The major stochastic optical reconstruction microscope (STORM) techniques include data localization and reconstruction algorithms with respect to a large number of images. However, the existing open source algorithms are limited by their slow speed or computer memory when processing an ultralarge dataset, restricting the extensive application of STORM techniques. Therefore, we propose WindSTORM PLUS for performing single-molecule localization data processing using MATLAB and parallel computation. The outcomes obtained using the simulated large datasets demonstrate that the data processing speed of WindSTORM PLUS is greater than those of the existing WindSTORM and ThunderSTORM by 1000%. Furthermore, the memory requirements are reduced by 60% compared with those in case of WindSTORM. In addition, we establish an easySTORM system and conduct a test using some samples to verify the superiority of our algorithm. The time-consuming of WindSTORM PLUS is only 9% of WindSTORM and Gauss-WLS. We believe that this open source algorithm can provide a novel high-speed STORM data processing approach.

Owing to the advantages of optical coherence tomography (OCT), such as high resolution, deep imaging depth, and fast imaging speed, it facilitates a new method for the evaluation of renal status. The renal ischemia-reperfusion (IR) process can cause damage to renal functional units; such damages can be quickly estimated using noninvasive optical imaging in real time. Herein, using spectral-domain OCT (SDOCT) with 1300-nm center wavelength, two- and three-dimensional images of Wistar rat kidneys were collected in vivo. The obtained images clearly show the microstructure of uriniferous tubules in the renal cortex. Moreover, results demonstrate that OCT imaging is prominent in the evaluation of renal status owing to the sensitivity of OCT to IR process.

In this study, we propose a space four-quadrant concept to realize active positioning guidance and high-speed communication of the space carriers according to the requirement of space precise positioning technology. Four light spots are sequentially obtained in space within fixed time interval using the beam scanning method. The receiving detector sequentially receives the partial energy of the four light spots and calculates the position as well as offset angle of the receiving end with respect to the transmitting center based on centroid calculation. Further, the Monte Carlo method is used to model and simulate the space four-quadrant limited positioning system, and an experimental system is developed to verify and analyze the simulation results. The results denote that the space four-quadrant positioning technology is feasible and can provide technical support for specific space positioning and navigation applications.

In this study, we propose a vector mode conversion method based on tilted long-period fiber grating written in ring fiber to realize mode conversion with respect to the mode division multiplexing system. In addition, we study the influences of the grating parameters, including the tilt angle modulated based on the refractive index, the amplitude function, the grating length, and the coupling coefficient, on mode coupling using the finite difference method and the coupled-mode theory. The obtained results indicate that the fundamental mode can be converted to high-order vector modes at specific wavelengths under the phase-matching constraint; further, the wavelength interval is greater than 150 nm. The tilt angle plays a major role during the mode coupling process, and the maximum conversion efficiency can be obtained when the tilt angle is approximately 84°. The proposed converter has the advantages of larger mode interval, lower crosstalk, and higher conversion efficiency; therefore, it exhibits considerable potential for application in orbital angular momentum multiplexing and vector mode multiplexing when compared with those of the existing vector mode conversion methods.

In this study, a novel approach is proposed to generate and transmit the ultra-wideband linear frequency modulation (LFM) signal using frequency-sweeping lasers. In this approach, the frequency-sweeping continuous-wave light from frequency-sweeping lasers is introduced into the Mach-Zehnder modulator to generate a carrier-suppression double sideband (CS-DSB) signal. The Sagnac loop containing a fiber Bragg grating is used to separate the CS-DSB signal. Beat occurs in the reflected light of the Sagnac loop and the transmitted light after some delay; hence, the ultra-wideband LFM signal is generated. The simulation results denote the generation of the ultra-wideband continuous and pulse LFM signals with carrier frequency of 30 GHz, bandwidth of 16 GHz, and time-bandwidth product of 8000. The proposed approach solves the problem of power periodic fading observed when the ultra-wideband LFM signal is transmitted through an optical fiber in case of antenna stretching. Furthermore, using the proposed approach, the carrier frequency, time duration, chirp rate, and chirp sign can be independently tuned, providing an effective strategy for generating and transmitting the ultra-wideband LFM signal.

