Journals >Chinese Journal of Lasers
Contents
2017
Volume: 44 Issue 6
39 Article(s)
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[in Chinese]
Fine Adjusting Fiber Laser Pulse Generation System in Time-Frequency Domain
Zhou Dandan, Xu Dangpeng, Tian Xiaocheng, Zhang Rui, Zong Zhaoyu, Fan Mengqiu, Zhu Na, Xie Lianghua, and Li Hongxun
In order to suppress the nonlinear effect caused by the interaction between laser and plasmas, precision physics experiments on inertial confinement fusion require a high power laser driver with the capability of fine adjusting in time-frequency domain. Based on technologies of polarization-maintaining fiber and singleIn order to suppress the nonlinear effect caused by the interaction between laser and plasmas, precision physics experiments on inertial confinement fusion require a high power laser driver with the capability of fine adjusting in time-frequency domain. Based on technologies of polarization-maintaining fiber and single-polarization fiber, double oscillators with temperature tuning combined with two-class waveguide phase modulators are adopted to achieve the precise adjustment for laser pulse in frequency domain. Besides, the technology of two-class high speed electro-optic modulation pulse shaping is used to achieve laser pulse precision control in time domain. The sampling detection for microwave radio frequency signal is interlocked with the acoustic-optic switch to ensure the safe operation of the whole system. The continuous adjustable laser pulse in micro-joule level is experimentally obtained with bandwidth range of 0.15-0.3 nm, central wavelength range of 1052.4-1053.6 nm and wavelength tuning accuracy of 0.1 nm. The contrast ratio of shaping laser pulse is as far as 500∶1 in micro-joule level, and the modulation degree of pulse time waveform at top is lower than 10%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 606001 (2017)
Demultiplexing Technology for Mode Division Multiplexing System Based on Unconstrained Frequency-Domain Equalization
Huang Chengbin, and Hu Guijun
An unconstrained frequency-domain equalization (FDE) based on multi-input multi-output algorithm is proposed for demultiplexing of the 6×6 mode-division multiplexing (MDM) system. It is used for eliminating the effects of mode coupling and differential mode group delay (DMGD) on signal. To verify the effectivenessAn unconstrained frequency-domain equalization (FDE) based on multi-input multi-output algorithm is proposed for demultiplexing of the 6×6 mode-division multiplexing (MDM) system. It is used for eliminating the effects of mode coupling and differential mode group delay (DMGD) on signal. To verify the effectiveness of unconstrained FDE for demultiplexing, the unconstrained frequency-domain least mean square (FD-LMS) algorithm and the unconstrained frequency-domain constant-modulus algorithm (FD-CMA) are used for the MDM system. Besides, the equalization performance of the unconstrained FD-LMS algorithm and the unconstrained FD-CMA are compared with the constrained FD-LMS algorithm and the constrained FD-CMA. Simulation results show that the demultiplexing performance of the unconstrained FDE is comparable with that of the constrained FDE. However, the unconstrained FDE has great advantage over the constrained FDE in computation complexity..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 606002 (2017)
Optimized Design for Dispersion Compensation Based on Gires-Tournois Etalon
Liu Yuhong, Liu Ningliang, and Chen Jianjun
Group delay and dispersion properties of a Gires-Tournois (G-T) etalon are deduced with the transfer matrix, the principle of using G-T etalon in multi-channel dispersion compensation is analyzed, and the cascaded G-T etalons are proposed to improve the dispersion compensation capacity. A dispersion compensation deviceGroup delay and dispersion properties of a Gires-Tournois (G-T) etalon are deduced with the transfer matrix, the principle of using G-T etalon in multi-channel dispersion compensation is analyzed, and the cascaded G-T etalons are proposed to improve the dispersion compensation capacity. A dispersion compensation device based on cascaded G-T etalons with temperature control is introduced. When we control the inner temperature of each etalon, the refractive index of etalon can be adjusted, and the fitting for the target dispersion can be realized. The simulation is carried out with Matlab software. The simulation results show that the device could compensate all channel dispersion of both C and L bands with high dispersion compensation precision and small group delay ripple. In conclusion, the device can meet the dispersion compensation requirement of high speed optical communication system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 606003 (2017)
Beam Transmission and Control
Effect of Wavefront Distortion on Beam Pointing Detection in Coherent Combination of Large Aperture Beams
Mu Jie, Zhou Kainan, Wang Xiao, Zuo Yanlei, Zeng Xiaoming, Wang Xiaodong, Xie Na, Zhou Song, Li Zhilin, Zhao Dan, Zhu Qihua, and Su Jingqin
In order to study the effect of wavefront distortion on the beam pointing detection, the simulation analysis of beams is done with Monte Carlo method under the conditions of entire aperture and sub-apertures with different sizes and arrangements. The study results show that, when the root-mean-square of wavefront distoIn order to study the effect of wavefront distortion on the beam pointing detection, the simulation analysis of beams is done with Monte Carlo method under the conditions of entire aperture and sub-apertures with different sizes and arrangements. The study results show that, when the root-mean-square of wavefront distortion is less than 0.163λ, the beam pointing detection error is under 0.5 μrad. When the root-mean-square of the wavefront distortion is less than 0.234λ, the beam pointing detection error is under 1 μrad. Sub-beam areas with relatively low wavefront distortion are suitable for calculating the beam pointing of an entire aperture..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 605001 (2017)
Biomedical Photonics and Laser Medicine
A Delay Correction Algorithm for Swept Source Optical Coherence Tomography Based on Cross Correlation Operation
Lu Yu, Li Zhongliang, Nan Nan, Bu Yang, Chen Yan, Wang Xuan, and Wang Xiangzhao
A new algorithm of k-clock delay correction for swept source optical coherence tomography is proposed. The algorithm is based on cross correlation operation and can effectively correct the delay of the swept source k-clock signal. Due to the instability of the swept source and the external environment, as well as lack A new algorithm of k-clock delay correction for swept source optical coherence tomography is proposed. The algorithm is based on cross correlation operation and can effectively correct the delay of the swept source k-clock signal. Due to the instability of the swept source and the external environment, as well as lack of precision of the synchronous trigger hardware, the k-clock signal of the swept source may have an uncertain delay with the interference signal when resampling the interference signal, resulting in decreased system resolution. A standard k-clock signal is acquired by experiments, and then the delay of the k-clock signal is calculated using the cross correlation operation. According to the calculated delay, the k-clock signal is shifted left or right to correct the difference with the standard k-clock, and then the corrected k-clock signal is used to resample the interference signal at evenly wavenumber domain interval. The experimental results show that the system performance is improved. The average running time of the algorithm is 0.18 s, and the resolution of the system is improved by 18.2%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 607001 (2017)
