In order to realize the large field, high resolution and dynamic measurement of optical component phase defects, we design a dynamic Twyman interferometer. Based on low-coherence laser and Michelson interferometer, a pair of orthogonal polarized light produced with phase delay is used as light source. By phase matching of the interference cavity, the phase delay between reference light and test light is compensated. The polarization camera is used to collect four interferograms with phase-shifting step of π/2, and the information of the phase defect is solved by phase-shifting algorithm. The effect of secondary diffraction on measurement results is analyzed based on the theory of the angle spectrum of plane wave. The influence of the polarizer error on the measurement results is analyzed by Jones matrix method. In the experiment, a laser-damaged optical plate is measured by this interferometer and Veeco NT9100 white light interferometer, and the relative error is 2.4%. In addition, this method is used to detect phase defects of optical flat in high power laser system, and the peak-to-valley value of wavefront is 199.2 nm. The results show that the interferometer can be used to detect phase defects of optical components, effectively.

The effect of complementary dual Mach-Zehnder modulators (MZM) structure on photonic time-stretched analog-to-digital converter (PTS-ADC) is studied. The principle that the complementary dual Mach-Zehnder modulators suppress second-order harmonic generation in PTS-ADC is theoretically proved. The PTS-ADC based on dual Mach-Zehnder modulators is designed and simulated in the Optisystem software. The recovery radio-frequency (RF) signal frequency values of PTS-ADC are simulated and compared between dual Mach-Zehnder modulators and single output Mach-Zehnder modulator as electro-optical modulator under the condition of five different input RF signals (10, 15, 20, 25, 30 GHz). The simulation results show that dual Mach-Zehnder modulators can effectively suppress the generation of second-order harmonics and improve the quantization resolution.

Based on transfer matrix method, the output characteristics of Mach-Zehnder interferometer are analyzed. Results show that Mach-Zehnder interferometer has differential characteristics when difference of two interference arms′ length is an integer multiple of the ratio of the center wavelength to the effective refractive index, and the differential order is proportional to the number of cascaded interferometers. Based on signal system theory and the differential characteristic of Mach-Zehnder interferometer, the ultrashort optical pulse synthesis system based on Mach-Zehnder interferometer is designed. By adjustment of the weighting coefficients of input Gaussian pulse and its differential order, input Gaussian pulses are synthesized into flattened pulse, triangular pulse and parabolic pulse, respectively. When the weighting coefficients and input width of Gaussian pulse are changed, the output pulse waveform is basically invariable, which proves the system has good stability.

A gamma irradiation experiment is conducted on erbium-doped fiber, and its′ absorption and emission cross sections are calculated according to measured absorption and emission coefficients of erbium-doped fiber before and after irradiation. Radiation models of absorption and emission cross sections are built up based on power law model. Radiation effects on the output spectrum shape and characteristics parameters of erbium-doped fiber source are simulated and analyzed based on the radiation models of absorption and emission cross sections being put into the model of erbium-doped fiber source. The simulation results show that after gamma irradiation, the output power of source decreases from 9.32 mW to 4.30 mW, the mean wavelength moves from 1531.60 nm to 1531.19 nm, and the band width varies from 8.79 nm to 6.78 nm. Finally, the simulation results are verified experimentally.

Fiber Fabry-Perot (F-P) sensors have been widely used in the detection of aircraft engines. Polarization cross-correlation demodulation is one of the most common methods for F-P cavity length demodulation. In a polarization cross-correlation demodulation system, the axial chromatic aberration of the optical system will cause the zero-order interference fringe shift and decrease the light intensity, which decreases the demodulation accuracy and the signal amplitude. The effect of axial chromatic aberration of the optical system on demodulation is analyzed. In order to reduce the influence of the axial chromatic aberration of the system on demodulation, an apochromatic optical system used in the polarization cross-correlation demodulation interrogator is introduced. The axial chromatic aberration along the wedge length is 1.9×10-4 m-1, and the maximum optical path difference is 0.021λ0 (λ0 is the central wavelength), which is far less than the F-P cavity length. For a certain demodulation system, the shift of the measured zero-order interference fringe is 2.85 μm, which is less than half of the pixel width of CCD, and the illuminance of any pixel of CCD is improved by 3.75 times.