In this study, an efficient hybrid modulation scheme suitable for indoor visible light communication is proposed to improve the performance of the indoor visible light communication links. The multi-dimensional carrierless amplitude and phase (CAP) modulation technique exhibiting high spectral efficiency and the multi-pulse position modulation (MPPM) technique exhibiting high power efficiency are combined in the proposed hybrid modulation scheme. The transmission intervals of the CAP signals are controlled by the different pulse time slots of MPPM. Based on Lambertian illumination model, the theoretical symbol error rate (SER) expression of the multi-dimensional DCO(DC offset)-CAP-MPPM scheme over the Gaussian channel is derived and verified via simulation. In addition, the performances of the proposed, ordinary MPPM and multi-dimensional DCO-CAP schemes are comparatively analyzed. The numerical results denote that the SER performance of hybrid modulation is related to its pulse ratio, modulation level, and CAP dimensions. Flexible multiple access can be achieved using multi-dimensional DCO-CAP-MPPM modulation. The SER performance of the hybrid scheme is better than those of the ordinary MPPM and CAP mudulation obtained using appropriately selected parameters.

By considering the temperature-induced variation in the refractive index of optical fiber, a theoretical model of the proportion consistency between time delay variations and single-wavelength signal and time delay difference variations of dual-wavelength signals in one-way and round-trip dual-fiber links was obtained. Furthermore, a dual-fiber one-way time transfer method compatible with the existing optical communication network was proposed. The time delay difference variations of dual-wavelength and proportion with wavelength and temperature were investigated via simulation. The experiment for one-way time delay measurement using 75-km dual-fiber link was conducted to investigate the proportion consistency model. Results show that the measured proportion at the remote site after 50-km transmission is -266.9 and that after transmission back to the local site using 75-km round-trip dual-fiber link is -256.4. The difference between theoretical and practical values of the one-way time delay variation is 520 ps. The simulated and measured results validate the feasibility of the proposed one-way time transfer method based on a dual-fiber link.

In this study, to solve the problem of interference of the pulse signal with the dither, which makes the Mach-Zehnder electro-optic modulator (MZM) operating point unstable, a dither-adaptive bias-control technique is proposed. A digital control system was used to generate a dither with variable frequency. The MZM can be locked at the minimum operating point of the transmission curve by the harmonic components of the feedback signal analyzed by fast Fourier transform. By the real-time monitoring of the output bias voltage, the dither frequency is able to automatically change, thus avoiding the influence of the pulse signal. Accordingly, laser pulse modulation with high extinction ratio is realized. Experiment results show that the pulse signal will affect the stability of the modulator operating point when the laser pulse frequency is close to the first harmonic frequency of the dither. The system can realize adaptive change of the dither frequency in the range of 0.45--2 kHz to meet the requirements of laser pulse modulation at different repetition frequencies. When the peak value of the pulse is 10 V and the duty cycle is 10%, the extinction ratio of the modulated optical pulse can reach 26 dB, which is approximately 24 dB higher than that when the pulse signal interferes with the dither.

A KTiOAsO4 (KTA) Stokes parametric oscillator is placed in the cavity of a laser diode (LD) side-pumped Q-switched 1064-nm Nd 3+∶YAG resonant cavity. By non-collinear stimulated polariton scattering in the KTA crystal, a Stokes laser with discontinuously tuned wavelength in the range of 1078.20--1088.20 nm is obtained herein. This Stokes laser is used as the pump source of a collinear Raman lasers to achieve stimulated Raman scattering in the same KTA crystal. The output mirror transmittance of the Stokes resonant cavity is designed to output the first-order Raman laser with discontinuous tunability in the range of 1106.08--1116.62 nm. At an LD pump power of 94.20 W and a pulse repetition frequency of 5 kHz, a 1116.34-nm Raman laser with a maximum power of 1.62 W is obtained.

In this work, a first-Stokes Raman lasers based on ZnWO4/Nd∶YAG was constructed for the first time. The output characteristics of the lasers under different repetition frequencies and with different output couplers were studied. Using ZnWO4 crystal as the Raman crystal and diode-pumped Nd∶YAG crystal to produce the fundamental laser, the first-Stokes laser at 1177.6 nm was realized. A maximum average output power of 886 mW at the first-Stokes wavelength of 1177.6 nm is obtained for output coupling mirror transmittance of 35%, pump power of 22.1 W, and repetition frequency of 9 kHz. Moreover, the corresponding pulse width and output peak power are 2.2 ns and 43.9 kW, respectively.

