Show all abstracts
View Session
- Front Matter: Volume 9543
- Third International Symposium on Laser Interaction with Matter
Front Matter: Volume 9543
Front Matter: Volume 9543
Show abstract
This PDF file contains the front matter associated with SPIE Proceedings Volume 9543, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.
Third International Symposium on Laser Interaction with Matter
Nuclear excimer concept
Show abstract
Excimer laser technology has played a commanding role in the study of nonlinear electromagnetic phenomenon. Examined herein is the possibility that the excimer concept could be lifted into the nuclear region for the generation of amplification in the gamma-ray range. There exists a fundamental structural/dynamic analogy that supports this possibility.
Apply high-power fiber laser in oil/gas wells drilling
Show abstract
The concept of using lasers to drill through rock has been discussed in the oil and gas industries since the development of the high-power laser. To evaluate the possibility of fielding a laser drilling system, two laser-related problems have to be investigated. The first is the irradiation effects of laser upon rocks; the second is the effects in laser transmission from the source to the rock deep in the well. This transmission includes two stages: the first stage is the transmission inside a fiber, which is packaged in a cable and has about the same length with the well depth; the second stage refers to the transmission process when the laser leaves the fiber and some transforming optics and transmits to the rock surface, during which the well conditions may impose tough restrictions. In this paper, experiment results of laser irradiation upon siliceous sandstone and granite are reported, and the fiber transmission loss is simulated, considering the main absorbing or scattering mechanisms inside fiber. And the laser transmission from the fiber end to the rock surface, in my view, may impose great challenge on the laser drilling technology.
The influence of molten pool geometry on forced convective heat transfer
Show abstract
An investigation was conducted to determine the relationship between heat transfer coefficient and molten pool’s geometry. It was accomplished by performing an experimental and numerical investigation using a cylinder dimple with two different serials of geometry: (1) cylinder dimples with fixed print diameter D=50mm and different depth, and (2) cylinder dimples with fixed depth d=10mm and different print diameter. The airflow speed varies from 50m/s to 250m/s in the turbulent regime. The results consist of flow characteristics, mainly velocity profile and heat transfer characteristics, including heat transfer coefficient and Nusselt number along flow direction, were obtained. The comparison was held against the smooth surface. Results showed that a centrally-located vortex was formed due to the flow separation. For heat transfer coefficient, such augmentations are present near the downstream edges and diminutions are present near the upstream edges of dimple rims, both slightly within each depression. It was found that the convection heat transfer coefficients with different geometry parameters have similar distribution along flow direction. A uniform piecewise linear function was built to describe the heat transfer characterizes for different molten pool print diameter.
Extinction characterization of soot produced by laser ablating carbon fiber composite materials in air flow
Show abstract
In order to research the dynamic process of energy coupling between an incident laser and a carbon fiber/epoxy resin composite material, an extinction characterization analysis of soot, which is produced by laser ablating and located in an air flow that is tangential to the surface of the composite material, is carried out. By the theory analyses, a relationship of mass extinction coefficient and extinction cross section of the soot is derived. It is obtained that the mass extinction coefficients of soot aggregates are the same as those of the primary particles when they contain only a few primary particles. This conclusion is significant when the soot is located in an air flow field, where the generations of the big soot aggregates are suppressed. A verification experiment is designed. The experiment employs Laser Induced Incandescence technology and laser extinction method for the soot synchronization diagnosis. It can derive a temporal curve of the mass extinction coefficient from the soot concentration and laser transmittance. The experiment results show that the mass extinction coefficient becomes smaller when the air flow velocity is higher. The reason is due to the decrease of the scatter effects of the soot particles. The experiment results agree with the theory analysis conclusion.
TiO2/SiO2 dielectric film damage induced by combination of pulsed and continuous wave infrared laser irradiation
Menglian Zhou,
Yue Cai,
Minbo He,
et al.
Show abstract
This paper describes the combined irradiation effect of 2.7μm pulsed and 10.6μm continuous wave (CW) lasers on TiO2/SiO2 dielectric films. There were four combined irradiation time sequences, two of which were irradiation one after another and two were irradiation overlap. Single laser irradiation on the films was also carried out for analyzing the different results. The transmission spectrums of the films in visible and NIR region were measured before and after laser irradiation, which was taken as one of the measures of the damage degree. Typical damage morphologies under different conditions and the standing electromagnetic wave field of two laser wavelengths in the film samples were given. Comparing the irradiation results of different time sequences, especially when the pulsed laser ahead or behind of CW laser, conclusion can be drawn that the overlap of pulsed and CW laser had the most serious damage degree of the films.
Anisotropic study of thermal stresses of (110) Silicon induced by millisecond laser
Show abstract
A 3D numerical model has been built to investigate anisotropic thermal stresses of (110) silicon induced by millisecond laser. The 12 slip systems resolved shear stress field of the silicon was obtained by using the FEM. The excess resolved shear stress field is identified. comparing to the experiment of the millisecond irradiating (110) PIN photodiode, we conclude that the thermal slips are introduced duo to the anisotropic thermal stresses of silicon surpassed the critical yield stress and brittle cracks are introduced due to the initiation points offered by the thermal slips which will reduce the fracture strength greatly. These thermal slips and brittle cracks increase the dark current of the photodiode greatly.
Surface damage features of sapphire by 1064nm Nd: YAG pulsed laser irradiation
Show abstract
The problem of laser induced damage of optical materials is one bottleneck to restrict laser power levels and beam quality enhances unceasingly. The research on laser induced optical material damage, improving optical material laser damage threshold, becomes a hot issue in the development of laser technology. In this paper, laser-induced sapphire damage morphology using nanosecond 1064nm Nd: YAG is reported. Analyzed the temperature variation of sapphire inclusion under different laser fluence irradiation, and the temperature variation of inclusion's dimension radius by finite element method. The laser-induced damage experiment of sapphire materials are investigated (pulse width is 6ns). At the same time, the sapphire laser-induced damage threshold, the damage position distribution, the influence of different laser fluence on the damage area and damage growth characteristics are analyzed. Results show that the inclusion absorption mechanisms can better explain the sapphire under the nanosecond laser pulse irradiation damage, and simulation results are in agreement with the experimental results. In addition, for 1-on-l irradiation, the surface damage area for sapphire surface increase linearly, for s-on-1 irradiation, the damage area on the back surface increases exponentials with the increase of shot number.
Diffuse reflectivity of gold plating with high power laser irradiation
Show abstract
The discoloration and optical characteristics of the gold plating film under long-time high power laser irradiation are investigated. The fabrication process of gold plating on nickel underplate on rough surface of copper and aluminum alloy substrates is introduced. The measurement results of the diffuse reflectivity for the samples with different surface roughness indicate that roughness of the gold layer surface should be 4μm to obtain the maximum value of diffuse reflectivity. The discoloration and variation of diffuse reflectivity are experimentally studied under 2000W irradiation. The research results show that the discoloration and degrading of reflectivity are caused by the diffusion of Ni to the gold plating surface and forming NiO thin film due to the porosity of the gold film and high temperature treatment. A change of diffuse reflectivity related mechanism is described. Several plating solution recipes are used to eliminate the discoloration and mitigate the degrading of the reflectivity on gold surface.
Typical effects of laser dazzling CCD camera
Show abstract
In this article, an overview of laser dazzling effect to buried channel CCD camera is given. The CCDs are sorted into staring and scanning types. The former includes the frame transfer and interline transfer types. The latter includes linear and time delay integration types. All CCDs must perform four primary tasks in generating an image, which are called charge generation, charge collection, charge transfer and charge measurement. In camera, the lenses are needed to input the optical signal to the CCD sensors, in which the techniques for erasing stray light are used. And the electron circuits are needed to process the output signal of CCD, in which many electronic techniques are used. The dazzling effects are the conjunct result of light distribution distortion and charge distribution distortion, which respectively derive from the lens and the sensor. Strictly speaking, in lens, the light distribution is not distorted. In general, the lens are so well designed and fabricated that its stray light can be neglected. But the laser is of much enough intensity to make its stray light obvious. In CCD image sensors, laser can induce a so large electrons generation. Charges transfer inefficiency and charges blooming will cause the distortion of the charge distribution. Commonly, the largest signal outputted from CCD sensor is restricted by capability of the collection well of CCD, and can’t go beyond the dynamic range for the subsequent electron circuits maintaining normal work. So the signal is not distorted in the post-processing circuits. But some techniques in the circuit can make some dazzling effects present different phenomenon in final image.
Theoretical and experimental analysis of mode size optimization in all-solid-state Cr:LiSAF lasers
Show abstract
A general model has been developed for the optimization of the end-pumped solid-state lasers by including the effect of beam quality of the pump, and ellipticity of pump and oscillation beam into the overlap integrals. Previous models of mode-matching between oscillation and pump beam just consider of the ellipticity of pump beam, and assume the Gaussian oscillation beam to be circle TEM00 mode. Our model of mode-matching considers not only the ellipticity of the pump and oscillation beam, but also the angle of the long axis of the pump and oscillation beam. To illustrate the utility of the present model, an end-pumped Cr:LiSAF laser pumped is considered and the experimental results fit well with the theoretical results.
