Journals >Chinese Journal of Lasers
Contents
2012
Volume: 39 Issue 1
43 Article(s)
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[in Chinese]
Design of an X-Ray Framing Camera with Wide Microstrip Line
Cai Houzhi, Liu Jinyuan, Peng Xiang, Li Wenfei, Ye Yanping, Wu Jianfeng, Zhang Taohua, Deng Qijun, Niu Lihong, Niu Hanben, Liu Shenye, and Yang Guohong
An X-ray framing camera with wide microstrip line is described. It is designed for the flat field grating spectrograph. The microstrip line cathode deposited on the microchannel plate (MCP) with width of 20 mm is driven by four gating electrical pulses. The camera with modular design is made up of five basic componentsAn X-ray framing camera with wide microstrip line is described. It is designed for the flat field grating spectrograph. The microstrip line cathode deposited on the microchannel plate (MCP) with width of 20 mm is driven by four gating electrical pulses. The camera with modular design is made up of five basic components: the airbox, the MCP imager, the electric control system, the CCD camera system and the embedded computer. The camera is remote controlled by the embedded computer PC104. The camera is tested and the results show that the exposure time of the camera is 71 ps, the spatial resolution is 20 lp/mm, the gain uniformity of the microstrip line photocathode transverse to the pulse propagation direction is 1.51, and the gain uniformity along the pulse propagation direction is 5.11..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 117001 (2012)
Influence of Guiding Parameters and Propagation Constants on Photorefractive Surface Waves
Tian Ning, Lu Keqing, Zhang Xianfeng, Chen Weijun, Sun Tongtong, and Yao Fengxue
In terms of the particle oscillator model and numerical techniques, the influences of guiding parameters and propagation constants on surface wave types and localized surface modes at the interface between the photorefractive crystal and the linear dielectric medium are studied. When the guiding parameter is greater thIn terms of the particle oscillator model and numerical techniques, the influences of guiding parameters and propagation constants on surface wave types and localized surface modes at the interface between the photorefractive crystal and the linear dielectric medium are studied. When the guiding parameter is greater than the propagation constant, delocalized surface waves can occur at the interface between photorefractive crystal and linear dielectric medium. When the guiding parameter is less than the propagation constant, shock surface waves and localized surface waves can occur at the interface between photorefractive crystal and linear dielectric medium. In localized surface wave systems, the wave energy in the photorefractive crystal for the positive guiding parameter is more collective than the one for the negative guiding parameter. For a given physical system of the localized surface wave, the higher the propagation constant, the faster the surface wave attenuation in the linear dielectric medium and the photorefractive crystal, and the closer the crest factor of corresponding surface mode toward the boundary..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 117002 (2012)
Research Article
Beam Spread Characteristics of Laser Fuze in the Rain
Guo Jing, Zhang He, and Wang Xiaofeng
The laser fuze working in the rain would be scattered and attenuated by the raindrops, so that the beam quality will decrease and echo power reduce, consequently affect the function of detecting system. Based on Monte-Carlo method, the transmission model of laser in the rain is founded, and beam spread characteristics The laser fuze working in the rain would be scattered and attenuated by the raindrops, so that the beam quality will decrease and echo power reduce, consequently affect the function of detecting system. Based on Monte-Carlo method, the transmission model of laser in the rain is founded, and beam spread characteristics at different simulation conditions are analyzed, and the model is validated by experiments. The simulation results indicate that the raindrop scattering induced to beam spread and power density decreasing, and along with the augment of rainfall rate, transmission distance and beam divergence, the photon scattering times increase and spot diameter extendes, the photons arriving at the receiving surface decreases and beam power attenuates. Experimental results are consistent with the simulation calculations and the largest error is not more than 4%, which greatly agree with the model..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 113001 (2012)
Analysis of Sovling Power of Telescopes for Non-Kolmogorov Turbulence
Peng Qi, Chen Hongbin, Wang Jihong, and Cao Lei
The solving power of non-Kolmogorov turbulence is calculated for analyzing resolution of telescopes in different atmosphere condition. Modulation transfer function (MTF) of long exposure and short exposure is deduced by using the structure function of no-Kolmogorov turbulence, then the solving power is generalized, andThe solving power of non-Kolmogorov turbulence is calculated for analyzing resolution of telescopes in different atmosphere condition. Modulation transfer function (MTF) of long exposure and short exposure is deduced by using the structure function of no-Kolmogorov turbulence, then the solving power is generalized, and the limiting resolution is gotten, which are functions of power-law exponent β. Finally, the normalized resolution is achieved by dividing by the 'limiting resolution'. The results show that the larger β is, the smaller resolution is, and the smaller β is, the larger resolution is. Also, D/r0 is different for the best solving power of long exposure and short exposure, if the β is different..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 113002 (2012)
Biomedical Photonics and Laser Medicine
Signal Compensation in Long-Focal-Zone Photoacoustic Imaging Systems
Xie Wenming, Zeng Zhiping, Li Li, Chen Shuqiang, Li Zhifang, and Li Hui
Signal attenuation is highly concerned in many research fields. Imaging quality and depth in photoacoustic (PA) imaging system are often limited by the attenuation of PA signal. The PA signal attenuation is induced by many factors in PA imaging system. The factors leading to the signal attenuation and its characteristiSignal attenuation is highly concerned in many research fields. Imaging quality and depth in photoacoustic (PA) imaging system are often limited by the attenuation of PA signal. The PA signal attenuation is induced by many factors in PA imaging system. The factors leading to the signal attenuation and its characteristics are discussed based on tissue optics, acoustic transport and detection in a long-focal-zone PA imaging system. Considering to recover the PA signal from optical to ultrasonic attenuation, a method to compensate the detected PA signals is presented. The proposed method is evaluated by simulant sample and employed to image a thyroid tissue in vitro. The experimental results demonstrate that the method could be used to recover the PA signal and to improve the imaging depth and quality in the PA system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 104001 (2012)
Correction of Axial Intensity Drop for Digital Tomosynthesis Reconstructed Image
Miao Hui, Zhao Huijuan, Gao Feng, and Zhou Zhongxing
