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2008
Volume: 35 Issue 2
30 Article(s)
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Research Article
Pulse Duration Stability of Stimulated Brillouin Scattering in SF6 Pumped by a Broadband KrF Laser
Lin Dianyang, Jiang Xiaocun, Wang Shujie, Wang Shuangyi, and Lü Zhiwei
The pulse duration stability of stimulated Brilloiun scattering (SBS) in SF6 gas pumped by a broadband KrF laser was studied theoretically and experimentally. The dependence of the pulse duration stability of SBS on the power density stability, pulse duration stability of the pump laser and medium gas pressure was obtaThe pulse duration stability of stimulated Brilloiun scattering (SBS) in SF6 gas pumped by a broadband KrF laser was studied theoretically and experimentally. The dependence of the pulse duration stability of SBS on the power density stability, pulse duration stability of the pump laser and medium gas pressure was obtained. The results showed that the pulse duration stability of SBS is directly correlated with the stability of the pump laser; the pulse duration stability of the SBS increases as the stability of the pump laser does. The instability of SBS pulse duration occurrs when pulse duration and energy of pump laser were instability. Under lower pump power density, the influence of the pulse duration and pump laser energy fluctuation on the pulse duration of SBS is not ignored; but under higher pump power density, the pulse duration stability of SBS is mainly influenced by the fluctuating in pump pulse-width. The experimental results were analyzed and discussed. And for obtaining better pulse duration stability of SBS, pump laser with stable pulse duration should be used. And enhancing pump density of pump laser and medium gas pressure without other nonlinear effects are also necessary..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 163 (2008)
Laser-Diode Arrays Symmetrically Side-Pumped Thin Disk Laser
Zhang Shenjin, Zhou Shouhuan, Lü Huachang, Tang Xiaojun, Guo Lina, Wang Chao, Du Tao, and Li Fei
The five laser-diode (LD) arrays symmetrically side-pumped Nd:YAG thin disk laser is investigated experimentally and simulatively. The coupling system is composed of astigmatic lenses and hollow wave-guide, and a 15 mm×1.5 mm Nd:YAG disk was used during the primary experiment. The average output power of the diskThe five laser-diode (LD) arrays symmetrically side-pumped Nd:YAG thin disk laser is investigated experimentally and simulatively. The coupling system is composed of astigmatic lenses and hollow wave-guide, and a 15 mm×1.5 mm Nd:YAG disk was used during the primary experiment. The average output power of the disk laser was 65.7 W in experiment with 10.5% optical-to-optical efficiency, and there is good fluorescence distribution in medium. The pump distribution of thin disk is obtained and analyzed by the ray tracing method. The divergence characteristics of the fast axis and the slow axis of LD and the scattering characteristic of thin disk side are homogeneously considered during the simulation. The simulation shows that the coupling efficiency of the coupling system is 88.3%, and the pump distribution in thin disk is ideal, which is accordant to the experimental result..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 168 (2008)
Analysis of Working Distance of CCD Gaze Imaging Tracking System in Space
Dong Jihui, and Hu Qiquan
Based on analysis of background radiations characteristic in space and the different reflection characteristic of diffuse target to the coherent light and natural light, through using statistical signal detection theory, the formula of working distance of space-borne charge coupled device (CCD) gaze imaging tracking syBased on analysis of background radiations characteristic in space and the different reflection characteristic of diffuse target to the coherent light and natural light, through using statistical signal detection theory, the formula of working distance of space-borne charge coupled device (CCD) gaze imaging tracking system under laser illuminating active tracking mode and sun illuminating passive tracking mode are studied, respectively. The result indicates that the space-borne CCD gaze imaging tracking system can track 1 m2 diffuse target in 10 km distance under 1 mJ pulse energy laser active tracking mode, and the working distance of sunlight passive tracking mode is as high as hundreds kilometers..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 173 (2008)
Influence of Wavy Sea Surface on Airborne Lidar Underwater Beam Quality with Monte Carlo Method
Xia Min, Yang Kecheng, Zheng Yi, and Rao Jionghui
The influence of the wavy sea surface on the quality of airborne lidar′s laser beam that transmitted through the wavy sea surface was studied with Monte Carlo method. Simulation results of laser beam energy distribution and the analytical conclusion were presented. In order to obtain the laser beam energy distribution,The influence of the wavy sea surface on the quality of airborne lidar′s laser beam that transmitted through the wavy sea surface was studied with Monte Carlo method. Simulation results of laser beam energy distribution and the analytical conclusion were presented. In order to obtain the laser beam energy distribution, the classic Monte Carlo model was modified by adding the wavy surface model and the function to calculate the energy distribution of receiver plane. By Monte Carlo simulation, the laser beam energy distributions on certain depth with different sea-surface wind velocities were obtained. From these data, conclusion can be drawn that with the increase of sea surface wind velocity, the laser beam quality decreases, as well as the detection ability of the airborne lidar..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 178 (2008)
