logically. Here a 2×2 microfluidic optical switch is proposed. It switches the optical path by ionic liquid and air in a microchannel, and uses the magnetohydrodynamics (MHD) microfluidic drive technology. The proposed optical switch possesses the merits of simple structure, easy operation and low actuation voltage. There are no movable mechanical parts in this optical switch, so its volume is small. The structure, working principle and related theory of the proposed optical switch are described in this paper. The conducted research can promote the application of microfluidics in the optical communication.
Observation of diverse passive harmonic mode-locked soliton pulses in an all-normal-dispersion fiber laser
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Diverse passive harmonic mode-locking were observed in an all-normal-dispersion Yb-doped passively mode-locked fiber laser with a long cavity based on the nonlinear polarization rotation (NPR). Using a cascaded long-period fiber grating as a spectral filter, several modes of passively harmonic mode-locking including passive high-order harmonic mode-locking, passive multiple-pulse harmonic mode locking and passive large-pulse-width harmonic mode locking (over 300 ns ) were obtained by adjusting the tunable CW semiconductor laser (pumping source in the experiment) and polarization controller, in which the intense nonlinear effects, large fiber dispersion and phase bias played an important role. It is expected that the observed various modes of passive harmonic mode-locking may find applications in industrial fields where different pulse widths and repetition rates are needed and provide experimental evidence to the research of ultrafast lasers.
Design of a charge sensitive spectroscopy amplifier for CdZnTe-based high energy x-ray detector
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Wide band-gap CdZnTe material, which is widely used in the detection of the hard X-ray and the Gamma ray irradiation, has great advantages in the energy resolution and the detection efficiency. In the design of the conventional nuclear spectroscopy system using CdZnTe crystal, the requirement to eliminate the influence of the electric noise and improve the energy resolution has high priority consistently. The crucial part of the detector processing is to convert the signal which is generated by the CdZnTe detector into a Gaussian-pulse which has smaller enough pulse-width. Generally, the transient current signal which comes from the CdZnTe detector needs to be amplified by using a Charge Sensitive Amplifier (CSA) because the nA magnitude signal (Dozens of nA). The application of the CSA can also improve the system SNR and decrease the influence of the external interference in the signal transmission. Based on the theory of the nuclear electronics, researches of the CSA and the pseudo-Gaussian shaping-filter for the CdZnTe spectroscopy detector were accomplished. On the classic theory of the traditional CSA, we present a new CSA circuit structure. the time constant of attenuation can be altered without changing the value of RF and CF. In addition, there was no obvious influence on the rising time and the noise characteristics of the output-pulse of the CSA simultaneously. Moreover, we demonstrated the application of our CSA improved the sensitivity of the CdZnTe detector that we used in previous experiment. In the simulation of this paper, the optimal parameters of each component were determined according to the analysis of the functional characteristics of the CSA and the pseudo-Gaussian shaping-filters. Experiment results show that the rising time of the CSA output signal is 20ns approximately, the falling time is 150μs and the output pulse of the two stage pseudo-Gaussian shaping filter has minimum 200ns pulse width (FWHM). Based on the performance in our experiment, the designed CSA and the multi-stage pseudo-Gaussian shaping-filter can improve the energy resolution of our CdZnTe detector for the hard X-ray radiation effectively, and the energy resolution for the 137Cs(the source of Gamma) can reach up to 3.5%.
Application of reflection transform imaging in trace detection
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Fast, accurate and high-quality extraction of trace information is important in the fields of criminal investigation, archaeology and inspection. Reflection transformation imaging is based on a digital photography and surface reflection imaging model, and can record and process the surface texture information of the object, thereby realizing a three-dimensional visual rendering image of the object. In different occasions, the objects carrying the traces are different in the type and color, and the dimensions, types, colors, etc. of the traces are also different. In order to make the different trace features clear, this paper builds a detection device based on the principle of reflection transformation imaging. LED used in the device has four colors: white, red, green and blue. Traces with different colors and types have different reflectivity for different wavelengths of illumination light, thus a high contrast trace image is achieved by using the device. And the device can render the image and get clear visibility of traces. The local histogram equalization algorithm is further used to extract edge information of the traces of different rendering effects, and the detail information of the trace image is further enhanced. This paper introduces a non-reference image evaluation function to evaluate the quality of the image. In this paper, the device is used to detect the traces written by colorless pen, colorless ballpoint pen, black pen and black ballpoint pen on the white paper. Then the device is used to detect traces written by different color water-based pen and oily-based pen on the white paper. Compared with monochromatic source illumination, the device can obtain higher contrast trace information according to the color and type of the trace. Furthermore, edge extraction of these rendered trace images makes the traces easier to identify. For different colors of papers and traces, the device can obtain high contrast images by selecting the appropriate illumination wavelength. Therefore, the device will have important application prospects in the fields of criminal investigation and ancient cultural relics identification.
930nm diode laser source by spectral beam combining based on a transmission grating
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We demonstrate spectral beam combining of a 930 nm diode laser bar based on an external cavity structure with -1st transmission grating. This technique is based on the wavelength selection characteristic of the grating and the feedback by external cavity. Beams from each emitters of the diode laser array are locked at different wavelengths and overlap in the near and far fields. With the maximum continuous wave (CW) injection current of 90 A, a CW output power of 49.6 W and a spectral beaming combining efficiency of 61.3% are achieved.
A tunable CW dual-wavelength Cr:ZnSe laser with collinear output
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We report a tunable CW dual-wavelength Cr:ZnSe laser with collinear output pumped by a thulium doped fiber laser. By using birefringent plates, we obtained stable dual-wavelength operation between 2365 nm and 2492 nm. The maximum wavelength separation was 127 nm corresponding to a frequency offset of 6.46 THz.
An improved fitting method of birefringence dispersion for liquid crystal variable retarder
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In order to accurately obtain the birefringence dispersion of liquid crystal variable retarder (LCVR) with wavelength ranges from 414nm to 702nm. Here, we propose an improved fitting method of birefringence dispersion by using the theory of polarized light interference. The birefringence of LCVR in 478nm is 0.3863 based on the improved method. The experimental result is 0.3862 and the percentage error is 0.026%, compared to the 1.761% of the original fitting method. This work provides an improved way to character the birefringence dispersion of LCVR.
