In order to study the difference in tensile mechanical properties between laser cladding 304 stainless steel and rolled 304 stainless steel, a single laser cladding 304 stainless steel experiment was carried out on the surface of 27SiMn steel substrate at different laser scanning speeds, and the macroscopic morphology and microstructure of the single pass cladding layer were obtained. A multi-pass lapping experiment was carried out at a single pass laser scanning speed of good formability, and the cross-section macroscopic morphology of the cladding layer was obtained. Finally, multi-layer accumulation was carried out to obtain the tensile mechanical property curve and the tensile fracture morphology. The results show that with the increasing laser scanning speed, the single pass cladding layer has poor formability. Under the condition of 50% lap rate, the obtained cladding layer has good formability. The tensile strength of laser cladding 304 stainless steel is 551.32 MPa, and the tensile fracture morphology shows obvious ductile fracture, the tensile strength of the original rolled 304 stainless steel is 713.11 MPa, and the tensile fracture morphology shows obvious brittle fracture.

AlSi10Mg alloy displays excellent properties, such as good air tightness, good fluidity, small thermal cracking tendency, small shrinkage and high strength. It is widely used in automotive, aerospace and other fields. With the increasing demand for lightweight components, the structure and shape of aluminum alloy parts become more complex, and traditional casting techniques is difficult to meet market demands. In view of this, the rapid solidification of AlSi10Mg alloy by selective laser melting (SLM) was studied. The AlSi10Mg alloy was prepared by selective laser melting (SLM) technique. The microstructure, phase composition and mechanical properties of the alloy after laser treatment and melting at different temperatures were analyzed. The experimental results show that the microstructure of the AlSi10Mg alloy by selective laser melting consists of the matrix region and the heat-affected zone. The molten pool between the different layers are elliptically superposition. The width of the molten pool is about 250～300 μm, and the depth is about 100～200 μm. After the aging treatment, due to the diffusion of Si atoms, the eutectic silicon in the dendritic state is completely transformed into a granular shape, and as the aging temperature increases, the average size of the eutectic silicon increases. The phase of the alloy consist of Al matrix phase and Si phase before and after the aging treatment. However, after aging, the peak of the Al phase shifts to the left due to precipitation of Si atoms in the supersaturated Al(Si) solid solution. After the selective laser melting, the alloy has the highest hardness value, and the hardness value decreases sharply after the aging temperature. When the temperature rises at any time, the hardness value decreases. Selective laser melting technology can effectively refine the microstructure of AlSi10Mg alloy and significantly improve the mechanical properties of the alloy.

The nano tungsten carbide and cobalt-based alloy powder containing ZrO2 and SiO2 were coated on the surface of the test ball valve substrate by using a 5 kW fiber laser. The microstructure of the cladding layer was observed and analyzed, and the microhardness and friction performance of the strengthened layer was tested. The test results show that the microstructure of 50% mass fraction cobalt, 40% mass fraction nano tungsten carbide and 10% mass fraction metal oxide sample is uniform and compact without cracks and pores. The average thickness of the laser cladding strengthening layer is 1.4 mm, and a metallurgical bond is formed between the reinforcing layer and the substrate. There are network-like and point-like distribution strengthening phases in the strengthening layer. The network-like strengthening phase is mainly WC, and the point-like distribution strengthening phase between the networks is mainly metal oxides ZrO2 and SiO2. The average microhardness of the surface layer of the strengthening layer is 65 HV, which is more than 110% higher than that of the matrix material. At 20 ℃ and 300 ℃, the sample wear amount decreased by 75.3% and 68.2% compared with the substrate. Among them, the network-like WC strengthening phase enhances the hardness of the coating. The metal oxide strengthening phase dispersed between the networks enhances the wettability of the alloy powder and reduces the generation of pores and inclusions. The main wear mechanism of the strengthening layer is a small amount of adhesive wear, and the strengthening layer is beneficial to improve the wear resistance of the ball valve and the service life in actual working conditions.

