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2018
Volume: 45 Issue 11
39 Article(s)
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Beam Transmission and Control
Tunable Bottle Beam of Semiconductor Laser
Yang Zhikun, Ma Xiaohui, Fang Junyu, Jin Liang, Xu Yingtian, and Zhang He
We obtain a bottle beam by focusing a Bessel beam with the semiconductor laser as the light source to realize the tunability of a bottle beam. The plano-convex cylindrical lens and the gradient index lens are used for beam shaping to obtain a laser beam with a variable divergence angle, and thus a size tunable bottle bWe obtain a bottle beam by focusing a Bessel beam with the semiconductor laser as the light source to realize the tunability of a bottle beam. The plano-convex cylindrical lens and the gradient index lens are used for beam shaping to obtain a laser beam with a variable divergence angle, and thus a size tunable bottle beam is obtained. The numerical simulation results show that, when the divergence angle of the beam incident on the axial cone varies continuously in the range of 0°-1.5°, the maximum radial size of the bottle beam can be tunable in the range of 90.23-64.05 μm, however the length of the bottle beam varies from 1.85 mm to 1.47 mm. A tunable bottle beam makes optical tweezers more flexible..
Chinese Journal of Lasers
- Publication Date: Jun. 26, 2018
- Vol. 45, Issue 11, 1105001 (2018)
Biomedical Photonics and Laser Medicine
Measuring Velocity of Blood Flow Based on Photoacoustic Correlation Spectroscopy
Pan Liuhua, Zhang Xiangyang, Li Zhongliang, Nan Nan, Bu Yang, Chen Yan, Wang Xuan, and Wang Xiangzhao
Velocity of blood flow is measured by photoacoustic correlation spectroscopy. The effects of the laser repetition frequency and the angle between the blood flow direction and incidence laser propagation direction on the measurement of velocity of blood flow are studied. Research results show that the faster the blood fVelocity of blood flow is measured by photoacoustic correlation spectroscopy. The effects of the laser repetition frequency and the angle between the blood flow direction and incidence laser propagation direction on the measurement of velocity of blood flow are studied. Research results show that the faster the blood flow velocity, the higher the laser repetition frequency required. When the blood flow orientation is perpendicular to the direction of incident laser propagation direction, the range of velocity of blood flow that the system can measure is 0.059-92.3 mm/s. The correlation coefficient between the measured flow velocities and the actual flow velocities is 0.992. When the blood flow orientation is not perpendicular to the direction of incident laser propagation direction, the ratios of the measured velocities of blood flow to the original ones are cosine to the tilted angle of sample..
Chinese Journal of Lasers
- Publication Date: Jun. 15, 2018
- Vol. 45, Issue 11, 1107001 (2018)
Handheld Optical Coherence Tomography Based on Logarithmic Compensation and Motion Threshold
Yue Zhang, Wanrong Gao, Lanlan Zhang, and Weisong Shi
A handheld swept optical coherence tomography system capable of rapidly imaging subcutaneous human microvascular is established. Three algorithms are used to reconstruct the blood flow distribution images: power intensity differential (PID) without logarithmic compensation, logarithmic-compensated power intensity diffeA handheld swept optical coherence tomography system capable of rapidly imaging subcutaneous human microvascular is established. Three algorithms are used to reconstruct the blood flow distribution images: power intensity differential (PID) without logarithmic compensation, logarithmic-compensated power intensity differential (LCPID), and logarithmic-compensated power intensity differential with motion threshold (MTPID). Then, microvascular en-face images obtained by three imaging algorithm are compared. The results show that the LCPID algorithm can reveal deeper blood flow information, and the MTPID algorithm can get more details of the blood flow distribution and high image resolution. So, the superiority of MTPID algorithm has significance for the application of OCT system in biomedical optics..
Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1107002 (2018)
Fiber Optics and Optical Communication
Graphene Optical Modulator Based on Optical Tamm States
Wang Lei, Luan Kaizhi, Zuo Yifan, and Li Peili
By using the local field enhancement of the optical Tamm state (OTS) at the interface of metal-distributed Bragg reflector(DBR) and the electronic control characteristics of graphene, we propose a graphene based light modulator based on OTS. The proposed optical modulator is simulated by finite element method and finitBy using the local field enhancement of the optical Tamm state (OTS) at the interface of metal-distributed Bragg reflector(DBR) and the electronic control characteristics of graphene, we propose a graphene based light modulator based on OTS. The proposed optical modulator is simulated by finite element method and finite difference time domain method. The results show that when the incident wavelength is 850.7 nm, OTS can be engendered at the metal-DBR interface and the reflectivity of incident light is relatively low. When the driving voltage is greater than 7.5 V, the intrinsic wavelength of OTS drifts and the reflectivity of incident light increases, so that intensity modulation can be achieved. The maximum modulation depth of the optical modulator can be up to 0.96 and the extinction ratio is 14.45 dB. Without considering the effect of RC time constant on the modulation rate, the modulation rate is above 600 GHz. The proposed graphene modulator can be modulated with different modulation depths in a certain wavelength range. It has a good application prospect in the optical communication system and the optical information processing system in the future..
Chinese Journal of Lasers
- Publication Date: Jun. 14, 2018
- Vol. 45, Issue 11, 1106001 (2018)
Experimental Study on Linearity of Microwave Photonic Link with Direct Modulation or External Modulation
Chen Hua, Zou Xihua, Yu Ge, and Lu Bing
The linearity of microwave photonic link with direct modulation mode or external modulation mode is theoretically studied. The direct modulation short-range microwave photonic link, which is used direct modulation laser as the core device, has obvious advantages in linearity. Then the experiments are carried out to obtThe linearity of microwave photonic link with direct modulation mode or external modulation mode is theoretically studied. The direct modulation short-range microwave photonic link, which is used direct modulation laser as the core device, has obvious advantages in linearity. Then the experiments are carried out to obtain key performance parameters through analysis of acquired signals under the two modulation modes, including the link loss, compression dynamic range (CDR) and spurious free dynamic range (SFDR). The dynamic ranges of fiber links with different lengths are compared, and the performance of the microwave photonic link with direct modulation drops significantly after the 10-km optical fiber transmission. In addition, considering the linewidth and chirp of directly modulated laser, dispersion effects for fiber links with different lengths are studied experimentally. The result shows that the microwave photonic link with direct modulation has high linearity for short-distance transmission..