As a new and developing medical imaging technique, the digital tomosynthesis imaging (DTS) can provide researchers with confidence to distinguish the overlapping lesion tissue and make exact lesion-localizing. DTS employs the filtered backprojection algorithm for its rapid reconstruction speed and high reconstruction qAs a new and developing medical imaging technique, the digital tomosynthesis imaging (DTS) can provide researchers with confidence to distinguish the overlapping lesion tissue and make exact lesion-localizing. DTS employs the filtered backprojection algorithm for its rapid reconstruction speed and high reconstruction quality and reconstructs a series of the coronal images. However, the digital tomosynthesis insufficient dataset causes the hat-like intensity drop in its filtered backprojection reconstructed images along the rotation axis. The cone angle impact on the digital tomosynthesis axial intensity drop is analyzed and a reciprocal-cosine weighted intensity correction is introduced. To validate the effect of the axial intensity drop correction method, a DTS system is designed and built up and the anthropomorphic breast phantom is reconstructed with the reciprocal-cosine weighted correction method under different cone angle respectively. The reconstruction results demonstrate that the correction method can effectively minimize the axial intensity drop in digital tomosynthesis reconstructed images..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 104002 (2012)
Laser Manufacturing
Tribological Behaviors of Laser Shock Processing AISI 8620 Steel
Zhong Junwei, Lu Jinzhong, Luo Kaiyu, Yang Chaojun, Dai Fengze, Zhong Jinshan, Wang Qinwei, Qi Han, and Zhang Lei
The effects of laser shock processing (LSP) on the wear behaviors of AISI 8620 steel are investigated. The dry-sliding wear tests of untreated and treated samples by LSP are conducted on a uni-directional ball-on-disk sliding wear tester (CETR UMT-2). Wear track of AISI 8620 steel are observed by scanning electron micrThe effects of laser shock processing (LSP) on the wear behaviors of AISI 8620 steel are investigated. The dry-sliding wear tests of untreated and treated samples by LSP are conducted on a uni-directional ball-on-disk sliding wear tester (CETR UMT-2). Wear track of AISI 8620 steel are observed by scanning electron microscope in order to investigate the wear resistant of AISI 8620 steel. Results show that LSP can induce the layer in compressive residual stress state, and the compressive residual stress will increase the resistance of fatigue wear, but it can reduce the resistance of oxidative wear and adhesion wear. As a result, LSP can double the wear resistance of AISI 8620 steel. Multiple LSP impacts can achieve better effect by comparing with a single LSP impact. The average friction coefficient decreases first and then increases with the loading force increasing during the dry sliding..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 103001 (2012)
High-Temperature Tensile Rupture Life and Fracture Procedure of Laser Direct Deposited Ti60 Alloy and TiCp/Ti60 Composites
Sun Jingchao, Zhang Yongzhong, Gong Xinyong, and Liu Mingkun
Ti60 alloy and TiCp (mass fraction of 5%)/Ti60 titanium matrix composites are fabricated by laser direct deposition process. The microstructure and tensile rupture life under 600 ℃ are investigated and compared. The results indicate that, for laser direct deposited TiCp/Ti60 composites, primary TiC appears as dendritesTi60 alloy and TiCp (mass fraction of 5%)/Ti60 titanium matrix composites are fabricated by laser direct deposition process. The microstructure and tensile rupture life under 600 ℃ are investigated and compared. The results indicate that, for laser direct deposited TiCp/Ti60 composites, primary TiC appears as dendrites and distributes at the original β grain boundary, and the eutectic TiC appears as particulate and distributes between α laths. The existence of TiC results in refinement of the matrix. Compared with the Ti60 alloy, TiCp/Ti60 composite exhibits a superior rupture life and creep resistance under 600 ℃. The creep rupture of the composite is primarily initiated by a mixture of interface debonding between TiC and the matrix and interface voiding between α-Ti and β-Ti, which is followed by the ductile failure through the matrix..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 103002 (2012)
Control of Laser Power During Titanium Alloy Thin Plate Welding
Zhang Jian, and Yang Rui
TC4 titanium alloy thin plates with the thickness of 1.5 mm are welded by Nd:YAG pulsed laser. A coaxial machine vision system that used high speed charge coupled device (CCD) is designed to acquire welded spot pictures. The welded spot pictures quality is significantly improved with the help of auxiliary illuminant. TTC4 titanium alloy thin plates with the thickness of 1.5 mm are welded by Nd:YAG pulsed laser. A coaxial machine vision system that used high speed charge coupled device (CCD) is designed to acquire welded spot pictures. The welded spot pictures quality is significantly improved with the help of auxiliary illuminant. The welded spot edges are extracted by means of cellular neural network algorithm. The information of thin plate fenestration or insufficient depth of fusion can be acquired by analysis of welded spot pictures, and it is used as an input signal for closed-loop control. Experimental results demonstrat that this method can efficiently reduce thin plate fenestration or insufficient depth of fusion improve the welding quality..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 103003 (2012)
Numerical Simulation and Experiment Contrast about Laminated Plate under Laser Irradiation
Zhu Kai, and Long Lianchun
Through the simulation of laminated plate irradiated by laser, the distribution of stress and strain is found. Firstly, temperature field is gotten through numerical simulation, and then the thermal stress and strain are obtained by inputting the temperature field to the analysis model. The result shows that stress aloThrough the simulation of laminated plate irradiated by laser, the distribution of stress and strain is found. Firstly, temperature field is gotten through numerical simulation, and then the thermal stress and strain are obtained by inputting the temperature field to the analysis model. The result shows that stress along the fiber decreases after the transition from the maximum tensile stress at the center point to the minimum compressive stress at the point about 5 mm away from the edge of the laser spot; stress perpendicular to the fiber is always compressive stress in the laser spot and the surrounding area; Mises stress reaches the maximum at the center point and decreases with the increase of the distance to the center point. Thermal strike causes the fluctuation, and the larger the laser intensity, the earlier the fluctuation happens. In order to verify the numerical model, the strain gauges are stuck around the laser spot on the front face of laminated plate under laser irradiation. The strains of the points are tested with dynamic strain instrument. The strain of simulation coincides with experiment nicely, the maximum relative error is 18.4% between the simulation and experiment results..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 103004 (2012)
Influence of Target-to-Substrate Distance on Velocity and Density Distributions of Ablated Particles during Their Propagations
Ding Xuecheng, Fu Guangsheng, Zhai Xiaolin, Liang Weihua, Chu Lizhi, Deng Zechao, Zhao Yajun, and Wang Yinglong
The influence of the target-to-substrate distance on the spatial density distribution of the particles (Si and He) and the velocity distribution of the Si particles is investigated via Monte Carlo simulation. The results indicate that the distance of the mixed regions from the target increases with the target-to-substrThe influence of the target-to-substrate distance on the spatial density distribution of the particles (Si and He) and the velocity distribution of the Si particles is investigated via Monte Carlo simulation. The results indicate that the distance of the mixed regions from the target increases with the target-to-substrate distance increasing at the same time, and the time of reaching the maximum distance from the target increases with the target-to-substrate distance increasing. The peak positions and intensities of the curves of velocity distributions periodically oscillate and increase with the target-to-substrate distance increasing..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 103005 (2012)
