Journals >Chinese Journal of Lasers
Contents
2015
Volume: 42 Issue 11
46 Article(s)
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Research Article
Thermal Conductivity of Nanostructures in an External-Cavity Surface-Emitting Laser
Zhang Peng, Jiang Maohua, Zhu Renjiang, Cui Yuting, and Zhang Yu
Optimizing the quantum structures in the active region and improving the thermal management are crucial for upgrading the output power of an external-cavity surface-emitting laser. The above two methods are all based on the accurate thermal analysis of the laser, and depended on a key material parameter, the thermal coOptimizing the quantum structures in the active region and improving the thermal management are crucial for upgrading the output power of an external-cavity surface-emitting laser. The above two methods are all based on the accurate thermal analysis of the laser, and depended on a key material parameter, the thermal conductivity. Because the multiple quantum wells and the distributed Bragg reflector in an external-cavity surface-emitting laser are typical nanostructures, properties of nanoscale thermal conduction are considered, and three analytical methods are used to calculate thermal conductivities of GaAs/AlAs distributed Bragg reflectors with different thicknesses. Theoretical results are compared with reported experiments and the method which is more proper to compute the thermal conductivity of GaAs/AlAs system nanostructure is selected. By use of the selected analytical method, thermal conductivities of InGaAs/GaAs multiple quantum wells and GaAs/AlAs distributed Bragg reflector in a 980 nm external-cavity surface-emitting laser are simulated. It is found that the cross-plane thermal conductivity of distributed Bragg reflector is about 40% of the value of corresponding bulk material, while the cross-plane thermal conductivity of multiple quantum wells is less than half of the bulk material. Numerical analysis of the temperature rise in the gain chip is carried out using the obtained thermal conductivities, and the results are in good agreement with experiments..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1102001 (2015)
A Compact and Highly Efficient Intracavity Frequency-DoubledGreen Laser Based on Periodically Poled Lithium Niobate
Gui Shixin, Chang Jianhua, Yan Na, Guo Yue, and Wu Yu
A compact and highly efficient intracavity frequency- doubled green laser has been researched and designed based on periodically poled lithium niobate (PPLN) crystal. The laser system adopts a 808 nm laser diode (LD) end directly pumped Nd∶YVO4 crystal, then uses a poling period of 7 mm of PPLN crystal to generate 532 A compact and highly efficient intracavity frequency- doubled green laser has been researched and designed based on periodically poled lithium niobate (PPLN) crystal. The laser system adopts a 808 nm laser diode (LD) end directly pumped Nd∶YVO4 crystal, then uses a poling period of 7 mm of PPLN crystal to generate 532 nm green light by frequency-doubling. The coating Nd∶YVO4 and PPLN crystals compose a laser cavity, without using any discrete optical components such as optical lens, reflector, thus reducing the volume and cost of the system. The experimental results show that with the resonator cavity length being set at 12 mm, pump power at 4.1 W, the green light output power of 1.343 W and the corresponding optical- optical conversion efficiency of 32.8% are achieved. Controlling the incident pump power at about 3.33 W, the fluctuation of green light output power within 2 h is less than 2%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1102002 (2015)
Analysis of Influence of Tip/Tilt Phase Error on a Large Scale Coherent Beam Combination of Fiber Laser
Huang Zhimeng, Tang Xuan, Liu Cangli, Li Jianfeng, Zhang Dayong, Wang Xiaojun, and Han Mei
A model of coherent beam combination (CBC) of fiber laser with 7-channel and 37-channel is establishedaccording to Fraunhofer diffraction theory. The far-field intensity distribution and beam quality of coherent beamcombination with different duty ratios and tilt angles are simulated. The influences of tip/tilt phase eA model of coherent beam combination (CBC) of fiber laser with 7-channel and 37-channel is establishedaccording to Fraunhofer diffraction theory. The far-field intensity distribution and beam quality of coherent beamcombination with different duty ratios and tilt angles are simulated. The influences of tip/tilt phase error, duty ratioand the number of sub-beams on CBC of far field beam quality are analyzed. Simulation results show that the farfield intensity in the Airy disk decreases with increasing tilt angle, which means degraded combination effect. Thepower in the bucket (PIB) of the far field decreases more rapidly with tilt angle increased in a large- scalecombination, which means that the accumulated effect of tip/tilt phase error with the number increase of sub-beamscan appear. In order to improve the efficiency of CBC, the tip/tilt phase error and piston phase error should becontrolled simultaneously..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1102003 (2015)
High Speed Random Number Generator Based on Digitizing Bandwidth-Enhanced Chaotic Laser Signal
Yan Qiurong, Cao Qingshan, Zhao Baosheng, Zhang Hua, and Liao Qinghong
A high speed random number generator based on digitizing bandwidth-enhanced chaotic laser signal is proposed and demonstrated. In order to remove the weak periodicity in optical feedback chaotic semiconductor laser signal, the optical feedback chaotic semiconductor laser is injected into another semiconductor laser to A high speed random number generator based on digitizing bandwidth-enhanced chaotic laser signal is proposed and demonstrated. In order to remove the weak periodicity in optical feedback chaotic semiconductor laser signal, the optical feedback chaotic semiconductor laser is injected into another semiconductor laser to obtain a bandwidth-enhanced chaotic laser signal. The bandwidth-enhanced chaotic laser signal is converted using an 8-bit high speed analog-to-digital convertor to achieve generating multi bits by each sampling point. In order to remove the bias existing in original extracted random bits and improve the efficiency of random bit generation, fieldprogrammable gate array based secure hash algorithm 256 is proposed to extract random bit. Due to the use of 4-channel parallel processing technology, online random number generation rate of 2.94 Gbit/s is obtained and each sample could produce average 4.65 random bits. The obtained random numbers pass all the tests in random testing program of ENT and STS..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1102004 (2015)
Research of Non-Conjugated Aberration Compensation in Passive Unstable Resonator
Cai Haidong, Shang Jianli, Su Hua, Wu Jing, Yu Yi, An Xiangchao, Wang Xiaojun, and Wan Min
The effects of intra- cavity aberration compensation based on negation of phase or calculation of geometrical optics in positive-branch confocal unstable resonator is not ideal because of the different sizes of oscillation laser (plane wave and spherical wave) on optical elements and light deflection caused by the aberThe effects of intra- cavity aberration compensation based on negation of phase or calculation of geometrical optics in positive-branch confocal unstable resonator is not ideal because of the different sizes of oscillation laser (plane wave and spherical wave) on optical elements and light deflection caused by the aberration.A non-conjugated intra-cavity aberration compensation method based on the relaxation iterative approximation algorithm using a collimated probe beam wavefront as the reference is presented. In experiment,the effects of compensation referenced single pass probe and round-trip probe are compared. It can be found that the beam quality of output guided light cannot be improved in the compensation using single pass probe. The round-trip probe wavefront can begin to stabilize and the root mean square (RMS) of residual error is less than 0.1 mm after 7~9 iterative steps, when the value of RMS of the random intra-cavity aberration is 0.3~0.4 mm. The β value of output guided light, which is as the evaluation criterion, can be decreased from 11.2 to 2.6 with the compensation. By analyzing of the relationship and difference between the guided light and the oscillation laser, it can be inferred that the beam quality of output laser in an active unstable resonator will be improved using this aberration compensation method..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1102005 (2015)
Research of Hollow Broadband Laser Cladding Method
Lei Dingzhong, Shi Shihong, Fu Geyan, Jia Shuai, and Shi Tuo
Broadband laser cladding technology is widely used in the reinforcement, repair and modification of large surface, and less lap times make it easier to get better quality and the higher efficiency. In order to solve the problems of uneven heating of metal powder and low coaxial coupling accuracy in the current broadbanBroadband laser cladding technology is widely used in the reinforcement, repair and modification of large surface, and less lap times make it easier to get better quality and the higher efficiency. In order to solve the problems of uneven heating of metal powder and low coaxial coupling accuracy in the current broadband laser cladding, an inside-laser powder feeding broadband laser cladding method has been designed, which can realize uniform powder feeding and exactly perpendicular to the surface of molten pool inside the laser. Two cladding accumulation experiments have been done on the horizontal and 30° inclined walls, and both of them achieve straight wall with uniform height of melt layer. The results show that molten pool is not sensitive to gravity. The microstructure analysis of molten layer shows that the microstructure in secondary remelting zone is relatively coarse, and the microstructure in non- overlapping zone is composed of more dendrites. The microhardness fluctuation of them is about 90HV0.5. The microstructure of the cladding layer is relatively uniform and densification..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1103001 (2015)