Herein, the effect of extreme ultraviolet (EUV) source parameters, such as discharge frequency, electric pulse energy, and buffer gas pressure, on the focused beam performance of the EUV radiation-damage-test system was studied. Results show that the focal depth of the EUV radiation-damage-test system was approximately ±1.5 mm. Although the discharge frequency has no significant effect on them, the focal spot size and single pulse energy increased with increasing electric pulse energy. Under typical working conditions, the range of focal spot size was 0.79-1.44 mm and that of single pulse energy was 112.09-436.06 μJ. The highest single pulse energy and single pulse energy density were 436.06 μJ and 31.53 mJ/cm 2, respectively, with 200-Hz source discharge frequency and 5.0-J electric pulse energy. Moreover, the highest power density of 32.87 W/cm 2 can be achieved with 1500-Hz source discharge frequency and 4.6-J electric pulse energy. The optimal buffer gas pressure (Ar) was 1-2 Pa, and the corresponding single pulse energy of focused beam is the best. This study can provide guidance for the optimization and setting of the system parameters for the study of EUV radiation damage.

Laser gyroscope cavity materials exhibit low thermal conductivity. When the ambient temperature changes, a thermal relaxation occurs when the external heat enters the cavity. In the gyroscope temperature cycling experiment, the parameters of the frequency stabilization control system are deviated from the ideal values owing to thermal relaxation, affecting the accuracy of the gyroscope. In this study, the finite element analysis method is used to simulate the temperature field distribution of the gyroscope from -40 ℃ to 70 ℃. According to the simulation results, the functions of the temperature difference between the inner and outer of the cavity and time is mathematically fitted. Based on the control characteristic of the prism laser gyroscope frequency stabilization servo system, the ideal control parameters of the frequency stabilization system under different temperature ranges are calculated. By the temperature-dependent digital frequency stabilization control in the prism laser gyroscope, the control parameters are changed in real time, and the experiments show an improved precision of gyroscope.

The Ptychography algorithm can be implemented to realize the super-resolution reconstruction of ultrashort pulses when the frequency-resolved optical gating (FROG) method is used for their diagnosis. We obtained an arbitrary FROG trace by multiplying matrices, exploited the extending property of “sinc” functions, and then demonstrated the coding phase principle of the FROG method. The proposed analysis provides theoretical support for the super-resolution reconstruction of ultrashort pulses. Furthermore, a numerical simulation revealed the phase recovery results of the Ptychography algorithm with undersampling in both the delay axis and frequency axis of FROG trace. These results are conducive for making the FROG measurement more accurate and less time-consuming.

In view of the complex dynamic coupling interference of the reaction force of piezoelectric fast steering mirror to the effective optical elements, we have proposed a reaction force analysis method based on rigid-flexible coupling and based on the piezoelectric coupling theory. The reaction force of the piezoelectric fast steering mirror was analyzed and compensated, and the hotspot stress of the central flexure hinge was measured. The simulation and experimental results show that the piezoelectric coupling method can be used to evaluate the reaction force characteristics more accurately than the rigid-flexible coupling method. During the experiment, the reaction force compensation ratio can become 90.14%, which is 3.96% less than that of numerical value. The proposed reaction force analysis method and momentum compensation structure could provide a reference to calculate and eliminate the coupling disturbance of the reaction force of the piezoelectric fast steering mirror to the optical system.

In the optical parametric chirp reversal pulse amplification (OPCPA) system, both stretcher and compressor can use parallel grating pair, to prevent the spectral shear effect in conventional stretcher and simplify the structure of the stretcher. The effect of residual dispersion on the output pulse waveform is analyzed, the corresponding theoretical model and numerical calculation method are given, and a third-order dispersion-compensation scheme for OPRCPA system is proposed in this paper.

In this study, we develop a ring laser gyroscope beam precision coupling assembly system to solve the problems of low assembly efficiency and poor quality consistency associated with manual beam precision coupling. Further, we analyze the principle of beam precision coupling with respect to ring laser gyroscope. Thus, the light field intensity of coupling beam is observed to follow a Gaussian distribution. Accordingly, we propose the photodetector pose adjustment method. Subsequently, the optical path change observed during the rotation of the optical prism is analyzed and a method is proposed to adjust the position of the combined prism. Additionally, an adjustment strategy is formulated with respect to the position of the photodetector and the attitude of the combined prism. Then, a beam coupling assembly experiment is conducted on the ring laser gyroscope beam precision coupling system according to the aforementioned adjustment methods and strategies. The experimental results demonstrate that the proposed experimental assembly platform can complete the beam precision coupling assembly task.