Relation knowledge of physical optics, Collins diffraction integral formula and the complex Gaussies function decomposition method of hard edge aperture are used to deduce the temporal distribution expressions of the reflection light of the coherent base mode Gaussian beam passing through the Cassegrain lens at back point. Influences of the fringe spacing and center shade ratio on the temporal distribution of the reflection light of Cassegrain lens are analyzed by numerical simulation. Experiments are designed and numerical results are verified. Results show that when the fringe spacing increases, peak number and peak intensity of the reflection light temporal distribution of Cassegrain lens reduce, and the frequency component of the echo envelope decreases. The increase of the center shade ratio leads to the loss of the energy and frequency components of the reflection light temporal distribution. With the increase of scanning speed, the distribution of echo signal becomes dense, and shows the trend of decreasing variance and increasing skewness and kurtosis. Kurtosis characteristics of the echo signal of Cassegrain lens and transmission lens are numerically different, and the two lens targets can be distinguished by the statistical characteristics of the echo signal. Results are meaningful to the application of laser active interferometric detection and recognition technology.

Based on the generalized Huygens-Fresnel diffraction integral formula, field distribution expressions of Bessel beams passing through a spherical aberration fractional Fourier transform system with an aperture are derived when we take Lohmann Ⅰ type optical system as an example. Propagation characteristics of Bessel beams in ideal fractional Fourier transform system and the influence rule of aperture and spherical aberration on beam propagation are calculated by numerical simulation. The results show that Bessel beams do not maintain propagation invariability after passing through a fractional Fourier transform system. When the system only contains an aperture, a hollow beam can be obtained at the conventional Fourier transform plane. When the system contains aperture and spherical aberration, beams with good focusing property and high central light intensity can be obtained with positive spherical aberration. Light intensity distribution on the axis is mainly affected by the aperture when the aperture size is small, and it is influenced by spherical aberration when the aperture size exceeds a critical value.

In the research on laser driven inertial confinement fusion, laser-plasma interaction (LPI) is a key issue of affecting ignition. Many beam smoothing technologies are proposed and adopted to suppress the instability of laser-plasma. To obtain a smoother focal spot, the smoothing by spectral dispersion (SSD) technology based on bundle multiple-frequency modulation is proposed and studied theoretically. The technology adopts one modulation frequency in one single beam, and then a bundle of multiple beams with different modulation frequencies focuses on one point. The results indicate that intensity modulation caused by interference of multiple beams can be suppressed and the uniformity of far field intensity distribution can be improved by the proposed technology. Compared with the traditional multiple-frequency modulation SSD technology, the proposed technology has a better smoothing performance when the color cycle number is closer to practical situation.

In the petawatt (PW)-class ultra-intense ultra-short laser system based on the Ti∶sapphire (Ti∶S) chirped pulse amplification (CPA) technique, there is gain narrowing and redshift of the spectrum caused by the different spectral emission cross section and the effect of saturation amplification. The redshift of the spectrum appears widely in the process of laser amplification, especially in the high energy and saturation amplification process. In this paper, aiming at the spectrum control of Apollon-10 PW, we theoretically propose a new spectral shaping technique to suppress redshift of the spectrum in saturated laser amplifiers based on optical-optical synchronization amplification. The technique is based on the experimental results of 5.0 PW laser system in Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences. The technique is based on the conventional amplification model and optical-optical synchronization amplification through introducing the pump with short pulse width in power amplifier. The technique does not need to introduce other optical devices and does not introduce additional losses, and its operation is simple. Theoretical simulations show that the technique can effectively realize the shaping of amplified spectrum, which suppresses the redshift effect of the spectrum.

By pumping the Ti∶sapphire crystal cutted by the Brewster angle with a homemade all-solid-state high-power 532 nm single-frequency green laser, we design a compact, stable and self-compensating embedded six-mirror ring resonator structure. By adjusting the best mode matching relationship between pumping light and oscillating light, we establish an all-solid-state single-frequency tunable Ti∶sapphire laser with high beam quality and high conversion efficiency at 900 nm. With the pump power of 15 W and the output mirror fixed point transmission of 4.5% at 922 nm, the broadband tunable single-frequency infrared laser with average output power of more than 2 W and tunable wavelength range from 852 nm to 934 nm is obtained. The power stability is better than ±0.7% within 3 h and the beam quality factor M2 is less than 1.04.

