Journals >Chinese Journal of Lasers
Contents
2016
Volume: 43 Issue 4
39 Article(s)
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Laser Manufacturing
Microstructure and Mechanical Properties of AF1410 Ultra-High Strength Steel Using Laser Additive Manufacture Technique
Wang Zhihui, Wang Huaming, and Liu Dong
AF1410 ultra-high strength steel plate sample is fabricated using the laser additive manufacturing (LAM) technique and homogenization treatment combined with the traditional heat treatment of AF1410 is conducted as the heat treatment. Microstructures, hardness and tensile properties of the steel are investigated. ResulAF1410 ultra-high strength steel plate sample is fabricated using the laser additive manufacturing (LAM) technique and homogenization treatment combined with the traditional heat treatment of AF1410 is conducted as the heat treatment. Microstructures, hardness and tensile properties of the steel are investigated. Results show that the microstructures of as-deposited AF1410 exhibit some characteristics of directional solidification with a hardness of about 360 HV. After the heat treatment, the directional solidification microstructure disappears while a refined microstructure and tempered martensite are obtained with hardness of about 510 HV. Meanwhile, yield strength and tensile strength at room temperature of the heat treated steel reach to 1490 MPa and 1610 MPa, respectively, with the elongation of 12.8% and the reduction of area of 70%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 403001 (2016)
Study on Microstructure and Micro-Mechanical Properties of Porous Aluminum Alloy Fabricated by Selective Laser Melting
Qian Deyu, Chen Changjun, Zhang Min, Wang Xiaonan, and Jing Hemin
Selective laser melting (SLM) is a typical rapid forming technique, and complex metallic components with high performance are fabricated directly by using high energy laser beam for melting the metallic powder and layer- by- layer deposition. To investigate the properties of porous aluminum alloy fabricated by SLM, surSelective laser melting (SLM) is a typical rapid forming technique, and complex metallic components with high performance are fabricated directly by using high energy laser beam for melting the metallic powder and layer- by- layer deposition. To investigate the properties of porous aluminum alloy fabricated by SLM, surface morphology, porosity, microstructure, phase composition and micro-mechanical properties of porous aluminum alloy are studied by the scanning electron microscope, energy dispersive X-ray spectroscopy and nanoindentation. The results show that the porosity of the porous aluminum alloy reaches its maximum, the microstructure is refined and the grain size reaches the nanometer level when the laser power is 130 W. The nano hardness of the porous aluminum alloy changes with laser power, while the the elastic modulus does not change obviously. The elastic modulus of the α-Al phase is around 65 GPa, and the elastic modulus of the α-Al+Si phase is around 85 GPa..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 403002 (2016)
Temperature Field During Selective Laser Melting of Metal Powder Under Different Scanning Strategies
Chen Dening, Liu Tingting, Liao Wenhe, Zhang Changdong, and Zhang Kai
Three-dimensional finite element simulation is used to investigate the temperature field with the island scanning strategy paralleled with the S-shaped scanning strategy. Considering the influence of heat conduction, heat radiation and heat convection, nonlinear relationship between thermophysical properties of metal mThree-dimensional finite element simulation is used to investigate the temperature field with the island scanning strategy paralleled with the S-shaped scanning strategy. Considering the influence of heat conduction, heat radiation and heat convection, nonlinear relationship between thermophysical properties of metal material and temperature, and enthalpy processing utilizing latent heat of phase change, we established a finite element model of metal selective laser melting (SLM) is established. It is found that the molten pool is in the shape of a water droplet, and the temperature contour at front-end is denser than that at back-end. Compared with the S-shaped scanning strategy, island scanning has the phenomenon of secondary temperature elevation at the island edge. The whole temperature field of the model is uniform, which is beneficial to reducing the stress concentration. It was observed that the average width of the β phase in the samples built with the island scanning strategy is significantly larger than that with the S-shaped scanning strategy. The influence of the island scanning on the boundary of the islands is quality of overlapping areas, and the overlap between adjacent islands is poor..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 403003 (2016)
Corrosion Resistance Research of Laser Additive Manufactured TC11 Titanium Alloy
He Bowen, Ran Xianzhe, Tian Xiangjun, and Wang Huaming
The corrosion resistance of laser additive manufactured (LAM) TC11 titanium alloy is studied in hydrochloric acidic solution with immersion and electrochemical corrosion test methods. Surface morphologies are analyzed by scanning electron microscope. The results indicate that α phase of laser additive manufactured TC11The corrosion resistance of laser additive manufactured (LAM) TC11 titanium alloy is studied in hydrochloric acidic solution with immersion and electrochemical corrosion test methods. Surface morphologies are analyzed by scanning electron microscope. The results indicate that α phase of laser additive manufactured TC11 titanium alloy contains low-content Mo element, and easily selective dissolves preferentially. In hydrochloric acidic solution, with the extending corrosion time, the open circuit potential first decreases and then increases gradually, and the charge transfer resistance Rct sharply decreases before maintaining stability. Self-corrosion current density icorr increases with the increase of the corrosion time. The α+ β basket- weave microstructure of laser additive manufactured TC11 titanium alloy possesses finer α phase than that of bimodal microstructure of forged alloy, and exhibits better corrosion resistance. Microstructure of the heat-treated specimen contains higher volume fraction and coarsening α-phase, but a slight decrease in the corrosion resistance..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 403004 (2016)
Research on Hot-Corrosion of Inconel718 Nickel-Based Alloy Treated by Warm Laser Shock Peening
Zheng Gang, Meng Xiankai, Chen Songling, Mu Dan, Yang Xiangwei, Sheng Jie, and Zhou Jianzhong