Spectrum method for laser induced damage in dielectric thin films
Show abstract
This paper shows some tentative results with which laser induced damage on dielectric thin films is analyzed by using the transmission spectrum. The damage characters were extracted in high-resolution images of damaged films, and transmission spectrum of damaged thin films was measured. The mathematical model of transmission was built based on the matrix optics theory with the optical properties, which include the effective refractive index, effective extinction coefficient, effective thickness and wavelength, and so on. Changes of optical properties in different damaged degree were analyzed by the transmittance spectrum. Through which laser-induced damage mechanisms had been analyzed with the micro-examinations of films.
Experimental investigation on thermal ablation of carbon-fiber/epoxy composite irradiated by continuous wave laser
Show abstract
The tests of carbon-fiber/epoxy composite laminates, subjected to a tangential gas-flow and 1070 nm continuous wave laser，are carried out to acquire the ablation laws of samples on the conditions of different gas-flow. Simultaneously, considered the images from camera of large dynamic range, the damage laws of samples are also obtained for various laser power densities. Experimental results reveal that, without airflow on sample surface, the smoke caused by laser heating can be quickly on fire which causes a burn damage on the surface of samples so that the mass loss is most of all. However, the tangential airflow can remove away the smoke which has a weakening effect on the energy of incidence laser. So the ablation depth has an obvious increase in laser irradiation area. Unlike airflow, nitrogen flow can obviously restrain oxidation ablation on surface so that the ablation damage in laser irradiation area is relatively not severe. On the other hand, as laser power density increases, the mass loss of samples continues to rise but isn’t proportional. And the ablation heat with the increase of power density shows a complex change. Below power density of 390 W/cm2, the mass loss mainly depends on the pyrolysis of epoxy while the ablation heat has a gradual decrease. Along with power density increasing but less than 1330 W/cm2 , the oxidation ablation of carbon fibers will be a leading factor and the ablation heat shows a little increase. Above power density of 1330 W/cm2 , the carbon fibers turn up the phenomenon of sublimation. What’s more, airflow removed effects will be enhanced in high temperature. In this case, the ablation heat again has a trend of decrease.
Thermal response model of polymer matrix composites under laser irradiating
Show abstract
A numerical study is conducted to determine which model could be used to compute temperature fields of polymer matrix composites under laser irradiating. By using the local thermal non-equilibrium model, solid and gas temperature on surfaces of materials with different volume convection coefficients have been computed and compared under different heat flux. The results show that the assumption of local thermal equilibrium is not reasonable until the heat flux applied to composites is low enough and the volume convection coefficient is big enough. And the gas may be not important for solid temperature when the volume convection coefficient is small.
Ultrasonic guided wave based horizontal crack imaging in metal plate by local wavenumber analysis
Show abstract
Ultrasonic guided waves are one of the most prominent tools for SHM in plate-like structure. However, complex propagation characteristics of guided waves as well as traditional contact ultrasonic transducers limit its application in the practical damage detection. Scanning Laser Doppler vibrometer (SLDV) technology is an effective non-contact method to obtain ultrasonic guided wavefield with ultra-high spatial resolution. Based on abundant wavefield data, wavenumber imaging algorithms are capable of not only damage location, but also assessment of damage characteristics such as size and shape. In this work, we adopt local wavenumber analysis method for horizontal crack detection in platelike structure. Instead of using SLDV in experiment, 3D finite element numerical method is adopted to obtain full ultrasonic guided wavefield data. Since the horizontal cracks result in decrease of local thickness, the wavenumber in corresponding area shows significant increase, which is used as indicators for crack imaging. The effects of different damage shapes, depths and spatial window sizes on imaging are also discussed. Numerical simulation results and imaging algorithm laid the foundation for the method applied in experiment and practice.
Numerical modeling of guided ultrasonic waves generated and received by PZT wafer in a beam
Show abstract
The spectral finite element method (SFEM) is developed to predict guided ultrasonic waves in the surface-bonded piezoelectric wafer and beam structure. The Timoshenko beam theory, the Euler-Bernoulli beam theory and linear piezoelectricity are used to model the base beam and electric-mechanical behavior of the piezoelectric wafer respectively. Using Hamilton’s principle, the governing equations are obtained in the time domain, and then the SFEM are formulated from coupled differential equations of motion transformed into the frequency domain via the discrete Fourier transform. The SFEM is used to analyze the dispersion characteristics, mode conversion of guided waves and the interaction of waves and notch. The high accuracy of the present SFEM is verified by comparing with the finite element method results.
Three-dimensional thermal response numerical simulation of laser irradiating simulative warhead target
Show abstract
The thermal response of a cylindrical simulative warhead consisting of the steel casing and the TNT explosive irradiated by laser is simulated, basing on the smoothed particle hydrodynamics method. Preliminary computational simulation results show that, when the power density of 500W/cm2 continuous laser irradiation on a sealed explosive device consisting of the type 304 steel casing with thickness of 5mm and TNT explosive, compared with no airflow, the speed of 200m/s tangential airflow can reduce the thermal initiation time of 0.6s. In the case of incident laser power density is high, the convection cooling effect of tangential airflow can be neglected. The oxidation of airflow can significantly shorten the thermal initiation time of internal explosive.
Laser-induced damage of GaAs/Ge solar cells by 532nm laser
Show abstract
Single-heterogeneous junction GaAs/Ge solar cells induced by 532nm laser with the pulse width of 12ns are investigated. Results indicate that the GaAs/Ge solar cells would mostly be damaged when laser is focused on its grid lines. Its surface damage morphology initially occurs at 0.35J/cm2 by the single laser pulse with nanosecond duration. Theoretically, the nanosecond laser pulse leaded damage mainly comes from both the thermal and the mechanical effects. These experimental conclusions are tested and verified by scanning electron microscope with energy dispersive spectroscopy and X-ray photoelectron spectroscopy.
Optical properties and thermal response of Au/Cr double-layer metal films induced by femtosecond lasers
Show abstract
Femtosecond pulse laser was used to induce Au/Cr double-layer metal films. The time dependence of transient relative reflectivity was measured by optical pump-probe experiment for 400 nm pump light and 800 nm probe light. The pulse width was 90 fs. The drastic changes in reflectivity were observed, and double-layer films with different thickness of Au layer leaded to different reflectivity changes. Next, a critical points model with the Drude model was proposed to describe the permittivity of Au in the 200-1000 nm range. This model was combined with a two-temperature equation to investigate optical properties and thermal response of Au/Cr double-layer metal films induced by femtosecond lasers. The simulated results provided more physical information for femtosecond laser induced double-layer metal films.
355nm and 1064nm laser damage of quartz glass
Show abstract
In this paper, the laser damage thresholds of the quartz glass with/without HF acid etching are investigated induced by the wavelength of the 355nm and 1064nm respectively. Laser-induced damage threshold of the quartz glass can be improved by optimizing the HF concentration and etched time. The experimental results shown that laser induced damage thresholds of quartz glass for 355nm and 1064nm were 7.1×108 W/cm2 and 1.15×109 W/cm2 respectively, after HF acid treatment with the 10% HF concentration and etched time 15 minutes, laser induced damage thresholds of quartz glass for 355nm changed to 1.29×109 W/cm2 and improved 81.7%, while for 1064nm changed to 1.73×109 W/cm2 and improved 50.4%. The surface damage morphologies of quartz glass induced by the 355nm and 1064nm with/without HF acid etching were comparative analyzed. Finally, the laser induced damaged mechanisms of quartz glass for 355nm and 1064nm were given.
Characteristics and detecting of laser-induced single bubble collapse noise
Show abstract
Shock waves emission after collapse of a laser-induced bubble in the liquid was studied experimentally by using a PTZ hydrophone. An experimental method and a Cavitation detection system was designed to investigate bubble collapse noise in this article. When a focused short laser pulse was focused in a liquid near a solid wall, it induced optical breakdown, the emission of shock waves and the generation of cavitation bubbles. A PZT hydrophone was used to detect the shock wave emitted during bubble oscillations. In addition, a software based on MATLAB was designed for analyzing cavitation noise. The software system had multiple functionalities, namely signal reading, noise reduction, signal analysis in frequency domain, and display. The results showed that the software can not only reflect the spectral characteristics of the noise quickly but also can interpret the current cavitation station according to the changing rules of different cavitation station. The results of the research have strong implications for cavitation phenomena analysis and cavitation warning systems in turbines, propellers, and other irrigation machinery.
Comparison of bare and sol-gel coated of mitigated site on fused silica
Show abstract
The performance of mitigated site coated with antireflective (AR) coating is investigated, and its
discrepancy is also investigated by comparing the bare site with substrate from surface morphology and
profile, transmittance and laser induced damage threshold (LIDT). The results indicated that more SiO2 sol
will be deposited in the crater of mitigated site during the dipping process, while the coated site does not
seriously influence the performance of the entire sample. The LIDT results indicate that both the coated
substrate and mitigated site are lower than that of un-coated substrate and mitigated site.
Keywords: fused silica; mitigated site; coating; sol-gel.