Microstructure and Property of Co-Based Carbide Composite Coating Fabricated by Laser Cladding on 40Cr Tool Steel Surface
Li Chuang, Liu Hongxi, Zhang Xiaowei, Tao Xide, and Jiang Yehua
WC/Co, WC/Co50 and WC-TiC/Co50 carbide composite coatings are prepared by laser cladding process on 40Cr tool steel surface through designing different composition ratio of WC, TiC, Co and Co50 powder. The influence of laser cladding process parameters and powder composition ratio on the composite coating phase structuWC/Co, WC/Co50 and WC-TiC/Co50 carbide composite coatings are prepared by laser cladding process on 40Cr tool steel surface through designing different composition ratio of WC, TiC, Co and Co50 powder. The influence of laser cladding process parameters and powder composition ratio on the composite coating phase structure, macroscopic morphology and microstructure are investigated by X- ray diffraction (XRD), optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), respectively. The results show that the WC/Co50 and WC-TiC/Co50 composite coatings surface morphology is good, smooth and without continuous macroscopic crack under the laser power of 4.2 kW and scanning speed of 350 mm · min- 1 conditions. Hardness and friction wear tests indicate that the composite coating has high hardness and good wear resistance, the highest microhardness is 1211 HV0.2 and the minimum wear weight loss is 2.1 mg. The maximum microhardness and minimum wear weight loss is 3.03 times and 34.4% of the substrate, respectively. A lot of WC, TiC and in-situ W2C, Fe3W3C carbide reinforced phases play a major role on improving the cladding coating hardness and wear resistance..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1103002 (2015)
Study on Design and Properties of Porous CoCrMo Alloy Structure Manufactured by Selective Laser Melting
Zhang Guoqing, Yang Yongqiang, Song Changhui, Wang Yunda, and Yu Jiakuo
To obtain porous medical implants with excellent mechanical properties and biocompatibility, compression performance analysis of CoCrMo alloy parts manufactured by selective laser melting (SLM) is performed. Compression experiments are conducted on the electronic universal testing machine along longitudinal direction, To obtain porous medical implants with excellent mechanical properties and biocompatibility, compression performance analysis of CoCrMo alloy parts manufactured by selective laser melting (SLM) is performed. Compression experiments are conducted on the electronic universal testing machine along longitudinal direction, in which the CoCrMo alloy parts are made and fractal interpolation theory is used to analyze the influence caused by relevant parameters on compression performance. The experiment results show that the main deformation is slippage. Both of the elastic modulus and the compressive strength decrease with increasing porosity and average pore size, while decrease with the reduction of surface area to volume ratio. When the regular octahedral and regular hexahedral porous structures are with porosity in the range of 55%~84%, average pore size of 0.51~0.99 mm, and surface area to volume ratio from 2 to 4.2, the elastic modulus will meet the requirement. Regular octahedral cylindrical porous structures have better performance than the square structures, but regular hexahedral square porous structures have better performance than the cylindrical structures. The conclusions above provide important basis for selective laser melting process of porous CoCrMo alloy structures used as medical implants..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1103003 (2015)
Warm Laser Shock Peening and Low Cycle Fatigue Behavior of Extruded AZ80-T6 Magnesium Alloy
Zhang Qinglai, Liu Hui, Zhang Bingxin, Li Xingcheng, Wang Rong, and Shao Wei
In order to study the effect of laser shock processing on low cycle fatigue behavior of extruded AZ80- T6 magnesium alloy, laser shock peening (LSP) and warm laser shock peening (WLSP) have been carried out on fatigue specimens using Nd: glass laser as well as tensile- tensile fatigue test. The results show that residuIn order to study the effect of laser shock processing on low cycle fatigue behavior of extruded AZ80- T6 magnesium alloy, laser shock peening (LSP) and warm laser shock peening (WLSP) have been carried out on fatigue specimens using Nd: glass laser as well as tensile- tensile fatigue test. The results show that residual compressive stresses generated by LSP and WLSP at 300 ℃ are -125 MPa and -158 MPa, and their fatigue lifes are improved by 11.42% and 75.74%, respectively. The crack initiation time is delayed obviously by WLSP so that fatigue life of AZ80-T6 alloy is improved. Laser shock induced microstructures of magnesium alloy and low cycle fatigue behavior are analyzed and discussed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1103004 (2015)
Suppression Effect of a Steady Magnetic Field on Surface Undulation During Laser Remelting
Wang Liang, Hu Yong, Song Shiying, Lai Sanpin, and Yao Jianhua
A steady magnetic field is applied to suppress the surface undulation after laser remelting without changing the laser processing parameters. A two dimensional (2D) transient multi- physics numerical model, concerning heat transfer, fluid dynamics, phase transition, electromagnetic field and the surface morphology of mA steady magnetic field is applied to suppress the surface undulation after laser remelting without changing the laser processing parameters. A two dimensional (2D) transient multi- physics numerical model, concerning heat transfer, fluid dynamics, phase transition, electromagnetic field and the surface morphology of molten pool, is established. Comparing with the experimental results and numerical results, the suppressing mechanism of surface undulation related to the temperature field and velocity field in the molten pool is discussed. The results indicate that the Lorenz force supported by the steady magnetic field is a sort of drag force, whose direction is opposite to the melt flow all the time. With increasing the magnetic flux density, the velocity of molten pool is reduced gradually, while the temperature field remains changeless. When the magnetic flux density is higher than 0.5 T, the shape of molten pool is changed and the height of surface undulation is decreased obviously without changing the microstructure..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1103005 (2015)
Properties Study of Co-Cr Alloy Fabricated by Selective Laser Melting
Zhao Jinyan, Zhang Yongzhi, Li Dongfang, Liu Chunchun, Liu Furong, and Yuan Yanping
A systematic study on the three dimensional (3D) prototyping of cobalt-chromium alloys are carried out by using a self-developed laser melting equipment. The optimizations of properties which involve the surface roughness, surface morphology, relative density, hardness of the workpieces are further discussed. Results sA systematic study on the three dimensional (3D) prototyping of cobalt-chromium alloys are carried out by using a self-developed laser melting equipment. The optimizations of properties which involve the surface roughness, surface morphology, relative density, hardness of the workpieces are further discussed. Results show that melting shrinkage and thickness accumulation of the powder layer are two important factors to affect the forming quality; the smaller of the surface roughness cumulative effect, the less pore are observed, which lead to a high relative density; Furthermore, macro-hardness of the part has a significant dependence on relative density. The relative density of 98.04% and the macro-hardness of 40HRC under the optical process parameters are obtained, conforming to American society of testing materials (ASTM) standards..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1103006 (2015)
Influence of Ultrasonic Vibration on Melt Pool in Laser Melting Process
Wang Wei, Yue Yaomeng, Yang Guang, Qin Lanyun, and Ren Yuhang
The influences of ultrasonic field on temperature field, flow field and the melt pool morphology during laser melting are studied through numerical simulation and experiment. A new three-dimensional mathematical model describing the ultrasonic field and temperature field in the laser melting with ultrasonic vibration iThe influences of ultrasonic field on temperature field, flow field and the melt pool morphology during laser melting are studied through numerical simulation and experiment. A new three-dimensional mathematical model describing the ultrasonic field and temperature field in the laser melting with ultrasonic vibration is developed. The temperature field and flow field of the laser melt pool variation are analyzed systematically by the finite volume method for coupled ultrasonic field and temperature field in laser melt pool simulation analysis. The results show that the temperature of molten pool under the effect of ultrasonic field is slightly lower than that of not applying ultrasonic field. The flow rate increases by 72%, but the effect of ultrasonic field does not change the circulation tendency of Marangoni flow without ultrasonic. The width of melt pool increases by 0.5 mm and depth reduces by 0.1 mm under the influence of ultrasonic field. It′s verified that the numerical simulation results are consistent with actual situation by laser melting experiment basically..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1103007 (2015)
