In order to control the comprehensive properties of 316L stainless steel (316L-SLM) prepared by SLM, the microstructure and properties of 316L-SLM at different scanning speeds were studied, and the corrosion resistance of 316L-SLM in PBS solution was analyzed at different scanning speeds and heat treatment temperatures. The results show that when the scanning speed is less than 900 mm/s, it has little influence on relative density and microhardness, but when the scanning speed is more than 900 mm/s, the density and microhardness decrease with the increase of scanning speed. Scanning by inter-layer rotation of 67° produced periodic patterns of weld profile on the cross section. The specimen has stronger compression resistance and higher elastic modulus when high scanning speed is used. The specimens has stronger tensile properties and higher elongation when low scanning speed is employed. The microstructure of the samples treated at 650 ℃ and 1 050 ℃ has coarse columnar crystal, while the width of the columnar crystal of the samples treated at 1 050 ℃ slightly increases. The contour of the weld bead and the morphology of fish scale pattern are clearly observed in the samples treated at 650 ℃ and 1 050 ℃. Both heat treatments significantly improve the corrosion resistance, especially at 1 050 ℃. Defects and sensitization are the main controlling factors of corrosion behavior. With the increase of scanning speed, sensitization tendency decreases and defect tendency increases. Therefore, the corrosion resistance of 316L-SLM sample increases first and then decreases when the scanning speed increases, and the corrosion resistance is the best when the scanning speed is 900 mm/s.

921A high strength steel is widely used as hull material because of its excellent mechanical and corrosion resistance properties. Hyperbaric underwater laser cladding repair is one of the preferred technologies for on-line repair of ships in complex marine environment. In order to explore the distribution law of temperature field, stress field, and strain field of 921A ship steel repaired with hyperbaric underwater laser wire filling cladding, the numerical simulations of atmospheric pressure and 0.3 MPa pressure environment are carried out by SYSWELD software. The results show that: with the change of environmental pressure, the temperature field of the specimen at each stage is spindle shaped, and higher laser power is required to melt the same specimen under high pressure. The equivalent stress and the stress in different directions for both high pressure and atmospheric pressure are less than the yield strength of 921A ship steel. The transverse, longitudinal and axial deformation of the specimen in high pressure environment is slightly larger than that in atmospheric pressure environment, which distributed more clearly in the axial direction.

Based on the hot deformation behavior of selective laser melting forming 316L stainless steel at temperatures of 900~1 100 ℃, strain rates of 0.001~1 s-1was investigated by using the Gleeble-3800 thermal simulator. The results show that the flow stress decreases significantly with the increase of deformation temperature or decrease of strain rate during the deformation process. The strain-modified Arrhenius constitutive model is established for the whole deformation process, and the accuracy of the model is evaluated by using statistical parameters. The R-value of the model is 0.988 63 and the average absolute relative error of the model is 5.45%. The hot processing map of SLM forming 316L stainless steel at the strain of 0.9 is drawn, combining with microstructure analysis in different processing areas indicated that the instability mechanism is the formation of adiabatic shear zone and flow localization, and the optimal working conditions for SLM forming 316L stainless steel is low strain rate and high temperature strain rate area.

The quality of selective laser melting forming is mainly determined by the combination of process parameters and scanning strategy. In this experiment, the layer partition scanning strategy is obtained through the combination of different layering methods, stacking methods, and scanning methods. The TC4 samples were formed by combining appropriate process parameters with different layer partition scanning strategies. The quality of TC4 samples was studied. The results show that the samples formed by layer partition scanning strategy have higher density and finer distribution of acicular martensite in the microstructure under electron microscope. When the samples with 100 μm layer thickness were formed by layer partition scanning strategy, the side length size error rate and surface roughness become smaller. The samples formed by layer partition scanning strategy have stronger ability to adjust the forming environment and better forming quality than the samples not formed by layer partition scanning strategy.

