Functional near-infrared spectroscopy imaging has become the preferred choice as a neuroimaging technique of brain function research. To obtain the imaging system with high sensitivity, large dynamic range and high temporal resolution, we develop a multi-channel near-infrared brain functional imaging system based on improved lock-in photon-counting. The light source module consists of 16 laser diodes with wavelength of 785, 808 and 830 nm, respectively, which are modulated by square wave with frequency space of 252 Hz. The detection module includes nine photon counting photomultiplier tubes. This system combines the ultra-high sensitivity of the photon-counting technology with the simple parallelism of the digital lock-in detection based on square wave modulation mode, and system performance meets requirements. The linear correlation coefficient can reach 0.9989, cross talk between channels is negligible. The system has strong anti-interference ability and the ability to locate accurately.

Indoor visible light communication (VLC) based on light-emitting diodes (LED) can meet the needs of illuminance and high-rate data communications. However, the optical power and illuminance intensity distributions for the downlink of a VLC system on the same receiving plane are nonuniform owing to the LED Lambertian radiation pattern, the inherent ray multipath effect, and so on. Thus, it is difficult to ensure the fairness of communication services. An improved genetic simulated annealing algorithm (IGSAA) is proposed to search a set of optimal power regulating factors and adjust the transmitting power of LED arrays. In the IGSAA, the adaptive function is designed in the view of the received power differences among different positions on the receiving plane. A two-point crossover operation mode is used and a adaptive mutation probability is designed based on the optimal chromosome information of the population and the evolutional generation to enhance the search ability of the algorithm. Besides, to maintain the diversity of population, the probability crossover and mutation methods based on subgroup division are used to increase the population diversity. The numerical results show that the proposed IGSAA can effectively improve the coverage uniformity of an indoor VLC system within limited evolutional generations.

In coherent optical communication system, the polarization state of the signal light is uncertain because of the influence of atmospheric turbulence, and the optical mixer is sensitive to the polarization of signal light and local oscillator light. Based on the principle of optical mixer, the relationship among the polarization state of the signal light, the intermediate frequency signal and the mixing efficiency is deduced, The amplitude of the intermediate frequency signal is used as feedback control signal to increase the mixing efficiency, and a single particle optimization algorithm for coherent optical communication systems is designed. Experimental results show that in closed loop state, the amplitude of the intermediate frequency signal increases rapidly, the mixing efficiency increases about 64%, and the fluctuation variance of amplitude of intermediate frequency signal decreases to 0.001. The polarization control in the coherent optical communication system is realized.

The delay response characteristics of bias drift caused by the non-reciprocity phase errors of a fiber coil in the fiber optic gyroscope (FOG) are investigated. The correlation between temperature and delay time is revealed and the modified temperature drift compensation model is established. In addition, the high-precision FOG experimental system is built. The delay characteristics of the non-reciprocity phase errors are verified using the approximate "square wave" temperature variation at different temperature ranges, and the model parameters of the experimental fiber coil are obtained as well. The test of FOG bias drift in full-temperature is carried out. The experimental results show that the modified model can used to achieve a better compensation effect based on the thermal diffusion mechanism, and the correctness and validity of the new model are verified.

A method for selective edge extraction in an optical scanning holography system is proposed based on annular pupil filters, in which a single two-dimensional optical scan is used to acquire the holographic information of a three-dimensional object based on the two-pupil heterodyne scanning technique. First, a small aperture filter and an annular pupil filter are used as two pupils to form a composite light field for scanning an object and extracting the edge information of an object. Then, the selective extraction of the anisotropy of an object is achieved by moving and destroying the symmetry of an annular pupil filter and simultaneously selecting two identical annular pupil filters. The computer simulation results show that the selective edge extraction of isotropy and anisotropy can be well achieved by using annular pupil filters in an optical scanning holography system.

Microwave photonic frequency conversion and phase-shifting technology are both key technologies of microwave photonic radar. The complexity and volume of the microwave photon radar system can be greatly reduced if the phase shift is completed while the microwave photon frequency conversion is realized. A microwave photonic frequency conversion and phase-shifting method is proposed based on the optoelectronic oscillator loop. The fundamental frequency microwave signal is up-converted by using the photoelectric oscillation loop. The 1.6-21.16 GHz tunable up-conversion signal is regenerated by adjusting the frequency of the optoelectronic oscillator. The tuning range can reach 50.4° by adjusting the output wavelength of the tunable laser and using the delay effect of dispersion compensating fiber to change the phase of up-conversion signal. The two technologies of microwave photon frequency conversion and phase shifting are combined, which not only extend application scope of optoelectronic oscillator, but also give some references to the application of microwave photon radar.