To develop a new microchannel cooling structure for end-pumped solid-state lasers, the temperature distribution of gain medium and flow resistance in the cooling structure were studied using the fluid-thermal-solid coupled numerical method, which provides a theoretical basis for optimization of the new cooling structure. Results show that there is no obvious decrease in maximum temperature of gain medium when the coolant flow rate increases to 15 L/min, and the flow resistance in the microchannel cooling structure at this flow rate does not dramatically influence the working condition of the cooling system. The inlet and outlet positions of the cooling structure and the flow direction greatly influence the temperature distribution of gain medium.

Recently, the magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) device was successfully fabricated in combination with cold atoms and ultrafast and super intense laser technology. Herein, the MOTRIMS principle was introduced, and the density, temperature, and velocity of the target were analyzed and calibrated using the absorption imaging method and photoionization method. Results indicated that the temperature of the 3D MOT target is (130±30) μK, velocity is (0.1±0.1) m/s, density is approximately 10 9 atom/cm 3, and the densities of the 2D MOT and molasses targets are approximately 10 7 and 10 8 atom/cm 3, respectively. Compared with the hot vapor target, the momentum resolution of the cold atom target in the direction of ion flight improved by approximately 14 times and the mass resolution of the time-of-flight spectroscopy is up to 3000. Moreover, the three-dimensional momentum distribution of Rb + was detected using 800-nm femtosecond laser; an obvious above-threshold ionization phenomenon was observed at a low laser intensity of 10 11 W/cm 2, indicating that Rb + atoms exhibit a large above-threshold ionization cross section. MOTRIMS is a new tool for investigating the strong field quantum micro dynamics of metal atoms owing to its ability to image the momentum distribution of ions in full space.

In this study, a magnesium alloy/steel butt joint was taken as research material. A combined heat source model was implemented to simulate a laser-induced tungsten inert gas (TIG) hybrid welding heat source. The coupling effect between the laser and TIG and the formation of Fe-Ni solid solution zone were analyzed. ANSYS software was employed to simulate the welding temperature distribution and thermal cycle curve. Simulation and experimental results were in good agreement, verifying the accuracy and applicability of the proposed heat source model. The peak temperature of the joint reached 2249 ℃, and the Ni interlayer and adjacent steel base material were exposed to a high temperature, promoting interfacial metallurgical reaction and element diffusion and providing the temperature condition for the formation of Fe-Ni solid solution zone, AlNi phase, and an interface layer with a double solid solution structure. The residence time of the magnesium alloy molten pool was 0.28 s, which ensured that the liquid magnesium alloy could be fully wetted and spread on the steel and eventually achieved good joint formation. Under the agitation of the molten pool, the strength of the magnesium alloy weld was enhanced by dispersion distribution of strengthening phase AlNi.

In this study, B powders of different contents are added into TC4 powders and the laser additive manufacturing (LAM) experiment is conducted. Influence of the addition of B on the microstructure and mechanical properties of samples is investigated. Results show that the addition of trace B can effectively refine the microstructure size of TC4 alloy produced using LAM. The growth of the prior-β grains in LAM-TC4 alloy is restrained by an addition of 0.05% B, and the grain width is significantly decreased. An addition of 0.1% B can promote the transformation from coarse prior-β crystals to equiaxed crystals and result in a great reduction of the size of α bundle. Plasticity of the TC4-0.05B alloy is evidently improved compared with that of the boron-free TC4 alloy, whereas the change in the strength is not significant. Anisotropy of the as-deposited TC4-0.05B alloy and TC4-0.05B-solution aging is low.

In this study, the steady magnetic and electric fields are coupled in the laser remanufacturing process to generate the directional Lorentz force to study the influence of electromagnetic field on the pore regulation in the laser remanufactured V-groove. The influences of the laser power and electromagnetic field parameters on the porosity of narrow V-grooves are studied using laser remanufacturing experiments. Results show that when the laser power is less than 1400 W, the boundaries between the original part and the added material are prone to poor fusion, and a large number of pores exist in the repaired area. With the increase of the magnetic field intensity, the poor fusion at the bottom of the V-groove is controlled, and the porosity in the repair area gradually decreases. When the magnetic induction is increased to 1200 mT, the porosity of the repair area decreases to 0.006%, and almost no porosity and poor fusion defects appear in the repair area. The downward Lorentz force provided by steady magnetic and electrical fields drives the metal melt to fill downward and accelerate the escape of the bubbles by the eletromagnetic squeezing force, finally obtaining a dense repair area.