Fabrication of Low-Density Blazed Gratings
Jia Wei, Zhou Changhe, Dai Enwen, and Di Caihui
The process of fabricating low-density blazed gratings is presented. Some novel improvements have been reported, which lead to gratings with better quality. In experiment, 40 μm period blazed gratings with uniform surface are obtained, and the diffraction efficiency of the first order is more than 70%. Compared with trThe process of fabricating low-density blazed gratings is presented. Some novel improvements have been reported, which lead to gratings with better quality. In experiment, 40 μm period blazed gratings with uniform surface are obtained, and the diffraction efficiency of the first order is more than 70%. Compared with traditional method, the efficiency is increased by 5%～10%. Finally, the efficiency of experimental results is compared with theory value, and the reasons of experimental errors are given. It is found that if tips introduced by experiment errors can be removed, the efficiency will be increased greatly, which provide bases on getting better gratings and higher diffraction efficiency..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 183 (2008)
355 nm Laser Based on a Nd:YAG/Cr:YAG Composite Crystal
Shen Gao, Tan Huiming, Fu Xihong, Nan Nan, and Zhao Yuhuan
Design and experiment results of an all solid-state 355 nm ultraviolet (UV) laser based on Nd:YAG/Cr:YAG composite crystal are reported. The 1064 nm fundamental frequency radiation of high peak power and small waist was generated by plano-plano cavity. Outside the cavity, the fundamental beam was passed through a KTP cDesign and experiment results of an all solid-state 355 nm ultraviolet (UV) laser based on Nd:YAG/Cr:YAG composite crystal are reported. The 1064 nm fundamental frequency radiation of high peak power and small waist was generated by plano-plano cavity. Outside the cavity, the fundamental beam was passed through a KTP crystal and a LBO crystal without been focused. The KTP crystal was used for frequency doubling of the 1064 nm radiation to generate second harmonic 532 nm radiation, and the LBO crystal was used as a sum-frequency of the 1064 nm radiation and the 532 nm radiation to generate 355 nm radiation. Although both Nd:YAG and Cr:YAG are isotropic crystals, the 1064 nm fundamental frequency radiation was near-linearly polarized in particular situations. This characteristic is benificial for the conversion of fundamental radiation to second harmonic generation (SHG) and enhance the conversion efficiency of the whole laser system. And divergence angle and bandwidth of the fundamental beam related to conversion efficiency of both SHG and the third harmonic generation (THG) should be within the range of crystal acceptance angle and acceptance bandwidth. Considering these factors, the cavity had been designed carefully. When the laser diode (LD) pump power is 8 W, the peak power of the fundamental beam was 28 kW, and finally, the 355 nm radiation average power of 124 mW was achieved..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 191 (2008)
Improving Coupling Efficiency of Optical Fiber for High-Power Laser Beam
Wang Baohua, Jiang Menghua, Hui Yongling, and Li Qiang
Beam quality parameter plays an important role in the optical fiber coupling for the high-power laser. For high-power laser, its laser beam is always multimode, so it is an effective method to use equivalent basic mode to replace multimode for calculating. The beam width of this equivalent basic mode is measured by incBeam quality parameter plays an important role in the optical fiber coupling for the high-power laser. For high-power laser, its laser beam is always multimode, so it is an effective method to use equivalent basic mode to replace multimode for calculating. The beam width of this equivalent basic mode is measured by including 98% of the beam energy, and this is an effective way to calculate the beam quality parameter. A high-efficiency coupling system was designed by using theory of optical fiber coupling for the high-power laser and the beam transform, and in the system numerical values of lens′ aperture and focus were optimized. Experiment proves that the coupling system has a high coupling efficiency. The efficiency is more than 94% when the input power is 2000 W, and the figure of the experiment on coupling efficiency was displayed and analyzed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 195 (2008)
Simultaneous Dual-Wavelength Quasi-Continuous-Wave Laser-Diode-End-Pumped Nd:YAG Laser for Terahertz Wave Sourse
Zheng Fanghua, Liu Huan, Li Xifu, and Yao Jianquan