Reflectivity and laser irradiation of plasma sprayed Al coating
Show abstract
It's well known that Al has a very high reflectivity in the visible/near-infrared range, which makes it become a promising anti-laser material. But for a plasma sprayed coating, there are usually many defects, such as pores, cracks and interfaces among particles, which lead to properties difference with its bulk material. In this paper, the reflectivity of plasma sprayed Al coating and its laser irradiation effect were investigated. Its reflectivity, surface roughness, porosity, microstructure, and cross-section microstructure were characterized. The results show that a high reflectivity (98.1% at CO2 laser 10.6μm wavelength) of plasma sprayed Al coating, which is comparable with bulk material, could be obtained. Its optical laser damage threshold is 2×104W/cm2 that makes its reflectivity obviously decrease. Its damage mechanism is oxidation.
Effect of focus position of ns pulse laser on damage characteristics of K9 glass
Show abstract
Laser-induced damage of optical glasses has been investigated for more than fifty years. Due to the residual scratches, inclusions and other forms of defects at surfaces of optical glasses after the processes of grinding and polishing, it is well known that the sample surface can be damaged more easily than bulk. In order to get the relationship between the damage threshold and the location of the laser spot, we carried out damage experiments on K9 glasses with a 7ns pulse laser. Since ns pulse laser-induced damage of optical glasses always accompanies with the generation of the plasma, a optical microscope connected with a CCD camera was used to observe the plasma flash, which can provide a real time detection of damage sites. The laser pulse was first focused into the bulk, then the spot was moved toward the direction of incident laser beam step by step until the beam was completely focused in ambient air. Damage threshold curves were measured for each focus position, and low thresholds and high thresholds were extracted from those curves. Finally, the relationship between damage thresholds and focus position was analyzed.
3D numerical simulation of laser-generated Lamb waves propagation in 2D acoustic black holes
Show abstract
Acoustic black holes have been widely used in damping structural vibration. In this work, the Lamb waves are utilized to evaluate the specified structure. The three-dimensional numerical model of acoustic black holes with parabolic profile was established. The propagation of laser-generated Lamb wave in two-dimensional acoustic black holes was numerically simulated using the finite element method. The results indicated that the incident wave was trapped by the structure obviously.
Interferometry and shadow method observation millisecond laser interaction with silicon plate
Show abstract
Studied steam velocity and observed liquid molten splash phenomenon during the millisecond laser interaction with silicon plate. First, the interference pictures are obtained about the millisecond laser interaction with silicon plate. The energy of the laser is 7.38 J, and the pulse width is 1 ms. The thickness of silicon plate is 0.3 mm. The results show, When the laser irradiated 233 μs, the front surface of the silicon plate has been generated gasification; and When the laser irradiated 466 μs, the back surface of the silicon plate also has been generated gasification. By two pictures of fringe locations and time intervals, during the laser irradiation 233-466 μs, the steam velocity is 27.52 m/s in the front surface of the silicon plate, and during the laser irradiation 466-699 μs, the steam velocity is 20.47 m/s in the back surface of the silicon plate which are calculated. Then, the shadow pictures are obtained about the millisecond laser interaction with the same silicon plate. The results show, When the laser irradiated 466 μs, the front surface of the silicon plate has been generated molten liquid splash phenomenon; and When laser irradiated 699 μs, the back surface of the silicon plate also has been generated. Meanwhile, Laser interaction with silicon plate at later, the front and back surface of the silicon plate appears molten liquid splashing at the same time, and splashing in the direction and other issues were discussed. Finally, use blackbody radiation theory, explained the reasons for melt splashing brightness higher than the illumination lightness.
Simulations of high power laser-produced multi-keV X-ray source
Show abstract
Multi-keV x-ray source produced by high power laser interaction with solid metal target are widely used in high energy density physics research. This work proposed a numerical simulation method for designing the laser plasma X-ray source. The simulation was conducted using a collisional-radiative spectral code combined with one-dimension hydrodynamics code. Quite good agreement was found between the simulations and the experimental results. This work indicates that it is possible to apply this method in x-ray source optimizing.
The jet impact force of laser-induced bubble under the water-film with different thickness
Show abstract
The effect of water-film on the laser-induced bubble was investigated by a piezoelectric ceramic transducer (PZT) sensor. Both of the collapse time and liquid-jet impact force of the bubble under the water-film were obtained, and the experiments were also completed in different laser energy. The collapse time increase with the thickness of the waterfilm, but the liquid-jet impact force decrease. We consider that the collapse time was affected by both of the rigid boundary and surface, and the increasing of the collapse time is the reason the decreasing of the liquid-jet impact force. The velocity of bubble wall is lower with the longer collapse time for the uniform bubbles energy, so the liquid-jet impact force is lower. For the other reasons, more laser energy would be absorbed by the thicker water-film, but the water was also splashed for the thinner water-film. So, for the thinner water-film, the bubble energy is higher, the liquidjet impact force is higher, but the maximal radius is smaller because of the splash process. In the other hand, both of the collapse time and the liquid-jet impact force are increase with the laser energy. These researches are useful for the laser processing under water.
Determination of the nucleation region of Si particles produced by pulsed-laser deposition in Monte Carlo simulation
Show abstract
The nucleation and growth of Si nanoparticle produced by pulsed laser ablation in helium gas ambient is investigated via direct simulation Monte Carlo method with a real physical scale of target-substrate configuration. The nucleation area is important for the formation of Si nanoparticles, and the average size and size distribution of Si nanoparticles formed in this region depend on its range. The narrower the nucleation area and, therefore, the less the maximum times of collisions between Si atoms in the region, the smaller and the more uniform the Si nanoparticles. A nucleation and growth process is clearly observed. It is shown that the nucleation region and the nucleation growth internal is changing with time. The ambient gas pressure is important to nucleation region. The suitable pressure range under certain conditions is given and our simulated results are approximately in agreement with the previous experimental data.
Target micro-displacement measurement by a “comb” structure of intensity distribution in laser plasma propulsion
Show abstract
A “comb” structure of beam intensity distribution is designed and achieved to measure a target displacement of micrometer level in laser plasma propulsion. Base on the “comb” structure, the target displacement generated by nanosecond laser ablation solid target is measured and discussed. It is found that the “comb” structure is more suitable for a thin film target with a velocity lower than tens of millimeters per second. Combing with a light-electric monitor, the ‘comb’ structure can be used to measure a large range velocity.
Isolated attosecond pulse generation via the interference of ionized multi-recollision wave-packets
Show abstract
We propose and theoretically demonstrate a method for generating an intense isolated attosecond pulse by a few-cycle strong laser pulse. The numerical simulations show that a broadband supercontinuum spectrum can be obtained by the interference of the ionized multi-recollision wave-packets with different energies, which are produced from the laser field at different ionization instants. By controlling the peak intensity of the few-cycle laser pulse, the atom can be completely ionized in the rising edge of the few-cycle laser pulse. Therefore, the probability of ionized wave packet is large enough to ensure the continuous harmonics with high efficiency, and an intense isolated 77 as pulse can be achieved successfully. Moreover, it is shown that our scheme can modulate the duration of the isolated attosecond pulse by adjusting the initial population of the atom.
Laser driven performance of a multilayer flyer with carbon absorption layer
Show abstract
Laser driving flyer technology has been studied for many years and widely used in dynamic high-pressure physics and impact dynamics, rapid initiation of high explosives, simulation of space debris and micro-forming of metal foil. The coupling efficiency between the flyer kinetic energy and the laser energy could be improved by introducing a layer with stronger absorption at the 1064nm wavelength Nd:YAG laser, resulting in higher flyer velocity for a given laser energy. So a multilayer flyer (C/Al/Al2O3/Al) with Carbon absorption layer was designed and compared the flyer velocity with the flyer (Al/Al2O3/Al) without Carbon absorption layer. The experimental study was performed via the Photonic Doppler Velocimetry (PDV). The results show that the velocity of flyer with Carbon absorption layer rose with fluctuations as laser energy increasing, and was lower than that without Carbon layer at the same laser energy. That means the addition of Carbon absorption layer decreased the flyer coupling efficiency.
Influence of initial phase on spatial emission characteristics from electron oscillation driven by a linearly polarized few-cycle laser pulse
Show abstract
Full spatial emission characteristics of radiation generated from electron oscillations driven by a linearly polarized few-cycle laser pulse have been investigated theoretically and numerically using a single electron model. It is discovered that the influence of the initial phase on the process of full spatial characteristics of the radiation is apparent for few-cycle laser pulse. These phenomena are primarily governed by the electron dynamics and properties of the linearly polarized few-cycle laser pulse.
Numerical investigation on electrical characterization of a capacitive coupled radio-frequency plasma
Show abstract
This paper presents the main electrical features of capacitive coupled radio-frequency (CCRF) discharges in gas. A two-dimensional, time-dependent fluid model was established. Capacitive coupled plasmas (CCP) were produced by applying radio-frequency voltage to a pair of parallel plate electrodes which are separated from the plasma by dielectric layers. The electron equation and the electron transport equations were solved and yielded the electron number density and electron temperature. The electrostatic field was obtained by the solution of the Poisson equation. The distribution of electron temperature and electron number density was studied under different conditions: radio-frequency applied voltages (VRF=100-2000V), frequencies (f=3.0-40.68MHz), pressures (p=0.001-1torr), and gas species (O2, Ar, He, N2). The results show that electron number density presents a minimum near the electrodes, and presents a maximum between the positive and the negative electrodes. The distinguishing feature of CCP is the presence of oscillating sheaths near electrodes where displacement current dominates conduction current. These informations will help us to analyze the characters of CCP for application.
