The optical microscope and electron backscattered diffraction (EBSD) technology were used to observe and analyze the microstructure and crystal orientation of 316L stainless steel under different scanning angles of selective laser melting (SLM). The relationship between scanning angle and molten pool formation, solidification, tensile strength and elongation was studied. The results show that the anisotropy of the crystal changes with the laser scanning angle. The scanning angle directly affects the stability of the obtained molten pool and the temperature gradient during solidification, and also further affects the uniformity of the final crystal. The results shows that the tensile strength and elongation of the workpiece changed. Therefore, the structure and mechanical properties of the shaped part can be controlled by changing the angle of the scanning direction.

An experimental study was conducted on the forming performance of 316L stainless steel samples formed by selective laser melting technology (SLM). The relationship between different parameters and the forming performance was established by using the energy density formula, and the influence of different energy densities on the density and wear resistance of the samples was investigated. The results show that when the laser energy density increases from 34.72 J/mm3 to 69.44 J/mm3, the density of the specimen increases from 91% to 99%. This is because the increase in energy density leads to an increase in the fluidity inside the molten pool. As a result, the surface tension of the metal solution decreases, and the density increases accordingly. After that, the energy density increased from 86.81 J/mm3 to 121.53 J/mm3, and the density did not change significantly; while the wear resistance of the specimen increased first and then decreased with the increase of energy density, when the energy density was 86.81 J/mm3, the sample has the best wear resistance and the highest density.

In order to improve the defects such as coarse columnar crystals, cracks and pores in the traditional laser cladding coating, the test of ultrasonic vibration assisted laser cladding to prepare Ni-based WC+CeO2 coating on the surface of 42CrMo steel, and the influence of different ultrasonic power on the phase composition, microstructure, microhardness and wear resistance of the coating was studied. The results show that the introduction of ultrasound does not change the phase composition of the coating, the coating phases are all composed of solid solution γ-Ni (Fe), intermetallic compounds Ni3Fe, WC, Cr23C6, M7C3 (M=Fe, Cr)and so on. With the increase of ultrasonic power, the thinning effect of cavitation effect and acoustic current effect on the coating increases. When the ultrasonic power is 350 W, the microstructure of the coating is improved most obviously, the thick columnar crystals at the bottom of the coating disappear, and a large number of small dendrites are distributed in the coating. The hardness curve fluctuates smoothly, and the average microhardness is 1 074.9 HV. The average friction factor is 0.28, and the minimum amount of wear is 8.43×10-3 mm3, which is 27% and 25% less than the coating without ultrasonic vibration.

Aiming at the problem that the cladding layer with high content of ceramic phase is prone to crack, the forming characteristics of Ni45 + 20% Cr3C2 cladding layer with different process parameters were studied, which provides the corresponding theoretical guidance for preparing the crack free cladding layer with high content of ceramic phase by adjusting the process parameters. The results show that: with the increase of laser current, the dilution ratio, melting height and melting width increase, the increase value of melting width is bigger than that of melting height, the microstructure of cladding layer is coarse, the crystal spacing is large, and the crystal growth mode changes from fine dendrite to cellular dendrite. Under the optimized process parameters (current 150 A, scanning speed 200 mm/min, lapping rate 60%), the rarefaction ratio of cladding layer is 25.3%, and the hardness of multi pass cladding layer is slightly lower than that of single pass cladding layer, but the performance is relatively uniform and stable. For the cladding layer with high content of ceramic phase, the control range of dilution ratio should be appropriately relaxed. By adjusting the process parameters, the cladding layer with good crack free forming quality can be obtained.

In order to improve the forming accuracy of the selective laser melting part, 316L stainless steel parts with different sloping angles were fabricated by selective laser melting equipment. The influence of sloping angle on the forming accuracy of 316L stainless steel was studied by density measurement, forming dimension measurement and surface roughness measurement. The results show that with increasing the sloping angle, the density of SLM samples decreases firstly, and then increases to the maximum value of 99.82% at 0°. The dimension error in the x and z directions increases first and then decreases, while the dimensional error in the y direction changes in the shape of "W". The surface roughness of A and C plane increases firstly and then decreases, the upper surface roughness of the sample is the minimum at 0° and 90°, which is 6.79 μm and 6.43 μm, respectively. The surface roughness of the B plane is basically the same.