The methods to generate terahertz (THz) waves can be divided into electronics and photonics. We use nonlinear optical difference frequency generation to obtain THz waves which belongs to photonics method. It is portable and run at room temperature, with high power and low cost. A simultaneous dual-wavelength quasi-contThe methods to generate terahertz (THz) waves can be divided into electronics and photonics. We use nonlinear optical difference frequency generation to obtain THz waves which belongs to photonics method. It is portable and run at room temperature, with high power and low cost. A simultaneous dual-wavelength quasi-continuous wave (CW) laser-diode-end-pumped Nd:YAG laser polarized operating at 1319 nm and 1338 nm has been demonstrated and the laser at 1064 nm is suppressed successfully. A total polarized quasi-CW output power of 2.22 W is obtained at a pump power of 20 W with a pulse repetition rate of 50 kHz, and the slope efficiency is 12.72%. The corresponding pulse width is 71.91 ns. The beam quality factor M2 is as low as 1.165 and the instability of the output power is less than 0.487% at the polarized wave output power of 2.17 W. Using the simultaneous dual-wavelength laser, the highly coherent THz wave radiation of 3.23 THz will be generated by nonlinear optical difference frequency method in DAST (4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate) crystal. The ideal output peak power is 4.71 mW. The simultaneous dual-wavelength laser provides theoretically basis for generating highly coherent terahertz wave radiation by nonlinear optical difference frequency method..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 200 (2008)
High Repetition Rate Short Pulse Width Nd:YVO4 Slab Laser
Li Xiaoli, Shao Jie, Zang Huaguo, and Lu Yutian
Partially end-pumped hybrid resonator slab laser is one kind of novel solid-state laser. High repetition rate Q-switched operation using this structure was achieved. An output pulse train with 4.6 ns pulse width and 4.5 mJ pulse energy was obtained at 1 kHz repetition rate. In the condition of continuous pumping with 5Partially end-pumped hybrid resonator slab laser is one kind of novel solid-state laser. High repetition rate Q-switched operation using this structure was achieved. An output pulse train with 4.6 ns pulse width and 4.5 mJ pulse energy was obtained at 1 kHz repetition rate. In the condition of continuous pumping with 5 kHz operation, Q-switched laser with pulse width of 6 ns and pulse energy of 3.1 mJ was obtained, and output power was more than 15W. The width and energy were 9.5 ns and 1.2 mJ respectively when the repetition rate reached 25 kHz, and output power was 30 W. Experimental results show that the output level has great potential for further development..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 206 (2008)
Effect of Output Power on the Pressure of Cavity in Continuous Wave DF Chemical Lasers
Yan Baozhu, Yuan Shengfu, Lu Qisheng, Hua Weihong, and Wang Hongyan
To study the effect of output power on the pressure of cavity in continuous wave (CW) DF chemical lasers, a series of experiments are conducted based on a small-scale combustion-driven CW DF chemical laser. The result shows that greater specific power will result in lower cavity pressure. An algebraic model from combusTo study the effect of output power on the pressure of cavity in continuous wave (CW) DF chemical lasers, a series of experiments are conducted based on a small-scale combustion-driven CW DF chemical laser. The result shows that greater specific power will result in lower cavity pressure. An algebraic model from combustor to the exit of cavity is constructed by using one-dimension steady state theory and cavity dynamics theory, then the dependence of cavity pressure on specific power is attained. The result is consistent with experiments, so the model explains the effect of output power on the pressure of cavity, and the result indicates that the model is logical. Both the model and experiments show that cavity pressure falls down because of output power. When specific power is 50 J/g, cavity pressure will be reduced by 7.4% theoretically in the experimental condition..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 211 (2008)
Beam Transmission
Finite Difference Beam Propagation Analysis of Wide-Angle Crossed Waveguide
Wang Shijun, Ma Huilian, and Jin Zhonghe
The characteristic of the light propagation across the wide angle crossed waveguide is analyzed using the finite difference beam propagation method (FDBPM). Padé approximation is used to deal with the wide angle problem and the transparent boundary condition is used to deal with the optical reflection at the boundThe characteristic of the light propagation across the wide angle crossed waveguide is analyzed using the finite difference beam propagation method (FDBPM). Padé approximation is used to deal with the wide angle problem and the transparent boundary condition is used to deal with the optical reflection at the boundary. Through calculating the finite difference equations using the pursue after method, the relationship between the propagation loss and the intersection angle has been obtained. On this basis, the crossed silica waveguides are fabricated on silicon substrate by low pressure chemical vapor deposition method. Experiments show that the presented FDBPM has good accuracy and can be used to analyze wide angle crossed waveguides..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 231 (2008)
Gaussian Approximation for Mode Field Distribution of Dielectric Planar Waveguide TE0 Mode
Guo Fuyuan, Li Lianhuang, and Wang Minghua
