Journals >Chinese Journal of Lasers
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2015
Volume: 42 Issue 12
37 Article(s)
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Research Article
Monte Carlo Simulation of Polarization Lidar Multiple Scattering by Multi-Layer Discrete Random Media
Sun Xianming, Xiao Sai, Wan Long, Wang Haihua, and Shen Jin
The polarized multiple scattering of multi-layer discrete random media by laser is simulated by the Monte Carlo method. The simulation steps of a fast semi-analytic Monte Carlo method are given based on the properties of the polarization lidar. The free path adjustment is considered when the photon crosses the interfacThe polarized multiple scattering of multi-layer discrete random media by laser is simulated by the Monte Carlo method. The simulation steps of a fast semi-analytic Monte Carlo method are given based on the properties of the polarization lidar. The free path adjustment is considered when the photon crosses the interface of different media. The scattering angles for different media layers are sampled based on the Mie theory. The relationship between lidar depolarization ratio and the penetration depth of two-layer and three-layer water clouds is studied. The results show that the depolarization ratio increases with the depth of penetration, and the increasing speed of depolarization ratio is also different when laser is incident from one medium to another medium. The influence of effective size, single scattering phase function, extinction on the lidar depolarization is analyzed. The method can be used to retrieve the microphysical and optical characteristics of inhomogeneous clouds or aerosols with the polarization lidar..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1213001 (2015)
Study of the Drift Characteristics of Airy Vortex Beam in Atmospheric Turbulence
Cheng Zhen, Chu Xingchun, Zhao Shanghong, Deng Boyu, and Zhang Xiwen
The drift characteristics of Airy vortex beam in atmospheric turbulence are simulated based on multiple phase screens method. The drift characteristics influenced by topological charge p, the off-axis dislocations xd, yd of the vortices core from the optical center and the intensity of turbulence C2n are investigated iThe drift characteristics of Airy vortex beam in atmospheric turbulence are simulated based on multiple phase screens method. The drift characteristics influenced by topological charge p, the off-axis dislocations xd, yd of the vortices core from the optical center and the intensity of turbulence C2n are investigated in different distances. It is shown that the drifts increase with the increase of C2n in the same distance. When the distances are short, the drifts are nearly equal because of the weak influence of p and xd, yd. When the distances are long enough, the drifts decrease with the increase of p, but increase with the increase of xd, yd. In addition, by comparing the drifts of single Airy vortex beam with the Airy vortex array beams, it is shown that the drifts of Airy vortex array beams are smaller..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1213002 (2015)
Biomedical Photonics and Laser Medicine
An Automatic Delay Correction Algorithm for Improving Imaging Resolution of Swept Source Optical Coherence Tomography System
Chen Xiaojie, Bai Baoping, Chen Xiaodong, Wang Yi, and Yu Daoyin
In the swept source optical coherence tomography (SS-OCT) instruments, an unfixed delay between the spectral calibration signal k-clock and the OCT signal makes the result of spectral calibration incorrectly, which reduces the imaging resolution. An automatic delay correction algorithm is proposed to automatically corrIn the swept source optical coherence tomography (SS-OCT) instruments, an unfixed delay between the spectral calibration signal k-clock and the OCT signal makes the result of spectral calibration incorrectly, which reduces the imaging resolution. An automatic delay correction algorithm is proposed to automatically correct the delay between k-clock signal and OCT signal accurately. The algorithm based on the proposed average peak method and average full width at half maximum (FWHM) method, through processing and analyzing the OCT signal, divides into coarse adjustment, fine adjustment and accurate adjustment to search for delay point automatically. According to the search result, the delay time is corrected. After delay correction, high resolution reconstructed image is realized through spectral calibration of OCT signal evenly distributes in the wave-number (k) space. Experimental results show that, the imaging resolution improves 60% by correcting the delay automatically, which proves the effectiveness of the proposed algorithm..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1204001 (2015)
Holography and Information Processing
Three-Dimensional Profile Data Representation Based on Gray Value Encoding
Zhang Shaoze, Zhang Jianqi, Huang Xi, and Liu Delian
Recently, the online three-dimensional(3D) digital museum is becoming an emerging method for the protection and resource sharing of the heritage. However, the size of 3D profile data obtained by 3D scanning techniques is too large for 3D digital museums to properly load and display in real time. To solve this problem, Recently, the online three-dimensional(3D) digital museum is becoming an emerging method for the protection and resource sharing of the heritage. However, the size of 3D profile data obtained by 3D scanning techniques is too large for 3D digital museums to properly load and display in real time. To solve this problem, a representation method of 3D profile data based on gray value encoding is proposed. On the basis of the virtual fringe projection system, the gray values are encoded into an 8 bit gray image or an 8 bit gray image along with a binary image according to the resolution of the virtual camera in the horizontal direction, and then the images are projected as projection fringes. By utilizing the virtual camera to capture the projection fringes that have been distorted, 3D profile data are represented as images. The experimental results show that the loading and display time of the data within the proposed method is reduced by more than 98% compared with the traditional 3D data format, and it is very suitable for the real-time loading and display of digital museums based on 3D profile data..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1209001 (2015)
Spectral Analysis and Filtering of Moire Fringes Generated by Using Digital Image Processing
Zhu Lijun, Wang Yurong, Meng Xiangfeng, Yang Xiulun, and Jiang Shan
Moire topography, a generation and analysis technique of moire fringes, is one of the techniques usually applied to three-dimensiond (3D) object shape measurement. Three kinds of methods, shadow moire, projection moire and digital moire, are mainly used to generate moire fringes. At present, low- pass filtering is usedMoire topography, a generation and analysis technique of moire fringes, is one of the techniques usually applied to three-dimensiond (3D) object shape measurement. Three kinds of methods, shadow moire, projection moire and digital moire, are mainly used to generate moire fringes. At present, low- pass filtering is used for extracting the moire fringes, since the low-frequency region contains lots of unwanted frequency components, the extracted moire fringes are not satisfactory and need to be improved. After theoretical analysis, a new method for extracting moire fringes, the band-pass filtering method, is proposed. This method can be used to extract moire fringes generated by multiplication, addition or subtraction of the reference fringes and deformed fringes by digital image processing. Compared with the traditional low-pass filtering method, the contrast of moire fringes with bandpass filtering is higher, and the intensity distribution is standard cosine. Besides, there is a phase shift of π between the moire fringes produced by addition and subtraction operation, so their bright and dark fringes are justly reversed. The correctness and validity of the proposed method and analysis have been verified by computer simulations and experiments..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1209002 (2015)
