Aiming at the requirements of high-power large-blocking ratio narrow-ring thin-tube lasers for ring aberration correction, a new ring-shaped edge-driven deformable mirror-based method for ring aberration correction is proposed herein. An adaptive optics closed-loop control system is constructed using the ring-shaped edge-driven deformable mirror to correct the wavefront of the high-power, large-blocking, thin-tube laser. A novel ring-shaped edge-driven deformable mirror is used to verify the correction ability of the proposed method for single-circular low-order aberrations, and analyze its correction effect on thin tube lasers with a large obstruction ratio. Experimental results reveal that the proposed ring aberration correction method can effectively correct the wavefront distortion of a thin tube laser with a large obstruction ratio and a narrow ring, significantly improving the beam quality.

A new optical transmission network structure is proposed based on the two-dimensional magneto-optical photonic crystal and topological photonics theory, which is composed of a series of rectangular photonic crystals and air. To create coding units, the three conditions of applying a positive magnetic field, a negative magnetic field, and an air area are marked as “+1”, “-1”, and “0”, respectively. Then, three types of optical path matrix networks of 2×2, 3×3, and 4×4 are constructed. Finally, COMSOL software package is employed to simulate the transmission path of light waves. The simulation results prove that through different coding sequences, flexible and diverse control of the optical path can be achieved. The proposed control fulfils the requirements of high density optical path transmission and large-capacity information processing in the photonic integrated circuits to emerge in the future.

Aiming at the requirement of illumination uniformity and backscattering suppression in laser-driven inertial confinement fusion (ICF) facilities, we propose a polarization rotation (PR) smoothing scheme based on the interference of circularly polarized vortex beamlets, which makes the simultaneous control of intensity and polarization of the focal spot. The basic mechanism is that a conjugate spiral phase plate is first used to transform the beamlets with certain wavelength difference into vortex beams with conjugate helical charges, and then the polarization control plate is used to change the polarization states of the beamlets into counter-rotating ones. Finally, the rapid rotation of both the local intensity and polarization of the focal spot can be realized by means of the interference of the circularly polarized vortex beamlets in the target plane. The physical model of the PR scheme based on the interference of circularly polarized vortex beamlets is established and the variations of illumination uniformity and polarization of the focal spot with the beamlet wavelength, the helical charge of the spiral phase plate, and the parameters of the incident beams are analyzed. The results indicate that the proposed PR scheme can be used to realize the intensity and polarization rotation at a specific rotation frequency by selecting the suitable wavelength combination. When this novel scheme is implemented together with the conventional spectral dispersion smoothing scheme, the smoothing performance can be further improved and the backscattering suppression can be effectively achieved.

Herein, the generation of Hermite-Gaussian beams using a spatial light modulator was experimentally investigated and the relation between mode conversion efficiency and transverse distribution of the input beam was theoretically analyzed. High-quality Hermit-Gaussian beams with HG6,0, HG8,0, and HG10,0 modes, whose purity was 96.2%, 94.9%, and 93.4%, respectively, were experimentally generated using the optimum input beam with an elliptical transverse distribution. Moreover, the 217-mW HG10,0 mode was obtained and the mode conversion efficiency reached 14.45%, which is 5.6 times higher than that of the traditional input beam with fundamental Gaussian mode. The generation method of Hermite-Gaussian beam with high quality and efficiency has promising application potentials in the precision measurement of small displacement and preparation of a high-order spatial squeezed light field.

To achieve simultaneous measurements of biochemical properties and physical structures, we proposed an endoscopic probe that combines optical coherence tomography (OCT) imaging and fluorescence ratio imaging. Based on the OCT imaging principle, the center wavelength of the OCT system was determined to be 1300 nm. Based on the absorption and reflection spectra of the selected pH indicator, the excitation wavelength of the fluorescence was determined to be 520 nm. Moreover, the basic structure of the probe was calculated and determined according to the ABCD matrix. The processing of the optical element and actual assembly of the probe were performed based on the theoretical calculation results. Furthermore, the dual-modality system was built to measure the transverse resolution and working distance of the probe. The ability of simultaneous imaging and pH detection was demonstrated on pork intestine. The probe can simultaneously perform OCT imaging and pH measurement with high accuracy. The resolution of OCT imaging in air is approximately 37.3 μm, and the working distance is approximately 13.4 mm. Moreover, the proposed system can measure the pH value of 0.01 units.