Improving Lateral Resolution of Light Sheet Fluorescence Microscopy with SOFI Method
An Kun, Wang Jing, Liang Dong, and Liu Jun
In order to improve the speed of super-resolution optical fluctuation imaging(SOFI) method, a modified SOFI algorithm is combined with light sheet fluorescence microscopy (LSFM). Two wavelet-based filters are utilized separately in the temporal and spatial domains to eliminate the low-frequency background noise and reaIn order to improve the speed of super-resolution optical fluctuation imaging(SOFI) method, a modified SOFI algorithm is combined with light sheet fluorescence microscopy (LSFM). Two wavelet-based filters are utilized separately in the temporal and spatial domains to eliminate the low-frequency background noise and readout noise of the raw image, which successfully reduces the image amount that SOFI needs. And it is used to process 50 frames of raw images of quantum dot and zebrafish, respectively. The result shows that introducing improved SOFI algorithm can improve the lateral resolution of a LSFM two times without changing the optical structure, which can be expanded to the biological research of living samples and overcome the limitations of numerical aperture of objective lens for LSFM..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 607002 (2017)
Fluorescence Intensity and Photon Dynamic Treatment Enhancement of Au NBPs with Different Aspect Ratios to Photosensitizer
Wang Shimiao, Wang Jing, Liu Jun, and Li Ruxin
Metal-enhanced fluorescence (MEF) theory is a hot research topic in recent years. In this study, the fluorescence intensity and photon dynamic treatment (PDT) enhancement of gold nanobipyramids (Au NBPs) with different aspect ratios (3.1-6.5) to photosensitizer AlPcS is quantitively analyzed using spectral measurement,Metal-enhanced fluorescence (MEF) theory is a hot research topic in recent years. In this study, the fluorescence intensity and photon dynamic treatment (PDT) enhancement of gold nanobipyramids (Au NBPs) with different aspect ratios (3.1-6.5) to photosensitizer AlPcS is quantitively analyzed using spectral measurement, cell confocal imaging and flow cytometry method (FCM). The results of flourscence spectrum and confocal imaging show that Au NBPs with high aspect ratios can greatly enhance the fluorescence intensity of AlPcS, and the maximum enhancement factor is 6. Au NBPs with low aspect ratio can greatly reduce the fluorescence intensity of AlPcS, because its plasma resonance band is close to the fluorescence band of AlPcS. Hela cells (human epithelial cervical cancer cells) apoptosis measurements show that the join of Au NBPs, especially Au NBPs with high aspect ratios, improves drug-loading rate and singlet oxygen production of AlPcS. Then the survival rate of Hela cell is reduced and PDT effect of AlPcS is enhanced. These results provide a new avenue for the research of surface-enhancement fluorescence and expand the bioapplications of metal nanoparticles..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 607003 (2017)
Laser Devices and Laser Physics
Influence of Path Length Control Mirror on the Dynamic Stability of Ring Laser Gyro
Ma Yanghua, Yu Wendong, Quan Bingxin, Han Zonghu, and Zhang Wei
The ring resonator is the central role of ring laser gyro (RLG). Based on the ray transport matrix theory of the ring resonator, the influence of the path length control mirror (PLCM) deformation on the resonator stability is analyzed numerically by solving the self-consistent equation. Furthermore, the influence of thThe ring resonator is the central role of ring laser gyro (RLG). Based on the ray transport matrix theory of the ring resonator, the influence of the path length control mirror (PLCM) deformation on the resonator stability is analyzed numerically by solving the self-consistent equation. Furthermore, the influence of the PLCM structural parameters on its comprehensive performance is simulated with the aid of the finite element software Ansys and demonstrated in experiments. The experimental results exhibit great agreement with the simulation, showing that the resonator dynamic stability can be greatly enhanced by the PLCM structural optimization, without almost any impact on PLCM length compensating efficiency. And the optimized PLCM can meet the gyro requirements in the vibration environment of conventional airborne navigation system. This will be of great value for the optimization of the ring resonator for RLG, especially for miniature RLG..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 601001 (2017)
Output Properties of Self-Heated Alkali Laser with Mini Vapor Cell
Han Gaoce, Li Zhiyong, Tan Rongqing, Huang Wei, and Li Hui
The pump light unabsorbed by gain medium is used to heat alkali vapor cell in a self-heated alkali laser with a mini vapor cell. A theoretical model of alkali laser under semiconductor laser double-end pumping is constructed, and the influences of the length of gain medium, the temperature of vapor cell and the linewidThe pump light unabsorbed by gain medium is used to heat alkali vapor cell in a self-heated alkali laser with a mini vapor cell. A theoretical model of alkali laser under semiconductor laser double-end pumping is constructed, and the influences of the length of gain medium, the temperature of vapor cell and the linewidth of pumped source on the output laser of the self-heated alkali laser with a mini vapor cell are analyzed. The results show that, pumped by a common external cavity semiconductor laser, the W-class output laser can be achieved when the length of gain medium is 2 mm. The output power of the self-heated alkali laser can be improved with a high pump power. The research results offer the theoretical foundation for the self-heated alkali laser experiment, and expand the application of alkali laser with low power..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 601002 (2017)
Energy Coupling Properties Between Laser and Metal in Airflow
Jin Yunsheng, Zhang Li, Zhang Yongqiang, He Jia, Tan Fuli, Zhao Jianheng, and Sun Chengwei
Temperature measurement experiment of laser irradiated 30CrMnSiA steel with mach number of 0.5 airflow is performed, experimental results show that the temperature rising rate and maximum rising temperature are declined in airflow comparing with static condition. And the absorbed heat flux density and temperature histoTemperature measurement experiment of laser irradiated 30CrMnSiA steel with mach number of 0.5 airflow is performed, experimental results show that the temperature rising rate and maximum rising temperature are declined in airflow comparing with static condition. And the absorbed heat flux density and temperature history on laser irradiated surface with airflow are achieved by numerical inverse method. Comparing with the result on static condition, the absorbed and conducting heat flux with airflow is more than the one on static condition at the same temperature. It is analyzed that this result is due to accelerating oxidation reaction by airflow and influencing the reflectivity on laser irradiated surface of metal..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 601003 (2017)
Development of 808 nm Quasi-Continuous Wave Laser Diode Bar with 600 W Output Power
Wang Zhenfu, Li Te, Yang Guowen, and Song Yunfei
