Journals >Chinese Journal of Lasers
Contents
2008
Volume: 35 Issue 7
32 Article(s)
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Research Article
Laser Diode Pumped Solid State Laser with 14 kHz Q Pulse Output
Wang Xijun, Dai Qin, Geng Xiaotao, Li Desheng, Su Shaochang, and Wang Yajun
A high speed spinning prism Q-switch driven by a brushless direct current (DC) motor (BLDC) has been designed with right-angle reflector in laser diode pumped solid state laser (DPSSL). Some laser pulse series disappear gradually and the number of the output pulses decreases gradually as decreasing the Q-switch shuttinA high speed spinning prism Q-switch driven by a brushless direct current (DC) motor (BLDC) has been designed with right-angle reflector in laser diode pumped solid state laser (DPSSL). Some laser pulse series disappear gradually and the number of the output pulses decreases gradually as decreasing the Q-switch shutting period with the increased spinning speed in the experiment, and as increasing the number of the prism to get to high pulse repetition rate, a spinning disk has been designed with 20 prisms, so at the spinning speed of 4.3×104 r/min, the minimum pulse duration is 89 ns, and the repetition rate is 14.3 kHz at the wavelength of 1064 nm. When the pumping power was 795 W, the output peak power of 78.3 kW was obtained at the repetition rate of 20 kHz, and the average output power of 100 W, electro-optic conversion of 12.5% were realized. The preliminary experimental results show that the spinning prism Q-switch as a feasible technology of kilohertz Q pulse plays an important turning-off-ability role in the high repetition rate and high-power DPSSL..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 972 (2008)
Third Harmonic Generation Experiment of Super Intense Femtosecond Laser with a Single BBO Crystal
Li Kun, Zhang Bin, Diao Xu, and Li Keyu
Third harmonic generation (THG) experiment of supper intense femtosecond laser with a single BBO crystal of 1.5 mm was carried out. The pulse width of the input fundamental field is about 100 fs, the bandwidth is about 25 nm, the energy is about 6 mJ, and the maximum intensity is 200～900 GW/cm2 after focusing by a lensThird harmonic generation (THG) experiment of supper intense femtosecond laser with a single BBO crystal of 1.5 mm was carried out. The pulse width of the input fundamental field is about 100 fs, the bandwidth is about 25 nm, the energy is about 6 mJ, and the maximum intensity is 200～900 GW/cm2 after focusing by a lens. The conversion efficiency was 0.8% with the intensity of the input fundamental field of about 300 GW/cm2. Based on the numerical techniques such as split-step Fourier transformation and fourth-order Runge-Kutta method, theoretical analysis was presented and the results show that the third harmonic field is mainly produced by the third-order nonlinear effect; the large bandwidth of the fundamental field is one of the chief reasons that limit the conversion efficiency; the nonlinear phase-mismatching and the conversion efficiency could be compensated well after optimizing the incidence angle and the azimuth angle of the fundamental field..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 976 (2008)
Sideband Polarization Instability in Fiber Ring Lasers
Lu Dan, Ge Tingwu, Xu Kun, Wu Jian, and Lin Jintong
To investigate the output stability of a high power fiber ring laser system containing a birefrigent fiber, a kind of vector modulation instability — sideband polarization instability (SPI) was proposed. Nonlinear Schrdinger equations describing the polarized light propagating in a unidirectional fiber ring laser were To investigate the output stability of a high power fiber ring laser system containing a birefrigent fiber, a kind of vector modulation instability — sideband polarization instability (SPI) was proposed. Nonlinear Schrdinger equations describing the polarized light propagating in a unidirectional fiber ring laser were deduced based on the methods of polarization instability and sideband instability. General coupling equations governing the evolution of sidebands caused by SPI in strongly birefringent fiber ring lasers were derived. Analytical solution was obtained for the case when the signal light was polarized along one principle axis of the fiber. The results show that in normal dispersion region, the sideband gain induced by perturbations to signal light propagating along the principle axis evolves in a saw-tooth manner, and approaches a fixed value with the increase of signal power..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 982 (2008)
Q-Switched Fiber Laser with a Ring Interferometer
Huang Lin, Dai Zhiyong, Liu Yongzhi, and Zhang Qianshu