This work aims to investigate the selective laser melting (SLM) process of TA7 ELI on the density through analyzing the influence of process parameters such as laser power P and scanning speed V. The influence of laser energy density on defects was further analyzed, and the microstructure and mechanical properties were analyzed based on the optimal forming process parameters. Results show that the density of TA7 ELI formed by SLM firstly increases and then decreases with the increase of laser power P and laser energy density. When the laser power P is 280 W, the scanning speed V is 1 000 mm/s, the scanning spacing H is 120 μm, and the coating thickness t is 30 μm, the highest density of the formed sample is 99.89%, and the corresponding laser energy density is 78 J/mm3. TA7 ELI formed by SLM shows epitaxial columnar crystal growth along the deposition direction and equiaxed crystal structure along the direction perpendicular to the deposition direction, which is composed of fine needle-like α′ martensite with parallel or staggered distribution. The as-deposited tensile strength of material is more than 1050MPa and the elongation rate reaches 15%. The tensile fractures are evenly and densely distributed with equiaxed dimples, showing typical ductile fracture characteristics.

The high-quality deposited samples with no metallurgical defects were investigated by laser direct deposition to research the effects of solution temperature (910-970 ℃) and aging temperature (500-600 ℃) on the phase composition, microstructure, and tensile properties of the deposited samples. The result shows that the alloy microstructure of the as-deposited and solution-aging samples contain a large amount of α-Ti (α) phase and a small amount of β-Ti (β) phase. In addition, as solution and aging temperatures increase, the α-Ti (α) phase of microstructure changes from the acicular to the short rod-like. For the tensile properties, there is a higher tensile strength index in the solution aging state (940 ℃/1 h/WQ+550 ℃/4 h/AC, 970 ℃/1 h/WQ+550 ℃/4 h/AC, 940℃/1 h/WQ+600 ℃/4 h/AC) than the national standard requirements (σb≥895 MPa, σ0.2≥828 MPa, δ≥10%) for forgings. The fracture morphology is plastic.

In order to improve the low strength and precision of selected laser sintering of polystyrene (PS) powder, the PS/PMMA composite powder was prepared by adding PMMA powder. Taking dimensional accuracy and tensile strength of the workpiece as indexes, orthogonal experiments were carried out by selecting layer thickness, scanning speed, laser power and scanning distance. The range analysis was used to optimize the forming process and study the performance. The results show that the optimal process parameters for selecting the size accuracy of PS/PMMA composite powder sintering are preheating temperature 101 ℃, scanning speed 4 m/s, laser power 20 W, hatch spacing 0.25 mm, and layer thickness 0.24 mm. The X, Y and Z dimensional accuracy of PS/PMMA composite powder sintering can reach 0.004, 0.033, and 0.020, respectively. Through mechanical properties analysis, selected laser sintering PS/PMMA can improve the strength of SLS specimen, and the tensile strength is increased by 2.4% compared with PS sintered parts.

Laser additive manufacturing (AM) technology has great advantages for producing metal components with complex structures. The high reflectivity metals exhibit different laser absorptivity under different wavelengths. To obtain high-quality AM parts, short wavelength laser sources such as blue laser and green laser can be used to manufacture high reflectivity metal materials. In the present manuscript, the absorption mechanism of laser source has been introduced. The current status of blue laser has been summarized. The research status of selective laser melting and laser deposition technologies using blue laser source of high reflectivity metals have been analyzed and summarized. In addition, its future development trend has also been prospected. HORN T J, HARRYSSON O L A. Overview of current additive manufacturing technologies and selected applications［J］. Science Progress, 2012, 95(3): 255-282.

This paper presents a process for the fabrication of particle-reinforced Ti/B4C/dr40 composite coatings on the surface of shaft parts by laser cladding technology. The mechanism of in situ ceramic particle and its refinement of the grains during the solidification process, the transformation from columnar to equiaxed crystals, the generation of cracks on the composite coating surface, and the effect of the temperature gradient and solidification rate on the microstructure were investigated and analyzed. In order to analyze the mechanical properties of the composite coating, indentation and scratch tests were carried out. The results show that the composite coating exhibits good metallurgical bonding with the substrate and the TiC and TiB2 hard particles generated during the solidification process play a skeletal role during wear process, inhibiting the plastic deformation of the matrix, reducing the material removal, and improving the microhardness and wear resistance of the composite coating. The research indicates that the fabricated Ni-based composite coatings by laser cladding technology can be used to achieve surface strengthening and remanufacturing of shaft parts.