In order to explore the mode of orthogonal Porro prism, the output mode of an orthogonal Porro prism resonator is investigated on the basis of the Fresnel-Kirchhoff diffraction integral formula and is simulated by using the fast Fourier-transform algorithm. By analyzing the manufacturing errors in different apex widths and right angles of these prisms, the conditions for maintaining the single-transverse-mode operation of the orthogonal Porro prism cavity are determined. The simulation results show that the output spot integrity can be guaranteed when the machining error of Porro prism is below 18 μm and the angle error is below 2″.

In this paper, a ring cavity Tm-doped fiber laser with both single longitudinal mode and ultra narrow linewidth is proposed and demonstrated. An unpumped polarization maintaining Tm-doped fiber (PM-TDF) and a narrowband F-P filter are combined to realize the single longitudinal mode lasing operation and ultra narrow linewidth. Experimental results show that the proposed laser is stably operating at central wavelength of 1942.03 nm and the optical signal-to-noise ratio is 63 dB at room temperature. Through 100 minutes of continuous measurement, the output power fluctuation is less than 0.62 dB and the center wavelength shift is less than the minimum resolution of the spectrometer of 0.05 nm. This indicates that it has good stability for a certain period of time. Through the linewidth measurement based on frequency noise, linewidth of the laser under the measuring time of 0.01 s and 0.1 s are 300 Hz and 3 kHz, respectively. The proposal will be applied significantly in the field where the longitudinal mode and linewidth specificity of a laser are strictly required for 2 μm wave band.

In this study, we describe a passively Q-switched Nd∶YAG nanosecond laser capable of operating stably over 100 ℃ and at low temperatures. The resonator is based on a stable, double-Porro-prism cavity structure. A Nd∶YAG slab is side-pumped via a vertical-cavity, surface-emitting laser array, and the temperature is controlled by a thermoelectric cooler. The passively Q-switched crystal is Cr4+∶YAG. We have tested the performance of the laser at different temperatures with a 1 kW peak pump power and 1 Hz repetition frequency. The results show that the average output energy of the laser is 18.79 mJ, the standard deviation is 2.29 mJ, the pulse width is ~4 ns, the near-field spot diameter is ~5 mm, and the far-field divergence angle is less than 0.9 mrad in the temperature range of －75-40 ℃. The lasers has a small size, compact structure, and high reliability. It is thus suitable for space-laser applications under a wide range of low-temperature conditions.

A method for feature points extraction of planar weld seams based on genetic algorithm is proposed. In order to reduce the image noises, we use median filtering method and threshold segmentation method to preprocess welding images. The seed filling method is used for the image segmentation, and the mathematical model of laser stripe skeleton extraction is obtained according to the characteristics of the image. The skeleton extraction method of laser stripe based on genetic algorithm is mainly studied, and the coordinate of center point is extracted with linear scanning method. The Pauta criterion is used during the linear fitting of the skeleton to iteratively eliminate the noise data, and the accurate position of the skeleton and feature points are obtained. The experimental results show that the method can effectively eliminate many noises and the interference of laser stripe width in weld image and can extract the weld feature points quickly and accurately.

The 2.8 mm thick 800 MPa grade hot-rolled high strength steel plates are welded with fiber laser. The fully-penetration laser welded joints are obtained by adjusting the laser power. The microstructures of laser weld joints are observed, and the microhardness, tensile properties and impact toughness of the laser welded joints are tested. The relationship between microstructure and mechanical properties of laser welded joints is studied. The results show that there was no softening zone in the welded joint, the tensile strength of the welded joint can reach that of the base metal, and the impact energy of the welded joint can reach 85.6% of the base metal.

The 304 stainless steel plates are double-sided shocked by laser beam with a wavelength of 1064 nm and the pulse width of 10 ns, the surface morphology of sample treated by laser shock processing (LSP) is observed by a three-dimensional profilometer, and the residual stress of the specimen surface is measured by an X-ray diffractometer, respectively. And a servo-hydraulic fatigue test machine is employed to implement the fatigue experiments on samples without and with LSP to obtain the fatigue crack growth rate curves. In addition, a scanning electron microscope (SEM) is applied to detect the fracture morphology at different crack growth stages. The experimental results indicate that LSP can not only cause plastic deformation to a maximum value of 25 μm and form compressive residual stress with a maximum value of -218 MPa on the sample surface, bust also transfer the crack source to the inside of the sample. And the crack growth rate at the shocked region is significantly retarded by LSP. The validity of utilizing LSP to improve the fatigue resistance of 304 stainless steel can be verified according to the fatigue crack growth rate curves.