Theoretical study on the electron energy distribution function and electron transport parameters of argon plasma
Show abstract
Fluid model of argon plasma require the input of transport parameters that depend on the electron energy distribution function (EEDF). The EEDF and electron transport parameters of reduced field and electric field frequency in argon plasma are investigated by solving the Boltzmann equation with the two-term approximation. It is found that the EEDF closes to Druyvesteyn distribution and decreases sharply after several eV when the reduced field is less than 10Td. The low energy part of EEDF flats with the reduced field, and the high energy tail of EEDF increases with the reduced field. The EEDF approaches to dual temperature Maxwellian distribution when the reduced field is larger than 50Td. When the reduced field is larger than 300Td, the high energy tail of EEDF decreases more slowly than Maxwellian distribution, and the shape of EEDF tends to concave. The electron mobility decreases with the reduced field, and tends to a const . The electron diffusion coefficient increases with the reduced field, but exists a local minimum at 50Td. The relationship between EEDF and electric field frequency shows that the EEDF approaches to Maxwellian distribution in a high frequency field because of the collision with electrons and neutral particles. In this case, the electron mobility and diffusion coefficient are complex number, and the imaginary parts raise with the field frequency. The absolute value of transport parameters decrease with the field frequency.
High power CO2 coherent ladar haven't quit the stage of military affairs
Show abstract
The invention of the laser in 1960 created the possibility of using a source of coherent light as a transmitter for a laser radar (ladar). Coherent ladar shares many of the basic features of more common microwave radars. However, it is the extremely short operating wavelength of lasers that introduces new military applications, especially in the area of missile identification, space target tracking, remote rang finding, camouflage discrimination and toxic agent detection. Therefore, the most popular application field such as laser imaging and ranging were focused on CO2 laser in the last few decades. But during the development of solid state and fiber laser, some people said that the CO2 laser will be disappeared and will be replaced by the solid and fiber laser in the field of military and industry. The coherent CO2 laser radar will have the same destiny in the field of military affairs. However, to my opinion, the high power CO2 laser will be the most important laser source for laser radar and countermeasure in the future.
Single shot thermometry using laser induced thermal grating
Show abstract
With the concern of environmental protection and reducing the fossil fuel consumption, combustion processes need to be more efficient and less contaminable. Therefore, the ability to obtain important thermophysical parameters is crucial to combustion research and combustor design. Traditional surveying techniques were difficult to apply in a confined space, especially the physically intrusions of detectors can alter the combustion processes. Laser-based diagnostic techniques, like CARS, SVRS, PLIF and TDLAS, allow the in situ, non-intrusive, spatially and temporally resolved measurements of combustion parameters in hostile environments. We report here a new non-intrusive optical diagnostic technique, based on laser-induced thermal grating. Thermal gratings generated in NO2/N2 binary mixtures, arise from the nonlinear interaction between the medium and the light radiation from the interference of two pulsed, frequency-doubled Nd:YAG lasers (532 nm). This leads to the formation of a dynamic grating through the resonant absorption and the subsequent collisional relaxation. By the temporally resolved detection of a continuous wave, frequency-doubled Nd:YVO4 probe laser beam (671 nm) diffracted by LITG. The temporal behavior of the signal is a function of the local temperature and other properties of gas, various parameters of the target gas can be extracted by analyzing the signal. The accurate singleshot temperature measurements were carried out at different test conditions using a stainless steel pressurized cell, data averaged on 100 laser shots were compared with simultaneously recorded thermocouple data, and the results were consistent with each other. The LITG signal is shown to grow with increasing the gas pressure and is spatially coherent, which makes the LITG thermometry technique a promising candidate in high pressure environments.
Application comparison of LIDAR single-pulse and multi-pulse mode in high elevation difference area
Show abstract
Multi-pulse technology of airborne light detection and ranging (LIDAR) system is on the rise in recent years. A flight experiment in high elevation difference area was done by using LiDAR single-pulse and multi-pulse mode. The data acquisition can be completed successfully with low point density by using the single-pulse mode, while can’t be completed with multi-pulse mode for the influence of blind zone and atmospheric margin although it has a high point density. It is proved that multi-pulse mode has an advantage in point density but the influence of atmospheric margin must be avoided. Through elevation analysis and rational flight line design, a survey task in high elevation difference area was completed with good effect.
Indoor carbon dioxide monitoring with diode laser absorption at 2 μm
Show abstract
In order to investigate the variation of indoor carbon dioxide concentration and how it changes with human activities, a tunable diode laser absorption spectroscopy (TDLAS) system was used to monitor the indoor CO2 concentration. Based on Wavelength Modulation Spectroscopy double frequency detection (WMS-2f), the 2v1+v3 characteristic line (4991.26 cm-1) of CO2 was measured by a DFB laser. The measured concentration values were calibrated by means of a cell filled with reference gas. The results show that the daily average indoor CO2 concentrations is about 419ppm which is slightly higher than that of the outdoor and the changing range is between 380ppm and 510ppm in a day. The indoor CO2 concentration was influenced by the change of ventilation and indoor staff. The respiration of the indoor staff makes a greater impact on a relatively confined indoor CO2 concentration. The CO2 increasing rate is measured to be 80ppm/hour in the case of occupant density of 0.06 people/m3. Therefore, the staff crowded indoor should ventilate timely to prevent excessive CO2 causing people discomfort.
Measurements of CO concentration distribution for Mars atmospheric entry by combining OES and TDLAS
Show abstract
Shock tube experiments are carried out to study the physical and chemical processes during a vehicle entry into the Mars atmosphere using optical emission spectroscopy (OES) and tunable diode laser absorption spectroscopy (TDLAS). Gas temperature and CO concentration distribution are diagnosed behind a shock wave in a CO2-N2 mixture with two different conditions of initial pressure and velocity. The strong shock wave is established in a shock tube driven by combustion of hydrogen and oxygen. Time-resolved spectra of the Δv = 0 sequence of the B2Σ+→X2Σ+ electronic transition of CN have been observed through OES. A precise analysis of the CN violet spectra is performed and used to determine rotational and vibrational temperatures. Two absorption lines in the first overtone band of CO near 2.33 μm, are selected from a HITRAN simulation to calibrate laser wavelength and detect the CO concentration. Combined with these temperature results using OES, CO concentrations in the thermal equilibrium region are derived, which are 2.91 × 1012 cm-3 and 1.01 × 1013 cm-3, corresponding to equilibrium temperatures equal to 7000 ± 400 K and 6000 ± 300 K in low and high pressure conditions, respectively.
A novel measurement method of microorganism growth by tunable diode laser-absorption spectroscopy
Show abstract
The objective of this work was to attain essential parameters by using a Gompertz model that employed a new approach of wavelength modulation spectroscopy (WMS) to describe the microorganism growth. The measurement method of WMS introduces noninvasive technique instead of complicated invasive microorganism operation analysis and quickly obtains the accurate real-time measurement results. By using the WMS measurement, the specific growth curve of microorganism growth clearly displayed every three minute, which has characteristics of high sensitivity, high spectral resolution, fast time response and overcomes the randomness and error operation of traditional analysis methods. The measurement value of BF and AF in the range of 1.008 to 1.043 and the lower MSE showed that Gompertz model can fit the data well and be capable of describing bacteria growth rate and lag time. The results of experiment data suggested that the specific growth rate of microorganism depends on the temperature. With the increase of temperature ranging from 25 °C to 42 °C , the lag time of bacteria growth has been shortened. And the suitable temperature of bacteria growth is about 37 °C . Judging from the growth rate of microorganisms, we can identify the microbial species, not only to improve the precision and efficiency, but also to provides a rapidly sensitive way for microbial detection. The lag time of microorganism growth also provides a great application prospect for shelf life of the food safety.
Gold nanoparticles decorated liposomes and their SERS performance in tumor cells
Show abstract
Due to their unique properties, liposomes have been widely used as drug nanocarriers. Herein a liposome-Au nanohybrid has been demonstrated as a SERS active intracellular drug nanocarrier. In this study, cationic Raman reporter tagged gold nanoparticles (Au@4MBA@PAH) were anchored onto the surfaces of anionic liposomes via electrostatic interactions. Using SKBR3 cells as model cells, we revealed that the hybrid formulation can be effectively taken up by tumor cells and tracked by the SERS signals. Collectively, the liposome-Au nanohybrids hold great promise in biomedical applications.