Chinese Journal of Lasers
- Publication Date: Jun. 22, 2018
- Vol. 45, Issue 11, 1106002 (2018)
Side-Glowing Optical Fiber as Directional Backlight in Autostereoscopic Display
He Yong, Li Zirun, Gao Feifei, Liu Chujia, Qi Yu, and Zhuang Qiren
A kind of uniformly-side-glowing optical fiber is designed and studied, which is obtained by scattering points graved on the plastic optical fiber (POF) by laser marking. This new fiber can be used as a directional backlight source for the autostereoscopic display. The model for a uniform side-glowing POF with laser maA kind of uniformly-side-glowing optical fiber is designed and studied, which is obtained by scattering points graved on the plastic optical fiber (POF) by laser marking. This new fiber can be used as a directional backlight source for the autostereoscopic display. The model for a uniform side-glowing POF with laser marking engraved concave scattering points is established and used to derive the formula for calculating the scattering point coordinates. With the designed concave scattering point parameters, the model of side-glowing plastic optical fiber is established by the SolidWorks software, and the light ray tracing simulation is carried out based on the TracePro software. The results show that the tiny length semicircular angle change of scattering points, used for the characterization of depth and horizontal length of concave scattering points, has a large impact on the luminance uniformity. In contrast, the tiny axial width change of concave scattering points has a little impact on the side-glowing luminance uniformity. When the parameters are optimized, one can get the POF radius of R=0.25 mm, the concave scattering point width of d=0.15 mm, the scattering point length semicircular angle of θ=15°, the POF length of L=600 mm and the POF side-glowing luminance uniformity of 87.5% obtained by the TracePro simulation. According to the optimized design parameters, laser marking is used for graving scattering points on the POF surface and the obtained side-glowing luminance uniformity of single POF is 80.90%. Furthermore, a luminescence uniformity of 88.91% can be realized if the surface light source is composed of 100 side-glowing POFs. The experimental results show that the proposed design method and the fabricated POF surface light sources can meet the requirements of the directional backlight source design for 3D autostereoscopic display..
Chinese Journal of Lasers
- Publication Date: Jun. 22, 2018
- Vol. 45, Issue 11, 1106003 (2018)
Polarization Mode Dispersion Measurement Based on Wavelet Threshold Denoising
Sha Yuyang, Xi Lixia, Zhang Xiaoguang, Tang Xianfeng, and Zhang Wenbo
The fixed analyzer method commonly used for measuring the polarization mode dispersion of optical fibers can introduce errors and reduce measurement accuracy, and thus a novel scheme based on wavelet threshold denoising is proposed to further improve the measurement accuracy. The specific workflow of the scheme is presThe fixed analyzer method commonly used for measuring the polarization mode dispersion of optical fibers can introduce errors and reduce measurement accuracy, and thus a novel scheme based on wavelet threshold denoising is proposed to further improve the measurement accuracy. The specific workflow of the scheme is presented and the selection principle and scheme of wavelet threshold, threshold function, mother wavelet and wavelet decomposition layer number are discussed in detail. An experimental platform is built and the measurement is conducted. The measurement results are compared with those by the commonly used Fourier transform method and commercial polarization mode dispersion measurement instruments. The experimental results show that the proposed wavelet threshold denoising scheme can be used to effectively reduce the impact of noises on the measurement results and is also suitable for different types and lengths of test fiber samples. If the measurement results by commercial instruments are taken as the reference standard, the maximum error by the proposed scheme is 2.27%, which indicates the polarization mode dispersion measurement accuracy by the fixed analyzer method is significantly enhanced..
Chinese Journal of Lasers
- Publication Date: Jul. 17, 2018
- Vol. 45, Issue 11, 1106006 (2018)
Fiber Optics and Optical Communications
Multi-Stopband Microwave Photonic Filter Based on Stimulated Brillouin Scattering
Yiming Xu, Wei Pan, Bing Lu, and Ge Yu
Based on the stimulated Brillouin scattering, a variable multi-stopband microwave photonic filter with aperiodic spectral response is designed and experimentally demonstrated. Variable multi-tone pump light is generated and the multi-frequency optical sideband is simultaneously processed by the usage of a programmable Based on the stimulated Brillouin scattering, a variable multi-stopband microwave photonic filter with aperiodic spectral response is designed and experimentally demonstrated. Variable multi-tone pump light is generated and the multi-frequency optical sideband is simultaneously processed by the usage of a programmable electrooptic modulator driven by the radio-frequency signal. The number of stopbands, central frequencies of stopbands and out-of-band rejections of stopbands are controlled by the radio-frequency signal. As the experimental result shows, the spectral response of this microwave photonic filter is aperiodic, and the central frequencies of all stopbands are mutually uncorrelated and irrelevant with the number of stopbands, which can be tuned within 2 GHz to 8 GHz independently. The maximum out-of-band rejection can reach to 49 dB..
Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1106004 (2018)
Coupling Loss Analysis Between Polarization Maintaining Fiber and Y-Waveguide Based on Digital Image
Alignment coupling between polarization maintaining fiber and input end of Y-waveguide is studied. The influence of alignment deviation on coupling loss at five degrees of freedom is simulated by mode-field overlapping integral method, and an experimental scheme based on digital image is designed. The simulation resultAlignment coupling between polarization maintaining fiber and input end of Y-waveguide is studied. The influence of alignment deviation on coupling loss at five degrees of freedom is simulated by mode-field overlapping integral method, and an experimental scheme based on digital image is designed. The simulation results are consistent with the experimental data, which proves the feasibility of the experimental scheme. The results reveal that the transverse misalignments X and Y have the greatest influence on the coupling loss, while the vertical spacing Z has less influence on the coupling loss. And the coupling loss generated by the deflection angle α or pitch angle β is mainly caused by additional transverse displacement, while the mere change of angle has minimal impact on coupling loss. When the coupling loss is required to be under 0.5 dB, the tolerance range of transverse misalignment and vertical spacing should be restricted within -1 μm to 1 μm and -20 μm to 20 μm, respectively. The conclusions provide references for subsequent research on automatic alignment system..
Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1106005 (2018)
Laser Devices and Laser Physics
Mid-Infrared High Energy Fe2+∶ZnSe Laser at Room Temperature
Pan Qikun, Xie Jijang, Chen Fei, Zhang Kuo, Xiao Feng, Yu Deyang, He Yang, Sun Junjie, Zhang Laiming, and Guo Jin
The transversal parasitic oscillation characteristics of Fe2+∶ZnSe laser operating at room temperature are theoretically analyzed, and the results show that the population inversion threshold of parasitic oscillation can be effectively increased via the decrease of pump spot size, and thus the transversal parasitic oscThe transversal parasitic oscillation characteristics of Fe2+∶ZnSe laser operating at room temperature are theoretically analyzed, and the results show that the population inversion threshold of parasitic oscillation can be effectively increased via the decrease of pump spot size, and thus the transversal parasitic oscillation of Fe2+∶ZnSe laser can be effectively suppressed. The experimental setup of Fe2+∶ZnSe laser end-pumped by a non-chain pulsed hydrogen fluoride (HF) laser is established. By inserting irises with different apertures, the output characteristics of Fe2+∶ZnSe laser are experimentally studied under different pump spot diameters. The experimental results show that, as for a Fe2+∶ZnSe crystal with end size of 20 mm×20 mm, the phenomenon of transversal parasitic oscillation can be effectively suppressed when the pump spot diameter is smaller than 9.2 mm，which is consistent with the theoretical analysis result. At room temperature, the maximum Fe2+∶ZnSe laser pulse energy that one can obtain is 136 mJ, the slope efficiency is 33.2%, and the optical to optical efficiency is 26.5% relative to the pump light energy..