Laser Manufacturing
Ultrasonic Nondestructive Testing of Hole Type Defects in Laser Solid Forming TC4 Alloy
Ruan Xueqian, Lin Xin, Huang Chunping, and Huang Weidong
The interaction between the inner, surface and near- surface defects of laser solid forming TC4 alloy and ultrasonic are studied. The results show that under the same testing conditions, reflection amplitude value increases with the increasing of long lateral hole diameter for the long lateral hole defects with the samThe interaction between the inner, surface and near- surface defects of laser solid forming TC4 alloy and ultrasonic are studied. The results show that under the same testing conditions, reflection amplitude value increases with the increasing of long lateral hole diameter for the long lateral hole defects with the same depth and different diameters; and the reflection amplitude value decreases with the increasing of the depth of long lateral hole for the long lateral hole defects with the same diameter and different depths; holes within 0.6 mm diameter can be found in laser solid forming TC4 alloy using 5PФ8 straight longitudinal wave probe. The ability of SAW to found defects less than 4mm from the surface in the depth direction is less than 4 mm and the hole defect is harder to find than the groove..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1203001 (2015)
Numerical Simulation of Residual Stress Induced in 7075 Aluminum Alloy by Repeated High-Power Laser Pulses
Zhang Xingquan, Li Huan, Huang Zhilai, Zhang Xin, She Jianping, Zhang Yan, and Duan Shiwei
Laser shock peening (LSP) is a novel surface modified technique. In practical applications, due to the diameter of laser beam smaller than 20 mm, the overlapping LSP technology needs to process workpiece surface with large area. The residual stress fields induced by laser spots in different center distances are discussLaser shock peening (LSP) is a novel surface modified technique. In practical applications, due to the diameter of laser beam smaller than 20 mm, the overlapping LSP technology needs to process workpiece surface with large area. The residual stress fields induced by laser spots in different center distances are discussed with finite element methods and experiments. The influences of overlapping rate on the distributions of residual stress are investigated. The characteristics of residual stress distributions induced by different shocking sequences are also analyzed. The results show that the center distances of laser spots have significant influences on the residual stress of region between two laser spots. With the center distances of two laser spots decreasing, the residual stress fields at the region between two laser spots turn from tensile residual stress into compressive residual stress. The magnitude of compressive residual stress is increased with the increment of laser spot overlapping rate, and the distributions of residual stress generated by larger overlapping rate are more uniform. The multiple shocking sequence of mid-left-right can induce a large and uniform compressive residual stress field ..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1203002 (2015)
Laser Direct Forming Process of Thin-Walled Blade Using Variable Spot by Inside-Beam Powder Feeding
Lu Bin, Zhu Gangxian, Wu Jizhuo, Shi Shihong, and Fu Geyan
With unequal width structure characteristics of thin-walled blades, single track by variable laser spot based on coaxial inside-laser powder feeding rather than multi-track overlapping is adopted, and the thin-walled blade can be fabricated layer by layer directly. The forming quality of thin-walled blades is investigaWith unequal width structure characteristics of thin-walled blades, single track by variable laser spot based on coaxial inside-laser powder feeding rather than multi-track overlapping is adopted, and the thin-walled blade can be fabricated layer by layer directly. The forming quality of thin-walled blades is investigated by variable laser spot based uniform height and stepped single track. The experimental results show that a uniform height cladding layer with different widths can be got by controlling scanning speed and laser power under the condition with sufficient powder mass flow rate. The growth rate of cladding layers isn′t consistent based on uniform height single-trace cladding layer, and the large ratio of width to height position increases quickly. The theoretical model among layer thickness of Z axis, height of single-trace cladding layer and the section curve order of cladding layer is established, and the stepped single track method is put forward to solve the problem of inconsistent growing height. The thin-walled blade with good forming quality can be achieved. This new method can be provided for forming unequal width blade by laser direct forming with coaxial inside-laser powder feeding..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1203003 (2015)
Study on Surface Morphology and Roughness Variation of NiCr Alloy Curved Surface Manufactured by Selective Laser Melting
Mai Shuzhen, Yang Yongqiang, and Wang Di
In order to directly fabricate customized metallic parts with complicated surface, the surface quality of curved surface feature manufactured by selective laser melting (SLM) technology should be ensured. The parameters of NiCr alloy are optimized by orthogonal experiment and two kinds of cylinders are fabricated with In order to directly fabricate customized metallic parts with complicated surface, the surface quality of curved surface feature manufactured by selective laser melting (SLM) technology should be ensured. The parameters of NiCr alloy are optimized by orthogonal experiment and two kinds of cylinders are fabricated with X-Y inter-layer staggered scan strategy. The surface morphologies of curved surfaces of the parts are studied using three dimensional super depth digital microscope and scanning electron microscope, and the corresponding surface roughness is measured. The results show that when fabricating the parts with curved surface placed in different spatial positions, contour error in layer and stair effect among layers stacked lead to the staircase-shaped profile and anastomosing morphology on curved surfaces, and even the worm-like or granular morphology on overhanging curved surfaces when the tilt angle is larger than 60° . Variation of the value of Ra is consistent with surface morphology. The results provide important guidance to improve surface quality of the parts with curved surface fabricated by SLM..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1203004 (2015)
Research on Laser Surface Micro Texturing Processing of Single Pulse Intervals
Fu Yonghong, Liu Qiangxian, Ye Yunxia, Hua Xijun, Kang Zhengyang, and Fu Hao