Based on the characteristic of the beam propagation factor of the diffractive beam from the end surface of dielectric planar waveguide, the rationality of the Gaussian approximation for the mode field distribution of planar waveguide TE0 mode is clarified. As the computing formula of the matching efficiency between twoBased on the characteristic of the beam propagation factor of the diffractive beam from the end surface of dielectric planar waveguide, the rationality of the Gaussian approximation for the mode field distribution of planar waveguide TE0 mode is clarified. As the computing formula of the matching efficiency between two field distributions is engaged, the method of equivalent matching efficiency is advanced for ascertaining the equivalent mode field half width of the Gaussian approximation expression, and the computing formula of equivalent mode field half width which is expressed by the half thickness of core layer, the normalized standing wave parameter of core layer and the normalized evanescent wave parameter of cladding layer of the planar waveguide are acquired, and the matching efficiency between the Gaussian distribution and the eigen mode field distribution of planar waveguide TE0 mode is presented. The rationality of the method of equivalent matching efficiency for computing equivalent mode field half width is explained. Finally, as the method of solving the equations is introduced, the fitting expression of equivalent mode field half width which is expressed by the half thickness of core layer and the normalized frequency of planar waveguide is suggested, and the accuracy of fitting expression is showed by the error analysis..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 235 (2008)
Laser Manufacturing
Effect of Welding Parameters on Formation of Welds during Laser Welding of NiTi Shape Memory Alloy
Wang Wei, Chen Li, Zhao Xingke, and Huang Jihua
Nd:YAG laser was used to weld 2 mm thick tapes of NiTi shape memory alloy (SMA). The effect of main welding parameters including laser power, welding speed, defocusing amount, gas-assisting blowing on weld shaping was investigated. The results show that appropriate matching of main welding parameters is the key of realNd:YAG laser was used to weld 2 mm thick tapes of NiTi shape memory alloy (SMA). The effect of main welding parameters including laser power, welding speed, defocusing amount, gas-assisting blowing on weld shaping was investigated. The results show that appropriate matching of main welding parameters is the key of realizing good weld shaping. Linear heat input between 59～75.6 J/mm can acquired optimal formation of welds. The defocusing amount between -2～3 mm can relize full penetration of 2 mm thick tapes of NiTi alloys. The defocusing amount between 0～1 mm can obtain the optimal formation of welds. The protective effectiveness and the weld formation is the best when side-blow shielding gas flow rate is from 15 to 20 L/min. Different matching of laser power and welding speed effecting on different formation of welds were experimentally acquired which supply references to laser welding and engineering application for NiTi alloy..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 291 (2008)
Numerical and Experimental Study on the Laser Micro-Bending Process
Liu Jie, Sun Sheng, and Guan Yanjin
A three-dimensional (3D) thermal-mechanical finite element analysis model for laser micro-bending of 0.1 mm thick stainless steel foil is developed. The software MSC.Marc is used in the numerical analysis of this process. The detailed simulation results such as temperature distribution, deformation filed, stress and stA three-dimensional (3D) thermal-mechanical finite element analysis model for laser micro-bending of 0.1 mm thick stainless steel foil is developed. The software MSC.Marc is used in the numerical analysis of this process. The detailed simulation results such as temperature distribution, deformation filed, stress and strain field are obtained. The inner relationship among them is investigated and the temperature gradient mechanism (TGM) is expressed. Laser micro-bending experiments have been carried out on the steel foil samples, and the simulation results are in good agreement with the experimental results. Through analyzing the experimental results, the influence of laser power, scanning velocity and scanning times on bending angles is described. The works of the finite element method (FEM) simulation and experiments of the laser micro-bending are helpful for further studying on this process..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 276 (2008)
Effects of Laser Remelting on Wear Resistance of Ni-WC Composite Coatings by Flame-Spraying
Wang Ling, Chen Zhigang, Zhu Xiaorong, Zhao Xiaobing, and Kong Dejun
Ni-WC composite coatings prepared by flame spraying were remelted with CO2 laser, and the morphologies of the composite coatings by laser remelting were observed with scanning electron microscopy (SEM). The micro-hardness (HV) of samples with the different volume fraction of WC particle was tested, and the effects of WNi-WC composite coatings prepared by flame spraying were remelted with CO2 laser, and the morphologies of the composite coatings by laser remelting were observed with scanning electron microscopy (SEM). The micro-hardness (HV) of samples with the different volume fraction of WC particle was tested, and the effects of WC particles on microstructure and wear resistance were analyzed. It is shown that the coating pores prepared by flame spraying increase with the content of WC particle, and the pores are reduced obviously after laser remelting; The coating hardness after laser remelting increases 20% than that by flame spraying, which attains the biggest when WC volume fraction is 6%; The coating resistance wear after laser remelting increases with the increase of WC content. The best wear resistance is obtained when the WC volume fraction is as high as 6%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 281 (2008)
