The sound wave movement can change the surrounding atmospheric pressure and further affect the atmospheric refractive index distribution. Based on the wave equation and superposition principle of acoustic waves and the calculation formula of atmospheric refractive index, this paper solves the spatial distribution of artificial atmospheric refractive index heterogeneous body excited by point-array coherent sound source. Based on the Rytov approximation, the numerical relationship between the pressure excited by the point-array coherent sound source and the light wave flicker index is given, and the influence of the change of the point-array coherent sound source parameters on the light wave scintillation index is analyzed. The results show that the sound source can excite the uneven refractive index of the atmosphere, causing light intensity fluctuations. Changes in various parameters of the sound source can cause fluctuations in the light wave flicker index to varying degrees. The research results in this paper have preliminary explored the influence of array coherent acoustic waves on the laser transmission characteristics under the condition of artificial atmospheric refractive index heterogeneous body.

This study investigates the performance of the hybrid free space optical/radio frequency (FSO/RF) communication system based on the selective combination technology under the conditions of the Málaga turbulent channel and the Nakagami-m fading channel. Considering the pointing errors, we deduce the expressions of the average bit error rate and the outage probability of the hybrid FSO/RF system that adopts the subcarrier modulation and intensity modulation direct detection scheme. Their closed-form solutions are then obtained using the Meijer G function and the extended generalized bivariate Meijer G function. The bit error rate and the outage probability performances of the hybrid FSO/RF and only-FSO systems are investigated under different subcarrier modulation schemes, turbulence intensities, pointing errors, and RF channel fading parameters. The simulation results show that compared with the only-FSO system, the hybrid FSO/RF communication system can effectively improve the communication system performance.

To transmit high power optical energy through optical fiber array and aiming at fundamental-mode Gaussian light, a general parameter design method to satisfy the Dammann grating constraint conditions of beam splitting coupling is proposed. First, the components of the system are determined and their mathematical models are given. Then, 1×6 Dammann grating beam splitting is simulated by MATLAB, obtaining sub-spots with beam waist radius of 20.31 μm and distance of pairwise spacing is 127.7 μm, with a total diffraction efficiency of 84.50%, and an inhomogeneity of 0.23%. According to the optical grating diffraction theory and laser divergence angle, the sub-spots radius is calculated. Comparing the simulation results, for incident fundamental-mode Gaussian beam, the sub-spots radius formula derived from plane wave is not applicable. The radius of the sub-spots is inversely proportional to the radius of the incident light and the number of grating periods has no effect on it. And it is proved by experimental result. In order to satisfy the coupling constraint condition, a general system parameter design method is presented, which adjusts the spot radius, waist radius, collimation ratio, grating unit period length, and focal length of the focusing lens, the spot radius and spacing required by precise coupling are obtained.

Fiber Bragg gratings （FBGs） have advantages such as excellent multiplexing capability, high sensitivity, compact structure, and corrosion resistance. Therefore, they have been widely used in various practical engineering applications. In this study, we used a 193-nm excimer laser to fabricate a highly reflective FBG array on a standard communication single-mode fiber （Corning, SMF-28）. We performed a long-term annealing experiment for about two months. High-temperature optical fiber sensing systems are designed to achieve quasi-distributed measurement of environment temperature below 400 ℃, with temperature measurement errors of less than 0.2 ℃.

Light source layout is one of the key factors that affects indoor LED optical communication lighting and communication performance. Compared with the large divergence angle Lambertian LED used in the traditional layout, small divergence angle LED has the advantages of small reflection area and high central light intensity. This article uses LED with small divergence angle as light source, and aiming at the optimal uniformity of illumination and the minimum number of LEDs, the light source layout of square and rectangular rooms are optimized, and the system performance of the optimized layout is analyzed. The results show that the illuminance uniformity of the optimized layout in both rooms are greater than 90%, and the received optical power is also greater than -2 dBm. Moreover, in the square room, under the premise of reducing the number of LEDs by 16, the system performance is better than the traditional layout, the average illumination is improved by 7.7%, the average signal-to-noise ratio is improved by 0.89 dB, and the mean variance of signal-to-noise ratio is reduced by 0.04 dB.