Effect of single pulse intervals (SPI) processing on the laser micro texture is discussed. An investigation on the 45 steel samples is performed by using a nanosecond frequency doubling Nd3+∶YAG laser. The influencing laws of laser parameters (the laser fluence, number of pulses) and the geometrical parameters of microEffect of single pulse intervals (SPI) processing on the laser micro texture is discussed. An investigation on the 45 steel samples is performed by using a nanosecond frequency doubling Nd3+∶YAG laser. The influencing laws of laser parameters (the laser fluence, number of pulses) and the geometrical parameters of micro-crater as well as surface plasma absorption rate of laser are investigated. Compared with continuous pulses processing, the advantage of SPI are analyzed from experiment and temperature field simulation. The results show that with the increase of the laser fluence, the micro-crater diameter increase with a logarithmic function, while the micro-crater depth increases, then level off, finally fall slightly down. Effect of pulse number on micro-crater diameter is not significant, but the micro- crater depth increases linearly. Compared with continuous pulses processing, SPI minimizes the heat effect which is negative, and the effect of multiple pulse on micro texture internal morphology has a "smooth" role; when ensuring the material removal rate of a single pulse, the efficiency of the laser processing high quality micro texture is improved..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1203005 (2015)
Laser Physics
Effect Analysis of Self-Correction Method Based on the Prediction Model of Deformable Mirror with Thermal Deformation
Hu Xiaochuan, Wang Du, Chen Lixia, and Zhang Bin
In the process of wavefront correction, the thermal deformation appears on deformable mirrors(DMs) radiated by high-power continuous wave (CW) laser, leading to the additional wavefront distortion to the incident laser, and further the restriction of the correction ability of deformable mirror and the degradation of thIn the process of wavefront correction, the thermal deformation appears on deformable mirrors(DMs) radiated by high-power continuous wave (CW) laser, leading to the additional wavefront distortion to the incident laser, and further the restriction of the correction ability of deformable mirror and the degradation of the beam quality. A prediction model of deformable mirror with thermal deformation radiated by high-power continuous wave laser is presented based on Zernike polynomial decomposition. According to the prediction of the thermal deformation of the deformable mirror, the control signal of the actuators have been obtained by finite element simulation, and further control the actuators to compensate the thermal deformation distribution of the deformable mirror in real time. Simulation results indicate that,the self- correction method can compensate the thermal deformation distribution of the deformable mirror effectively and reduce the influence of thermal deformation on the correction ability of the deformable mirror. As a reference, the local heat transfer method can only reduce the piston and defocus of the distorted wavefront caused by the thermal deformation of the deformable mirror to a certain extent, and the effect on beam quality is not efficient enough. However, the self-correction method can eliminate almost all the optical path difference caused by the thermal deformation of the deformable mirror and further improve the beam quality effectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1202001 (2015)
Research on Modified Nonlinear Amplifying Loop Mirror Mode-Locked Lasers
Zhou Xiaokang, Song Youjian, Liao Ruoyu, Liu Bowen, Hu Minglie, Chai Lu, and Wang Qingyue
A modified nonlinear amplifying loop mirror mode- locked laser is demonstrated. In this setup, nonreciprocal elements are included into traditional“figure eight”and“s-like”cavities in order to decrease the length of essential fiber required to accumulate nonlinear phase shift. As a result, the repetition rate of these A modified nonlinear amplifying loop mirror mode- locked laser is demonstrated. In this setup, nonreciprocal elements are included into traditional“figure eight”and“s-like”cavities in order to decrease the length of essential fiber required to accumulate nonlinear phase shift. As a result, the repetition rate of these lasers is significantly increased. In addition, the self-starting characteristic is also improved. The passive mode-locking operation of traditional“figure eight”polarization maintaining (PM) fiber lasers requires real saturable absorbers, such as semiconductor saturable absorber mirror, or carbon nanotube. In this work, by using nonreciprocal elements, passive mode locking in a modified“figure eight”polarization maintaining Er-fiber laser is realized. The laser works in soliton regime and generates 308 fs pulses with an average power of 23.6 mW at a repetition of 22 MHz . The repetition rate of traditional“figure eight”fiber lasers is limited to 10 MHz. By using nonreciprocal elements, a non PM Er-fiber laser based on a modified“s-like”cavity working at stretched pulse regime generates pulses with an average power of 36 mW at a repetition of 80 MHz. The same laser working at normal dispersion domain generates pulse train with an average power of 14 mW at a repetition of 53.6 MHz..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1202002 (2015)
Study on Broad Tuning Range and Narrow Line-Width 405 nm Blue-Violet Diode Laser with Grating External Cavity
Li Bin, Gao Jun, Zhao Jun, Yu Anlan, Wang Xinbing, and Zuo Duluo
Free-running diode lasers can not satisfy the demands of spectroscopy applications such as Raman scattering which requires narrow line-width. In order to obtain narrow line-width laser at 405 nm band, external cavity with reflective holographic gratings for blue-violet laser diode (LD) is studied. The spectra of the blFree-running diode lasers can not satisfy the demands of spectroscopy applications such as Raman scattering which requires narrow line-width. In order to obtain narrow line-width laser at 405 nm band, external cavity with reflective holographic gratings for blue-violet laser diode (LD) is studied. The spectra of the blue-violet LD with a grating external cavity in Littrow configuration are measured by a high resolution monochromator, and the characteristics of threshold and tuning property are investigated through its output power and spectra. It is found that the threshold current of LD is reduced from 30.0 mA to 19.7 mA or 21.3 mA when the groove density of the grating is 2400 l/mm or 3600 l/mm respectively, and the line-width is suppressed within 0.03 nm in the full scope of injection currents while the line-width of the free running LD is approximately 1nm. Furthermore, tuning ranges of 5.45 nm and 5.33 nm are achieved. These results is helpful for the spectroscopy applications of blue-violet LD..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1202003 (2015)
Continuous Wave and Wavelength Tuning Performances of Diode-Pumped Yb∶YAG Ceramic Laser
Wang Ke, Zhu Jiangfeng, Gao Ziye, Li Jiang, Wang Junli, Xie Tengfei, Pan Yubai, and Wei Zhiyi