The ANSYS finite element software is used to established a single-layer multi-trace stress field model by thermal-structural indirect coupling method, and the stress field of AlSi10Mg fabricated by selective laser melting is simulated. The distribution and evolution of internal stress and the influence of different exposure times and point distances on residual stress are analyzed. It is found that after the temperature is homogenized, the residual stress in overlap region of molten pool is high (the highest residual stress), and the residual stress in the central region is low (the lowest residual stress). As ET and PD increase, the maximum residual stress gradually increases. However, by further increasing PD, the formation of defects leads to a decrease in stress. As the ET increases and the PD decreases, the minimum residual stress increases.

The effect of layer thickness on the density, microstructure and mechanical properties of ti-5al-2.5 Sn (Ti-Al-Sn) titanium alloy was studied. The results show that with the decrease of thickness, the energy density of the laser body will be increased, and the Ti-Al-Sn alloy sample with a density greater than 99.0% can be produced when the layer thickness reaches 60 mu m.Using SLM technology of Ti-Al-Sn alloys mainly includes three kinds of microstructure, the needle alpha′ martensite structure respectively, needle alpha′ martensite + island shape alpha m mixed groups and the pure form of alpha m group. As the thickness of the layer increases and the scanning rate slows down, the cooling rate of the sample decreases gradually. When the thickness of the layer was increased, the mechanical properties of the ti-al-sn samples were reduced. The Ti-Al-Sn samples obtained at different layers were characterized by ductile fracture at room temperature.

Laser cladding remanufacturing technology has been widely used in parts repair for decades. When applied, the cladding layer is prone to uneven formation and produce defects such as pores and cracks. The quality of the cladding layer directly affects the repair effect of parts. Therefore, effective control of the quality of the cladding layer is the key to the application of this technology. The quality evaluation methods based on the cross-section morphology, dilution rate and heat-affected zone width of the cladding layer are analyzed. The quality monitoring technology based on image and temperature and so on as monitoring signals is introduced. The adaptive control systems is reviewed, and then the basis for the improvement of the forming quality of the cladding layer is provided based on the current research progress.

Laser and plasma arc are used as two kinds of high energy beam heat sources for composite welding. Compared to laser welding alone, it can achieve greater penetration and higher welding speed. The 304 stainless steel plates with 2 mm and 4 mm thickness are used as the base metal for flat plate welding and butt welding respectively. The weld formation and the plasma shape under different laser powers are observed. Under the premise of ensuring double-sided formation for single-sided welding, the optimal current matching range of different laser powers and the adaptability of 4 mm thick stainless steel in the butt welding for gap and misalignment are studied in the 2 mm flat-plate high-speed welding . The tests show that under the premise of ensuring double-sided formation for single-sided welding and a minimum welding speed of 1 000 mm/min, the larger the laser power is, the wider the current range is matched, and the higher the welding speed can be achieved. Laser-plasma arc hybrid welding has good adaptability to gap and misalignment in flat-plate butt welding, the maximum adaptive gap is 0.5 mm and the maximum adaptive misalignment is 1.5 mm.

Aiming at the weld seam formation rules and mechanism of 1J79 soft magnetic alloy 0.3 mm thick thin sheet pulsed laser welding, the control experiments of different laser power, pulse width and welding speed are designed. The results show that the thin sheet pulsed laser welding weld is formed by a series of equally spaced weld spots, which is a typical remelting feature. The weld cross section has a fusion line formed by multiple melting. The laser power and pulse width determine the penetration state of the weld, which has a great influence on the front and back surface of the weld and has little effect on the overlap rate of weld spots. The welding speed determines the weld spot overlap rate, which affects weld continuity and weld surface quality. Under the condition of full penetration welding, when the weld spot overlap ratio is more than 62%, a thin sheet pulsed laser welding weld with good shape and uniform surface can be obtained.