Chinese Journal of Lasers
- Publication Date: Jun. 26, 2018
- Vol. 45, Issue 11, 1101001 (2018)
Yb∶YAG Surface Gain Slab Laser Amplifier
Li Ning, Zhang Weiqiao, Liu Yang, and Tang Xiaojun
A novel Yb∶YAG surface gain slab laser amplifier is designed, with a fiber laser seed, using the geometry of master oscillator power amplifier (MOPA). Single-pass and double-pass amplifying are investigated theoretically and experimentally. The results show that 1030 nm laser output is obtained at room temperature. UndA novel Yb∶YAG surface gain slab laser amplifier is designed, with a fiber laser seed, using the geometry of master oscillator power amplifier (MOPA). Single-pass and double-pass amplifying are investigated theoretically and experimentally. The results show that 1030 nm laser output is obtained at room temperature. Under the conditions that the total pumping power is 11.2 kW and the injected power of fiber seed laser is 200 W, the output power of single and double pass amplified laser are 1.6 kW and 2.6 kW, respectively, and the optical efficiency of the two methods are 12.8% and 21.4%, respectively. The transmission wavefront of Yb∶YAG surface gain slab is measured and the wavefront distortion value is 1.3 μm. Yb∶YAG surface gain slabs have the potential as gain medium of high power lasers..
Chinese Journal of Lasers
- Publication Date: Jul. 26, 2018
- Vol. 45, Issue 11, 1101003 (2018)
Numerical Simulation of Combustion Driven HBr Chemical Lasers
Hui Li, Tingxuan Fan, Shuqin Jia, Liucheng Li, and Ying Huai
In order to identify the relationship between main reaction and key parameters, we use the sensitivity analysis method to study the reaction mechanism of HBr chemical laser. The sensitivity coefficients of temperature, pressure and key intermediate product are analyzed, and the effectiveness of temperature on controlliIn order to identify the relationship between main reaction and key parameters, we use the sensitivity analysis method to study the reaction mechanism of HBr chemical laser. The sensitivity coefficients of temperature, pressure and key intermediate product are analyzed, and the effectiveness of temperature on controlling the distribution of HBr is confirmed. A gain generator of HBr chemical laser is studied by computational fluid dynamics, and the distributions of temperature and concentration are given, respectively. The research results show that high vibrational state is obtained at the initial temperature of 500 K..
Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1101004 (2018)
Laser Manufacturing
Factors Influencing Weld Formation for Laser Welding of 5083 Aluminum Alloy in Vacuum
Wang Tiange, Tang Xinhua, Han Xiaoxiao, Lu Fenggui, and Cui Haichao
An orthogonal experiment is designed to investigate the laser welding of a 30 mm thick 5083 aluminum alloy plate under different process parameters. The results show that, the laser power, the welding speed and the ambient pressure have different effects on weld formation and porosity, in which the effects of the ambieAn orthogonal experiment is designed to investigate the laser welding of a 30 mm thick 5083 aluminum alloy plate under different process parameters. The results show that, the laser power, the welding speed and the ambient pressure have different effects on weld formation and porosity, in which the effects of the ambient pressure on the porosity, the penetration depth and the depth-width ratio are the strongest. When the ambient pressure is decreased to 5 kPa, the penetration depth is twice that at normal pressure and the porosity is only 0.057%. This research result provides a reference for the control of weld formation and porosity in the laser welding of aluminum alloys..
Chinese Journal of Lasers
- Publication Date: Jun. 14, 2018
- Vol. 45, Issue 11, 1102001 (2018)
Effect of Nickle Foil on Microstructure Properties of DP980/A6061 Dissimilar Laser Welded Joints
Chen Xiaming, Wang Xiaonan, Yan Qian, Wang Gaosong, Hu Zengrong, Zhang Min, and Chen Changjun
The experiment of the laser overlapped welding for the DP980 and A6061 sheets is conducted and the influences of the nickel foil on the microstructure, the microhardness and the tensile shear property of the weld seam (WS) and the fusion line (FL) of the laser welded joints are compared and analyzed. The results show tThe experiment of the laser overlapped welding for the DP980 and A6061 sheets is conducted and the influences of the nickel foil on the microstructure, the microhardness and the tensile shear property of the weld seam (WS) and the fusion line (FL) of the laser welded joints are compared and analyzed. The results show that, as for the sample without the nickel foil, the entry of the Al element into the weld pool results in the formation of a large number of soft phase δ ferrites and some lath martensites (LM) within the WS and FL. The brittle intermetallic compounds of FeAl2 and FeAl3 separate out near the steel-Al interface, whose peak thickness is about 50 μm, and thus there occur brittle fractures of welded joints at the interface during the tensile process. In contrast, as for the sample with the nickel foil, the nickel element effectively suppresses the Fe-Al metallurgical reaction, and thus the transformation of δ ferrites into austenite is promoted. At room temperature, the WS obtains the full LM microstructure. The WS hardness increases, there occurs the Ni-Al intermetallic compound near the interface, and both the hardness at interface and the thickness of the Fe-Al intermetallic compound layer decrease. The nickel foil makes the laser welded joint strength increase up to 61 MPa, which is 1.4 times that of the sample without the nickel foil..
Chinese Journal of Lasers
- Publication Date: Jun. 21, 2018
- Vol. 45, Issue 11, 1102002 (2018)
Effect of Interlayer Residence Time on Microstructures and Mechanical Properties of Laser Melting Deposited TC11 Titanium Alloys
Yan Zhenyu, Zhou Qingjun, Hou Yifei, Yang Guangwei, Ma Cunqiang, and Wang Fude
The TC11 titanium alloys are formed by the laser melting deposition technique and the effect of interlayer residence time on their microstructures and mechanical properties is investigated. The results show that the macrostructures of as-deposited samples change from equiaxed grains to columnar ones with the increase oThe TC11 titanium alloys are formed by the laser melting deposition technique and the effect of interlayer residence time on their microstructures and mechanical properties is investigated. The results show that the macrostructures of as-deposited samples change from equiaxed grains to columnar ones with the increase of interlayer residence time. For different interlayer residence time, there always exist extremely fine α+β basket-weave structures within the as-deposited samples, and as a result, the mechanical properties of these samples possess the characteristics of high strength and low plasticity. With the increase of interlayer residence time, the macroscopic layer band phenomenon becomes more and more clear, and simultaneously the anisotropy of mechanical properties at room temperature becomes more and more remarkable, which results from the coarsening of local microstructure, the increase of α phase proportion, and further regularity inhomogeneity of basket-weave microstructures in the deposition direction caused by surface remelting redeposition and annealing effects of current deposition layers..