Effect of Laser Shock Processing Parameters on Residual Principal Stresses and Its Directions of 2024 Aluminum Alloy
Nie Guifeng, Feng Aixin, Ren Xudong, Cao Yupeng, Zhou Pengcheng, and Li Bin
In order to study the effect of laser power density on principal stresses and their directions by laser shock processing (LSP). 2024 aluminum alloy samples are processed with five different laser power densities. Residual stresses of three directions are measured by X-ray diffraction (XRD), and the principal stresses aIn order to study the effect of laser power density on principal stresses and their directions by laser shock processing (LSP). 2024 aluminum alloy samples are processed with five different laser power densities. Residual stresses of three directions are measured by X-ray diffraction (XRD), and the principal stresses and their directions are calculated. Experimental results show that effect of laser power density on the amplitude of principal stresses and the spread of its direction, stress intensity and maximum shear stress by LSP. The variance of maximum principal stress and its direction of 2024 aluminum alloy are 1987 and 13905 respectively, with the laser power density of 2.8 GW/cm2. Residual stress is of uniform distribution, and the angles of principal stress directions are scattered. But the average of maximum principal stress of 2024 aluminum alloy is -158 MPa. The average of maximum principal stress of 2024 aluminum alloy is -239 MPa with the laser power density of 2.1 GW/cm2. The variance of maximum principal stress and its directions of 2024 aluminum alloy is 5471. Residual stress is less uniformity..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 103006 (2012)
Heat-Treated Microstructures and Mechanical Properties of TA15 Titanium Alloy Fabricated by Laser Rapid Forming
Xi Mingzhe, and Gao Shiyou
A thick-wall part of TA15 (Ti-6Al-2Zr-1Mo-1V) titanium alloy is prepared by laser rapid forming (LRF). The influence of annealing temperature on the microstructures and the tensile properties at room temperature of laser rapid formed TA15 titanium alloy is also investigated. Results show that the volume fraction of priA thick-wall part of TA15 (Ti-6Al-2Zr-1Mo-1V) titanium alloy is prepared by laser rapid forming (LRF). The influence of annealing temperature on the microstructures and the tensile properties at room temperature of laser rapid formed TA15 titanium alloy is also investigated. Results show that the volume fraction of primary α lath inside coarse β grain decreases and that of the transformed β increases, and the pattern of the transformed β changes from lath (β)→layered tablets (α+β)→finer layered tablets (α+β) with the annealing temperature increasing. Results also show that after the heat treatment of 940 ℃/1 h, air cooling, the tensile properties of the formed TA15 alloy are optimal; when the annealing temperature is no less than 970 ℃, the tensile properties of the formed TA15 alloy decrease greatly, and the fractographs show that the tensile failures are brittle fracture..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 103007 (2012)
Effects of Incident Angle on Welding Performance of Fiber Laser Butt Welding of High-Strength Automobile Steel
Chen Genyu, Kang Bin, Zhang Yi, Li Shichun, and Tan Lipeng
The effects of incident angle on welding performance of fiber laser butt welding of high-strength automobile steel are researched. The ideal parameters obtained by the previous test is used. The 4 kW fiber laser is used to weld the dual-phase high-strength steel B340/590DP with the thickness of 1.6 mm at different inciThe effects of incident angle on welding performance of fiber laser butt welding of high-strength automobile steel are researched. The ideal parameters obtained by the previous test is used. The 4 kW fiber laser is used to weld the dual-phase high-strength steel B340/590DP with the thickness of 1.6 mm at different incident angles with a butt joint. Then the effects of incident angle on the weld topography, cross section topography, tension and shearing property and micro-structure are analyzed. The results show that good weld topography, fine micro-structure and greater tension and shearing property can be obtained when the laser beam incident angle is less than 40°. When the incident angle is more than 40°, the single-sided weld is obtained on the back of the bead..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 103008 (2012)
Study on Welding Process and Microstructure of Laser Welding High Volume Fraction SiCp/2024Al Matrix Composite with Ti-6Al-4V Filler
Tao Wang, Li Liqun, Wang Yasong, and Wang Yang
The fusion weldability of high volume fraction (45% of SiC) SiCp/2024Al matrix composite is considerably difficult due to the loss of SiC and formation of Al4C3. The Al4C3 will seriously reduce the mechanical properties of the weld. The weldability of SiCp/2024Al matrix composite with 45% volume fraction of SiC is inveThe fusion weldability of high volume fraction (45% of SiC) SiCp/2024Al matrix composite is considerably difficult due to the loss of SiC and formation of Al4C3. The Al4C3 will seriously reduce the mechanical properties of the weld. The weldability of SiCp/2024Al matrix composite with 45% volume fraction of SiC is investigated by using a thin Ti-6Al-4V foil as the intermediate material. The results clearly show that the Ti content prevents the formation of Al4C3 during laser welding. The weld appearance is excellent. A weld joint reinforced with Ti5Si3 and TiC is produced. The maximum tensile strength is 258 MPa, which is 50% of the base metal..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 103009 (2012)
Fiber Laser Welding Characteristics of Laser Melting Deposited TC17 Alloy
Li Xu, Liu Dong, Tang Haibo, Zhang Shuquan, and Wang Huaming
Laser melting deposited TC17 alloy and forged TC17 alloy are welded by fiber laser. The microstructure, phase constitution and mechanical properties of the weld joint are studied by optical microscopy, scanning electron microscopy, X-ray diffraction and microhardness tests. Results indicate that the fusion zone (FZ) maLaser melting deposited TC17 alloy and forged TC17 alloy are welded by fiber laser. The microstructure, phase constitution and mechanical properties of the weld joint are studied by optical microscopy, scanning electron microscopy, X-ray diffraction and microhardness tests. Results indicate that the fusion zone (FZ) mainly consists of fine dendrite which nucleated and epitaxially grows from the substrates. The heat input makes the β grain of forged TC17 grow more seriously than that of laser melting deposited TC17. The heat affected zone (HAZ) of laser melting deposited TC17 is much narrower than that of forged TC17. Laser melting deposited TC17 exhibits better thermal stability than forged TC17. The microhardness of FZ is higher than that of the base metal, and the microhardness of HAZ is lower than that of the base metal..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 103010 (2012)
Laser Physics
Mid-Infrared, Singly Resonant and Continuous-Wave Optical Parametric Oscillator Pumped by a Single-Frequency Fiber Laser
Liu Lei, Li Xiao, Xiao Hu, Xu Xiaojun, and Jiang Zongfu