Dual-phase steel DP590 and aluminum alloy 6061 sheet was welded through pulsed laser welding technology, in a form of lap joints.The microstructure, element distribution and mechanical properties of the welded joint were measured and analyzed. The test results show that the lap joint of DP590 duplex steel and 6061 aluminum alloy sheet can be welded by using laser pulse welding technology. The weld zone is mainly columnar crystal structure with coarse grain, and the heat affected zone is martensite with fine and uniform grain and ferrite with continuous distribution.The maximum hardness (3 N test force) of the steel side is 440.1 HV in the heat affected zone, and the maximum hardness of the aluminum side is 325.4 HV in the weld zone. The maximum tensile strength of the joints is 35.0 MPa. The fracture postions of the joints are mainly two situations in the following. It directly fracturesfrom the weld interface in the shallow deep joints or near the aluminum side of the fusion line in the deep welding joints.

In order to study the Effects of quenching on the microstructure and properties of AS300/MBW500 unequal-thickness laser wire-filled welded joints, experiment of water quenching heat treatment on the basis of AS300/MBW500 unequal thickness steel laser wire filling welding. By analyzing the microstructure, Vickers hardness and element composition of the welded joint, the effect of water quenching heat treatment on the performance of the welded joint is obtained. As the quenching temperature increases, the accumulation of Al elements in welded joints increases and the hardness of weld decreases. When 930 ℃, the hardness step value between sheet and weld, weld and thick plate is equal, the tensile strength of weld is 908 MPa, the elongation is 7.5%, which increases the mechanical properties of laser wire filling welded of unequal thickness steel.

TC4 titanium alloy was welded with 50 steel by Nd: YAG laser. The crack propagation, microstructure and phase composition of the joint were studied. The results show that the crack type is related to the position and process parameters, and the crack propagation in the weld is transgranular, and the joint fracture is brittle fracture. The high carbon martensite formed in the weld and the middle ridge existed in the high carbon martensite. Ti-Fe phase in weld seams is TiFe, TiFe2 intermetallic compound, and the number of TiFe is higher than TiFe2. High hardness and poor toughness and plasticity of high carbon martensite and TiFe and TiFe2 intermetallic compounds are the main causes of crack initiation and propagation.

In order to study the effect of the amount of direct defocus on the weld quality、microstructure and mechanical property of TA2 industrial titanium plate welded by vacuum laser. A vacuum chamber and a high-power disc laser are used to weld with different defocus at a vacuum degree of 4.0×10-1 Pa. The results show that：the amount of positive defocus can effectively complete the welding of plate. In the vacuum environment, with the increase of defocus, the forming quality of the weld surface is improved and the weld width is increased. However, the increase of defocus will lead to the dispersion of spot energy. Therefore, when the defocus reaches +4 mm, the weld width reaches the maximum and then begins to decline. The grain size and form of the weld and heat-affected zone are different under different defocusing amount, and the grain size decreases with the increase of defocusing amount. Through the research on the effect of positive defocus on vacuum welding of TA2 industrial titanium plate. When the defocus is 0 mm, the microhardness of the weld is increased 1-2 times. When the defocus is +4 mm and +8 mm, the microhardness of the weld has no obvious change. The tensile force and tensile strength of the weld reached the maximum value of 57 759 N and 292 N/mm, respectively, when the defocus amount of +8 mm was used. The conclusion is drawn: using vacuum welding of TA2 industrial titanium plate with +4 mm to +8 mm defocus can get better comprehensive performance of weld seam. This is of great significance to its application in the field of shipbuilding.

In order to improve the welding quality of dissimilar steel materials, nickel coating was added as the middle layer of the base metal. Using DP590 dual phase steel and 304 stainless steel as base materials, Nd: YAG laser was used to carry out laser splicing welding of the dissimilar steel materials. The microstructure, hardness, mechanical properties and corrosion resistance of the weld were studied by means of optical microscope, scanning electron microscope and tensile testing machine. The results show that the addition of nickel coating improves the content of Ni element in the weld compared with the no nickel coating dissimilar weld, which is beneficial to the formation of lath martensite in the weld. The average hardness of the weld area is increased by 12%, and the tensile strength is higher than 370 MPa. The corrosion rate of the weld can be slowed down and the corrosion resistance of the weld can be improved by increasing the nickel coating.