The evolution of residual stresses in the thermal barrier coating around the hole after femtosecond laser drilling was investigated by step-by-step measurement of residual stresses around the cooling hole prepared by different femtosecond laser processes using the cosα method. The results show that the surface stress of the sprayed thermal barrier coating and the coating around the hole after laser drilling are both residual tensile stresses dominated by quenching stresses. Under different femtosecond laser processing processes and different hole sizes, there is an obvious radial residual stress zone around the gas film hole, and the residual stress is linearly decreasing in this zone. There is no significant difference in the radial residual stress field around the gas film hole prepared by different processes due to the influence of the spatter formed by the thermal effect of femtosecond laser, and changing the diameter of the gas film hole cannot improve this thermal effect.

To improve the capillary performance of microgroove suction core, v-shaped scanning method was used to etch non-equal section microgrooves on copper plate. The effects of laser path spacing, scanning speed, scanning times, pulse width, and frequency on the morphology and size of non-equal section microgrooves were studied. It is found that with the increase of laser path spacing, the width of grooves increases, the depth of grooves increases first and then decreases, and the roughness of grooves decreases first and then increases. When the path spacing is between 10 μm and 30 μm, the groove morphology is the best, and the capillary pressure difference between the two ends is large. When the number of laser scanning is 50, the scanning speed is 100 mm/s, the frequency is 40 kHz, the pulse width is 120 ns, and the capillary pressure difference between the two ends of the non-equal section groove etched by nanosecond laser is large. The research can provide reference for improving the heat transfer performance of groove type vapor chamber.

The surface of 316 stainless steel was treated by laser texturing with a nanosecond pulse laser to study the effect of surface morphology on the adhesive properties of electronic labels. The adhesion force was measured by microcomputer controlled universal testing machine. The influence of laser texturing on the surface morphology and adhesion properties of materials was studied, and the optimal laser texturing process parameters were determined. Laser texturing can effectively improve the surface roughness and contact area of the material. When the best laser texturing process is 200 W laser power, scanning speed is 4 050 mm/s, repetition frequency is 50 kHz, pulse width is 270 ns, and filling line spacing is 0.081 mm, the surface roughness of the material after laser texturing is 0.024 higher than that before the treatment μm raised to 2.406 μm. After laser texturing, the adhesive strength is 48.5 N, which is 166% higher than that of untreated adhesive strength of 18.2 N.

In order to solve the problem of fast collection of point for power line inspection with banding area, a multi-modal LiDAR is designed, where asymmetrical scanning model is realized to improve the efficiency of point cloud collection. The newly presented multi-modal LiDAR takes advantages of double optical wedges scanning unit whose utilization rate of laser pulse can reach as high as 100%. Double optical wedges are driven by servo DC motor whose rotating velocity and rotating position can be accurately controlled. It offers the advantages that the scanning trace can be controlled for different model, especially an asymmetrical scanning model of regional point cloud multiplication is realized to improve the collection efficiency of zonal point cloud. Data collection by flight and automatic inspection of power line by UAV are presented using the designed LiDAR. The vertical takeoff and landing (VTOL) UAV is applied to data collection test. The dense point cloud is collected by LiDAR, automatic inspection of power line is presented using DJI Phantom 4pro. The multiplicity of point location of DJI Phantom 4pro is evaluated. The results show that the density of point cloud collected by the designed multi-modal LiDAR which carried by the VTOL UAV with flight velocity of 25 m/s can reaching as high as 146 pts/m2. The efficiency of data is improved more than 4 times compared with the efficiency of LiDAR with traditional scanning ways. Multiplicity of point location of DJI Phantom 4pro for automatic inspection based on point cloud can reach 0.15 m, meeting the requirements of UAV precision operation.