A SpitLight2000 nanosecond laser is used to conduct warm laser shock peening (WLSP) experiment on Inconel718 nickel-based alloys. Thermal corrosion test is conducted on the WLSP-samples and untreated samples in mixed molten salt (75%Na2SO4+25% NaCl, percentage mentioned above denotes mass fraction) at 700 ℃. Then the mA SpitLight2000 nanosecond laser is used to conduct warm laser shock peening (WLSP) experiment on Inconel718 nickel-based alloys. Thermal corrosion test is conducted on the WLSP-samples and untreated samples in mixed molten salt (75%Na2SO4+25% NaCl, percentage mentioned above denotes mass fraction) at 700 ℃. Then the mechanism of WLSP to improve the corrosion resistance of Inconel718 nickel-based alloys is researched by quality detection, X-ray diffraction (XRD) diffraction analysis and corrosion morphology observation. The results show that quality losses in 260 ℃- WLSP- samples after 10 h and 25 h are 18.9% and 17.9% of that in untreated samples. In addition, after thermal corrosion for 10 h, Cr2O3 oxidation doesn′t peel obviously on the corrosion surface of WLSP-samples and thus CrS or NiO is not formed. It is indicated that WLSP-samples can prevent implantation of S and thus effectively suppresses thermal corrosion of materials. The reason is that WLSP can lead to grain refinement and γ″ -phase precipitates, which effectively prevents invasion of O and S, and thus improves thermal corrosion resistance of Inconel718 nickel-based alloys..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 403005 (2016)
Hole-Drilling with High Depth-Diameter Ratio Using Multi-Pulse Femtosecond Laser
Hu Mengning, Ge Licheng, Zhang Jinping, Chen Yuping, and Chen Xianfeng
An improved two-temperature model is proposed to characterize the ablation of thick metal aluminum by multi-pulse femtosecond laser, and the model is proved in experiments. In order to achieve hole-drilling with high ratio of depth-diameter, three dimensional numerical simulation to the temperature field in the processAn improved two-temperature model is proposed to characterize the ablation of thick metal aluminum by multi-pulse femtosecond laser, and the model is proved in experiments. In order to achieve hole-drilling with high ratio of depth-diameter, three dimensional numerical simulation to the temperature field in the process of femtosecond laser ablation on metal aluminum surface is carried out. The aperture and depth of hole are predicted with different laser parameters, such as laser energy density, pulse number, laser waist radius and so on. The experiments show that the laser energy density and pulse number are the main factors affecting the morphology of holes, and the multi-pulse ablation threshold is much lower than the single-pulse one. The non-diffraction characteristics of aquasi Bessel beam within the maximum collimating distance are discussed and the enhancement on hole-drilling processing of Bessel beams is analyzed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 403006 (2016)
Corrosion Behavior of Laser Beam Welded Joint of 2198 Aluminium-Lithium Alloy with Filler Wire
Yin Shikun, Lü Junxia, and Xiao Rongshi
2198 aluminium-lithium alloy is extensively used in the field of aerospace due to the favorable properties, such as low density, good mechanical property, high specific strength, good thermostability and plasticity. 2198 aluminium-lithium alloy is welded by fiber laser using the filler of ER4047 Al-Si. The microstructu2198 aluminium-lithium alloy is extensively used in the field of aerospace due to the favorable properties, such as low density, good mechanical property, high specific strength, good thermostability and plasticity. 2198 aluminium-lithium alloy is welded by fiber laser using the filler of ER4047 Al-Si. The microstructure and corrosion behavior of joint in NaCl solution with 3.5% mass fraction is studied. The micromorphologies, precipitate species and their distribution have been examined using the optical micrograph, scanning electron microscope and transmission electron microscope. The corrosion behavior of weld and base metal has been compared by the methods of immersion test and electrochemical corrosion test at room temperature. The results indicate that the microstructure of 2198 aluminium-lithium alloy base metal, compared to the weld, is coarser and grows along to the rolling direction. Plenty of T1 precipitates with the diameter of hundreds of nanometers distributed randomly in the base metal. After laser welded with the filler ER4047 Al- Si, the heat affected zone is narrow, the microstructure is tiny, the component is uniform, the kind of precipitate is various, and the fine grain is equiaxed, the columnar crystal is vertical growth close to fusion line. At room temperature in NaCl solution with 3.5% mass fraction, the weld and heat affected zone show the uniform corrosion behavior, the small corrosion spot area, the shallow corrosion spot. By comparison, the parent metal shows the pitting corrosion. With the immersion time increasing, the pitting area is enlarged and the depth is deeper. The open circuit potential, self-corrosion potential and polarization resistance of weld are all higher than those of the parent metal, but the corrosion current density is less than that of the parent metal..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 403007 (2016)
Determining Process Parameters for Laser Derusting of Ship Steel Plates
Xie Yufei, Liu Hongwei, and Hu Yongxiang
Aiming at the requirements of ship steel plate cleaning for green shipbuilding, laser derusting with an optical fiber laser is investigated to obtain the proper process parameters to satisfy the surface quality of derusting. The relationships between groove geometry characteristics and the laser energy density are explAiming at the requirements of ship steel plate cleaning for green shipbuilding, laser derusting with an optical fiber laser is investigated to obtain the proper process parameters to satisfy the surface quality of derusting. The relationships between groove geometry characteristics and the laser energy density are explored through the single-line laser scanning experiments. The results show that the groove depth, groove width and cross-sectional area of single-line scanning grooves are approximately linearly related to the laser energy density the under the condition that the laser energy density comes within the range of 0.5~5 J/mm2. According to the requirements of ship steel plate derusting, a method to determine the process parameters for laser derusting via single line scanning groove geometry characteristics is proposed. Experiments of overlapping scanning laser derusting show that the proposed method is effective in a certain range so that laser derusting can reach cleanliness standards of ship coatings, and can obtain the specified different surface roughness. The results demonstrate that laser derusting with a pulsed fibre laser can satisfy the requirements of surface cleaning for ship steel plates..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 403008 (2016)
Influence of WC Content on Microstructure of WC/Ni60A Laser Cladding Layer
Li Fuquan, Feng Xinyou, and Chen Yanbin