Fatigue Properties Research of Titanium Alloy Repaired by Laser Cladding and Laser Shock Processing
He Weifeng, Zhang Jin, Yang Zhuojun, Yang Zhufang, Li Yuqin, and Li Jing
When repaired by laser forming repair, there generates tensile residual stress and bulky grains in the repair zone of titanium alloy components. Meanwhile, microstructures and performances are ill-distributed between the repair and matrix zone. Due to all above, fatigue strength of the repaired components is reduced seWhen repaired by laser forming repair, there generates tensile residual stress and bulky grains in the repair zone of titanium alloy components. Meanwhile, microstructures and performances are ill-distributed between the repair and matrix zone. Due to all above, fatigue strength of the repaired components is reduced seriously. Laser shock processing is adopted to treat the specimens which are repaired by laser cladding. The effect of laser shock processing on fatigue strength of the repaired specimens is researched. Mechanism of the effect is demonstrated by residual stress and microstructure analysis. The results suggest that fatigue limit of the matrix specimens is 401 MPa, but that of the laser cladding specimens is 365 MPa, which decreases by 9%; while treated by laser shock processing, fatigue limit of laser cladding specimens is improved up to 450.80 MPa, which increases by 23.5% . Considerable compressive residual stress is introduced by laser shock processing in the material surface, and depth of it reaches at 430 μm. Moreover, microstructures and performances are well-distributed. Compressive residual stress and improved microstructures are the reasons for that fatigue strength is enhanced..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1103008 (2015)
Investigation on Fabrication and Properties of N-Doped Fe-Based Amorphous Composite Coatings on High Strength Steel
Hou Jixin, Zhang Shunhu, Zhou Wei, Wang Xiaonan, Jiang Xiaozhou, and Zhu Guangjiang
With the IPG YLS4000 optical fiber laser, N-doped Fe-based amorphous composite coatings are prepared on a high strength steel substrate by three laser processes. The three coatings show amorphous structure with crystalline phase on them. The hardness, wear resistance and corrosion resistance of the coatings are evaluatWith the IPG YLS4000 optical fiber laser, N-doped Fe-based amorphous composite coatings are prepared on a high strength steel substrate by three laser processes. The three coatings show amorphous structure with crystalline phase on them. The hardness, wear resistance and corrosion resistance of the coatings are evaluated, indicating that the coatings have higher hardness, better wear resistance and corrosion resistance than substrate. The coating 2 fabricated under laser power of 1.5 kW and laser beam scanning speed of 180 mm/min has the highest amorphous phase content among the three coatings, and it also exhibits the best performance compared with the other two coatings. The results show that proper laser process parameters are important and coatings with higher amorphous phase content have better properties..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1103009 (2015)
Scintillation Index of Echo Wave in Slant Atmospheric Turbulence
Jia Rui, Wei Hongyan, Zhang Hongjian, Cai Dongmei, and Li Zhenjun
Based on the modified Rytov method, a model of scintillation index of echo wave from the point target in slant atmospheric turbulence is proposed. The model extends the scintillation index from weak fluctuation regimes to the moderate and strong fluctuation regimes in both monostatic system and biastatic system. BesideBased on the modified Rytov method, a model of scintillation index of echo wave from the point target in slant atmospheric turbulence is proposed. The model extends the scintillation index from weak fluctuation regimes to the moderate and strong fluctuation regimes in both monostatic system and biastatic system. Besides the inner scale, the model also contains the outer scale which changes with altitude. Numerical analysis results show that the outer scale affects the scintillation index little in the weak regime but plays an important role in the strong regime. The results above can be used for forecasting the influence of atmospheric turbulence on laser communication systems or laser detection systems..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1113001 (2015)
Modal Reconstruction for Three-Dimensional Wavefront of Atmosphere Turbulence in Star Oriented Multi-Conjugate Adaptive Optics
Yan Zhaojun, and Yang Pengqian
Three-dimensional wavefront reconstruction of atmospheric turbulence is key technique for star oriented multi- conjugate adaptive optics (SO- MCAO), and the algorithm for three- dimensional wavefront mode reconstruction of atmospheric turbulence in SO-MCAO is analyzed theoretically and researched by simulations. The anThree-dimensional wavefront reconstruction of atmospheric turbulence is key technique for star oriented multi- conjugate adaptive optics (SO- MCAO), and the algorithm for three- dimensional wavefront mode reconstruction of atmospheric turbulence in SO-MCAO is analyzed theoretically and researched by simulations. The analysis result shows that the global piston and tip/tilt modes are singular and cannot be localized in altitude due to the fact that piston of turbulence cannot be measured in the case of two turbulence layers by using nature guide stars. Global piston, tip/tilt, defocus, astigmatism modes are singular and cannot be reconstructed in altitude because piston and tip/tilt of turbulence cannot be measured while using laser guide stars. For three turbulence layers, a growing number of singular modals produce enormous aliasing error that cannot be avoided. In spite of the inaccurate wavefront reconstruction for three turbulence layers respectively, the wavefront from observed object can be completely reconstructed if its footprints on layers are fully covered by nature guide stars..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1113002 (2015)
Spreading of Annular Beams Propagating through Atmospheric Turbulence along a Slanted Path
Chen Hong, and Ji Xiaoling
Taking the encircled-power width defined by the power of 86.5% in the bucket as the characteristic parameter, the spreading of annular beams propagating through atmospheric turbulence along a slanted path is studied by using the numerical simulation method. It is shown that in free space, the lobe of the far-field inteTaking the encircled-power width defined by the power of 86.5% in the bucket as the characteristic parameter, the spreading of annular beams propagating through atmospheric turbulence along a slanted path is studied by using the numerical simulation method. It is shown that in free space, the lobe of the far-field intensity distribution appears with the obscure ratio increasing. The lobe disappears due to the turbulence, and the far-field intensity distribution is not a Gaussian profile. The beam spreading increases as the obscure ratio and the zenith angle increase, and the influence of turbulence on the beam spreading increases when the zenith angle increases. However, when the obscure ratio is large or small, the influence of turbulence on the beam spreading decreases as the obscure ratio increases; when the obscure ratio is middling, the influence of turbulence on the beam spreading is nearly unchanged versus the obscure ratio. Compared with previous work, it is found that the law of the influence of turbulence on the spreading of annular beams is different if the percentage of the power in the bucket is different. The results are useful for practical applications..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1113003 (2015)
Study on Helicity Flip of Backscattered Circular Polarized Light
Yu Yang, Fan Zhiguo, u Shaohan, and Gao Jun
Compared with the linear polarized light, circularly polarized light has more potential advantages, especially in suppressing the influence of the scattered light when detecting targets in turbid medium using the helicity of circularly polarized light. Based on the description method of classic single-particle polarizaCompared with the linear polarized light, circularly polarized light has more potential advantages, especially in suppressing the influence of the scattered light when detecting targets in turbid medium using the helicity of circularly polarized light. Based on the description method of classic single-particle polarization state, the helicity reversion and maintenance mechanism of the circularly polarized light is illustrated from the perspectives of scattering medium properties and scattering angle, and the backscattering helicity reversion characteristic of circularly polarized light is analyzed by Monte Carlo simulation method. The simulation results show that the helicity maintenance or reversion after single scattering depends on the properties of scattering medium and the size of scattering angle. After multiple scattering it is also related to the intersection angle between incident photon and photon receiving surface. Specifically the helicity flipping of backscattering circularly polarized light occurs in a low concentration of scattering medium or short distance transmission. But in the turbid medium namely high concentrations of scattering medium or long distance transmission, the helicity maintains its initial polarization state..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1113004 (2015)