A method of polarization-mode conversion based on birefringent film in immersion lithographic illumination system
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In immersion lithographic illumination system, appropriate polarization illumination can improve the resolution and imaging quality. Thus it is of great significance to realize different polarization-modes. The zero-order half-wave plates are usually used to achieve conversion of different polarization-modes. However, large-diameter zero-order half-wave plate is too thin to manufacture and assembling. This paper presents a polarization-modes conversion method based on birefringent film. The properties of birefringence film is similar to zero-order half-wave plate, and the film is easy to manufacture. Theoretically, it can be estimated that the film thickness is 2.4μm correspond to 180° retardation in 193nm wavelength. The experiment indicates that the 180° birefringent film can convert linear polarization-modes successfully, which verifies the feasibility of the film as a substitute of zero-order half-wave plate in immersion lithographic illumination system. The method solves the problem that it is difficult to manufacture large-diameter zero-order half-wave plates, and provide a reference for the design of lithographic illumination system.
A new lidar technology using frequency comb light source
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As the increasing demands of the environmental protection, meteorological monitoring, ecological detection and other fields, lidars are needed to simultaneously measure a variety of atmospheric parameters (especially simultaneous measurement of various pollutants, such as volatile organic solvent VOCs). Multi-wavelength Raman lidar, differential absorption lidar (DIAL) and high spectrum resolution lidar (HSRL) can be implemented these fields. But either technique needs multiple laser sources to meet their requirements. This paper proposes a new lidar based on Frequency Comb Light Source, which can provide multiple frequency components through a single light source for simultaneously measuring various multiple atmospheric parameters. The frequency comb laser light source is used to emit seed light of frequency ωc from the seed laser, and then after passing through the frequency comb laser, a series of equally spaced spectral frequency components are emitted centered on ωc; then emitted into the atmosphere, and the laser reacts with the atmosphere. The echo signal enters the receiving optical path through the telescope, and is sent through the beam splitter or the discriminator to detect by the detector. Based on different pollutants have different absorption cross sections, similar differential absorption lidar(DIAL), the λon and λoff can be determined. The lidar using the frequency comb light source can be easy designed into a compact structure, which is convenient to carry and maintain. It’s also a very advantageous for the lidar miniaturization and industrialization with a wide application prospect.
Development of multi-wavelength Mie-scattering aerosol lidar system
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Atmospheric aerosol refers to liquid or solid particulate systems suspended in the atmosphere. Most of them exist in the atmosphere below 2-3km, which can directly cause pollution near the surface atmosphere and seriously affect human health. Lidar is an important tool for measuring aerosols. Using lidar to detect atmospheric aerosols can effectively monitor air pollution and improve the level of environmental monitoring. The Nd:YAG solid-state pulse laser is used to output lasers having wavelengths of 1064 nm, 532 nm, and 355 nm respectively, and receive backscattered light through a telescope. The received backscattered light is divided into four channels through the subsequent optical path, and the optical signal is converted into an electrical signal by a photomultiplier tube, and a three-dimensional distribution map of the extinction coefficient with height and time is obtained. The lidar is continuously observed around the clock to obtain the change of aerosol, which is of great significance for studying the concentration, distribution and scattering of aerosol.
Research on distributed 3D printing model slicing system based on cloud platform
Jianzhuo Yan,
Zhongqi Li
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Model slicing is a key process in 3D printing technology from digital model to entity. Traditional slicing technology takes a long time to slice massive model files. Using distributed computing technology and cloud platform technology, distributed model slicing can be realized to improve processing efficiency. In this paper, we propose a distributed 3D printing slice cloud platform based on cloud computing, which combines model layout algorithm to segment massive model printing tasks. In this paper, 25 models are used to carry out the distributed slicing experiment. The maximum acceleration ratio is 2.25. The results show that the problem of too long slicing time in 3D printing production can be effectively solved by using distributed computing technology combined with model layout algorithm.
Temperature field and influence analysis of magneto-optical modulation system
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In the actual operation of the magneto-optical modulation system based on the Faraday effect, the internal temperature change will cause the drift of the Faraday rotation angle signal, which is a key problem that further improves the accuracy of the system. In this paper, the system heat transfer model is constructed by in-depth analysis of the system heat generation mechanism. Then the finite element simulation software is used to establish the equilibrium process of the system temperature field, and the internal temperature change of the magneto-optical material is analyzed. Finally, the typical paramagnetic material TGG is taken as an example. Analyze the effect of temperature changes on the Faraday rotation angle and the accuracy of the magneto-optical modulation system. The results show that with the increase of working time, the internal temperature of the system gradually increases, causing the attenuation of the magnetic field amplitude and the decrease of the Verdet constant of the magneto-optical material. Both of them work together on the solution of the Faraday rotation angle, which ultimately affects the overall accuracy of the magnetooptical modulation system.
Incoherent polarization beam combination for mid-infrared semiconductor lasers
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The mid-infrared band of 3~5 μm wavelength is a very important atmospheric window. The mid-infrared lasers are widely applied in laser countermeasure, laser illumination and trace gas detection. At present, the mid-infrared laser sources mainly include solid-state optical parametric oscillation lasers, fiber lasers, mid-infrared supercontinuum spectrum laser and mid-infrared semiconductor lasers, i.e. quantum cascade lasers. In these lasers, quantum cascade laser is the only one that can realize the conversion from electricity to light. In this paper, the method of incoherent beam combination of mid-infrared semiconductor lasers is studied. Two lasers are combined in a common aperture by using a single polarizer based on the polarization characteristics of the output laser of quantum cascade laser. Results show that the incoherent power superposition of mid-infrared quantum cascade lasers can be achieved by polarization beam combining, and the beam combining efficiency is not less than 90%. The farfield divergence angle is about 5 mrad, which is consistent with the farfield divergence angle of the two sub-beams.
One dimensional incoherently coupled spatial soliton pairs in biased two-photon photovoltaic photorefractive crystals
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We investigate two mutually incoherent spatial solitons in biased two-photon photovoltaic photorefractive crystals under steady-state conditions in one dimensional. It is show that incoherently coupled bright-bright, dark-dark and bright-dark two-photon soliton pairs can be established in the crystals provided that the mutually incoherent incident beams have the same polarization and the same wavelength. We also show that when the bias field is much stronger than the photovoltaic field, these soliton pairs are just like the two-photon screening soliton pairs, and when the applied field is absent, these soliton pairs degenerate into the two-photon photovoltaic soliton pairs.
Research on nonlinear compensation technology of wireless optical communication system
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In a wireless optical communication system, since the attenuation of the response of the light source becomes higher as the frequency of the signal is higher, it is more difficult to modulate the high frequency signal.In order to compensate for the attenuation of the frequency response of the light source when transmitting high frequency signals, we design a nonlinear compensation method acting on the transmitter of the wireless optical communication system based on cascaded transistor amplifier circuit. In order to verify the role of the nonlinear compensation method, we selected the blue LED as the light source and built a wireless optical communication system. The experimental results show that the nonlinear compensation method extends the 3dB modulation bandwidth of the system from 12MHz to 235MHz.