Herein, the dynamic characteristics of the laser deep penetration welding plume were observed using high-speed camera, and plume formation reasons were analyzed. Results show that plume was divided into the periodic oscillating plume at the bottom and narrow plume, which was similar to a laser-focused form. When laser-induced evaporation steam on the front wall of the keyhole was close to the keyhole orifice, the swinging angle of the periodic swing plume at the bottom was the largest, whereas that of the narrow plume was smallest. Moreover, the intensity of the narrow plume increased with increasing defocusing amount (or the diameter of the keyhole in deep penetration). Further analysis showed that the formation of the periodic oscillating plume at the bottom was related to the steam generated from laser-induced evaporation on the front wall of the keyhole, and a large number of particles were observed in the eruption process of the bottom-oscillating plume. The formation of the narrow plume was related to the particles in the plume entering the beam and being heated by the laser beam.

Spectral intensity and electron density are two key features of plasma during the laser additive manufacturing of ceramics. Pore and crack defects significantly affect the performance of ceramic parts. We built a platform for plasma monitoring and extracted the porosity defect through a thresholding method. The effects of the process parameters on the plasma spectrum intensity and electron density were studied by analyzing the plasma plume and spectrum. The relationship between the plasma characteristics and the forming defects was then obtained. The experimental results show that both the ejection height and the plasma plume area formed by the ionization of the alumina ceramics steam were larger than those of metal materials. The plasma spectral intensity increased with the increase in the laser power and scanning speed, but decreased with the increase in the powder flow rate. The electron density increased with the increase in the laser power, scanning speed, and powder flow rate. During the forming process, the plasma spectral intensity and the electron density highly correlated with the pore and crack defects.

PA-1Cr18Ni9Ti joints were welded by fiber laser. The thermal process at the interface during the welding process was calculated to analyze its effect on the plastic pyrolysis. Thus the welding heat input was optimized. The calculated results were verified by experiments, in which a stable welded joint of PA-1Cr18Ni9Ti was obtained. In addition, the interfacial connection mechanism was also studied. The results show that the pyrolysis of the PA plastic during the welding process is related to temperature and rate of temperature increase. When the heat input of laser welding is 77.8 J·mm -1 (laser power is 700 W, welding speed is 9 mm·s -1 and defocus amount is 70 mm), the PA plastic can be fully melted and spread at the interface while reducing the pyrolysis, ablation and carbonization. Chemical bond of Cr—O—C can be formed at the PA-1Cr18Ni9Ti interface, which is benefit for joint strength.

Herein, a Stellite-6 cobalt-based coating was prepared on a 42CrMo steel surface using laser cladding technology; heat treatment was then conducted on the coating at different temperatures. Moreover, the effects of heat treatment on the microstructure, hardness, corrosion resistance, and tribological properties of the coating were investigated. Results show that the heat treatment can effectively reduce the residual stress in the coating and eliminate defects, such as cracks and holes. After heat treatment at 900 ℃, the faced centered cubic structure of cobalt evolves to hexagonal close-packed structure and metastable M7C3 carbide changes to stable M23C6 carbide. After 1 h of heat treatment at 900 ℃, the near surface hardness of the coating is 1.5 times that of the untreated coating, which is approximately 1300 HV. The friction coefficient of the untreated coating is 0.42, and its main wear mechanisms are plastic deformation, furrowing, and brittle spalling. However, after heat treatment, the friction coefficient of the coating reduces to 0.29, and its main wear mechanisms are abrasive and adhesive wear. The stable M23C6 carbide produced after heat treatment can strengthen the alloy and improve the mechanical properties of the coating. The self-corrosion current density of the coating after heat treatment is approximately 3.3×10 -3 A·cm -2, the self-corrosion potential is approximately -0.29 V, and the characteristics of the individual capacitive arcs nearly coincide. Further, the recrystallization and grain size variation during the heat treatment and martensitic transformation have no significant effect on the corrosion resistance of cobalt-based coatings.

Linearly graded transmittance films are a key component of variable attenuators in lithography systems. In this work, the design and fabrication of a 248-nm near-linearly graded optical transmittance film were realized using electron beam evaporation technology. Through sensitivity calculation and optimization, a low-sensitivity nonregular film design was obtained using an anti-reflection film. High-precision film thickness monitoring method with UV light control-crystal control combination realized a film thickness control accuracy of 0.3% and an error tolerance of 0.5%. The transmittance film, which was deposited on a JGS1 fused silica substrate using Al2O3 and SiO2 as film materials, realized linear transmittance control from 10% to 97.8% in an incidence angle range of 21°--35° under 248-nm S-polarized light, which meets the performance requirements of optical variable attenuators.