The high efficiency continuous wave and wavelength tuning properties of a diode-pumped domestic Yb∶YAG ceramic laser is studied. The laser performances of ceramics with different atomic fractions (1%、2%、5%、 10%、15%) and thickness (3、6 mm) are compared. The highest output power of 2.4 W is obtained from a 3 mm 15 % dopiThe high efficiency continuous wave and wavelength tuning properties of a diode-pumped domestic Yb∶YAG ceramic laser is studied. The laser performances of ceramics with different atomic fractions (1%、2%、5%、 10%、15%) and thickness (3、6 mm) are compared. The highest output power of 2.4 W is obtained from a 3 mm 15 % doping ceramic, pumped by an absorbed pump power of 6.3 W, corresponding to a slope efficiency of 47% . Wavelength tuning is realized by inserting a prism in the laser cavity, and the broadest tuning range is from 1017 to 1095 nm. The experimental results indicate the high-quality Yb∶YAG ceramic is a promising candidate in highpower all-solid-state ultrashort pulse generation and amplification..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1202004 (2015)
Hundred Micro-Joules Level Femtosecond Fiber Laser Amplification System
Li Feng, Yang Zhi, Zhao Wei, Li Qianglong, Hu Xiaohong, Yang Xiaojun, and Wang Yishan
A fiber chirped pulse amplification system based on Yb3 + doped fibers is demonstrated. The seeder is a mode-locked fiber laser with semiconductor saturable absorber, the chirped pulse amplification technique is applied to stretch the 1030 nm pulse to several hundred picoseconds to be amplified. The single mode picosecA fiber chirped pulse amplification system based on Yb3 + doped fibers is demonstrated. The seeder is a mode-locked fiber laser with semiconductor saturable absorber, the chirped pulse amplification technique is applied to stretch the 1030 nm pulse to several hundred picoseconds to be amplified. The single mode picosecond pulses with average power of 50 W and repetition rates of 211 kHz are achieved by using multistage pre-amplifier consisted with Yb3+ doped single mode fiber amplifier and double cladding fiber amplifier and the main amplifier with a large mode area rod-typed photonic crystal fiber as the laser gain material. Properly controlled the gain and the nonlinearity in every step of the amplification system, the influence of nonlinear effects are effectively suppressed on the pulse of time domain in high energy amplification. Laser pulses with pulse duration of 887 fs are generated by a reflective grating-pair compressor, corresponding to single pulse energy of 124 μJ and peak power of 139.8 MW. This experimental result of hundred micro joules level femtosecond laser based on fiber structure is firstly reported in China..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1202005 (2015)
Propagation Characteristics of Laser Quad in Spherical Hohlraum for Indirect Drive Facility
Hou Pengcheng, Wen Ping, Zhong Zheqiang, and Zhang Bin
In indirect-drive inertial confinement fusion facilities, aimed at the spherical hohlraum structure and the laser quads configuration, and based on the beam smoothing scheme implemented by the combined use of smoothing by spectral dispersion, continuous phase plate (CPP) and polarization control plate, the propagation In indirect-drive inertial confinement fusion facilities, aimed at the spherical hohlraum structure and the laser quads configuration, and based on the beam smoothing scheme implemented by the combined use of smoothing by spectral dispersion, continuous phase plate (CPP) and polarization control plate, the propagation model of laser quads in the spherical hohlraum has been built up. Because of the high spherical symmetry of spherical hohlraum and laser quads configuration, the plane of the laser entrance hole (LEH) is taken as the observation plane for analyzing the characteristics of laser quads propagating through the LEH, and the LEH closure problem is mainly analyzed. A series of concentric spherical surfaces have been taken as the observation surfaces for analyzing the propagation characteristics of laser quads in spherical hohlraum and the illumination characteristics on hohlraum wall. Simulation results indicate that, When different incident angles of the laser quads are used with the same CPP, with the increasing of the laser quads incident angle, the laser energy injection rate at LEH decreases and it is easier to bring about the LEH closure, while the cross and overlap of laser quads reduce gradually, the illumination uniformity on the hohlraum wall slightly improves and the duty ratio of all laser quads on the hohlraum wall is also improved, which is helpful for achieving the irradiation uniformity of the target. As different incident angles of the laser quads using the different CPP, the LEH closure problem is improved, While the duty ratio of the hohlraum wall decreased. In practical applications, it is required to design the laser quads incident angle appropriately by taking the LEH injection rate and the LEH closure problem, the overlap and uniformity of laser quads in hohlraum, as well as the irradiation uniformity of all quads and the duty ratio on hohlraum wall into consideration..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1202006 (2015)
Theoretical Analyses of an Alkali Vapor Amplifier End-Pumped by Diode Lasers
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After the introduction of technical background and unique merits of a diode-pumped alkali laser (DPAL), the present research conditions are described in development of master oscillator power-amplifier (MOPA) for DPALs. The systematic calculation is carried out after construction of a rate-equation model of an end-pumpAfter the introduction of technical background and unique merits of a diode-pumped alkali laser (DPAL), the present research conditions are described in development of master oscillator power-amplifier (MOPA) for DPALs. The systematic calculation is carried out after construction of a rate-equation model of an end-pumped DPAL-MOPA system using the three-level stimulated absorption-stimulated emission theory of an alkali atom. The output power and extraction efficiency are analyzed when the temperature, cell length, pump power, and waist radius are varied, respectively. Compared with the experimental data, the calculated results are in coincident with them, which demonstrates the developed model is effective. The research is thought to be useful in realization of the power scaling of a DPAL system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1202007 (2015)
Study on Thermal-Lens-Free Orientations of a Yb3+∶KGd(WO4)2 with Different Polarized Directions
Gao Ming, Wang You, Jiang Zhigang, Han Juhong, An Guofei, Xue Liangping, Zhang Wei, Cai He, Wang Hongyuan, and Zhou Jie
Using the anisotropic thermal expansion coefficients and the negative refractive index gradients in temperature of an optical-pumped Yb3+∶KGd(WO4)2, it is possible to find some special directions without thermallyinduced lens effects which is called“the thermal-lens-free orientation”. Considering there are some defectsUsing the anisotropic thermal expansion coefficients and the negative refractive index gradients in temperature of an optical-pumped Yb3+∶KGd(WO4)2, it is possible to find some special directions without thermallyinduced lens effects which is called“the thermal-lens-free orientation”. Considering there are some defects in the theoretical models created by other researchers, the thermal expansion tensors and thermal-lens-free orientations at different polarized directions have been evaluated by using the least square method and two-order tensor rotation approach. The thermal-lens-free orientations have been determined as follows: The directions located ±46.3° from the p axis in the p-g plane when the light is polarized in the m axis, the directions located 24.9° clockwise from the m axis in the m-g plane and 81.2° counterclockwise from the m axis in the m-g plane when the light is polarized in the p direction. When the light is polarized along the g direction, there is no thermal-lens-free direction for the crystal. The theoretical results in the previous reports are compared and some defects are also pointed out. The optical path changes have been analyzed along the directions of both 17° rotated clockwise from the m axis in the m-g plane (p-polarized) and the b axis (m-polarized) to compare with the previous experimental results. The effectiveness of our theoretical simulation has been therefore demonstrated through the comparison analyses..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1202008 (2015)