Monte Carlo Simulation of Polarization Lidar Multiple Scattering nDepolarization by Water Cloud
Sun Xianming, Xiao Sai, Wan Long, Wang Haihua, and Shen Jin
The polarization lidar returns exist a depolarization signal in liquid water clouds due to the occurrence of multiple scattering when the optical and microphysical characteristics of liquid water clouds are detected by lidar. The detailed process of semi- analytic Monte Carlo simulation is given to study the backscatteThe polarization lidar returns exist a depolarization signal in liquid water clouds due to the occurrence of multiple scattering when the optical and microphysical characteristics of liquid water clouds are detected by lidar. The detailed process of semi- analytic Monte Carlo simulation is given to study the backscattering depolarization of polarization lidar. The backscattering Muller matrix 2D images are given for the liquid water clouds with the laser at 0.532 μm as the light source. The 2D images of backscattering Stokes parameters are given for the horizontal linear polarization, vertical linear polarization, +45° linear polarization and right circular polarization states of light incidence. The depolarization and the polarization ratios are given for different lidar receiver field of view angles and depth from the cloud base. From the results, it can be seen that the impact of multiple scattering increases with the increase of receiver field of view angle. The proposed Monte Carlo simulation method has great value for remote sensing of water clouds and spherical aerosol characteristics..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1113005 (2015)
Design of Compensator of Convex Aspheric Surface with Small Apertures
Xing Zhenchong, Zhang Bao, and Hong Yongfeng
While testing the secondary mirror with convex aspheric of off- axis three- mirror optical system, compensation method is used to achieve high-precision aspheric testing. Thus design of compensator is a key technology. Compensation in transmission form can′t be used for small- caliber convex aspheric surface with greatWhile testing the secondary mirror with convex aspheric of off- axis three- mirror optical system, compensation method is used to achieve high-precision aspheric testing. Thus design of compensator is a key technology. Compensation in transmission form can′t be used for small- caliber convex aspheric surface with great quadratic surface coefficient and non- transmissive back surface. So the convex aspheric surface is directly taken as a reflection in auto- collimation parallel light compensation test. According to the design ideas, the initial structure is built by the Zemax firstly, which simplifies the calculation of the initial structure, and can get the desired compensation system structure. The design and tolerance analysis process of convex aspheric secondary mirror compensator system is given with the diameter of 80 mm, the quadratic surface coefficient of - 6.5, and the F number of 5.00375. The system operating wavelength is 632.8 nm. The root mean square (RMS) of wavefront error is 0.000015λ. Analysis results show that the total residual wave aberration of the system is 0.0104708λ, which satisfies the requirement of assembling accuracy..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1116001 (2015)
A Common Aperture Coaxial Three-Mirror Optical System with High Resolution
Chen Zhe, Zhang Xingxiang, Chen Changzheng, and Ren Jianyue
In order to realize the round-the-clock space-to-earth observation with high resolution, a visible and infrared bands common aperture optical system is designed, taking full advantage of the high resolution of the space optical system with long focal length and large aperture. The system consists of a visible spectrum In order to realize the round-the-clock space-to-earth observation with high resolution, a visible and infrared bands common aperture optical system is designed, taking full advantage of the high resolution of the space optical system with long focal length and large aperture. The system consists of a visible spectrum optical system and an infrared (IR) subsystem. The fields of view for the two spectral ranges are both 1.3°×0.1° which is convenient for push-broom imaging simultaneously. A coaxial three-mirror structure with a middle image plane and a real exit pupil to facilitate suppressing the stray light is utilized by the visible spectrum optical system whose working wavelength band is 0.38~0.78 μm, focal length is 25 m, and F-number is 10. The beam is split near the exit pupil of the visible spectrum optical system, to which an IR subsystem is designed and connected. Then the coaxial threemirror optical system and the IR subsystem are integrated into a common aperture IR optical system, whose working wavelength band is 8~10.5 μm, focal length is 4 m and F-number is 1.6. After optimization, the structure of the whole system is compact, and the image quality in the two bands approaches the diffraction limit satisfying the design requirement. The tolerance analysis of the two systems is accomplished, and the result of Monte-Carlo analysis indicates that a static modulation transfer function(MTF) better than 0.2 is achievable..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1116002 (2015)
Effect of Laser Shock Processing on Electrochemical Corrosion Behavior of 7075 Aluminum Alloy Plasma Arc Weldments
Wang Jiangtao, Zhang Yongkang, Chen Jufang, Zhou Jinyu, Lu Yalin, and Zhang Chaoyang
The effect of laser shock processing (LSP) on electrochemical corrosion behavior of 7075 aluminum alloy plasma arc weldments has been studied by using polarization curves, electrochemical impedance spectroscopy, residual stress tested by X- ray diffraction technique and scanning electron microscope (SEM) morphology of The effect of laser shock processing (LSP) on electrochemical corrosion behavior of 7075 aluminum alloy plasma arc weldments has been studied by using polarization curves, electrochemical impedance spectroscopy, residual stress tested by X- ray diffraction technique and scanning electron microscope (SEM) morphology of corrosion surface. The results show that the surface residual stress of weldments with LSP has been changed from tensile to compression, which leads to the improvement of the free-corrosion potential and pitting potential. The free-corrosion potential of weldments with 4 times LSP impacts is about 700 mV higher than that without LSP, and the pitting potential also occurs in about 1000 mV, besides the polarization curves exhibit an anode passivation zone in a wide range of potential with 712.9 mV. After grains being refined by LSP, the number of the microscopic holes and the volume of cavitation have been reduced, and the compactness of its surface microstructure has been improved. The infiltration of atoms such as Cl- in the NaCl solution has been effectively prevented, thereby the corrosion rate can be reduced, and the corrosion current density has been decreased by one orders of magnitude. The grains have been well-distributed along the β -phase in weldments with LSP. The activity of micro-galvanic made up of β phase and α base phase has been reduced, and the impact of passive resistance is nearly 30 times higher than that without LSP. Concentration polarization has been greatly improved..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1203006 (2015)
Effect of Laser Beam Displacement on Characteristics of Laser Welded Ti2AlNb/TC4 Dissimilar Alloy
Lei Zhenglong, Liu Ming, Zhang Kezhao, and Chen Yanbin
In view of the high porosity susceptibility in laser welded Ti2AlNb/TC4 dissimilar alloy, different beam displacements are applied in laser welding of Ti-22Al-27Nb and Ti-6Al-4V alloy. The results show that porosity can be successfully suppressed when laser beam acts on Ti-22Al-27Nb alloy. The fusion zones consist of BIn view of the high porosity susceptibility in laser welded Ti2AlNb/TC4 dissimilar alloy, different beam displacements are applied in laser welding of Ti-22Al-27Nb and Ti-6Al-4V alloy. The results show that porosity can be successfully suppressed when laser beam acts on Ti-22Al-27Nb alloy. The fusion zones consist of B2 and B2+ α′ when the beam acts on Ti-22Al-27N band Ti-6Al-4V alloy, respectively. The heat affected zone (HAZ) of Ti-22Al-27Nb is entirely composed of B2. A mixture of acicular α′ and primary α are formed in the HAZ of Ti- 6Al-4V alloy. Due to the second phase strengthening of acicular α′ in the fusion zone when laser acts on Ti-6Al- 4V alloy, the welded joint exhibits higher tensile strength and ductility compared with those produced when the beam acts on Ti-22Al-27Nb alloy or at the middle of two base metals..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1203008 (2015)
Design of Generic Adaptive Optics Wave-Front Real-Time Processor
Chen Shanqiu, Liu Chao, Xu Bing, and Ye Yutang