A reusable biosensor chip for SERS-fluorescence dual mode immunoassay
Show abstract
Research continues in an effort to develop a versatile platform for clinical diagnosis with easy operation and low cost. In the present study, a biosensor chip has been designed and fabricated for surface enhanced Raman scattering (SERS)- fluorescence dual mode immunoassay. Here, a dual channel microfluidic chip was employed for simultaneous SERS and fluorescence detection. Unlike previously reported microfluidic immunoassays using fluorescence or SERS method independently, the proposed dual mode biosensor combined the advantages of these two optical detection techniques. The fluorescence mode can be used for fast screening of biomolecules while the SERS mode can be employed for accurate and sensitive quantitative analysis. In addition, the chip-based microfluidic platform greatly reduced the reagents cost and complicated operation. The whole detection process from sample preparation to optical detection can be finished in 90 min. Moreover, the reversibly bonded biosensor chip could be reused after cleaning, which further reduced the cost for each assay. All these merits make it a potential powerful tool for practical clinical diagnosis.
The synthesis and application of two mesoporous silica nanoparticles as drug delivery system with different shape
Show abstract
Mesoporous silica nanospheres(MSNSs) have been obtained utilizing the conventional reverse micelles synthesis method while the mesoporous silica nanorods(MSNRs) have been acquired by means of changing certain parameters. Afterwards, the prepared mesoporous silica nanospheres and nanorods were used as drug carriers to load and release the classical cancer therapeutic drug—DOX. According to the absorption spectra, the encapsulation efficiency of the mesoporous silica nanospheres is almost as high as that of the nanospheres. Different from the familiar encapsulation efficiency, the release characteristic curves of the mesoporous silica nanospheres and nanorods possessed certain differences during the release process. Finally incellular fluorescence imaging was achieved to observe the endocytosis of the mesoporous silica materials. Our results show that although both of the two kinds of nanoparticles possess favourable properties for loading and releasing drugs, the mesoporous silica nanospheres perform better in dispersity and controlled release than the nanorods, which probably endow them the potential as incellular drug delivery system.
A SERS-based microfluidic immunoassay using an in-situ synthesized gold substrate
Show abstract
A sensitive SERS (surface-enhanced Raman scattering)-based immunoassay in microfluidic system has been developed with in-situ synthesis of gold substrate and immune reporter named as 4MBA (4-Mercaptobenzoic acid)-labeled immuno-Ag aggregates. The gold substrate was fabricated simply by introducing the hydrogen tetrachloroaurate (III) trihydrate (HAuCl4) solution to microchannels using a microfluidic pump. It was found that the obtained deposited gold nanoparticles were uniform in size and shape. Then the sandwich immunoassays were performed using the gold substrates based on SERS signals. In the immunoassay, the gold nanoparticles decorated surface was modified with certain antibodies to recognize the specific kind of antigen, which was flowed through the microfluidic channel afterwards. Then 4MBA-labeled immuno-Ag aggregates were employed as the SERS probes to quantitatively detect the antigen. The experimental results showed a good specificity and limit of detection (LOD) about 1 ng/mL.
Photodissociation of 2, 4, 6-trinitrotoluene with a Nd:YAG laser at 532nm
Show abstract
2, 4, 6-Trinitrotoluene (TNT) belongs to the group of aromatic nitro compounds which have extended use in industrial applications, in particular as explosives or additives to explosives. Understanding the initial step of laser induced decomposition of common explosives is important to the reliability and safety of laser initiators and firing systems. Lasers coupled with mass spectrometer find wide application in photochemical studies for identification of different ions formed due to photoexcitation/ionization of molecules by laser. In this paper, a pulsed Nd: YAG (15ns, 532nm) laser was used for ionizating the condensed TNT sample, and the ions produced in the ionization process were detected by a time of flight mass spectrometer (TOFMS). The influence of laser fluence and the delay time to the decomposition was also studied. According to the assignment of both positive and negative ions, possible laser induced dissociation pathways were proposed. The results may tell much about the initiation process and the chemical reaction that may occur in TNT when exposed to laser pulse.
Evaluation of surface and bulk qualities of semiconductor materials by a laser-induced photothermal technique
Show abstract
Non-destructive evaluation of defects for semiconductor materials is critical to the quality control process. The existing evaluation methods, including radiographic testing, ultrasonic detection, fluorescence and infrared imaging, are widely used in industrial applications. In this paper an instrument based on laser-induced photothermal technique was applied to study various semiconductor materials. With a specially arranged pump-probe configuration, this system can do three dimensional mapping of local properties and defects. By using this photothermal instrument, several semiconductors, such as bulk CdZnTe (CZT) crystals and monocrystalline silicon wafers under different processing conditions, were investigated. The surface and internal structures and defects of these materials were tested nondestructively by the 3-D photothermal microscope. The results show intersting correlation between the photothermal characterizations and the processing conditions. In addition, the details of the development of the 3-D photothermal microscope were also presented. The system provides user-friendly operations of the defects characterization process and shows great potential of application for characterization of semiconductor materials.
The development and progress of XeCl Excimer laser system
Show abstract
A large angularly multiplexed XeCl Excimer laser system is under development at the Northwest Institute of Nuclear Technology (NINT). It is designed to explore the technical issues of uniform and controllable target illumination. Short wavelength, uniform and controllable target illumination is the fundamental requirement of high energy density physics research using large laser facility. With broadband, extended light source and multi-beam overlapping techniques, rare gas halide Excimer laser facility will provide uniform target illumination theoretically. Angular multiplexing and image relay techniques are briefly reviewed and some of the limitations are examined to put it more practical. The system consists of a commercial oscillator front end, three gas discharge amplifiers, two electron beam pumped amplifiers and the optics required to relay, encode and decode the laser beam. An 18 lens array targeting optics direct and focus the laser in the vacuum target chamber. The system is operational and currently undergoing tests. The total 18 beams output energy is more than 100J and the pulse width is 7ns (FWHM), the intensities on the target will exceed 1013W/cm2. The aberration of off-axis imaging optics at main amplifier should be minimized to improve the final image quality at the target. Automatic computer controlled alignment of the whole system is vital to efficiency and stability of the laser system, an array of automatic alignment model is under test and will be incorporated in the system soon.
Edge-emitting diode lasers with narrow circular beam output
Show abstract
We report near circular beam output from 808 nm edge-emitting diode lasers based on Bragg reflection waveguide design. Increasing quantum well number combined with reducing defect layer index and thickness was used to achieve high power output and extremely low vertical far field divergence. The TQW-BRLs achieve the lowest vertical divergence of 4.91° (full width at half maximum) and 9.8° (95% power). The maximum power of 4.6 W was achieved in the mounted DQW-BRL device under continuous-wave operation, being limited by thermal rollover.
Gain-switched 2.8μm Er3+-doped double-clad ZBLAN fiber laser
Show abstract
A pulsed Er3+-doped ZBLAN fiber laser at 2.8 μm in fundamental-transverse-mode operation is reported. Stable gainswitching
is achieved with the repetition rate range from 0.5 to 10 kHz. The maximum laser pulse energy of up to 4.2 μJ
and pulse duration of 1.18 μs at a repetition rate of 10 kHz, yielding the maximum peak power of 3.5 W, has been
obtained. The maximum slope efficiency with respect to the launched pump power at 975 nm is determined to be 12.2%.
Pulse spikes occur by increasing the pump energy of larger than 75 μJ.
Development of optically pumped XeF laser technology in NINT
Show abstract
The investigations of the XeF laser bumped by ultraviolet radiation have been studied for more than 20 years in Northwest Institute of Nuclear Technology (NINT Xi’an China). Up to now, several XeF laser devices were developed and an integrative experimental system has been set up which is comprised of a laser device, an electrical power supply, a high voltage trigger generator and a mixture gas supply device. Many key technologies were studied in detail and have been applied now. These technologies include section surface discharge, XeF2 photodissociation, synchronal trigger generating, double-sides optical pumping from opposite directions, active mixture gases supplying in real time, gases circulation, and so on. The XeF laser system operating on pulse repetition frequency (PRF) is up to 10 Hz. Two kinds of operating modes were applied. For the open gas flowing mode, the pulse energy of 3.2 J and the average power of 32 W at 10Hz is obtained. For the gases circumrotate mode, the average energy of 20 laser pulses is more than 0.5J.
Simulation of adaptive optics systems for laser transmission applications
Show abstract
Adaptive optics systems are highly complicated networks of devices that makes an analytical study of such systems difficult. Hence numerical simulations are crucial in providing a quantitative evaluation of capabilities of adaptive optics systems. The integrated simulations of atmospheric turbulence, wind profiles, Fresnel light propagation, model of Shack- Hartmann wavefront sensor, and wavefront reconstruction are done, and the aim is to simulate adaptive optics correction process and investigate the atmospheric turbulence and Shack-Hartmann sensor parameters on optimal results. The results of simulation of light propagation through turbulent atmosphere are presented.
The influence of electric field uniformity on the discharge characters of SF6 mixture
Show abstract
SF6 and C2H6 are the working gas mixture of non-chain HF laser. In our work, we use a simple pumping circuit to study the influence of the electric field uniformity on the discharge characters. Three groups of electrodes with different designs have been manufactured, and different discharge characters have been got. We have analyzed the results qualitatively, and find that without preionization, uniform electric field is not the best choice to form a large volume discharge in strong negative gas such as SF6-based mixture; approximate uniform electric field may be its substitution. In such electric field the gap breakdown voltage decreases and discharge can perform much easily. The discharge channels away from the cathode surface can also diffuse together to form a large volume discharge to deposit the electric energy into the laser working gas.