To achieve the high-dynamic-range measurement for weak signal, a method of realizing contrast measurement in high dynamic range for nJ-level weak signal is proposed based on second-order autocorrelation. The effects of energy (power), phase matching, and measurement noise are theoretically analyzed. The dynamic range can be effectively enhanced via the photon-counting detection of the measurement noise, selection of non-collinear angle in phase-matching and suppression of measurement noise by focusing and filtering. Thus a high-dynamic-range measurement system is established for a weak signal. A high measurable dynamic range of 1.0×10 11 is achieved for the nJ-level weak signal when using the laser source of the Shenguang II high-energy petawatt laser, which is in agreement with the theoretical result. Furthermore, accurate screening is realized for a laser source having a contrast of 4.3×10 8. The obtained results are significant for improving the contrast of the high-energy petawatt laser system.

In this study, we propose an algorithm for extracting the building feature information based on point cloud slices and minimum bounding rectangles to enhance the efficiency and accuracy of building feature information extraction. First, the algorithm denoised and sliced the point cloud horizontally and vertically. Then, the horizontal and vertical angle differences with respect to the adjacent points in each slice were used to automatically and quickly extract the contour points of the entire building, doors, and windows. Subsequently, the contour points were filtered, classified, and sorted. Finally, the overall sizes of the regular building and the information of windows and doors were extracted using the minimum bounding rectangle. In this study, three experiments were conducted to compare the extracted sizes of the entire building, windows, and doors with their actual sizes. The results denote that the information extraction accuracy with respect to windows, doors, and the entire building is within 3 cm, the overall accuracy is greater than 97.4%, and the time required to extract the information of approximately 1.6 million building point cloud data is less than 8 s, proving the effectiveness of the proposed algorithm.

Edges in a point cloud are important intermediate features for structuring point clouds and converting them into high-quality surfaces or solid models. To effectively extract the edge of the point cloud, an adaptive point cloud edge detection method based on local edge feature descriptor is proposed herein. The proposed method aims at addressing the problem of inaccurate edge detection caused by setting a unified neighborhood value or neighborhood radius in the existing point cloud edge detection algorithm. First, we provide the definition of a normal vector feature model, introduce the normal vector change rate, and propose a neighborhood adaptive method based on the normal vector change rate. Second, we combine the curvature density of the local area of the point cloud to define the local edge feature descriptor. Finally, we automatically adjust the threshold according to the characteristics of the value of the feature descriptor consistent with the Gaussian distribution, which solves the problem of manually adjusting the parameters for different point cloud models. Experiments on a variety of different point cloud datasets prove that the algorithm can accurately extract model edge information while maintaining the original information of the model. Furthermore, it exhibits repeatability and certain degree of robustness.

Aiming at the influence of fringe structured light system on the fitting result from the measurement error, an error determination method based on measurement circumstance is proposed in this study. First, the height measurement error under different lighting conditions and measurement distances is counted. Then, the probability density function is obtained using parametric or non-parametric fitting. The abovementioned error combined with the plane measurement error is added to the ideal plane model. Finally, the normal vector and fixed point coordinates are calculated using the least square method. Experiment results show that the model parameters calculated using the proposed method are consistent with those from the actual measurement. The vector and coordinate errors are less than 0.001 rad and 0.233 mm, respectively. The proposed method can effectively solve the low accuracy problem of the measurement results of the fringe projection structured light system in different environments. In addition, it can cope with situations wherein it is difficult for an actual point cloud to achieve high-precision fitting owing to data loss, which provides a basis for subsequent error corrections.

The misalignment between the azimuth axis of telescope and rotation axis of earth induces object-side field rotation, and the relative motion of folding mirrors in the Coude optical path induces image-side field rotation. The misalignment and rotation both occur during the process of the alt-azimuth telescope tracking observation. A K-mirror can compensate for the rotation but is inappropriate in high-precision polarimetry owing to its higher instrumental polarization. By optimizing the design, the depolarized derotator comprising five mirrors can reduce instrumental polarization while eliminating field rotation. However, its irregular structural design leads to a more complex alignment process. Herein, an auto-collimation dual optical path alignment scheme was designed for the depolarized derotator. The influence of mirror position error and optical axis deviation on the alignment process was analyzed using MATLAB simulation. The alignment and polarization detection for the depolarized derotator were conducted in the lab. Results indicated that the alignment error of the depolarized derotator was within 15 arcsec, and its instrumental polarization was significantly lower than that of the K-mirror.