Intensity Distribution Design of Two-Dimensional Spot-Array for Pulsed Laser Transformation Hardening
Dang Gang, and Yu Gang
Spatial intensity distribution is a critical factor of pulsed laser transformation hardening. The existing two-dimensional spot-array designed as uniform density distribution cannot satisfy application requirements completely. A reverse method was proposed to design the intensity distribution based on finite element (FSpatial intensity distribution is a critical factor of pulsed laser transformation hardening. The existing two-dimensional spot-array designed as uniform density distribution cannot satisfy application requirements completely. A reverse method was proposed to design the intensity distribution based on finite element (FE) analysis. A FE model for simulating pulsed laser transformation hardening was established. In the model, temperature-dependent thermo-physical properties of material and transformation were taken into account. Temperature field and shape of predicted hardening calculated from the model was verified with experimental results. Research on relationship between distribution parameters and temperature field was carried out. With the validated FE model, the target temperature field or shape hardening layer was achieved by adjusting distribution parameters of the spot-array, and the optimal design of the intensity distribution was subsequently obtained. Aiming at surface hardening requirements of automobile′s stamping die, the method had been applied to gain an intensity distribution design with application value. The results showed that the method was feasible and capable of providing bases for designing shaping lens and making the design more predictable..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 287 (2008)
Control of Shaping of Welds for CO2 Laser Welding Shipbuilding T-Section Aluminum Alloy
Qi Junfeng, Niu Zhen, Zhang Dongyun, and Zuo Tiechuan
Characteristics of shipbuilding T-section aluminum alloy have been analyzed. The method of laser welding shipbuilding T-section aluminum alloy has been put forward. Fillet welds of 6.0 mm thick 5083 aluminum alloy T-joints have been completed through laser beam welding with wire filler material. Based on plate welding,Characteristics of shipbuilding T-section aluminum alloy have been analyzed. The method of laser welding shipbuilding T-section aluminum alloy has been put forward. Fillet welds of 6.0 mm thick 5083 aluminum alloy T-joints have been completed through laser beam welding with wire filler material. Based on plate welding, the influences of laser beam incident angle, working position and relationship between welding speed and wire feeding speed on shaping of welds have been studied. On the condition of 3300～3500W laser power, 0 mm defocusing length, Ar and He blending shield gas, 22°～25° laser incident angle, 0.8～1.0 mm from laser working position to the cross plate, 2.2～2.5 m/min welding speed and 2.5～2.8 m/min wire feeding speed, satisfied weld shape can be achieved. The reasons of porosities production and process instability in CO2 laser welding shipbuilding T-section aluminum alloy are also discussed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 297 (2008)
Laser Cladding Reparation of Aluminum Alloy
Guo Yongli, Liang Gongying, and Li Lu
Experiment of repairing aluminum (Al) alloy 7050 (Al 7050) by laser-cladding techniques was investigated. A 5 kW CO2 laser was used as the heat source. Experiemnts of single trace cladding, multi-trace overlapping cladding, and multi-layer cladding were performed on the Al 7050 plates shielded in a closed box with inerExperiment of repairing aluminum (Al) alloy 7050 (Al 7050) by laser-cladding techniques was investigated. A 5 kW CO2 laser was used as the heat source. Experiemnts of single trace cladding, multi-trace overlapping cladding, and multi-layer cladding were performed on the Al 7050 plates shielded in a closed box with inert gas. A set of optimized laser-cladding repairation parameters for damaging Al 7050 samples were found, and the microstructures in different cladding regions and micro-appearances of fracture surface were studied. The optimized laser-cladding repairation parameters were laser power of 1.84×104～2.12×104 W/cm2, scanning speed of 5 mm/s, powder feeding rate of 1.8～2.4 g/min, and overlapping width of 1.5 mm. With the optimized repairing parameters, the cladding zone displayed a superior metallurgical bonding with its substrate, the repaired sample surface appeared smooth without any substrate distortion, and the defect formation in the cladding zone was effectively prevented by strengthening shielding of the molten pool with dry argon..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 303 (2008)
Microstructure and Corrosion Resistant Property of Laser Surface Melting Layer of AM50 Magnesium Alloy
Chen Jufang, Zhang Yongkang, and Xu Renjun