The co-operation of stimulated Rayleigh scattering (SRS) in fiber interference loop and stimulated Brillouin scattering (SBS) in fiber can change Q value in resonant cavity, based on which an all-fiber Er-doped Q-switched fiber laser with interference loop is designed. In the experiments, the attributes of output laserThe co-operation of stimulated Rayleigh scattering (SRS) in fiber interference loop and stimulated Brillouin scattering (SBS) in fiber can change Q value in resonant cavity, based on which an all-fiber Er-doped Q-switched fiber laser with interference loop is designed. In the experiments, the attributes of output laser exploiting interference loops with different coupling ratios and lengths were investigated. A train of pulse laser with pulse duration of 7.2 ns, repetitive frequency of 212.4 kHz, average output power of 5.4 mW at pump power of 37 mW was obtained which had a good waveform and a peak power fluctuation of ～30%. The results show that the interference loop with very high coupling ratio has no contribution to the generation of pulse laser and the coupling ratio of ～10% is suitable for it. Even if the coupling ratio of ～10% is chosen, the length of the loop has influence on the attribute of the output laser pulse and good output can be obtained at the length around 2 m..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 987 (2008)
Synchronization of Chaotic Erbiun-Doped Fiber Lasers by Multivariable Unidirectionally Couple
Yang Lei, Pan Wei, Luo Bin, Zhang Weili, Jiang Ning, Zhou Zhi, and Yang Guobiao
Based on the theoretic modal of the erbium-doped fiber dual-ring lasers, the chaotic synchronization by using multivariable unidirectionally coupled scheme is set up. Two different fiber lasers have been investigated and the condition for realizing chaotic synchronization is given. Numerical simulation of the model is Based on the theoretic modal of the erbium-doped fiber dual-ring lasers, the chaotic synchronization by using multivariable unidirectionally coupled scheme is set up. Two different fiber lasers have been investigated and the condition for realizing chaotic synchronization is given. Numerical simulation of the model is established on Simulink and results show that one of the erbium-doped fiber dual-ring lasers as the master laser drives the another slave laser, and they can be completely synchronized even though the decay rate of the two lasers are different and the larger the feedback coefficient is, the faster two lasers achieve synchronization. The feedback coefficient have relationship with decay rate and coupling coefficient. It is also shown that the initial value of the lasers cannot affect the synchronized system, the synchronization is maintained very well. And when the effects of the Gauss noises are considered in the system, they can still reach good synchronization..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 992 (2008)
A Discharge Driven Continuous Wave Single Line DF/HF Chemical Laser for Atmospheric Absorption Measurement
Wang Hongyan, Yuan Shengfu, Li Qiang, Li Wenyu, Hua Weihong, Chen Jinbao, Hu Ming, Xu Jisheng, and Fan Chengyu
A discharge driven two-module small scale continuous wave (CW) DF/HF single line chemical laser applied to atmospheric absorption measurement was built. The structure, running manner, and the performance of the laser were described in detail. With the first order oscillating, first order output Littrow grating dispersiA discharge driven two-module small scale continuous wave (CW) DF/HF single line chemical laser applied to atmospheric absorption measurement was built. The structure, running manner, and the performance of the laser were described in detail. With the first order oscillating, first order output Littrow grating dispersion laser cavity, 17 DF lines and 11 HF lines are selected. Most of the single lines’ fundamental mode output exceeds 1 W and stabilizes in 5% scale through the 30 min running time. By altering grating to spherical cavity mirror, 20 W multi-line DF lasing and multi-line HF lasing could be realized with this device, and with an aperture inside the laser cavity to discriminate the higher order transverse modes, 6～8 W multi-line fundamental mode lasing could be obtained..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 997 (2008)
Reflective Characteristics of Target in Laser Rangefinder
Zhang Leihong, Yang Yan, Zang Huaguo, Hu Shanjiang, Chen Weibiao, and Lu Yutian
For a laser range finder to measure the smallest non-cooperative target, the reflective characteristics of the target surface are significant for echoed signal. A experimental setup to measure the bidirectional reflection distribution (BRDF) of the surface is developed. The BRDF functions of white-painting coating and For a laser range finder to measure the smallest non-cooperative target, the reflective characteristics of the target surface are significant for echoed signal. A experimental setup to measure the bidirectional reflection distribution (BRDF) of the surface is developed. The BRDF functions of white-painting coating and F36 cladding heating reflective materials at 1064 nm are obtained. The results show that the white-painting coating has small specular reflection and large scattering angle, it is better for laser range finder. While, the specular reflection of F36 material is too magnitude, and the scattering angle is only -2°～2°. The echoed signal of laser rangefinder will be great fluctuation with the incident angle. Through comparing the minimal receiving power obtained by BRDF and Lambertian diffuse reflection, the echoed signal is very small, when the incident angle is larger than 45° and 2° for white-painting coating and F36 cladding, respectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1001 (2008)
Confocal Fabry-Perot Interferometer for Frequency Stabilization of Laser
Sun Xutao, Liu Jiqiao, Zhou Jun, and Chen Weibiao