The GH4169 alloy samples are fabricated by the high-deposition-rate laser metal deposition (HDR-LMD) technique and their microstructures and tensile properties are investigated when the deposition rate is 2.2 kg/h. The precipitated phases of the HDR-LMDed samples mainly include Laves phase, acicular δ phase and non-uniformly distributed γ″ and γ′ phases. The tensile test results show that the plasticity and strength of the as-deposited superalloy are both lower than the forging standard.

The laser cleaning technology is utilized to clean anodic oxide film of 2219 aluminum alloy before welding and the effect of cleaning speed on removal effect is studied. In order to verify the feasibility of laser cleaning, we perform the welding experiments on the cleaned aluminum alloy. At last, the mechanism and characteristic of laser cleaning are analyzed. Results indicate that 2219 aluminum alloy can obtain good appearance and internal quality after laser cleaning. The laser cleaning rate threshold is 1079 mm·min-1. The main mechanisms of laser cleaning of 2219 aluminum alloy anodic oxide film are evaporation and explosion, and also accompany with some elastic vibration stripping.

The Co-based alloy coatings are prepared on the GCr15 bearing steel surfaces by the ultrasonic vibration assisted laser cladding technique. The microstructure and the high-temperature oxidation behaviors are analyzed in detail under the condition of 750 ℃/100 h. The results show that the ultrasonic vibration does not change the phase compositions of cladding layers and only more uniform and fine equiaxed structures are formed in the near surface layers. After high-temperature oxidation for 100 h, the coating follows the parabolic oxidation rule. Compared with those of traditional laser cladded coatings, the oxidation films on the surfaces of coatings by ultrasonic vibration assisted laser cladding are finer and denser, and there are no obvious oxidative cracks and spalling defects. Meanwhile a large number of high-temperature CoCr2O4 spinel phases with good stability are generated. The oxidation weight gain and oxidation index are reduced by 19.2% and 50.8%, respectively. The high-temperature oxidation resistance is enhanced.

The 4Cr5MoSiV1 die steel samples are fabricated by the selective laser melting (SLM) technique. The influence of laser linear energy density η on microstructures, carbon loss and micro-hardness of samples is investigated. The results show that the microstructures of SLM-formed 4Cr5MoSiV1 die steel samples are mainly martensite and a little amount of residual austenite. The decarburization reaction, splashing behavior and elemental ablation together cause carbon loss, and the carbon loss rate is as high as 17.7% at η=950 J·m-1. With the increase of η, the grain sizes of samples increase, the carbon loss rate increases and the martensite content decreases. Under the same η, the grain size and the carbon loss rate in the transition zones of samples are the smallest, while those in the heat affected zones are the highest. With the decrease of η, the pore defects become more. When η is too large, the cold cracks appear. When η is 905 J·m-1, the samples possess uniform microstructures, high densities, and relatively high micro-hardness (that in central zone of molten pool is 710.3 HV and that in transition zone is 732.4 HV).

To explore the technological characteristics in fiber laser cutting of medium-thickness aluminum alloy sheets, the fiber laser cutting of an 8 mm thick AA2219 Al alloy is carried out. The effects of process parameters such as laser power, cutting speed, defocusing distance and assistant gas pressure on the kerf quality are systematically investigated. The kerf quality is assessed by the dross height and the fraction of oblique striation zone of the lower part of kerf. The experimental results show that the kerf quality is mainly determined by laser power and assistant gas pressure. The dross height of the kerf is reduced to minimum when laser power increases to 5.4 kW and the range of gas pressure increases to 1100-1500 kPa. Moreover, in order to further improve the kerf quality of medium-thickness aluminum alloys, a simple Laval nozzle is designed and made by the hydrodynamics simulation based on the aerodynamics theory. The experiment with this nozzle discloses shows that the fraction of oblique striation zone is reduced from 0.5 to 0.14, while the dross height does not nearly change.