Laser cladding of nickel-based composite layer is much helpful to improve surface properties of H13 steel. WC/Ni60A composite powder with WC mass fractions of 20%, 33% and 50% is respectively cladded on the H13 steel surface. Based on optimized parameters of laser cladding process, the microstructure of the cladding laLaser cladding of nickel-based composite layer is much helpful to improve surface properties of H13 steel. WC/Ni60A composite powder with WC mass fractions of 20%, 33% and 50% is respectively cladded on the H13 steel surface. Based on optimized parameters of laser cladding process, the microstructure of the cladding layer is studied. The results show that the phase composition of the laser cladded WC/Ni60A composite layer is complex. WC content has a significant effect on the formation and morphology of the cladding layer structure. When the mass fraction of WC is 20%, the cladding layer is composed of much γ-(Fe, Ni) branch crystal and a small amount of Wrich carbide; when the mass fraction of WC is 33%, the cladding layer, with a special structure, is composed of a large amount of flocculent eutectic structures which are concentrated by M23C6 blocks and surrounded by eutectic structure composed of M23C6 and γ- (Fe, Ni); when the mass fraction of WC is 50% , much block- shaped M6C, snowflake-shaped M23C6 and needle-like Cr4Ni15W structure is generated in the cladding layer. The hardness of the laser cladding layer increases remarkably compared with that of the substrate and is up to 730, 760, 810 HV, when the mass fraction of WC is 20%, 33% and 50%, respectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 403009 (2016)
Characteristics of Bead Formation and Plasma Plume in Fiber Laser Welding Under Vacuum
Jiang Meng, Tao Wang, Chen Yanbin, and Wang Shuliang
In order to reduce the distractions of plasma plume in laser welding and expand the applications of high power laser welding, the characteristics of bead formation and plasma plume in fiber laser welding under vacuum are studied. The results show the sound bead formations and an increase in penetration depth are obtainIn order to reduce the distractions of plasma plume in laser welding and expand the applications of high power laser welding, the characteristics of bead formation and plasma plume in fiber laser welding under vacuum are studied. The results show the sound bead formations and an increase in penetration depth are obtained. The penetration depth under vacuum is approximately three times as deep as that under atmospheric pressure when the welding speed is 0.5 m/min. The experiment results also show the penetration depth increases drastically with the pressure decreasing under a low welding speed and a long negative defocused distance is suitable for a deep penetration and a sound weld beam formation under vacuum. The camera observations show the plasma plume is suppressed under vacuum. The suppression of plasma plume under vacuum is a reason for the increase in penetration depth under vacuum..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 403010 (2016)
Laser Physics
Active Suppression of Residual Amplitude Modulation in Laser Frequency Stabilization by Multi-Frequency Mixing
Fan Xialei, Jin Shangzhong, Zhang Shu, Li Ye, Lin Yige, and Fang Zhanjun
A wideband waveguide electro-optical modulator (EOM) is driven by multiple frequencies signal. By synthesizing three frequencies and using these frequencies to drive the wideband waveguide EOM, three pairs of sidebands are added to the carrier laser frequency. Three sidebands on one single side of the carrier are used A wideband waveguide electro-optical modulator (EOM) is driven by multiple frequencies signal. By synthesizing three frequencies and using these frequencies to drive the wideband waveguide EOM, three pairs of sidebands are added to the carrier laser frequency. Three sidebands on one single side of the carrier are used to laser frequency stabilization by Pound-Drever-Hall (PDH) technique. By adjusting the phase of one frequency signal, the baseline drift of the PDH error signal is controlled. The residual amplitude modulation (RAM) noise in frequency locking system also causes error signal baseline drift, through active phase modulation frequency signal feedback control system, the residual amplitude modulation noise suppression is realized. Experimental results show that after applying the active closed loop feedback system, the RAM noise is suppressed over 30dB, and noise drift is suppressed effectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 402001 (2016)
Dual-Wavelength Fiber Laser Based on Er3+-Doped Superimposed Fiber Gratings
Wang Feng, Bi Weihong, Fu Xinghu, Jiang Peng, and Wu Yang
Based on gain homogeneity technology, a new type of dual-wavelength fiber laser is proposed and demonstrated. Linear cavity structure is used in the fiber laser, two Er3+-doped superimposed fiber gratings with reflectivity above 99% are used for wavelength selection, and Er3+-doped fiber is used as the gain medium. TheBased on gain homogeneity technology, a new type of dual-wavelength fiber laser is proposed and demonstrated. Linear cavity structure is used in the fiber laser, two Er3+-doped superimposed fiber gratings with reflectivity above 99% are used for wavelength selection, and Er3+-doped fiber is used as the gain medium. The experimental results show that precise adjustment of the mechanical stress at two ends of the superimposed fiber gratings can regulate the reflectivity (or transmissivity) of cavity lenses at the output end at wavelengths of λ1 and λ2, i.e. regulate the laser loss, which makes the gain and loss at two wavelengths in the resonance cavity match well, inhibits mode competition in the resonance cavity, and achieves stable simultaneous dual-wavelength laser emission with wavelength interval of 0.932 nm. The threshold power of the proposed laser is 4 mW, the 3 dB band width is 0.02 nm, the 30 dB band width is less than 0.2 nm, and the side mode suppression ratio is 51.96 dB. This laser have such advantages as simple structure, stable output at room temperature, narrow band width and low threshold..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 402002 (2016)
Research on Stability of Fabry-Perot Cavity Based on PDH
Guo Yong, Qiu Qi, Wang Yunxiang, Wang Zhiyong, Su Jun, Shi Shuangjin, and Yu Zhenfang
A scheme for stabilizing the Fabry-Perot (FP) cavity based on the Pound-Drever-Hall (PDH) technique is proposed for the need of more stable FP cavity. According to the theoretical calculation model, the static and dynamic response characteristics of the FP cavity resonant optical system are analyzed in details. The errA scheme for stabilizing the Fabry-Perot (FP) cavity based on the Pound-Drever-Hall (PDH) technique is proposed for the need of more stable FP cavity. According to the theoretical calculation model, the static and dynamic response characteristics of the FP cavity resonant optical system are analyzed in details. The error signal obtained by the static analysis can be used to lock the FP cavity, and the frequency response obtained by the dynamic response analysis helps to design a control loop to maintain the FP cavity at the chosen operating point. The numerical simulation results show that when the optical gain is 0.785 W/(°) and the error signal stays at the milliwatt level, the length stability precision of the FP cavity achieves 4 pm. The validity and feasibility of the scheme are verified by comparing the beam spot size and shape of the reflected light before and after the FP cavity locking..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 402003 (2016)
Spectral Beam Combining Based on High Power Narrow Linewidth Ytterbium-Doped All-Fiber Superfluorescent Source