1.5 kW Near-Diffraction-Limited Narrowband All-Fiber Superfluorescent Source
Liu Guangbo, Yang Yifeng, Lei Min, Hu Man, Zheng Ye, Liu Chi, Qi Yunfeng, He Bing, Zhou Jun, Wei Yunrong, and Lou Qihong
A sub-nanometer linewidth, near-diffraction-limited superfluorescent source with a record power of 1509 W based on all- fiber master oscillator power amplifier (MOPA) configuration is established. The slope efficiency of the main amplifier is up to 85.2 % and the beam quality at maximum power stays stable around M 2= 1A sub-nanometer linewidth, near-diffraction-limited superfluorescent source with a record power of 1509 W based on all- fiber master oscillator power amplifier (MOPA) configuration is established. The slope efficiency of the main amplifier is up to 85.2 % and the beam quality at maximum power stays stable around M 2= 1.4. The back reflection power maintains a linear behavior which confirms the considerable stimulated Brillouin scattering (SBS) suppression capability of our system. The performance of this high power source is robust with respect to the environment perturbations. No self-pulsing and relaxation oscillation is observed in the whole power range..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1202009 (2015)
Materials and Thin Films
Microstructure and Properties of Heat Treatment GH4169 Alloy by Laser Deposition Repair
Bian Hongyou, Zhao Xiangpeng, Yang Guang, Qin Lanyun, Wang Wei, Wang Shijie, and Ren Yuhang
Strength and plasticity of laser deposition repair GH4169 alloy reach only the casting standard Q/5B 453- 1995. Heat treatment is an important method to improve the mechanical property. The effects of heat treatment on the microstructure and mechanical properties of laser deposition repair GH4169 alloy are investigatedStrength and plasticity of laser deposition repair GH4169 alloy reach only the casting standard Q/5B 453- 1995. Heat treatment is an important method to improve the mechanical property. The effects of heat treatment on the microstructure and mechanical properties of laser deposition repair GH4169 alloy are investigated. As compared with as-deposited (AD) samples, after the direct aged (DA) heat treatment for laser deposition repair GH4169 alloy, the interdendritic Laves phase is slightly dissolved, the tensile strength of DA samples increase obviously, equaling to the wrought standard of Q/3B548-1996 at room temperature, however, the plasticity of DA samples decreases slightly. The strength and plasticity of DA samples is not improved when prolonging aged time. The solution heat treatment results in further dissolution of Laves phase and precipitation of a large number of needle d phase around it, the tensile strength of the solution samples reach the wrought standard, the elongation after fracture increase by 21% compared with as- deposited samples. The homogenization heat treatment results in almost entirely dissolution of Laves phase, and the d phase is precipitated in the grain and grain boundary, the tensile strength of the homogenization samples is roughly equivalent to the wrought standard, the elongation after fracture surpassed the wrought standard by 27.1%. The results show that the strength and plasticity of laser deposition repair GH4169 alloy can be effectively improved by the suitable heat treatment..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1206001 (2015)
Study on the Residual Stress of SiCp/Cu Gradient Coating by Laser Deposited
Li Deying, Zhang Jian, Zhao Longzhi, and Wang Xinguo
The residual stresses of SiCp/Cu gradient coating by laser deposited are simulated using finite element software ANSYS. The finite element analysis model of the gradient coating is established. The residual stresses of SiCp/Cu gradient coating are discussed based on the gradient distribution factor and the single layerThe residual stresses of SiCp/Cu gradient coating by laser deposited are simulated using finite element software ANSYS. The finite element analysis model of the gradient coating is established. The residual stresses of SiCp/Cu gradient coating are discussed based on the gradient distribution factor and the single layer thickness. The results show that the larger residual stresses are mainly distributed on the interface edge between the gradient coating and substrate. When the layer number is 4, the gradient distribution factor is 1, and the single layer thickness is 0.6 mm, the residual stress relaxation of SiCp/Cu gradient coating is excellent. SiCp/Cu gradient coating with clear interfaces and excellent combination between the different gradient layers is prepared by laser deposited based on the optimization results. Compared with the homogeneous coating, the hardness and wear resistance are increased by 23.2% and 5.2%, respectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1206002 (2015)
Microstructure analysis on Laser Welding Joint of Steel/Magnesium Dissimilar Metal with the Addition of Sn Foil
Tan Zhe, Liu Jinshui, Zhou Dianwu, Lu Yuanzhi, Jia Xiao, and Hu Linxi
Laser welding of DP600 dual-phase steel to AZ31 deformation magnesium alloys is carried out in steelon- magnesium overlap configuration by using fiber laser as heat welding source with the addition of Sn foil. The best welding has been achieved based on the optimization of welding parameters, and microstructure, phase Laser welding of DP600 dual-phase steel to AZ31 deformation magnesium alloys is carried out in steelon- magnesium overlap configuration by using fiber laser as heat welding source with the addition of Sn foil. The best welding has been achieved based on the optimization of welding parameters, and microstructure, phase distribution, grain size, elements distribution and phase compositions of the welding joint are studied by using the horizontal microscope, scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) and electron backscatter diffraction (EBSD) probe and X-ray diffraction (XRD). The results show that joining iron to magnesium can be realized due to the formation of new phases in welding transition region, and it is suitable for laser welding steel to magnesium alloys with the addition of Sn foil. In addition, the experimental results suggest that there are no softening organization in heat affected zone of the upper dual-phase steel, some defects, such as oxides, pores, etc can be avoided in the transition region of steel/magnesium. Besides, FeSn, Fe1.3Sn and Fe3Sn phases are formed in the transition zone of steel side, while columnar Mg2Sn phase is seen in the transition region of magnesium side, which is befit for jointing steel/Mg dissimilar metals by the metal lurgical reaction among the iron, Sn and magnesium..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1206003 (2015)
Improved Upconversion Luminescence and Temperature Sensing Performance of ZrO2∶Er3+/Yb3+/Li+ Nanocrystals
Li Dongyu, Huang Zhen, Quan Jun, Xie Mubiao, Nie Zhongquan, Huang Chuanhai, and Wang Yuxiao