Application of reflection transform imaging in handwriting trace detection
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Handwriting is a special kind of trace, which carries important information such as writing content, writing tools and writing habits. Reflection transform imaging (RTI) is a computational photography method that creates an interactive image to further display the 2D and 3D texture features of the inspection surface. In this paper, Reflection Transform Imaging is applied to study the colored and colorless handwriting traces produced by pen and water-based pen. By combining different lighting directions and rendering modes, not only the writing content of different handwriting traces can be obtained, but also the three-dimensional texture information of handwriting traces can be obtained. Especially for the colorless handwriting trace, the two-dimensional and three-dimensional texture of the handwriting detail features can reveal the differences between different writing tools and show the shape of the brush. The experimental results show that reflection transform imaging technique can clearly display the colored and colorless handwriting traces, and it can provide powerful help for the case detection by revealing various information hidden in the handwriting traces.
1.9W single-frequency, grating external-cavity tapered laser with narrow linewidth
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A high-power tunable Littrow grating external-cavity tapered semiconductor laser is designed in this paper. By using the grating external cavity to lock the wavelength and narrow the linewidth, we gained a series of single-frequency laser with the central wavelength at 927 nm, tunable range >20nm and linewidth < 980 fm with the continuous pumping. When the wavelength is 926.8 nm, the threshold current is 1.25A and the oblique efficiency is 0.682 W/A. When the injection current increases to 4A, the maximum output power is up to 1.906W, with the electro-optic efficiency of 21.7%, the linewidth of 700fm, and the beam quality of 1.948 and 3.788 in the fast and slow axis respectively.
Research on real-time detection system of underwater polarization imaging based on focusing plane method
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In order to achieve simultaneous imaging of the target. According to the principles of polarization and spectral detection, this paper proposes a laser underwater polarization detection system based on the focal plane method, which is mainly composed of imaging lens, laser, analyzer, liquid crystal tunable filter (LCTF), and focal plane polarized camera. The composition can acquire images of multiple polarization angles at the same time, and realize polarization detection of multiple spectral bands by tuning the liquid crystal tuning filter, and then perform polarization polarization fusion processing on the image by extracting polarization spectral information of the target image. The detection of underwater targets yields the expected image. Through underwater detection experiment, the effects of sediment concentration in water on polarization imaging detection are studied. The results show that the sediment concentration in water has a great influence on the polarization image acquisition.
Generation and manipulation of the circular Airy vector beams by dielectric metasurface
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We propose and experimentally demonstrate an approach to generate and manipulate the circular Airy vector beams by a spatial light modulator and metasurfaces. It is found that the metasurface can realize the rotational symmetry reserved transmission of the circular Airy vector beams, which is stemmed from the rotational symmetry of circular Airy beam and cylindrical vector beams. The study may provide an alternative way for generating and manipulating of the circular Airy vector fields, which is primary based on the dielectric metasurface.
Temperature sensor with micro-ring assisted Mach-Zehnder filter
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A temperature sensor with micro ring-assisted Mach-Zehnder filter is presented. It has a micron size. A micro-ring cavity is coupled in one of the arms of the Mach-Zehnder interferometer, in which some temperature-sensitive liquid is injected into the cavity by using the microfluidic technique. The temperature change can be detected by analyzing the output spectrum of the sensor. In order to achieve the good filtering performances, the arm-length difference of common MachZehnder filters is usually the order of millimeter. While the M-Z arm-length difference of the temperature sensor presented in this paper is only about 10um. The sensor has good filtering performances. Its extinction ratio is 10dB and the 3dB bandwidth is less than 1nm. In addition, the resolution of the temperature detection is 0.1°C. Moreover, the temperature detection range of the proposed sensor can be adjusted by changing the refractive index of liquid in the micro ring cavity.
Preparation of SiO2 antireflective coatings by spray deposition
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Silica antireflective films were prepared on flat glass substrates by spraying method. By adding n-propanol, isopropanol, n-butyl alcohol and low vapor pressure solvent 1,3-butanediol to form gradient volatilization solvents, the “whitish” in color of coating was solved. Spray coating is a single side coating technology which is suitable for flat or weakly bent substrates. This method can be flexibly applied to single-side coating, double-side heterogeneous coating and rapid coating of large-scale components. The results show that the antireflection coating prepared by spraying method has good optical properties, the transmittance can reach 99.61%, the root mean square roughness is 1.22 nm and the uniformity of the coating was smooth. The spraying method has been successfully applied to the preparation of antireflection films on flat substrates.
Microfluidic Mach-Zehnder filter
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In this paper, a microfuidic Mach-Zehnder (M-Z) filter is proposed. It has the advantages of small size, simple structure, convenient manufacture and flexible adjustment. In the proposed filter, one arm of the M-Z Interferometer is the sensing arm and the other arm is the reference arm. The sensing arm has adjustable refractive index because the microchannel is filled with liquid which could be replaced. The reference arm is not contacted with the outside. The comb filter spectrum of the M-Z filter can be adjusted by changing the refractive index of liquid in the microchannel. This paper presents the structure, working principle and related theories of the microfluidic M-Z filter. The proposed M-Z filter can promote the application of microfluidics in the optical communication.
Feature analysis of wrapped phases of nucleated cells in polar coordinates
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Digital phase microscopy has made great progress in the study of morphology and dynamics of biological cells, especially the homogeneous cells. For the heterogeneous nucleated cells with relatively complex internal structures, there are still few methods of phase unwrapping suitable for observation and measurement. In this paper, a method is proposed to identify the substructure of cells only with their wrapped phases. According to the structural features of real nucleated cells, their similar models are established firstly, and then their wrapped phases are obtained in Cartesian coordinates and polar coordinates. Based on the relationship between the parameters of the two coordinate systems, the pattern recognition and image processing techniques are used to analyze the parcel phase of the single-core and multi-core, regular and irregular kernels, and the central and boundary kernel models. Then, the texture shape distribution, the texture overlap condition, the opening and closing state of the equal phase line, the peak number and the peak position are selected as reference features, and these reference features are combined and optimized as the judgment condition for identifying the nuclear structure model, and the wrapped phase in polar coordinates is screened and identified, which effectively distinguishes three typical types of nuclear cell models. It provides a new, unpacked method for the classification and identification the substructures of the nucleated cells.