A experimental study about a triple-pass grazing incidence Nd∶YVO4 slab laser amplifier is carried out based on a semiconductor saturable absorber and passively Q-switched microchip lasers. Influences of the mode matching ratio in horizontal direction and grazing incidence angle on thermal distortion of slab laser amplifier are analyzed theoretically. The experiment verifies that the mode matching ratio of the grazing incident slab laser amplifier in horizontal direction is optimized to be 0.6. Meanwhile, with a small grazing incidence angle, thermal distortion in horizontal direction can be alleviated and high gain can be obtained. When the repetition rate is 100 kHz and the seed source is with an average power of 2 mW and a seed beam quality factor M2 of 1.17, a laser output of 12.6 W can be obtained after triple-pass amplification of grazing incidence Nd∶YVO4 slab with a mode matching ratio of 0.6 and a triple-pass grazing incident angles of 3°, 5° and 7°, respectively. The optical-optical extraction efficiency reaches 28%. The peak pulse power is 1.4 MW, the pulse energy is 126 μJ, and M2 is 1.4.

Beam smoothing by spectral dispersion (SSD) technology is widely adopted in larger laser fusion facilities. Using intensity distribution of SSD beam at its focus plane as boundary condition of laser plasma simulation code LAP3D, we simulate the propagation of SSD beam in large scale hohlraum underdense plasma. High efficiency parallel calculation of intensity distribution of a SSD beam at its focus plane is accomplished with improved algorithm, and then the simulation of entire beam propagation can be processed. The effect of modulation frequency of SSD beam on beam propagation is analyzed.

Taking Nd:YAG planar waveguide as gain medium of a laser amplifier, we study the factors affecting optical-optical efficiency of laser with wavelength of 1064 nm during amplification. A free operational Nd∶YAG rod oscillator with wavelength of 1064 nm is used as seed source, and a diode laser array with wavelength of 808 nm is used as the pump source. The pulse width of pump beam is equal to that of seed, and the output of pump beam and seed is synchronous. The size of the Nd∶YAG planar waveguide is 60 mm×10 mm×1 mm, and the core thickness is 100 μm. The effects of seed energy, pump energy, and pump direction on the laser amplification efficiency are studied. The results show that when the input seed energy is 10 mJ, the quasi-continued laser with maximum energy of 713 mJ is obtained at the pulse repetition frequency of 100 Hz, the pump pulse energy is 1478 mJ, and the corresponding optical-optical efficiency is 47.6%.

After the pulsed laser truing and dressing,the graphitized deterioration layers of bronze-bonded diamond grinding wheels are investigated theoretically. When the laser power density is 1.68×108-3.359×108 W·cm-2, the temperature evolution on the diamond surface is numerically simulated. The study results show that the time for which the diamond temperature reaches the graphitization temperature is 435-440 ns, and the graphitization degree is low. A new method for pulsed fiber laser truing and dressing of bronze-bonded diamond grinding wheels assisted by liquid column flows is proposed, which clearly reduces the graphitization degree.

Based on the established three-dimensional rough surface model, the transient finite element model and the thermal contact model, the effects of laser power, welding speed and clamp pressure on the contact thermal conductivity of laser transmission welding of polycarbonate are studied, and the comparison between simulated and experimental results is also conducted. The study results show that, with the increase of the welding speed, the contact thermal conductivity decreases and the decrease becomes slow. With the increase of laser power, the contact thermal conductivity increases and the increase becomes slow. When the clamp pressure is within the range of 0-0.25 MPa, the contact thermal conductivity increases with the increase of the laser power. A relatively high contact thermal conductivity can be achieved when the conditions of high laser power, low welding speed and high clamp pressure are satisfied. The contact thermal conductivity can be well predicted based on the built mathematical models.