In middle-upper atmosphere LIDAR observation, the quality of the LIDAR return signal is highly correlated with the result of transmitter-receiver matching. This technology has become a bottleneck restricting the development of domestic and foreign LIDAR groups. In this paper, a self-adaptive transmitter-receiver matching algorithm and a compatible hardware and software system are developed to achieve accurate and efficient automatic transmitter-receiver matching. The method is able to select the detection range adaptively, adjust the direction and step size by the detected echo signal, and greatly reduce the matching steps while ensuring the matching accuracy, achieving high-precision and high-efficiency automatic transmitter-receiver matching. The algorithm and the associated software and hardware system provide important technical support for the daily observation, and also establish a solid foundation for the subsequent automation and intelligent operation of LIDAR.

In view of the characteristics of narrow and long environments such as roadways and tunnels, as well as the current limited scanning range of multi line lidar and the problem that the three-dimensional shape reconstruction largely stays in a single distance information, this paper proposes a realization system of full scene three-dimensional scanning and color three-dimensional shape by using mobile platform to carry multi line lidar, and optimizes the system to improve the reconstruction accuracy and running speed of the system. After preprocessing the original point cloud data, the intensity information of the point cloud data is converted to get the color information. Then the three-dimensional reconstruction is carried out through Poisson reconstruction, and the color information is assigned to the Poisson reconstruction results to get the color three-dimensional model. Finally, the feasibility and practicability of this system are verified by experiments.

The automatic classification of massive 3D point cloud obtained by the vehicle laser scanning system is of great significance for target recognition and reconstruction. Traditional point cloud classification requires manual intervention, while most of the existing automatic classification algorithms suffer from low classification accuracy and high computing costs. In this regard, this paper proposes an automatic classification method of vehicle point cloud based on LightGBM. The method first calculates the surface change three-dimensional feature, density feature, elevation feature, and fast point feature histogram of the point cloud. Second, the point cloud normal vector and its neighbors are calculated. The normal vector angle of the domain point and the angle between the normal vector and the horizontal plane are used as constraint features. All the results are combined to obtain a 48-dimensional feature vector. Finally, the LightGBM is constructed to train the point cloud feature vector to complete the classification and prediction. Experiments show that the algorithm can accurately and efficiently complete the automatic classification of vehicle radar point clouds. Compared with the control algorithm, the total accuracy is increased by 8.1% on average, the Kappa coefficient is increased by 18.9% on average, and the calculation time is reduced by 73.7% on average.

The accurate identification of aircraft wake vortex core is the premise of dynamically reducing the wake interval. Firstly, the evolution model of the wake vortex field was established, and the wake vortex field was simulated. Secondly, the simulation analysis was carried out on the combined wake vortex velocity field detection results of different intensities and heights. Finally, the "Maximum-Submaximum" method of vortex core position estimation was proposed to improve the accuracy of vortex core position recognition. The research shows that the larger the difference between the maximum and the second maximum at the two peaks of standard deviation is, the closer the distance gate corresponding to the vortex core and the maximum standard deviation is. In the verification of the substituted example, the deviation of the radial distance estimation results is not more than 1.5 m, and the deviation of the vortex core position is within 3 m. Compared with the range method and gradient method, the position deviation has been corrected by more than 60%, and the maximum is 86%.

A portable laser Raman spectrometer was used to scan 208 adulterated flaxseed oil (FSO) samples of extra virgin olive oil (EVOO). Combined with principal component analysis (PCA) and partial least squares regression (PLSR), the quantitative detection of EVOO adulterated flaxseed oil was realized. Partial least squares regression (PLSR) calibration models were developed and validated internally (using cross validation, leave-one-out method) and externally (using independent sample sets). The correlation coefficient (R2), root mean square error (RMSE) and relative analysis error (RPD) were used to evaluate the prediction performance of the system. The experimental results show that the root mean square error of the prediction system is 2.31% and the correlation coefficient of the prediction set is 0.995. The root mean square error of cross validation is 2.24%, the correlation coefficient of cross validation set is 0.995, and the relative analysis error of the system is 14.19. The results show that the system has excellent predictive performance in quantitative detection of EVOO adulterated flaxseed oil. The system can be used for simple, rapid, and nondestructive quantitative detection of EVOO adulteration.