Based on the mechanism of ablation, we study the quantitative removal of low thermal conductivity resin-based paint with high repetition rate pulse laser. The selection of scanning mode of a two-dimensional galvanometer system is studied, as well as the distribution characteristics of laser spots on material surface. The temperature change of material surface is simulated and it is found that the pulse interval has little influence on the material temperature change. The experiments of high repetition rate pulse laser ablating low thermal conductivity paint are carried out. The relation between the pulse number acting on paint surface and the ablation depth is linear, and a linear equation is established.

Ti-based composite coating is successfully fabricated on Ti811 titanium alloy surface by laser cladding. The phases, microstructures, microhardness, friction and wear resistance of the coating are studied, and the formation mechanism of TiB2-TiC composite mosaic structure is analyzed. The results show that the main phases of the coating are reinforced phases of TiC and TiB2, intermetallic compound Ti2Ni and matrix α-Ti. The misfit between the (0001) face of TiB2 and the (111) face of TiC is only 1.057%, which indicates that TiB2 can be the most effective heterogeneous nucleation core of TiC to form a TiB2-TiC composite structure. Due to dispersion strengthening, solid solution strengthening and fine-grain strengthening effect, the microhardness of the coating can reach 617 HV, which is 1.62 times that of Ti811 titanium alloy. The coating has good friction and wear resistance, its wear volume, wear depth and average friction coefficient are 175×10-3 mm3, 80.13 μm and 0.39, respectively, and the wear volume of the coating is about 26% lower than that of the substrate.

In the process of dual-path frequency-modulated continuous-wave laser ranging, the vibration converts the optical-path difference into an unnecessary phase modulation of a beat-frequency signal. In addition, the Doppler shift is introduced into this beat-frequency signal, which results in the serious broadening and frequency shift in the spectrum of beat-frequency signals. Thus the distance cannot be calculated according to the beat-frequency. To solve this problem, we propose a vibration compensation method based on the four-wave mixing effect, in which the four-wave mixing technology is utilized to generate a new frequency-sweeping signal opposite to the sweeping direction of the original frequency-sweeping signal, and the distance value can be calculated according to the measured beat-frequency signal of two frequency-sweeping signals. The results show that when the sweeping bandwidth is 10 nm, the measurement distance is 5 m and the target has a periodic displacement of 100 μm at a frequency of 2 Hz, the influence of vibration on laser ranging can be effectively eliminated with the vibration-compensation method based on the four-wave mixing effect, and the measurement standard deviation is reduced from 1.062 mm before compensation to 29 μm. In this method, the distance value after elimination of vibration influence can be directly obtained without the need of measuring vibration displacement, and the hardware part of the system is greatly simplified.

A conjugate-reflection-based time-synchronization measurement method is proposed for target points of a high power laser facility. First, two parallel reflectors with equal distances from the target point are placed on both sides of the target point, and simultaneously two high-speed photodiodes are placed on the conjugate image point of the target point. Second, two laser beams from the up and down hemispheres in the target chamber are reflected to the two photodiodes placed on the conjugate image point of the target point, and the time interval between two output signals from the two photodiodes is just the time-synchronization difference between the optical paths to be measured. The proposed measurement technology possesses nice characteristics of simple operation, high test efficiency, which has been successfully applied in the time-synchronization measurement of multiple laser beams in high-power laser facilities.

Based on the three-dimensional shape measurement system of iGPS positioning and tracking, a mathematical model of this system is established, and the main principle of the traditional hand-eye calibration technology is introduced. Then the system conversion relationship is established with the laser tracker. A calibration method based on feature point fitting is proposed and the transformation relationship is solved by the feature point constraint and the Rodrigue matrix based algorithm. The point cloud splicing contrast experiments based on the robot base coordinate system and the iGPS world coordinate system are performed on the calibration system. The experimental results show that the calibration method based on fusion feature point fitting improves the precision of point cloud splicing.

In order to realize the laser ranging of Chang′e-4 repeater satellite, the study of lunar laser ranging (LLR) is needed to be carried out for technical verification. Yunnan Observatories of Chinese Academy of Sciences develops a common optical path LLR system based on the 1.2 m telescope. After many technical difficulties are overcame, the echo signal from the Apollo 15 reflector on the lunar surface was successfully detected on January 22, 2018, and the LLR is realized. Repeated experimental results show that the LLR system has the ability to detect very weak laser signals, and the measurement accuracy of the system reaches meter level.