Wei Shouyu, Jin Dongchen, Sun Ruoyu, Cao Yi, Hou Yubin, Wang Jing, Liu Jiang, and Wang Pu
We obtained stable narrow bandwidth superfluorescent sources with central wavelengths at 1060 nm and 1078 nm by using a segment of ytterbium-doped double-cladding fiber as the gain medium, multi-mode diode lasers operating at 976 nm and 915 nm as pumping sources, and fiber Bragg gratings as filters. Two three-stage higWe obtained stable narrow bandwidth superfluorescent sources with central wavelengths at 1060 nm and 1078 nm by using a segment of ytterbium-doped double-cladding fiber as the gain medium, multi-mode diode lasers operating at 976 nm and 915 nm as pumping sources, and fiber Bragg gratings as filters. Two three-stage high power fiber amplifier systems are used to boost the output power up to 57.4 W and 56.6 W respectively with the slope efficiencies of 66.6% and 66.7%. The superfluorescent bandwidths at 1060 nm and 1078 nm are 0.05 nm. Two output beams are spectrally combined with a transmission diffraction grating, the output beam is with the power of 104.2 W, power efficiency of 91.3% and the beam quality M2 is superior to 1.7..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 402005 (2016)
Backward Raman Scattering and Amplification Based on Dual Raman Cells
Zhou Dongjian, Guo Jingwei, Zhou Canhua, Zhao Weili, Liu Jinbo, Liu Dong, and Jin Yuqi
The characteristics of backward Raman scattering and amplification based on two hydrogen Raman cells are investigated. Both cells are filled with high-pressure hydrogen. The first cell is used to generate the Stokes seed light, and the second cell is used to amplify the seed light. The Stokes energy is measured at diffThe characteristics of backward Raman scattering and amplification based on two hydrogen Raman cells are investigated. Both cells are filled with high-pressure hydrogen. The first cell is used to generate the Stokes seed light, and the second cell is used to amplify the seed light. The Stokes energy is measured at different pump energies, and different pump distributions between the two cells. When the pulsed pump energy of first and second cell separately is 100 mJ, 175 mJ, a pulsed Stokes energy of 44.0 mJ can be generated, and the corresponding photon conversion efficiency is 28.6% . The rate equations are employed to simulate the amplification process, and the theoretical results are agree with the experimental results on the whole. When the pulsed energy of Stokes seed light is as much as or greater than the pump laser, the Stokes can still keep a constant increment according to the numerical simulation. Based on the simulation results, the Raman amplification method is proposed to realize multiple laser series synthetic output..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 402006 (2016)
Thermal Characterization of Electrically Injected Elliptical Microcavity Lasers
Lu Ri, Xu Liuyang, Gao Xin, Huang Yongzhen, Xiao Jinlong, and Bo Baoxue
The thermal behaviors of the elliptical microcavity laser are analyzed experimentally and theoretically. The major axis of the elliptical microdisk is 12 μm, the minor axis is 10 μm, and the output waveguide with width of 2 μm is connected directly. The thermal characteristics are investigated based on the lasing charaThe thermal behaviors of the elliptical microcavity laser are analyzed experimentally and theoretically. The major axis of the elliptical microdisk is 12 μm, the minor axis is 10 μm, and the output waveguide with width of 2 μm is connected directly. The thermal characteristics are investigated based on the lasing characteristics for continuous-wave electrical injection operations. The mode wavelength shift is used to estimate the temperature impedance (ZT=0.846 K/mW) during continuous operation. Based on the finite- element modeling, the thermal impedance is simulated for the elliptical microcavity laser and the simulation results are in good agreement with the experimental data. The maximum temperature impedance deviation between the simulated and experimental results is about 5%. The temperature rise in the active region as a function of the substrate size is investigated. The simulated results indicate that the heating performance of the benzocyclobutene-confined elliptical microcavity laser can be greatly improved by using an interlayer thermal shunt..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 402007 (2016)
Investigation on Gain Properties of N31 Neodymium Glass Slab Amplifiers
Wen Lei, Chen Lin, Liu Jianguo, Chen Yuanbin, Xie Xudong, Liu Yong, Zheng Kuixing, Chen Wei, Hu Lili, and Wu Yiqun
As one of the most important element in the inertial confinement fusion (ICF) laser device, slab amplifier provides over 99% energy. The integration-test-bed (ITB) is established for the research of ICF in China with the single- beam output energy up to 19.6 kJ (pulse width 5 ns, center wavelength 1053 nm). This paper As one of the most important element in the inertial confinement fusion (ICF) laser device, slab amplifier provides over 99% energy. The integration-test-bed (ITB) is established for the research of ICF in China with the single- beam output energy up to 19.6 kJ (pulse width 5 ns, center wavelength 1053 nm). This paper studies characteristics of N31 neodymium glass in 400 mm aperture, single-segment amplifying system of ITB. The N31 glasses with size of 810 mm×460 mm×40 mm and Nd3+ ion concentration of 3.5×1020 cm-3 are used. Results show that combined with the optimized parameters of discharge circuit for slab amplifier and structure of pump cavity, the small signal gain coefficient reaches 5.28% cm-1, the gain ratio is 15:1 , and the gain uniformity is 1.063∶1 (maximum/ average) within 360 mm beam diameter..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 402008 (2016)
Materials and Thin Films
Design and Fabrication of Broadband Mo/Si Multilayer Films for Extreme Ultra Violet Lithography Illumination System
Yu Bo, Li Chun, Jin Chunshui, and Wang Chunzhong
To meet the wide angular bandpass requirement of a small-size mirror in extreme ultra violet (EUV) lithography illumination system, the designed broadband molybdenum (Mo) /silicon (Si) multilayer stack is deposited by using the relationship between effective thickness of Si layers and velocity and the relationship betwTo meet the wide angular bandpass requirement of a small-size mirror in extreme ultra violet (EUV) lithography illumination system, the designed broadband molybdenum (Mo) /silicon (Si) multilayer stack is deposited by using the relationship between effective thickness of Si layers and velocity and the relationship between periodic thickness of multilayers and velocity. Mo/Si periodic multilayers with different periodic thicknesses and G (ratio of Mo layer thickness and periodic thickness of multilayer films) are deposited by magnetron sputtering and characterized by small-angle X-ray reflectometry. The relationship between periodic thickness of multilayers and velocity, the relationship between effective thickness of Mo and Si layers and velocity, and the interface roughness of multilayers are provided by characterization of X-ray reflection spectrum. The broadband multilayer stack is designed by utilizing the Levenberg-Marquardt algorithm, and the designed EUV reflectance is R=42%±1% at the range of 16.8°~24.8°. The designed stack is deposited according to the relationship between effective thickness of Si layers and velocity and the relationship between periodic thickness of multilayers and velocity. The measured EUV reflectance of the broadband Mo/Si multilayer stack is 41.2%~43.0% at the range of 16.8°~24.8°, which is very close to the designed value. Further fabrication error reversion indicates that the small difference between the experimental and designed results is mainly caused by the systematic error in the calibration of G value and interface roughness of Mo/Si multilayers..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 407001 (2016)