Using 10 mm Q345B steel plate as experimental material, laser-MAG hybrid welding was used to explore the feasibility of high speed backing welding of Y-shaped groove by adjusting welding current, wire feeding speed, welding speed, wire spacing and other hybrid welding parameters. During the experiment, the behavior characteristics of welding arc and droplet transition were analyzed by means of high-speed camera and voltage and current collector. The results show that laser-MAG hybrid welding can realize high speed backing welding with a maximum of 6 mm blunt edge and a minimum angle of 35°groove. The welding speed is 1 m/min, and the adaptability to the gap and the wrong side is better. The matching of laser and arc current has a great influence on the welding stability.

To research the effects of the pre-welding laser cleaning technology applied to the automobile plates coated with Al-Si covering, the Al-Si coating is cleaned firstly. And then the automobile plates are butt welded. Comparing with the tensile tests’ outcomes of welding the laser power P＝50 W, scanning speed S＝1～4 m/min, scanning times N＝2, which remains 20～21 μm coating thinckness. Meanwhile, the tensile strength of the welding line can satisfy 94% of the base metal, and as fast (4 min per component) as the efficiency could.

In order to study the effects of laser cleaning on the surface microhardness, surface roughness, corrosion resistance and surface chemical composition of the high-speed train slip ring, a 1 064 nm pulsed laser was used to clean the surface of the collector ring. The surface roughness and microhardness were measured before and after cleaning by surface roughness tester and microhardness tester. The corrosion resistance was measured before and after cleaning by an electrochemical workstation, and the surface chemical composition was analyzed by X-ray fluorescence spectroscopy. The results show that the surface microhardness after laser cleaning reaches 210.7 HV, which is higher than the hardness of the substrate. The surface roughness after cleaning reaches Ra 2.5, which is 68.7% lower than that of the uncleaned surface. Moreover, the surface corrosion resistance of the slip ring after laser cleaning is enhanced compared with the substrate. The oxygen content of the slip ring after laser cleaning is decreased compared with the uncleaned surface, and the oxygen content is 3.840%.

Aiming at the cleaning requirements of surface oxide after arc welding of stainless steel car body with excellent performance. The process, mechanism and surface element test after laser cleaning of stainless steel post-weld surface by fiber laser were studied. The effects of laser power, laser frequency and cleaning times on the cleaning process were investigated by comparative experiments with different process parameters, and two possible stripping mechanisms of post-weld oxide on stainless steel surface were proposed. The stainless steel surface after laser cleaning and mechanical grinding was tested. Comparing the results, it was found that the surface cleanliness after laser cleaning was superior than that of the traditional mechanical grinding. This discovery contributes to the widespread promotion of laser cleaning in stainless steel surface dirt cleaning applications.

In order to achieve the green environmental protection requirements of removing the bridge protective lacquer layer, the application of layer cleaning technology in the removal of paint from bridges was carried out by using the short pulse and high peak power characteristics of pulsed laser. Through the orthogonal test method, the effects of process parameters such as average power, frequency, scanning speed, number of scans and other parameters on the quality of laser cleaning, as well as the influence weight of each process parameter, and the best process parameters are obtained. The best parameters are average power 50 W, frequency 70 kHz, scan speed 300 mm/s and 1 scan. According to the optimized parameters, a good cleaning area with roughness Ra 6.6 μm and Rz 30.1 μm without paint residue is obtained, which verifies the feasibility and scalability of laser removal paint in bridge protection applications.

As a very popular metal surface cleaning process nowadays, Laser de-rusting is great development prospect in the field of rust removal on the surface of HT200. A 1 064 nm wavelength of pulsed fiber laser have been investigated in this experiment, the influence of laser power, laser frequency, scanning speed and scanning times on rust removing effects have been studied by the by the mechanism and model of laser de-rusting in this article. The good effect of laser de-rusting was demonstrated by observing the content of elements on the surface of HT200 and scanning electron microscope observation after cleaning. Hardness and surface roughness measurements show that hardening occurs on the surface of HT200 under the action of laser, and the surface of HT200 reaches the standard of finishing, and the cleaning grade reaches Sa 2.5, thus achieving the ideal laser cleaning effect.