A continuous-wave (cw) singly resonant optical parametric oscillator (OPO) with the wavelength of 3.81 μm is obtained by pumping the periodically poled MgOLiNbO3 (PPMgLN) crystal with a homemade Yb single-mode fiber laser at 1064 nm. The laser uses the all optical master oscillator power amplifier (MOPA) structure. TheA continuous-wave (cw) singly resonant optical parametric oscillator (OPO) with the wavelength of 3.81 μm is obtained by pumping the periodically poled MgOLiNbO3 (PPMgLN) crystal with a homemade Yb single-mode fiber laser at 1064 nm. The laser uses the all optical master oscillator power amplifier (MOPA) structure. The cw singly resonant OPO used the e→e+e phase matching in crystal. The PPMgLN is 50 mm long and the period is from 28.5 μm to 31.5 μm. The cavity is formed of two mirror linear strusture. Pumped by the 49 W linear polarized ligth field at 30 ℃, the idler light 3.81 μm is obtained. It′s maximan power can reach 4.25 W. The threshold value of the pumping laser power is 5 W, corresponding to the output efficiency of 31.1%. When the temperature of the PPMgLN is changed from 21 ℃ to 170 ℃, the wavelength of the output laser changes from 3.65 μm to 3.82 μm. And the corresponding spectrum of OPO is measured. The experiment results are different from the theoretical results when the temperature of the PPMgLN exceeds 110 ℃..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 102001 (2012)
Self-Phase-Locking Action in a Phosphate Twin-Core Fiber and Its Fabrication
Zhang Guang, Li Kefeng, Hu Lili, and Chen Danping
Nd-doped phosphate glass twin-core fiber (TCF) is prepared by stack-and-draw method. By combining with rod-in-tube technical, a novel design to produce TCF with a various ratio of core diameter to their separation is obtained. The TCF laser employs an 808 nm laser diode (LD) as pump source, a phosphate TCF with a lengtNd-doped phosphate glass twin-core fiber (TCF) is prepared by stack-and-draw method. By combining with rod-in-tube technical, a novel design to produce TCF with a various ratio of core diameter to their separation is obtained. The TCF laser employs an 808 nm laser diode (LD) as pump source, a phosphate TCF with a length of 6 cm and a diameter of 620 μm is gain medium, and a resonant cavity is formed by a broadband high reflector and Fresnel reflection provided by perpendicular cleaved end of the active TCF. Above laser threshold, clear and stable interference strips are observed by CCD in far field, showing that TCF laser operates in self-phase-locking. A maximal output power of 52 mW and a slope efficiency of 27.1% with respect to absorbed pump power are obtained. Characteristics of the TCF laser spectra at different output power are also investigated..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 102002 (2012)
Theoretical and Experimental Study of Chaos Generation with Single Optical Feedback in the He-Ne Laser
Zhang Yuanfang, and Yang Lingzhen
Chaos generation of the He-Ne laser, whose central wavelength is 632.8 nm, is demonstrated theoretically and experimentally based on the external optical feedback mechanism. The impact of different feedback coefficients on the dynamics of the He-Ne laser is studied under the condition of fixed pump current and of fixedChaos generation of the He-Ne laser, whose central wavelength is 632.8 nm, is demonstrated theoretically and experimentally based on the external optical feedback mechanism. The impact of different feedback coefficients on the dynamics of the He-Ne laser is studied under the condition of fixed pump current and of fixed external cavity length. The numerical and experimental results show that the He-Ne laser can enter chaos by the route of periodic state with the feedback coefficient increasing..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 102003 (2012)
Coherent Beam Combining of Two Nanosecond Fiber Pulse Lasers
Su Rongtao, Zhou Pu, Ma Yanxing, Wang Xiaolin, and Xu Xiaojun
An experiment of coherent beam combining (CBC) of pulse laser in master oscillator power amplifier (MOPA) configuration using stochastic parallel gradient descent (SPGD) algorithm is reported. An output power of 50 mW is obtained by CBC of two pulse lasers with repetition rate of 10 MHz and pulse duration of 10 ns. WheAn experiment of coherent beam combining (CBC) of pulse laser in master oscillator power amplifier (MOPA) configuration using stochastic parallel gradient descent (SPGD) algorithm is reported. An output power of 50 mW is obtained by CBC of two pulse lasers with repetition rate of 10 MHz and pulse duration of 10 ns. When the system evolves from open-loop to closed-loop, the energy encircled in the target is enhanced by a factor of 1.76, and the fringe visibility of the long exposure pattern is increased by a factor of 4.38..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 102004 (2012)
Focusing Characteristics of Partially Coherent Square Flat-Topped Electromagnetic Pulsed Beams Focused by a Phase Modulated Lens
Zhang Guowen, Tao Hua, Pu Jixiong, Lu Xingqiang, and Ma Weixin
Unified theory of coherence and polarization of stationary beams is applied to pulsed light beams research. Partially coherent square flat-topped electromagnetic pulsed beams have been constructed, and analytical expressions for cross-spectral density matrix of a class of the pulsed light beams focused by a phase modulUnified theory of coherence and polarization of stationary beams is applied to pulsed light beams research. Partially coherent square flat-topped electromagnetic pulsed beams have been constructed, and analytical expressions for cross-spectral density matrix of a class of the pulsed light beams focused by a phase modulated lens have been derived. A detailed study on effects of phase distortion radii, phase distortion depth, phase modulated position and correlation length on spectral density in focused filed is carried on. It is shown that local phase modulation will produce another spectral density peak in the focused field, and correlation parameter of source and phase modulation parameters determine the value of intensity peak, and make it shift in some cases. Especially when parameters of correlation of the source are chosen to be some values, a focal switch phenomenon will occur. Change of spatial coherent length of the source produces the spatially focal shift and pulse time correlation length also produces spectral density peak shift on frequency..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 102005 (2012)
Study on kW-Class Small Wavefront Distortion End Pumped Slab Gain Module
Hu Hao, Tang Chun, Lei Jun, Li Jianmin, Li Mi, Shi Yong, Zhao Na, Wu Yingchen, Wu Deyong, Lü Wenqiang, and Li Yi
The master oscillator power amplifier (MOPA) based on end pumped slab gain medium is one way to develope high average power laser diode pumped laser (DPL), attracts widespread attention in recent years. By using theoretical analysis and numerical simulation, the design models of slab gain module are established, and thThe master oscillator power amplifier (MOPA) based on end pumped slab gain medium is one way to develope high average power laser diode pumped laser (DPL), attracts widespread attention in recent years. By using theoretical analysis and numerical simulation, the design models of slab gain module are established, and then the small-signal gain coefficient, the output characteristics, the temperature and the thermal stress of the slab gain module are obtained. The size of module is 50 cm(length)×30 cm(width)×20 cm(height). The static wavefront distortion is 0.22 μm (excluding tilt). The uniformity of fluorescence distribution is achieved by 94%. The average output power is achieved by 1086.3 W at duty cycle of 60%, and the slope efficiency is 41.7%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 102006 (2012)
Study on Gain Stability of Main Amplifier in High Power Laser Facility
Li Ping, Liang Yue, Xu Bing, Li Hai, Geng Yuanchao, Zhao Runchang, and Su Jingqin