Measurement and Metrology
Unambiguous Laser Ranging Technology Based on Extended Pseudo-Random Modulation
Wu Xingguo, Yang Yi, and Hao Peiyu
In single photon ranging, increasing repeating frequency can improve the echo signal-to-noise ratio and result in ambiguous distance. To avoid ambiguous distance, an arithmetic based on modulation ranging and time-correlated photon counting theory is proposed, by which the unambiguous time and multiple of laser emittinIn single photon ranging, increasing repeating frequency can improve the echo signal-to-noise ratio and result in ambiguous distance. To avoid ambiguous distance, an arithmetic based on modulation ranging and time-correlated photon counting theory is proposed, by which the unambiguous time and multiple of laser emitting periods are calculated, and then the unambiguous distance is obtained. This technology needs less computation and is more effective. Extended pseudo-random sequences with variable proportion of“1”are derived from msequence, and they act as noise model and modulation signal. In simulation, ranging results with three different sequences are compared and it shows the pseudo-random sequences with proportion of“1”as 7/8 are random and noise resistant, of which the ranging result is better than that of all“1”sequence and m-sequence.
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 408001 (2016)
Effective Echo Extraction for Space Debris Laser Ranging Using Randomized Hough Transform
Liu Tong, Chen Hao, Shen Ming, Gao Pengqi, and Zhao You
The signal-to-noise (SNR) of space debris laser ranging (DLR) data is too low to extract the effective echo with fast and effective methods. To solve this problem, a DLR echo extraction method based on randomized Hough transform (RHT) is proposed. Considering the time correlating property of O-C residuals′ adjacent echThe signal-to-noise (SNR) of space debris laser ranging (DLR) data is too low to extract the effective echo with fast and effective methods. To solve this problem, a DLR echo extraction method based on randomized Hough transform (RHT) is proposed. Considering the time correlating property of O-C residuals′ adjacent echo, the effective echo extraction problem is transformed to the curve recognition of the image space. N pixels that determine a curve are randomly picked and they are mapped into one point in the parameter space. The parameter score accumulation strategy is used for curve recognition in the parameter space, which extracts the effective echo. The processing of DLR data of Yunnan Observatory shows that this method can extract echo signal on the approximated curve effectively with high speed, small storage and low misdetection rate. And it provides a new thought for fast and automatic DLR echo extraction..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 408002 (2016)
Effect and Experiment Analysis of First Specular Reflection Error on Absolute Radiometers
Tang Xiao, Fang Wei, and Wang Yupeng
In order to enhance the measurement accuracy of spaceborne solar irradiance and make its traceability value closer to the world radiometric reference, a finite element method is used to correct the opto- electric nonequivalence of solar irradiance absolute radiometers (SIAR). The positive cone cavity is used in the SIAIn order to enhance the measurement accuracy of spaceborne solar irradiance and make its traceability value closer to the world radiometric reference, a finite element method is used to correct the opto- electric nonequivalence of solar irradiance absolute radiometers (SIAR). The positive cone cavity is used in the SIAR and the heating wires are embedded into the thin walls. Thus, the opto-electric nonequivalence of SIAR is mainly derived from the drift driven by the first specular reflection. As it is difficult to measure the error in laboratory, the finite element system based on the structure of SIAR is established to quantitatively correct the nonequivalence, the relative error between the results obtained by the experiment and the finite element system is 0.86%. The results show that the power distribution of laser heating and electric heating is different due to the drift driven by the first specular reflection, the nonequivalence factor is 1.0000589, and the uncertainty is 3.4 × 10- 6. The radiant power measurement is modified according to this factor, and the final total solar irradiance value is (1365.70 ± 1.24) W/m2. The correction improves the revision system of SIAR..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 408003 (2016)
Micro and Nano Optics
Effect of Evaporation Process on Surface-Enhanced Raman Scattering Properties of Carbon Nanotubes Composite Strusture
Zhang Xiaolei, Zhang Jie, Gong Tiancheng, and Zhu Yong
In order to analyze the effect on surface enhanced Raman scattering (SERS) properties of threedimensional (3D) substrate during evaporation process of the probe molecules solution, a 3D composite structure of silver nanoparticles modified vertically aligned carbon nanotubes array(Ag/CNTs) is produced by magnetron sputtIn order to analyze the effect on surface enhanced Raman scattering (SERS) properties of threedimensional (3D) substrate during evaporation process of the probe molecules solution, a 3D composite structure of silver nanoparticles modified vertically aligned carbon nanotubes array(Ag/CNTs) is produced by magnetron sputtering and thermal annealing processes. Relevant experiments use the time-course SERS mapping test method and select 1 μmol/L Rhodamine 6G (R6G) and 10-2 μmol/L malachite green (MG) as probe molecules respectively. The results indicate that: with the increase of evaporation time, the Raman signal of probe molecules enhance firstly and then decrease. It is this main reason that, during evaporation process of analyst molecule, the capillary forces make the hotspots between the probe molecule and three- dimensional structure change, and then lead the electromagnetic field enhancements to change; in addition, the depth of focus and concentration change also influence the Raman signal..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 410001 (2016)
Optical Communication
All-Optical Repetition Rate Multiplication of Return to Zero Pseudorandom Bit Sequences Using Duty Ratio Compressor Based on Terahertz Optical Asymmetrical Demultiplexer
Sun Zhenchao, Wang Zhi, Wu Chongqing, Wang Fu, and Li Qiang