Chinese Journal of Lasers
- Publication Date: Jun. 22, 2018
- Vol. 45, Issue 11, 1102003 (2018)
Effect of Heat Treatment on Microstructure of Laser Solid Formed DZ125 Superalloy
Yang Haiou, Han Jiajun, Lin Xin, and Huang Weidong
The effect of heat treatment on the solidification microstructure of the laser solid formed DZ125 superalloy is investigated. The results show that, with the increase of solution treatment temperature, the more primary γ′ particles are dissolved and these particles can be completely dissolved after treatment at 1240 ℃ The effect of heat treatment on the solidification microstructure of the laser solid formed DZ125 superalloy is investigated. The results show that, with the increase of solution treatment temperature, the more primary γ′ particles are dissolved and these particles can be completely dissolved after treatment at 1240 ℃ for 2 h. There occurs solid-state phase transition for the Ni5Hf phase and MC(1) carbides at high-temperature insulation. When treated at 1180 ℃ for 2 h, the Ni5Hf phase can be completely decomposed and the released Hf subsequently reacts with C atoms in solid solution matrix to form MC(2) carbides. Some MC(1) carbides transform into M23C6 or M6C carbides when maintained at 1000 ℃ for 12 h. The coarsening behavior and the empirical distribution function of the γ′ phase are consistent with those given by the Lifshitz-Slyozov-Wagner (LSW) theory when aged at 1100 ℃ and 870 ℃ after the complete solution heat treatment. The fitted coarsening activation energy of the γ′ phase is 231.43 kJ·mol-1 and the coarsening of γ′ particles is controlled by the diffusion of Al and Ti species in Ni..
Chinese Journal of Lasers
- Publication Date: Jun. 26, 2018
- Vol. 45, Issue 11, 1102004 (2018)
Microstructure and Mechanical Properties of Laser Melting Deposited TC11 Titanium Alloys
Qingjun Zhou, Zhenyu Yan, Xu Han, Quan Song, Jingwei Liu, and Fude Wang
The microstructural characteristics and mechanical properties of laser melting deposited TC11 titanium alloys are investigated by the reappearance of actual forming thermal process of large structural parts. The results show that, the α+β basket-weave microstructures in the coarse columnar grains of the as-deposited saThe microstructural characteristics and mechanical properties of laser melting deposited TC11 titanium alloys are investigated by the reappearance of actual forming thermal process of large structural parts. The results show that, the α+β basket-weave microstructures in the coarse columnar grains of the as-deposited samples are more uniform and finer than those in the equiaxed grains. The large α colonies are found in the equiaxed grains and there are a lot of continuous α phases on the grain boundaries. Due to the interlayer surface remelting redeposition and annealing effects, the obvious coarsening of α phases occurs in the interlayer transition zone of as-deposited samples and the α phase proportion increases. As a result, the mechanical properties of as-deposited samples at room temperature exhibit an obvious anisotropy. After the double annealing under the schedules of 950 ℃, heat preservation for 1 h and 550 ℃, heat preservation for 2 h, the continuous α phases are nearly broken completely on the grain boundaries of the annealed samples, and the α+β basket-weave microstructures show a more uniform distribution. The anisotropy of the mechanical properties at room temperature is eliminated completely and the plasticity enhances considerably. The comprehensive mechanical properties are basically at the same level as those of the forged samples..
Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1102005 (2018)
Weak Defect Enhancement in Ultrasonic Testing of Laser Deposition Manufactured TA15 Alloys
Li Yibo, Han Yi, Yang Guang, Qin Lanyun, and Wang Chao
Based on the discrete wavelet transform, an algorithm is proposed to enhance the tiny and low-contrast defects in the ultrasonic testing images of the laser deposited TA15 alloys, in which the Penalized soft threshold is used to denoise the high-frequency detail information of the defects and the Gamma transform is useBased on the discrete wavelet transform, an algorithm is proposed to enhance the tiny and low-contrast defects in the ultrasonic testing images of the laser deposited TA15 alloys, in which the Penalized soft threshold is used to denoise the high-frequency detail information of the defects and the Gamma transform is used to enhance the contrast of the low-frequency information of the defects. Both the information entropy and the contrast are taken into account to test multiple groups of samples. The research results show that, as for the laser-deposited parts with a unique rapid solidification structure, the proposed algorithm has a better ability of weak defect enhancement compared with the Gaussian filtering and the fuzzy set enhancement theories..
Chinese Journal of Lasers
- Publication Date: Jul. 24, 2018
- Vol. 45, Issue 11, 1102006 (2018)
Softening Phenomenon of Heat-Affected Zone in Laser Welding of 6082 Al Alloys with Filler Wire
Fuquan Li, Shi Feng, Mingwei Li, and Yunhao Zhu
The laser welding of 6082 Al alloys with filler wire is conducted and the influence of the welding speed on the softening of the heat-affected zone (HAZ) of the welding joints is investigated. The results show that, the obvious dissolution of β″ reinforced phases in the HAZ occurs when the temperature is between 430 ℃ The laser welding of 6082 Al alloys with filler wire is conducted and the influence of the welding speed on the softening of the heat-affected zone (HAZ) of the welding joints is investigated. The results show that, the obvious dissolution of β″ reinforced phases in the HAZ occurs when the temperature is between 430 ℃ and 560 ℃. The number of β″ phases decreases substantially and thus the hardness and the tensile strength of these joints decrease. This deep softening effect of the HAZ occurs and the softening area of the HAZ becomes the weakest one of these joints. At a laser power of 4250 W and a welding speed of 2.7 m·min
-1, the local deep softening phenomenon of the HAZ can be effectively suppressed. The average hardness is larger than 82 HV, the tensile strength increases up to 249 MPa, and the tensile fractures occur in welds.