ZrO2∶Er3+/Yb3+/Li+ nanocrystals are synthesized by sol- gel method. Li+ ions doped in ZrO2∶Er3+/Yb3+ nanocrystals can greatly enhance the upconversion luminescence intensity of Er3 + ions. And the effect of Li+ ions on enhancement of upconversion luminescenceis is discussed. The fluorescence intensity ratio of the greeZrO2∶Er3+/Yb3+/Li+ nanocrystals are synthesized by sol- gel method. Li+ ions doped in ZrO2∶Er3+/Yb3+ nanocrystals can greatly enhance the upconversion luminescence intensity of Er3 + ions. And the effect of Li+ ions on enhancement of upconversion luminescenceis is discussed. The fluorescence intensity ratio of the green upconversion luminescence bands and that of the green upconversion luminescence peaks are studied as a function of temperature in a range of 303 K~753 K. The maximum sensitivity is approximately 0.0050 K- 1 at 440 K by adopting the fluorescence intensity ratio of green upconversion luminescence peaks at 525 and 562 nm . It suggests that ZrO2∶Er3+/Yb3+/Li+ nanocrystals is a suitable probe for optical temperature sensing by the fluorescence intensity ratio technique..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1206004 (2015)
Measurement and Metrology
An Intrinsic Parameters Self-Calibration Technique Based on Infinite Homography between Orthogonal Vanishing Points
Hong Yang, Sun Xiuxia, Cai Ming, Liu Shuguang, and Fu Qiang
Based on the geometrical property of orthogonal vanishing point and the infinite homograph relationship between corresponding vanishing points in different camera positions of the camera image plane, a camera intrinsic parameter self-calibration method is proposed. The proposed method takes in two sets of orthogonal paBased on the geometrical property of orthogonal vanishing point and the infinite homograph relationship between corresponding vanishing points in different camera positions of the camera image plane, a camera intrinsic parameter self-calibration method is proposed. The proposed method takes in two sets of orthogonal parallel lines under any two positions, and four vanishing points in two images are achieved and decision algorithm is designed to determine their corresponding situations. Using the infinite homograph relationship between corresponding vanishing points, the constraint equation of orthogonal vanishing points and camera optical center line are established to realize the solution of the camera intrinsic parameters linearly. Aiming at restrain the influence of noise to the calibration result, the indicator function based on the inverse points of rectangle imaging is proposed, using LM optimization algorithm to achieve the intrinsic parameters of the nonlinear optimization. Experimental results show that the proposed method can judge corresponding vanishing points simply and effectively, the calibration results has high precision, strong real-time performance and wide application scope. The robustness of calibration algorithm is improved through parameter optimization to reduce the image noise..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1208001 (2015)
Absolute Testing of Interferometer Wavefront Using Cat′s-Eye Test
Su Dongqi, Miao Erlong, Qu Yi, and Sui Yongxin
The retrace error is one of the most important factors for high precision testing of Fizeau interferometer. The wavefront of interferometer is the mainly factor of retrace error. So in order to measure the wavefront of interferometer, a method of testing the wavefront of interferometer is proposed, which is based on thThe retrace error is one of the most important factors for high precision testing of Fizeau interferometer. The wavefront of interferometer is the mainly factor of retrace error. So in order to measure the wavefront of interferometer, a method of testing the wavefront of interferometer is proposed, which is based on the measuring function of interferometer itself and is very easy to carry on. Just an additional reflection flat is needed. In this method at least three cat,s-eye test results are used to get shearing of the wavefront, which is used to solve the wavefront map by shift-rotation absolute testing algorithm. Experimental results show that the wavefront testing uncertainty is about [root mean square (RMS)] 15 nm without the Power term. It can be utilized to test the wavefront quality of interferometer precisely, and the retrace error farther..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1208002 (2015)
Phase Retrieval Method of Single Interference Fringe Pattern Based on Shearing Interferometry
Guo Yuan, Wu Quan, Chen Xiaotian, Mao Qi, Zhen Wei, and Yang Zhen
The phase can be retrieved by the line integral of its gradient of horizontal and vertical directions, being calculated by the sine and cosine components, which are gained by Hilbert transform twice from a single carrier frequency interference fringe pattern. However, the result is not correct using the integral methodThe phase can be retrieved by the line integral of its gradient of horizontal and vertical directions, being calculated by the sine and cosine components, which are gained by Hilbert transform twice from a single carrier frequency interference fringe pattern. However, the result is not correct using the integral method when the gradient is discontinuous caused by fast phase change. Aiming at this problem, a two-dimensional optical field in the complex domain is built. By this way the principle of shearing interferometry is introduced to the digital phase retrieval to obtain a continuous phase gradient. The triple integral method is proposed to retrieve the original phase. Experimental results represent that the proposed method can solve the problems of phase discontinuity and fast phase change. The original phase can be retrieved more accurately..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1208003 (2015)
On-Line Calibration Method of Stockpile Volume Measurement Based on Laser Sensors
Zhao Qijie, and Meng Qingxu
In order to enhance the precision of the three-dimensional (3D) measurement system based on the laser sensors, an on-line calibration process based on structure parameter is proposed in this content. In this method, the structure object with known parameters is measured by the laser scanner, with its model being establIn order to enhance the precision of the three-dimensional (3D) measurement system based on the laser sensors, an on-line calibration process based on structure parameter is proposed in this content. In this method, the structure object with known parameters is measured by the laser scanner, with its model being established within the laser scanner coordinate system and inertial measurement sensor coordinate system separately, and the linear feature on the scanned plane being extracted, then the relative position and orientation relationship is calculated with the constraint conditions of the structure parameters. The initial value calibration experiment is conducted on the 3D measurement system, then the initial values is used to conduct on-line calibration experiment, and the average relative error of measurement is below 0.9%, which means the calibration and measurement method is accurate and can adapt to different work conditions..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1208004 (2015)
Instantaneous Frequency Measurement Using Multi-Step Approach with High Resolution and Tunable Range
Li Yueqin, Pei Li, Li Jing, Wang Yiqun, and Yuan Jin