Output energy of high power laser facility is mostly extracted from main amplifiers. Due to the circumstance complexity and diversity in paractice, it is difficult to build a precise microcosmic model in consideration of various factors. However, the existing predicting model of gain is imprecise, and no accurate modelOutput energy of high power laser facility is mostly extracted from main amplifiers. Due to the circumstance complexity and diversity in paractice, it is difficult to build a precise microcosmic model in consideration of various factors. However, the existing predicting model of gain is imprecise, and no accurate model and corresponding experimental results are reported so far. Statistical methods are proposed to analyze the gain stability of main amplifiers in high power laser facility. The varying rules of the gain are put forward, including low frequency change, variation by the sequence number in one day and high frequency stability. Based on above-mentioned rules, the gain prediction model with weight factor is built and verified by SG-Ⅲ prototype operation data. The results show that the accuracy of gain prediction can be improved by one time in comparison with that of the old method, giving powerful directions for efficient operations in high power solid laser facility..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 102007 (2012)
Research on the Pseudo-Thermal Light Made by Liquid Crystal Spatial Light Modulation
Qin Jiexin, Liu Shichao, Huang Genghua, and Shu Rong
How to get a high-quality pseudo-thermal light source is very important to the intensity quantum imaging experiment. The reason of using pseudo-thermal light instead of true thermal light is the coherence time of true thermal light is too short to respond by the common detectors, and its intensity very low. It is a comHow to get a high-quality pseudo-thermal light source is very important to the intensity quantum imaging experiment. The reason of using pseudo-thermal light instead of true thermal light is the coherence time of true thermal light is too short to respond by the common detectors, and its intensity very low. It is a common method to use dynamic speckles produced by the laser transmitting through a rotary ground glass as a pseudo-thermal light source in order to overcome these problems. The paper proposed using a liquid crystal spatial light modulation (LC-SLM) controlling the laser beam to get a pseudo-thermal light source. It can simulate the intensity fluctuation of true thermal light extremely, and it obeys to Gauss statistical distribution property. In addition, it is a non-mechanical system. The temporal and the spatial coherence can be treated separately, so the result is repeatable. The characteristic of the dynamic speckle is also studied..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 102008 (2012)
Investigation on Security Enhancement of Chaotic Optical Communication Systems via Coupling Delay
Zhang Qiao, Pan Wei, Li Nianqiang, Jiang Ning, and Xiang Shuiying
The security issue is of vital importance in chaos-based communications. The characteristics of feedback delay and coupling delay in chaotic optical communication systems has been numerically studied, based on a chaos-based communication system composed of two mutually coupled semiconductor lasers driven by an externalThe security issue is of vital importance in chaos-based communications. The characteristics of feedback delay and coupling delay in chaotic optical communication systems has been numerically studied, based on a chaos-based communication system composed of two mutually coupled semiconductor lasers driven by an external cavity semiconductor laser. Numerical simulation of the model is established with the Runge-Kutta method. The emphasis has been devoted to the following analysis: by adjusting some controllable parameters (coupling delay and injection strength), one can reasonably change the discrepancy between the amplitudes of feedback delay and coupling delay in autocorrelation function for the mutually coupled semiconductor lasers output. For this reason, the feedback delay is effectively concealed, and thus a better chaotic carrier can be obtained. More importantly, our numerical results demonstrate that the coupling delay is able to be employed to improve the security of chaotic optical communication systems. Finally, the discussion of synchronization quality of the dedicated system, under the optimized chaotic carrier circumstance, is given..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 102009 (2012)
Study of the Ohmic Contact of GaSb-Based Semiconductor Laser
Wang Yue, Liu Guojun, Li Juncheng, An Ning, Li Zhanguo, Wang Yuxia, and Wei Zhipeng
In order to improve the power efficiency and reliability of GaSb-based semiconductor lasers, the formation mechanism of ohmic contact of GaSb-based semiconductor lasers is investigated and a new four-layer metal structure (Ni/AuGe/Mo/Au) is proposed. Au/Mo/AuGe/Ni/n-GaSb annealed at 150 ℃~450 ℃ is studied. The results In order to improve the power efficiency and reliability of GaSb-based semiconductor lasers, the formation mechanism of ohmic contact of GaSb-based semiconductor lasers is investigated and a new four-layer metal structure (Ni/AuGe/Mo/Au) is proposed. Au/Mo/AuGe/Ni/n-GaSb annealed at 150 ℃~450 ℃ is studied. The results show that the new structure has good ohmic contact characteristics with a low contact resistance, which is conducive to improve the power efficiency of the semiconductor lasers. It is revealed that the atom in-diffusion is decreased and the new metallization has a smooth surface morphology by the analysis of Auger electron spectroscopy, which contributes to improve the reliability of GaSb-based semiconductor lasers..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 102010 (2012)
Materials and Thin Films
Design and Fabrication of 3.5~4.0 μm Band-Pass Filter Working at Cryogenic Temperature
Cai Yuan, Liu Dingquan, and Luo Haihan
There is a very high requirement for the spectrum of the band-pass filter in the new generation meteorological satellite that at working temperature (92 K), the spectrum curve of the filter must be within an area restricted by an inner rim and an outer rim. Using germanium (Ge) and silicon oxide (SiO) as the higher andThere is a very high requirement for the spectrum of the band-pass filter in the new generation meteorological satellite that at working temperature (92 K), the spectrum curve of the filter must be within an area restricted by an inner rim and an outer rim. Using germanium (Ge) and silicon oxide (SiO) as the higher and the lower refractive index materials respectively, a band-pass film system with 4 resonators is designed to obtain steep slopes at pass band boundaries. The ripple in the transmission region is flattened by means of optimizing the thickness of reflecting layers in the band-pass film system. The band-pass filter that satisfies the cryogenic spectrum requirements is designed, based on the refractive index versus temperature characteristic. Using vacuum evaporation technics and photometric extrema monitoring method, the band-pass filter has been developed and it meets the requirement of the inner-outer-rim specification at 92 K. In the transmission region, its maximum transmittance is 93.2%, the average transmittance is 91%, and the amplitude of the ripple is 5.2%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 107001 (2012)
Influence of Rapid Thermal Process Conditions on Electrical and Optical Properties of VO2 Thin Film
Hou Shunbao, Hu Ming, Lü Zhijun, Liang Jiran, and Chen Tao