The fluorescence pharmacokinetic parameters (permeability, etc.) based on dynamic diffuse fluorescence tomography (DFT) can provide reference for studying the dynamic physiological process and pathological information of different biological tissues. The adaptive extended Kalman filter (AEKF) (a method for dynamic analysis) has many advantages, such as precise modeling and multi-parameter online estimation. In this work, the metabolic process of indocyanine green (ICG) in healthy mice liver and tumor-burdened mice subcutaneous transplanted tumor tissue was measured using the dynamic DFT system. Then, we obtained the time-series fluorescence yield images of ICG by DFT method. On this basis, the time-series permeability images of ICG were reconstructed by the AEKF method based on a two-compartment model. The two experimental results verify that the permeability parameters Kpe and Kep of ICG in the tumor are less than that in the liver. Furthermore, the time-series permeability images of ICG also demonstrate that the AEKF method can effectively obtain the real-time and stable ICG pharmacokinetic parameters of complex organisms.

Gastrointestinal tumors are one of the most common types of tumors. Emerging photoacoustic imaging technology can sharply capture the information of the nourishing blood vessels surrounding the tumors, which may give potential contributions to accurate clinical diagnosis. The matched vessel enhancement algorithm can effectively highlight the vessel network. However, the detection angle of in vivo photoacoustic endoscopic imaging is limited, which results in obvious vascular structure abnormalities. It is difficult for current enhancement algorithms to effectively enhance blood vessels. Therefore, a three-dimensional vascular enhancement algorithm was developed in this investigation that fuses the information on structure and intensity of the colorectal vessel of rats, based on a self-designed endoscopic photoacoustic imaging system. The results indicate that this algorithm can effectively improve the imaging effect, suppress edge burrs brought about by mechanical vibration, and obtain in vivo high-quality three-dimensional images of the colorectal vessel, indicating that it has potential value in basic medical research and clinical applications.

A novel laser chaotic coding system was studied herein. The proposed system realized the application of cross emission and alternate parallel reception (CEAPR) in chaotic secure communications using two space-coupled lasers synchronizing with two other lasers. We theoretically determined two chaotic coding and decoding equations of the CEAPR. In addition, the mathematical physical principle of CEAPR coding and decoding of chaotic laser was defined and described. Two practical applications of the CEAPR technology were developed herein. The proposed system characterizes different parameters between the emitter laser emitting chaotic coding carrier and the receiver laser, which is different from the traditional chaotic communication system that has the same parameter secret-keys for the emitter and receiver. The emitters have multiple-parameters and multiple-variables, can implement alternating transmission of information security, and has a flexible application. It makes it difficult for invaders to decipher the communication contents from the carrier.

Optical delay-time loop-based radio frequency (RF) memory technology has received considerable attention in the field of electronic jamming owing to its broad instantaneous bandwidth and fast response time. To obtain a multipattern memory of complex RF pulse signals, different types of optical delay-time loop-based memory structures such as frequency shifting type, gated semiconductor optical amplifier (SOA) type, and cascade type have been successively realized. Through the comparison and optimization of delay-time loop-based structures, the storage schemes with high fidelity, high resolution, long delay and the reconfiguration of pulse width can be realized. More than 2000 pulse replications, storage with high resolution and time greater than 500 μs, and 200 ns--10 μs pulse-width reconstruction can be achieved in the cascaded structure, which can be applied in different application scenarios such as a wide range of pulse widths, complex modulation formats, and fast and long delay storage.

The transmission rate of the existing atmospheric optical communication systems can be improved using the faster-than-Nyquist transmission technology; however, atmospheric turbulence will considerably affect the system performance. Therefore, in this study, expressions are derived for obtaining the average bit error rate and average capacity of the faster-than-Nyquist atmospheric optical communication systems under a Gamma-Gamma atmospheric turbulence channel. Further, the effects of the turbulence intensity, transmission distance, and acceleration constant on the system performance are discussed. The Monte-Carlo simulation results demonstrate that the average capacity of the system can be improved using the faster-than-Nyquist transmission technology. In addition, the increasing transmission distance and decreasing acceleration constant significantly affect the bit error rate and average capacity of the system. Under the weak turbulence channel condition, the average capacity of the system using the faster-than-Nyquist transmission technology is better than 31% of the system without this technology when the acceleration constant is 0.75 and the signal-to-noise ratio is 18 dB.