The laser edge cleaning process in the preparation process of a-Si∶H thin film solar cell was experimentally studied by using a 1 064 nm MOPA fiber laser. The effects of process parameters such as laser pulse width, filling line spacing, scanning speed and others on the processing results were discussed. Under the parameters of pulse width 100 ns, repetition frequency 80 kHz, filling line spacing 35 μm, output power ratio 100%, scanning speed 3 500 mm/s, spot overlap ratio wx＝0.83, wy＝0.88, a good edge cleaning effect was obtained on the surface of the clear-edged area with a resistance ＞1 000 MΩ.

When the femtosecond laser is used in surface micro-structuring through a high NA objective lens, , too short of focal depth affects the processing performance. The focus discrete effects of the correction collar on the objective lens is analyzed. A method of holographic defocus control using spatial light modulator (SLM) is proposed. By varying the period of the annular blazed grating which is based on the diffractive axicon computer generated hologram (CGHs), defocus control is performed to form a long depth of focus. The distribution of focus axial intensity is expressed in the form of a row of micropores which are processed on the surface of polyimide film (PI), and the distribution is consistent with the simulation result. The defocusing process is performed using a 40× objective lens of 0.6 NA. When the center period of the annular blazed grating is 200 μm and increase progressively from inside to outside by 400 μm, a 50.90 μm uniform depth of focus can be obtained, which is 8.28 times the length of the depth of focus obtained by directly processing with high NA objective lens. In addition, the composite defocus process is performed by SLM and correction collar to further homogenize the entire region of depth of focus.

In order to solve the problem of poor microhole quality in millisecond/nanosecond laser processing, the 515 nm picosecond laser was used to ring cutting stainless steel with a thickness of 0.1 mm to process microholes with a diameter of 100 μm. Laser confocal microscopy was used to observe and characterize the morphology and quality of the processed microstructure. The effects of laser energy density, scanning speed and defocusing amount on the morphology and quality of microholes after processing were studied. The experimental results show that the energy density has a direct influence on the inner wall quality of the microholes. Controlling the energy density below 6.45 J/cm2 can effectively reduce the heat affected zone of the inner wall of the microholes under the premise of ensuring the removal ability. At the same time, it is found that appropriately increasing the scanning speed can improve the quality of the microhole incision and the inner wall of the ring cutting. When the laser energy density is 6.45 J/cm2 and the scanning speed is 200 mm/s, the hole taper is 2.72 degrees. As the scanning speed increases, the taper decreases, and finally stabilizes at about 2.29 degrees. The taper of the hole can also be reduced to some extent by the positive defocusing process. The results of this study show that the optimized process parameters can process microholes with small heat affected zone, good edge quality and small taper.

The water-guided laser processing technology exhibits superior processing capability due to the small thermal influence of the surface of the processed material and strong processing depth. Based on the mechanism of water-guided laser processing, a new water-guided laser shrinkage guide method is proposed, and the mechanism of shrinkage is analyzed. The feasibility of the processing method is verified by the high-efficiency coupling test and material processing test between laser and the shrinkage column. The test results show that when the air pressure is constant, the velocity, diameter and length of the laminar flow column of shrinkage increase with the increase of water pressure. When the water pressure is constant, with the increase of air pressure, the velocity of the laminar column increases, and the diameter and length gradually decrease. At the same time, the processing experiment is carried out by adjusting the laser and the laminar water column to couple the optimal conduction laser conditions. Compared with the processing results in air, the water-air shrinkage conduction laser processing technology has obvious improvement in the heat-affected zone and thermal accumulation, and the feasibility of the new water-air shrinkage conduction laser processing technology is preliminarily verified.

Taking W6Mo5Cr4V2 (M2) high speed steel cutter material as sample, the effect of laser shock on fatigue performance of M2 material is studied. Experiments of laser shock processing, metallographic observation, residual stress measurement and fatigue performance test on M2 samples are conducted. The mechanism of laser shock on surface microstructure, residual stress and fatigue performance is analyzed. The results show that after laser shock, the surface microstructure grains of M2 samples are refined and the grain boundaries increase, forming lattice imperfection such as dislocation and twin crystal. A certain depth of residual compressive stress layer is caused within shocked area. The residual compressive stress on cross section is decreased from surface to center. The surface residual compressive stress is maximum. In a certain distance from surface, the residual compressive stress is stable. Before and after laser shock, the average fatigue life of sample is significantly improved. Different laser shock process parameters have differert effects on the fatigue performance of the sample. By laser shock, the surface material of the M2 high speed steel is strengthened and its fatigue performance is improved.