A multi-step approach for instantaneous frequency measurement (IFM) with high resolution and tunable range is proposed. A single laser source and filter-less architecture are employed too. The principle of optical polarization modulation and polarization beam splitter are combined long with a polarization modulator andA multi-step approach for instantaneous frequency measurement (IFM) with high resolution and tunable range is proposed. A single laser source and filter-less architecture are employed too. The principle of optical polarization modulation and polarization beam splitter are combined long with a polarization modulator and polarization controllers to implement the process of loading and separating the microwave signal with identical wavelength but different polarization dimensions. By controlling the dispersion parameter of single mode fiber, a wide measurement range is achieved. Taking advantage of the dispersion- induced power fading effect, a monotonically decreasing fACF can be obtained by calculating the ratio of the microwave power via the photodiodes. Besides, by adjusting polarization angle or bias voltage, this approach can be applied to multi- step frequency measurement, thus it will lead to high measurement resolution for specific frequency. A frequency measurement range of 2~17.3 GHz with a measurement resolution of ±0.15 GHz is obtained..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1208005 (2015)
Particle Sizing by Interferometric Particle Imaging with Two Lights Illumination
Lü Qieni, Chen Tingting, Lü Tong, Wang Xiang, and Zhang Yujia
An experimental system of interferometric particle imaging with opposition of two laser- sheets illumination at scattering angle q=90° is presented. The center of particle imaged can be extracted through the template matching correlation operation between the particle focused images and the particle mask image. ThAn experimental system of interferometric particle imaging with opposition of two laser- sheets illumination at scattering angle q=90° is presented. The center of particle imaged can be extracted through the template matching correlation operation between the particle focused images and the particle mask image. The focused image of each particle can then be achieved by using the center coordinate, the shape and size of the particle mask image. The spacing of the doublet image of the individual particle is evaluated by the auto-correlation method and Gaussian interpolation, and sub-pixel accuracy of the glare point separation extraction is acquired. Then particle diameter is calculated. The result is that for particle diameter (46.54 ± 0.50) μm, the relative error is 3.42% for the standard particles with diameter of 45 μm. The research results show that the experimental system and algorithm presented in this paper are feasible..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1208006 (2015)
Multiframe Laser Differential Interferometer and Shadowgraph System for Z-Pinch Experiments
Chen Guanghua, Dan Jiakun, Liu Jun, Lei Jiangbo, Huang Xianbin, and Li Jianfeng
A multi-frame interferometer and shadowgraph system based on angular-spectrum-division all-optical frame imaging technique has been developed. The system is capable of shooting 2~4 high definition shadowgraphs or interferograms in one shot with frame interval of 3~12 ns. By the 4f differential interferometer structure,A multi-frame interferometer and shadowgraph system based on angular-spectrum-division all-optical frame imaging technique has been developed. The system is capable of shooting 2~4 high definition shadowgraphs or interferograms in one shot with frame interval of 3~12 ns. By the 4f differential interferometer structure, the system is applicable for diagnostics of electron density of Z-pinch plasma with high temporal and spatial resolution of large density gradient. In the cylindrical single-shell tungsten wire array Z-pinch experiments conducted on Primary Test Stand, a sequentially timed shadowgraphs of implosion plasma give implosion velocity, compression ratio, magneto Rayleigh Taylor (MRT) instability evolution, etc. In the planar tungsten wire array experiments conducted on XP-1, the interferograms and calculated electron densities give plasma distribution and evolution in the early stage of wire array ablation..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1208007 (2015)
Study on Photo-Assisted Microwave Frequency Measurement Method with Improved Real-Time Performance
Zhang Hualin
This paper proposes a novel photo-assisted microwave frequency measurement strategy with proved real-time performance to tackle with the defect of low real-time performance in conventional segmented photonassisted microwave frequency measurement. The microwave signal to be measured passes through the upper and lower brThis paper proposes a novel photo-assisted microwave frequency measurement strategy with proved real-time performance to tackle with the defect of low real-time performance in conventional segmented photonassisted microwave frequency measurement. The microwave signal to be measured passes through the upper and lower branches of dual- parallel Mach- Zehnder modulator (DPMZM) and simultaneously modulates the two branches of laser with different wavelengths. The modulated output laser of the two branches then demodulates the signal to be measured by single-mode fiber dispersion and photoelectric converter. Different bias voltages are provided to the two branches of DPMZM so that the upper branch measurement range is large, and the lower branch measurement range is small, respectively. Therefore, the frequency of the microwave signal to be measured can be obtained by a two-step calculating process in electric domain. This method eliminates the need of adjustment and recalibration of the device and thus achieves better real- time performance. Experimental results show a measurement time of less than 70 μs with resolution of ±0.4 GHz in rang of 4.3~18.7 GHz..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1208008 (2015)
Optical Communication
Transmission Characteristics and Structure Optimization of 60° Bent Chalcogenide Photonic Crystal Waveguides
Wei Fengjuan, Zhang Wei, Han Jintao, Wang Xianwang, Wu Yuehao, Zhang Peiqing, Dai Shixun, and Nie Qiuhua
The plane wave expansion method (PWE) is adopted to calculate chalcogenide photonic crystal bandgap, and finite difference time domain (FDTD) method is used to simulate transmission characteristics for 60° bent chalcogenide photonic crystal waveguide. Two symmetric air-holes are introduced in outer edge of line deThe plane wave expansion method (PWE) is adopted to calculate chalcogenide photonic crystal bandgap, and finite difference time domain (FDTD) method is used to simulate transmission characteristics for 60° bent chalcogenide photonic crystal waveguide. Two symmetric air-holes are introduced in outer edge of line defects in the 60° bent region, in order to improve the transmission efficiency by adjusting the radii of the air-holes. The simulation result shows that transmission bandwidth is widened from the initial 60 nm to 161 nm while the radius of the air-holes is 0.54R, however, the transmission efficiency fluctuates violently. Then some more air-holes are introduced in the central line defect in bent region. It is noticed that when 3 air-holes with radius of 0.48R are added, not only the transmission efficiency is improvement, but also the transmission bandwidth is widened to 340 nm. Continuous bend of 60° waveguide structure optimization is similar to that of single one, and the result shows that the transmission efficiency in continuous bend of waveguide can be significantly improved..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1205001 (2015)