A scheme for all-optical repetition rate multiplication of return to zero(RZ) pseudorandom bit sequences(PRBS)is demonstrated with a duty ratio compressor based on terahertz optical asymmetrical demultiplexer(TOAD) cascaded multichannel delay structure．Its feasibility is verified by experiments,which shows that the dutA scheme for all-optical repetition rate multiplication of return to zero(RZ) pseudorandom bit sequences(PRBS)is demonstrated with a duty ratio compressor based on terahertz optical asymmetrical demultiplexer(TOAD) cascaded multichannel delay structure．Its feasibility is verified by experiments,which shows that the duty ratio of PRBS is compressed from 50% to 12.5% and than the bit rate is promoted from 2.5 Gb/s to 10 Gb/s with a same code type by the four-channel precise delay．The power penalty for bit error rateless than 10-9 of the eventual PRBS is 2 dB compared to the original PRBS..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 405001 (2016)
Performance Analysis of Spatial-Diversity Reception over Combined Effects of Atmospheric Turbulence
Zhang Huiying, Li Hongzuo, Xiao Dongya, and Ning Suhuan
The improvement for the spatial-diversity reception technology with the combined effect of atmospheric turbulence and pointing errors based on differential phase shift keying (DPSK) modulation is analyzed and studied. The performance of spatical-diversity reception for multiple input multiple output (MIMO) and single iThe improvement for the spatial-diversity reception technology with the combined effect of atmospheric turbulence and pointing errors based on differential phase shift keying (DPSK) modulation is analyzed and studied. The performance of spatical-diversity reception for multiple input multiple output (MIMO) and single input multiple output (SIMO) systems is discussed, and the bit error rate (BER) and outage probability for three types of diversity reception technologies are investigated under different turbulence situations, and the novel closed form expressions of BER and outage probability for free space optical communication(FSO) system are derived with the generalized hypergeometric method. The analysis and experiment results show that the performance of BER can be improved, the outage probability can be degraded with the spatial-diversity reception technology, and channel fading caused by atmospheric turbulence can be effectively improved. With the number of diversity increased, performance of FSO system is improved obviously. Compared with three diversity reception technologies, the maximum ratio combining diversity reception technology is most advantageous..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 405002 (2016)
Analysis of Thermal Properties in a Polarization-Maintaining Air-Core Photonic Bandgap Fiber
Li Xuyou, Xu Zhenlong, Yang Hanrui, Liu Pan, and Ling Weiwei
A kind of air- core photonic band gap fiber (PBF) with outstanding polarization- maintaining (PM) property is proposed. The effects of temperature variation on the effective index, beat-length and confinement loss are studied numerically based on full vector finite element method (FEM). It is found that the birefringenA kind of air- core photonic band gap fiber (PBF) with outstanding polarization- maintaining (PM) property is proposed. The effects of temperature variation on the effective index, beat-length and confinement loss are studied numerically based on full vector finite element method (FEM). It is found that the birefringence of the PBF is as high as 6.19×10-3, and beat-length is as short as 0.25 mm at the wavelength of 1.55 μm. The beat-length of this PBF is insensitive to the temperature, and the temperature-dependent beat-length coefficient is as low as 2.86×10-8 m/℃, which is typically two orders of magnitude lower than those of conventional panda fibers. The loss of the PBF is sensitive to temperature, and the confinement loss of the two orthogonal polarized modes increase with the increasing temperature. The PM-PBF with ultra-low temperature-dependent beat-length coefficient can reduce errors induced by the thermally polarization crosstalk apparently in interferometric applications such as resonant fiber optic gyroscope (RFOG), which plays an important role in RFOG, optical communications, optical fiber sensors and so on..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 405003 (2016)
Triangular Waveform Generation Technology Based on SBS and Superposition of Optical Field Envelopes
Jia Zhenrong, Jiang Yang, Ma Chuang, Bai Guangfu, Tang Yanlin, Qi Xiaosi, Zi Yuejiao, Huang Fengqin, and Wu Tingwei
Combined with external modulation and stimulated Brillouin scattering(SBS) amplification technology, a new method of generating triangular waveform signal by synthetizing signal envelopes with proper time delay is proposed and demonstrated. In this scheme, the continuous light emitted by lasers is divided into two branCombined with external modulation and stimulated Brillouin scattering(SBS) amplification technology, a new method of generating triangular waveform signal by synthetizing signal envelopes with proper time delay is proposed and demonstrated. In this scheme, the continuous light emitted by lasers is divided into two branches. One is modulated by Mach-Zehnder modulator and the fundamental frequency modulation signal, one third of the Stokes frequency shift, is obtained. The other one is used as SBS pump light to amplify the positive 3rd-order sideband of the modulation signal, and a frequency tripling harmonic signal is obtained. After independently controlling the phase and power of envelopes of the two harmonic signals, a triangular waveform signal with good approximation is generated by synthetizing these two signal envelopes with proper time delay. By changing the wavelength of continuous wave, the frequency of the generated triangular waveform signal can be tuned in a certain range. The feasibility of this scheme is proved in theoretical simulation and experiment. The scheme avoids complex spectral lines manipulation and the system stability is improved. It provides a new idea for arbitrary waveform generation technology..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 405004 (2016)
Rapid Communications
[in Chinese]
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Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 419001 (2016)
1.89 kW 窄线宽、单偏振、准单模全光纤放大器
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 419002 (2016)
[in Chinese]
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 419003 (2016)
全光纤化高效率、窄线宽光纤激光器实现2.5 kW近衍射极限输出
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 419004 (2016)
Terahertz Technology
Mechanically Tunable Terahertz Plasmonic Waveguide Filter
Chen Meng, Fan Fei, Yang Lei, Zhang Zhenkun, Luo Youyang, and Chang Shengjiang