Design of 808 nm epitaxial layer structure is demonstrated, and a very low internal loss less than 0.5 cm-1 is achieved. The quasi-continuous wave (QCW) high peak power 808 nm laser bar is fabricated with this high efficiency wafer. The bar with a filled factor of 85%, emitter number of 60, emitting width of 140 μm, anDesign of 808 nm epitaxial layer structure is demonstrated, and a very low internal loss less than 0.5 cm-1 is achieved. The quasi-continuous wave (QCW) high peak power 808 nm laser bar is fabricated with this high efficiency wafer. The bar with a filled factor of 85%, emitter number of 60, emitting width of 140 μm, and cavity length of 2 mm is measured at QCW mode. The peak power is 613 W with a slope efficiency of 1.34 W/A (drive current of 500 A, pulse width of 200 μs, repetition frequency of 400 Hz, duty ratio of 8%). The peak wavelength is about 807.46 nm with a spectral half-width full-maximum of 2.88 nm. The lifetime test is also demonstrated at QCW 300 W (8% duty ratio), the lifetime of five bars is all above 3.63×109 shot, the current fluctuation is lower than 10% at the constant power of 300 W, which satisfies commercial application requirement..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 601004 (2017)
High Repetition Frequency Narrow Pulse Electro-Optically Q-Switched Laser for Space Applications
Liu Qi, Meng Junqing, Zu Jifeng, Jiang Jing, Chen Silu, and Chen Weibiao
A all solid-state laser with high repetition frequency and narrow pulse width for space applications is shown. The laser adopts ultra-stable double porro prism cavity, using laser diode side pumping, the rubidium titanyl phosphate (RTP) crystal as electro-optically Q-switched switch, and polarization-coupled outputtingA all solid-state laser with high repetition frequency and narrow pulse width for space applications is shown. The laser adopts ultra-stable double porro prism cavity, using laser diode side pumping, the rubidium titanyl phosphate (RTP) crystal as electro-optically Q-switched switch, and polarization-coupled outputting. The system achieves 1 kHz laser pulse repetition frequency, 1.15 W average power, 1.3 ns pulse width, the beam quality factor M2 of two directions of M2x =1.20, M2y=1.23, the output wavelength of 1064 nm. The laser has a compact structure and good performance, which can be used as the light source for the new space detection lidar in the future..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 601005 (2017)
Design of 930 nm Passive Mode-Locking Nd-Doped All-Fiber Laser
Shen Mo, Sun Ruoyu, Jin Dongchen, Liu Wei, Hong Chang, Liu Jiang, and Wang Pu
We report a compact 930 nm passive mode-locking Nd-doped all-fiber laser for the first time. The laser consists of a Nd-doped all-fiber oscillator and a Nd-doped all-fiber amplifier. The oscillator uses the linear cavity structure. The gain medium is an 8 cm highly Nd-doped silica fiber, and the pump source is a semicoWe report a compact 930 nm passive mode-locking Nd-doped all-fiber laser for the first time. The laser consists of a Nd-doped all-fiber oscillator and a Nd-doped all-fiber amplifier. The oscillator uses the linear cavity structure. The gain medium is an 8 cm highly Nd-doped silica fiber, and the pump source is a semiconductor laser with the central wavelength of 808 nm and the maximum output power of 200 mW. By using a semiconductor saturable absorber mirror as saturable absorber to realize passive mode-locking, the ultrashort pulse laser is achieved. The laser generates 8.8 ps pulse width with the average power of 1 mW and the repetition rate of 28.2 MHz. The spectrum has sharp edge with the 3 dB spectral width of 0.37 nm. To avoid the competition from 1060 nm wavelength, we make use of a 10 m W-typed Nd-doped fiber as the gain medium .As a result,the 1060 nm wavelength during the amplification is effectively suppressed. Finally, we achieve a laser output with the average power of 117 mW, the center wavelength of 930 nm, the repetition rate of 28.2 MHz, and the single pulse energy of 4.15 nJ. The pulse width is 8.8 ps and the 10 dB spectrum width is 2.98 nm..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 601006 (2017)
Investigation of Hundred-Watt All-Solid-State Continuous-Wave Single-Frequency 1064 nm Laser
Guo Yongrui, Lu Huadong, Su Jing, and Peng Kunchi
By utilizing the master oscillator power amplifier configuration which includes a continuous-wave single-frequency 1064 nm seed laser and four-stage Nd∶YVO4 amplifier, a continuous-wave single-frequency 1064 nm laser is realized experiment ally. When the pump power is 220.00 W, the highest output power reaches 103.80 WBy utilizing the master oscillator power amplifier configuration which includes a continuous-wave single-frequency 1064 nm seed laser and four-stage Nd∶YVO4 amplifier, a continuous-wave single-frequency 1064 nm laser is realized experiment ally. When the pump power is 220.00 W, the highest output power reaches 103.80 W and the total optical-optical efficiency of the amplified laser is 33.2%. When the output power of the amplified laser is 97.73 W, the long-term power stability within five hours is better than ±0.53% and the beam quality factor M2 is less than 1.38. The intensity noise reaches the quantum noise limit of 4.3 MHz..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 601007 (2017)
Design and Development Technique for Optical Frequency Comb Based on Femtosecond Fiber Lasers
Wu Haoyu, Shi Lei, Ma Ting, Ma Jindong, Lu Qiao, Sun Qing, and Mao Qinghe
A design and development technique for optical frequency comb based on femtosecond fiber laser is proposed. A dispersion-managed solution mode-locked erbium-doped fiber laser with pulse width of 55 fs and frequency of 210 MHz is designed, and the chirped pulse fiber amplification link is optimized. An octave supercontiA design and development technique for optical frequency comb based on femtosecond fiber laser is proposed. A dispersion-managed solution mode-locked erbium-doped fiber laser with pulse width of 55 fs and frequency of 210 MHz is designed, and the chirped pulse fiber amplification link is optimized. An octave supercontinuum from 1080 nm to 2320 nm is generated by a fiber with high nonlinear, which makes the signal-to-noise ratio of the detected carrier-envelope offset frequency reach 32 dB by the f-2f (f represents frequency) autodyne method. When the 4th harmonic wave of repetition rate and the carrier envelope offset frequency are locked to a commercial rubidium atomic clock, an optical frequency comb is locked with high precision. Measurement results show that the standard deviations of repetition rate and carrier envelope offset frequency are 0.65 mHz and 1.76 mHz at 1 s counter gate time, corresponding to the Allan deviations of 1.74×10-13 and 1.80×10-11 for 100 s sampling time, respectively. Such a fiber optical comb may meet applications in fields of optical frequency metrology, optical comb spectroscopy, timing and frequency transfer, microwave generation and so on..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 601008 (2017)
Optimization Design Scheme of Femtosecond Laser Induced Corona Discharge
Du Shengzhe, Zhu Zhongbin, Liu Yaoxiang, Wang Tiejun, and Li Ruxin
An optimization design scheme is proposed for the femtosecond laser induced corona discharge experiment. The differences between spherical electrode and traditional cone electrode are investigated by numerical analysis. The distribution of space electric field around femtosecond filament is demonstrated, and the threshAn optimization design scheme is proposed for the femtosecond laser induced corona discharge experiment. The differences between spherical electrode and traditional cone electrode are investigated by numerical analysis. The distribution of space electric field around femtosecond filament is demonstrated, and the thresholds of corona electric field around femtosecond laser filament tip under the two situations are compared. The experimental phenomena of corona discharge of the two electrodes induced by femtosecond laser are compared. The simulation and experiment results show that the new designed spherical electrode dramatically improves the coupling efficiency between the femtosecond laser filament and the external electric field and the efficiency of corona discharge induced by femtosecond laser..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 601009 (2017)