In order to reduce the fitting error caused by the broadening of the spectrum, this paper proposes to use the double-sideband continuous light as the detection signal and use its interference spectrum for sensing. Compared with the traditional Brillouin gain spectrum, the obtained spectrum has a narrower linewidth near the resonance spectrum, the error of the double-peak fitting in the pre-pump temperature sensor is reduced, and the frequency resolution of the system is improved, so as to achieve high spatial resolution and high frequency resolution of a pre-pump Brillouin optical time domain analysis （BOTDA） system based on double-sideband interference. Experimental results show that 50 cm spatial resolution and 0.37 MHz frequency resolution can be achieved on 100 m polarization maintaining fiber by using this method. Compared with the traditional single side band pre-pump system, the frequency resolution of the system is increased by 2 times under the same spatial resolution.

The vortex beam is a kind of special beam with orbital angular momentum. In recent years, it has been widely used in optical information transmission and encryption, astronomy detection, microscopic particle manipulation, and biomedicine. Traditional vortex beam generation methods have certain limitations, such as specific wavelength generation, large component size, and low degree of integration. The development of metasurface micro-nano technology provides a new possibility for the generation and control of vortex beams. In view of this, a vortex beam generation method based on a hook-shaped metasurface array is proposed. The metasurface structure can effectively reduce the size of the vortex beam generator and realize the integration of the device. Moreover, the supersurface structure does not depend on the circular polarization characteristic, wavelength and polarization direction of the specific incident light, so it can realize the generation of the vortex beam with high topological charge.

To correct and balance aberrations found in current systems, we designed a catadioptric telescope objective with a large relative aperture, long focal length, and short total length by adding a set of refraction optical elements before and after a double-mirror system. The working band of the objective system is 400-700 nm, focal length is 900 mm, diameter of the entrance pupil is 500 mm, obstruction ratio is 0.43, total length of the system is 495 mm, and value of modulation transfer function in the full field-of-view range is more than 0.5 at a cut-off frequency of 107.5 lp/mm. Tolerance analysis of the system was conducted. The results show that the telescope objective system designed in this study has the characteristics of a simple structure, high imaging resolution, and large tolerance.

In the process of fabrication and installation, defects will inevitably be introduced into the mirror used in laser gyro, which will modulate the incident light and induce light scattering. In order to study the variation law of scattering field when scratch defect size changes, the scattering model of single scratch defect with rectangular cross-section on the surface of high reflection mirror is established by using finite element method and multi physical field simulation software. Analyze the spatial distribution of laser scattering field by changing the width and depth of the defect; The integrated scattering measurement system is built to detect the defects with different depth and width, and compare them with the simulation results. Experimental results show that the change trend of scattering field of defects with different sizes is basically consistent with the change trend of simulation results, which provide theoretical basis and reference for the detection of surface defects of high-reflection mirrors.

The detection of food and medicine has important application value in the field of education and civic. Therefore, a detection method based on terahertz time-domain spectrum analysis is proposed. The terahertz time-domain spectroscopy detection technology is used to study the terahertz spectrum characteristics of materials covered by different packages, and the detection technology of terahertz samples under high relative humidity conditions is studied. A simple and effective spectral subtraction method is used to deal with the water vapor absorption interference in the sample spectrum, and to calculate the refractive index and absorption coefficient of the sample in the terahertz band. By calculating the refractive index and absorption coefficient of the samples shielded by different wrappers, the proposed method can accurately distinguish the types of samples.

To address the problem of coherent noise in laser interferometer measurements using a point source, the principle of coherent noise prevention using a ring source was described. Moreover, the relationship between the radius and thickness of the ring source and the visibility of fringes was analyzed. Further, to produce the ring source, an annular-lens-based optical system comprising a beam expanding system, annular lens, and double telecentric lens was proposed. The target parameters of the ring source were obtained according to the collimating lens and cavity length of the Fizeau interferometer. Additionally, ZEMAX was used to design three systems in the ring source system and ensure good connection between the optical systems. The annular lens was created by rotating an aspheric lens, and the double telecentric lens could reduce the ring source diameter to a reasonable range while ensuring that the outgoing beam from each off-axis point source in the final ring source was parallel to the optical axis. Finally, a ring source with an average ring radius of 0.38 mm and a thickness of 12.5 μm was designed. When the focal length of the collimating lens is 900 mm and the cavity length of the interferometer is 100 mm, theoretically, the visibility of interference fringes of greater than 0.98 can be achieved.