Two kinds of plasmonic crystal waveguides at terahertz band are designed and fabricated. Based on the property that the bandgaps of the waveguides can be manipulated actively by varying the air gap between the waveguide, the functions of optical switch and mechanically tunable filter have been realized. The transmissioTwo kinds of plasmonic crystal waveguides at terahertz band are designed and fabricated. Based on the property that the bandgaps of the waveguides can be manipulated actively by varying the air gap between the waveguide, the functions of optical switch and mechanically tunable filter have been realized. The transmission and filtering properties of the two plasmonic crystal waveguides are investigated by terahertz time-domain system. The transmittance is calculated by finite-difference time-domain method. The band gap properties and field distributions are simulated by finite element method. The results indicate that both of the two tunable filters achieve good performance. The extinction ratio of the one-dimensional plasmonic crystal waveguide is 30 dB, the tunable band gap range is 130 GHz, while the range of the two-dimensional plasmonic crystal waveguide is 110 GHz, and the extinction ratio is 40 dB..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 411001 (2016)
Optical Design and Fabrication
Development of 30 kHz Repetition Rate Swept Laser Source with Narrow Instantaneous Linewidth
Chen Minghui, Li Hao, and Fan Yunping
An all- fiber 30 kHz repetition rate swept laser source at a center wavelength of 1340 nm with narrow instantaneous linewidth is built for swept source optical coherence tomography. The phase and the intensity of the swept source are stable. The scanning range of the swept source is 10 nm, the full width at half maximuAn all- fiber 30 kHz repetition rate swept laser source at a center wavelength of 1340 nm with narrow instantaneous linewidth is built for swept source optical coherence tomography. The phase and the intensity of the swept source are stable. The scanning range of the swept source is 10 nm, the full width at half maximum is 6 nm, the instantaneous linewidth is less than 0.018 nm and the average output power is 9.1 mW. Based on the Fourier-domain mode locking, the swept laser source uses a Fabry-Perot interferometer tunable filter (FFP- TF) with finesse of 5578 and narrow transmission window. Spontaneous emission of the gain medium is used as background light, and passes through the long dispersion managed delay line into the FFPTF. After filtering and parameter matching, the system can resonate and produce an ultra- stable swept laser. The factors influencing the instantaneous linewidth of the swept source are discussed. The swept laser source shows high finesse which makes it suitable for high- speed molecular spectroscopy and molecular absorption spectroscopy..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 416001 (2016)
Coaxial and Off-Axial Hybrid Three-Mirror Optical System with Long Focal Length
Chen Zhe, Zhang Xingxiang, Chen Changzheng, and Ren Jianyue
One coaxial and off-axial hybrid three-mirror optical system is designed, by combining a coaxial threemirror system and an off-axial three-mirror system. A 10×0.1° field of view (FOV) is achieved by the F/7.3 coaxial system with spectral coverages of 0.38~0.78 μm and 1.2~1.7 μm. A 2°×0.1° FOV iOne coaxial and off-axial hybrid three-mirror optical system is designed, by combining a coaxial threemirror system and an off-axial three-mirror system. A 10×0.1° field of view (FOV) is achieved by the F/7.3 coaxial system with spectral coverages of 0.38~0.78 μm and 1.2~1.7 μm. A 2°×0.1° FOV is achieved by the F/18.9 off-axial system with spectral coverage of 0.38~0.78 μm. The above two systems have the same focal length of 14 m, and the simultaneously performing push-broom imaging ability. They both have a middle image plane and a real exit pupil which can supress stray light easily. After an optimization, near diffraction-limited performance can be obtained over all the FOVs and the spectral ranges. A minimum modulation transfer function (MTF), higher than 0.41 at Nyquist frequency, is acquired, which satisfies the design requirement to achieve a static MTF higher than 0.2. Moreover, the whole system structure is compact and its elements are easy to manufacture and align..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 416002 (2016)
Effect of Material Removal Function on Surface Shape Error Correction in Fluid Jet Polishing
Lü Liang, Ma Ping, Zhu Heng, Huang Jinyong, and Wang Gang
Material removal function characteristics in fluid jet polishing are discussed. According to the onedimensional profile characteristics of the material removal function, the analytical formulas of the removal function are established. Based on the formulas, the Matlab numerical simulation is utilized to simulate the onMaterial removal function characteristics in fluid jet polishing are discussed. According to the onedimensional profile characteristics of the material removal function, the analytical formulas of the removal function are established. Based on the formulas, the Matlab numerical simulation is utilized to simulate the one-dimensional material removal process under the partial overlap condition and different parameters. The root mean square of the waviness Wrms is introduced to discuss the effect of different parameters on one-dimensional error correction under the constant removal process and the linear removal process. The optimized parameters are adopted in the subsequent fluid jet polishing experiments. The polishing results on φ50 mm fused silica glass show that the peakvalley value of surface shape λPV decreases from 0.148l to 0.062l after two rounds of experiments. Especially, λPV decreases to 0.048l for 90% aperture, and to 0.032l for 75% aperture. The root mean square of surface shape λrms decreases from 18.86 nm to 4.87 nm, especially to 3.67 nm for 90% aperture, and 3.15 nm for 75% aperture..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 416003 (2016)
Remote Sensing and Sensors
Influence of Resonator Mirror Surfaces on Output Mode of Radio Frequency Slab CO2 Lasers
Wang Wei, Tang Xiahui, Qin Yingxiong, Xiao Longsheng, Wu Chao, Wang Zhen, and Wan Wen
For lasers with unstable resonator structure, the dimension of the spherical cavity mirrors increases dramatically when the Fresnel number of the system is large. Although it is possible to obtain high output power, the aberration of the resonator mirror has great influence on the output beam quality as the paraxial coFor lasers with unstable resonator structure, the dimension of the spherical cavity mirrors increases dramatically when the Fresnel number of the system is large. Although it is possible to obtain high output power, the aberration of the resonator mirror has great influence on the output beam quality as the paraxial condition is not satisfied. The output mode of a 2 kW radio frequency slab CO2 laser with an effective cavity Fresnel number of 675 and different types of cavity mirrors is analyzed by the Fox-Li iteration algorithm. Furthermore, experimental investigations are conducted. The results show that the spherical aberration affects the laser output mode seriously when two spherical mirrors are used, the output beam wavefront is approximately spherical, the M2 factor of the beam is 14.48 at the output plane, the beam quality is poor, and the beam is off the optical axis through the focusing lens, which makes it difficult to achieve a high power and high beam quality laser output. When two parabolic mirrors are used, the output beam wavefront is approximately planar, the beam quality is improved with an M2 factor of 3.96, and the simulation results are in good agreement with the experimental results..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 402004 (2016)