Surface of AM50 magnesium alloy was melted using continuous wave CO2 laser. The microstructure and composition of the melted layer were analysed by scanning electron microscope (SEM), energy dispersion spectrum (EDS) and X-ray diffraction (XRD). The corrosion behaviour of the laser-treated and untreated samples were stSurface of AM50 magnesium alloy was melted using continuous wave CO2 laser. The microstructure and composition of the melted layer were analysed by scanning electron microscope (SEM), energy dispersion spectrum (EDS) and X-ray diffraction (XRD). The corrosion behaviour of the laser-treated and untreated samples were studied in 3.5% (mass fraction) NaCl solution by measuring electrochemical polarization curves and immerging. The microstructure of the melted layer was refined highly, the composition and structure were more uniform, the β-phase was decreased, Al and impurity elements in solid solution were increased. The experimental results show that the corrosion potential of the laser melted sample is about 37 mV higher than that of the as-received sample, while the anodic current density is about one order of magnitude lower and the pitting corrosion develop more slowly. The corrosion resistance of the laser surface melting of AM50 is significantly improved..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 307 (2008)
Threshold Characterization for Laser Penetration Welding
Han Ning, Zhang Huanzhen, and Xiao Rongshi
The threshold characterization for penetration welding of A3 steel was investigated using a Nd:YAG and a CO2 laser with high speed camera and optical spectrometer. It is shown that the threshold ratio of the laser power to the beam spot diameter P/d for penetration welding is consistent with different beam spots. But tThe threshold characterization for penetration welding of A3 steel was investigated using a Nd:YAG and a CO2 laser with high speed camera and optical spectrometer. It is shown that the threshold ratio of the laser power to the beam spot diameter P/d for penetration welding is consistent with different beam spots. But the threshold power density changes with the beam spots. The transition threshold of welding mode of YAG laser is larger than the vaporization threshold of materials. The metal vaporizes obviously even in the period of conduction welding and the spectra of the vapor plume remain the same between the conduction and penetration welding modes in YAG laser welding. As for CO2 laser welding, the metal vaporizes weakly before the mode transition occurs from conduction welding to penetration welding, and the metal vaporizes violently and the vapor ionizes partly in penetration welding. Analysis shows that the formation of a vapor plasma enhances the absorption of metal to laser beam and thus promotes the establishment of the penetration welding process in CO2 laser welding..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 311 (2008)
Laser Shock Processing on 1Cr11Ni2W2MoV Martensite Steel
Cao Ziwen, Zou Shikun, Liu Fangjun, Fan Guofu, and Liu Yuanchun
The foundational study of laser shock processing (LSP) for 1Cr11Ni2W2MoV martensite stainless steel is presented in this paper. Capability of the laser system is 50 J per pulse, LSP experiment under water confinement regime perform at laser power density of 3.7～7.5 GW/cm2. Aluminum film is used as the absorption layer The foundational study of laser shock processing (LSP) for 1Cr11Ni2W2MoV martensite stainless steel is presented in this paper. Capability of the laser system is 50 J per pulse, LSP experiment under water confinement regime perform at laser power density of 3.7～7.5 GW/cm2. Aluminum film is used as the absorption layer and restriction layer, and uniform water flow. The laser beam is incidence by oblique way. Different samples are shocked for the following study. The measurement for laser shocked zone include surface profile, micro-hardness and residual stress, and the result confirm that laser power density has influence on the performance of laser shocked zone. Comparing the fatigue result of three types sample, the sample with drilling after shock show the best fatigue performance, because the intense compressive residual stress that around the surface of hole can restrain the initiation of the fatigue crack and retard the propagation of fatigue crack. Laser shock processing is a available method for enhancing the high cycle fatigue of martensite stainless steel via this investigation..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 316 (2008)
Laser Physics
Hot Electron Generation and Transport in Intense Field Physics
Wang Guangchang, Chen Tao, Zhang Ting, Deng Li, and Zheng Zhijian
Hot electron generation and its transport characteristics in the interaction of femtosecond laser with solid target were studied in experiments, on the 100 TW ultrashort Ti:sapphire laser. The energy spectrum, yield, fluence and total energy of hot electrons were obtained. It shows that more hot electrons are generatedHot electron generation and its transport characteristics in the interaction of femtosecond laser with solid target were studied in experiments, on the 100 TW ultrashort Ti:sapphire laser. The energy spectrum, yield, fluence and total energy of hot electrons were obtained. It shows that more hot electrons are generated at the rear normal direction of target with the increase of power density of laser, and the fluence and total energy of hot electrons decrease with the increase of target thickness. 80% hot electrons energy deposits in the place in front of the target about 10 μm, which is induced by the static electric field effect..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 216 (2008)
Measurement on Collisional Loss Rate Coefficient of Cesium Cold Atoms in a Magneto-Optical Trap
Wang Guiping, Ji Weibang, Ma Jie, Wang Lirong, Xiao Liantuan, and Jia Suotang