To improve the precision of traditional high-reflectivity measurement technology, we propose a high-reflectivity measurement method based on the coupled cavity ring-down technique. We introduce an intracavity mode monitoring module into the coupled cavity ring-down system to determine the state wherein the coupling efficiency between the initial cavity and the measured cavity is consistent. Subsequently, more precise measurements under the fundamental transverse mode condition of the cavity are achieved. The experimental results show that the intracavity equivalent loss remains almost the same while the initial cavity and the measured cavity are solely operating in the fundamental transverse mode. For the same high reflectance sample, the measurement precision of the coupled cavity ring-down technique can be 10.0%--27.1% higher than that of the traditional method.

The phase-shift deformation patterns effectively demodulate from the deformed composite pattern when composite grating phase-measuring profilometry is used to perform a three-dimensional measurement; in this case, selection of the filtering window is considerably important. Further, a mixed window is proposed to improve the measurement accuracy by analyzing the characteristics of noise and their different effects on different orientations of the spectrum components and searching the best filtering window with respect to the spatial spectrum in two mutually orthogonal directions. The digital simulations show that the designed mixed window exhibits better noise suppression when compared with those exhibited by the rectangular, triangular, Blackman, and Hanning filtering windows. The measurement results obtained with respect to the known-height plane denote that the smallest reconstruction error can be obtained using the mixed window equalizing noise and spectral leakage. The root mean square error of the mixed window is reduced by 9.64% compared to that of the Hanning filtering window, and the measurement accuracy is effectively improved. Furthermore, the feasibility and effectiveness of the proposed method are verified via the physical measurement experiments.

Herein, the effect of the angle of incidence on the characteristics of underwater plasma acoustic wave signals induced by 1064-nm nanosecond laser was studied. Result shows that when the laser is incident perpendicularly, the intensity of the laser-induced underwater plasma acoustic wave signal was the strongest. With the angle of incidence increasing, the intensity of the underwater plasma acoustic wave signal gradually decreased. Based on the plasma luminescent image, the laser-induced underwater plasma was found to exhibit multiple times of focusing. As the angle of incidence increased, the length of the underwater plasma gradually became longer, the radius of the plasma chamber gradually became smaller, and the luminescence intensity of the underwater plasma became weaker. Because of the optical refractive effect on the air-water surface, the equivalent focal length of the lens became larger and the Rayleigh length of the focusing lens was extended, thereby reducing the intensity of the laser-induced underwater plasma acoustic wave signal. The research results obtained herein have important significance in fields of laser underwater acoustic wave detection and laser communication.

Scientists have been exploring the optical computing system for decades, in hoping that it will have faster speed and lower energy consumption to break the limitations of the traditional electronic computing system. However, due to the ineffective optical logic units, slow electronic interconnects, and lack of optical memory, the idea of the optical computing did not go too far and was eventually abandoned. In the era of big data, the flow and usage of information have been increased exponentially, which provides a unique opportunity for the rapid development of the silicon photonic technology. The heterogeneous integration of electronics and photonics on the same silicon substrate, the Silicon Photonics, ensures a wide-bandwidth, high-speed, low-cost, low energy-consumption, and application-oriented optoelectronic computing platform. Here, we review the recent efforts of computing using silicon photonic technology, including artificial neural network accelerators, heuristic solvers of nondeterministic polynomial problems, analog calculations, quantum logic processors, and neuromorphic photonics, and propose a computing structure based on silicon photonic platform to take the advantages of high speed optical parallel processing and high capacity optical interconnections at the same time. We expect the Silicon Photonics will be the best technology to solve the computing challenges and problems in the electronical or optical domain.