A novel optical fiber acoustic emission sensor based on extrinsic Fabry-Perot cavity is proposed in this study. Digital optical processing 3D printing technology is used to create an acoustic vibration-sensitive diaphragm, and the structure is based on flexible digital model design and can be formed in one time. It is easy to integrate with the surface of a standard optical fiber ceramic insert. The experimental results show that the fabricated Fabry-Perot sensor exhibits a high extinction ratio. The acoustic emission sensor exhibits a high sensitivity in a frequency range of 600 Hz--2.4 kHz, and the pressure sensitivity is 2.81 mV/Pa at a frequency of 1.6 kHz. The proposed optical fiber acoustic emission sensor based on 3D printing technology is extremely stable and easy to be fabricated, and it has potential in the fields of acoustic emission detection.

Using polarization-maintaining all-fiber ring resonator as the transfer cavity, a frequency stability transfer from 1550 nm reference laser to 1572 nm slave laser is realized in this work. The influence of temperature on the long-term stability of the fiber resonator is studied. Theoretical and experimental results show that the frequency stability transfer could not be realized well only by tuning the cavity length of piezoelectric ceramic resonator. Therefore, it is proposed to realize the stability transfer of the ring resonator by using piezoelectric ceramic fast feedback and temperature control. The Allan variance of the frequency stability of the slave laser is 2×10 -12 when the integration time is 1 s and 5×10 -12 when the integration time is 1000 s.

To improve the quality of the reconstructed image of the holographic stereogram obtaines by the effective viewing angle image slice mosaic (EPISM) method, the stitching error is analyzed during synthetic parallax image generation by the traditional EPISM method, and the EPISM method with multiple reference planes is proposed. Theoretical analysis shows that there are no mosaicking errors in the synthetic parallax image of the part that coincides with the algorithm reference plane or optical axis on the three-dimensional object. The farther away the image reconstruction happen from the algorithm reference plane or optical axis, the more significant the synthetic parallax image error became. Reduction of the sampling camera interval can reduce errors to a certain extent. To further improve the EPISM method, the single algorithm reference surface of the traditional EPISM method is expanded into multiple, and the generated multiple combinations are recombined into parallax images to eventually obtain a synthetic parallax image with less significant errors. Simulation and optical experiment results show that the EPISM method with multi-reference planes can effectively improve the imaging quality of holographic stereogram.

To further improve the reconstruction speed under the premise of high-resolution millimeter-wave images, a fast backpropagation algorithm based on the dimensionality reduction strategy (DR-BP) is proposed. The proposed algorithm was experimentally verified via submillimeter-wave single-input and single-output (SISO) imaging (280-320 GHz) and orthogonal array multiple-input and multiple-output (MIMO) FEKO simulation imaging (70-80 GHz). The experimental results indicate that the DR-BP algorithm is able to obtain images with less margin interference compared with the fast Fourier transform-based algorithms for SISO imaging. Moreover, the DR-BP algorithm significantly improves the reconstruction speed—60 times that of the traditional BP algorithm, as shown by the results of the experiments.

The calculation method of shock wave energy source in discharge chamber of excimer laser was analyzed. Two-dimensional simulation of the physical process of discharge shock wave was carried out by Fluent software. The evolution process of transverse and longitudinal shock waves in 300 μs was revealed. In this process, the distributions of gas velocity, density, pressure, and temperature are obtained. Based on the analysis of the simulation results, the key points in the design of high repetition rate discharge chamber and the processing methods are given. The reference basis for choosing parameters such as the size and boundary of discharge chamber is put forward.

The energy characteristics of lithography excimer lasers are critical in the lithography process of integrated circuits and directly affect the accuracy of the exposure lines of the lithography machine. In order to design a laser energy control algorithm, a simulation model is built for the discharge characteristics of the excimer laser, and the validity of the model is verified. Then, design an energy control algorithm for excimer laser based on reinforcement learning. Finally, on the simulation model, the Z-N (Ziegler-Nichol) parameter tuning proportion integral (PI) algorithm, particle swarm optimization (PSO) tuning PI algorithm and reinforcement learning-based algorithm are used to control the pulse of laser output, and compare the final results. The experimental results show that under the control of the energy control algorithm based on reinforcement learning, the laser energy stability is less than 4%, the dose accuracy of is less than 0.3%, and the dynamic performance is better than the Z-N parameter tuning PI algorithm and PSO tuning PI algorithm. Prove the superiority of the algorithm, improve the robustness and practicability of lithography excimer laser, and meet the needs of photolithography.