In order to satisfy the requirement of high speed and real-time processing for 1000-unit class adaptive optics (AO) system in telescope and free space laser communication system, a generic high speed and real-time processing platform on one board is proposed. Multi-core center processing unit (CPU) is arranged for waveIn order to satisfy the requirement of high speed and real-time processing for 1000-unit class adaptive optics (AO) system in telescope and free space laser communication system, a generic high speed and real-time processing platform on one board is proposed. Multi-core center processing unit (CPU) is arranged for wave-front real-time computing, combined with high speed frame-grabber, to achieve the purpose of high frame-frequency. Xenomai real-time operation system combined with Linux operation system is used to satisfy the requirement of low latency. A compact real-time controller is assembled in one computer. Computing power of 51 giga floatingpoint operations per second (GFLOPS) and communication band-width of 102 GB/s are achieved in a computer with 6-core, via vector instruction optimization and processing in parallel with multi-core CPU. The emulation result shows that processing frequency can be up to 2000 Hz for 1145-unit AO system with 949 sub-apertures, and the delay is below 240 μs. This processor is introduced to AO system for laser communication via adjusting the parameters, and Strehl ratio of 0.61 is achieved after correction. This indicates the scheme can satisfy the requirement of high speed and low latency for AO system with actuators below 1145 unit, with the merit of general purpose..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1212001 (2015)
Fiber Optics and Optical Communication
Multi-Channels Self-Calibrating Gallium Arsenide Absorption Fiber Optic Temperature Monitoring System
Hu Kun, Fu Huinan, Luo Xingxing, Mei Yingchun, and Dong Yuming
Fiber optic temperature sensors are accessibly affected by the light source drive current changes, the optical path bending, the splice loss and other intensity variables. In order to solve the temperature deviation caused by the light intensity variations, the system regularly updates the original incident spectrum toFiber optic temperature sensors are accessibly affected by the light source drive current changes, the optical path bending, the splice loss and other intensity variables. In order to solve the temperature deviation caused by the light intensity variations, the system regularly updates the original incident spectrum to realize selfcalibration source waveform. The variation of ambient temperature causes the spectral drift of spectral analysis device which causes the deviation of temperature measurement. To solve this problem, the system uses wavelength locker to locate characteristic wavelength and uses spectral shift compensation method to achieve spectral selfcalibration. The optical multiplexing system is designed to achieve multi- channel fiber optic temperature measurement. Self- calibration verification experiments are designed to verify the validity of the system selfcalibration function. Experimental results show that the system self-calibrating temperature measurement deviation is less than ±1 ℃,when the environment changes. Therefore, the self-calibrating temperature measurement system can withstand the deviation of source spectral waveform changes, and make the spectrum analysis device overcome the interference of ambient temperature..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1105001 (2015)
Research on Visible Light Communication Receiving System Based on Artificial Neural Networks
Guan Weipeng, Wen Shangsheng, Huang Weiming, Chen Yingcong, and Zhang Guanghui
As the inter symbol interference increases the bit error rate(BER) of the visible light communication system，a new artificial neural network (ANN) equalization receiving system is proposed. Based on angle diversity receiving technology and artificial neural networks, the system can not only reduce the influence of inteAs the inter symbol interference increases the bit error rate(BER) of the visible light communication system，a new artificial neural network (ANN) equalization receiving system is proposed. Based on angle diversity receiving technology and artificial neural networks, the system can not only reduce the influence of inter symbol inference, but also improve the signal to noise ratio(SNR) and decrease the bit error rate. The signal transmission test is simulated by Matlab. The simulation results show that the proposed system has lower bit error rate compared with the traditional system which uses single input and single output technology(SISO), what′s more, the former can weaken the influence of inter symbol interference under the same signal to noise ratios of the environment and signal source. This advanced system can optimize the channels performance of visible light communication system, and it obviously has a vast application prospect..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1105002 (2015)
Scattering Loss Analysis and Structure Optimization of Hollow-Core Photonic Bandgap Fibers
Song Jingming, Sun Kang, and Xu Xiaobin
An accurate modeling method for the internal structure of hollow- core photonic bandgap fiber is proposed, and the effect of core structure on scattering loss is studied by full-vector finite element method. The fibers with different core walls thicknesses and different core radii are simulated, and the normalized inteAn accurate modeling method for the internal structure of hollow- core photonic bandgap fiber is proposed, and the effect of core structure on scattering loss is studied by full-vector finite element method. The fibers with different core walls thicknesses and different core radii are simulated, and the normalized interface field intensity is used to characterize the scattering loss. Calculation results show that scattering loss can be largely reduced with the relative core wall thickness Tc≈4. Furthermore, scattering loss decreases with the increase of core radius. With optimized core structure design, the scattering loss can be further reduced down to 50% of the present level in theory within the wavelength range from 1.5 μm to 1.56 μm..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1105003 (2015)
Time Estimation of the Link Stability in Inter-Satellite Optical Communications
Yu Siyuan, Yan Shen, Tan Liying, and Ma Jing
The concept of the bidirectional laser link tracking stability in inter-satellite optical communication is proposed for the problem of short effective time of the signal transmission in the current and the influence of various factors on the tracking stability is analyzed. Considering receiving signal-to-noise ratio(SNThe concept of the bidirectional laser link tracking stability in inter-satellite optical communication is proposed for the problem of short effective time of the signal transmission in the current and the influence of various factors on the tracking stability is analyzed. Considering receiving signal-to-noise ratio(SNR), relative motion velocity, link performance requirements and other factors, expectation formulas of tracking stability time are established. A relatively complete simulation model of bidirectional laser link tracking in inter- satellite communication with Simulink is established, which can prove the correctness of the theory formula. To maintaing inter-satellite optical communication link stability for a long time, a method utilizing different control parameters at different velocities between the satellites is proposed, and the control strategy in inter- satellite optical communication terminal is optimized. The results of this paper are significant for the aerospace engineering of satellite optical communications..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1105004 (2015)
Holography and Information Processing
Experimental Study of the Incoherent Digital Holography
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A holographic recording system is built under incoherent light illumination based on a spatial light modulator and the mathematical model of the system has been established, then we get the specific forms of the point spread function, the axial magnification and the reconstruction distance. The experiments give the thrA holographic recording system is built under incoherent light illumination based on a spatial light modulator and the mathematical model of the system has been established, then we get the specific forms of the point spread function, the axial magnification and the reconstruction distance. The experiments give the three phase-shift holograms and its reconstruction of a negative test slide. Then the holograms of two non-fluorescent dice are captured and digital reconstructed in different planes. The color holographic results are also given. The results show that the system can obtain holograms of real objects simply and rapidly. And we can get a clearly reconstruction without the zero-order and twin image by using the phase-shift algorithm..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1209003 (2015)
Laser Devices and Laser Physics
2 μm 波长红外风冷固体激光器首次实现2 W 级平均功率单频基模输出
郭新军, 蔡京辉, 梁惊涛, 李建国, 何宇峰, and 高艳磊
2015年6月，中国科学院理化技术研究所空间功热转换技术重点实验室采用深低温制冷技术将Tm∶YAG 激光晶体冷却至130 K，采用785 nm 波长半导体泵浦源抽运Tm∶YAG 激光晶体，在785 nm 波长半导体抽运源抽运功率为4.03 W 时，实现了最高平均功率2.12 W，单频波长2013.4 nm，线宽为10~20 KHz，基模的红外固体激光输出，功率稳定性为0.9%，经1/4波片矫正输出的线偏振光偏振度可以达到-0.22 dB以上，这是目前为止，课题组所知国际上公开报道的2013.5 nm 波长红外固体风冷激光器单频、偏振、基模输出的最高记录。2015年6月，中国科学院理化技术研究所空间功热转换技术重点实验室采用深低温制冷技术将Tm∶YAG 激光晶体冷却至130 K，采用785 nm 波长半导体泵浦源抽运Tm∶YAG 激光晶体，在785 nm 波长半导体抽运源抽运功率为4.03 W 时，实现了最高平均功率2.12 W，单频波长2013.4 nm，线宽为10~20 KHz，基模的红外固体激光输出，功率稳定性为0.9%，经1/4波片矫正输出的线偏振光偏振度可以达到-0.22 dB以上，这是目前为止，课题组所知国际上公开报道的2013.5 nm 波长红外固体风冷激光器单频、偏振、基模输出的最高记录。.