This article focuses on the research of fast-positioning method of one-plane two-hole feature, while aiming at the precise measurement and positioning of workpieces at a production site, and it builds a set of on-machine measurement system based on the computer numerical control (CNC) platform and line laser. Using the isotropy of the spherical surface, global calibration of the line laser on-machine measurement system is achieved through a standard sphere. The plane and holes are used as the positioning features. Based on the measurement data obtained by the line laser sensor, a fitting algorithm is designed and the size and position information of the relevant features are calculated. Finally, a test piece is used for the fast positioning test. The test results exhibit that the on-machine measurement system can meet the requirements of workpiece positioning and alignment in production and processing, and the system also possesses high accuracy and stability.

In this study, a new extraction method combining principal component analysis and gray gravity center is proposed. The algorithm is used to solve the problem that the efficiency and accuracy of linear structured light stripe center extraction affect the measurement results. First, the image is subjected to Gaussian convolution. The threshold segmentation method is initially applied to extract the effective light stripe information from the image. Then, the gradient distribution and amplitude of the light stripe image are estimated, and the point with zero amplitude is considered to be the initial point. Subsequently, the principal component analysis is used to get the normal direction of the point. Along the normal direction, the two points with the maximum amplitude on both sides of the initial point are taken as boundary points. Finally, the gray center of gravity method is used to find the center of the light stripe within the boundary for determining the next initial point. The center of the light stripe is extracted through iteration. The proposed method is verified based on its average processing time and root mean square error. Experimental results show that the average processing time of the proposed method is approximately 1.701 s. Furthermore, the extraction accuracy of the proposed method is less than 0.0500 pixel compared with the Steger method.

To effectively improve the wear resistance of TC4 alloy, TC4 + NiCr/Cr3C2 is used as the cladding material. In addition, the TiC-reinforced Ti-based coating is prepared on the TC4 alloy surface using the TRUMPF 4002 coaxial powder-feeding laser. Using various experimental characterization techniques and test equipments, the microstructure and wear resistance of the coating are investigated and analyzed. The results indicate that the cladding layer formation is mainly composed of the reinforcing phase TiC and the continuous matrix phase α-Ti. The TiC in the subsurface layer of the coating is mainly in the form of granular phase; the middle region, in the form of dendrite phase; the bonding zone, in the form of feather phase. The Ni, Cr, Al, and V elements, which are matrix solid solution elements, form reaction precipitates with the Ti element. The improvement in the average microhardness （536 HV0.5） of the coating is attributed to the TiC and strengthening solid solution of the Ni, Cr, Al, and V elements in the matrix, and the microhardness is approximately 50% higher than the microhardness of the TC4 substrate. The wear volume and friction coefficient of the coating are 27% and 25% lower than those of the TC4 substrate, respectively, with the wear mechanism being abrasive wear.

The combination of powders with different particle sizes plays a vital role in the quality of samples formed by selective laser melting. In this paper, the effect of IN738 alloy with different particle size powders on the powder characteristics and the quality of the shaped parts have been systematically studied. The results show that the powder fluidity increases with the increase of the volume fraction of the large particle size powder. When powders with large and small particle sizes （50% particle size of 31 μm to 53 μm and 50% particle size of 15 μm to 30 μm） are matched with each other, the particle size distribution shows that D10 is 15.1 μm, D50 is 27.9 μm, and D90 is 52.9 μm, the apparent density and tap density of the powder are higher. And the density of shaped part reaches 99.3%, with the better surface roughness and the lower porosity and crack density. The study exhibits that the cracks of the printed parts are solidification cracks, and the cracks are mainly distributed and propagated along the epitaxially grown 〈001〉 oriented columnar grain boundaries.