The frequency excursion of laser source of Doppler lidar should be less than 1 MHz. To satisfy this demand, a confocal Fabry-Perot (F-P) interferometer was manufactured as the frequency standard for frequency stabilization. After analyzing and contrasting the center frequency excursion of confocal Fabry-Perot interferoThe frequency excursion of laser source of Doppler lidar should be less than 1 MHz. To satisfy this demand, a confocal Fabry-Perot (F-P) interferometer was manufactured as the frequency standard for frequency stabilization. After analyzing and contrasting the center frequency excursion of confocal Fabry-Perot interferometers that are made of three different types of material with the change of temperature, the zerodur material was selected to fabricate the interferometer, and the cavity mirrors were optically contacted onto the end of spacer. The confocal Fabry-Perot interferometer was situated within a double-walled chamber, and the change of temperature in the chamber was less than 0.01 K. The experimental results indicate that the free spectral range is 370 MHz, the full-width at half maximum (FWHM) is 1.7 MHz, and the finesse is 220. Using this interferometer as frequency standard of frequency stabilization, the theoretical frequency excursion is 0.15 MHz, which satisfies the need of frequency stabilization of single mode laser of Doppler lidar..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1005 (2008)
Femtosecond Laser Pulse Compressor Based on Multi-Level Reflection Gratings
Jia Wei, Zhou Changhe, and Dai Enwen
Reflection grating pairs are usually used for femtosecond pulse compressing and stretching because of its advantage of negative dispersion. In this paper, a multi-level reflection grating based pulse compressor was presented, which is also called double-line-density gratings structure. It contains two four-step reflectReflection grating pairs are usually used for femtosecond pulse compressing and stretching because of its advantage of negative dispersion. In this paper, a multi-level reflection grating based pulse compressor was presented, which is also called double-line-density gratings structure. It contains two four-step reflection gratings with periods of 40 μm and 20 μm, respectively, and the compressor has the efficiency of more than 70%. The input femtosecond pulses will go back along the input direction after diffractions of the two gratings, and in this way, the positive group velocity dispersion (GVD) of the input pulses is compensated. Using this compressor, the input pulses 66.8 fs are compressed into Fourier-transform-limited ones with the bandwidth of 46.6 fs. So it is demonstrated that, with high efficiency, low density reflective grating pair is an alternative approach different from prism pair as a compressor for both inside and outside femtosecond laser cavities..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1009 (2008)
Application of One-Dimensional Wavelet Transformation in Time Domain Optical Coherence Tomography Imaging
Zhang Yudong, Dai Yun, Shi Guohua, and Ding Zhihua
Short time Fourier transform (STFT) is usually used to demodulate the interferometric signal and image reconstruction for time domain optical coherence tomography (OCT). STFT algorithm is simple, but cannot obtain good de-noising performance when the interferometric signal is demodulated. Therefore an additional de-noiShort time Fourier transform (STFT) is usually used to demodulate the interferometric signal and image reconstruction for time domain optical coherence tomography (OCT). STFT algorithm is simple, but cannot obtain good de-noising performance when the interferometric signal is demodulated. Therefore an additional de-noising in two-dimensional (2D) image domain is needed for reconstructed image. This method is time-consuming and incompact. In this paper, one-dimensional (1D) wavelet transformation (WT) was applied to demodulate signal and image reconstruction, furthermore, de-noise in wavelet domain could be completed at the same time. The interferometric signal was decomposed into different frequency ranges by WT and reconstructed only with these filtered coefficients whose frequency range covers the modulating frequency. After demodulating, tomographic image of sample could be reconstructed. Comparing with STFT followed by image de-noising, this method is more compact and efficient. Combining advanced de-noising technique in wavelet domain, this method has great potential in application..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1013 (2008)
Controllable Eight-Well Optical Trap and the Two-Dimensional Optical Lattices for Cold Atoms or Molecules
Lu Junfa, Ji Xianming, and Yin Jianping
We propose a novel scheme to form a controllable eight-well optical trap for cold atoms or molecules by using an optical system of a binary π-phase plate and a lens illuminated by a plane light wave. We calculate the intensity distribution of the eight-well optical trap and the characteristic parameters of the eight-weWe propose a novel scheme to form a controllable eight-well optical trap for cold atoms or molecules by using an optical system of a binary π-phase plate and a lens illuminated by a plane light wave. We calculate the intensity distribution of the eight-well optical trap and the characteristic parameters of the eight-well trap (including geometric parameters, the intensity distribution, intensity gradients, and their curvatures), and discuss the evolution process of the optical trap from eight-well to four-well or from eight-well to double-well. The result shows that the proposed eight-well trap can be continuously changed into a four-well or double-well trap by moving the π-phase plate. We discuss the controllable optical lattice of eight-well which comes from combination of binary π-phase plate illuminated by single light beam and the rectangle lens combined system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1017 (2008)