An edge extraction method from LiDAR point cloud data based on rotation difference kernel estimation is proposed. For any point in the point cloud, the symmetrical center is the data point in a given direction, and the symmetrical window is constructed with a certain distance.The Kernel function about distance is defined in symmetric windows, and the weighted mean of elevations for the data points within the two windows is calculated. The absolute value of difference between the two weighted mean values is employed as edge magnitude of data point in the direction, and the maximum edge magnitude in all directions is selected as criterion for edge points. Then variances of elevations for the data points within the two windows in the direction corresponding to maximum edge magnitude is calculated, and the boundary points between buildings and ground are extracted by combining the absolute value of the difference between the two variances and the criterion of the edge points. By adjusting the distance between two windows, the maximum absolute value of the difference between the elevation variance in all directions is obtained, and this absolute value is used as the criterion of tree points. The absolute value of the difference between the two variances is used as the criterion of tree points, and the tree points are extracted after removing the junction between the building and the ground from the set of points detected by the criterion. The tree points in point cloud data are filtered by laser propagation characteristics, and then the complete building edges are extracted. The experimental results show that the proposed method effectively overcomes the influence of trees, and the accuracy of building edge extraction is about 80%.

Sheath flow is one of the key technologies for the optical detection of high concentration aerosol particles. Based on the aerodynamics theory and the related researches abroad, a gas sheath flow jet is designed to achieve the effective measurement of high concentration aerosol particles. First, a group of optimal design parameters are determined according to the simulation analysis by the Gambit and Fluent modules in the large-scale general finite element analysis software of ANSYS, and a real sheath flow jet is made as well. In addition, the simulation results show that the sheath flow jet can compress the diameter of sample air flow from 1 mm to 0.34 mm, and the compression effect is obvious. Then, a kind of experiment scheme is put forward, in which the compression effect of a sheath flow jet is indirectly analyzed using the size distribution errors of a particle counter. Finally, the comparison and analysis of 0.3 μm particle distributions are achieved for 1.0 mm ordinary jet, 0.5 mm ordinary jet and sheath flow jet on the same particle counter. The experimental results show that the sheath flow jet designed here can effectively reduce the overlap rate of dust particles and significantly increase the concentration detection limit of a particle counter. These results verify the feasibility of hydrodynamic analysis and provide an important basis for the optical measurement of high concentration aerosol particles.

A method is proposed to estimate the mass centre position and tumbling motion of rocket body using diffuse reflection laser ranging data. The tumbling motion of rocket body is analysed and the diffuse reflection laser ranging model is built. The theoretical and simulation methods are presented to estimate the tumbling axis orientation and tumbling period of rocket body. The laser ranging data of last stage Soyuz rocket body measured at Wettzell station are processed with the fast Lomb-Scargle algorithm. The length and mass centre position of rocket body are deduced by comparing the histograms of simulated and measured data. The tumbling period is estimated to be 11.4 s, the right ascension is 203°, and the declination is 23°.

The measurement of the topological charges of a composite vortex beam is challenging. Therefore, this study proposes a method to detect the orbital angular momentum of each sub-beam using the light intensity distribution characteristics and diffraction patterns with an elliptical aperture occluding partial azimuth. Simulation results reveal that the number of bright stripes and the direction of the tail in the intensity distribution of the composite beam represent the absolute value of the topological charge difference and the symbols of the higher order topological charge, respectively. The number of dark stripes and their distribution characteristics in the diffraction patterns reflect the size and symbol of the low-order topological charge, respectively. Thus, the proposed method can successfully detect the topological charges of composite vortex beams.

In this study, we propose a ZEMAX simulation analysis method for laser tracking measurement using a dual-wavelength method to compensate for the refractive index of air. We first develop an energy model for the system using optical elements to transform its polarization characteristics. We then establish an optical-system model based on ZEMAX to analyze the influence of the non-ideal performance of optical elements on the visibility of fringe pattern. The simulation results show that the interference pattern is most obvious when the splitting ratios of the beam splitters in the spectroscopic part of the system, the tracking part, and the receiving part are 2∶8, 6∶4, and 5∶5, respectively. The polarization beam splitters in the optical system have little influence on the visibility of the fringe pattern under non-ideal conditions.