Silicon carbide ceramic matrix composite (CMC-SiC) has many advantages, such as low density, high strength, high-temperature resistance, and corrosion resistance. It has application prospects in the field of aerospace. However, CMC-SiC is a kind of difficult-to-machine material, with ultra-high hardness and anisotropy. Conventional processing technologies are unsuitable for the high quality and efficient processing of CMC-SiC. Laser processing with high processing quality, non-contact, low heat input, wide range of application, and easy to combine with numerical control technology to achieve automation, has prospects of becoming the mainstream technology for precision processing of CMC-SiC. We analyze the typical thermally induced defects in laser processing based on the interaction mechanism of CMC-SiC with laser. We describe the advantages of ultrashort pulse laser in the CMC-SiC precision processing. In this context, we spotlight the development trend of laser processing technology for CMC-SiC and provide a theoretical basis and technical reference for the precision manufacturing of new aerospace CMC-SiC components parts.

To further improve the anti-noise capability of laser methane remote sensors, on the basis of the property of “coherent detection, low 1/f noise” of wavelength modulation spectroscopy, we further use the ability of “multi-scale, multi-resolution analysis” of wavelet denoising to denoise the absorption signal. Herein, a methane remote sensor system was established, and the relevant parameters of wavelet denoising were optimized through simulations. Moreover, the effects of wavelet denoising based on empirical mode decomposition were discussed. Comparative experiments were conducted to verify the feasibility of the proposed technique in the sensor system for cases where the wavelet denoising algorithm was used and not used. For a methane gas sample with integral concentration level of 200×10 -6 m, measurement results showed that the signal-to-noise ratio was improved from 116.4 to 179.8 using the wavelet denoising algorithm to extract the second harmonic signal. The calibration experiments demonstrated that the amplitude of the extracted second harmonic signal was directly proportional to the gas concentration. For the cases where the wavelet denoising algorithm was not used and used, the goodness of fit was 0.990 and 0.996, respectively. Based on the Allan deviation results, the detection limit was 3.4×10 -6 m without using the wavelet denoising algorithm and 1.7×10 -6m using the wavelet denoising algorithm, with an improvement in detection accuracy by 1 times. The proposed laser methane remote sensing method based on wavelength modulation spectroscopy and wavelet denoising technology exhibited high signal-to-noise ratio, linearity, and stability. The proposed method can be popularized and used in existing methane remote sensor systems.

For understanding the temporal profiles of the atomic emissions in high-repetition-rate laser-ablation spark-induced breakdown spectroscopy (HRR LA-SIBS), a 925 silver alloy sample was experimentally analyzed by HRR LA-SIBS. With different capacitances in the discharge circuit, the temporal profiles of atomic emissions of Ag I 328.07 nm, Ag I 338.29 nm, Ag I 520.91 nm, Ag I 546.55 nm, Cu I 324.75 nm, and Cu I 510.55 nm were experimentally studied. Under the excitation of the spark discharge, these six transitions exhibited close temporal profiles, even with different corresponding upper energy levels. The electric characteristics of the spark discharge were key factors that determine the persistence times and attenuation characteristics. Moreover, the influence of the upper energy level on them was negligible. In HRR LA-SIBS, the spectra recorded in non-gated signal recording mode were approximately equivalent to those recorded in gated signal recording mode for quantitative elemental analysis, which is helpful for simplifying the requirement of this technique for gated photon detectors.

Phase-matching is necessary to improve the efficiency of high-order harmonic generation. However, traditional phase-matching cannot be achieved in isotropic gas medium. As a feasible alternative, quasi-phase-matching breaks through the limitation of coherent length, which enables the harmonic intensity to continuously increase with the propagation distance. In this study, a quasi-CW counterpropagating terahertz field is used to modulate the generation of high-order harmonics to achieve quasi-phase-matching. The relationship between the harmonic spectra and the parameters of the modulation field is discussed through simulation. Results show that the quasi-phase-matched photon energy is inversely proportional to the wavelength of the terahertz modulation field and is directly proportional to the ratio of the field strength of the modulation to the pump field.

In this paper, a metamaterial terahertz broadband reflector, which is composed of a middle layer of polyimide film sandwiched between upper and lower metal gratings, is proposed. This new design overcomes the incapability of existing reflectors to simultaneously optimize the reflectivity and reflection bandwidth. The reflection performance of the reflector was analyzed by the finite difference time domain method, and the number of metal layers, thickness of the polyimide film, length of the grating period, and grid width were optimized for achieving wide-band reflection and high reflectivity. Results show that this reflector has excellent reflection performance and large reflection bandwidth in the terahertz frequency band. In the 0-4.0-THz working band, the bandwidth with reflectivity above 0.98 can reach 2.04 THz. The proposed method provides a design scheme for high-performance reflectors for the development of terahertz broadband communication technology.