An all-polarization-maintaining erbium-doped mode-locked fiber laser based on carbon nanotube was designed and built. The output power was 2.141 mW, the repetition rate was 61.6924 MHz, the spectral center wavelength was at 1563.94 nm, and the full width at half maximum was 7.031 nm. The environmental stability of the laser in vibration is studied. The femtosecond fiber laser was placed on a shaking table to perform the identification-grade sinusoidal vibration test with accelerations up to 12g and the identification-grade random vibration test with root mean square acceleration of 12.81grms in the X, Y, and Z directions, respectively. After each test, the mode-locked threshold power, output power, signal-to-noise ratio of the mode-locked signal, repetition rate, center wavelength, and spectral width were measured. It was found in the experiment that the laser after vibration can still be stable in the mode-locked state, and the optical performance was not changed. This study provides an important reference for future spaceborne mode-locked fiber laser sources.

Based on the 100-joule grade Nd∶glass laser built in the pump source system of the superintense utrafast laser facility, the experiment measured the thermally induced wavefront distortion of the Nd∶glass laser operating at repetition frequencies of one minute, two minutes, and three minutes. By collecting the laser wavefront information to reflect the size of the heat effect, the analysis and experimental results finally determine the repetition frequency of the 100-joule grade Nd∶glass laser that can work stably. At present, the Nd∶glass laser can stably output high-beam-quality laser pulses with a wavelength of 526.5 nm and an energy of about 100 J at the repetition frequency of three minutes, and the output spot energy shows a nearly flat-top distribution. Finally, the pump source system composed of several 100-joule grade Nd∶glass lasers can stably output pump light, and it has been successfully applied to pump the main Ti∶sapphire amplifier of SULF 10 PW system.

Based on the theory of chirped pulse broadband amplification dynamics, this paper systematically analyzes the amplification characteristics and pulse width compression characteristics of chirped pulses in Nd:glass multi-pass amplification systems using numerical simulation. The effects of different input parameter configurations of the amplification system on the characteristics of the amplified pulse parameters, the pulse width and the compressed pulse signal-to-noise ratio were analyzed without spectral pre-compensation. By using the forward iterative algorithm based on the modified input pulse, the required input pulse waveform and spectral distribution were obtained for a given output pulse. The inversion calculation of chirped pulses with three-dimensional spatial distribution is performed, and the amplification characteristics of small signal gain coefficient with spatial inhomogeneous distribution are analyzed. A solution to the large amount of data in broadband amplification calculation is given. The results of this paper can be used as a reference for the optimal design of chirped pulse amplification in high power Nd:glass multi-pass amplification system.

The butt joint of A7204P-T4 aluminum alloy sheets with a thickness of 6 mm was welded via fiber laser-cold metal transition (CMT) arc hybrid welding, with various sizes of niobium foil attached to the butt interface before welding (niobium mass fractions were 0.74% and 1.36% in the weld). Well-formed joints were obtained by optimizing the process parameters. The effects of niobium contents on microstructure and mechanical properties of hybrid welded joints were studied, and the tensile fracture mechanism and fracture morphology of welded joints were also analyzed. Experimental results show that the microstructure of niobium-free welds mainly comprises fine crystal regions, columnar crystalline regions, and equiaxed dendrite regions. After adding niobium foil, grain refinement was observed in the weld metal due to the segregation of niobium solute and heterogeneous nucleation of niobium precipitates, and the apparent disappearance of columnar and dendritic structures were also obserbed. After mass fraction of 0.74% niobium was added, the average grain sizes of fusion zone and weld center decreased by 57.9% and 55%, respectively. The average tensile strength of the joints without niobium, 0.74% and 1.36% mass fraction of niobium were 325 MPa, 334.5 MPa and 328 MPa. The post-break elongation of the welded joint with a mass fraction of 0.74% niobium was 6%, increasing by 71% compared to joint without niobium addition. The fracture surfaces of the three tensile test samples were mainly dimples accompanied by obvious tearing edges, showing microporous aggregate fracture characteristics.

Herein,a joint with quality of excellent grade was obtained based on an optimal laser-metal active gas arc welding (MAG) hybrid-welding process for SUS301L-HT stainless steel. The microstructure characteristics of the welded joint were analyzed through optical microscopy. The analysis showed that the weld exhibited the most serious softening, and its microstructure comprised columnar austenite grains and ferrite. The heat affected zone (HAZ) exhibited different degrees of recovery and recrystallization, and its hardness was higher than that in the weld. The crack growth testing was conducted in the weak area of joint strength (weld) to study the crack propagation characteristics and fracture feature at different stages and to discuss the impact of the weld microstructure on the crack growth process. Results indicated that ferrite was usually the initiation site of fatigue cracks and the preferred crack propagation channel. Resistance to crack propagation in the fusion zone can be improved through further process optimization.