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1119001 (2015)
Materials
Magneto-Optical Storage System Based on the Coupling of the One-Way Edge Modes and Micro Cavity Modes
Fang Yuntuan, Hu Jianxia, Xu Qingsong, Ni Zhiyao, and He Hanqing
Optical storage system is the key role for the future all-optical communications and computer. Through numerical study, we design a new kind of magneto-optical storage system based on the coupling of one-way edge modes of magneto-optical photonic crystals and microcavity modes. A close field circulation loop is achieveOptical storage system is the key role for the future all-optical communications and computer. Through numerical study, we design a new kind of magneto-optical storage system based on the coupling of one-way edge modes of magneto-optical photonic crystals and microcavity modes. A close field circulation loop is achieved from the one-way edge modes. By designing a magnetic cavity and another edge waveguide, we can not only take out the signal from the loop but also write the signal into the loop. Through controlling the magnetic field on the cavity, we can dynamically achieve the operation of reading and writing of electromagnetic signals..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1106001 (2015)
Microstructural Characteristics of WC/Stellite 6 Composite Coating Prepared by Supersonic Laser Deposition
Li Zhihong, Yang Lijing, Li Bo, Zhang Qunli, and Yao Jianhua
Supersonic laser deposition (SLD) is a new coating and fabrication process in which a supersonic powder stream produced by cold spray (CS) impinges on a substrate simultaneously heated by laser irradiation to expand the range of materials deposited under solid-state during SLD process. WC/Stellite 6 metal matrix composSupersonic laser deposition (SLD) is a new coating and fabrication process in which a supersonic powder stream produced by cold spray (CS) impinges on a substrate simultaneously heated by laser irradiation to expand the range of materials deposited under solid-state during SLD process. WC/Stellite 6 metal matrix composite (MMC) coating prepared by SLD and laser cladding (LC) are studied and compared in terms of macro- morphology, microstructure, interface dilution and unmelted WC proportion of coating, crack propagation resistance. The results show that the dense, crack-free coatings with uniform distribution of WC are achieved by SLD coating because of solid-state deposition, which can avoid the root causes of WC decomposition and dissolution in high temperature processing. The dilution rate of laser cladding coating is about 8.9%, while no macroscopic dilution zone is found in SLD coatings. The unmelted WC proportion of SLD coatings is about 27.6%, which is much higher than that of LC coatings. The results show that a great number of cracks around the indentation in LC coating while no cracks is found in SLD coatings under 50 kg load indentation indicate that the crack propagation resistance of supersonic laser SLD coating is superior to that of LC coating.
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1106002 (2015)
Third-Order Nonlinear Optical Properties of Graphene-CdS Composites
Wang Ji, Han Junhe, Zhu Baohua, Dai Shuxi, Tan Yunlong, and Gu Yuzong
Graphene- cadmium sulfide (G- CdS) composites are synthesized by a solvothermal method. The composites are characterized by X-ray diffraction, transmission electron microscopy and ultraviolet visible (UVvis) absorption on their structure, size and morphology, which demonstrate that cadmium sulfide quantum dots with an Graphene- cadmium sulfide (G- CdS) composites are synthesized by a solvothermal method. The composites are characterized by X-ray diffraction, transmission electron microscopy and ultraviolet visible (UVvis) absorption on their structure, size and morphology, which demonstrate that cadmium sulfide quantum dots with an average diameter of about 7 nm attached to the graphene surface. The third-order optical nonlinearities of G-CdS composites using picosecond Z-scan technique at wavelength of 532 nm is investigated, pulse width of 30 ps. The results show that G-CdS composite has a positive nonlinear refractive index and properties of saturable absorption. The third-order nonlinear susceptibility of G-CdS composite is calculated to be 4.36×10-12 esu, nonlinear absorption coefficient to be - 6.54 × 10-11 m/W. Comparing with cadmium sulfide quantum dots, the third- order nonlinearity of composites are improved..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1106006 (2015)
Measurement and Metrology
Measurement Method of Film Parameters of Metal Based on Imaging Ellipsometry and Surface-Plasmon Resonance
Hu Shiyu, Zeng Aijun, Gu Liyuan, Huang Huijie, Hu Guohang, and He Hongbo
A measurement method of film parameters of metal based on imaging ellipsometry and surface-plasmon resonance is presented. p polarized light is applied to generate surface-plasmon resonance effect at the interface of metal film and air in layout of imaging ellipsometry. The influence of back light is avoided by s polarA measurement method of film parameters of metal based on imaging ellipsometry and surface-plasmon resonance is presented. p polarized light is applied to generate surface-plasmon resonance effect at the interface of metal film and air in layout of imaging ellipsometry. The influence of back light is avoided by s polarized light which can′ t lead to surface- plasmon resonance effect. Then the normalized reflectance profile along the perpendicular direction of absorption ring of surface- plasmon resonance is obtained. We measure metal film parameters by numerical fitting the reflectance profile along long axis of the elliptical fringe. This method is not necessary to solve the transcendental equation and data processing is simple and fast. The experimental result with this method is coincident with that of standard ellipsometer, which verifies the validity of this measurement method..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1108001 (2015)
Micro In-Plane Displacement Measurement Using New Speckle Phase Singularities Method Generated by Two-Dimensional Directional Wavelet
Gao Yuling, and Pan Guangzhen
A new speckle phase singularities method generated by two-dimensional directional wavelet is proposed to measure micro in-plane displacement. A phase singularities image is generated by polarization analysis of twodimensional directional wavelet, setting the rotation angle be π/2 in order to analyze the image before anA new speckle phase singularities method generated by two-dimensional directional wavelet is proposed to measure micro in-plane displacement. A phase singularities image is generated by polarization analysis of twodimensional directional wavelet, setting the rotation angle be π/2 in order to analyze the image before and after displacement of x and y directions, which has network structure stable distribution. The new two-step displacement measurement method is proposed. Preliminary displacement is obtained in the output two correlation points image by using twice Fourier transform and subtraction. The precision displacement of object to be measured is calculated by half the grid width of the initial displacement and displacement between the closest matching singular point. It is studied that simulation and laser mouse positioning experiment. Results show that correct matching singularities are still more than 90% under different noise conditions and the error between actual value and measured value of mouse displacement and direction is less than 0.5 pixel and 1°. This method has many advantages, such as high rate of singularity correct matching, high accuracy, insensitive to noise and good stability, which can precisely locate the displacement and direction of the laser mouse..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1108002 (2015)
Method of Velocity Measurement Based on Moire Fringe and Total Differential Equations
Wang Yazhou, Wan Qiuhua, Wang Shujie, Yang Shouwang, and Du Yincai
For the purpose of improving the velocity measurement accuracy of photoelectric encoders, a velocity measurement method based on the signal of moire fringe is proposed. A velocity measurement model based on moire fringe is established using the total differential equations. The main factors affecting velocity measuringFor the purpose of improving the velocity measurement accuracy of photoelectric encoders, a velocity measurement method based on the signal of moire fringe is proposed. A velocity measurement model based on moire fringe is established using the total differential equations. The main factors affecting velocity measuring accuracy are analyzed and the influence of different factors is compared. An improved algorithm is deduced and the measurement system is established based on the velocity model. Measurement results on some 21- bit photoelectric encoder indicate that the root mean square of measurement error has reduced from 0.0367 rad/s to 0.0216 rad/s. This method can achieve fast and high-accuracy measurement, and be suitable for the control system requiring for high real-time capability..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1108003 (2015)