Cold cesium atoms are obtained using magneto-optical trap (MOT) technology. Under different trapping laser powers, the collisional loss rate coefficients for cold cesium atoms were measured by observing the fluorescence intensity variance of cold atoms clouds when MOT was loading. The experiment was achieved in a singlCold cesium atoms are obtained using magneto-optical trap (MOT) technology. Under different trapping laser powers, the collisional loss rate coefficients for cold cesium atoms were measured by observing the fluorescence intensity variance of cold atoms clouds when MOT was loading. The experiment was achieved in a single trap, thus it is convenient and easy. In addition, it is found that the collisional loss rate coefficient depends on and increases with trapping laser power, which is in agree with the Gallagher-Pritchard theoretical model. It validates that the radiative escape and fine-structure-changing collisions are the main reasons for cold atoms lossing in a MOT. The results are of significance for further improvement on trapping efficiency of MOT..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 221 (2008)
Materials and Thin Films
Effect of Bound Diamond Abrasives Fabrication Technology on Subsurface Damage in Nd-Doped Phosphate Glass
Zhang Wei, and Zhu Jianqiang
Loose abrasive grinding and bound abrasive grinding are two principal grinding methods in optical cold process, but they are different in grinding removal mechanism. Nd-doped phosphate glasses are dominating materials in high average power laser solid state lasers. For little investigative experience in subsurface damaLoose abrasive grinding and bound abrasive grinding are two principal grinding methods in optical cold process, but they are different in grinding removal mechanism. Nd-doped phosphate glasses are dominating materials in high average power laser solid state lasers. For little investigative experience in subsurface damage (SSD) in Nd-doped phosphate glasses, this paper investigated the grinding removal mechanism using different bound diamond abrasives. The effects of abrasive size, load, spindle speed, bonding material and the coolant on the subsurface damage in Nd-doped phosphate glasses were surveyed as well. Subsurface damage produced by loose abrasives was presented for comparation. All the results provide essential foundation for choosing and optimizing fabrication technology of high-quality Nd-doped phosphate glasses..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 268 (2008)
Exponential Fitting of Laser Damage Threshold and Analysis of Testing Errors
Li Dawei, Zhao Yuan’an, He Hongbo, Shao Jianda, and Fan Zhengxiu
The exponential fitting model of damage probability and 1-on-1 laser damage threshold of optical components was presented, and the effects of irradiated spot size and number of spots tested for one pulse energy density on damage probability were investigated. The damage probability was calculated, when the defects is dThe exponential fitting model of damage probability and 1-on-1 laser damage threshold of optical components was presented, and the effects of irradiated spot size and number of spots tested for one pulse energy density on damage probability were investigated. The damage probability was calculated, when the defects is distributed as complete degeneracy, and then further modification was done to fit the incomplete degeneracy situation. The damage probability to fit the damage data is called exponential fitting model and the experiment results in the paper showed that the exponential fitting could get more accurate damage threshold. The test errors induced by laser beam spot and the sites tested at one pulse energy density were studied through numerical simulation. It is shown that the larger beam area and more sites exposed at one pulse energy density, the more accuracy of damage possibility..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 273 (2008)
Measurement and Metrology
Nonlinear Error Analysis of Laser Synthetic-Wavelength Nanomeasurement Interferometer
Chen Benyong, Mu Ruizhen, Zhou Yanjiang, and Li Dacheng
The principle of laser synthetic-wavelength nanomeasurement interferometer is described. The nonlinear errors which affect on this interferometer are analyzed. Theoretical analysis results show that nonlinear errors caused by nonorthogonal polarization, elliptic polarization of laser source, nonideal polarization beam The principle of laser synthetic-wavelength nanomeasurement interferometer is described. The nonlinear errors which affect on this interferometer are analyzed. Theoretical analysis results show that nonlinear errors caused by nonorthogonal polarization, elliptic polarization of laser source, nonideal polarization beam splitter and corner prism are second or higher order polarization error, the comparable experiment of laser synthetic-wavelength nanomeasurement inteferometer and a heterodyne interferometer was performed. The maximal error of laser synthetic-wavelength nanomeasurement inteferometer is 2.1 nm, while the maximal error of heterodyne interferometer is 7.5 nm..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 240 (2008)
Characteristic of Micro-Opto-Electro-Mechanical System-Cantilever of Tunable Micro-Cavity Light Emitting Diodes
Guan Baolu, Guo Xia, Gu Xiaoling, Yang Hao, Deng Jun, Gao Guo, and Shen Guangdi
