In order to obtain the dual-frequency laser output with tunable frequency-difference, a design scheme of dual-frequency Nd:YAG laser with two standing-wave cavities sharing the common gain medium has been proposed, which is based on the principle of longitudinal mode selection of the Fabry-Perot etalon. Both linear and right-angle cavities including a piece of Fabry-Perot etalon, the p- and s-polarized components of the 1064nm laser will be forced to oscillate simultaneously in single longitudinal mode in the linear and right-angle cavities, respectively. As a result the orthogonally and linearly polarized dual-frequency laser at 1064nm can be output; the frequency-difference can be tuned by adjusting the tilt angles of the intra-cavity Fabry-Perot etalons, the maximum frequency-difference is predicted theoretically to approach the oscillating bandwidth of the Nd:YAG laser. The principles of single longitudinal mode selection and frequency tuning of the Fabry-Perot etalon have been analyzed, and two fused quartz-made Fabry-Perot etalons have been designed and fabricated. An experimental system of diode-pumped two-cavity dual-frequency Nd:YAG laser at 1064nm has been established, the characteristics of single longitudinal mode oscillation and frequency tuning have been investigated experimentally. The orthogonally and linearly polarized dual-frequency laser output at 1064nm has been obtained, the frequency-difference of which being 21GHz and 76GHz, respectively. Such a two-cavity dual-frequency all-solid-state laser will be widely used in the synthetic-wave absolute-distance interferometry and other fields.

Coherent Doppler wind lidar has made significant progress in wind profile measurement because of its high temporal and spatial resolution. All-fiber Coherent Doppler wind lidar has caused most interest in mobile wind detection due to its excellent stability and reliability. A theoretical model was analyzed based on the signal-to-noise ratio (SNR) function, the SNR of continuous-wave and pulsed lidar with different focusing distances was evaluated. A 1550 nm all-fiber mobile Doppler wind lidar was designed for wind profile measurement. The system consists of a narrow-linewidth seed laser, a single-mode fiber amplifier, transceiver optics, and a data processing system. In order to verify the performance of the mobile laser lidar, a velocity calibration experiment was carried out on a moving car with a speed of 10-30 m/s in December 2020. The wind velocity of laser lidar and ultrasonic anemometers was measured and compared with a different elevation angle of laser. Results show good agreement between both measurements. The correlation coefficient is great than 0.96, and the standard deviation of velocity is less than 0.79 m/s.

In this study, different colors with a large variation in color gamut were induced by 1064 nm nanosecond pulsed laser on TC4. Then, we tested the stability and durability of the color marking made by nanosecond pulsed laser under various chemical agents and aggressive temperature conditions. The results showed that colors marking on TC4 have high sustainability to acidic and neutral solutions and also can stand the high temperature. Due to the high stability and durability of the induced colors, it is not easy to secondarily revise the colored areas, which will reduce the applicability of laser coloring technology. Here, we proposed using ultrafast pulsed laser to selectively erase the colored areas in ethanol and nitrogen atmosphere. We found that ultrafast pulsed laser had high erasing quality on the colored surface. The ΔE* before and after erasing is less than 7, and the reflectance spectra of erased areas is similar to the untreated areas. These results are essential to provide a proper solution for the lack of applicability and flexibility in laser coloring technology, which can open new perspectives in industrial applications.

With the increasing output power of lasers, the problem of poor beam quality in most of them also arises. Therefore, we design, simulate and fabricate a hollow-core antiresonant fiber that can reduce high-order modes loss. The fabricated fiber has a rod structure (710 μm outer diameter) to resist the influence of bending, and its cladding is composed of ten noncontact capillaries. The fiber has a 128 μm core inscribed circle diameter, an average 40 μm cladding capillary inner diameter, and a tube wall thickness of about 650 nm. The test results of this fiber show that the transmission loss at 1 μm and 1.5 μm is close to 0.1 dB/m and in 2.6-4 μm band is mostly below 0.5 dB/m (except molecular absorption peak). The beam quality test results of this fiber show that its M² is basically inversely proportional to the wavelength at 2.6-4 μm, and M² below 3 μm is about 2. By observing the output spot of this fiber at 1 μm and 1.5 μm wavelength with a CCD camera, we can intuitively see its multimode transmission characteristics.