A T-shaped cavity coupled metal-insulator-metal (MIM) waveguide structure with a rectangle cavity is proposed based on the transmission characteristics of surface plasmon polaritons (SPPs) in a sub-wavelength structure. The Fano resonance occurs due to the destructive interference between the narrow discrete state formed by the T-shaped cavity and the broad continuous state formed by the rectangular cavity. The coupled mode theory (CMT) is adopted to analyze the formation mechanism of Fano resonance. The finite element method is used to simulate this structure and analyze the influences of structural parameters on its refractive index sensing characteristics. The results show that after the optimization of structural parameters, its figure of merit is 6.04×104, and the sensitivity is 1120 nm/RIU. This research can provide a theoretical reference for the integration of photonic circuits and the design of nanoscale sensors in the future.

A bionic moth-eye sub-wavelength periodic micro-nanostructure of ZnS MS material, with broadband and wide-angle antireflection properties is designed by the rigorous coupled-wave analysis method. According to the rigorous coupled wave theory, a suitable control of periodic size, smaller than the ratio between the incident wavelength and the refractive index of materials, makes the high-order diffracted wave as an evanescent wave, and thus the broadband antireflection efficiency of this moth-eye structure is enhanced. The finite difference time domain algorithm is used to investigate the effects of moth-eye structural period, bottom diameter, structural height and top diameter on spectral transmissivity. Moreover, four structural parameters are optimized. In addition, three characteristic wavelengths in the visible, near-infrared and middle-infrared regime are selected for the electric field analysis under a wide-angle incidence. The research results show that in the short-wavelength range, the moth-eye wide-angle anti-reflection performance is determined by the anti-reflection and forward-scattering ability of this structural surface, while in the long-wavelength range, the moth-eye structure is regarded as a ZnS MS plane film, and its spectral properties are mainly affected by the Fabry-Perot interference. This study provides a theoretical basis and a design method for the design of moth-eye wide-angle structures under different wavelengths.

Crystal cascading is widely used for the compensation of walk-off angles in the nonlinear optical frequency conversion process. However, it is discovered that the conversion efficiency dramatically decreases when one of the cascaded crystals is rotated by 180° along the optical axis in the second harmonic generation experiment based on KTiOPO4 crystal cascading. The theoretical analysis indicates that the crystal rotation of 180° changes the sign of the effective nonlinear coefficient, which is equivalent to the generation of a phase mismatch of π and thus the second harmonic generation conversion efficiency decreases. A method based on air dispersion is proposed for the compensation of phase mismatch, which is characterized by simple configuration, solid temperature stability, low insert loss and low cost if compared with those for the compensation method based on wave plates. The experimental results show that the phase mismatch is compensated by air dispersion and the influence of crystal rotation on second harmonic generation conversion efficiency is eliminated. The validity of the theoretical analysis and the feasibility of the compensation method based on air dispersion are demonstrated.

The echo waveform is one of the core data from the laser altimetry satellite, and the simulation analysis of echo waveform has important reference value in parameters designing and data processing for the satellite. In this paper, the effects of three factors such as ground reflectivity, emission waveform and laser profile array (LPA) on the echo simulation results are considered, and the contrast experiment is conducted. The optimal simulation method is discussed. In the experiment, a certain research area is selected, and the data of ice, cloud and land elevation satellite (ICESat)/geo-science laser altimeter system (GLAS) is used as the verification data, and the echo simulation accuracy is evaluated by the correlation coefficients. The results show that the echo simulation accuracy can be significantly improved after the actual ground reflectivity and emission waveform are considered, and the correlation coefficient of the simulation results is improved from 0.9337 to 0.9492. Due to the low spatial resolution of the pixels in the LPA, there exists a large error in simulation accuracy. With the increase of pixel resolution by cubic spline interpolation, the simulation accuracy can be improved to 0.9513.

Multi-angle Polarization Imager (MAI) uses a back-illuminated area array CCD detector to quantitatively acquire cloud and aerosol parameters. Dark current is one of the main factors affecting the data quality of the area detector CCD and its quantitative application. In order to analyze the characteristics of CCD dark current and its channel dependence and improve the imaging quality of CCD, based on the analysis of the characteristics of MAI level 0 data, we propose a method for analyzing the dark current characteristics of each channel of MAI based on the nighttime scene. The period from February 2 to 16, 2018, MAI nighttime scene observation experiment is accomplished. Comparing the observations during daytime and nighttime of the MAI light blocking channels, the result shows that there is no significant difference in dark current characteristics observed in daytime and nighttime. Therefore, based on the night observation data, the dark current characteristics of 13 channels of MAI are analyzed. The results show that the distribution of dark current for each channel has some degree of non-uniformity and “bad points”, and the distribution within each channel has good stability, but it is significant difference for each channel. Based on the image method to correct “bad spots”, after correcting the non-uniformity distribution of pixels based on linear, non-linear relationship, the standard deviation of dark current images decrease from 12.1% to 6.9%. Taking the observation of the clear-air ocean as reference, the maximum possible impact of dark current and “bad points” on pixel observations decreased from 9.1% to 3.0%. The analysis results show that dark current monitoring based on nighttime observation can not only monitor the dark current characteristics of each channel, but also handle the channel dependence of dark current relative to setting dark current monitoring channel. Therefore, in the subsequent design of satellite-borne observation instruments, the dark current of each channel can be directly monitored and corrected by nocturnal observation, and there is not necessary to set a dark current monitoring channel separately, which will reduce the design weight of the load.