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Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1102007 (2018)
Effect of Heat Input on Microstructure and Mechanical Properties of Laser Welded Medium Mn Steel Joints
Cao Yang, Zhao Lin, Peng Yun, Ma Chengyong, Tian Zhiling, and Zhong Minlin
The 0.1C-5Mn steels are welded by a fiber laser, and the effect of heat input on the microstructure, micro-hardness, tensile properties and formability of steel joints is investigated. The results show that the fusion zones (FZs) of joints under different heat inputs are always full of martensite structures, and in conThe 0.1C-5Mn steels are welded by a fiber laser, and the effect of heat input on the microstructure, micro-hardness, tensile properties and formability of steel joints is investigated. The results show that the fusion zones (FZs) of joints under different heat inputs are always full of martensite structures, and in contrast the heat-affected zones (HAZs) are composed of fine martensite/bainite mixed structures, austenite and ferrite. The average micro-hardness of the FZs is always higher than that of the base materials. A slightly softened zone occurs in the subcritical HAZ when the heat input is 100 J·mm-1. All the tensile samples of welded joints fracture at the base materials and the fractures belong to the ductile ones. The ultimate tensile strength of joints is higher than that of base materials. The Erichsen cracks of welded joints initiate in the FZ and extend perpendicular to the weld towards the base material zone. The forming performance of tailor-welded blank parallel to the rolling direction is superior to that of the perpendicular..
Chinese Journal of Lasers
- Publication Date: Jul. 05, 2018
- Vol. 45, Issue 11, 1102008 (2018)
Microstructure and Properties of Composite Coatings by Magnetic Field Assisted Laser Deposition
Yan Shi, Kuiming Chen, Jia Liu, Lingyu Li, and Zhiheng Jiang
The Fe106+5%Ni/WC composite coatings are prepared on the 304 stainless steel surfaces by the rotating magnetic field assisted laser deposition technique, and the changes of their macro-morphologies, microstructures, microhardness, and friction and wear properties under different magnetic field rotating speeds are invesThe Fe106+5%Ni/WC composite coatings are prepared on the 304 stainless steel surfaces by the rotating magnetic field assisted laser deposition technique, and the changes of their macro-morphologies, microstructures, microhardness, and friction and wear properties under different magnetic field rotating speeds are investigated. The results show that, the rotating magnetic field has a small effect on the surface roughness of the deposition layer when the magnetic field strength is 70 mT and the magnetic field rotating speed is 100-400 r·min
-1. With the further increase of the magnetic field rotating speed, the surface roughness of the deposition layer gradually decreases, the melt width increases, and the wetting angle gradually decreases, which indicates the surface quality is obviously improved. In addition, the microhardness of the deposition layer gradually increases with the increase of the magnetic field rotating speed. When the magnetic field rotational speed is 600 r·min
-1, the average hardness microhardness of the deposition layer reaches 825 HV, which is about 1.178 times that of the magnetic field free deposition layer. Simultaneously, the wear quality of the deposition layer gradually decreases, and the minimum average weight loss is only 2.2 mg, which is 1.33 times higher than that of the magnetic field free deposition layer.
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Chinese Journal of Lasers
- Publication Date: Nov. 22, 2018
- Vol. 45, Issue 11, 1102009 (2018)
Microstructure and Mechanical Properties of Laser Welded Ti/Al Alloys
Shun Guo, Yong Peng, Jun Zhu, Qiong Gao, Qi Zhou, and Chong Cui
The welding of TC4 Ti alloy and 6082 Al alloy is realized by 3 kW fiber laser offset welding on Al sheets. The macro- and micro-structures and mechanical properties of joints are tested. The temperature field distribution of joints and the thermal cycling curves at Ti/Al interfaces are simulated by the finite element mThe welding of TC4 Ti alloy and 6082 Al alloy is realized by 3 kW fiber laser offset welding on Al sheets. The macro- and micro-structures and mechanical properties of joints are tested. The temperature field distribution of joints and the thermal cycling curves at Ti/Al interfaces are simulated by the finite element method. The results show that the joints without cracks and porosity and with good tensile strength can be obtained by Ti/Al laser offset welding. During the welding process, the Ti substrate is partially melted and its surface becomes uneven. In the solidification process, there occurs a thin intermetallic compound layer at the Ti/Al bonding interface, whose main phase is TiAl3. The tensile test show that the maximum tensile strength of joints is 153 MPa, 72.9% that of Al substrate. The fracture mode of joints is a brittle cleavage one. The fractures occur in the intermetallic compound layer, and brittle phases which cause the fracture are TiAl and TiAl3..
Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1102010 (2018)
Fiber Laser High-Frequency Focus Rotation Spot Welding Process Based on Thermal Conductivity
Shusheng Peng, Jianglin Zou, Xintong Li, Qiang Wu, and Rongshi Xiao
The fiber laser spot welding process is studied with the high-frequency laser focus rotation method and compared with the traditional laser spot welding processes. The results show that, under the thermal conduction welding mode, the spot weld morphology can be effectively controlled by using the heat accumulation effeThe fiber laser spot welding process is studied with the high-frequency laser focus rotation method and compared with the traditional laser spot welding processes. The results show that, under the thermal conduction welding mode, the spot weld morphology can be effectively controlled by using the heat accumulation effect from the laser focus high-frequency repetitive scanning and the adjustment of the laser rotation process parameters. With the further heat accumulation, the spot weld morphology changes from the double “V” shape to the “W” shape and until to the “U” shape. Compared with those for the traditional laser spot welding process, the width-depth ratio of the spot welds is relatively larger for the high-frequency focus rotation spot welding process and substantially free of porosity defects. Simultaneously, the microstructure and microhardness of spot welds can be effectively regulated by the proposed method..
Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1102011 (2018)
Fatigue Properties of Ti-6Al-4V Produced by Selective Laser Melting
Tao Ma, Tingting Liu, Wenhe Liao, Liyi Jiang, and Zhennan Xiao
Based on the analysis of the static mechanical properties of Ti-6Al-4V specimens fabricated by selective laser melting, the effects of surface defects, internal defects and microstructures on the fatigue properties of specimens are investigated under cyclic loading. The stiffness-fitting fatigue cycle method is used toBased on the analysis of the static mechanical properties of Ti-6Al-4V specimens fabricated by selective laser melting, the effects of surface defects, internal defects and microstructures on the fatigue properties of specimens are investigated under cyclic loading. The stiffness-fitting fatigue cycle method is used to obtain the cycle times of the specimen in each stage of the fatigue cycle. It is found that the fatigue source nucleation stage is the main reason for the difference in fatigue life of the specimen. The surface of directly formed specimens is seriously viscous and forms several fatigue sources, resulting in very short fatigue life. Polishing treatment can reduce the surface roughness, and the annealing treatment can improve the microstructure and enhance the specimen fatigue performance. After polishing treatment, however, internal defects are exposed on the surface. The cycle of defect nucleation fatigue source of different types and different sizes has a large difference, leading to a greater discreteness of fatigue performance..
Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1102012 (2018)
Equiaxed Grains in Laser Welded 2060 Al -Li Alloys and Their Formation Mechanism
Ling Xia, Yue Kang, Haisong Yu, Youfa Wu, and Xiaohong Zhan
Based on the demand of weight reduction in the aeronautic and aerospace field, laser welding of aluminum-lithium alloys has received more and more attention from domestic scholars. The laser butt welding of 2 mm thick 2060-T8 Al-Li alloys is conducted and the micro-morphologies of weld seam is investigated. Moreover, tBased on the demand of weight reduction in the aeronautic and aerospace field, laser welding of aluminum-lithium alloys has received more and more attention from domestic scholars. The laser butt welding of 2 mm thick 2060-T8 Al-Li alloys is conducted and the micro-morphologies of weld seam is investigated. Moreover, the formation mechanism of the fine equiaxed grain zones (EQZ) at the boundary of fusion weld seam is clarified based on the molten pool flow mechanism. The analysis results show that the effects of laser heating and molten pool convection make the amounts and distributions of heterogeneous nucleation particles in different boundary regions of weld seam different, the EQZ width in the upper part is narrow and the EQZ width in the waist part is relatively large. In addition, part of the nucleation particles in the upper part and waist part of the weld boundary are brought into the molten pool along the tangent direction of the upper fusion line according to the molten pool flow mechanism, and on this basis, the grain grows to form a curved colony of equiaxed grains extended into weld seam..
Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1102013 (2018)
Materials and Thin Films
Fabrication of High-Reflective Cavity Mirrors for 457 nm Laser Based on Intracavity Frequency Doubling
Dongmei Liu, Wuyi Li, Xiuhua Fu, Jing Zhang, and Gong Zhang
Based on the design theory of frequency doubling reflective films, the design of multi-band high-reflective films on laser cavity surface is realized with the film design software. In the fabrication process, the deterioration problem of the thin film spectral performance caused by the accumulation of the film thicknesBased on the design theory of frequency doubling reflective films, the design of multi-band high-reflective films on laser cavity surface is realized with the film design software. In the fabrication process, the deterioration problem of the thin film spectral performance caused by the accumulation of the film thickness control error is solved based on the relationship between the residual evaporation amount and the film thickness established by the least square method. The reflectivity of the fabricated thin films at 457 nm and 914 nm is 99.9% and 99.6%, and the transmissivity at 808 nm, 1064 nm and 1342 nm is 97.2%, 96.8% and 93.1%, respectively, which satisfies the requirements of the 457 nm laser..
Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1103001 (2018)
Measurement and Metrology
Spacing Calibration of Adaptive Null Compensator in Free Form Surface Interferometer
Lei Zhang, Dong Li, Sheng Zhou, Jingsong Li, and Benli Yu
The axial spacing calibration between the two big compensators, the deformable mirror (DM) and the partial null optics in the adaptive null compensator (ANC), is investigated. A multi-null constraint method is proposed, in which the deformation of the DM is used to acquire the null measurements at different positions wThe axial spacing calibration between the two big compensators, the deformable mirror (DM) and the partial null optics in the adaptive null compensator (ANC), is investigated. A multi-null constraint method is proposed, in which the deformation of the DM is used to acquire the null measurements at different positions with the help of a calibrating mirror. Thus the multiple measurement equations are constructed to constrain the error coupling and the self-calibration of spacing distance in ANC is realized. The high efficiency of this method is verified by simulations and experiments. The direct measurement way is discarded in this method, which makes the integration between ANC and the whole interferometer possible..
Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1104005 (2018)
Measurement and Metrology
Optical Damage Inspection Based on Local Signal Enhancement
Tian Yuting, Wu Rong, and Yang Ye
To realize the recognition of surface damages with a low missed detection rate on large aperture optical elements in a high power laser driver and according to the low signal-to-noise ratio characteristic of micro-size damages, an adaptive detection algorithm is proposed based on the improved local signal intensity ratTo realize the recognition of surface damages with a low missed detection rate on large aperture optical elements in a high power laser driver and according to the low signal-to-noise ratio characteristic of micro-size damages, an adaptive detection algorithm is proposed based on the improved local signal intensity ratio. The signal intensity difference between the damages and their neighbored non-damage area in signal images is adopted to construct a filter template for the adaptive local enhancement of signal images. Thus, the damage signal intensity can be enhanced effectively and the signal-to-noise ratio of damage on signal images can also be improved significantly. As for the seed images, the seed selection and the adaptive regional growth are performed, and the complete segmentation of damage regions is finished by the accurate extraction. The improved local area signal intensity ratio algorithm can be used to effectively recognize the small-size damage points with a low signal-to-noise ratio. Under the total internal reflection lateral illumination in dark fields, the damage points with size of about 30 μm can be recognized. The missed detection rate is lower than that of the existing local area signal strength algorithm. The results show that the missed detection rate is below 0.4% for damage points with equivalent diameter of above 50 μm..
Chinese Journal of Lasers
- Publication Date: May. 11, 2018
- Vol. 45, Issue 11, 1104001 (2018)
Ranging Technology for Frequency Modulated Continuous Wave Laser Based on Phase Difference Frequency Measurement
Ji Ningke, Zhang Fumin, Qu Xinghua, Zhang Tong, Zhang Tieli, Liu Xiaoxu, and Xie Yang
In view of the problems that the sampling nonlinearity and the low accuracy of the Fourier transform, a frequency estimation based on phase difference method to measure the distance of the target point is used based on the ranging system of frequency modulated continuous wave, which is based on the equispaced-phase resIn view of the problems that the sampling nonlinearity and the low accuracy of the Fourier transform, a frequency estimation based on phase difference method to measure the distance of the target point is used based on the ranging system of frequency modulated continuous wave, which is based on the equispaced-phase resampling. The principle is analyzed and deduced. The stability of distance measurement and the error of distance measurement are analyzed based on the system. The research results show that the residual error of the measured distance with phase difference frequency measurement and the theoretical distance is not more than 100 μm and the stability of the single point range is between 50-95 μm in the range of 8.3-9.3 m. Compared with the fast Fourier transform, phase difference frequency measurement has better accuracy and stability in ranging..
Chinese Journal of Lasers
- Publication Date: Jun. 06, 2018
- Vol. 45, Issue 11, 1104002 (2018)
Photon Counting Experiment Based on InGaAs Detector in Daylight
Ding Yuxing, Li Yongfu, Liu Hongbin, Huang Genghua, and Wang Jianyu
The photon counting experiment based on the InGaAs single photon avalanche diode in daylight is introduced. The dead time of the InGaAs single photon detector is reduced by ultra-fast active quenching circuits, and thus the photon counting experiment based on the InGaAs single photon detector in daylight is successfullThe photon counting experiment based on the InGaAs single photon avalanche diode in daylight is introduced. The dead time of the InGaAs single photon detector is reduced by ultra-fast active quenching circuits, and thus the photon counting experiment based on the InGaAs single photon detector in daylight is successfully conducted via the compression of field of view, the usage of ultra-narrow band filters and the reduction of dead time. The acquired experimental data are analyzed. The InGaAs-based system parameters such as detection sensitivity and ranging accuracy are also analyzed and compared with the parameters for the system based on Si-based single photon detectors. The experimental results show that the InGaAs detector after optimization by the high-speed active quenching circuit has a dead time comparable to that of the Si-based detector. In the case of a certain background light noise, the InGaAs detector can be used to increase the detection sensitivity and the maximum detection range of the system. Thanks to the low jitter time of InGaAs detectors, the ranging accuracy of the system is not affected while increasing its maximum detection range..