Laser Manufacturing
Effects of Powder-Mixing Homogeneity and W-Powder Morphology on Forming Quality in Laser Direct Forming of W-Cu Composites
Yan Shenping, Zhang Anfeng, Li Dichen, Cao Weichan, Zhang Lianzhong, Wang Tan, and Liang Shaoduan
The experiments of laser direct forming W-Cu composites are conducted. The effects of W-Cu powder-mixing homogeneity and W-powder morphology on the forming quality in the laser direct forming of W-Cu composites are studied. The microstructures of forming samples are analyzed and the relative density of forming samples The experiments of laser direct forming W-Cu composites are conducted. The effects of W-Cu powder-mixing homogeneity and W-powder morphology on the forming quality in the laser direct forming of W-Cu composites are studied. The microstructures of forming samples are analyzed and the relative density of forming samples is measured. The study results show that the pores of forming samples are mainly caused by the agglomeration of W-powder particles, and the number of pores increases with the increase of laser power which leads to the decrease of the relative density of forming samples. By using the spherical W-powder with diameter of 54-100 μm and as a result of good fluidity, the forming sample has a relative density of larger than 99%. By using the W-powder with diameter of 25-54 μm and as a result of powder-flowing-apart during the powder-delivering process, the nonuniform distributions of W and Cu and uneven surface in the forming sample occur..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 602001 (2017)
Laser Direct Writing Technique of Diffraction Optical Element on Curved-Surface Substrate
Jiang Jun, Liu Jinqiao, Xu Ying, and Yu Yanhao
Femtosecond laser direct writing (FsLDW) has been widely applied in the field of mico-nano fabrication for its advantages such as excellent three-dimensional processing ability, high spatial resolution and low additional damage. However, there are contradictions between machining efficiency, machining area and machininFemtosecond laser direct writing (FsLDW) has been widely applied in the field of mico-nano fabrication for its advantages such as excellent three-dimensional processing ability, high spatial resolution and low additional damage. However, there are contradictions between machining efficiency, machining area and machining accuracy in the conventional FsLDW. In order to realize high speed, large area and high precision in the process of laser micro-nano fabrication, we have built a new FsLDW system based on polar coordinates, which is composed of large scale horizontal linear stages and high speed rotary stage. The approaches for the alignment of axisymmetric sample′s center and the calibration of surface curvature have been investigated based on the proposed system, and a multilevel three-dimensional structure has been fabricated on a curved surface. Finally, a diffractive circle grating structure with diameter of 10 mm has been fabricated on curved surface of the lens, and the femtosecond laser fabrication of large area three-dimensional structure with high speed, large scale and high precision has been realized. The research provides strong technical support for the fabrication of high performance hybrid refractive-diffractive optical element..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 602002 (2017)
Multi-Scale Analysis Model of Thermal-Mechanical Damage Effect in High-Power Continuous-Wave Laser Irradiation of CFRP Laminates
Zhao Weina, Huang Yihui, Song Hongwei, and Huang Chenguang
A multi-scale analysis model which can reflect thermal-mechanical damage effects, such as ablation, pyrolysis and delamination within layers in the high-power continuous-wave laser irradiation of carbon fiber reinforced polymer (CFRP) laminates is built. The pyrolysis kinetic equations of fibers and matrices are deriveA multi-scale analysis model which can reflect thermal-mechanical damage effects, such as ablation, pyrolysis and delamination within layers in the high-power continuous-wave laser irradiation of carbon fiber reinforced polymer (CFRP) laminates is built. The pyrolysis kinetic equations of fibers and matrices are derived from the meso-scale analysis, and the pyrolysis kinetic parameters are obtained from the thermo-gravimetric analysis, thereafter the macroscopic thermal-physical and mechanical property parameters of CFRP laminates are obtained. Based on the cohesive model, an analysis model is built to describe the laser induced delamination behavior within layers. Meanwhile, a thermal-resistance model is also proposed and built to describe the attenuation of thermal energy due to pyrolysis and delamination within layers. By combining the thermal-mechanical property parameters obtained from the multi-scale model with the thermal-mechanical numerical model, the ablation, pyrolysis and delamination within layers of CFRP laminates irradiated by high-power continuous-wave lasers can be simulated. The numerical results show good agreement with the experimental data..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 602003 (2017)
Research on Laser Cladding Forming of Close-Packed Multivariant Twisty Thin-Wall Parts
Wang Cong, Shi Shihong, Fang Qinqin, Fu Geyan, Lu Lin, and Zhou Liang
Based on the inside-laser powder feeding technology, the forming research of close-packed multivariant twisty thin-wall parts is performed. The spatial motion trajectory and the pose of the cladding nozzle are obtained. According to the analytic relationship between the cladding layer section and the process parametersBased on the inside-laser powder feeding technology, the forming research of close-packed multivariant twisty thin-wall parts is performed. The spatial motion trajectory and the pose of the cladding nozzle are obtained. According to the analytic relationship between the cladding layer section and the process parameters as well as the single-pass experiment, the height process model is set up and the forming of binary twisty thin-wall parts is performed. The close-packed multivariant twisty thin-wall parts are accumulated by the intermittent cladding process. The testing results show that the surface of formed parts is smooth, the minimum clearance among blade units is 6.5 mm, and the thickness of blades is mainly stable around 2.7 mm. The distributions of the microstructure and microhardness are relatively homogeneous..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 602004 (2017)
Propagation and Dislocation Development Properties of Laser Shock Waves in Monocrystalline Titanium Under Cryogenic Environment
Xu Gaofeng, Zhou Jianzhong, Meng Xiankai, Huang Shu, Sun Yunhui, and Xu Yangyang