With the experiment of laser welding of X100 pipeline steels, the influence of heat input on the microstructure and hardness of welded joints is studied, and the mechanical properties of typical samples with full penetration are analyzed. The study results show that the full penetration welds can be obtained when the heat input reaches 1.5 kJ·cm-1 and the corresponding welding width and heat-affected zone width reach 1.8 mm and 1.0 mm, respectively. In a certain range of heat inputs, the influence of heat input on the microstructures of welded joints in each micro-area is not obvious. The microhardnesses of the weld zone, the coarse grain zone and the fine grain zone are all higher than that of the base metal, while the microhardness of the mixed zone is lower than that of the base metal. The tensile fracture occurs in the base metal. The impact energy of welded joints with full penetration reaches the level of the base metal, and the impact energy of the heat affected zone reaches 66% of that of the base metal, all of which are typical ductile fractures.

By using the laser cladding technique, three kinds of Ni-Mo-Si coatings are prepared on copper substrate surfaces. The phase compositions and microstructures of these coatings are researched, and the hardness and toughness of these coatings are studied with the indentation method. The study results show that the phase compositions of three kinds of coatings are MoSi2+Ni2Si+γ-Ni (coating 1, Ni-20Mo-40Si), Mo5Si3+Ni2Si+γ-Ni (coating 2, Ni-30Mo-30Si), and Mo2Ni3Si+Moss+γ-Ni(coating 3, Ni-40Mo-20Si), respectively. The average hardness of coating 1 is 1100 HV and its average friction coefficient is 0.44. The average hardness of coating 2 is 1200 HV and its average friction coefficient is 0.50, but its toughness of fracture is poor. The average hardness of coating 3 is 860 HV, its average friction coefficient is 0.55, and its toughness of fracture is good. The wear track depths for coatings 1-3 are 6.30, 5.26 and 7.00 μm, respectively.

Aiming at the process need of surface cleaning before aluminum alloy welding in the development of lightweight, the mechanism of fiber laser cleaning for aluminum alloy is investigated. Laser arrangement in laser cleaning is determined by analyzing the laser space and energy distribution parameters. Laser cleaning process experiment is conducted to study the influence of laser parameters on surface state, explore and optimize the oxide film stripping process. Two possible kinds of aluminum alloy oxide film stripping mechanism are proposed. The results of welding evaluation for cleaning parameters after optimization show that laser cleaning can improve the formation quality of the welding line and mechanical property of the joint, which verifies that the fiber laser cleaning can improve the quality of aluminum alloy joint. The research will promote the widespread application of high strength aluminum alloy joint in the manufacturing industry.

By the experiment of the overlap welding of dissimilar materials for the polymethyl methacrylate and 304 stainless steels, the physical phenomena and weld defects during the welding process are analyzed. By the orthogonal tests, the optimized process parameter combination is obtained, and the well-formed weld joints are realized. The influences of the process parameters on the shear stress are analyzed. The study results show that the influences of laser welding speed, pulse width, spot size and pulse frequency on the shear stress are strong, and the maximum shear force of weld joints is 191 N·mm-2. The key factors determining the failure of weld joints are weld defects and energy densities.

In selective laser melt (SLM) molding process, the edge position is usually higher than the inner surface, which is also called elevated edge phenomenon. Elevated edge has bad effects on SLM molding process. We theoretically analyze the production mechanism of elevated edge in SLM molding process, and propose a contour-entity control method and an edge remelting control method. Effects of processing parameters on edge height are studied. Processing parameters include contour spacing, border thickness, scanning speed and laser power. Results show that these methods can effectively reduce the elevated edge. For the contour-entity control method, the height of elevated edge decreases with the increas of scanning speed, increases with the increas of laser power, and is not susceptible to contour spacing. For the edge remelting method, edge height decreases with the increas of scanning speed, and increases with the increas laser power and contour thickness.

By the micro-arc-oxidation process, oxide coatings with different thicknesses are prepared on aluminum alloy surfaces, and the laser transmission welding of the micro-arc-oxidation aluminum alloy and the high-aluminum ultrathin glass is conducted. The effect of micro-arc-oxidation coating thickness on the shear force, the weld morphology and the weld joint interface is investigated and the formation mechanism of welds is also analyzed. The results show that the micro-arc-oxidation coating can effectively act as the laser-energy-absorbing layer and the buffer layer of weldments, and the main reason for realizing the connection between these two materials lies in the mixed mosaic structure formed within welds. The smaller the thickness of the micro-arc-oxidation coating is, the greater the shear force of weldments is.