To solve the problem that it is difficult to accurately reflect the temperature change in laser transmission welding process by experimental methods, this paper takes the polyarylsulfone (PASF) laser transmission welding based on zinc powder absorbent as the research object, and established a three-dimensional finite element model reflecting the welding process in COMSOL. The accuracy of the model is verified by comparing the weld width obtained by simulation with the actual weld width. The effect of different welding parameters (laser power, welding speed and zinc powder absorbent level) on the temperature field was analyzed. The results show that with the increases of laser power, the maximum temperature increases. With the increases of welding speed, the maximum temperature decreases. With the increases of zinc powder absorbent level, the maximum temperature increases but the rate of heating is falling, and begins to decrease after reaching the maximum value.

In this paper, the morphology and texture characteristics of the original β-grains in the deposited samples of TC21 titanium alloy obtained by laser solid forming (LSP) were studied, and the application of LSP in high performance metal processing was analyzed. The results show that the microstructure of TC21 titanium alloy is typical epitaxial growth columnar β grain, and the fiber texture characteristics are obvious; along the direction of deposition height, the size, morphology and volume fraction of α phase exist obvious inhomogeneity, which indicates that the precipitation of α phase in TC21 titanium alloy is more sensitive to the thermal history of forming process. When there is a transition to β, the phase selection occurs. In the absence of any intervention, the thermal history is different when the deposition position is different. Because of the lower temperature at the bottom of the deposited sample, the cooling rate is faster, and the temperature of the sample increases, α ′phase decomposes into fine α + β phase.

Laser welding technology is an important technical means to improve the machining precision, machining efficiency and service safety of ultra-high strength steel solid rocket motor. The article combed the research progress in all position welding, single pass full penetration welding, laser power modulation welding and welding molten pool simulation of the ultra-high strength steel structures at home and abroad. The potential application perspective of these research progress of key technologies in laser welding quality control of super-high strength steel solid rocket motor shell are systematically expounded. The research progress described in this paper can provide reference for the high quality and efficient manufacture of ultra-high strength steel solid rocket motor shell in china.

Based on the relationship between the material′s thermophysical parameters and temperature change, a 3D transient model of waterguided laser for removing paint on the surface of stainless steel matrix was established with Ansys, and the distribution of temperature field was obtained through numerical simulation during the simulation process. The influence of peak laser power, pulse width and processing speed on the distribution of simulated temperature field is found through single-factor simulation test. The simulation results show that the maximum temperature is concentrated in the center of heat source, and increases with the increase of laser peak power and pulse width, and decreases with the increase of processing speed. According to the maximum working temperature of 316 L stainless steel substrate and the melting temperature of fluorocarbon paint layer combined with the distribution of simulated temperature field, the optimum technological parameters were determined. The simulation predicted value was close to the test result, which proved the feasibility of the finite element simulation of water-guided laser on the surface of stainless steel substrate for paint removal.

Insulator is exposed to air for a long time, which may cause pollution flashover and threaten the safety and reliability of power grid. Based on the method of laser cleaning insulator contamination, the finite element simulation model of laser cleaning insulator contamination is established. The distribution of temperature field in the process of laser cleaning insulator contamination is studied. The central point of laser spot has the highest temperature and the maximum temperature of the contamination surface reaches 473 K when the average power density of the laser is 200 W/cm2. The temperature around the spot and in the depth direction decays rapidly. The calculation results show that the temperature increases linearly with the increase of power density and decreases with the increase of scanning rate. The maximum temperature of the substrate surface in the cleaning process is analyzed and it is considered that there is no thermal damage to ceramic insulator. Finally, laser cleaning experiment was carried out. The experimental results show that the laser cleaning can effectively remove the dirty layer and will not damage the substrate material. The maximum temperature in the cleaning process is slightly lower than the simulation results, and the error is within 8%.