The dislocation development induced in monocrystalline titanium under cryogenic environment (77 K) is simulated by using the molecular dynamics method. The effect of the temperature on the dislocation development is analyzed by using the common-neighbor analysis (CNA) method, and the propagation properties of laser shoThe dislocation development induced in monocrystalline titanium under cryogenic environment (77 K) is simulated by using the molecular dynamics method. The effect of the temperature on the dislocation development is analyzed by using the common-neighbor analysis (CNA) method, and the propagation properties of laser shock waves along the ［0001］direction under the cryogenic and room-temperature environments are investigated systematically. The results show that the laser shock waves along the ［0001］direction exhibit an elastic-plastic two-wave structure. Under the cryogenic environment, a large number of dislocations occur within materials after the laser shock waves. The plastic deformation mainly manifests as the emission and the propagation of partial dislocations. The impact stress and the shear stress both have the linear relationship with the speed of shock waves. The speed and the pressure of laser shock waves under the cryogenic environment are both higher than those under the room-temperature environment. The speed increases by 9%-10% and the pressure increases by 8%. By means of suppressing the dynamic recovery under the cryogenic environment, laser peening can induce high density dislocations and thus dramatically strengthen the material strength, which provides a reference for the investigation of laser shock peening mechanism under the cryogenic environment..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 602005 (2017)
Abrasion Resistance Mechanism of New Co-Based Alloy by Diode Laser Cladding
Wu Guolong, Ren Fangcheng, Yao Jianhua, Mao Wei, and Li Huiwen
Stellite 3, Stellite 21 and new Co-based alloy (Co-3) coatings are prepared on the 316 stainless steel surface by laser cladding. The microstructure and phase composition of the cladding layers are analysed and the microhardness distribution and abrasion resistance mechanism are also studied. The experimental results sStellite 3, Stellite 21 and new Co-based alloy (Co-3) coatings are prepared on the 316 stainless steel surface by laser cladding. The microstructure and phase composition of the cladding layers are analysed and the microhardness distribution and abrasion resistance mechanism are also studied. The experimental results show that the microstructure of the Co-3 is homogeneous, compact, and without cracks and cavity, where the main phases consist of (Co,W)3C, Cr23C6, Cr7C3, and Co3Mo. The average microhardness of the cladding layer is about 624 HV0.2, which is more than 3 times higher than that of the substrate. The abrasion resistance performance of Co-3 is superior to that of the 316 substrate. Under the load of 0~150 N condition, when the scratching length s≤3.3 mm, the main scratch mechanism is plastic deformation; when the scratching length 3.3＜s≤6.9 mm, the main scratch mechanism is grain sliding and crack formation caused by plastic deformation; when the scratching length s＞6.9 mm, the main scratch mechanism is crack propagation and plastic removal..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 602006 (2017)
Experimental Study and Design of Dual-Wavelength Coaxial Hybrid Laser Welding System
Zhang Jian, Zhang Jinchao, Zhang Qingmao, Pan Xiaoming, Yu Yanling, Cao Yu, Feng Aixin, and Tang Xiahui
Due to the good thermal conductivity and high reflectivity, copper and its alloys are difficult to be welded by the single laser. The method of green-infrared dual-wavelength pulsed laser coaxial hybrid welding is proposed, and the welding system is developed. In this system, the pulsed green laser is with the energy oDue to the good thermal conductivity and high reflectivity, copper and its alloys are difficult to be welded by the single laser. The method of green-infrared dual-wavelength pulsed laser coaxial hybrid welding is proposed, and the welding system is developed. In this system, the pulsed green laser is with the energy of 255.4 mJ and the power stability of ±2%. The achromatic welding head ensures the coaxial hybrid precision welding of T2 red copper by a dual-wavelength laser. The microstructure and microhardness of welds are tested. The results show that the welds are smooth with no defects. The weld height of topside equals that of the base metal zone. The weld height of backside is slightly lower than that of the base metal zone. The weld widths of topside and backside are 0.5 mm and 0.4 mm, respectively. The average microhardness of welds is 134 HV, and 64.8% of that of the base metal zone. No serious softening problems occur..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 602007 (2017)
Melting Behavior of Materials in Grooves During Fiber Laser Pressure Welding of Thin-Sheet Aluminum Alloy
He Yue, Wu Qiang, Zou Jianglin, Ha Na, and Xiao Rongshi
The effects of groove angle, focal length of lens and defocusing amount on the melting behavior of the materials in the grooves are studied by utilizing the fiber laser to scan and weld aluminum alloy V-grooves. The results show that the V-groove can focus fiber laser apparently, and the better melting effect in grooveThe effects of groove angle, focal length of lens and defocusing amount on the melting behavior of the materials in the grooves are studied by utilizing the fiber laser to scan and weld aluminum alloy V-grooves. The results show that the V-groove can focus fiber laser apparently, and the better melting effect in grooves can be obtained when the focal length is 300 mm, the defocusing amount is 0~10 mm, and the incident angle is 5°. Further analysis demonstrates that, this is attributed to the low absorptivity of aluminum to fiber laser at the Brewster angle. In addition, because of the energy losing for each laser reflection, the overmuch number of reflection of fiber laser in V-grooves is inappropriate..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 602008 (2017)
Influence of Processing Conditions on Formation of Stray Grains in DD5 Single-Crystal Superalloys by Laser Melting Multi-Traced Deposition
Liu Xiaoxin, Cheng Xu, Wang Huaming, and Li Jia
The influences of the substrate as-heat-treated condition and the laser scanning speed on the nucleation position and the number of stray grains (SGs) in multi-traced deposition of DD5 single-crystal superalloys are studied. The formation mechanism of SGs under different conditions is also investigated. The results shoThe influences of the substrate as-heat-treated condition and the laser scanning speed on the nucleation position and the number of stray grains (SGs) in multi-traced deposition of DD5 single-crystal superalloys are studied. The formation mechanism of SGs under different conditions is also investigated. The results show that, when the laser scanning speed increases from 5 mm/s to 20 mm/s, the number of SGs decreases as a result of the columnar to equiaxed transition (CET) on the top of deposition traces. As for the solution-treated substrates, the number and the sizes of SGs at the bottom of the deposition traces are obviously smaller than those for the casted substrates. The overlapping among deposition traces does not create new SGs. When the solution-treated substrates are used and the laser scanning speed is 20 mm/s, an overlapping interface without SGs by multi-traced deposition can be achieved..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 602009 (2017)
Heat-Processing Technology for Laser Additive Manufacturing of 05Cr15Ni5Cu4Nb Precipitation-Hardening Stainless Steels
Liu Zhengwu, Cheng Xu, Li Jia, and Wang Huaming