An GaAs-based micro-opto-electro-mechanical system (MOEMS) cantilever tunable light emitting diode was presented. It is fabricated by standard surface micromachining technology. The relation of cantilever loading and displacement was measured, and the tunable spectrum of this cantilever tunable light emitting diode wasAn GaAs-based micro-opto-electro-mechanical system (MOEMS) cantilever tunable light emitting diode was presented. It is fabricated by standard surface micromachining technology. The relation of cantilever loading and displacement was measured, and the tunable spectrum of this cantilever tunable light emitting diode was also measured. When the current is 40 mA and applied voltage is from 4 V to 22 V, the wavelength is tuned from 974.5 nm to 956.9 nm and a wide tuning range of 17.6 nm was achieved under the room temperature. The optical and mechanical characters of the cantilever with distributed Bragg reflector (DBR) multiple layers in detail were studied by the finite element method. Further numerical simulations with MOEMS-cantilever show when the length of cantilever is 400 μm, the max-displacement of center of cantilever is 411 nm, and max-voltage is 24 V..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 245 (2008)
Measuring Phase Retardation and Fast Axis Azimuth of a Wave Plate Using Michelson Interferometer
Ren Hongliang, Wang Jiuyang, Lou Liren, Zheng Hong, and Li Yinmei1
Based on measuring the intensity of components of polarized light, the methods for determining the parameters of a wave plate are discussed and uncertainty of measuring arbitrary wave plate is indicated by the methods. It is concluded that the real phase retardation and fast axis of a wave plate cannot be determined byBased on measuring the intensity of components of polarized light, the methods for determining the parameters of a wave plate are discussed and uncertainty of measuring arbitrary wave plate is indicated by the methods. It is concluded that the real phase retardation and fast axis of a wave plate cannot be determined by this kind of methods, because the phase retardation of a wave plate is a multiple valued function of measured light intensity. A method for measuring phase retardation and fast axis of a wave plate using Michelson interferometer is brought forward, in which the rainbow fringe of the Michelson interferometer could be used as an indicator for the zero optical path difference. The method was demonstrated by measuring a commercial quarter-wave plate. The influence of the dispersion of the wave plate material on the measurement is analyzed, and the applicable scope of the method is discussed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 249 (2008)
Influence of the Frame Integral Time to Detecting Distance of Low Light Level-TV
Zhu Ying, Chang Benkang, and Liu Lei
The low light level (LLL) night vision system now plays a more important role in military affairs, and people always focus it on the detecting distance. This thesis analyzed the diatance detecting equation, and brought forward a new way to increase the detecting distance suitable for low speed object. This method is muThe low light level (LLL) night vision system now plays a more important role in military affairs, and people always focus it on the detecting distance. This thesis analyzed the diatance detecting equation, and brought forward a new way to increase the detecting distance suitable for low speed object. This method is multiplying the frame integral time. Based on the revised apparent distance detecting equation, the affect of the frame accumulation to the detecting distance was studied. The influence of the frame accumulation on the detecting distance at different illumination intensities was analyzed theoretically. At about 10-4 lx and 10-3 lx, it can raise the distance to 157% and 131%, respectively. The field experiment at weak illumination showed that this method was effective..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 259 (2008)
Design of Hybrid Refractive-Diffractive Optical System of Infrared Laser Scanning Testing Equipment
Liu Qi, Liu Liping, and Yuan Pusheng
For the sake of laser scanning testing equipment with high testing precision and general purpose, it is required that the optical system of the testing equipment operates at wide field of view and wide spectrum with high image quality. For these purposes, based on conventional 7-element optical lens in visible band, a For the sake of laser scanning testing equipment with high testing precision and general purpose, it is required that the optical system of the testing equipment operates at wide field of view and wide spectrum with high image quality. For these purposes, based on conventional 7-element optical lens in visible band, a hybrid refractive-diffractive optical system is designed for infrared laser scanning testing equipment by using a hybrid refractive-diffractive singlet instead of doublets. The main parameters of the hybrid lens are 60° field of view, 0.8～1.06 μm action spectrum, 30 mm effective focal length and 30 mm back working distance. The modulation transfer function (MTF) of the hybrid refractive-diffractive lens is near 0.7 at the spatial frequency of 42 lp/mm. The full field of view distortion of the lens is less than 1.9%. The weight decreases by 35.3%. The results show that with the characters of high image quality and miniaturization, the system can meet the general requirements of laser scanning testing equipment..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 2, 263 (2008)
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