A laser diode end-pumped passively Q-switched Raman yellow laser based on Yb 3+∶YAG/Cr 4+∶YAG/YAG composite crystal is developed in this work. The passively Q-switched fundamental-frequency laser generated by the composite crystal passes through the Raman crystal YVO4 and the frequency-doubling crystal KTP, and finally obtains a laser output of 578.5 nm. A coupled cavity structure is used to reduce the loss of Raman light and frequency-doubled light, and an etalon is used to suppress dual-wavelength operation to improve the conversion efficiency of frequency-doubling. Experimental results show that when the pump power of the incident wavelength is 9.51 W, yellow light with a power of 183 mW, a wavelength of 578.5 nm, a pulse width of 6.537 ns, and a repetition frequency of 6.542 kHz can be detected.

In the optomechanical design of laser radar, the light source center of lidar does not coincide with the mechanical rotation center because the parameters need to meet the requirements of the actual project, which will lead to the bending of point cloud image and seriously affect the performance of lidar. Therefore, combined with the actual scanning situation of the three-dimensional radar, first, the reason for the bending of the lidar point cloud image is analyzed and the error calculation formula for each scan line is derived. Then, by modifying the parameters, the pixels in the relative coordinate system are transformed into the depth values in the world coordinate system, so as to complete the transformation of the coordinate system. Finally, the bending of the point cloud image is corrected. At the same time, the reliability of the modified algorithm is analyzed in detail combined with five point cloud images. Experimental results show that after correcting the algorithm, the point cloud image is flat everywhere, almost no bending, the contour of all test obstacles has no obvious deformation, the pixel points are arranged orderly, and the ranging error is reduced from 10.2 cm to less than 2 cm. In addition, the lateral range resolution of the nearest （0,1.8 m） and the longitudinal range resolution of the radar in the monitoring area are 7.5 cm and 4.8 cm, respectively, and the lateral range and longitudinal range resolution of the farthest point （25 m, 4.5 m） are 20 cm and 6.1 cm, respectively. Compared with the traditional data matching and splicing model, it is proved that the proposed algorithm of coordinate system transformation can fundamentally solve the two kinds of nonlinear errors caused by the misalignment of coordinate centers and the rotation of galvanometer. Moreover, it is proved that the algorithm has high stability through the test experiments in snow and complex environment.

In this paper, the used powder of 316L stainless steel with low cost was selected for selective laser melting （SLM）, and process parameter optimization and post-heat treatment were performed to improve the properties of the products. To be specific, after multiple groups of samples were prepared under different process parameters through the used powder with an average particle size of 27.6 μm, their microstructures were observed and their mechanical properties were tested. Then, some samples with good forming properties were adopted to study the effect of the heat treatment process with different cooling modes on the mechanical properties, corrosion resistance, and phase composition. The results show that when the laser energy density was 54 J/mm 3, the forming properties （hardness, tensile strength, elongation, etc.） of the samples were optimal, and the forming properties of the samples were closely related to the laser power and scanning speed in the case of constant laser energy density. After heat treatment, the hardness and tensile strength of the samples decreased, and the elongation and corrosion resistance improved. Besides, the austenite structure was not transformed, and only the grain size became larger. In conclusion, when the used powder of 316L stainless steel was employed for SLM, selecting reasonable forming parameters and heat treatment method can achieve good mechanical performance of the products.

Fabry-Perot etalon is an important device in many classical and modern optical fields. A simple and stable air gap Fabry-Perot etalon is designed to act as core device of spectrally resolved interferometry for absolute distance measurement of femtosecond pulse laser. The Fabry Perot etalon is placed in the place where two beams of Michelson interferometer converge so as to filter out the femtosecond optical frequency comb. The spectral power density of interference signal measured by femtosecond laser absolute distance is accurately monitored, thus the absolute distance is calculated. The parameter design of the Fabry Perot etalon is introduced in detail. The experiment of regulation system of the Fabry Perot etalon is carried out. The principle of spectrally resolved interferometry for absolute distance measurement of femtosecond pulse laser is analyzed briefly. Experimental results show that the measuring distance within ± 1 mm has the accuracy less than ± 5 μm.