Chinese Journal of Lasers
- Publication Date: May. 13, 2018
- Vol. 45, Issue 11, 1104003 (2018)
An Automatic Segmentation Algorithm for Dense Pipeline Point Cloud Data
Huang Kai, Cheng Xiaojun, Jia Dongfeng, Hu Danhua, and Hu Minjie
An algorithm for the automatic segmentation of dense circular pipeline point cloud data is proposed. The cloud data is divided into several sub-blocks based on the octree structure, among which the spatial neighborhood relationship is established. The random sampling consensus algorithm based on the normal vector constAn algorithm for the automatic segmentation of dense circular pipeline point cloud data is proposed. The cloud data is divided into several sub-blocks based on the octree structure, among which the spatial neighborhood relationship is established. The random sampling consensus algorithm based on the normal vector constraints is used to remove the large area plane within each sub-block and simultaneously, the Euclidean distance clustering and the region growing segmentation algorithm based on the smoothness constraints are used to refine the data again. The experimental results show that a 4 thread parallel computation only takes 9 s and the precision is larger than 90% when the proposed automatic segmentation algorithm is used to process the data with a size of 6 m×12 m×16 m in the point cloud space. Thus the proposed algorithm can be used for the quick and accurate segmentation of pipeline point cloud data and has a high application value..
Chinese Journal of Lasers
- Publication Date: Jul. 24, 2018
- Vol. 45, Issue 11, 1104004 (2018)
Probability Distribution of Laser Short-Range Dynamic Ranging Based on Optical Multiplexing Mechanism
Gan Lin, and Zhang He
A laser short-range dynamic scan detection method is proposed based on the optical-multiplexing mechanism. Based on the heavy-tail function, a mathematical model of pulsed laser emission waveforms is established, and the shock responses and the echo equation in the pulsed laser short-range dynamic detection are deducedA laser short-range dynamic scan detection method is proposed based on the optical-multiplexing mechanism. Based on the heavy-tail function, a mathematical model of pulsed laser emission waveforms is established, and the shock responses and the echo equation in the pulsed laser short-range dynamic detection are deduced. A statistical probability distribution model of the pulsed laser ranging is established, and the influence mechanisms of the pulsed laser emission power, pulse width, threshold detection voltage, equivalent root-mean-square (RMS) noise voltage, and the laser exit angle on the probability distribution of the ranging are studied. The results show that, the ranging precision increases and the distribution curve gradually deviates from its true value with the increase of the laser emission power. The ranging precision decreases progressively as the laser emission pulse width increases. As the threshold voltage increases, the distribution curve shifts to the right. As for the distance measurement distribution curve, its width increases and its amplitude decreases with the increase of the equivalent RMS noise voltage. The ranging distribution curve shifts to the right and the ranging precision decreases as the laser exit angle increases..
Chinese Journal of Lasers
- Publication Date: Jul. 05, 2018
- Vol. 45, Issue 11, 1104006 (2018)
Remote Sensing and Sensor
DEM Interpolation Algorithm of Data from Spiral Scanning Lidar
Yang Shujuan, Zhang Keshu, and Shao Yongshe
An algorithm for the digital elevation model (DEM) interpolation in the spiral scanning airborne lidar system is proposed. First, the scanning characteristics of this spiral scanning lidar system is described and the principle of real-time calculation of the overlapping area is clarified. Then the improved method of trAn algorithm for the digital elevation model (DEM) interpolation in the spiral scanning airborne lidar system is proposed. First, the scanning characteristics of this spiral scanning lidar system is described and the principle of real-time calculation of the overlapping area is clarified. Then the improved method of triangulation iterative encryption filtering is introduced and is also used to separate the terrestrial and non-ground points. Finally, the DEM interpretation is carried out based on the random forest. The experimental results show that with this method, the DEM interpolation in the spiral scanning airborne lidar system can be realized with an interpolation accuracy meeting the data requirements for industrial production..
Chinese Journal of Lasers
- Publication Date: Aug. 17, 2018
- Vol. 45, Issue 11, 1110006 (2018)
Design and Implementation of CCD Imaging System for Aerosol Detector
Liang Shaolin, Wang Yongmei, Jia Nan, Shi Entao, and Mao Jinghua
A CCD imaging system in the absorbent aerosol detector is designed, whose hardware includes timing driving circuit, pre-processing and analog-front-end circuit, power management circuit, FPGA main control unit, Camera Link communication circuit, and so on. A kind of driving timing with reverse transfer is introduced toA CCD imaging system in the absorbent aerosol detector is designed, whose hardware includes timing driving circuit, pre-processing and analog-front-end circuit, power management circuit, FPGA main control unit, Camera Link communication circuit, and so on. A kind of driving timing with reverse transfer is introduced to effectively eliminate the residual charge in the frame transfer process and improve the signal-to-noise ratio. The performance of this CCD imaging system is tested. The experimental results show that as for this imaging system, the 14 bit image data can output steadily with a frame frequency of 1.8 frame/s, the shortest exposure time of 17.28 ms and a nonlinearity error of 1.68%. Under the condition of 80% saturation exposure, the imaging signal-to-noise ratio is 54.36 dB, and the dynamic range of CCD detectable signals is 61.55 dB. The operational requirements of this detector such as stable output, high time resolution, excellent linear performance, high signal-to-noise ratio, and large dynamic range of signals are satisfied..
Chinese Journal of Lasers
- Publication Date: May. 22, 2018
- Vol. 45, Issue 11, 1110001 (2018)
Onboard Polarimetric Calibration Methods of Spaceborne Scanning Polarimeter
Yang Hongchun, Yang Benyong, Song Maoxin, Zou Peng, Sun Xiaobing, and Hong Jin
In order to guarantee the long-term on-orbit polarimetric measurement accuracy of scanning polarimeter, the onboard calibration mechanism and method of scanning polarimeter are studied. First, the system detection matrix is derived according to the technical characteristics of aperture-division and amplitude-division aIn order to guarantee the long-term on-orbit polarimetric measurement accuracy of scanning polarimeter, the onboard calibration mechanism and method of scanning polarimeter are studied. First, the system detection matrix is derived according to the technical characteristics of aperture-division and amplitude-division and with the consideration of practical error sources. Second, the onboard polarimetric calibration equation is deduced according to the instrument parameters and by use of the linearly polarized light and the non-polarized light with the known polarization states. Third, the linear polarization and non-polarization calibrators are designed for the onboard polarimetric calibration. Finally, the radiometric calibration data with the known polarization degree from the onboard solar diffuser is proposed to correct the low polarimetric measurement accuracy and stability. The proposed onboard polarimetric calibration method possesses the characteristics of high precision, high frequency, high efficiency, and so on, which can satisfy the application requirement that the long-term on-orbit polarimetric measurement accuracy is 0.005..