In this paper, the safety configuration scheme and application of the pressure vessel laser welding production line are studied. According to the process specification of the laser welding production line, the number of main safety station equipment of the pressure vessel production line is configured. According to the requirements of the pressure vessel safety production and lean production, the layout of the welding production line is in the core area of the whole plant with its production process, from left to right. According to the laser welding process, the main laser welding stations are arranged, the auxiliary stations are arranged around the main laser welding stations, and the same process is arranged at the intersection of the conveyor line to reduce the distance of the conveyor line. And the main laser welding station special machine design of the production line, including equipment configuration, the characteristics of each special machine are discussed, including teaching characteristics, structural characteristics, laser welding characteristics and so on. After completing the layout of the whole production line, the workshop has straight and circular green channels, and the conveyor line is divided into cross straight conveyor line and trunk road conveyor line, so that the production is continuous, smooth flow and no stagnation.

It is difficult to repair the aero-engine titanium alloy blade when it is damaged after the service, so it is important to use the laser deposition technology to deep repair the titanium alloy blade. In this experiment, the mechanical properties of the repaired samples were tested by selecting reasonable laser deposition parameters. The results show that the room temperature tensile properties and the high fatigue properties of the repaired blades are comparable to those of the same batch of forgings, and the deformation of the repaired blades is 0.130.37 mm, which meets the design requirements.

AlSi10Mg thin-walled parts were formed by laser powder deposition technology. The method of negative defocusing of powder and prolonging the interval time of cyclical cladding process were adopted to solve the problems of rough edge and collapse of cladding layer. The microstructure and mechanical properties of the thin-walled part were analyzed both in the direction of scanning and deposition. The results showed that the optimal process parameters of single-pass cladding were laser power density P=370 W/mm2, scanning speed Vs=1.2 m/min, powder feeding rate Vf=8.5 g/min. The edge collapse of thin-walled parts was improved with prolonging the interval time of cyclical cladding process, but worsened by increasing the powder negative defocusing. The microstructure of the thin-walled parts was mainly fine dendrites and a small amount of equiaxed grains in the scanning direction, but the deposition direction was mainly coarse dendrites. The hardness, tensile strength and elongation of thin-walled parts in scanning direction are 130 HV, 280.12 MPa and 12.12% respectively, which are better than those in deposition direction.

In order to aviod the complexity of extracting feature points from 2D images and performing 3D reconstruction, and to meet the requirement of high precision of 3D measurement index of chip pins, this paper proposes a horizontal calibration method of point clouds based on difference of normal vectors by using point cloud processing technology, and combines this method with the minimum outer bounding box algorithm to eliminate the point clouds of chip internal pins. After clustering and segmenting the remaining point clouds, the plane equation parameters of each external pin, upper and lower surfaces of the chip are fitted by using the sampling consistency algorithm, and the midpoint of each pin area is solved. Calculate packege height, stand off and foot angle through the data obtained above. Finally, the effectiveness of this chip measurement scheme is verified by experiments.

In order to improve the accuracy of the four-quadrant detector used in the laser semi-active guidance system to locate the laser spot center, the positioning principle of the four-quadrant detector is analyzed, and the common positioning algorithms under different spot models are simulated and analyzed. Based on the analysis of the traditional positioning algorithm, aiming at the shortcomings of the positioning algorithm under the Gaussian flare model and combining the characteristics of the standard normal distribution, the positioning algorithm under the Gaussian flare model was reasonably improved. Through simulation analysis and design experimental verification, the results show that the root-mean-square error of the improved Gaussian algorithm is reduced by 60.4% compared with the traditional Gaussian algorithm, which improves the accuracy of positioning the laser spot center position and Linear range.

In view of the difficulties of traditional slope monitoring methods, such as heavy workload, incomplete data, difficult model establishment, poor effect and low accuracy, a slope deformation monitoring method based on three-dimensional laser scanning technology and T-splines surface fitting is proposed in this paper. In this method, firstly, the 3D laser scanning technology is used to scan the slope in the field to obtain the slope data; then the processed point cloud data are fitted by T-splines to obtain the five phase high-precision surface model and analyze the deformation of the whole slope body; the shape variables of the stability monitoring points in the slope body are selected for consistency test with the total station measurement data. The experimental results prove that the slope deformation monitoring method combining three-dimensional laser scanning technology and T-spline surface fitting meets the requirements of slope deformation monitoring.