Analysis on one-way dual wavelength time transfer via fiber link based on TIVGVD
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In order to meet the increasing requirement of accurate time synchronization in the “single-fiber one-way” fiber optic WDM-network, a one-way dual wavelength time transfer scheme based on the temperature-induced variations of group velocity dispersion (TIVGVD) is proposed. We set up a model of one-way time transfer by using time delay difference of dual wavelength to reversely derive the one-way delay variations with the help of Sellmeier expression. The influence of wavelength difference and temperature on one-way delay variationsis simulated and analyzed. The impact of wavelength drift and temperature estimation error on measurement accuracy is studied, which provides quantitative guidance on experimental research and application of one-way time transfer.
Detection of latent fingerprints on papers
Liqing Ling,
Lihua Huang,
Kai Guo,
et al.
Show abstract
Fast and high resolution detection of latent fingerprints plays an important role in criminal investigation and court science litigation. Researches show that fingerprint has a main absorption peak in the short-wave ultraviolet region, and the corresponding fluorescence peak appears in the long-wave ultraviolet region. In the paper, the scanning module is adopted to realize the shift of 266nm laser spot on the surface of paper, meanwhile, the fingerprint fluorescence emitting from the scanning area is collected. The experimental parameters are optimized according to the contrast of fingerprint image. Two modes of rough detection and fine detection are used to realize fast and high resolution fingerprints detection. According to the natural width of two adjacent ridges of fingerprint(0.2-0.7mm), the optimum detection resolution of rough and fine detection mode is studied. In this paper, the rough detection resolution is 0.2mm, and the fine detection resolution is 0.06mm. Histogram stretching and exponential enlargement are used to enhance fingerprint image contrast. Image filtering and binarizing are carried out to show fingerprint image stripes. By above method, characteristics in latent fingerprints can be detected, and fast and high resolution detection of latent fingerprints is realized, and the fingerprint image features are accurate, high contrast and rich in details. It has important applications in criminal investigation, forensic science and other fields.
Laser projection optical path design and speckle suppression
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In order to improve the imaging quality of the existing projector and simplify the optical path structure of the projection system, this paper involves a new type of optical system of projection system, using three-color LD light source as illumination source of projection system, using tapered light guide tube as the light guide. This article studies the principle of diffusers to suppress speckles, and derives the influence of diffuser number, divergence angle and gap between diffuser on speckle contrast. Using the Tracepro to build a three-dimensional model. The optical path structure was simulated and the results of simulation were analyzed. It shows that the speckle contrast of the projection system is 5% and the spot uniformity is up to 95.8%. Compared with the traditional laser projection light path, reduce the color wheel、Color-combination prism, dichroic mirror, mirrors and other components, simplifies the light path structure.
Observation of greenhouse gases and their impacts on atmospheric transmittance
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A ground-based Fourier transform spectrometer has been established in Hefei, China to remotely measure H2O, CO2, CH4 and CO based on near-infrared solar spectra. The continuously retrieved time series of total column results for H2O, CO2, CH4 and CO are presented on April 2nd, 2018. The observation results show the variation of total column of CO2, CH4 and CO. The total columns of H2O, CO2, CH4 and CO are 1.35×10 23, 8.91×1011, 4.08×10 19 and 4.09×10 18 molecules/cm2, respectively. In order to reduce the systematic error of the instrument, we also calculate the column-averaged dry air mole fraction by the oxygen molecule as the internal standard. The column-averaged dry air mole fraction of H2O, CO2, CH4 and CO are 5289.43, 415.04, 1.907 and 0.178ppm, respectively. Furthermore, we analyze the atmospheric transmittance by using MODTRAN 5.0 based on the retrieved results. The comparison results show that the atmospheric transmittance has gaps in the absorption band
Laser beam shaping based on wavefront sensorless adaptive optics with stochastic parallel gradient descent algorithm
Yan Li,
Tairan Peng,
Wenlai Li,
et al.
Show abstract
A wavefront sensorless adaptive optics system with a 61-element unimorph deformable mirror is proposed for laser beam shaping. The actuator voltages of the DM are adaptively adjusted with the help of the stochastic parallel gradient descent (SPGD) algorithm. The difference of the target beam and the actual beam recorded by a CCD camera is used as feedback. The experimental results show that this method not only realizes the aberrations correction of the optical system, but also generates annular beam, ratio line focus beam and square beam which agree with the desired targets.
Development of a new Mie scattering lidar and its aerosol detection
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A miniaturized Mie scattering lidar system for atmospheric aerosol optical properties and atmospheric transmittance measurement was developed. The structure, basic principles and data inversion methods of the system were introduced. Through the continuous observation of aerosols over Hefei Science Island, the distribution profiles of atmospheric extinction coefficients at different times were measured. The observations show that the system can effectively measure the optical properties of aerosols.
A multi-wavelength chaotic light source based on a semiconductor optical amplifier fiber ring laser
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In this paper, a dual-wavelength chaotic light source is proposed and demonstrated based on a fiber ring laser (FRL) with a semiconductor optical amplifier (SOA) as the intra-cavity gain element. By properly adjusting the bias current and the polarization, the SOA-FRL generates a high-dimension chaotic optical output with 24-nm optical bandwidth. The temporal instability of the output originates from the optical feedback, as well as the nonlinear effects of both the SOA and the long fiber. With optical-to-electrical conversion, the output electrical signal presents a bandwidth of 13 GHz, which is only limited by the bandwidth of the detection system. By inserting a tunable bandpass filter (TBPF) into the cavity, the chaotic emission bandwidth is limited to 3.2 nm. The output is then divided into two parallel channels using a wavelength division multiplexer (WDM). Autocorrelation of the two outputs confirms fair randomness, while the cross-correlation result verifies the independence of the two. With multi-bit sampling and over-sampling, dual-channel true random number generation (TRNG) up to 960 Gbps per channel is achieved. Random sampling periods are adopted to reduce the influence of the time-delay signature (TDS), which originates from the round-trip delay of the laser cavity and affects the randomness of the output. At a significance level of 0.01 and a random sampling ratio of 10-4 , the generated random bits can pass all the tests provided by the NITS SP800-22 test tool.