The numerical simulation method was used to study the spectral characteristics of chirped Gaussian pulses constrained by Gaussian aperture in a dispersive medium. A model of chirped Gaussian pulses constrained by Gaussian aperture in a dispersive medium was established. The expression of the power spectrum was derived. Based on the power spectrum expression, the influence of factors such as the Gaussian aperture radius, chirped parameters, the distance of propagation , and off-axis radius on the spectral characteristics was simulated and analyzed. The results show that the influence of the chirped parameter on the spectrum depends only on its absolute value, the chirped parameter deviates the near-field spectrum from the Gaussian distribution, and the limitation of Gaussian aperture can effectively suppress this deviation. The larger the absolute value of the chirped parameter, the slower the spectrum in the far field is attenuated in the direction of propagation, the faster the attenuation in the off-axis direction, and the more concentrated the energy is on the optical axis. The spectrum attenuates faster in the direction of propagation with the limitation of Gaussian aperture than that without it, while slower in the off-axis direction, and the red-shift and the spectral width compression are significantly reduced in the off-axis direction. As the distance of propagation increases, the spectrum shifts blue on the axis and approaches the Gaussian distribution in the far field and the center frequency of the spectrum approaches a asymptotic value.

At present, most of the laser scanning galvanometer control boards need to connected the industrial computer to work under the Windows operating system, which is very inconvenient to operate on the handheld laser cleaning equipment. In order to improve the integration and effectiveness of the laser scanning galvanometer, a laser galvanometer assist control board based on XY2-100 protocol is designed, which uses XC7A100T chip of XILINX′s ARTIX-7 series as the main control chip. The common I/O port of the XC7A100T chip is used to generate 4-channel control signal for controlling the galvanometer, and the scanning range and scanning speed of the laser galvanometer are adjusted by a knob, so that the galvanometer of the handheld laser cleaning equipment can work independently.

Aiming at the problems of easy deformation, complicated debugging and inconvenient operation the laser drilling process for the soft micro-spray belt with the thickness of 1.2 mm or less, a set of micro-spray belt laser drilling positioning fixture with high flexibility and versatility is designed. The fixture is primarily composed of a support mechanism, a centering mechanism and an anti-penetration mechanism. Through experimental improvement, it can ensure the precise positioning and alignment of the micro-spray belt with the bandwidth within 100 mm, and realize the dynamic continuous precision drilling of the micro-spray belt with a dynamic on-line speed of 57 m/min, which achieves the expected production effect and is suitable for the industrialization development requirements of the micro-spay belt, and serve as a reference for the processing fixtures design of the same type of parts.

When the pulsed laser detection system is applied to the conventional ammunition process, the single-beam forward detection structure cannot meet the circumferential positioning requirements. At the same time, the system structure requirements are as simple as possible, so the traditional beam layout cannot be directly applied. Therefore, a multi-beam large field of view pulse laser circumferential detection scheme is proposed. According to the optical field characteristics and detection requirements of the laser transceiver system, based on the aspherical optical design theory, the array lens optical system of laser shaping expansion and large field of view is designed, and the narrow pulse high current pulse laser driving circuit, high sensitivity and high signal to noise ratio photoelectric amplifying circuit are designed. Based on the FPGA target azimuth discrimination and anti-interference strategy, the anti-interference ability of the system is effectively improved. The projectile rendezvous is established，and the model is also analyzed for target capture rate. The prototype machine is processed and static experiments are carried out. The results show that the prototype can effectively detect the short-range targets of not less than 5 m, and realize the 360 degree large-field circumferential detection of conventional ammunition laser proximity fuze.