Molecular sieve separation of ground state HF molecules in a non-chain HF laser
Show abstract
A 3A molecular sieve separation device was designed and mounted in a closed-cycled non-chain HF laser to separate the ground state molecule being produced in discharge region from gas stream in order to improve the stability of laser output energy. Experiments were carried out with several different discharge voltages and gas flow velocities, and the preliminary results show that the molecular sieve separation device could dramatically decrease the decay of output energy of HF laser while improving the laser energy stability.
Influence of excitation on physical features of a diode-pumped alkali laser
Show abstract
In recent years, a diode-pumped alkali laser (DPAL) has become one of the most hopeful candidates to achieve the high power performance. A series of models have been established to analyze the DPAL’s kinetic process and most of them were based on the algorithms in which only the ideal 3-level system was considered. In this paper, we developed a systematic model by taking into account the influence of excitation of neutral alkali atoms to higher levels on the physical features of a static DPAL. The procedures of heat transfer and laser kinetics were combined together in our theoretical model. By using such a theme, the continuous temperature distribution has been evaluated in the transverse section of a cesium vapor cell. The calculated results indicate that the excitation plays an important role during the lasing process, which might deepen the understanding of the kinetic mechanism of a DPAL.
Narrowing the linewidth to a desired value with a reflecting volume-Bragg-grating (RVBG) for high-powered LDs
Show abstract
In recent years, reflecting volume-Bragg-gratings (RVBGs) have been considered as the perfect elements to narrow the spectrum with highly adjustable parameters. In fact, the effects of narrowing the linewidth of high-powered LDs are determined by the parameters such as the grating thickness, refractive index modulation, and grating spatial frequency. By use of the theoretical regime, the relationships between the effective diffraction efficiency and these parameters of a RVBG have been systematically investigated to narrow the linewidth to a desired value. Although the results reveal that a higher effective diffraction efficiency may be achieved by adopting three parameters mentioned above with higher values, by considering the difficulties and confinement in production process of a RVBG, the characteristic parameters should be carefully selected as some appropriate values. From the evaluation, one also understands that the narrow linewidth of a RVBG-coupled LD and the high effective diffraction efficiency cannot be arbitrarily realized at the same time for a real case. The conclusions are thought to be valuable in construction of a practical narrow linewidth LD system.
Mode controlling study on narrow-linewidth and high power all-fiber amplifier
Show abstract
In this paper, we demonstrate an ytterbium-doped all-fiber master-oscillator power amplifier (MOPA) system which uses a narrow-linewidth seed source, generating narrow-linewidth and high power continuous-wave output power at 1064nm. Our MOPA configuration system consist of three amplifier stages. We use single-mode Yb-doped fiber as the gain fiber in the first and second pre-amplifier stages, so it can keep good beam quality before entering the main amplifier stage. In order to raise the threshold of nonlinear effects, such as SBS and SRS, and to relieve heat effect, our high power system choose large mode area (LMA) fiber as the gain fiber in the main amplifier stage. For the sake of suppressing high-order modes in LMA fiber, we design novel watering cooling plates of different sizes, and using them in our main amplifier stage. By optimizing its structure, we get very good laser beam pattern on CCD at high power output. The beam quality factor (M2) was about 1.4 at 1.31 kW.
Partial feedback unstable resonator on small scale supersonic large aperture chemical laser
Show abstract
There is always a challenge on large aperture medium power laser’s resonator design, stable resonator would supports significant higher order transverse modes, folded and telescope stable resonator are too complex and not preferred by engineers, unstable resonator need rather large round trip gain to compensate its high geometric out-coupling, which is difficult for this kind of laser since its gain length is limited due to the power level and large aperture. Partial feedback unstable resonator had been proposed to tackle this difficulty since the early days of laser development, however, the debates of its effect never stopped even with those distinguished optical resonator scientists such as Siegman, Anan’ev, and Weber. Recently integrated partial feedback unstable resonator design had been successfully demonstrated on a medium size chemical oxygen iodine laser. In this paper, we carry this resonator configuration on a small scale discharge driven supersonic nozzle array Hydrogen Fluoride chemical laser, a typical large aperture short gain length device. With magnification equals 4/3, we successfully get ten Watts level ring beam output.
Design of very large-mode-area Yb-doped photonic crystal fiber for high-energy pulsed laser output with squared shape
Show abstract
The rare earth-doped active fibers owning ten thousands of square-micron core-area but also delivering laser with high beam quality have little been reported. In this paper, we have designed a large-mode-area Yb3+-doped photonic crystal fiber in the cladding region with square-array air holes. Simulations demonstrate that only fundamental mode (FM) with mode-field-area (MFA) of ~15500 μm2 can be amplified and propagated at the gain saturation, and the beam quality M2 is less than 1.5. It is predicted that almost 58 mJ per-pulse can be available from such a 1.0 meter-length fiber, and the beam shape of amplified laser is near squared. It will be potential for so huge pulse-energy output from the VLMA LPF to be applied in the remote detecting, high-intensive welding and so on.
Research on nonlinear optical limiting properties of organic liquid crystal materials
Show abstract
Nonlinear materials for optical limiting applications have drawn great attention because of its special features such as high linear transmission, strong nonlinear absorption and ultrafast response time. Optical limiting properties of two organic liquid crystal materials ( ILC and L34 ) are tested and analyzed in this paper. Firstly, Optical limiting test platform of ILC and L34 materials is set up by Nd:YAG laser with a pulse width of 5ns and the wavelength of 532nm. Then the transmittance of ILC and L34 materials irradiated by different laser energy density is measured. Finally, optical limiting mechanism of ILC and L34 materials is analyzed basing on two photon absorption (TPA) properties. The research results show that ILC and L34 materials have good nonlinear optical limiting properties to the 5ns, 532nm laser. The transmittance of ILC and L34 materials gradually drop with the increase of laser energy density. When laser energy density is less than 0.2J/cm2, the transmittance of ILC material is roughly 80%. While once laser energy density is more than 2 J/cm2, the transmittance decreases to 40%. In addition, nonlinear optical limiting property of L34 material is better than ILC material owing to high TPA properties of L34 material, and Optical limiting threshold of ILC material is higher than L34 material. Optical limiting threshold of ILC and L34 materials are 3J/cm2 and 1.4J/cm2 respectively. The conclusions have a reference value for laser protection on ILC and L34 materials.
Theoretical analysis of SBS suppression in fiber amplifier with multi-point pump
Show abstract
The output power of a narrow line-width laser is usually limited by the Stimulated Brillouin Scattering effect. In Master Oscillator Power Amplifier structures, multi-point pump could rearrange the gain distribution along the fiber, leading to the suppression of the Stimulated Brillouin Scattering effect with maintained amplification efficiency. A theoretical model concerning 100W-level fiber amplifiers is proposed. Stimulation is performed to analyze the amplification process of the laser signal and Stimulated Brillouin Scattering. The results demonstrate that the power of scattering light decreases from 3.2W to 6.8mW (with two-point pump) indicating the effectiveness of this new technology in Stimulated Brillouin Scattering suppression.
Design of fast, high-resolution terahertz imaging system based on laser and nonlinear crystal LiNbO3
Show abstract
In this paper, we introduced the design of a fast, high-resolution terahertz imaging system based on nonlinear crystal LiNbO3. Compared with the fast developed THz pulse imaging technique, THz Continuous Wave imaging system has many advantages such as high average power, high integration, small volume, and low cost. So, THz Continuous Wave imaging system without the need of scanning system is one of the best ways to improve the imaging resolution and the speed of a THz imaging system at the same time.
Portable atomic frequency standard based on coherent population trapping
Show abstract
In this work, a portable atomic frequency standard based on coherent population trapping is designed and demonstrated. To achieve a portable prototype, in the system, a single transverse mode 795nm VCSEL modulated by a 3.4GHz RF source is used as a pump laser which generates coherent light fields. The pump beams pass through a vapor cell containing atom gas and buffer gas. This vapor cell is surrounded by a magnetic shield and placed inside a solenoid which applies a longitudinal magnetic field to lift the Zeeman energy levels’ degeneracy and to separate the resonance signal, which has no first-order magnetic field dependence, from the field-dependent resonances. The electrical control system comprises two control loops. The first one locks the laser wavelength to the minimum of the absorption spectrum; the second one locks the modulation frequency and output standard frequency. Furthermore, we designed the micro physical package and realized the locking of a coherent population trapping atomic frequency standard portable prototype successfully. The short-term frequency stability of the whole system is measured to be 6×10−11 for averaging times of 1s, and reaches 5×10−12 at an averaging time of 1000s.