Numerical simulation is carried out for the collimating and focusing lens of the 10 kW expanded beam fiber connector under different cooling modes and different parameters. The coupling lens size parameters （diameter of 40 mm to 60 mm and edge thickness of 5 mm to 25 mm） are obtained by using the ZEMAX simulation design. The thermal distribution of the lens is simulated by COMSOL Multiphysics to obtain the maximum surface temperature of the lens using the cooling method and the influence of lens size on temperature under different output powers using this cooling method. The simulation analysis of 20 sets of aspherical lenses with different size parameters but the same optical performance shows that when the power is above 20 kW, the lens can be cooled by side air cooling mode, the wind speed is 9 m/s, the lens diameter is greater than 50 mm, and the thickness is less than or equal to 5 mm. When the power is greater than 7 kW, the lens can be cooled by plane air cooling, the wind speed is 5 m/s, the lens diameter is greater than 30 mm, and the thickness is less than or equal to 5 mm. When the power is lower than 7 kW, the lens can be cooled by edge water cooling, the water flow rate is 1 m/s, and the lens thickness is less than 7 mm.

Surface-enhanced Raman scattering （SERS） detection systems based on silver nanomaterials can be used to improve the weak Raman signal in bioactive substances detection. In the present work, SERS technology was used to detect joint fluid samples of 18 synovial arthritis patients and 15 normal people,and the spectral peak assignment methods, principal component analysis （PCA）-linear discriminant analysis （LDA） algorithm were applied to analyze the sample data after collecting SERS spectral data. The results of this study show that higher concentrations of polysaccharide （477 cm -1）, DNA （722 cm -1）, δ（CH2） （1439 cm -1）, guanine （N3） （1576 cm -1）, and amide I bands （1676 cm -1） in arthritis patients compared to normal people, while the glycogen （490 cm -1）, phosphatidylinositol （596 cm -1）, protein tyrosine （640 cm -1）, glucose （1071 cm -1）, and protein glutamine absorptions （1645 cm -1） were comparatively less than normal people. The specificity and sensitivity of disease diagnosis by PCA-LDA algorithm were 83.3% and 80%, respectively. Consequently, the results of this research demonstrate that SERS spectroscopy based on silver nanomaterials has considerable feasibility and potential value in diagnosis and analysis of synovial arthritis disease.

Currently, optical coherence tomography is one of the most sensitive methods for detecting diabetic retinopathy. However, the artificial detection of diabetic retinopathy is time consuming and prone to subjective errors. Accordingly,this paper proposed an improved deep learning network based on transfer learning for automatic classification of retinal images. First, the image was preprocessed via adaptive threshold combined with the Gaussian filter algorithm. Then, on the basis of the pretraining model, the problem of sample difference was solved through fine-tuning, and the traditional fully connected layer was replaced by the global average pooling method for extracting deep features and reducing overfitting. The network was validated based on the experimental data, with the accuracy of the retinal image classification being 97.3%. Results reveal that the proposed network is effective for the automatic classification of retinal macular lesions.

Aiming at the moving mirror tilt in the Michelson interferometer, the influence factors of interference modulation degree under the rectangular and circular clear apertures are analyzed by the interference theory. Simulation results show that the interference modulation degree is related with the clear aperture r,wavenumber v?, and tilt angle θ. In order to ensure the performance of the interferometer, the degree of interference modulation should not be less than 90%. When the wavelength is λ, the tilt angle θmax of the moving mirror for the rectangular and circular apertures should be less than or equal to λ/(16r) and λ/(14r), respectively. Within the control range of the tilt angle of the moving mirror, Matlab is used to simulate the influence of monochromatic light on the sinusoidal tilt error and random tilt error. The results show that the tilt angle of the moving mirror should be controlled at about 1″, which has certain reference value for the structural design and development of the spectrometer.