Vanadium dioxide (VO2) samples are deposited by reactive magnetron sputter. And then a series of rapid thermal process (RTP) conditions: 500 ℃/10 s、500 ℃/15 s and 500 ℃/20 s are employed to treat the samples. In the temperature cycle 20 ℃~80 ℃, electrical and optical properties of VO2 thin film are measured by four-proVanadium dioxide (VO2) samples are deposited by reactive magnetron sputter. And then a series of rapid thermal process (RTP) conditions: 500 ℃/10 s、500 ℃/15 s and 500 ℃/20 s are employed to treat the samples. In the temperature cycle 20 ℃~80 ℃, electrical and optical properties of VO2 thin film are measured by four-probe meter and terahertz time-domain spectroscopy (THz-TDS) technology, respectively. It is observed that the electrical phase transition can reach up to more than two orders of magnitude and maximal change of the THz transmission is 57.9% before and after semiconductor-metal phase transition. Moreover, both electrical and optical phase transition amplitudes of sample treated by 500 ℃/10 s are larger than the other two samples. In fact, the transition amplitude does not change any more when the RTP time reaches about 15 s. The phase transition temperature is almost the same among the different samples. But the electrical phase transitions temperature is lower than the optical transitions temperature. Electrical transition temperature is about 56 ℃ and optical transition temperature is nearly 60 ℃..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 107002 (2012)
Measurement and Metrology
Internal Macroscopic Defects Perspective Imaging Detection System for Infrared Chalcogenide Glasses
Wu Ligang, Li Zupan, Wang Xunsi, Shen Xiang, Song Baoan, Dai Shixun, and Xu Tiefeng
Chalcogenide glasses are widely used in optical systems of thermal imagers for its high transmission and broad spectral band width. However, internal defects brought by composition’s disproportion of glasses during the melting and solidification can affect the imaging performance. A detection system of internal macroscChalcogenide glasses are widely used in optical systems of thermal imagers for its high transmission and broad spectral band width. However, internal defects brought by composition’s disproportion of glasses during the melting and solidification can affect the imaging performance. A detection system of internal macroscopic defects is introduced by using the principle of perspective imaging based on resolution estimate. The optical power of system is adjustable, which can detect the thickness and diameter of glass samples within several millimeters to dozens of millimeters. It’s resolution can reach 0.19 mm at the distance of 300 mm, and it can make a full image of an object at 63.4 mm. The distinct stripes inside the glasses are obtained by glass edge extration of internal stripe through Sobel operator..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 108001 (2012)
Calibrate Method for Scanning Direction of 3D Measurement System Based on Linear-Structure Light
Zeng Xiangjun, Huo Jincheng, and Wu Qingyang
A calibrating method for the scanning direction of 3D measurement system based on linear-structure light using a plane calibration board is proposed. In the calibration, the camera′s inner parameters are calculated with the plane calibration board first. Then the plane calibration board is placed on a position, the 3D A calibrating method for the scanning direction of 3D measurement system based on linear-structure light using a plane calibration board is proposed. In the calibration, the camera′s inner parameters are calculated with the plane calibration board first. Then the plane calibration board is placed on a position, the 3D sensor moves along the scanning direction and collects pictures at the same time. The outside parameters of the camera for every position of the 3D sensor are worked out. With these pictures and the camera coordinates of homologous points on each picture can be worked out with the inner and outside parameters. At last, linear equation is acquired by linear fitting with the camera coordinates of homologous points. The scanning direction is equal to the direction of the line. The experimental result shows that the method has high precision and it is practical in 3D measurement..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 108002 (2012)
Testing of Root Mean Square of Mid-Spatial-Frequency Wavefront for Large Flat
[in Chinese]
In high-power laser system, mid-spatial-frequency wavefront of large flat influences safety of the system and root mean square of mid-spatial-frequency wavefront (PSD1) is used to evaluate corresponding wavefront. Because large-aperture interferometer can′t fully meet the demand of the need of system transfer function In high-power laser system, mid-spatial-frequency wavefront of large flat influences safety of the system and root mean square of mid-spatial-frequency wavefront (PSD1) is used to evaluate corresponding wavefront. Because large-aperture interferometer can′t fully meet the demand of the need of system transfer function (STF) for testing mid-spatial-frequency wavefront, a statistical method based on small-aperture interferometer is proposed, and the uncertainty is analyzed. Testing system is set up, and the sub-region tilt compensating method is developed. Testing resolution is improved. Theoretical and experimental result shows that for 400 mm×400 mm analyzing region, when the number of sub-region is set to 4×4 and confidence level is 95.4%, uncertainty is ±0.266 nm. In comparing test with large-aperture interferometer, deviation between two methods in analyzing region of 400 mm×400 mm is less than 5%. Sub-region statistical analyzing method is a useful compensation for large-aperture testing method and plays a critical role for optimization of advanced optical fabrication technics..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 108003 (2012)
Measurement of in-Plane Micro-Rotations and Rotation-Center Location of a Rigid Body by Using Digital Image Correlation
Gu Guoqing, Wang Kaifu, and Xu Xing
Due to the necessity and importance of the measurement of in-plane micro-rotations of a rigid body in the field of experimental mechanics, an investigation of quantitative measurement of rotation angle and rotation-center location is developed with digital image correlation method (DICM). The relation between the rotatDue to the necessity and importance of the measurement of in-plane micro-rotations of a rigid body in the field of experimental mechanics, an investigation of quantitative measurement of rotation angle and rotation-center location is developed with digital image correlation method (DICM). The relation between the rotation angle and the in-plane displacement components is analyzed through theoretical analysis. The study of numerical simulation is carried out by specklegram produced by computer simulation. The measurement errors of both rotation angle and rotation-center location are within 2%. It shows that digital image correlation method is quite competent for the quantitative measurement of in-plane micro-rotations. The unknown in-plane rotation of a rigid body is practically measured by using digital image correlation method. The obtained rotation angle is compared with the result obtained from the geometrical optics experiment. The relative error is 3.1%. It shows that they are in good agreement. Experimental results indicate that digital image correlation method can be regarded as an efficient method to measure in-plane micro-rotations of a rigid body quantitatively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 108004 (2012)
Correction of Geometric Distortion of Wide-Angle Imaging System by Cross Ratio Invariability
Ai Saijiang, and Wang Xiang