The TiN/TiB-reinforced titanium matrix composite coatings are prepared on the surface of Ti3Al2V by laser cladding using different CeO2 contents in Ti and h-BN powders as the raw materials. The effects of different CeO2 contents on the strengthening phase microstructure morphology, microhardness and wear property of the laser cladding coating are studied and characterized. The results indicate that the cladding layers of TiB and TiN matrix composite is in-situ synthesized. The addition of appropriate CeO2 refines the structure of the reinforced phase, enhances the microstructural uniformity and improves the microhardness and wear property of coating. When the mass fraction of CeO2 is 2%, the surface hardness of the coatings is up to 1400 HV, and the wear property of coating is optimum.

To restrain agglomeration of nanoparticles in polishing powders and improve properties of polishing slurry, so as to achieve better polishing properties of optical glass such as polishing rate, surface roughness and so on, we add a kind of anionic surfactant Medialan into ceria polishing slurry and study the effects of Medialan mass fraction on size and dispersion of particles, and material removal rate, as well as surface roughness of polished optical glass. The results show that the addition of trace Medialan can significantly improve dispersion of particles in the polishing slurry, restrain agglomeration of ceria particles, and improve quality of the polishing slurry. When the mass fraction of Medialan is between 0 and 0.32%, the chemico-mechanical polishing rate increases firstly and then decreases with the increase of Medialan mass fraction. When the mass fraction of Medialan is 0.26%, the chemico-mechanical polishing rate reaches the maximum value of 122 nm/min. The surface roughness firstly decreases and then increases with the increase of Medialan mass fraction, and the surface roughness reaches the minimum value of 0.928 nm when the mass fraction of Medialan is 0.13%.

Grazing incident X-ray reflection (GIXR) is widely used in film detection and high accuracy characterization because of its high detection accuracy and nondestructive measurement. However, it is a kind of indirect measurement method, and therefore it requires a superior numerical optimization algorithm when solving thin film parameters, especially for complicated multilayers. A new method based on quantum-inspired genetic algorithm (QIGA) is proposed to realize GIXR fitting. The proposed algorithm is applied in fitting the GIXR of Si single layers and periodic Mo/Si multilayers. The results indicate that the algorithm based on QIGA has fast solving speed and high fitting precision, and QIGA has potential values in the field of thin film characterization.

A technique based on off-axis digital holographic microscopy is proposed to measure three-dimensional position of particle in a liquid environment. The technique uses the transmitting off-axis digital holographic microscopy system, and the method combines the optical path length (OPL) difference method and fringe removing method. The OPL difference method is used to measure the axial position of the particle by locating the inflection point of OPL difference curves of two specific points in the particle. The fringe removing method is utilized for the off-axis holograms to measure the in-plane displacement of the particle with frequency filtering and Hough transform combined. Compared to the traditional digital holographic particle tracking techniques, the OPL difference method applies the OPL between two points to relative calculation instead of plane calculation. As a result, the measurement efficiency is improved, auto-focusing of particles is not needed, and the particle position is not constrained by the defocusing plane. The experimental results of nano-scale three-dimensional particle measurement show that the resolution ability reaches nano-scale when the OPL difference method is combined with the fringe removal method to measure the three-dimensional displacement of particles in the liquid environment.

To realize fast and high precision tracking measurement of fiber optic gyroscope (FOG) eigen frequency, a eigen frequency tracking method based on sawtooth wave modulation is proposed. Based on the eigen frequency measurement theory of fiber-optic gyroscope from even times eigen frequency sawtooth wave modulation, the sawtooth wave modulation signal with nearly even times eigen frequency is applied on the phase modulator, and phase of the wave is modulated. The demodulated error signal intensity represents the degree of sawtooth wave modulation frequency away from even times eigen frequency. The frequency of sawtooth wave modulation signal is modulated by the intensity of error signal, and the error signal is set to zero. At this time, the frequency of sawtooth wave signal is equal to even times eigen frequency, and the bias modulation of square wave is located at the eigen frequency exactly. The experiment results show that the proposed method can realize tracking of fiber-optic gyroscope eigen frequency. Compared with the traditional measurement method, the proposed method have the advantages of speediness and high precision. The accuracy of the measurement is better than 1 Hz.