Effect of I-shaped metamaterial on microstrip antenna
Show abstract
In this paper, a near-zero-index metamaterial is proposed by the composite I-shaped unit cell and the refraction index of this metamaterial is close to zero from 6.12GHz to 6.19 GHz. To study the characteristics and application of this near-zero-index metamaterial, especially the ability of focusing energy, a microstrip antenna is designed. According to the formulations for designing microstrip patch antenna, the conventional microstrip antenna, which resonance at 6.19GHz, is designed and optimized. This metamaterial is placed right above the conventional microstrip antenna and this system is tested by the finite element method (FEM). Simulation results show that the maximum radiation gain in H-plane of the microstrip antenna with this near-zero-index metamaterial is 9.24dB, while the maximum radiation gain in H-plane of the conventional microstrip antenna is 2.63dB, improving about 6.61dB than conventional microstrip antenna; the maximum radiation gain in E-plane of the microstrip antenna with this near-zero-index metamaterial is 9.24dB, while the maximum radiation gain in E-plane of the conventional microstrip antenna is 5.12dB, improving about 4.12dB than conventional microstrip antenna. Simulation results also show that the directivity of the microstrip antenna with this near-zero-index metamaterial is much higher, compared with the conventional microstrip antenna. Radiation gain at other frequencies, from 6.12GHz to 6.19GHz, is also obtained, the value is much higher than the conventional microstrip antenna at the corresponding frequency. The results indicate that near-zero-index metamaterials can improve the radiation gain and the directivity of the conventional microstrip antenna.
Study on the influence of dispersion and chirp on femtosecond Airy pulse propagation in Kerr media
Show abstract
We present the influence of second order dispersion(GVD), third-order dispersion(TOD), and initial chirp on femtosecond Airy pulse propagation in Kerr media by solving the Nonlinear Schrodinger Equation with the split-step Fourier Method. In the time duration of femtosecond pulse, the effect of TOD should not be neglected. TOD can lead to waveform distortion and lower the quality of optical pulses. We also study the propagation of femtoscond Airy pulse in anomalous dispersion Kerr media. According to the numerical results, we show that when the parameter of the TOD and the propagation distance are selected as some typical values, the pulses will broadening first and then appear a process of compression. Finally, we discussed the influence of the initial pulse chirp on the propagation of the pulse profile and broadening factor.
Effect of atomic density on propagation and spectral property of femtosecond chirped Gaussian pulses
Zhendong Wang,
Feng Gao
Show abstract
We theoretically investigate the effect of the atomic densities N on propagation and spectral property of femtosecond chirped Gaussian pulse in a three-level Λ-type atomic medium by using the numerical solution of the full Maxwell- Bloch equations. It is shown that, when the positive chirped pulse with area 3π, propagate in the medium with smaller N, pulse splitting doesn’t occur and many small oscillations at the trailing edge of the pulse appear, in addition, the level |2< population ρ22 of the pulse exhibits an oscillation feature with time evolution, moreover, the spectral component near the central frequency of the pulse shows an oscillation characteristic too, and the propagation and spectral property of the negative chirped 3π pulse is very similar to that of the positive chirped 3π pulse. For the positive chirped 3π pulse pulses, propagate in the medium with larger N, pulse splitting also doesn’t occur but many small oscillations both at leading edge and the trailing edge of the pulse appear, and the population ρ22 of the pulse only exhibits an scarcely oscillation feature with time evolution, at the same time many oscillations both in blue shift and red shift components of the pulse appear but the spectral component near the central frequency of the pulse oscillate more severely, and the propagation and spectral property of the negative chirped 3π pulse is very similar to that of the positive chirped 3π pulse, but comparing with the case of the negative chirped 3π pulse, the propagation of the positive chirped 3π pulse is delayed at the same distance and the delayed time becomes longer with the distance increasing.
Photothermal microscopy: an effective diagnostic tool for laser irradiation effects on fused silica and KDP
Show abstract
In this paper, an automated microscopic instrument based on this technique is developed and used for the measurement and analysis of weak absorption properties of optical materials. This system shows a measuring sensitivity of absorbance down to 10 ppb, and provides user-friendly operation of the whole absorption measurement process. Compared with a typical bench-top system, the automated system requires little special skills from the operators and is therefore more reliable and reproducible. By using this system, a study of laser irradiation effects on optical materials induced by high power laser pulses is performed. The in-situ monitoring of a laser induced damage process at 355 nm in fused silica is realized, which indicates that the photothermal system is a useful tool for analysis of laser-material-interaction dynamics. Other specific applications of this system include measuring weak absorption, detecting local absorption defects. Experimental results show that both surface/sub-surface absorption defects on fused silica and bulk absorption defects on KDP are clearly determined.
Experimental analysis of beam aiming and pointing system with phased only spatial light modulators
Show abstract
In this paper, an advanced non-mechanical beam aiming and pointing system is presented. Traditional beam steering is based on the mechanical systems. In the complex and expensive systems, beam jittering and many other problems are major limitations. However, beam steering with optical phased array (OPA) devices can realize agile beam control with random access pointing and high efficiency. Our system is mainly based on phased only spatial light modulators (SLM), which can realize beam steering non-mechanically. Based on the conventional one dimensional beam steering method of SLM, two dimensional beam steering method was presented at first in order to demonstrate the feasibility of the whole system. Then the whole system was tested. Our beam steering system can steer beam to a target which was moving at the speed of 3.8mrad/s within the field of view. The RMS error of the system was 0.0246mrad in one dimension, and 0.139mrad in two dimension respectively. Meanwhile the whole process was recorded by another camera in order to show the results.
Beam profile measurement and evaluation of far field high energy laser
Show abstract
The far field beam profile is of significant importance to the analysis of the atmospheric propagation effect and evaluation of the beam control capability, tracking and aiming precision of laser system. In the paper, technology of laser beam measurement such as mid-infrared laser detection at wide temperature range, power density attenuation, photoelectric and calorimetric compound method for laser measurement, synchronous detecting of multi-channel pulsed signal are introduced. A series of instrumented target with detector array are developed for laser beam power density distribution measurement at far field. The power in the bucket, strehl ratio, centroid and jitter of beam can be calculated from the measured results.
Precipitation of Au nanoparticles induced in silicate glass by ultraviolet femtosecond laser
Show abstract
Precipitation of gold nanoparticles is achieved in silicate glass doped with Au ions by UV femtosecond laser irradiation and subsequent annealing treatment. The influences of different power and annealing temperature on the formation of Au nanoparticles are studied: the higher the laser power, the larger the diameter of Au nanoparticles. As the annealing temperatures increase, the colors of the samples are from light purple to purple-red. The peaks of absorption spectrum of the nanoparticles move to the long wavelength.
Improving friction performance of cast iron by laser shock peening
Show abstract
According to different purpose, some high or low friction coefficient of the material surface is required. In this study, micro-dent texture was fabricated on cast iron specimens by a set of laser shock peening (LSP) experiments under different laser energy, with different patterns of micro dimples in terms of the depth over diameter. The mechanism of LSP was discussed and surface morphology of the micro dimples were investigated by utilizing a Keyence KS-1100 3D optical surface profilometer. The tests under the conditions of dry and lubricating sliding friction were accomplished on the UMT-2 apparatus. The performance of treated samples during friction and wear tests were characterized and analyzed. Based on theoretical analysis and experimental study, friction performance of textured and untextured samples were studied and compared. Morphological characteristics were observed by scanning electron microscope (SEM) and compared after friction tests under dry condition. The results showed that friction coefficient of textured samples were obvious changed than smooth samples. It can be seen that LSP is an effective way to improve the friction performance of cast iron by fabricating high quality micro dimples on its surface, no matter what kind of engineering application mentioned in this paper.
Numerical research on characteristics of a teeth-shaped nanoplasmonic waveguide filter
Show abstract
Transmittance spectra of double-sided teeth-shaped nanoplasmonic waveguide filters formed in the metal-insulator-metal (MIM) waveguides are systematically investigated. It is found that a staggered double-sided teeth-shaped structure exhibits a wide and sharp bandgap, furthermore the two staggered double teeths combination can realize the narrow band filter with ultracompact size in the length of a few hundred nanometers. The finite element method is employed in the simulations. Our results may open a way to construct nanoscale waveguide filters for high-density nanoplasmonic integration circuits.
Numerical simulation of heat transfer and fluid flow in laser drilling of metals
Show abstract
Laser processing as laser drilling, laser welding and laser cutting, etc. is rather important in modern manufacture, and the interaction of laser and matter is a complex phenomenon which should be detailed studied in order to increase the manufacture efficiency and quality. In this paper, a two-dimensional transient numerical model was developed to study the temperature field and molten pool size during pulsed laser keyhole drilling. The volume-of-fluid method was employed to track free surfaces, and melting and evaporation enthalpy, recoil pressure, surface tension, and energy loss due to evaporating materials were considered in this model. Besides, the enthalpy-porosity technique was also applied to account for the latent heat during melting and solidification. Temperature fields and melt pool size were numerically simulated via finite element method. Moreover, the effectiveness of the developed computational procedure had been confirmed by experiments.
The ejection angle of molten aluminum induced by millisecond pulsed laser
Show abstract
The experiment for investigating the ejection angle of molten Aluminum induced by millisecond pulsed laser is designed. Two kinds of ejection modes are found from the experimental result. The molten droplets distribution of these ejection modes are in the shapes of sprinkled stars and circular ring, respectively. The mechanism of these different ejection modes are analyzed and discussed. The ranges of ejected droplets vary widely with the change of millisecond laser pulse energy. The droplets distribution in the circular ring shape becomes thinner with the increasing power density of pulsed laser. The ejection angle of major molten droplets dependence of pulsed laser power density is obtained from the experimental result. The influence of vaporization on the particle size and the distribution of ejected droplets are discussed.