Detection of the effect of Moxibustion on QI-blood by optical coherence tomography
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The theory of Chinese medicine meridian Qi-blood has a close correlation with human skin microcirculation. To explore the mechanism of moxibustion acting on human microcirculation and obtain more accurate detection results of moxibustion effect, a non-invasive detection method based on optical coherence tomography imaging was proposed. Moxibustion experiments were carried out on 10 healthy volunteers at the Laogong and Daling Point. The changes of OCT backscattered signals at the skin of different acupuncture points were directly observed. Based on the single scattering model of the OCT signal, the A-SCAN at the acupoint is fitted to obtain the attenuation coefficient of the acupoint skin. The results showed that within 30 minutes after moxibustion, compared with other acupoints on the hand, the intensity of the backscattered signal was decreased about 5 dB in the depths of 0.5-2mm at the skin of acupuncture points of the same meridian. The attenuation coefficient increased significantly over time and reached a peak then decreased. At the peak, the attenuation coefficient increased to twice that before experiments. The optical coherence tomography system can directly reflect the changes of skin microcirculation, and further validate the theory of traditional Chinese medicine meridian Qi and blood. This method can effectively detect the physiotherapy effect of moxibustion.
Investigation on the radiation recovery effect on BOTDR system
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Brillouin Optical Time Domain Reflectometer (BOTDR), as a distributed optical fiber sensing technique, has been widely used in health monitoring of large structures on the ground in recent years. Space engineers also have a strong interest in it. However, in space environment, the optical performance of sensing fibers in BOTDR will decrease due to space radiation. Usually, the ground simulation space radiation experiment only considers the influence of radiation damage on optical properties of optical fibers. However, the performance variation of optical fibers after radiation is a combined result of radiation damage and self-recovery. If the restoring characteristic is introduced into the radiation damage model, the accuracy of BOTDR radiation assessment will be greatly improved. To study the radiation recovery characteristics of BOTDR, a 1 km single-mode G.652.D YOFC fiber is used as the sensing optical fiber of BOTDR, and is placed in the radiation field of Co 60 to receive 200Gy gamma radiation with 1.42 Gy/min dose rate. After the radiation procedure, the radiation recovery characteristics of BOTDR were monitored for 1506 hours. The experimental results show that the radiation recovery effect has little effect on Brillouin frequency shift and stress coefficient, but the attenuation coefficient of optical fiber caused by radiation can be restored obviously in the first 100 hours. The attenuation coefficient of optical fiber recovers from 3.5 dB/km to 1.5 dB/km. The above results are of great significance to modify the radiation model of BOTDR in space radiation environment.
Generation of optical needle with wavelength magnitude by tight focusing of circular partially coherent beams
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Based on Richards-Wolf vectorial diffraction integral, the expression of electric cross-spectral density matrix of linearly polarized circular partially coherent (LPCPC) beams, near the focus of a high numerical aperture (NA) objective, are derived. Numerical calculations are performed to show the influence of initial coherent length and NA of the objective, on the intensity distribution and degree of coherence of the LPCPC beams in the focal region. The results indicated that after focusing the LPCPC beams through a high NA objective a super-length optical needle (<12λ) with wavelength beam size can be obtained. Moreover, the numerical calculations illustrate that the length of the optical needle can be controlled by adjusting the initial coherent length of the LPCPC beams. The influence of NA of the objective on the length of the optical needle is much less than the initial coherent length. Setting the reference vector position on the z-axis, we can find that the coherence of the optical needle on the same wavefront remains unchanged.
Laser medical image processing based on neighborhood concerning Gaussian mixture model
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The traditional Gaussian Mixture Model is sensitive to noise in laser medical image processing, and its segmentation accuracy is not high enough. In order to remedy these defects, the Neighborhood Concerning Gaussian Mixture Model is adopted. The gray value of the center pixel in every neighborhood block is updated by the information of the neighborhood pixels according to the close correlation between them. After remolded, the image is decomposed by double Gaussian Mixture Model, which further refines the decomposition of the mixture model and improves the accuracy and anti-noise performance of image segmentation. Finally, experiments are carried out to verify the feasibility of the method. The results of the experiments show that the method of image segmentation based on the Neighborhood Concerning Gaussian Mixture Model can significantly improve the noise suppression ability, and achieve a good segmentation effect with high efficiency, while retaining the image contour and details better.
High-dimensional chaotic laser secure communication system based on variable laser power
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In recent years, with the development of eavesdropping technology, how to improve the security of data transmission has become a hot research issue. In order to enhance the security of the secure communication system, a chaotic laser secure communication system with variable laser power is proposed in this paper. Based on the original optoelectronic feedback chaotic laser communication system, the change of laser power is regarded as a new key. The simulation results show that the error rate of the eavesdropper is above 10-2 over most of the laser power, and the average error bit rate of the eavesdropper is 7 orders of magnitude higher than the average error rate of the authorized receiver. In addition, the appropriate masking efficiency will reduce the bit error rate of the eavesdropper, while it has little effect on the eavesdropper. The system scheme can be used in communication with high confidentiality requirements in the future.
Enhanced aluminum doping profile in 4H-SiC by wet-chemical laser doping
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In this paper, enhancement of Aluminum doping profile in semi-insulating 4H-SiC by using Eximer laser in AlCl3 aqueous solution is focused. Several active parameters like number of shots, laser power and dopants solution density affect the doping mechanism. Laser doping with increase of AlCl3 solution concentration from 28 to 36 wt.% results in more efficient doping with merging features like better ohmic contact formation having ideal symmetry factor. Hall Effect measurement using Van der Pauw method show that laser produces a highly doped p-type layer with increasing carrier concentration from 1012/cm2 to a maximum 1015/cm2 by tuning parameter . Current-Voltage characteristics of modified region show the ohmic behavior with reduction in resistance. UV spectrometer absorption tangent line shifts from 375 nm to 401 nm indicating that Al impurity has been introduced in 4H-SiC.
Comparative study of pulse and FMCW laser detection performance in fuzzy environment
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A fuzzy environment such as smoke and dust can cause laser energy attenuation, signal-to-noise ratio reduction, and even false alarms caused by backscatter interference. It seriously affects the performance of the detection system and even makes the system unusable. In order to study the performance variation of pulse and frequency modulated continuous wave (FMCW) laser detection in fuzzy environment, this paper selects the ranging error and the equivalent target peak to backscatter peak ratio (TBR) as the evaluation index, and compares the performance of the two systems in fuzzy environment. The variation of detection performance under different degrees of fuzzy environment is also discussed. The results show that the detection performance of the two systems has different degrees of degradation in the fuzzy environment. In the case of different environmental visibility, the ranging error of the FMCW system is better than the pulse system. When the environmental visibility is high, the TBR of the pulse system is higher than the FMCW. As the visibility decreases, the TBR of the FMCW is gradually higher than the pulse. In comparison, the FMCW's detection performance is better than the pulse system in the case of low visibility, which is more obvious as visibility decreases.