In order to improve the accuracy and maneuverability of self-contained land navigation system, the application of high-accuracy laser Doppler velocimeter (LDV) in the field of land navigation is studied in this paper. The structure and basic principle of the split reuse-type LDV are expounded. Based on the analysis of the advantages and disadvantages of the inertial navigation system (INS) and LDV which are developed by our own department, the integrated technology of marching initial alignment, dynamic calibration and real-time errors compensation are discussed in detail. Expounded in theory that the attitude correction for marching vehicles, dynamic LDV parameter error estimation and high-precision autonomous navigation can be achieved by introducing velocity into the error equation of inertial navigation system. The results of dynamic vehicle tests show that the navigation error of inertial navigation system decreases from 2000 m to 6 m in 1.2 h without parking. It is even proved by theory and experiment that the performance of land navigation system is greatly improved after the application of high-accuracy LDV in land inertial navigation system.

Mesh is an important component of electronic optical instruments such as streak cameras. In this paper, the finite difference method is used to model the wire diameter and wire hole of the mesh. The effects of the mesh on the disturbance of uniform electric field and the sub-lens effect of electron motion are analyzed. The secondary electron emission problem of collisions of electrons and mesh is studied by Gryzinski theory. The results show that the disturbances of the structural parameters are 0.31%, 0.07% and 0.04%, respectively, for the 10 line/mm, 33 line/mm and 50 line/mm mesh in the streak camera. For the electrons with energy of 15 keV, the non-elastic scattering collision free paths of Ni, Cr and Cu atoms are 6.85 nm, 10.34 nm and 7.25 nm, respectively, and it is difficult to produce secondary electron emission. The results have reference significance for the optimization of electronic optical instrument design and mesh parameters.

A new active atmospheric detection means of the imaging lidar is used in the horizontal atmospheric transmittance detection. A matrix image dislocation addition method is proposed to improve the signal to noise ratio. When the signal which is changing with the distance is obtained, an inversion method combined with the slope method and Klett integration is adopted to retrieve the extinction coefficient distribution in 1 km horizontal transmission path. The horizontal atmospheric transmittance can be achieved based on the path integral of extinction coefficient. By comparing the inversion results of comparing experiments with the atmospheric transmittance obtained in direct measurements, we find that the correlation coefficient is over 0.7 and the relative error is within 20%. The imaging lidar can be an instrument for the study on detecting the horizontal atmospheric transmittance in the finite range.

As the technology of lithography extending to 10 nm and below process nodes in advanced semiconductor manufacturing, lithography has put forward high requirements for the precision of overlay, and the corresponding alignment accuracy has reached sub-nanometer level. In this paper, a new alignment technique using Moire fringes based on self-coherence in lithographic tools is presented. The principle is that the same diffraction order beams from the alignment mark of the phase grating are split and image-rotated by using optical structure of alignment system. Two groups of interference fringes with different periods are formed on the image plane of the alignment system. The two group of interference fringes are further interfered and superimposed to form self-coherence Moire fringes. The two interference fringes move toward opposite direction when the alignment mark position is displaced, and this displacement of the alignment mark can be enlarged. The position measurement accuracy of the alignment mark is improved. The Fourier transform and phase extraction are carried out by self-coherence Moire fringe image, and the position of alignment mark is got by the analysis of its phase information. Simulation results show that the alignment accuracy and the alignment repetition accuracy can reach 0.07 nm and 0.11 nm respectively.

Fiber optic sensors based on the Fabry-Perot (F-P) interferometer have been widely used because of its simple structure, small size, and high sensitivity. The refractive index of liquid can be measured by the open F-P interferometer. We can make an open F-P interferometer through mechanical cutting, femtosecond laser breakdown and some other methods. An open F-P interferometer sensor is fabricated with an open hollow capillary and two segments of single-mode fibers welded together by glass flux. Absolute measurement of refractive index of liquid can be achieved when the cross-correlation signal processing technology is used. Refractive index measurement experiments are performed for NaCl solutions with different concentrations. The measurement resolution for refractive index can reach 10-5 RIU magnitude, and the temperature sensitivity of the sensor is 39.59 nm/℃.