Design and Research of Biosensor Characteristics Based on Grating Waveguide Angle Modulation with MEMS Micro-Mirror
Lu Anjiang, Bai Zhongchen, Xiao Wei, Zhang Zhengping, and Qin Shuijie
The label- free, real- time and high sensitivity bio- detection serves as an important technology in analytical biology field. Biosensor model is constructed with optical waveguide mode theory, and a miniaturized biological sensing detection system is designed based on MEMS micro-mirror. Its dynamic response characteriThe label- free, real- time and high sensitivity bio- detection serves as an important technology in analytical biology field. Biosensor model is constructed with optical waveguide mode theory, and a miniaturized biological sensing detection system is designed based on MEMS micro-mirror. Its dynamic response characteristic is tested and analyzed. By calculating and simulating, the relationship between sensitivity and thickness of waveguide and effective refractive index is obtained. Glucose solution is detected in TE mode and TM mode, experimental result shows that a well linear relationship between concentration of the glucose solution and incidence angle is presented, and the precision can reach 5 ng/mL. Compared with the traditional immunological detection methods, it has a relatively high sensitivity. Due to the small system and simple structure and label-free, it can realize the in-situ detection to avoid damaging the activity of protein, and it is a label-free optical detection method with great potential..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 414001 (2016)
Index Sensing Characteristics for Mirror Symmetrical Porous Silicon Photonic Crystals
Chen Ying, Han Yangyang, Cao Huiying, Zhu Qiguang, and Bi Weihong
Based on the local characteristics of photonic crystals and the optical sensing principle of porous silicon, the mirror symmetrical porous silicon photonic crystal index sensing structure is proposed. The sensing theoretical model is obtained based on layered transfer matrix method. The relationship between the resonanBased on the local characteristics of photonic crystals and the optical sensing principle of porous silicon, the mirror symmetrical porous silicon photonic crystal index sensing structure is proposed. The sensing theoretical model is obtained based on layered transfer matrix method. The relationship between the resonant wavelength and the structural parameters of the porous silicon photonic crystal is deduced. By adjusting the structure parameters of porous silicon for both high and low refractive index layers, the full width at half maximum of the band gap will be narrowed and the quality factor (Q value) can be improved. Based on the transfer matrix method, when the methanol vapors with different concentrations enter the porous silicon photonic crystal index sensor structure, the theoretical simulation is performed using MATLAB. The relationship model between the change of the resonant peak wavelength and the variation of the effective refractive index for the porous silicon layer is established, and the refractive index sensing properties are analyzed in the numerical simulation. The simulation results show that the Q value of the refractive index sensing structure is 3114.75 and the sensitivity can attain to 903.9 nm/RIU, which demonstrate the effectiveness of the sensing structure, and it can provide certain practical reference value for the design of high Q and high sensitive refractive index sensors..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 414002 (2016)
Automatic Registration of Terrestrial Point Clouds without Additional Information
Chen Maolin, Lu Weixin, Wan Youchuan, Tian Siyi, and Yang Wei
An automatic point clouds registration method is proposed based on geometric information. This method can realize point cloud automatic registration without additional intensity and images information. Feature points of registration scans are extracted by feature distance histogram, and the initial matching sets of matAn automatic point clouds registration method is proposed based on geometric information. This method can realize point cloud automatic registration without additional intensity and images information. Feature points of registration scans are extracted by feature distance histogram, and the initial matching sets of matching points are searched by K closet neighbor search in feature space. Relative height and the normal vector similarity measure are put forward, false match is eliminated combining with the root mean square distance and the initial conversion parameters are calculated. Points of low complexity are selected by Shannon entropy to participate in iterative closet point (ICP) accurate registration. Experimental results of real point cloud data show that, the proposed method can eliminate false matching of initial matching set, get better initial transform parameters, and improve the efficiency and precision of ICP algorithm..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 414003 (2016)
Spectrum Filter Performance Analysis on Near-Infrared High-Spectral-Resolution Lidar
Zhang Yupeng, Liu Dong, Yang Yongying, Luo Jing, Cheng Zhongtao, Zhou Yudi, Bai Jian, Wang Kaiwei, Shen Yibing, and Yang Liming
Near- infrared high- spectral- resolution lidar (HSRL) is more difficult to develop as its molecule scattering echo signal has a narrower spectrum width and a weaker energy strength than that of the ultraviolet and visible HSRLs. As one of the key components of HSRL, the spectrum filter has significant influences on thNear- infrared high- spectral- resolution lidar (HSRL) is more difficult to develop as its molecule scattering echo signal has a narrower spectrum width and a weaker energy strength than that of the ultraviolet and visible HSRLs. As one of the key components of HSRL, the spectrum filter has significant influences on the retrieval accuracy of HSRLs. Based on the relationship between the spectral filter′ s signal transmittance and spectral discrimination ratio and the retrieval accuracy of the HSRL, the performances of two typical interference spectrum filters are modeled and simulated by analyzing the characteristics of lidar echo at 1064 nm. Results show that Fabry- Perot interference filter has moderately good performances when the divergence of incident beam is small. While the requirement for surface precision is fairly high and it is not easy to be processed and installed. Field-widened Michelson interferometer (FWMI) is insensitive to the divergence of incident beam and has a stronger ability to gathering the lidar echo. And the requirement for surface precision is relatively low. In practical application, it is more suitable for the application requirement of near-infrared HSRL..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 43, Issue 4, 414004 (2016)
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