When using the wide-angle imaging system to obtain large flat-screen scene information close and tilt, images will produce nonlinear geometric distortion consisted with perspective distortion and radial distortion. Based on imaging the grid template and the cross ratio invariability of collinear points with perspectiveWhen using the wide-angle imaging system to obtain large flat-screen scene information close and tilt, images will produce nonlinear geometric distortion consisted with perspective distortion and radial distortion. Based on imaging the grid template and the cross ratio invariability of collinear points with perspective projection, the radial distortion model parameters by nonlinear optimization is obtained, and the radial distortion is corrected. The transform matrix is built to calculate the transform coefficients by perspective transform method and correct the trapezium distortion. The non-linear geometric distortion is corrected for the images of square template with the side length as 1200 mm, the focal length of wide-angle lens as 14 mm, and the camera tilt angle as 43.34°. By the accuracy analysis of points in different locations, the relative error of identification points are less than 1%, the results show that the algorithms are suitable for the correction of nonlinear geometric distortion and have a high correct accuracy..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 108005 (2012)
Optical Communication
Dynamic Dispersion Compensation for the Polarization Coupling Measurement System of Polarization Maintaining Fiber
Zhang Hongxia, Ren Yaguang, Ye Wenting, Chen Xinwei, Jia Dagong, Liu Tiegen, and Zhang Yimo
In the polarization coupling measurement system using white light interferometry (WLI), birefringent dispersion would broaden the envelope of the interference pattern along the polarization maintaining fiber (PMF), which leads to a noticeable decline of the spatial resolution and the available measurement ranges of theIn the polarization coupling measurement system using white light interferometry (WLI), birefringent dispersion would broaden the envelope of the interference pattern along the polarization maintaining fiber (PMF), which leads to a noticeable decline of the spatial resolution and the available measurement ranges of the system. To reduce the influence of birefringent dispersion, a new method is proposed for compensating the dispersion phase in frequency domain. By multiplying the dispersed spectral phase and the compensating phase, which is extracted by dividing the width of the principal maximum, we can obtain the non-dispersed signals with inverse Fourier transform. In the experiment, 400 m and 1000 m long fiber was tested respectively, and the birefringent dispersion coefficient of the fiber was obtained as 0.0116×10-9 ps/(nm·km). The spatial resolution of the coupling point at 1000 m PMF was improved from 62.85 cm to 6.03 cm. This makes the fast and real-time compensation of any dispersion in long distance fiber be possible..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 105001 (2012)
Characteristic Measurements of Fiber Brillouin Scattering Using Fiber Bragg Grating Based Microwave-Sweeping Single Sideband Modulation
Liu Yu, Ren Liyong, Hu Manli, Liang Jian, Han Xu, and Ma Chengju
Single sideband modulation output is demonstrated by using of the fiber Bragg grating (FBG) and the Mach-Zehnder electro-optic modulator. Based on the microwave-sweeping single sideband modulation technique, a method to measure the characteristics of the fiber stimulated Brillouin scattering (SBS) is proposed. It can bSingle sideband modulation output is demonstrated by using of the fiber Bragg grating (FBG) and the Mach-Zehnder electro-optic modulator. Based on the microwave-sweeping single sideband modulation technique, a method to measure the characteristics of the fiber stimulated Brillouin scattering (SBS) is proposed. It can be used to measure the Brillouin frequency shift together with the Brillouin gain spectrum effectively. The properties of the stimulated Brillouin scattering in a 50 m photonic crystal fiber are measured, where the Brillouin frequency shift is 9.7443 GHz, the linewidth of the Brillouin gain spectrum is 22.472 MHz, and the Brillouin gain coefficient is 7.874×10-12 m/W, respectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 105002 (2012)
Theoretical Studies on Mid-Infrared Gain Characteristics of Erbium-Doped Chalcogenide Glass Fibers
Yu Xingyan, Dai Shixun, Zhou Yaxun, Wang Xunsi, Zhang Peiqing, Liu Yongxing, Xu Tiefeng, and Nie Qiuhua
The Er3+ doped (the mass fraction is 1%) Ga5Ge20Sb10S65 chalcogenide glasses are fabricated and the refractive index, absorption spectrum and emission spectra are measured. The spontaneous emission probability, absorption cross-section and emission cross-section are calculated using the theories of Judd-Ofelt and the FThe Er3+ doped (the mass fraction is 1%) Ga5Ge20Sb10S65 chalcogenide glasses are fabricated and the refractive index, absorption spectrum and emission spectra are measured. The spontaneous emission probability, absorption cross-section and emission cross-section are calculated using the theories of Judd-Ofelt and the Futchbauer-Ladenburg equation. Based on the rate equations and light propagation equations, the numerical simulations on mid-infrared gain characteristics for the Er3+ doped Ga5Ge20Sb10S65 chalcogenide glass fiber are calculated. Effects of energy transfer between Er3+ levels due to cross-relaxation, cooperative up-conversion and excited state absorption are considered in simulation. The results show that the Er3+ doped Ga5Ge20Sb10S65 chalcogenide glass fiber has a bigger signal mid-infrared gain and wider mid-infrared gain spectrum, and its maximum signal gain and gain width at 20 dB exceeds 40 dB and 200 nm, respectively. The results indicate that the Er3+ doped Ga5Ge20Sb10S65 chalcogenide glass is a better gain medium which can be applied to broadband amplifiers in mid-infrared..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 105003 (2012)
Encoding and Decoding Method of Orthogonal Space Time Block Code in Free Space Optical Communication Systems
Xu Jianwu, Wang Hongxing, Hu Hao, Sun Xiaoming, and Yang Xiao
In order to reduce the influence of turbulence and improve the performance of free space optical communication systems, a system model based on the multiple-beam transmission and reception techniques with 4 transmission antennas and 4 reception antennas and orthogonal space time block code (OSTBC) method is proposed. TIn order to reduce the influence of turbulence and improve the performance of free space optical communication systems, a system model based on the multiple-beam transmission and reception techniques with 4 transmission antennas and 4 reception antennas and orthogonal space time block code (OSTBC) method is proposed. The method′s average bit error rate performance is studied. The simulation results show that the scheme possesses superiority on diversity and could achieve the largest space diversity gains with diversity degree is 16. It also can realize full transmits speed, which is similar to the traditional Alamouti scheme. The revised decoding algorithm can be applied in multiple-beam transmission and reception systems with 1, 2 or 3 receiving antennas..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 105004 (2012)
Terahertz Technology
Optimization and Design of Composite Terahertz Achromatic Wave Plate
Zhang Pengcheng, and Ren Guobin
Based on simulated annealing algorithm, the terahertz composite achromatic quarter-wave plate is designed for two frequency bands, 0.2~2.0 THz and 0.2~3.0 THz bands. Remarkable design results (retardation deviation is 2% from 0.2 to 2.0 THz and retardation deviation is 4% from 0.2 to 3.0 THz) are got. The influence of Based on simulated annealing algorithm, the terahertz composite achromatic quarter-wave plate is designed for two frequency bands, 0.2~2.0 THz and 0.2~3.0 THz bands. Remarkable design results (retardation deviation is 2% from 0.2 to 2.0 THz and retardation deviation is 4% from 0.2 to 3.0 THz) are got. The influence of different numbers of quartz plates on the key parameters of the quarter-wave plate, such as achromatic performance, thickness and loss is analyzed. It is shown that with the increase of the number of quartz plates, the achromatic performance of the quarter-wave plate will be improved and phase delay detuning will also be reduced; however, the thickness of the quarter-wave plate is increased, leading to the increase of the loss. It is also shown that the optimized quartz plate number is five, with which good achromatic performance can be got, and the thickness and the loss are also practical for THz application..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 111001 (2012)