This paper aims to solve the problem that the thermal-mechanical coupled simulation almost impossible to predict the distortion of industrial-scale parts based on the modified inherent strain method. Firstly, the small-scale model is selected to simulate the laser melting deposition (LMD) process, and the inherent strain values are extracted from the thermal-mechanical coupled results. Secondly, the distortion of the substrate with clamped end is predicted by the inherent strain method after thin-wall parts deposited on it. By comparing with the thermal-mechanical coupled results, the deviation of the maximum distortion on the center line of the bottom surface is 3.27%, and the average distortion on the edge line is 4.15%. Meanwhile, it is found that 3 mm is the optimal height of equivalent numerical layer in the inherent strain method. Finally, the scanning path is optimized. On this basis, the distortion results of industrial-scale camshaft model fabricated by LMD process is calculated. The results show that the maximum distortion of the camshaft is 1.47 mm. After removing the support, both ends are warped upward, and the maximum distortion increases to 2.16 mm. The whole calculation process only takes 9.5 h, which is of great significance for the rapid distortion prediction of industrial-scale LMD parts.

For laser cutting equipment that uses galvanometers for processing, in order to improve cutting accuracy, the galvanometer must be calibrated. The common calibration method is using galvanometers to cut a matrix of fixed patterns (usually called mark point), and then use the camera to read the specific position of each pattern in the matrix one by one, and calculate the correction grid based on this and implement the correction. Circle and cross are two commonly used mark point shapes. In this paper, a comparative experiment was carried out on the influence of the two kinds of mark points on the calibration accuracy of the galvanometer. The results show that the accuracy of the circular mark point calibration is better. When the standard deviation of the repeated positioning of the platform is about 1 μm, the average error of the galvanometer after the circular mark point calibration is 1.99 μm, and the standard deviation is 1.09 μm; the average error of the galvanometer after the cross mark point calibration is 2.95 μm, the standard deviation is 1.60μm.

When using the TDLAS technique to measure the CO2 concentration distribution in a high-temperature combustion environment, due to the non-uniform distribution of the flow field and the weak absorption of the CO2 spectral line in the near-infrared band and easy to be interfered by the absorption of H2O, the reconstruction measurement of the two-dimensional concentration field is especially difficult. In order to solve the above problems, this paper proposes a two-dimensional concentration distribution reconstruction method of non-uniform flow field based on TDLAS technology. This methodbased on the absorption line R(50) of CO2 having the characteristic that the amplitude of R2f/1f at the center frequency approximately meet with linear superposition relationship combines the absorption information of a single spectral line with the algebraic iterative algorithm to realize the reconstruction of the CO2 concentration field of the non-uniform flow field. The simulation and experimental results show that the maximum relative error of the CO2 concentration measured by the orthogonal projection mode and the result of the flue gas analyzer is less than 13%, and the average relative error is 4.16%. The overall distribution trend is similar to the result of the flue gas analyzer.

For the limited power capacity of single dipole antenna, the lens antenna and photoconductive antenna array were designed to improve the radiation performance. At first, the lens antennas with radius of 0.5 mm, 1.0 mm and 1.5mm were designed, and the influence of the radius and extension length of the lens on the antenna performance was studied. The results indicated that when the ratio of extension length to radius was 0.28, the directivity of the lens antenna was better, and the peak gain of the 0.5 mm lens antenna reached 26.1 dB. Further, a 2×2 photoconductive antenna array was designed. The radiated power of the array element was about 10 μW, and the signal-to-noise ratio of the array element was about 50 dB. The experimental results showed that experimental results show that the combination efficiency of terahertz signals was close to 90%, which improved the output power of terahertz. It provided basis for the design and manufacture of miniaturized antenna arrays with more array elements. The factor affecting the noise generated by the terahertz photoconductive antenna was also studied.

The characteristics of the semiconductor laser current control output optical power change were combined by field effect tubes and precision op amp, and a semiconductor laser power supply control system, power source real-time data acquisition, multiplex current output, feedback adjustment stability. The active temperature control strategy design is used, and the temperature is collected in real time. The control fan speed is compared to the set temperature, ensuring the temperature constant, and further ensuring that the laser output optical power is stable. The test results show that the power control system current is accurately adjustable from 0 to 20A, the modulation frequency reaches 50 kHz, and the output laser power error is controlled at ± 2%, which has the advantages of high frequency modulation performance，stable output and active temperature.