Fiber laser welding is an effective and reliable technology for thin-walled structures with intensive welds, which are important structures in aerospace, ship, and rail traffic, etc. However, welding of such structures is challenging owing to welding deformation and dimensional shrinkage. High-frequency peening was conducted during welding to perform related experiments. Thereafter, the effects of the method on weld morphology, surface stress, welding formation, and dimensional shrinkage were systematically studied. A self-built experimental platform was used to simulate the welding of a thin-walled structure with intensive welds. Further, the optimal peening position was obtained in the high-temperature weld zone in the trailing end of a molten pool. For the GH3128 high-temperature alloy thin plate, the method could adjust the longitudinal residual stress of the weld without peening during welding from the average value of 390.9 MPa to 116.1 MPa, showing a 70% reduction. Moreover, this method could reduce the warpage deformation of the component perpendicular to the weld direction by 74.5% and the dimensional shrinkage along the weld direction by 80%. Moreover, for the multi-pass welding of cylindrical thin-walled 06Cr19Ni10, the dimensional shrinkage was reduced from 0.95 mm (without peening) to 0.29 mm (with peening during welding).

To improve the overlap welding strength and metallurgical compatibility of copper/steel transition joints, a dissimilar metal microtexture-melting laser overlap welding method was proposed. First, ultrafast green laser was used to prepare microtextures on the surface of the steel substrate to improve the wettability and occlusion strength of the steel side interface during the overlap welding, and then copper/steel fusion overlap welding was performed on different microtextured surfaces by pulsed green laser. The microtexture morphology, joint microstructure, bonding interface, tensile properties and fracture mechanisms were studied. The results show that the higher laser power and etching times, the greater the degree of thermal ablation, which easily leads to the deterioration of the internal quality of the groove. The surface texturization has a significant effect on the joint microstructure and tensile strength, and surface texturization can strengthen convective mass transfer, enhance the diffusion of copper to the bottom of the molten pool (steel side), and help the formation of α-Fe and γ-Fe solid solutions with higher copper content, which makes the microhardness of the bottom of the molten pool higher. When the groove depth is 89.91 μm, the tensile strength of the textured joint is the largest, which is 112.5 MPa, 19.5% higher than that of the untextured joint. The fracture mechanism of joints is ductile fracture. The improvement of tensile properties is due to solid solution strengthening, the increase of fusion volume and the vortex bite.

In ultrafast laser glass welding, the laser beam is usually focused by a large numerical aperture micro objective lens. The welding is strictly limited to a very small focal volume with short working distance, low welding speed, and narrow weld width, which limit its industrial applications. In this work, a 75 W green femtosecond laser equipped with a 255 mm-long focal scanning galvanometer was employed to achieve non-optical contact high-speed welding of display screen glasses. The effects of the focal position, pulse energy, and scanning speed on the weld formation were obtained, the welding process window was also obtained. An extremely high welding speed of 6 m/min was achieved without weld defects. In addition, the welds exhibited a shear strength of 20 MPa as well as good seal performance and transmittance, indicating that our method has a great prospect in industrial applications.

This study aims at investigating the effect of the periodic surface microstructures on the coloring mechanism of laser-induced oxidation films. The variation characteristics of ripple width, ripple height, and ripple overlap of laser-induced surface microstructures under different process parameters are particularly studied herein. First, the samples are fabricated by varying the defocusing, pulse frequency, scanning speed, ripple spacing, power, and marking times. The influence of the energy density and spot overlapping on the ripple width of the samples is observed and analyzed to estimate the ripple width. Thereafter, the ripple height is approximately calculated through the ripple width and the measured surface roughness, and the error between theoretical and practical height are obtained from -0.375 μm to 0.430 μm. Furthermore, the ripple overlap is calculated using the ripple width and ripple spacing, and the relationship among ripple height, ripple overlap, and surface roughness is analyzed. Finally, the grating blaze angle is calculated using the surface roughness and ripple spacing. It is found that the degree of ripple concave and convex can be better described with the blaze angle of grating. The color saturation effect of multiple marking samples is determined, and a multilayer color marking model is proposed.