Impact of filling factor on correction of piston and tip/tilt in coherent beam combination
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Numerical analysis model of impact of filling factor on correction of piston and tip/tilt was established based on Fourier optics and Fraunhofer diffraction theory. The variation trend between PIB and rms of piton or tip/tilt was obtained through numerical analysis, which includes 4 kinds of apertures, that was 3, 7, 19, 37 regular-hexagon-distribution circular flat top beam or circular Gauss beam and 4, 9, 16, 25 square-distribution square beam. The results showed that the bigger filling factor was, the slower variation trend of PIB and rms of piston was. Besides, the phenomenon was more marked when there were more apertures for coherent beam combination. The results also showed that there was no business between PIB and rms of tip/tilt. It was uncovered that, for different filling factor and apertures, if the piston was corrected below 0.08λ and the tip/tilt was corrected below 0.25λ/q, the 80% of best PIB would be achieved.
High power and high efficiency 1060nm semiconductor laser mini-bar with multi-active regions
Menghuan Wang,
Jianjun Li,
Yonggang Zou,
et al.
Show abstract
Aiming at the urgent demand of small volume, high efficiency and high power laser source in the field of laser ranging, we proposed a multi-active-regions mini-bar (MAMB) structure of semiconductor laser diodes, in which multi-active regions (or sub-LDs) are cascaded by reverse-biased tunnel junctions (TJs) transversely, meanwhile, several sub-cells composed of sub-LDs form mini-bar laterally. The entire structure was epitaxially grown on GaAs substrate by MOCVD. In order to minimize the additional series resistance introduced by the tunnel junction, InGaAs double quantum wells (DQWs) TJ is adopted. To increase the COMD level, each sub-LD uses an AlGaAs asymmetric large optical cavity, in which the active region is a compressive strained InGaAs DQWs. After the standard chip post-process, the MAMB was fabricated with the ridge-shaped sub-cells, which has a strip width of 200μm and cavity length of 1mm. The MAMB was then soldered on C-mount and mounted on TO3 to test at room temperature with a frequency of 20 Hz and a pulse width of 20 μs. The output power of a MAMB with 3 active regions and 3 sub-cells reaches 47.76 W (28 A), corresponding to a slope efficiency of 2.02 W/A, and the peak wavelength is 1060.6 nm. The results show that the MAMB structure could effectively improve the output power and reduce its volume.
Experimental study of the transverse mode instability in different core diameter fiber laser oscillators
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With the increase of fiber laser output power, stimulated Raman scattering (SRS) and transverse mode instability (TMI) effects have become the main factors limiting the power boost of high-power, high-brightness fiber lasers. In this work, the TMI effect in different core diameter fiber laser oscillators are studied experimentally. In the 25/400YDF laser oscillator, the TMI threshold is around 1780W, while the TMI threshold of the 30/400YDF is around 1070W. A new type gain fiber (25-30-25YDF) by precisely splicing 25/400YDF with 30/400YDF is employed in the fiber oscillator. When the launched pump power is ~2044W, the maximum average power of the 25-30-25YDF laser oscillator is up to ~1573W without any sign of the TMI. The experimental results show that the larger the efficient core diameter of the gain fiber, the lower TMI threshold of the fiber laser oscillator under the identical experimental structure. By optimizing the length of different core diameter fibers in the cavity and improving the fusion quality of each splice point of the laser, the output average power and beam quality of the fiber laser can be further improved.
Finite element analysis of stimuli-responsive mesoscopic hydrogel via ultrafast laser processing (Withdrawal Notice)
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This paper, originally published on 17 May 2019, was withdrawn on 24 July 2019 at the request of the authors.
Generation of soliton molecules in a 2-μm mode-locked fiber laser
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We report the experimental results of various soliton molecules in a passively mode-locked thulium-doped fiber laser based on nonlinear polarization rotation (NPR) technology. Not only stable single solitons but also soliton molecules can be observed in the same cavity. With the increase of the pump power, soliton triplets composed of three solitons can also be observed. It is found that the ratio of the pulse separation to the pulse width is less than 5, which indicates that the direct soliton interaction leads to the formation of bound states. On the other hand, the effect of the dispersive wave is to suppress the random relative phase change between the solitons and leads to phase-locking. Meanwhile, we analyzed the complex nonlinear interactions that form soliton molecules and enriched the nonlinear dynamics of soliton molecules at 2-μm.
Photoacoustic properties of metal-insulator-metal nanostructures
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By combining the advantages of high resolution in optical imaging and deep penetration depth in ultrasound imaging, photoacoustic(PA) imaging enables high resolution deep imaging in vivo. A nanoprobe with high conversion efficiency is usually used in order to increase the amplitude of the photoacoustic signal. Here, highly efficient PA conversion is demonstrated in metal-insulator-metal(MIM) nanostructures. A magnetic resonance can be formed to achieve nearly 100% absorption of incident light near the resonant wavelength. In this paper, the absorbance of the MIM structure in the visible and near-infrared wavelength is demonstrated at first. Then, multiphysics coupling approach is used to solve the electromagnetic, thermodynamic and transient acoustic pressure physics. The results show that the photoacoustic signal amplitude of the MIM structures is much higher than that of the same structures without the top metal strips. Due to its high PA conversion efficiency, the MIM nanostructures can generate strong PA signals with low laser incident power, resulting in better biocompatibility. In this way, it can be applied not only as a PA probe to biomedical PA imaging, photoacoustic tomography, but also to medical related fields such as photothermotherapy and precision drug delivery.
Carbon nanotube-doped electric hydrogels via ultrafast laser processing and loading conductive polymer
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Carbon nanotube, the smallest nanoelectronic materials, has been extensively used as electric materials for chip-scale electronics due to their high electronics conductivity, desirable mechanical properties, and easy surface functionalization. Also the conductive polymer, well-known for its high work function, real-time responsiveness, easy film-formation ability and stretchability. Herein, we combine the carbon nanotube-doped hydrophilic materials with conductive polymer via two-photon hydrogelation for conductivity-tunable functional devices. Taking advantage non-covalent π-π effect, we interpenetrated π-conjugated poly (3,4-ethylenedioxythiophene) into multiwall carbon nanotube-embedded mesoscopic hydrogels, which sustains electronic conductivity, hydrogel-like mechanical properties and desirable tolerance to humid/acid environments. Some reliable, nanostructured, metal-free electronic circuits and interdigital capacitors were fabricated and identified. Carbon nanotube-doped electric hydrogels successfully breaks current limitations by making better use of two photon hydrogelation and intermolecular force with conductive polymer. Moreover, a fast-speed two-photon fluorescence imaging technique using same optical system was deployed to detect the distribution of conductive polymer around electric patterns. Keywords: multi-wall carbon nanotube, conductive polymer, two-photon hydrogelation, mesoscopic electric hydrogels.