Severe haze occurred in Beijing frequently during December 2015, which had launched two red alerts for atmospheric heavy pollution. In this paper, according to the lidar stereo data at the tower of the institute of atmospheric physics of the Chinese academy of sciences, the atomspheric boundary layer height of Beijing city is retrieved by gradient method, and the simulation results of the mesoscale numerical WRF model are evaluated. The results show that the two methods have good consistency, but the extreme values are not very consistent. The correlation between lidar inversion of daily variation of boundary layer height and WRF simulation results reaches 0.76, the root mean square error is 163 m, and the average deviation is -61 m. Meanwhile, the accuracy of WRF simulation in clean weather is higher than that in polluted weather. In addition, the correlation between the observed PM2.5 mass concentration and the ABLH of lidar inversion is -0.85.

By analyzing monitoring data of atmospheric pollutions in Meiyu season measured by AML-2 mobile lidar, we study the temporal and spatial distribution characteristics of aerosol and ozone in troposphere over Hefei in Meiyu season, and analyze the effect of precipitation on pollution reduction. The results show that the aerosol extinction coefficient is small in Meiyu season and decreases with the increase of altitude on the whole. At 0.5 km, the extinction coefficient is from 0.1 km-1 to 0.18 km-1 in multiple days in Meiyu season. Continuous precipitation plays a significant role in reducing aerosol concentration, the mean aerosol extinction coefficient before Meiyu season and in Meiyu season is 0.37 km-1 and 0.14 km-1, respectively. The temporal and spatial variation characteristics of ozone are obvious in Meiyu season. The ozone concentration decreases with the increase of altitude and shows large daily variation. In June 20 and 24, 2008, the difference of mass concentration of ozone at 0.4 km is about 59.5 μg/m3. Compared with concentration of ozone before Meiyu season, the concentration in Meiyu season is greatly reduced with the maximum difference up to 41.8 μg/m3 at the same height.

Shanghai Superintense Ultrafast Laser Facility (SULF) is one of the key projects as major science infrastructures belonging to science and technology innovation center with global influence in Shanghai. Combining the research status and trends of superintense ultrafast laser at home and abroad, we briefly introduce the background, current status, and major potential applications of SULF.

As a large-scale high-power and sophisticated laser facility, Shenguang-Ⅱ (SG-Ⅱ) is a milestone in the history of laser driver development in China. SG-Ⅱ laser facility has evoked comprehensive and essential leap-style improvements in laser engineering, laser technologies, fusion researches and fundamental physics researches. We provide brief introductions on the great innovative developments of engineering solutions and technologies during the project implementation, and we also list some of the numerous researches of international influence, which have been achieved based on the high-quality operation of SG-Ⅱ laser facility in the past 20 years. With the continuous great progresses of last decade and thanks to the support from leadership departments, facilities with delivery capacity of 104 J-level in nanoseconds, 103 J-level and petawatt-level in picoseconds, as well as 102 J-level and multi-petawatt-level in femtoseconds have been established, and will surely continue to operate as one of the key platforms on the researches of inertial confined fusion, strong field physics and high energy intensity physics in China.

The overall scale and performance of a huge-scale high peak power laser facility are the concentrated expression of the integrated strength of a country in the field of high-power laser technological researches and applications. The basic structure, key science and technology and engineering problems as well as the overall design elements are briefly introduced. The basic state and technical characteristics of two Chinese second generation huge-scale peak power laser facilities are reviewed, and the trend of the future Chinese high peak power laser technology and engineering development is also prospected.