We proposed an effective design of multifunctional switchable broadband terahertz absorber based on hybrid graphene-vanadium dioxide metamaterials. Due to the symmetry of the unit cell, the absorber has polarization-insensitive properties when electromagnetic waves are incident perpendicularly, and can still maintain excellent absorption performance over a wide range of incident angles. Numerical simulation results show that the amplitude of the broadband absorption (from 1.69 THz to 3.21 THz) can be dynamically adjusted by adjusting the conductivity of the vanadium dioxide due to its unique transition characteristics from insulator to metal. Furthermore, by applying an external bias voltage to adjust the Fermi energy of graphene, the peak absorptance of the proposed absorber in the same broadband can be dynamically tuned from 0.226 to 0.992. By altering the two independently controllable parameters (the conductivity of vanadium dioxide and graphene''s Fermi energy) simultaneously, the proposed device can be switched among a transparent insulating dielectric, a perfect reflector, and a broadband absorber in a wide frequency range. The designed system can be extended to the infrared and visible bands, offering a new method for high-performance terahertz devices.

The single measurement area in traditional spatial carrier digital speckle pattern interferometry (SC-DSPI) is limited by its small viewing angle owing to its optical path limitation. In this paper, a SC-DSPI optical path with a large field of view is proposed. A 4F optical system based on the traditional SC-DSPI optical path is added for image transmission, which enables a short-focus lens used in the optical path for imaging to expand the measurement viewing angle, thus realizing a large field of view measurement. The experiment results show that when the measurement distance is 310 mm, the proposed SC-DSPI optical path with a large field of view can realize the entire field deformation measurement of an object with a 180 mm diameter; the obtained phase diagram has high quality. The proposed SC-DSPI facilitates effective measurement.

To determine the influence of carrier phase delay and modulation depth drift on the accuracy of phase demodulation in sinusoidal phase modulation interferometers, a phase-generated carrier (PGC) demodulation nonlinear error compensation method based on a Kalman filter is proposed. First, we establish a Kalman filter state space observation model composed of PGC orthogonal component parameters. Next, the amplitude and offset of the orthogonal components of the PGC demodulation are optimally estimated and corrected to reduce the nonlinear error of the phase demodulation. Finally, a theoretical analysis is conducted and used to explain the principle of the compensation method, and we carry out the phase demodulation simulation test of an analog interference signal and a sinusoidal phase modulation interference displacement measurement experiment. The experimental results show that the proposed method can effectively reduce the nonlinear error of PGC phase demodulation and facilitate displacement measurement with nanometer precision.

For the precise calibration of laser triangular displacement detection based on position sensitive devices (PSD) with the influence of complex photoelectric noise, a joint calibration method based on multivariate adaptive Kalman filter (MAKF) and non-uniform B-spline is proposed. The nonlinear characteristic of displacement sensor is shown in detail by analyzing the measurement principle and computing methods. Aiming at the nonlinear problem, the method of curve fitting for the calibration is given. In consideration of the characteristic of curve fitting, in this paper, a preprocess method called MAKF is proposed for the photoelectric noise elimination. Then, the B-spline curve fitting model is built by dividing the knot vector nonuniformly, which makes the precision of the sensor further promoted. Calibration experiments are carried out under actual working conditions. The experimental results show that the curve fitting calibration method can complete the high-precision calibration of the laser displacement sensor. The positioning accuracy is 0.7%, the average measurement error can reach 0.012 mm, and the calibration mean square error is 2.12×10 -5 mm 2.

Aiming at the influence of refraction on underwater vision system and to achieve portability of the vision system, an underwater vision measurement system based on the constraint of light-plane is established in this paper. First, the underwater structured light measurement model based on the light-plane constraint is proposed. It is theoretically proved that when the projector is perpendicularly projected to the refraction plane and the light-plane passes through the projection optical axis, the light-plane in the air formed by the projection light on land and the projection optical axis is the same with the light-plane in water formed by the underwater refraction light and the normal vector of the refraction plane, which theoretically proves the feasibility of land calibration instead of underwater calibration, avoiding the underwater calibration process of the light-plane. Then, the center rotation light mode is designed based on the light-plane constraint, and the light pattern is decoded through the light-plane rotation angle. Finally, the optimized land calibration method is proposed based on the light-plane constraints. Experiments show that the proposed underwater structured light system can achieve a measurement accuracy of 1.72 mm at a measurement distance of less than 2 m. The system can compensate the lack of short distance, high accuracy, and high resolution in the current underwater acoustic three-dimensional topography measurement. Furthermore, the proposed system can effectively avoid underwater calibration operation, improve the portability of underwater vision system, and expand the application of vision measurement system in underwater engineering detection, underwater three-dimensional topography measurement, and underwater structural defect detection.