The traditional solution uses a single two-dimensional MEMS （Micro-Electro-Mechanical System） micromirror as the scanning structure, but its manufacturing process is complicated and there is a problem of high failure rate in the working process. In view of this, two cheaper one-dimensional electrostatic MEMS micromirrors are packaged and combined to obtain a two-dimensional scanning device module. Through the research of device design and manufacturing process, a MEMS two-dimensional scanning device model is finally developed. The entire device module has the advantages of compact structure, simple manufacturing process, low cost, high reliability and easy mass manufacturing. Experimental results show that the scanning optical angle of the MEMS two-dimensional scanning device module in the X-axis direction can reach 48.0° （driving frequency is 28.25 kHz, voltage is 160 V）, and the scanning optical angle in the Y-axis direction can reach 12.5° （driving frequency is 3.80 kHz, voltage is 160 V）, and its optical performance is comparable to that of a single two-dimensional MEMS micromirror, which can meet the needs of the field of micro laser projection.

With the development of laser technology and quantum communication technology, an acousto-optic modulator has become an important device in many fields. The diffraction efficiency and polarization maintaining ability are important indexes of an acousto-optic modulator. In this paper, through the theoretical and experimental investigation of the diffraction efficiency of an acousto-optic modulator, we propose a theoretical method to improve the acousto-optic diffraction efficiency and design a positive feedback acousto-optic modulation system, which can make the polarization of any arbitrarily polarized light maintained. The experimental results show that this acousto-optic modulation system can significantly enhance the diffraction efficiency of the acousto-optic modulator and guarantee the polarization maintaining of any arbitrarily polarized light during propagation in the field of quantum communications. The research results provide a reference for the research of optical fiber coupled acousto-optic modulators and quantum devices based on acousto-optic modulators.

In order to reduce the capacity of the navigation star database, an algorithm for screening navigation stars on star sensors is proposed. Uniformly distributed optical random vectors on the celestial sphere are generated and used for the Monte Carlo samples. The bright stars in the circumferential field of view （FOV） determined by each optical axis vector are in turn taken as the star subsets. The stars not found in the constructing star database are added to the constructing database in these star subsets and simultaneously the duplicate stars are discarded. After traversing all the implementation samples, one can finally obtain the navigation star database. The simulation condition is set as follows. The FOV of the star sensor is 15°×15°, the limiting star magnitude is 5.6 m, the angular distance threshold between stars is 1°, and the number of navigation stars required for star map matching is 15. The navigation star database constructed by this algorithm improves the uniformity of the navigation star′s distributions. In the necessary and sufficient sense of star map matching, the number of navigation stars in the star database reach the minimum. It thus reduces the number of matching pattern databases and reduces the memory requirements, which shows the engineering and practical value for the design of star sensors.

The optical drive rotation of the magnetically levitating pyrolytic graphite sheet provides a way to convert solar energy into kinetic energy, and the study on this phenomenon is of great significance in the field of energy conversion. The equivalent magnetic charge method is used to calculate the spatial distribution of the magnetic field of the permanent magnet. The force, torque, and potential energy of the pyrolytic graphite sheet are calculated. Based on this, the optical drive rotation phenomenon of the circular pyrolytic graphite on the nested cylindrical permanent magnet is calculated, analyzed, and explained. It is found that when the nested cylindrical permanent magnet is strictly coaxial, the circular pyrolytic graphite sheet will not rotate under laser irradiation. However, the nested permanent magnet will inevitably produce a certain amount of eccentricity during assembly, resulting in asymmetric magnetic field distribution, which makes the torque of the circular pyrolytic graphite sheet change periodically with the laser irradiation point, so the optical drive rotation phenomenon occurs.

The thermal entanglement characteristics in the two-qubit Heisenberg XYZ chain model under the Dzyaloshinskii-Moriya DM interaction along the z direction is studied by the calculation of the symbiotic entanglement in the presence of an external magnetic field. The research results show that as for the Heisenberg XYZ chain model in the antiferromagnetic case, with the increase of the DM interaction parameter D, the spin chain without original thermal entanglement becomes thermally entangled. Meanwhile, as the DM interaction increases, the thermal entanglement of the spin chain gradually tends to be stable and the maximum entanglement degree of the spin chain also increases. With the gradual increase of the spin coupling parameter Jz, the maximum entanglement degree of the spin chain increases and the range of thermal entanglement is extended. The increase of the anisotropy parameter γb helps to expand the range of thermal entanglement, but it has no obvious effect on the maximum entanglement degree of spin chains.