The 05Cr15Ni5Cu4Nb precipitation-hardening stainless steel plate is fabricated by the laser additive manufacturing technique. The microstructure, precipitated phase and mechanical property of the as-deposited, adjusted and solid solution state microstructures after aging heat treatments are analyzed, and the technologyThe 05Cr15Ni5Cu4Nb precipitation-hardening stainless steel plate is fabricated by the laser additive manufacturing technique. The microstructure, precipitated phase and mechanical property of the as-deposited, adjusted and solid solution state microstructures after aging heat treatments are analyzed, and the technology for the heating processing is optimized. The results show that the as-deposited microstructure mainly consists of epitaxial columnar grains where there are several cellular-like dendrites and residual ferrite exists in the inter-dendritic region. The tensile strength of the as-deposited state microstructure is 1128.5 MPa. After aging heat treatments, the residual ferrite is eliminated, the NbC particles and a large number of nano-sized ε-Cu phases distribute dispersedly in the martensite lath. There are significant increase in both the microhardness and the tensile strength. Compared with that of the as-deposited state microstructure, the plasticity of the direct-aging and solid-solution-aging state microstructure is lower, but the tensile strengths are 1440 MP and 1367 MPa, respectively. The adjusted state microstructure has a favorable ratio of strength and toughness, and the elongation rate and tensile strength are 16% and 1164.5 MPa, respectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 602010 (2017)
Materials and Thin Films
New Method for Non-Destructive Quantitative Measurement of Subsurface Damage Within Glasses
Wu Xiupin, Gao Wanrong, Zhang Yunxu, and He Yong
A new method for the non-destructive quantitative measurement of subsurface damages (SSDs) within glass samples is proposed based on the spectral-domain optical coherence tomography (SDOCT) technology. The imaging principle and characteristics of the built SDOCT system are illustrated. The reconstructed two- and three-A new method for the non-destructive quantitative measurement of subsurface damages (SSDs) within glass samples is proposed based on the spectral-domain optical coherence tomography (SDOCT) technology. The imaging principle and characteristics of the built SDOCT system are illustrated. The reconstructed two- and three-dimensional images of glass SSDs are given, from which the depths, sizes and shapes of glass SSDs can be obtained quantitatively. These results have significant importance for the manufacture and the applications of optical components..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 603001 (2017)
Development of Wide-Band Low-Noise Filter for Solar Blind Detection System
Fu Xiuhua, Guo Kai, Xiong Shifu, Zhang Jing, Sun Bing, and Jiang Hongyan
In order to meet the technical requirements of the solar blind detection system, a kind of optical filter is developed, which can realize high transmittance in the ultraviolet light field (200-270 nm) and deep cutoff from near ultraviolet to near infrared (300-1200 nm). By analyzing the optical properties of the materiIn order to meet the technical requirements of the solar blind detection system, a kind of optical filter is developed, which can realize high transmittance in the ultraviolet light field (200-270 nm) and deep cutoff from near ultraviolet to near infrared (300-1200 nm). By analyzing the optical properties of the material, combining optical film theory and optimizing the film system structure, the film system combined with medium and metal is designed. The metal film is deposited by electron beam heating and evaporation. Through the experiment on the deposition rate, the control error of the film thickness is effectively reduced under the premise of ensuring the optical properties of the metal. By using the reverse inversion method and the film sensitivity analysis, the process parameters of the resonant layer are optimized, and the control error of the resonant layer is effectively reduced. The average transmittance of the filter film is 51.21% in the range of 200-270 nm, and the average transmittance in the inhibition region of 300-1200 nm is 0.90%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 603002 (2017)
Measurement and Metrology
Laser Target Localization Based on Symmetric Wavelet Denoising and Asymmetric Gauss Fitting
Sun Junling, Sun Guangmin, Ma Pengge, Dong Tao, and Yang Yi
Aiming at the problem of range error caused by signal processing algorithm of digital airborne multi-pulse laser rangefinder, a noise reduction algorithm to reduce the distortion of pulsed laser echo waveform and correction measures to improve the accuracy of laser ranging are proposed, which can be used for precise poAiming at the problem of range error caused by signal processing algorithm of digital airborne multi-pulse laser rangefinder, a noise reduction algorithm to reduce the distortion of pulsed laser echo waveform and correction measures to improve the accuracy of laser ranging are proposed, which can be used for precise positioning of pulsed laser targets. First of all, the range error introduced by the digital signal processing algorithm is analyzed by combining target detection process of digital multi-pulse laser. It is pointed out that the signal sampling rate limits the range resolution of the target location, and the nonlinear phase frequency characteristic of the low-pass filtering is the main factor that causes the distortion of the waveform and the peak offset. Then, aiming at these problems, a specific algorithm for improving the accuracy of multi-pulse laser target localization is given. The wavelet decomposition of the echo signal is implemented based on the symmetric wavelet basis, and the wavelet coefficients are processed by the improved Donoho threshold to reduce the offset of the peak position of the reconstructed target waveform. The peak point of the target echo is searched by the differential combinatorial function, and based on the asymmetric Gauss pulse model, the high sampling rate fitting is performed to correct the position of the peak point and improve the accuracy of localization. Finally, the suitable wavelet bases are selected through simulation, the improvement of signal-to-noise ratio (SNR) and the performance of peak point localization with different algorithms are compared. In the outdoor tower, the extinction ratio laser ranging experiment is carried out. The results show that the laser target localization accuracy is less than 2 m when the SNR is 1.5 and the performance of the multi-pulse laser target precise positioning algorithm is verified..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 604001 (2017)
Measurement Method of Lens Central Thickness with High Precision Based on Low Coherence Interferometry
Jin Chaoqun, Yang Baoxi, Hu Xiaobang, Zhang Fang, Ma Jian, and Huang Huijie
A lens central thickness measurement method based on low coherence interferometry technique is presented. The cavity measurement structure is designed to measure the central thickness of the material with unknown refractive index. The measurement system is an all-fiber structure including low coherence measurement and A lens central thickness measurement method based on low coherence interferometry technique is presented. The cavity measurement structure is designed to measure the central thickness of the material with unknown refractive index. The measurement system is an all-fiber structure including low coherence measurement and laser ranging. The design of common optical path of low coherence measurement structure reference arm and laser ranging structure reference arm reduces the influence of environmental disturbances and obtains a higher measurement stability. The interference signal can be located and extracted by seven-step phase shifting method. By using the balanced differential structure of low coherence measurement method, the direct current item in the interference signal is removed and the positioning accuracy of the weak signal is improved. The experimental results show that the measurement accuracy for Invar standard block from the cavity measurement structure is below 0.5 μm. The system can realize high precision measurement of lens central thickness, and satisfy measurement request of high precision optical system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 604002 (2017)