Numerical simulation of the decomposition of carbon fiber polymer composite subjected to a high power laser irradiation
Show abstract
In order to simulate the interaction between high power laser and carbon fiber polymer composites, a 1D finite element model has been developed to research the decomposition process of composite pyrolysis. Mass and energy balance equations and gas convection have been solved in the model. The results of the computer simulation show a narrow reaction region formed in the composite with a huge pore pressure.
The damage morphology of momocrystal silicon irradiated by continuous wave fiber laser
Show abstract
The interaction of CW fiber laser and monocrystal silicon <100> is investigated experimentally and numerically. In the experiment, the damage morphologies are detected by a CCD and an optical microscope. The damaged silicon appears an evident molten pool within the laser spot and several cracks on the surface and slip damage, which indicate that the damage mechanism includes melting and thermal stress damage. The damage morphologies show two types of cracks including radial crack and circumferential crack. Otherwise, an obvious central hillock is found in the molten pool, which may be produced by the fluctuation of the thermal-stress filed and resolidification of the central molten silicon after irradiation. In the numerical simulation, a two-dimensional axisymmetric physical model is established based on the thermo elastic-plastic and classical heat transfer theory and Von Mises yield criterion. The simulation results indicate that the temperature and the stress in the irradiation center are always the highest on the specific condition, which may contribute to the occurrence of the central hillock. The gradient of hoop stress is bigger than the radial stress, thus, it can be inferred that the appearances of the radial cracks in the experiment were closely related to the hoop stress.
On-line measurement of wavefront aberration on optics caused by intense lasers
Zuodong Xu,
Fuhua Liu,
Chang Jiang,
et al.
Show abstract
It is presented that the thermally induced transmitted wavefront aberration of a high-reflectivity sampling mirror was detected on line using a Shack-Hartmann wavefront sensor (SHWS) in the beam quality measurement of an intense laser. As a result of heat absorption in the sampling mirror with active aperture of 120 mm, thermally induced wavefront aberration emerged when the mirror was exposed to high laser intensity of several kilowatts per centimeter square. Time-dependent wavefront aberration curves were acquired, and the transmitted wavefronts were reconstructed based on Zernike mode reconstruction theory. The experimental results indicate that the magnitude of the dynamic transmitted wavefront aberration increases gradually with the growing heat deposit during laser irradiation. The maximum of wavefront aberration observed after irradiation for 5 seconds reaches 0.11 μm of root-mean-square value. After further analysis, the experimental results of dynamic aberration can be applied in modifications for the measurement results of intense laser beam quality or tests for the thermal stability of optics used in the intense laser systems.
Thermoinduced laser-assisted deposition of molybdenum from aqueous solutions
Show abstract
Local molybdenum deposit obtainment is promising for micro thermocouples creation on dielectric surfaces. This paper is dedicated to development of method of laser-induced molybdenum deposition from water-based solution of inorganic salt on Sitall st-50 and glass dielectric substrates, as well as research of solution composition, pH and substrate optical properties influence on result of laser-induced molybdenum deposition from solution. It was shown that depending on dielectric substrate type, as a result of laser-induced deposition metallic molybdenum or molybdenum dioxide deposit forms: molybdenum dioxide deposits in case of optically clear substrate and metallic molybdenum deposits in case of opaque glass-ceramics. While modelling interim case via using clouded glass, mixture of molybdenum and its oxide was successfully obtained.
Preparation and ion conductivity of composite films AgI-ZnO
Sergey S. Fateev,
Yu S. Tveryanovich,
V. V. Tomaev,
et al.
Show abstract
It has been proven that with laser deposition silver iodide retains its chemical composition and structure. A film has been produced with the help of laser deposition, consisting of finely divided crystals of ZnO and AgI. Its structure has been reviewed using X-Ray phase analysis, and its electric conductivity has been reviewed using impedance measurement. Special attention has been given to the effect of phase interaction on ion transport.
Laser-induced deposition of nanostructured copper microwires on surfaces of composite materials
Show abstract
Microelectronics industry is growing fast and the rate of new devices’ development increases every year. Therefore, methods for simple and high-precision metal coating on dielectrics are needed. Existing methods do not allow performing the high-precision metal deposition without using photomasks, while making photomask for each prototype is long and expensive process. One of the methods of maskless metal deposition is laser-induced chemical liquid-phase deposition (LCLD). In this work we show the effect of substrate surface type on a result of LCLD. Deposited copper structures were characterized by SEM, EDX and impedance spectroscopy. The results show that laser-induced copper deposition is highly affected by the surface being homogeneous or composite material. It was found that the deposits with low resistivity and high quality metal localization mostly appear on the two-phase surfaces. In contrast, deposits on one-phase surfaces exhibited poor topology of copper material.
A new approach to obtain nanostructured nickel deposits on the surface of dielectrics by direct laser writing
Evgeniia M. Khairullina,
Svetlana M. Araslanova,
Sergey A. Fateev,
et al.
Show abstract
Nanostructured nickel deposits can be applied in hydrogenation reactions catalysis and electrochemical systems development. Laser-induced liquid-phase metal deposition allows creating microscaled nickel structures with a developed surface. In this paper a possibility of abandoning technologically imperfect plating solutions containing various reducing agents such as hypophosphite, boron hydride is shown. Deposition was conducted from solutions only containing nickel salt and various organic ligands which allow avoiding phosphorus and boron codeposition. Influence of ligand nature, ligand concentration and solution pH on laser deposition results was studied. Obtained deposits were researched using SEM, EDX, XRD methods.
Laser-induced deposition of nanostructured copper tracks from solutions containing oxidising additives (withdrawal notice)
Show abstract
This paper was withdrawn from the SPIE Digital Library on 10 August 2015 by the publisher upon verifying that significant portions of the paper were copied from the following publications without attribution or permission:
Dmitrii Semenok, "Application of lower aliphatic alcohols as reducing agents for increasing efficiency of the LCLD process," Proc. SPIE 9135, Laser Sources and Applications II, 91350X (May 1, 2014); doi: 10.1117/12.2049576;
and
Dmitriy Vladimirovich Semenok, Sergey Vladimirovich Safonov, Vladimir Kochemirovsky, “The Technology of Laser-Induced Deposition of Nanostructured Metallic Conductors on the Dielectric Substrate,” in Proceedings of Nanomaterials: Application and Properties '2012, Vol. 1 No 4, 04NMEEE05(2pp), the Crimea, Ukraine (September 2012); http://nap.sumdu.edu.ua/index.php/nap/index/pages/view/ProcNAP
The citations are provided here so that interested readers can access the information from the original sources.
Dmitrii Semenok, "Application of lower aliphatic alcohols as reducing agents for increasing efficiency of the LCLD process," Proc. SPIE 9135, Laser Sources and Applications II, 91350X (May 1, 2014); doi: 10.1117/12.2049576;
and
Dmitriy Vladimirovich Semenok, Sergey Vladimirovich Safonov, Vladimir Kochemirovsky, “The Technology of Laser-Induced Deposition of Nanostructured Metallic Conductors on the Dielectric Substrate,” in Proceedings of Nanomaterials: Application and Properties '2012, Vol. 1 No 4, 04NMEEE05(2pp), the Crimea, Ukraine (September 2012); http://nap.sumdu.edu.ua/index.php/nap/index/pages/view/ProcNAP
The citations are provided here so that interested readers can access the information from the original sources.
Gas lasers pumped by runaway electrons preionized diffuse discharge
Show abstract
It was shown that run-away electron preionized volume (diffuse) discharge (REP DD) can be used as an excitation source of gas mixtures at elevated pressures and can produce laser emission. We report experimental and simulated results of application of the REP DD for excitation of different active gas mixtures. Kinetic model of the REP DD in mixtures of nitrogen with SF6 is developed allowing predicting the radiation parameters of nitrogen laser at 337.1 nm. Peculiarities of the REP DD development in different gas mixtures are studied, as well. It was shown that the REP DD allows obtaining efficient lasing stimulated radiation in the IR, visible and UV spectral ranges. New operation mode of nitrogen laser is demonstrated under REP DD excitation. Laser action on N2, HF, and DF molecules was obtained with the efficiency close to the limiting value. Promising prospects of REP DD employment for exciting a series of gas lasers was demonstrated. It was established that the REP DD is most efficient for pumping lasers with the mixtures comprising electro-negative gases.
Solvent-dependent optical limiting response of platinum nanoparticles stabilized by [60] fullerene derivative
Show abstract
The optical limiting performance of platinum nanoparticle protected by C60 derivative in chloroform, ethanol and dimethylformamide (DMF) was measured with 532nm, 8ns duration laser pulses. Experiments showed that the optical limiting is solvent-dependent. The origins and solvent effect of the optical limiting were analyzed. It was proposed that the absorption-induced scattering is the main mechanism causing the optical limiting behavior and solvent effect.