Herein, a radius-constrained iterative reweighted least squares circle fitting (RC-IRLSCF) method is proposed to address the problems of very small angle of the circle corresponding to arc characteristic data collected by the line laser displacement sensor, noise and outliers in the characteristic points, and others, which seriously affect the positioning accuracy of the circle center. To overcome the influence of noise and outliers on detection accuracy during the detection of existing arc features, a circle-fitting target optimization model based on radius constraints and robust loss function is constructed using iterative reweighting and Levenberg-Marquardt algorithm to further optimize the solution and achieve accurate fitting and positioning of arc features. The detection experiment of the service wheel tread surface shows the use of line laser in detecting contour arc characteristics. Moreover, the proposed method can realize accurate fitting and positioning of the arc under the condition that light scattering and local deformation produce adjacent outliers, with a certain degree of robustness and noise resistance.

Based on a new laser interferometer, the vibration state of transducer surface is measured and analyzed. The vibration waveforms of each point on the two-dimensional surface of the transducer are obtained by using a multi-channel detection unit laser interferometer. Three transducers (the center frequencies are 2.25, 5, 10 MHz) with large differences in performance are compared subsequently. According to the measured surface vibration waveform of transducer, the echo signal in ultrasonic testing is quantitatively calculated by finite element method, and the calculated results are compared with the experimental results. The results show that the laser interferometer can directly and quantitatively characterize the surface vibration state of ultrasonic transducer, and can clearly distinguish the working performance difference of ultrasonic transducer. The measurement results have a good application value for evaluating the performance of ultrasonic transducer and predicting the echo signal of ultrasonic testing.

The construction of high-power laser needs a lot of high precision optical windows, and the wavefront detection generally uses phase-shifting interference technology. Due to the multiple reflections of the test light beam in the optical window, there is a fixed pattern phenomenon caused by parasitic interference. Fixed pattern will introduce periodic phase noise into wavefront detection results, which greatly reduces the confidence level of wavefront detection results. To address this problem, this paper presents a method based on wavelet transform to directly filter out the noise from the wavefront detection results according to the characteristics of fixed pattern noise without additional hardware or adjusting the test state. Experimental results demonstrate that this method can effectively filter out the phase noise caused by fixed pattern, and preserve the processing features well.

The enhanced fluorescence effect of the heterojunction of CdSe quantum dots and a porous Al2O3 film was experimentally studied by using TiN nanoparticles (NPs). TiN NPs were deposited on the surface of porous Al2O3 film. Then, the CdSe QDs were self-assembled on the surface of TiN/Al2O3 film to prepare the CdSe/TiN/Al2O3 heterojunction. At the same time, the surface enhanced fluorescence effect was observed on the platform of a scanning near-field optical microscope. The results have showed that the interfacial fluorescence from the porous Al2O3 film was enhanced due to the increase of poto-generated carriers resulted in by TiN Nps from the CdSe QDs to the porous Al2O3 film. These results based on this paper could be widely applied for many fields of photovoltaic, lightshows, optical sensors devices and nano-biological imaging system.

For a three-level non-Hermitian quantum system with gain and loss, a new technique called non-Hermitian stimulated Raman shortcut to adiabatic passage (NH-STIRSAP) is proposed. This technique is based on the traditional stimulated Raman adiabatic passage (STIRAP), and the non-Hermitian terms in the NH system can be flexibly manipulated to effectively compensate the nonadiabatic coupling in the evolution and thus to accelerate the whole adiabatic evolution process. The detailed numerical calculation and theoretical analysis results confirm the rapidness and high-fidelity of the proposed technique. In addition, its application in beam splitting is demonstrated. Compared with the traditional shortcuts to adiabaticity, the new NH-STIRSAP technique has a wider range of applications.

Aiming at the disadvantage of the active decoy-state scheme to introduce extra information, we investigate the passive decoy-state measurement-device-independent quantum key distribution (MDI-QKD) protocol based on heralded pair coherent states and pulse-position modulation by means of the rotation-invariant photonic state. The performance comparison among the traditional MDI-QKD protocol, the passive decoy-state MDI-QKD protocol based on rotation-invariant photonic states, and the passive decoy-state MDI-QKD protocol based on rotation-invariant photonic states with different frame lengths is conducted. The simulation results show that the key generation rate and the secure transmission distance can be improved if rotation-invariant photonic states and the pulse-position modulation are introduced. Moreover, with the increase of frame length, the performance of the protocol is also improved. Therefore, in the absence of intensity modulation, this protocol can avoid the influence of light side channels and can be used to increase the key generation rate.