Orbit-Dynamics Model of Spacecrafts and Error Analysis of Ahead-Point
Ye Xiaowei, and Shen Feng
In order to improve the pointing precision of the laser-pointing system to moving objects, the motion characteristics of moving targets and the calculation precision of different ahead-point algorithms are studied. According to the movement rules of spacecrafts and celestial bodies, the orbit-dynamics model of the spacIn order to improve the pointing precision of the laser-pointing system to moving objects, the motion characteristics of moving targets and the calculation precision of different ahead-point algorithms are studied. According to the movement rules of spacecrafts and celestial bodies, the orbit-dynamics model of the spacecraft is built in the horizontal coordinate system based on the two-line-element (TLE) ephemeris, and the change rules of slant-range, angle, angular speed and angular acceleration are studied. According to the theoretical orbital data, the change rules of the 1st-order and the 2nd-order ahead-points of the laser-pointing system are analyzed. As for the actual non-time-continuous system, the error analysis of ahead-point with backward-difference method and central-difference method is carried out, respectively. The result shows that the angular speed, the angular acceleration and the jerk and other high-order terms of objects have all direct effects on the ahead-point, and the central-difference method is more advantageous..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 604003 (2017)
Flexible Calibration of Setting Relation of a Multi-Camera Rig for Non-Overlapping Views
Wang Gang, Shang Yang, Guan Banglei, and Yu Qifeng
In many measurement applications by using a multi-camera rig, there are some special conditions like non-overlapping views between cameras. Thus, setting relation calibration of a multi-camera rig under these conditions is very challenging. The traditional calibration method based on all station is pretty cumbersome. TIn many measurement applications by using a multi-camera rig, there are some special conditions like non-overlapping views between cameras. Thus, setting relation calibration of a multi-camera rig under these conditions is very challenging. The traditional calibration method based on all station is pretty cumbersome. The basic equation to solve the setting relation of multi-camera rig is presented on the basis of the equivalence relation between hand-eye calibration in the robotics and setting relation calibration of the multi-camera rig. The process of solution for the basic equation by using quaternions to represent rotation matrix is derived. And a novel calibration method of non-overlapping multi-camera rig based on hand-eye calibration is proposed. The experiment results show that the measurement accuracy of the proposed method is the same as that of the traditional calibration method. The proposed method greatly reduces the manual task, and it has features of easy and flexible operation and higher efficiency without the help of other measuring sensors..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 604004 (2017)
Internal Defects of Large Optics Detected by Total Internal Reflection Technique
Yang Feifei, Miao Jie, Xie Yujiang, Liu Dean, and Zhu Jianqiang
In order to detect the internal defects of the optics effectively, the scattering images of the defects are obtained after multiple total internal reflections of the laser beam in optics using total internal reflection technique. The three-dimensional position information of the defect is obtained by image processing tIn order to detect the internal defects of the optics effectively, the scattering images of the defects are obtained after multiple total internal reflections of the laser beam in optics using total internal reflection technique. The three-dimensional position information of the defect is obtained by image processing technique, such as ellipse fitting based on least squares method. The proposed method is verified experimentally, and the experimental results show that 35 scans can complete defect detection of large optics with size of 150 mm×120 mm×20 mm. The positioning accuracy of the defect depth for samples to be tested is smaller than 150 μm. It indicates that the method can detect the defects of large optics effectively. Furthermore, the error sources that influence experimental result and factors that limit the system resolution are analyzed. The results show that the system resolution can be effectively increased by increasing the lateral resolution of the imaging system or reducing the cross-section width of laser beam..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 604005 (2017)
Study on Beat Signal with High Signal-to-Noise Ratio in Terahertz Frequency Measurement
Yang Yi, Sun Qing, Deng Yuqiang, Feng Meiqi, and Zhao Kun
The measurement accuracy of terahertz frequency by using the frequency comb method depends on the locking accuracy of the repetition rate and the measurement accuracy of the beat signal. The frequency of the beat signal is measured by the frequency counter, so the signal-to-noise ratio (SNR) and the power of the beat sThe measurement accuracy of terahertz frequency by using the frequency comb method depends on the locking accuracy of the repetition rate and the measurement accuracy of the beat signal. The frequency of the beat signal is measured by the frequency counter, so the signal-to-noise ratio (SNR) and the power of the beat signal are required to be high enough. The higher the SNR, the higher the accuracy of the frequency measurement. Therefore, the detection of the beat signal and high SNR are very important in terahertz frequency measurement. The main factors of the SNR of the beat signal are studied systematically, including the generation method of the beat signal, the signal amplification, the beat frequency and the power of the measured terahertz source. Through comprehensive optimization, the beat signal with SNR better than 60 dB is achieved experimentally, which provides a good foundation for the high accuracy measurement of terahertz frequency..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 604006 (2017)
Tunable Fabry-Perot Optical Filter Based on Micro-Electro Mechanical System
Guo Zhihui, Li Yonghua, Yang Heng, and Zhong Shaolong
In order to realize the goal of wide tunable range, fast tuning, narrow bandwidth, low actuated voltage, and mass production, a novel tunable optical filter based on micro-electro mechanical system (MEMS) is presented. The Fabry-Perot (F-P) cavity is composed of a movable optical mirror with high reflectance and the faIn order to realize the goal of wide tunable range, fast tuning, narrow bandwidth, low actuated voltage, and mass production, a novel tunable optical filter based on micro-electro mechanical system (MEMS) is presented. The Fabry-Perot (F-P) cavity is composed of a movable optical mirror with high reflectance and the face of a fiber collimator. The output wavelength can be adjusted by changing the length of the F-P cavity through the electrostatic drive. The principles of wavelength tuning and electrostatic drive are analyzed. The structural parameters and comprehensive design method are discussed. The tunable filter is fabricated successfully by the bulk silicon technology and the experimental measurement is implemented. The test results show that the device can adjust between the 3 dB bandwidth and the free spectrum range by changing the original position of the fiber collimator. The filter takes the advantages of MEMS and fiber technology with compact structure, simple process and low actuated voltage. The device can be applied in many fields such as optical communications..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 604007 (2017)