In order to improve the accuracy and stability of one-dimensional position sensor detector (PSD) laser micro displacement measurement, a displacement measurement experiment system is designed. The system uses PSD as the displacement detection sensor. The current to voltage (I/V) signal conditioning circuit is designed with OPA211 low noise operational amplifier. The single chip microcomputer STM32F103 is used as the controller to control the moving laser light source by the stepping motor slide, and the ADS1256 is used to collect displacement signal. The automatic displacement and displacement measurement system is realized. The experimental results show that the system has a good linearity in the range of 014 mm, the displacement measurement error is small, and the measurement error dose not exceed ±20 μm.

Aiming at the problem of detection of floating targets by water surface cleaning robots, a method of fusion detection of 3D lidar point cloud data and visual information is proposed. First, the visual recognition part adopts CornerNet-Lite target detection network, through the training of a large number of samples to achieve the detection of floating objects on the water surface, and obtain the type and confidence of candidate targets. Then, through the calibration of the camera and lidar, the lidar three-dimensional point cloud data is projected onto the two-dimensional pixel plane, and the confidence of the lidar detection target is defined according to the concept of relative area size. Finally, adjust the confidence weight ratio of lidar and camera detection targets to form a new decision function, and determine whether the target is detected by comparing the size of the decision function with the set threshold. Experimental results show that this method has higher accuracy than CornerNet-Lite algorithm alone, eliminates the effects of water reflection and ripples, and reduces the false alarm rate.

In this paper, the thermal effect of laser welding is studied by ANSYS software combined with experiments under the environment of uneven mechanical properties. The stress field of laser cladding and laser induction composite cladding is simulated by ANSYS, and the stress can be reduced by 3/4; the laser induction composite cladding can improve the cladding efficiency to a certain extent, because of the induction, it will slow down the laser area cooling. However, with the increase of temperature, the heat affected zone becomes larger and the cladding speed is accelerated. After induction, with the cooling process, the highest temperature appears in the center of the workpiece, not in the cladding layer. The reason is that the final cooling here results in the generation of compressive stress, which can be obtained by solving the stress field. Compared with the measured temperature curve, the simulated temperature curve has good consistency with the measured temperature curve when the temperature range of the infrared temperature monitoring system is 400~1 200 ℃. Compared with pure laser, when the temperature is higher than 500 ℃, the existence time of laser induced composite cladding pool is significantly longer, which extends from 1.5 s to more than 60 s, which significantly alleviates the severe cooling and heating. In the depth direction, the stress distribution has a certain regularity, and the linear expansion coefficient is different due to the difference of cladding layer and base material. With the increase of depth, the stress decreases. According to the distribution of temperature field, the center of the workpiece is the last cooling part.

Coaxial powder feeding laser cladding is a surface strengthening method used to prepare a metallurgical bonding coating on the material surface to improve its performance. To better coupling the powder flow with the flat-top laser, effectively improve the powder utilization rate, and ensure the uniformity of power, this research used simulate software, high-speed camera and image processing software to establish the relationship between the laser cladding processing parameters and the power flow upon the laser focus pot. A better powder feeding parameters were designed by using fluid analysis software and combined with experiments, which improves the powder utilization rate and improves the quality of cladding forming. By using three-dimensional modeling and software analysis, the influence of process parameters on the coupling effect of coaxial powder feeding were investigated. When the powder disk speed is 1.2 r/min and the carrier gas flow rate is 4 L/min, the coupling of powder flow and laser beam has better performance, the powder flow utilization rate is high, and the convergence characteristics are good, The cladding layer has a good morphology.

In order to obtain a coaxial powder feeding nozzle matching a 3 kW broadband rectangular laser, the discrete phase model of Fluent software was used. Four factors and four levels of orthogonal simulation experiments were carried out to study the influence of the structural parameters on the concentration of the powder and the size of the powder spots. The results show that the powder concentration of the broadband coaxial powder feeding nozzle obeys the Gaussian distribution in the axial and radial directions, which verifies the rationality of the nozzle structure. The effects of the four factors on the powder concentration from large to small are: inclination angle, vertical height, contraction angle and outlet gap; when the optimal structural parameters are used, the nozzle can be formed a rectangular powder spot with a size of 3.08 mm×3.08 mm and a maximum density of 32.29 kg/m3 on a plane that 24.6 mm away from the powder outlet. In the end, the powder feeding experiment was carried out to verify its rationality, which provided a basis and reference for subsequent laser additive manufacturing experiments.