Fermat spiral photon sieve (FSPS) containing many circular holes arranged along several Fermat spiral lines is an interesting element to generate vortex beam because of its special chiral structure. This work models the FSPS and derive the diffraction field analytically. In addition to the familiar azimuthal periodicity at the focal plane in previous works, we find the longitudinal periodicity of the generated vortex beams which present themselves as many families and therefore the multi-foci property is also discovered. We relate the vortex families with the parameters of FSPS and shows the rules. This work is helpful for design of FSPS and generation of vortex beams.

In this paper, we investigated the enhancing and suppressing effects of the critical angle on the in-plane spatial spin-dependent (IPSS) shifts of the photonic spin Hall effect (PSHE) when a linear polarization Gaussian beam is reflected from a glass-air interface. We find that the IPSS shift becomes more significant when the incident angle approaches the critical angle. The direction of the IPSS shift will be reversed when passing through the critical angle. The maximum spin-dependent shift can almost reach 13.5 μm, much larger than previously reported values. Furthermore, the IPSS shift will be greater than 10 μm regardless of the polarization angle of the linearly polarized incident beam. Therefore, the IPSS can be enhanced and suppressed by slightly adjusting the incident angle near the critical angle. These findings provide a new way for modulating PSHE.

Coherent wind lidar is suitable for multiple scenarios. In this paper, a 1.55μm portable wind lidar with 10kHz 10μJ-level 200ns-pulsewidth output was developed. The theoretical model was established based on signal-to-noise ratio (SNR) function and coherent detection principle. The influence of linewidths and pulse widths of single frequency pulsed laser on the wind velocity measurement was studied and verified in comparison experiments. The blind area of the lidar was also analyzed. Solved from spectrum and SNR distribution in range bins, detection range of the lidar is an important detection parameter. The portable wind lidar reached the detection range to 2km with the inclination of 0°, and the range to 1.5km with the inclination of 90°.

Mapping through 3D lidar remains a popular technology. In the paper, we propose a method based on image to extract point cloud edge features. The image line features are mapped to the point cloud by using the camera internal and external parameter matrix obtained in advance. In addition, we propose an improved region growing method to extract the plane features in the point cloud, which has higher robustness than the method based on principal component analysis. In indoor experimental scenarios, we compare the existing methods (Li-Ho and Lili-OM) with our proposed methods. The results verified that our method can achieve a higher accuracy and frame rate.

Laser multi-focus separation technology is used as an efficient way to cut thick transparent materials and composites. In this paper, we propose a multi-focal design and experimental scheme based on refractive Fresnel lenses. Various refractive type multi-focal Fresnel lens designs were completed by combining theoretical calculations and Trace Pro software simulations, and the designed tri-focal optical system was experimentally verified by using N-BK7 glass, and the experimental errors were analyzed. The results show that the organic plastic (PMMA) processed multi-focal Fresnel lens can be applied to the high-power laser multi-focal optical system. The multi-focal optical system is highly stable and low cost, and has great application prospects.

In order to explore the law and mechanism of the action of near-infrared pulsed laser on silicon materials, 1064nm nanosecond pulsed laser and millisecond pulsed laser were used to act on silicon materials, and the damage effects of single nanosecond laser and millisecond-nanosecond combined laser were studied. Analyze the real-time evolution of plasma in laser irradiation process, reveal the mechanism of damage morphology, and discuss the influence and law of laser energy density and other parameters on the damage effect. Studies have shown that the plasma generated by a single nanosecond laser acting on silicon instantly forms a shock wave surface, which expands against the laser transmission direction. As the laser energy density increases, the plasma generation speed increases, and denser plasma clusters are formed. The ablation of the morphology is aggravated. When the millisecond-nanosecond combined pulse laser is applied, the delay time between two pulses is an important parameter that affects the effect. During the millisecond pulse time, as the delay time increases, the peak temperature rises. The same energy density combined laser acts on silicon under different delay time conditions, the damage morphology is quite different. The material properties of the silicon target change under the action of the millisecond pulse laser. The delay time determines the nanosecond injection in the shape of the specific silicon target. The nanosecond laser will give impact to the damaged silicon target. The cleavage damage morphology was observed under the action of the combined pulsed laser. This article can provide a reference for the research of laser processing and anti-laser damage silicon materials.