Using the definitions of quantum controlled not-gates and single qubit rotating-gates, we design four kinds of pulse sequences, which are logically equivalent to the nuclear magnetic resonance （NMR） realization of quantum controlled not-gates. Under the condition that the radio frequency pulse duration is much shorter than the interaction time between two nuclear spins, the two-body time-dependent Schr?dinger equation with NMR is approximately solved in the rotating reference frame and the optimal NMR pulse sequence parameter value for the quantum controlled not-gate is given. Meanwhile, according to the Suzuki''s symmetric product formula, the time-dependent Schr?dinger equation is numerically calculated, the performance of these four sequences of quantum controlled not-gates is demonstrated by numerical calculation, and the performance advantages and disadvantages of different pulse sequences are judged.

A light detection and ranging （LiDAR） system can actively emit laser light to capture the distance, direction, speed, and contour of an intrusion target with high accuracy and high resolution, and thus it is widely used in the urban security, industrial fields, etc. This paper briefly introduces the mainstream manufacturers of security LiDAR at home and abroad as well as the technical indicators of their products. The principle, characteristics and current status of security LiDAR under different technological regimes are mainly discussed in terms of LiDAR ranging schemes, scanning methods and light source selection, combined with different security applications. The application trend and development future of security LiDAR are summarized and prospected in the end. Security LiDAR will develop toward low-cost, high-performance, serialization, miniaturization, solidification, chip, and multi-source integration.

In recent years, porous graphene nanomaterials have attracted significant attention owing to their unique physical and chemical properties as well as their numerous potential applications in the fields of biology, materials, energy, and information technology. However, the synthesis of porous graphene usually requires high-temperature treatment or multistep chemical synthesis methods, making the process complicated. It is also challenging to form a patterned structure. In 2014, American researchers proposed laser-induced graphene （LIG） technology to achieve low-cost patterned porous graphene structures. LIG technology is a method that prepares three-dimensional porous graphene material by direct laser writing on a carbon precursor material using a laser in an ordinary atmospheric environment. This technology combines the preparation and patterning progress of three-dimensional graphene. It does not require traditional wet chemical steps, thus reducing the cost of production. Since its advent, LIG has stimulated researcher’s interest. Researchers have explored the LIG formation mechanism and its applications in various fields, such as energy, sensing, and environment. This study summarizes LIG’s various synthesis schemes, including controlling the LIG product quality, surface properties, electrical conductivity, and methods for converting different carbon precursors to LIG. Based on the characteristics of LIG, the application of LIG in supercapacitors, sensors, self-cleaning filters, triboelectric nanogenerators, and terahertz modulation devices has been investigated in recent years. Finally, this study prospects the development of LIG-based absorbing materials and metasurfaces.

Pulsed laser deposition has broad applications in scientific research and industry as a simple, versatile, and efficient film growth technology. The requirements for film quality are becoming more and more stringent in many high-tech applications. Reducing or eliminating the particulates inside and on the surface of a film has become an urgent problem. This paper introduces the source of particulates in pulsed laser deposition and discusses the advantages and disadvantages associated with various particulate control techniques. Finally, the trend of particulate control based on pulsed laser deposition is discussed.

Terahertz time-domain spectroscopy （THz-TDS）, as an emerging detection technology developed rapidly in recent years, has been widely used in the agriculture, chemical industry, pharmacy, and other detection fields due to its powerful perspectivity, high security, and efficient spectral resolution. In this paper, we introduced the recent research status of terahertz spectroscopy in the detection of inferior agricultural products, the detection of pesticide residues, the detection of banned additives, the identification of genetically modified crops, and the detection of moisture content in agricultural products. Furthermore, we summarized the main technical problems of terahertz spectroscopy in the detection of agricultural products and forecasted the development prospects of this technology. As science and technology develop forwards, terahertz spectroscopy will have more bright application prospects in the future.