Shanghai soft X-ray free-electron laser facility (SXFEL) is the first coherent X-ray light source in China with the shortest wavelength down to 2 nm. SXFEL is based on a 1.5 GeV C-band linac, including one seeded FEL line, one self-amplified spontaneous emission FEL line and five experimental stations. The development of SXFEL is in two stages, the test facility SXFEL-TF and the user facility SXFEL-UF. SXFEL-TF is based on a 0.84 GeV linac, aiming to master the key technologies of a cascaded FEL with high gain harmonic generation (HGHG) and echo-enabled harmonic generation (EEHG) scheme. Meanwhile, the object of SXFEL-UF is to start user operation at the end of 2019. This paper presents the design, construction and commissioning status of SXFEL.

Development of advanced light sources has become more and more important in the frontier scientific research. The development of new advanced light sources has pushed experimental studies from macroscopic world into the atomic and molecular levels, from studies of physical systems at static conditions to ultrafast dynamical processes, and from investigations at simple experimental conditions to more complex and real environment. Free electron laser (FEL) with high brightness, ultrafast laser pulses in the extreme ultraviolet (EUV) wavelength region is an ideal light source for excitation of valence electrons and ionization of molecular systems with very high efficiency. Dalian Coherent Light Source (DCLS) delivers 50-150 nm EUV beams with ultrafast pulse durations of 100 fs or ps to users. DCLS, as the first FEL user facility in China, has wide applications in the frontier researches of physics, chemistry, biology, especially in the field of basic energy sciences. This project is supported by National Natural Science Foundation of China and developed jointly by Dalian Institute of Chemical Physics and Shanghai Institute of Applied Physics, Chinese Academy of Sciences.

In order to study the kinetics of carbon plasma under different air pressure conditions, the carbon plasma is diagnosed by optical emission spectroscopy. The carbon target is ablated with a 1064 nm Nd∶YAG laser. The early emission spectrum is continuous spectrum, and the electron temperature of the carbon plasma is estimated by using the black body radiation formula. When the line spectrum appears, the electron temperature is calculated by Boltzmann mapping method, and the evolutions of electron temperature and density with time and the influence of different pressures on the evolutions are observed. The results show that the changes of the temperature and density of electrons are consistent with time under different air pressure conditions. And as the gas pressure increases, the plasma is limited. As the collision between particles increases, the electron temperature and electron density increase. Graphene films are deposited at pressure of 0.01 Pa.

Library-based matching recognition is the key to the application of Raman spectroscopy for material composition identification, which directly affects the accuracy of matching results. For the library matching, especially for the mixture spectrum, the single matching feature can not fully reflect the similarity between the measured sample spectrum and the spectral spectrum in the library. The spectral matching needs to comprehensively consider multiple matching features. In this paper, a new spectral integration matching method is proposed by using the logistic regression mathematical model to fuse the peak matching coefficient, the non-negative least squares matching coefficient and the cosine matching coefficient. The new method takes into account both the spectral peak information and full spectrum information of the sample. The experiment results based on the Raman spectroscopy library matching of 20 kinds of amino acid mixtures show that the spectral integration matching method has lower false positive rate.

A microstructural array to generate the interference of near-field vortex beams is designed, in which an Archimedean spiral line is formed by a pair of orthogonally arranged rectangular holes. Upon the excitation of a linearly polarized terahertz beam, the near field vortex beams with different topological charge numbers are formed by their left-handed and right-handed components and superimposed to generate a new field distribution. The numerical simulation results show that the field superposition of orthogonal vortex beams with arbitrary topological charge numbers can be achieved by the adjustments of the angle of each rectangular hole and the pitch of the helix.

An active electromagnetically induced transparency (EIT) metamaterial is designed based on photosensitive gallium arsenide. The photoelectric characteristics of gallium arsenide make the peripheral circular closed loop (PCCL) in a metamaterial structure respond to electromagnetic waves with different frequencies under different illumination conditions. It is coupled with its central split ring resonators (CSRRs) and thus a strong EIT effect is produced at two frequencies of 0.7 THz and 1.5 THz. The conductivity of gallium arsenide is changed by adjustment of light intensity, and the structures of surface metal rings are dismantled and compared. The photosensitivity of this metamaterial structure and the physical mechanism for the realization of a multiband EIT are analyzed. At the same time, the influences of gallium arsenide width, CSRRs opening size and substrate thickness on EIT are investigated. The simulation results show that this metamaterial structure can be used to achieve a strong hysteresis effect at multiple frequency points and simultaneously a relatively high refractive index sensitivity in the terahertz frequency range under different illumination conditions. It has certain application value in the fields of terahertz buffer devices and refractive index sensing.