Channel Estimation Method Based on Wavelet and Improved ISFA for CO-OFDM Syetems
Liu Jianfei, Shi Huimin, Zeng Xiangye, Lu Jia, Wang Mengjun, Liu Beilei, and Wei Chunge
A joint method of coherent optical orthogonal frequency division multiplexing (CO-OFDM) channel estimation based on wavelet denoising and improved intra-symbol frequency domain average (ISFA) is proposed. This method can be divided into three steps. Firstly, channel estimation is performed by least square (LS) method; A joint method of coherent optical orthogonal frequency division multiplexing (CO-OFDM) channel estimation based on wavelet denoising and improved intra-symbol frequency domain average (ISFA) is proposed. This method can be divided into three steps. Firstly, channel estimation is performed by least square (LS) method; secondly, the wavelet denoising processing is made for the results of estimation; finally, ISFA algorithm improved by Kaiser- window function is applied to the wavelet processing results. The simulation results show that the proposed method can effectively improve the precision of channel estimation. When the optical signal-tonoise ratio (OSNR) is 17 dB, bit error rate (BER) performance of the proposed method can be improved nearly one order of magnitude than that of ISFA method..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1205002 (2015)
Experimental Study on Free Space Optical Orthogonal Frequency Division Multiplexing System
Ke Xizheng, Lei Sichen, and Li Beilei
A reasonable free space optical orthogonal frequency division multiplexing (FSO-OFDM) experimental system model is set up according to the principle of orthogonal frequency division multiplexing (OFDM). The performance of this scheme is simulated under various channel conditions. And the impact of channel noise on OFDMA reasonable free space optical orthogonal frequency division multiplexing (FSO-OFDM) experimental system model is set up according to the principle of orthogonal frequency division multiplexing (OFDM). The performance of this scheme is simulated under various channel conditions. And the impact of channel noise on OFDM modulation constellation is tested experimentally, which provides an experimental basis for FSO-OFDM. The result shows that FSO-OFDM system has better performance to restrain inter-symbol interference, and its error rate is lower than that of the single carrier modulation system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1205003 (2015)
Optoelectronics
Manipulation of Surface Emission on Nanosilicon and Electronic Localized States Influenced by Interaction between Plasmon and Photon
Wang Gang, Huang Weiqi, Dong Taige, Wu Xueke, and Qin Chaojian
The period pattern emission in the Purcell cavity from plasmonic lattice structure is observed due to interaction between plasmon and photon. It is observed in preparing nanosilicon by pulsed laser, which is similar with the Wigner crystal structure. Manipulation of emission in the Si nanostructures is studied by the pThe period pattern emission in the Purcell cavity from plasmonic lattice structure is observed due to interaction between plasmon and photon. It is observed in preparing nanosilicon by pulsed laser, which is similar with the Wigner crystal structure. Manipulation of emission in the Si nanostructures is studied by the photoluminescence spectroscopy. The surface bonding and electronic localized states are characterized by several emission bands, which peak near 560, 600 and 700 nm on samples prepared in oxygen or nitrogen environment. Silicon quantum dots (QDs) is fabricated by laser irradiation in oxygen environment. The peak-shift in Raman spectra can be observed with increasing temperature on samples, which shows the decrease of phonon energy. The peak intensity in photoluminescence (PL) decreases and the emission band becomes broader at higher temperature, meanwhile the red- shift of PL peak is observed at 77 K compared with that at 279 K, which indicates that the localized states emission plays a main role on the nanosilicon activated. The electroluminescence wavelength is measured in the telecom window on silicon film coated by ytterbium..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1217001 (2015)
Study on Main Factors Affecting Position Detection Accuracy of Four-Quadrant Detector
Zhang Hui, Chen Yunshan, Geng Tianwen, Wu Jiabin, and Chen Tao
In order to improve the spot position detection performance of four-quadrant detector (QD), the main factors affecting QD position detection accuracy in the Gaussian spot model are studied. The basic principle of QD position detection is analyzed. Then on the basis of error theory, the mathematical model of the relatioIn order to improve the spot position detection performance of four-quadrant detector (QD), the main factors affecting QD position detection accuracy in the Gaussian spot model are studied. The basic principle of QD position detection is analyzed. Then on the basis of error theory, the mathematical model of the relationship between position detection accuracy and spot radius, centroid position, signal to noise ratio (SNR) is obtained when a laser spot of Gaussian energy profile illuminates QD. The validity of mathematical model is verified by numerical simulations and experimental analysis. The trends and degree of the factors impact on the position detection accuracy are further discussed. The results show that adoption of smaller spot radius, closer to the center of photosensitive area, and higher SNR, can effectively improve the accuracy of spot detection when the detection range of QD system is fixed. When system′s SNR is 57.48 dB and spot radius is 0.6 mm, the center position detection accuracy of QD can be up to 0.514 μm..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1217002 (2015)
Remote Sensing and Sensors
Calibration Technology for Line Structured Light Sensor with Large Scale
Xie Zexiao, and Liu Jingxiao
A calibration method for line structured light sensor with large scale is proposed for the requirement of large-size three-dimensional (3D) objects measurement.The initial values of camera intrinsic parameters are calibrated by planar target and optimized by Levenberg-Marquardt (LM) method based on the distance constraA calibration method for line structured light sensor with large scale is proposed for the requirement of large-size three-dimensional (3D) objects measurement.The initial values of camera intrinsic parameters are calibrated by planar target and optimized by Levenberg-Marquardt (LM) method based on the distance constrain between two adjacent control points. When calibrating structured light parameters using Quasi-one-dimensional target,a calculation method is proposed for solving the 3D coordinates of control points, which is based on the property of vanishing point and the geometric restrain between control points and coded points. The experimental results show that the proposed approach for calibrating the sensor and solving the 3D coordinates of control points can achieve good accuracy and stability,moreover, compared with the planar target, quasi-one-dimensional target has lower processing costs, can be used for calibration with more flexibility, and is more suitable for large scale field calibration..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 42, Issue 12, 1214001 (2015)
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