Theoretical Research of Terahertz Negative Dynamic Conductivity in Optically Pumped Graphene
Zhang Yuping, Zhang Xiao, Liu Lingyu, Zhang Hongyan, Gao Ying, Xu Shilin, and Zhang Huiyun
Due to the gapless energy spectrum and carriers relaxation characteristics, graphene causes a widespread concern in amplification of terahertz coherent sources. We consider the contribution of both interband and intraband transitions to the conductivity, and study the dynamic conductivity characteristics of a nonequiliDue to the gapless energy spectrum and carriers relaxation characteristics, graphene causes a widespread concern in amplification of terahertz coherent sources. We consider the contribution of both interband and intraband transitions to the conductivity, and study the dynamic conductivity characteristics of a nonequilibium two-dimensional electron-hole system in optically pumped single and multiple graphene layer (SGL and MGL) structures. The results demonstrate that the population inversion in graphene can lead to a negative dynamic conductivity in the terahertz range of frequencies at sufficiently strong pumping, and the phenomenon might be used in graphene-based terahertz coherent sources radiation and amplification. Meanwhile, by studying the dependences of the negative conductivity on momentum relaxation time, temperature, number of layers, and optical intensity, it is found that the minimum absolute value of the real part of conductivity in MGL structures is greater than that in SGL structures. Thus, the MGL structures have more advantages to be the active medium of terahertz laser..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 111002 (2012)
Optical Design and Fabrication
Investigation of Controllable Axial Conformity for Opto-Mechanical Structure
Sun Xiangyang, Zhang Guoyu, and Duan Jie
In order to sovle design difficulties about failure of opto-mechanical system features due to axial pre-loading caused by thermal deformation, a controlled design method with axial conformity for opto-mechanical structure is proposed. The relationship between the thermal deformation and axial pre-loading is got based oIn order to sovle design difficulties about failure of opto-mechanical system features due to axial pre-loading caused by thermal deformation, a controlled design method with axial conformity for opto-mechanical structure is proposed. The relationship between the thermal deformation and axial pre-loading is got based on the analysis of the thermal effect model. By comparing with the thermal analysis in the conventional axial pressure structure, a flexible element with controllable conformity between the axial pre-load and the thermal deformation is designed. The deformation analysis of the flexible elements with various model parameters showed that there is controllable conformity for the axial thermal deformation when the temperature is changed. A practice design method is given to built a model to calculate the axial thermal deformation and parameters for the flexible element. The controlled design method of axial conformity is used to design the construction of the star simulator. The measured results reveal that the method is feasible and effective..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 116001 (2012)
New Methods for Improving the Quality of Laser Beam Shaping
Yu Xiaochen, Hu Jiasheng, and Wang Lianbao
The quality of laser beam shaping is improved using binary optics element (BOE) in two ways：design algorithm and phase fitting method. In polar coordinates system, high quality flat-top beam is obtained by using profile-smoothing and Gerchberg-Saxton (GS) hybrid algorithm. In order to get annular output beam, an improvThe quality of laser beam shaping is improved using binary optics element (BOE) in two ways：design algorithm and phase fitting method. In polar coordinates system, high quality flat-top beam is obtained by using profile-smoothing and Gerchberg-Saxton (GS) hybrid algorithm. In order to get annular output beam, an improved profile-smoothing algorithm is presented. These two algorithms can maintain high energy conversion efficiency without loss in uniformity. Besides, we research how the radius of BOE, sampling number and initial radius influence the phase fitting accuracy. The machinable BOE phase is obtained in Zemax. The evaluation index shows that the phase structure meets the design requirements..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 116002 (2012)
Dispersion Compensation Based on Frequency Domain Analysis in Optical Coherence Microscopy
Dong Jingtao, and Lu Rongsheng
The dispersion compensation method based on frequency domain analysis (FDA) is proposed. The interference signal acquired from the optical coherence microscopy (OCM) is Fourier transformed to the frequency domain and the mean wavenumber corresponding to the peak frequency amplitude is obtained. A polynomial is fit to tThe dispersion compensation method based on frequency domain analysis (FDA) is proposed. The interference signal acquired from the optical coherence microscopy (OCM) is Fourier transformed to the frequency domain and the mean wavenumber corresponding to the peak frequency amplitude is obtained. A polynomial is fit to the unwrapped phase centered on the mean wavenumber in order to estimate the coefficient of the second order dispersion. In the experiment, dispersive elements with different thicknesses are inserted into the reference arm to calculate the second order dispersion coefficients corresponding to the optical path differences (OPDs) of the dispersive elements of two interference arms. A linear least squares fit demonstrates the good linearity between the second order dispersion coefficient and the relative thickness of the dispersive elements. In accordance with this linearity, a dispersive element with the appropriate thickness inserted into the reference arm will compensate the second order dispersion of the interference system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 116003 (2012)
Remote Sensing and Sensors
Analysis of IQ Demodulation and Signal Noise Ratio for 2 μm Dual-Balanced Heterodyne Detection
Pang Yajun, Gao Long, and Wang Chunhui
An IQ demodulation model for dual-balanced heterodyne detection is established, by rotating λ/4 wave plate to change the phase difference between the IQ signals. Signal-to-noise ratio (SNR) of balanced heterodyne detection is simulated with local excess intensity noise, shot noise and thermal noise. Simulation results An IQ demodulation model for dual-balanced heterodyne detection is established, by rotating λ/4 wave plate to change the phase difference between the IQ signals. Signal-to-noise ratio (SNR) of balanced heterodyne detection is simulated with local excess intensity noise, shot noise and thermal noise. Simulation results show that signal-to-noise ratio of conventional heterodyne detection is higher than that of balanced heterodyne detection, when the beam splitter coefficient adjusted by rotating λ/2 wave plate is less than 0.272 or much than 0.728. Whereas, signal-to-noise ratio of conventional heterodyne detection system is less than that of balanced detection system. Finally, 2 μm dual-balanced heterodyne detection system is proposed, in which the signal-to-noise ratio is 10 dB higher than that of conventional heterodyne system with 0.5 beam-splitter coefficient. This result verify feasibility and advantage of the balanced heterodyne detection system for detecting weak signal..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 39, Issue 1, 114001 (2012)
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