Study on Reconstruction Resolution of Integral Imaging Technique Based on Ray-Tracing Method
Zhang Juan, Zhou Liqiu, Zhang Bo, Zhang Zan, Zheng Yi, and Zhao Xing
Characterization method of reconstruction resolution of integral imaging technique is significant to the optimization and evaluation of integral imaging system. According to the principle of geometrical optics, considering the pixel discretization effect in the process of digital records, the projection and overlappingCharacterization method of reconstruction resolution of integral imaging technique is significant to the optimization and evaluation of integral imaging system. According to the principle of geometrical optics, considering the pixel discretization effect in the process of digital records, the projection and overlapping of corresponding pixels in image space of three-dimensional reconstruction processing are deeply analyzed, combining the correlations of corresponding pixels in elemental images array. The lateral and depth resolution of integral imaging in image space are defined, and their axial distribution character is studied. The theoretical analysis and experimental results demonstrate that the axial distribution character of lateral and depth resolution of integral imaging is inhomogeneous..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1108004 (2015)
Optical Communication
Study of Pattern Recognition Based on Multi-Characteristic Parameters for φ-OTDR Distributed Optical Fiber Sensing System
Zhang Yan, Lou Shuqin, Liang Sheng, and Wang Peng
In view of the present phase sensitive optical time-domain reflectometer (φ-OTDR) distributed optical fiber sensing system is difficult to distinguish the disturbance effectively. A disturbance modes recognition method based on multi-parameters is presented. A weighted average synthetic evaluation function is used for In view of the present phase sensitive optical time-domain reflectometer (φ-OTDR) distributed optical fiber sensing system is difficult to distinguish the disturbance effectively. A disturbance modes recognition method based on multi-parameters is presented. A weighted average synthetic evaluation function is used for characteristic parameters pattern recognization including square difference, short time level crossing rate, short time Fourier transform and duration of the disturbance. By the proposed method, four disturbance modes including stress damage (breaking), climbing, watering (simulate rain environment) and mild crushing (simulate harmless artificial disturbance) are effectively recognized. The recognition rate of disturbance pattern recognization is realized as 91.2%, 88.3%, 90% and 86.7%, respectively, for the corresponding four disturbance modes by analyzing the statistics of 60 groups of 240 samples. The proposed method breaks though the limitation of disturbance modes recognized by current single-characteristic parameter method and improves the reliability of disturbance pattern recognization..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1105005 (2015)
Remote Sensing and Sensor
Study on the Sensing Mechanism of Photonic Crystal Containing Metal Layer Based on the Coupling Analysis of Optical Tamm State
Chen Ying, Dong Jing, Liu Teng, Shi Jia, Zhu Qiguang, and Bi Weihong
Based on the coupling analysis of the optical Tamm states in the photonic crystal, a refractive index sensing structure containing metal inset layer is proposed. The formation mechanism of optical Tamm state is analyzed and the suitable thickness of the metal is chosen to realize the coupling of two optical Tamm statesBased on the coupling analysis of the optical Tamm states in the photonic crystal, a refractive index sensing structure containing metal inset layer is proposed. The formation mechanism of optical Tamm state is analyzed and the suitable thickness of the metal is chosen to realize the coupling of two optical Tamm states. The relationship model between the reflection peak wavelength and the refractive index of the sample solution is established, and its refractive index sensing characteristics are discussed. Through the discussion of the periodicity and the incident angle of the photonic crystal, it shows that the full width at half maximum (FWHM) can be reduced by increasing the periodicity (or the incident angle), which can improve the sensitivity of the sensor and the resolution of the refractive index obviously. The ethylene glycol is adopted as the sample detected, the sensitivity of the refractive index sensing structure is about 445.45 nm/RIU, and the quality factor (Q value) can attain to 1259.45. The sensor structure has several advantages such as simple preparation and compact structure, which can provide some theoretical references for the design of high Q value and high sensitivity refractive index sensors..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1114001 (2015)
Inversion of Corn Leaf Area Index Using Terrestrial Laser Scanning Data and Landsat8 Image
Zhang Mingzheng, Su Wei, and Wang Ruiyan
Optical spectral remote sensing images can be used to extract corn canopy structure information rapidly in a large area. However, it cannot provide vertical canopy structure information, which leads to underestimated leaf area index (LAI) result. Terrestrial laser scanning can provide high precision 3D structure informOptical spectral remote sensing images can be used to extract corn canopy structure information rapidly in a large area. However, it cannot provide vertical canopy structure information, which leads to underestimated leaf area index (LAI) result. Terrestrial laser scanning can provide high precision 3D structure information of corn canopy, but only in the limited sampling area. Therefore, these two technologies are combined to extract high precision canopy structure through canopy analysis by using terrestrial laser scanning data voxelization method. Reflectance of large area of corn canopy using Landsat8 optical images is obtained, and accurate corn canopy LAI results are got through regression analysis of canopy structure information of voxel-based canopy profiling. The results show that LAI has the strongest correlation with the normalized difference vegetation index (NDVI), the correlation coefficient R2=0.8086, the root mean square error (RMSE) is 0.1230, and the correlation between LAI and ratio vegetation index (RVI) is the worst, R2=0.7079, RMSE is 0.1520. Based on the validation analysis of the measured values, the average relative error of the three models is lower than 10%, and the credibility of the three models is relatively high..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1114002 (2015)
Research on Wideband Signal Generation for Ladar
Du Jianbo, Li Daojing, and Ma Meng
To improve the resolution and operating range of ladar, the transmission signal should be wideband phase-modulated signal or wideband linear frequency modulation (LFM) signal, for they have large time bandwidth product. It is hard to generate wideband LFM signal within short pulse width using the present laser frequencTo improve the resolution and operating range of ladar, the transmission signal should be wideband phase-modulated signal or wideband linear frequency modulation (LFM) signal, for they have large time bandwidth product. It is hard to generate wideband LFM signal within short pulse width using the present laser frequency modulation technology. Therefore a method based on Mach-Zehnder modulation technique is studied to generate laser wideband LFM signal. Using one dual-parallel Mach-Zehnder modulator (DPMZM) can realize IQ quadrature modulation and generate laser LFM signal.Based on this, a method to generate laser-band frequency tripling LFM signal by using two DPMZMs is proposed. Theoretical analyses and simulation results show that the proposed method has good ability in harmonic suppression, and can greatly decrease the bandwidth of input modulation signal and can be realized with low-speed digital to analog conversion..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1114003 (2015)
Spectroscopy
Detection of Polycyclic Aromatic Hydrocarbons Combining Fluorescence Analysis with ABC-BP Neural Network