Wide field Raman super-resolution microscopy
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The appearance of fluorescent probes has greatly promoted the development of optical microscopy, while Raman scattering detection is a further progress attracting more applications of microscopy. However, the research on the wide-field detection and imaging of Raman signals is a challenging project in recent years. We propose a method combining super-resolution structured illumination microscopy (SIM) and the wide-field narrow-bandwidth filtering technique of the tunable filter, using a digital micro mirror device (DMD) to generate structured patterns, and a pair of filters whose cutoff frequency can change as the angle of incidence changes, which allows us to obtain super-resolution images of samples at specific Raman shift peaks. We build up a microscopy system using this method, perform imaging experiments on fluorescent beads of different emission wavelengths and achieve the expected results. In the 3T3 Cell marked with SERS beads imaging experiments, good results are also achieved. We hope that this technology can be applied to more occasions, such as dynamic imaging of biological structures.
System development of productization Raman-Mie aerosol water vapor lidar
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The new-type all-weather Raman-Mie scattering lidar system applied to atmospheric aerosol pollution monitoring was introduced, and it was mainly used for automatic continuous monitoring of atmospheric boundary layer structure, tropospheric aerosol and cloud optimal characteristics, morphologies and water vapor mixture ratio. In the aspect of overall structure, this system utilizes mature Mie scattering, polarization and Raman lidar technologies as well as integrated design with compact structure and convenient transportation, and it doesn’t need installation and debugging in the out-field test. The system emits three wavelengths 355nm, 532nm and 1,064nm, single-pulse energies are 50mj, 90mj and 250mj respectively, repetition frequency is 20Hz, Cassegrain telescope with 400mm caliber is used as the receiving system and subsequent optical and sounding units consist of six sounding channels, where Raman sounding channel is used to measure 386nm Rama scattering signal generated due to reaction of 355nm emergent laser with nitrogen molecules in the atmosphere and 407nm Raman scattering signal generated due to the reaction with vapor molecules in the atmosphere. Vertical sounding channel is used to measure vertical component of Mie scattering signal generated due to the reaction of 532nm emergent laser with particles in the atmosphere and horizontal sounding channel is used to measure horizontal component of Mie scattering signal generated due to 532nm emergent laser with particles in the atmosphere. Measured data of six sounding channels used and the abovementioned inversion method combined, optical parameters of tropospheric aerosol and cloud and vertical distribution features of water vapor mixture ratio can be obtained. This lidar product was transported to Chongqing in February, 2018 for out-field test which lasted 4 months, the equipment was under normal operation in this period and remained unattended, measured data were automatically transmitted to users through network and data transmission functions, and measured results could be automatically processed and displayed in a real-time way, thus realizing product application requirements of lidar, and then it could be extensively applied to research fields like atmospheric environmental monitoring and atmospheric sciences.
Spatial regulation of thermal emission based on polar material
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The ability to regulate the emission angle of thermal source is crucial for improving the efficiency of many energy conversion systems. Here, we design a structure of Ge/Al2O3/Au which can realize the spatial regulation of thermal emission. It has been shown that nearly perfect absorption could be attained and the range of emission angle could be tuned without structural patterning. By utilizing Berreman mode and intrinsic loss of Al2O3, we could attain the expansion of the range of emission angle.
Non-reciprocal character in the microwave photonic sensing system utilized by the intensity optical modulator
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The microwave photonic sensing system is widely investigated recently. The transmission character between two types of optical sensing schemes interrogated by microwave approach is investigated. The first case is that the incoherent light is modulated by the electro-optic modulator firstly and then filtered, and the second case is that the incoherent light is filtered firstly and then modulated. Experimental results show that the optical loss and microwave loss of the links between two cases are different. By utilizing a fiber with the length of 2km between and optical filter, the optical loss of the links in case I is 1.8dB lower than that in case II, and the microwave loss of the links in case I is 3.8dB lower than that in case II. To conclude, the non-reciprocal character appears in this incoherent microwave photonics links.
The first harmonic generation and linear susceptibility tensor variation at crystal boundary
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It’s widely agreed that optical characteristics at crystal boundary may change comparing to the internal part of bulk crystal but, as far as we know, sometimes the phenomenon, for example, the variation of susceptibility usually can’t be intuitively, simply presented in experiments. Recently, we observe a kind of special harmonic generation which is at the same wavelength as incident light. Besides, this kind of harmonic generation behaves in a similar way with nonlinear Cherenkov radiation, thus we call it linear Cherenkov radiation (LCR). We theoretically predict and calculate the phase-matching scheme and radiation path of LCR. In our experiment, we employ a polished KDP to verify our theory about the conversion of polarization in this process, and the phenomenon also help to rule out the possibility of birefringence at boundary. Combining with the coupling wave equation, we can derive new elements in linear susceptibility tensor according to the polarization states of incident light and LCR. The result tells us the linear susceptibility at the KDP boundary is assuredly different from that in bulk crystal, and this is mainly because of the breakdown of crystal symmetry at boundary, in our opinion. The existence of LCR is evidence of the variation of linear susceptibility. And in return, we could use this phenomenon to probe the non-zero elements in the tensor.
Research on 940nm kilowatt high efficiency quasi-continuous diode laser bars
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High-power GaAs-based semiconductor lasers are the most efficient source of energy for converting electrical into optical power. 940nm diode lasers are used directly or as pump sources for Yb:YAG solid-state lasers, and are widely used in laser cladding and other fields. Improving electro-optic conversion efficiency and reliable output power are urgent requirements for current research hotspots and industrial laser systems. In this paper, we use an asymmetric epitaxial structure of InGaAs/AlGaAs, which reduces the optical loss and resistance, and adopt better cavity surface technology to present 940nm 1-cm quasi-continuous micro-channel cooling (MCC) laser bars. The lasers are tested under a high duty cycle of 9.6% (600us,160Hz) at 25°C with output power of 660.05W, electro-optic conversion efficiency of 64.71% at 600A and slope efficiency of 1.16 W/A. The peak efficiency reaches 72.4%. The increased efficiency results from a lower threshold current and a lower series resistance. Furthermore, the output power of 1025W (1000A) has been confirmed at a duty cycle of 4% (400us,100Hz).