Frequency-swept fiber lasers have extremely important application values in the fields of fiber sensing, biomedical, and spectroscopy. The parameters such as the center wavelength, sweep speed, sweep range, and output power of the frequency-swept fiber laser determine the performance of the fiber sensing system and the biological imaging system. Therefore, it is of great significance to study the frequency-swept fiber laser and its various performance parameters. The frequency-swept fiber lasers currently studied can be divided into two major categories, one is based on dispersion-modulated frequency-swept fiber lasers, and the other one is based on optical filters. This article mainly introduces the research progress of the frequency-swept fiber laser based on the optical filter and the research results on various performance parameters. At the same time, it points out its existing problems and prospects the development of frequency-swept fiber lasers.

Laser additive manufacturing （LAM） involves a complex heat-processed process, and the produced multilayer parts also have complex microstructure characteristics. The microstructure characteristics of the parts determine their mechanical properties, thus the optimization of microstructure characteristics is the key to further realize the precise control of the mechanical properties. This article reviews the microstructure characteristics of the LAM multilayer parts and summarizes the factors influencing the evolution of the microstructure characteristics, which provides a reference for the optimization of the microstructure characteristics of the LAM multilayer parts.

Due to the unique "fingerprint spectrum" characteristic, terahertz （THz） spectrum can be used to recognize the materials. With the development of artificial intelligence, deep learning is widely used in the field of THz spectrum recognition. However, the acquired THz spectral data are not always on a large scale due to the influence of experimental equipment, conditions and environment, which cannot meet the data size requirements of the deep learning algorithm. In order to solve this problem, we proposed a method of THz spectrum recognition based on generative adversarial networks （GAN） in this paper. Firstly, an S-G filter and a cubic spline interpolation method were employed to pre-process the THz spectral data. Secondly, the simulation data with the distribution of real THz spectral data were generated by the GAN. Finally, the generated data and real spectral data were taken as the training samples to train the deep neural networks （DNN）, thus obtaining the recognition results of the materials. The experimental results show that the THz spectral data generated by the GAN model can effectively simulate the overall characteristics of real THz spectral data and expand the THz spectral data samples, greatly elevating the spectral recognition accuracy.

Handwriting ink is an important physical evidence of the identification in judicial appraisal. In order to improve the accuracy of ink inspection, we employed Raman spectroscopy for the non-destructive inspection of ink samples. First, the pre-processed spectral data were dimensionally reduced to construct a model of partial least squares discrimination analysis. Then, after the prediction effect was verified by the area under the receiver operating characteristic curve, 36 feature variables with the highest variable importance for the projection were extracted. Furthermore, the feature variables were input as data into a multi-layer perceptron with 13 neurons in the hidden layer, and the final training accuracy rate was 87%, without overfitting. We also found that combining the feature extraction of variable importance for the projection with supervised multi-layer perceptron training could effectively compress the data and shorten the analysis time. Besides, the connection weight between perceptron layers could be adjusted through autonomous learning, which improved the credibility and accuracy of handwriting ink classification results.

In order to prevent the failure of the white balance algorithm of color digital reflection microscope and improve the accuracy of color acquisition, a colorimetric characterization method based on non-RAW data is proposed. First, a nonlinearity correction model based on power function is established by using the neutral patches of the color card. The non-RAW data is converted into the data linearly related to the scene radiance. Then, the colorimetric characterization model is established. Finally, experiments are conducted to test the accuracy of colorimetric characterization model before and after correction of non-RAW data, and the influence of luminance change of light source on nonlinearity correction model and the accuracy of colorimetric characterization is analyzed. The results show that the corrected non-RAW data will improve the accuracy of colorimetric characterization, and the improvement effect is especially obvious for the linear colorimetric characterization model. At the same time, the luminance change of the light source will cause the variation of the nonlinear correction model as well as the accuracy of colorimetric characterization, but when the luminance change is not sharp, the general nonlinear correction model can be used.