Thermal elastic-plastic finite element method was used to conduct numerical simulation for the hybrid welding test of 304 stainless steel based on Ansys Workbench software platform. The residual stress and deformation results obtained by numerical calculation were in good agreement with the welding test results. The changes of temperature field and structure field under different laser power are analyzed and the results show that the laser power has an effect on the maximum deformation and the peak value of residual stress. The larger the laser power is, the more the maximum deformation and the peak residual stress of 304 stainless steel are. Because the energy input of laser welding is concentrated, the influence of laser power on thermal deformation and residual stress distribution is not obvious.

An optical resonator with a 90° cone reflector has a better misalignment tolerance because of its special structure. In this paper, a high-power transverse flow CO2 laser is selected as a model for numerical simulation, and the Fox-Li iterative approach has been used to analyze the output beam mode of the laser resonator. Calculation process is simplified when the beam transformation occur at 90° cone reflector. Because a 90° cone reflector is a no-paraxial device, and linear polarization is not preserved by the reflection. A modified vector method is used to analyze mode distribution of the output beam, and the results show that when the reflectivity difference between P and S polarizations is more than 3%, the radially polarized or azimuthally polarized beam with a polarization purity of 1 can be obtained by such resonator.

In this paper, the laser ultrasonic detection technology in pipeline crack detection is applied to the test of X80 pipeline. The finite element method based on thermal-solid coupling is used to simulate the process of ultrasonic generation by laser irradiation on the pipeline. And from the distribution map of the surface temperature field of the pipeline, the simulation results are analyzed and relevant conclusions are drawn. By studying the propagation characteristics of ultrasonic waves excited by pulsed laser in the pipeline, the vibration curves of ultrasonic waves with and without cracks on the surface of the pipeline are obtained, and the effect of crack depth on ultrasonic surface waves is described. A non-contact experimental platform was established to verify the simulation method. Experiments show that the method can effectively simulate the process of laser ultrasonic detection of pipelines.

The particle size distribution of nebulizer is an important index to evaluate the performance and therapeutic effect of nebulizer. The laser diffraction particle size analyzer with Mie scattering algorithm was used to research the influence of different compression nebulizer, nebulization cups, detection carriers and detection environments on the size distribution of particles. The experiment showed that: under the same detection environment and conditions, the output flow rate of the compressed nebulizer is positively correlated with the particle size distribution and proportion, and inversely correlated with the particle size under the same size distribution and proportion; the use of matching nebulization cup can ensure the effective particle concentration distribution; according to different carriers, only by reasonably setting the particle size distribution and proportion parameters, can the performance test of atomizer be comparable. In order to avoid the interference of the external light environment, the detection should be carried out under the condition of no external light as far as possible， so that the obtained data can be reliable.

In order to evaluate the clinical effect of low dose laser therapy on postoperative complications of mandibular impacted third molars, 22 randomized controlled clinical trials on complications of mandibular impacted third molars treated with low dose laser were obtained from CNKI, Wanfang, CBM, Pubmed, Embase and Cochrane library databases. The literature quality was evaluated by Cochrane Handbook 5.1.0 “bias risk assessment” tool. The meta analysis was conducted by Review Manager 5.3 software. The sources of heterogeneity were detected by sensitivity analysis and subgroup analysis, and publication bias was detected by funnel chart. The results of Meta analysis showed that low-dose laser therapy could significantly relieve the trismus, postoperative pain and swelling on the 2nd and 7th day after operation. The subgroup analysis was carried out according to different irradiation location and different output power. the results showed that combined intraoral and extraoral irradiation and intraoral irradiation could significantly relieve the trismus, swelling and pain 2 days after operation. Extraoral irradiation could not significantly relieve the trismus, swelling and pain 2 days after operation. Output power ≤ 100mW could significantly relieve trismus, swelling and pain 2 days after operation, output power 100~≤300 mW or ＞300~≤500 mW could significantly relieve postoperative pain, but could not significantly relieve the trismus and swelling 2 days after operation. Conclusion: low dose laser therapy can effectively relieve the pain, swelling and the trismus caused by impacted third molar extraction, and the irradiation mode and output power may affect the effect.