Simulation software design for Guanlan lidar data link
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Guanlan is a Marine science satellite designed by Qingdao Pilot National Laboratory for Marine Science and Technology. Its application goal is to detect atmospheric parameters and ocean parameters of water bodies. In order to verify the rationality of the design of the parameters of spaceborne lidar, we use MATLAB as the basic simulation software development platform. By reasonable design of laser pulse signal source, atmospheric transmission channel, underwater transmission channel, optical system and detector receiving model, link simulation and parameter inversion. To capture the information carried by the echo signal more accurately, we use 1ns as sampling interval, the energy of each laser pulse is converted to the number of photons and then hashed in each sampling interval according to the Gauss shape, achieving the process of launching, transmitting and receiving simulated signals. The simulation results show that the software platform achieves the purpose of evaluating and guiding the design process of system parameters.
Gold nanosprings formed by rolled-up technique
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Three-dimensional helical nanostructures have attracted a great deal of attention by the virtue of anomalous properties in mechanics, electricity, electromagnetism and optics due to their intriguing shapes. This paper mainly introduces the fabrication of novel gold nanosprings by using the rolled-up technique and studies their mechanical and piezoresistive properties. Cutting across 80 nm thick gold film deposited on silicon substrate with defective nanofiber probes, we fabricate nanosprings with variable size. Maximum elastic elongation and electromechanical resonance of one gold nanospring are measured. Furthermore, we survey its piezoresistive property. It can be inferred that low stiffness, large displacement and strong piezoresistive effect of gold nanospring make it an excellent candidate for potential application as micro electro-mechanical sensor.
Label-free analysis of senescent cells by light sheet microfluidic cytometry with a disposable hydrodynamic focusing unit
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The detection of senescent cells becomes increasing important for tumor therapy and drug screening. Here a light sheet microfluidic cytometer with a disposable hydrodynamic focusing unit is developed for two dimensional (2D) light scattering measurements of single cells. The mixed polystyrene microspheres of 3.87 and 2.0 μm in diameter are successfully differentiated by our 2D light scattering microfluidic cytometer. The application of the 2D light scattering microfluidic cytometry for the label-free analysis of senescent cells without any labeling or staining is demonstrated by measurements of H2O2-treated U87 cells. Our light sheet-based 2D light scattering microfluidic cytometer is easy to assemble with a disposable hydrodynamic unit, which may find wild applications in clinics for label-free cell classification.
Reconfigurable linear-phase response spectral shaping filer
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The optical filters are studied according to the applications of photonic-assisted radio frequency (RF) signal gereration and all optical coherent signal processing. Firstly, the finite impulse response (FIR) filter is analyzed theoretically. And it points out that the advantages of FIR lies in the reconfiguration, real coefficients and linear-phase impulse response which could guarantee the coherence of the ultrashort pulse. Based on this, the specific filters for free spectral range (FSR) broadening and sinusoidal signal generation are designed and simulated. The results of the simulation showed that the FSR of comb filter is 20 GHz with a sidelobe suppression of 20 dB, the demand of FSR broadening is satisfied. Meanwhile, based on the FSP stacking over several ten nanometre optical spectrum, shaping filter is realized for sinusoidal signal generation. Finally, the potentials of low dimensional materials enhanced integrated filters for wide FSR (< 50 nm) are discussed in the last part.
Reflection-mode broadband photoacoustic microscopy based on surface plasmon resonance
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We developed a reflection-mode broadband photoacoustic microscopy (PAM) based on surface plasmon resonance (SPR). Taking advantage of high-sensitivity refractive index sensing and ultrafast time response of the SPR sensor, photoacoustic (PA) transients can be measured accurately. The PAM system shows, experimentally, the available detection bandwidth of up to ~109 MHz, giving an estimated axial resolution of around 12.1 μm. A reflective objective is combined with a miniature SPR sensor, enabling the reflection-mode PAM with a lateral resolution of 5.0 μm. Using our PAM system, we image melanoma cells in vitro, providing the spatial distribution of melanin particles within melanoma cells. Further, the microvasculature is acquired in a mouse ear in vivo, delineating three-dimensional morphological characteristics of both the major blood vessels and capillaries.
High-sensitivity reflection-mode in-vivo photoacoustic microscopy based on surface plasmon resonance sensing
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Photoacoustic (PA) microscopy can measure the optical absorption properties of tissues with high specificity. However, most photoacoustic microscopy (PAM) systems use piezoelectric ultrasonic transducers for PA pressure detection. Due to the limited bandwidth, the axial resolution of PA imaging is low (generally lager than 20-μm), resulting in inaccurate positioning of light absorbing biomolecules. Moreover, the large difference in spatial resolution between the axial and lateral directions severely degrades the reconstruction of the three-dimensional image of the tissue. Surface plasmon resonance sensing (SPR) has an ultra-fast time response and thus is expected to increase the detection bandwidth of PA waves. The disturbance of the PA pressure wave causes the refractive index change of the medium near the sensing layer, which modulates the SPR field. By detecting the change of the optical reflectivity, wideband PA detection can be realized. Here, we combine the SPR detector and an acoustic cavity with the ellipsoid inner surface for PA detection, which not only enhances the signal detection sensitivity, but also realizes the reflection-mode PA imaging. The experimental results show that the imaging signal-to-noise ratio (SNR) increases by around three times, and the detection bandwidth is more than 70-MHz. High resolution and high contrast vascular imaging of mouse ear is acquired in vivo.
Visible light propagation characteristics under turbulent atmosphere and its impact on communication performance of traffic system
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In this paper, mathematical modeling and statistical methods are used. establishing a simple bit error rate evaluation model of intelligent transportation optical communication system under ideal atmospheric conditions. The lognormal turbulence distribution model is introduced into the geometric model of visible optical communication system to further calculate the parameters of the whole communication system. The effects of signal-to-noise ratio, aperture size, visibility, wavelength and other factors on the bit error rate and channel capacity of visible optical communication are calculated and analyzed. After calculation, the bit error rate increases with the increase of signal-to-noise ratio (SNR), decreases with the increase of visible wavelength and increase with distance. besides, the stronger the turbulence is, the more violent the fluctuation of BER is. The simulation results based on this model are basically consistent with the actual situation. It can simulate the visible light communication of intelligent transportation system better and provide reference for the selection of communication parameters in different environments.
Optical switch with a hot bubble
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Based on microfluidics and optical communication technology, an optofluidic switch is proposed, where the hot bubble driving technology is used. And switch-on or switch-off and the optical path switching are realized by a hot bubble in the microchannel. The growth and condensation of the gas bubble in the microchannel is controlled by temperature. The optical switch has the advantages of small volume, simple and compact structure, low driving voltage, low power consumption, no mechanical moving parts and easy operation. This paper introduces the structure, processing technology and working principle of this optical switch.