Wang Shutao, Chen Dongying, Wang Xinglong, Han Huanhuan, and Wang Jialiang
Fluorescence spectrum properties of benzo [k] fluoranthene (BkF), benzo[a]pyrene (BaP), and their mixture are analyzed. The experimental results show that there are two characteristic fluorescence peaks existing in BkF and six characteristic fluorescence peaks in BaP. The optimal emission wavelength of BkF and BaP is 4Fluorescence spectrum properties of benzo [k] fluoranthene (BkF), benzo[a]pyrene (BaP), and their mixture are analyzed. The experimental results show that there are two characteristic fluorescence peaks existing in BkF and six characteristic fluorescence peaks in BaP. The optimal emission wavelength of BkF and BaP is 405 nm . The fluorescence characteristics of the mixture vary widely when there are different concentration ratios. But the optimal emission wavelength of the mixture with different concentration ratios does not change, remaining at 405 nm. When the excitation wavelength is 250~400 nm and the emission wavelength is 350~500 nm, serious overlapping occurs in the fluorescence spectra of BkF and BaP. In order to detect their concentrations in the mixture precisely, back propagation (BP) neural network optimized by artificial bee colony (ABC) algorithm is applied. The result indicates that the ABC-BP neural network is better than the genetic algorithm (GA)-BP method. The ABCBP neural network can accurately detect the concentration of BkF and BaP in their mixture when the concentration is in the range of 1.000~10.000 ng/L. The average recovery of BkF and BaP in ten mixture groups is 99.19% and 99.26%, respectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1115001 (2015)
Rapid Measurement of Particle Ratio in Soil by Laser Induced Breakdown Spectroscopy
Gu Yanhong, Zhao Nanjing, Ma Mingjun, Meng Deshuo, Yu Yang, Wang Yin, Hu Li, Fang Li, Jia Yao, Wang Yuanyuan, Liu Jianguo, and Liu Wenqing
Calibration- free laser induced breakdown spectroscopy (CF- LIBS) requires that the elements be normalized, various elements are involved in calculation. However, the spectral line of microelements in the soil is weak, and it is difficult to draw the Saha-Boltzmann plot. The element particle ratio method is used to calCalibration- free laser induced breakdown spectroscopy (CF- LIBS) requires that the elements be normalized, various elements are involved in calculation. However, the spectral line of microelements in the soil is weak, and it is difficult to draw the Saha-Boltzmann plot. The element particle ratio method is used to calibrate the concentration of Cr in soils from a variety of national standard samples as well as local acquisition. The temperature of the plasma is calibrated from Saha-Boltzmann equation and the electron density is determined from the line width of Al I 309.284 nm. The assumption of the local thermal equilibrium (LTE) is validated by the McWhirter criterion. The particle ratio of Cr and Si is calculated by Saha-Boltzmann plot and Saha equation. The concentration of Cr can be calculated. The relative error for the national standard soil samples is less than 7%, and is less than 16.438% for the field collected samples. The results indicate that the element particle ratio method can be used in the concentration analysis of Cr in soils to improve performance of the LIBS technique in rapid detection of soil element content..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1115002 (2015)
Study on Rapid and Non-Destructive Detection of Rice Seed Vigor Based on Photoacoustic Spectroscopy Combined with LS-SVR
Li Huanhuan, Lu Wei, Du Changwen, Ma Fei, and Luo Hui
Considering that the traditional method for vigor test is complex, time- consuming, with poor reproducibility, irreversible, and likely to cause damage to the seed, a rapid and non-destructive testing method of rice seed vigor based on photoacoustic spectroscopy technology and least squares support vector regression (LConsidering that the traditional method for vigor test is complex, time- consuming, with poor reproducibility, irreversible, and likely to cause damage to the seed, a rapid and non-destructive testing method of rice seed vigor based on photoacoustic spectroscopy technology and least squares support vector regression (LSSVR) is proposed. Under the condition of temperature of 45 ℃ and relative humidity of 90%, Nanjing46 (japonica rice) and Nei5you 8015 (hybrid rice) rice seeds are artificially aged for 0, 24, 48, 72, 96 h to get rice seeds with different vigor. Spectral data of 100 samples for the two types of rice seeds are collected and divided into a calibration set (60 samples) and a prediction set (40 samples). Wavelet packet analysis is used in spectral preprocessing. Dimensionality reduction of the spectrum data is realized by covariance analysis and principal component analysis (PCA). Prediction models of rice seed vigor are established respectively by partial least squares regression (PLSR), back propagation neural network (BPNN) and LS-SVR. The results show that the optimal model is constructed by covariance analysis and LS-SVR, and the model is not only suitable for single rice species, but also for different types of rice seed in vigor forecast. The experiment shows that it is feasible that rice seed vigor is detected rapidly and non-destructively by photoacoustic spectroscopy technology and LS-SVR. The model has better prediction accuracy in vigor detection, and provides a theoretical basis for the development of portable rice seed vigor spectrometers..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1115003 (2015)
Application of Gated Photomultiplier Tube in Signal Detection of LIBS
Tang Kunpeng, Li Runhua, and Chen Yuqi
The analytical sensitivity of laser-induced breakdown spectroscopy (LIBS) is significantly influenced by the electronic bremsstrahlung emission in plasma. Since the time duration of the background emission in LIBS is usually shorter than that of the atomic emission, it is possible to get high signal to background ratioThe analytical sensitivity of laser-induced breakdown spectroscopy (LIBS) is significantly influenced by the electronic bremsstrahlung emission in plasma. Since the time duration of the background emission in LIBS is usually shorter than that of the atomic emission, it is possible to get high signal to background ratio by using timeresolved signal detection technique. A gated photomultiplier tube with a simple new gating circuit is applied in LIBS signal detection and the copper impurity in aluminum alloy is analyzed with improved analytical sensitivity. The rejection ratio of the background reaches 15∶1. The limit of detection of copper in aluminum alloy is determined to be 1.02×10-6 in single-pulse LIBS, which is much lower than that obtained without gating technique. The gated photomultiplier tube can be used to reduce influence of the background emission and will be helpful with improving both analytical sensitivity and spatial resolution of LIBS..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1115004 (2015)
Effect of Laser-Induced Crater on Soil Plasma Radiation Characteristics
Xu Songning, Jiang Ran, Ning Ribo, Li Qian, and Duan Wenzhao
Single pulses exported from Nd: YAG laser are used to act on the same position of soil sample surface repeatedly to form laser- induced craters. Grating spectrometer and ICCD are used to record plasma emission spectra generated from each laser pulse. The effect of laser-induced craters on radiation characteristics of sSingle pulses exported from Nd: YAG laser are used to act on the same position of soil sample surface repeatedly to form laser- induced craters. Grating spectrometer and ICCD are used to record plasma emission spectra generated from each laser pulse. The effect of laser-induced craters on radiation characteristics of soil plasma is investigated. The experimental results show that there exists a trend that the line intensity and signalto- background ratio of Cr and Pb elements initially increase and then decrease along with increased number of laser shots under the confinement effect of crater walls. Overall, the best signal intensity can be obtained with a confinement laser-induced crater with 1.0 mm diameter and 2.5 mm depth. The experiment clearly indicates that self-absorption becomes weaker and then disappears along with increased number of laser shots. The results show that the line intensity and signal-to-background ratio are both improved and the electron temperature increases under the confinement effect of the crater walls, reducing the level of self-absorption spectral lines effectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 11, 1115005 (2015)
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