A high-speed point target acquisition and tracking measurement method based on laser pulse scanning measurement system is proposed. The constant velocity motion model is used to simulate the target trajectory and target distribution probability; considering pulse laser spot distribution parameters, the theory model of pulse laser scanning capture point target is established. A capture method based on time series method is proposed to solve the number of capture of the target model pulsed laser in one frame scanning process. On the basis of this, the main parameters of the laser distributed scanning spot layout are simulated and analyzed. Then, an optimal scanning method is proposed to improve the capture probability, the capture number and the acquisition time for the characteristics of motion target and laser sensor. The feasibility of optimal scanning method is verified through the semi-physical simulation experiment combined with an example. The proposed method provides the basis for the best matching of the pulse frequency, scanning frequency of the laser tracking system and target motion model.

The visual sensing technologies based on the laser structured light are the main technical means and foundation for the realization of welding groove detection, seam tracking and robot path planning in the welding industry. Their technical advantages applied in the welding industry are introduced, the basic detection principles are analyzed, and the research focuses and developing directions in the welding industry are concluded and summarized. Through discussion on the operational principles and characteristics of various visual sensors based on the laser structured light, the comprehensive summary and a novel classification are proposed, and their respective technical characteristics and research progress are introduced in detail. Finally, the existing problems of visual sensing technology based on the laser structured light are discussed in order to promote further research and application of this technology.

Terahertz back scattering intensity is a very important index to represent the scattering ability of targets to terahertz. Firstly, the feasibility of 2.52 THz back scattering properties measurement system is proved by the measurement of the calibration target, and the signal-to-noise ratio of the system is measured. The relative back scattering intensities of rectangular milling and sand blasting aluminum plate with six kinds of sizes are measured in the measurement range of 0°-3°. The experiment results show that the measured maximum dynamic range is 32.25 dB, back scattering intensity difference between sand blasting aluminum plate with different sizes is more obvious than that between milling aluminum plate, the average errors of milling and sand blasting aluminum plates with same surface area at 0° are 1.35 dB and 0.51 dB, respectively.

We use plasma enhanced chemical vapor deposition (PECVD) to grow graphene with high quality and high transparency by setting the power of plasma generator and growth time to control the layer number of graphene. In the experiment, a fiber Bragg grating with a tilted angle of 8° is coated graphene with thickness of 3.7 nm (about 11 layers). Near the low refractive index region of 1.33, the titled-fiber Bragg grating (TFBG) has a high refractive index sensitivity of －1.57161 RIU-1, and its sensitivity is about 20 times of the sensitivity of TFBG without coating graphene. The way of coating graphene on TFBG can significantly increase the sensitivity of TFBG in the low refractive index region, and the TFBG coated graphene has potential application in the fields of biology, chemisty, food safety, and monitoring of water-environment.

The digital quadrature demodulation algorithm of phase sensitive optical time domain reflectometer is investigated. The influence of the group delay of the digital filter in quadrature demodulation algorithm on the positioning accuracy is analyzed, and the relocation method is proposed to correct the positioning error. Meanwhile, the influences of the digital filter in the quadrature demodulation algorithm on the spatial resolution of the system is simulated and experimented. The results show that the relocation method can eliminate the positioning error caused by the digital filter in the quadrature demodulation algorithm. The spatial resolution of the system is determined by the system structure and the digital filter, and the spatial resolution of the digital filter improves with the increase of the order of the digital filter. In this experiment, the demodulation is appropriate to select 112 order filter.

Even if the airborne lidar is well calibrated, lidar data still may show residual system error, which results in the deformation of strips in each testing zone. We firstly calculates the placement angle based on the surface feature, which provides the initial point cloud for eliminating the residual system error. Then, under the condition of the same three-dimensional coordinate of the connection point, the nonlinear error of the scanning angle error is corrected based on the iterative closest point (ICP) method. Experiments show that the method can guarantee the absolute accuracy of high altitude flight data, and the point cloud accuracy can meet related requirements.