The airborne LiDAR (Light detection and ranging) scanning system consists of laser scanner (LS), global navigation satellite system (GNSS) and inertial navigation system (INS), which has a wide range of practical value and application prospects in 3D measurement and driverless driving. The installation error angle of the scanning system is one of the main factors affecting the accuracy of the laser point cloud. A calibration method for the installation error parameters of the airborne LiDAR scanning system without ground control points is proposed. The scan system placement parameter calibration model is deduced by repeatedly scanning the same name point, and finally the least squares iteration method is used to solve the optimal value of the calibration parameters. The feasibility and effectiveness of the proposed method are verified by unmanned airborne laser scanning system experiment, which can obviously improve the quality of the point cloud generated by the scanned data, which has certain feasibility and practicability.

Experiments and simulations of multi-pulse laser damage CCD detectors were carried out. Using a laser with a wavelength of 1 064 nm and a pulse width of 100 μs, the laser damage experiment was performed on the CCD detector under the operating conditions of 1, 3 and 5 Hz. The three stages of multi-pulse damage CCD were observed and the CCD detection were obtained. The simulation model of multi-pulse laser damage CCD detector was established. The finite element method was used to simulate the damage threshold of CCD. The research shows that under the same frequency of laser irradiation, the damage threshold of CCD decreases with the increase of the number of laser pulses. When the number of pulses is constant, the repetition frequency is low, and the repetition frequency has little effect on the CCD damage threshold. The simulation results agree well with the experimental results.

In order to overcome the inefficiency of traditional stockpile volume measurement methods, a 3D laser scanning technology based stockpile modeling system was designed and implemented, which allows the operator to quickly make a characteristically-detailed 3D model by circling the stockpile with the scanning device in hand. The scanning device uses a 2D laser scanner to scan the stockpile with high-precision sensors to track its position and orientation, and then integrates discrete scanning points into a 3D point cloud for modeling. The algorithm optimization was conducted upon the characteristics of the scanner and the stockpile to reduce the time consumed for the noise reduction of scanning points and to improve the efficiency of 3D modeling and volume calculation. As shown by the measuring experiment of several 3000～30000 m3 coal piles, the 3D modeling of the stockpile can be completed in a few minutes which mainly dependent on the walking speed of the operator circling the stockpile. The 3D model and its volume can be acquired within 20 seconds after the measurement completes, and the accuracy is within 0.75%.

In recent years, researchers from various countries have invested in the field of micro-processing research in order to make the processing technology more accurate and error-free. Femtosecond laser has become a hot research topic at home and abroad with its extremely high peak intensity, small damage threshold and high focusing force. In this paper, the research progress of femtosecond laser in the field of microfabrication is reviewed and the research progress in the fields of microfabricated metal materials, integrated optics, biomedical and nano-fabrication is discussed in detail. Finally, the existing problems of femtosecond laser development are pointed out and the expectations for the future are put forward.

With the rapid development of modern society, the energy and environmental issues have become increasingly prominent. Supercapacitors have attracted much attention because of their high power density, high energy density and long service life. The electrode material and structure determine the performance of the supercapacitor. Therefore, the development and optimization of the electrode material preparation process has become the top priority of research. The research status and development trend of supercapacitor electrode materials prepared by laser fine processing are introduced.

Objective: To investigate the clinical efficacy of Nd:YAG laser combined with Er:YAG laser as an adjunctive therapy on generalized aggressive periodontitis (GAgP). Methods: Twelve patients with generalized aggressive periodontitis were randomly assigned into 2 groups, the control group (subgingival scalling+ SRP) and the experimental group (subgingival scalling+ SRP+ laser). Clinical examination of patients with pre-treatment, 1 month, 3 months after treatment, the clinical parameters including probing depth (PD) and bleeding index (BI) were measured.Results: PD and BI in the experimental group were lower than those in the control group at 1 month and 3 months after treatment (P＜0.05).Conclusion: Nd:YAG laser combined with Er:YAG laser as an adjunctive therapy on subgingival scalling + SRP for the treatment of generalized aggressive periodontitis can achieve better curative effect than the simple subgingival scalling+ SRP.