The reflection coefficients of surface waves excited by pulsed laser at different normalized depths in the near field of surface defects were studied using finite element method, and the signal enhancement phenomenon of surface waves at the near field of defects was verified. At the same time, by analyzing the variation of reflection coefficient with distance, the concept of the radius of the reflection signal enhancement region was established, and it was found that the radius of the signal enhancement region is related to the depth of surface defects. A formula for measuring the depth of surface defects was fitted; We also analyzed the influence of rectangular defect width on depth measurement and corrected the formula for measuring surface defect depth. In addition, based on the phenomenon of reflection coefficient changing with defect depth, the relationship between normalized depth and surface wave length was analyzed. The research results indicate that there is a shortwave limitation when using reflection coefficient to measure defect depth, which means that when the surface wave length is less than half of the defect depth, the reflection coefficient is independent of the defect depth, and at this point, the reflection coefficient is 0.4.

Aiming at the measurement accuracy of laser on-machine measurement of workpiece features, the key error influencing factors and compensation applications of the measurement system are studied. When using the laser displacement sensor as a tool to measure the workpiece features on-machine, the measurement results are affected by the tilt error of the laser displacement sensor and the geometric error of the CNC machine tool. To correct the measurement error caused by the laser displacement sensor when the object surface is tilted, a tilt error experiment is designed, and the Legendre polynomial is used to model and compensate for the tilt error. After compensation, the tilt error can be reduced to within ±0.025 mm. Aiming at the influence of the geometric error of the linear axis of the CNC machine tool on the measurement results during the stationary laser on-machine measurement, a tilting installation experiment of the Double ball bar (DBB) is designed, and the geometric errors of the X-axis and the Y-axis are decoupled using parametric modeling. Finally, according to the established tilt error and geometric error models, the on-machine measurement results of workpiece features are compensated. The results show that after the error compensation of the workpiece feature on-machine measurement results, the linear dimension measurement error is less than 0.05 mm, and the angle measurement error is less than 0.08°, which is significantly improved compared to the on-machine measurement accuracy before compensation.

The Steger algorithm will produce a mass of redundant points when extracting the center line of laser fringe, a method of multi-line structured light center extraction based on improved Steger algorithm was proposed. First, the global thresholding method was used to extract the laser fringe region effectively, and the Steger algorithm was used to preliminarily obtain the center line of laser fringe. Second, the noise points were filtered out by threshold method and the collinear light fringe lines were fitted by least square method. The distance between the filtered points and the fitted line were calculated, then an appropriate threshold to recover valid laser points was set. Finally, the coordinates of the center points of laser fringe were corrected by fitting straight lines. Experimental results show that compared with Steger algorithm, the proposed method can effectively filter out the noise points and eliminate a large number of redundant points generated by Steger algorithm. When the accuracy value of the corresponding points is less than 1 pixel, the number of the center point of the laser fringe is reduced by 16%. Compared with the Steger algorithm, the difference of standard deviation of the distance between the laser point and the fitting plane after 3D reconstruction by the proposed method is 0.48×10-5 mm. However, the extracted laser line is more flat without redundant and noise points, which is more in line with the requirements of the project.

Silk has excellent optical properties and has broad application prospects in the field of optical devices. This article introduces the research progress of three silk optical devices: silk optical waveguides, silk optical sensors, and silk optical microstructures. The preparation methods and performance research progress of silk optical waveguides and silk microstructures are highlighted, while the application progress of silk optical sensors in the fields of biomedical, environmental monitoring, and industrial testing are emphasized. The research on these three silk optical devices demonstrates the theoretical research value and practical application value of this direction. In order to achieve a wider range of applications in the field of optical devices, future research should continue to investigate the optical properties of silk and further study the preparation methods and performance optimization of silk optical devices.

In recent years, with the development of laser medicine and the demand of rapid rehabilitation for patients with hemorrhoids, laser treatment of hemorrhoids has been widely used in clinical practice. This paper reviews the research progress of laser medicine in the field of hemorrhoid treatment, prognosis, and rehabilitation in the past 10 years. The action methods, advantages and disadvantages of gas laser, solid state laser, semiconductor laser, and other lasers for the treatment of hemorrhoids are preliminarily summarized to promote the treatment method and obtain better clinical efficacy.