Reviews
Progress of Research and Applications of Phase-Sensitive Optical Time Domain Reflectometry
Ye Qing, Pan Zhengqing, Wang Zhaoyong, Lu Bin, Wei Fang, Qu Ronghui, Cai Haiwen, Zhao Hao, and Fang Zujie
The safety of major infrastructure and key regions of a country has extremely important significance to the development of national economy, national safety, stability of society, and people′s daily life. A distributed fiber vibration sensing system based on phase-sensitive optical time domain reflectometry (Φ-OTDR) haThe safety of major infrastructure and key regions of a country has extremely important significance to the development of national economy, national safety, stability of society, and people′s daily life. A distributed fiber vibration sensing system based on phase-sensitive optical time domain reflectometry (Φ-OTDR) has unique technical superiority in intrusion detection, perimeter security, safe monitoring of infrastructure, and so on. The distributed fiber vibration sensing system based on Φ-OTDR attracts wide attention of scientists and industries in the world. We introduce the results of our researches in the field in recent ten years, including the Φ-OTDR quantitative phase demodulation technique, the mechanism of signal interference fading, the system with ultra-high frequency response band, the system with ultra-high spatial resolution, the low noise narrow linewidth single-frequency laser, and the technique for laser frequency sweeping. We also introduce the applications of Φ-OTDR system in perimeter security, railway safe monitoring, etc. A brief review of domestic and international development in Φ-OTDR is given..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 600001 (2017)
Remote Sensing and Sensors
Study on Kalman Filtering in High-precision Absolute Distance Measurement Based on Dual Femtosecond Lasers
Yu Jiahe, Shi Haosen, Song Youjian, Cao Hui, Hu Minglie, and Wang Qingyue
The absolute distance measurement system based on dual femtosecond lasers has the advantages of high measurement precision and high update rate. However, the effect of white Gaussian noises during the measurement will result in the decrease of measurement precision. The method based on Kalman filtering technique is proThe absolute distance measurement system based on dual femtosecond lasers has the advantages of high measurement precision and high update rate. However, the effect of white Gaussian noises during the measurement will result in the decrease of measurement precision. The method based on Kalman filtering technique is proposed to improve the absolute distance measurement precision based on dual femtosecond lasers. The Kalman filtering state space model is established to obtain the optimal state estimation of the distance measurement results, which can greatly reduce the measurement precision loss introduced by the stochastic process and meanwhile output the optimal estimated speed value. The experimental results show that the standard deviation of the distance measurement is reduced by nearly an order of magnitude by using the Kalman filtering technique when the target is in a statistic state. The standard deviation of the estimated speed is about 4 μm/s when the target is moving at a uniform speed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 610001 (2017)
Classification of Sea and Land Waveform Based on Multi-Channel Ocean Lidar
Huang Tiancheng, Tao Bangyi, Mao Zhihua, He Yan, Hu Shanjiang, Wang Congcong, Yu Jiayong, and Chen Peng
To solve the problem of sea and land waveform classification for domestic airborne lidar bathymetric system, support vector machine method is used to build the model for classification of sea and land waveform. This method is based on the features of multi-channel ocean lidar waveform data, and characteristic parameterTo solve the problem of sea and land waveform classification for domestic airborne lidar bathymetric system, support vector machine method is used to build the model for classification of sea and land waveform. This method is based on the features of multi-channel ocean lidar waveform data, and characteristic parameters of multi-channel waveform are extracted. The validation results indicate that overall accuracy and Kappa coefficient of the classification method are 99.03% and 0.9805, respectively. The accuracy of the sea and land waveform classification of the proposed method is good enough for the engineering application. And it is suit for the waveform classification treatment of domestic airborne lidar bathymetric system. Which can lay the foundation for correcting the velocity of light in the water medium during the depth calculation procedure, tide and wave correction..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 610002 (2017)
Inversion of Tropospheric Aerosol Extinction Coefficient Profile by Mie-Raman Scattering Lidar
Shen Ji, and Cao Nianwen
An observation experiment of atmospheric aerosol based on Mie-Raman scattering lidar in northern suburb of Nanjing is introduced. A soft and hard threshold method is used to deal with Raman scattering lidar′s echo signal with wavelet analysis, and different thresholds and different wavelet functions are selected to proAn observation experiment of atmospheric aerosol based on Mie-Raman scattering lidar in northern suburb of Nanjing is introduced. A soft and hard threshold method is used to deal with Raman scattering lidar′s echo signal with wavelet analysis, and different thresholds and different wavelet functions are selected to process the Raman scattering lidar′s echo signal. Smoothed Raman scattering lidar′s echo signal is obtained. Upper tropospheric atmospheric aerosol extinction coefficient profiles are inversed based on Raman scattering lidar principle. With the Fernald method and the Mie scattering lidar′s observation data of aerosol, the atmospheric aerosol extinction coefficient profile in low tropospheric can be obtained. There are three receiving channels in the experimental observation system, including Rayleigh, Mie and Raman scattering channels. The data observed in Mie and Raman scattering channels are mainly studied. Raman scattering lidar′s aerosol observational data on 2011-12-08 in northern suburb of Nanjing is processed by four different thresholds. Appropriate threshold is selected to denoise the experimental observed data, and we use the formula of the inversion principle and combine with the distance correction signal to inverse the observed data, and the extinction coefficient profiles of the upper tropospheric atmospheric aerosol are obtained. The aerosol extinction coefficient profiles of low troposphere atmospheric aerosol can be retrieved based on one of the aerosol extinction coefficients of upper tropospheric atmospheric aerosol. After the Mie-Raman scattering lidar joint inversion of tropospheric aerosol extinction coefficient profile, we can clearly find the distributions of aerosol characteristics. The maximum value of aerosol extinction coefficient of low tropospheric free atmosphere is generally about 0.1 km-1, and it shows that free atmospheric of low tropospheric is relatively clean. The aerosol extinction coefficient of upper tropospheric can reach 6 km-1 under the influence of the cloud, and the maximum value of aerosol extinction coefficient is about 0.1 km-1 when there is no cloud. The result shows that the upper atmosphere is relatively clean..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 44, Issue 6, 610003 (2017)
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