In response to the demand for the photoelectric performance evaluation of multi-angle polarization imaging detectors, a universal testing system for photoelectric performance parameters of image sensors is developed herein, and a Peltier effect-based thermoelectric cooler and low-temperature cycler are combined to control the temperature of the detector. Experimental results show that the light source stability of the integrating sphere is 0.036%, the uniformity of illuminance is ≥99.3%, the cooling rate of the detector refrigeration system is approximately 2.2 ℃/min, and the temperature control accuracy is better than ±0.15 ℃, and the temperature is -10--25 ℃. For the measurement of key performance parameters such as quantum efficiency, photo response non-uniformity, dark current, full-well charge, and optical response nonlinearity within the operating temperature range, the photo response non-uniformity of the multi-angle polarization imaging detector at different wavelengths is better than 3%, The optical response nonlinearity is better than 1%, the dark current increases by 1.25 times when the operating temperature from 0 ℃ to 9 ℃, and the quantum efficiency in the near-infrared band changes by 3.58 percentage. The performance evaluation of the detector guarantees the test performance and calibration requirements of the multi-angle polarization imaging detector.

Information on the spatial location of road facilities such as traffic signs is one of the basic element of urban three-dimensional (3D) modeling, and it is also an essential part of road facility maintenance and management. To this end, an automatic extraction scheme for small traffic signs based on mobile measurement data is proposed herein. Based on the improved convolutional neural network SlimNet model, small cross-marks on panoramic images are detected, and a 3D target geolocation based on depth maps is proposed. A distance assessment method based on the center point is used to extract the diagonal of the target. Measured data of the three types of small traffic signs are selected to verify and analyze the proposed method. Experiment results show that the average accuracy of the SlimNet model is 4.2 percentage higher than that of the classic VGG16 (Visual Geometry Group 16) model. Using the proposed geographic positioning and vectorization scheme, the recall rate and accuracy rate of the three types of targets in the experimental area reached over 86%, proving the effective feasibility of the overall scheme. Furthermore, the proposed method provides a new idea for an accurate 3D spatial geolocalization of urban multi-class targets.

Scanning lidar plays an irreplaceable role in driverless system, which is a research hotspot in recent years. Because the time of each point is different between the multi pulse periods, and the relative motion between the lidar and the imaging target will cause the distortion of the three-dimensional (3D) image reconstruction of the target, so it is necessary to compensate for the real high-precision 3D imaging. In this paper, a point by point compensation method for motion distortion based on the velocity measurement of coherent frequency modulated continuous wave lidar is proposed. The simulation and experimental results show that the relative velocity error and imaging distance error are 0.52% and ±4.76 cm, respectively. Compared with the traditional accelerometer method, the proposed method does not rely on external measurement such as accelerometer, and has higher universality, which is of great significance for the practical application of lidar.

During the laser powder bed fusion (LPBF) process, metal powder is rapidly melted and solidified under the action of a high-energy laser beam. The spatter phenomenon accompanies the complex heat conduction process. Spatter is essentially a process by which materials in and near the laser and metal powder areas move to the surrounding area. These materials not only fall to the molding area and affect the quality of the molded part but also fall to the non-molded area to contaminate the clean powder. This is a disadvantage of the molding process. In addition, spatter carries rich information, which can be used to monitor the forming process. Detailed analysis and study are expected to improve the theoretical basis of LPBF forming, solve the process reliability problem of LPBF technology, and ultimately improve the product quality. Therefore, this study takes the spatter behavior in the LPBF process as the research object, combines with the relevant research in recent years to summarize the spatter behavior in the LPBF process at home and abroad and the status of process monitoring and quality control technology based on spatter characteristics.

Laser-induced breakdown spectroscopy (LIBS) has been widely used in the field of material detection due to its advantages such as no sample preparation, multi-element simultaneous analysis and rapid detection. Selecting appropriate parameters of the experimental device is an important prerequisite for achieving a good detection effect. Based on the single factor experiment, a multi-factor response surface model for optimizing the parameters of the laser-induced breakdown spectroscopy experimental device is established with laser energy, delay time and depth of focus as the influencing factors and with spectral signal-to-background ratio as the response factor. The influence of different influencing factors and their coupling effects on the spectral quality are studied and the obtained optimal experimental parameters are laser energy of 114 mJ, delay time of 1.86 μs, and depth of focus of 1.75 mm. Finally, the optimal experimental parameters obtained by the response surface methodology are verified by experiments. The mean value of the signal-to-background ratio of the spectral line is 7.45, which is 1.92% higher than that by the single factor method, and the relative standard deviation is 3.16%, which is 0.94% lower than that by the single factor method. The results show that the response surface methodology is more effective and reliable than the single factor method.