Laser-induced breakdown spectroscopy (LIBS) technology has been widely used in many fields because it can achieve non-contact, fast, real-time, on-site, and multi-element detection. Based on the principle of laser-induced breakdown spectroscopy technology, this paper explores the use of passive Q-switched lasers instead of mainstream active Q-switched lasers. Finally, a simple and portable experimental device was designed for qualitative and quantitative sample analysis of several important elements in compound fertilizer.

A 2 μm single-frequency, all-solid-state laser is one of the preferred light sources for coherent laser wind lidar and differential absorption lidar. In order to obtain 2 μm single frequency pulse laser with the high energy and hundred nanoseconds pulse width, the Ho:YAG non-planar ring cavity laser pumped by Tm:YLF solid state laser was used as the seed source to design and develop an injection-seeding single frequency Q-switched Ho:YAG pulse laser. A 2090 nm single-frequency pulse laser with an average pulse energy of 18.51 mJ and pulse width of 110.9 ns was obtained at a repetition rate of 200 Hz. The beam quality M² factors of the output laser are 1.16 in the X direction and 1.25 in the Y direction, and the pulse spectrum width is 4.05 MHz.

Temperature-dependent impedance characteristics are investigated for high speed VCSELs. Through small signal reflection S11 measurements for a large current range at different temperature and fitting during a equivalent circuit modeling we show that our VCSELs have higher parasitic cutoff frequency at higher temperature. Parasitic is not a limitation for both room temperature and higher temperature operation for our small aperture diameter VCSELs. Also, the values of the equivalent-circuit elements are determined for a large range of current at different temperature operation. Oxide-aperture-diameter-depend impedance characteristics are analyzed at 85 °C, and shows that the larger capacitance is main reason for larger aperture VCSELs have lower parasitic cutoff frequency, and it is necessary to decrease the capacitance for large aperture VCSELs, in order to improve the parasitic cutoff frequency.

A method to obtain the thermal resistance as a function of ambient temperature is described. From the analysis of bandwidth verse internal temperature, we derive the thermal limits, providing a basis for next generation design.

A single longitudinal mode (SLM) polarization maintaining (PM) erbium-doped fiber laser (EDFL) with a crossed-double- ring passive subring resonator (CPSR) is put forward and experimentally investigated. The designed CPSR consists of two dual-coupler fiber rings, productively inhibiting large number of longitudinal modes oscillation and featuring narrow filtering bandwidth to achieve the SLM output. The configuration of all PM decreases the insertion losses of the polarization adjustment devices used in non-PM EDFL for the optimal SLM output. The experimental consequences illustrate that the linewidth of the put forward EDFL is approximately 278 Hz and the optical signal to noise ratio (OSNR) is about 70 dB, potential for the applications of requirements for narrow linewidth and high OSNR.

A novel spectral shaping mechanism for pre-compensating gain-narrowing is investigated numerically and experimentally. The spectral shaping is realized based on the mapping between the frequency and time domain, via the modulation of intensity in time domain can be casted to frequency domain. The optical ultrashort pulse is injected to a nonlinear amplifying loop mirror (NALM) and modulated both in the frequency and time domain. The pulse spectrum can be modulated in saddle-shape, and the sinking depth of spectrum can be tuning with the variation of the pump power of the NALM, which can pre-compensate the gain-narrowing and sustain a broadband spectrum in later high-gain amplifier. A proof-of-principle experiment is carried out. The spectral bandwidth of amplified optical pulse increases from about 10 nm to 19 nm, and pulse duration is shorten from 669 fs to 342 fs with the implementation of NALM spectral shaper, which shows a significant suppressing on the spectral gain-narrowing. This tunable NALM spectral shaper is employed with an all-polarization-maintaining (PM) and all-fiber structure, providing a flexible and practical solution to overcome gain-narrowing in high-gain amplifications.