Chinese Journal of Lasers
- Publication Date: Jun. 26, 2018
- Vol. 45, Issue 11, 1110002 (2018)
Optical Fiber Temperature Sensor Based on Surface Plasmon Resonance
Yong Wei, Jiangxi Hu, Zongda Zhu, Lu Liu, and Feng Peng
An optical fiber temperature sensor based on surface plasmon resonance (SPR) is designed. The ends of a single-mode fiber and a multi-mode fiber are ground into wedge shapes and spliced. The gold film with a thickness of 50 nm is plated on the polished surface of this single-mode fiber to form the Kretschmann configuraAn optical fiber temperature sensor based on surface plasmon resonance (SPR) is designed. The ends of a single-mode fiber and a multi-mode fiber are ground into wedge shapes and spliced. The gold film with a thickness of 50 nm is plated on the polished surface of this single-mode fiber to form the Kretschmann configuration. Then a layer of polydimethylsiloxane (PDMS) is coated as temperature sensitive medium and thus temperature sensing is realized. The experimental results show that the maximum sensitivity of this sensor can reach 4.15 nm/℃ when temperatures are between 20 ℃ and 70 ℃, much higher than those of other types of optical fiber temperature sensors. Compared with other SPR-based optical fiber temperature sensors, this sensor has a much narrower full width at half maximum and a larger figure of merit. In addition, this sensor has a relatively high stability with the maximum temperature standard deviation of 0.14 ℃. This sensor has a simple structure and low cost, and is expected to be widely used in the industrial field..
Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1110003 (2018)
Waveform Decomposition of Echoes for Airborne Lidar Based on Seeker Optimization Algorithm
Shen Jun, Shang Jianhua, Sun Jiatong, and He Yan
In order to improve the waveform decomposition precision of echoes for the airborne lidar, the waveform decomposition of echo signals for the airborne lidar is realized and also experimentally verified by taking the skewed normal distribution functions as fitting basis functions and by means of the layer stripping straIn order to improve the waveform decomposition precision of echoes for the airborne lidar, the waveform decomposition of echo signals for the airborne lidar is realized and also experimentally verified by taking the skewed normal distribution functions as fitting basis functions and by means of the layer stripping strategy as well as the combination of the seeker optimization algorithm and the LM algorithm with global convergence. The results show that the echo signal can be decomposed into the superposition of a series of skewed normal distribution functions and the key parameters such as signal amplitude, central position, half width and skewness coefficient can be obtained. The correlation coefficients of the fitted waveform and the echo signal are both larger than 99%, indicating an effective improvement of waveform decomposition precision. The proposed method can be used to realize the accurate decomposition of echo signals for the full-waveform airborne lidar..
Chinese Journal of Lasers
- Publication Date: Jul. 03, 2018
- Vol. 45, Issue 11, 1110004 (2018)
Wind-Field Vector Retrieval Method at Low Signal-to-Noise Ratio for Coherent Doppler Lidar
Meng Zhao, Pan Guo, Xunbao Rui, Siying Chen, Yinchao Zhang, and He Chen
In this study, the sequential quadratic programming (SQP) in nonlinear optimization theory is used to solve the filtered sine wave fitting (FSWF). Based on the speed azimuth display (VAD) algorithm, high-precision inversion of the vector wind field is achieved at low signal-to-noise ratio (SNR). In the simulation experIn this study, the sequential quadratic programming (SQP) in nonlinear optimization theory is used to solve the filtered sine wave fitting (FSWF). Based on the speed azimuth display (VAD) algorithm, high-precision inversion of the vector wind field is achieved at low signal-to-noise ratio (SNR). In the simulation experiment, the root mean square errors of the inversion results are used as the evaluation index, and the direct sine wave fitting (DSWF) algorithm and the SQP-FSWF algorithm are compared. In the FSWF calculation, based on the spatial-temporal continuity of the wind field inversion results, the SQP algorithm and the quasi-Newton method in the unconstrained optimization algorithm are compared. The comparison results show that the inversion effect of SQP-FSWF is better than those of DSWF and the quasi-Newton method at low SNR. To further evaluate the reliability of the proposed algorithm, we perform the wind field measurement contrast experiments based on lidar and synchronous sounding balloon, in which we obtain the real echo signal of lidar and the wind field data of synchronous sounding balloon. The wind speed inversion results simulated by the SQP-FSWF algorithm and the results measured by synchronous sounding balloon as the comparison object are compared. It can be seen that for horizontal wind speed, the correlation coefficient, the average error, the root mean square error are 0.993, 0.2 m/s, 0.28 m/s; for horizontal wind direction, the correlation coefficient, the average error, the root mean square error are 0.988, 3.28°, 4.62°, respectively. Based on the comparison between the spatial-temporal continuity of the wind retrieval results, the proposed method at low SNR is advantageous, which is consistent with the results of the simulated data..
Chinese Journal of Lasers
- Publication Date: Nov. 21, 2018
- Vol. 45, Issue 11, 1110005 (2018)
Reviews
13.5 nm Extreme Ultraviolet Light Source Based on Discharge Produced Xe Plasma
Yongpeng Zhao, Qiang Xu, Qi Li, and Qi Wang
The experimental setup of an extreme ultraviolet (EUV) light source is built. The EUV radiation spectrum with a central wavelength of 13.5 nm from the Xe plasma is obtained and the temporal characteristics are characterized. The multi-peak structure of a light pulse is clarified by the multiple pinch theory. The influeThe experimental setup of an extreme ultraviolet (EUV) light source is built. The EUV radiation spectrum with a central wavelength of 13.5 nm from the Xe plasma is obtained and the temporal characteristics are characterized. The multi-peak structure of a light pulse is clarified by the multiple pinch theory. The influence laws of the experimental parameters such as the current amplitude of main pulse, Xe flow rate, inner diameter of ceramic tube, plasma length, and auxiliary gas on EUV radiation intensity are obtained. In addition, a prototype of 13.5 nm EUV light source with a repetition rate of 1 kHz is built and its power supply system, discharge system, debris mitigation tool and collector system are described. The test results about the prototype are also given..
Chinese Journal of Lasers
- Publication Date: Nov. 22, 2018
- Vol. 45, Issue 11, 1100001 (2018)
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