Theoretical Analysis of Polarization Dependent Loss Induced by Fiber Gratings
Ge Tingwu, Lu Dan, Xu Kun, Wu Jian, and Lin Jintong
Employing coupling mode theory, the reflection and transmission coefficients of uniform fiber Bragg gratings with the grating induced birefringence were given. Based on the coefficients, analytical expressions of polarization dependent loss in fiber gratings were then deduced according to its deterministic and nondeterEmploying coupling mode theory, the reflection and transmission coefficients of uniform fiber Bragg gratings with the grating induced birefringence were given. Based on the coefficients, analytical expressions of polarization dependent loss in fiber gratings were then deduced according to its deterministic and nondeterministic measurement principles. The given expression can precisely determine the polarization dependent loss (PDL) of the uniform fiber Bragg grating written in the isotropic or low birefringence fiber, and can also numerically simulate the approximate PDL result of Bragg uniform fiber grating written in the high birefringence fiber. The derived result agrees well with the existed experimental curve..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1024 (2008)
All-Fiber High-Pressure Gas Cell Based on Hollow-Core Photonic Crystal Fiber
Sun Qing, Liu Erming, Qin Fenghua, Mao Qinghe, and Ming Hai
The high-pressure nitrogen-filling and the leaking characteristics for hollow-core photonic crystal fiber (HC-PCF) were investigated experimentally and analyzed with the micro-pipe flow theory. The results show that, the nitrogen-filling speed for the HC-PCF is slow, and the time required for building the pressure equiThe high-pressure nitrogen-filling and the leaking characteristics for hollow-core photonic crystal fiber (HC-PCF) were investigated experimentally and analyzed with the micro-pipe flow theory. The results show that, the nitrogen-filling speed for the HC-PCF is slow, and the time required for building the pressure equilibrium in the HC-PCF may be shortened efficiently by reducing the volume of the outlet cavity. When a HC-PCF with the length of 9 m was nitrogen-filled with 3.03×106 Pa after one of its ends has been spliced to the single-mode fiber (SMF), the time required for building such a pressure equilibrium was smaller than 4 hours. The leaking speed from one end of a 3.03×106 Pa nitrogen-filled HC-PCF and its evolution with the time were measured experimentally, and the results may be used for evaluating the final pressure of the gas cell. Finally, a HC-PCF nitrogen-filled cell with a pressure of 1.73×106 Pa and an insertion loss of 9.3 dB was manufactured..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1029 (2008)
Breakup Mechanisms for Chirped Pulse in the Single-Mode Fibers
Deng Chunnian, and Wen Shuangchun
Breakup mechanisms for chirped picosecond pulse in the single-mode fibers are numerically analyzed through solving nonlinear Schrdinger equation by the standard split-step Fourier method. The results show that, the breakup of shorter chirped pulse (10 ps) is caused by pulse collapse due to the high-order soliton compreBreakup mechanisms for chirped picosecond pulse in the single-mode fibers are numerically analyzed through solving nonlinear Schrdinger equation by the standard split-step Fourier method. The results show that, the breakup of shorter chirped pulse (10 ps) is caused by pulse collapse due to the high-order soliton compression, while the breakup of longer chirped pulse (200 ps) is caused by the nonlinear amplification of noise due to the modulation instability. For chirped pulse of intermediate durations (50 ps), its breakup is caused by modulation instability instead of high-order soliton compression due to the role of noise. Initial positive and negative chirps can speed and slow down the process of shorter pulse breakup, respectively. However, the initial chirp has little influence on the breakup of longer pulses. The effect of initial chirp on pulse breakup is closely related to the breakup mechanisms for pulse..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1035 (2008)
Effect of Power Saturation on Spectrum Expanding in Normal Dispersion Region of Microstructured Fiber by Femtosecond Laser Pulses
Li Shuguang, Cheng Tonglei, Zhang Huanping, and Hou Lantian
It is demonstrated that femtosecond pulses transmit in microstructured fiber manufactured by our group. An 800 nm central wavelength of input pulses locates in the normal dispersion regime of the microstructured fiber. When the average power of initial input pulses increases from 220 mW to 300 mW, output spectrum spreaIt is demonstrated that femtosecond pulses transmit in microstructured fiber manufactured by our group. An 800 nm central wavelength of input pulses locates in the normal dispersion regime of the microstructured fiber. When the average power of initial input pulses increases from 220 mW to 300 mW, output spectrum spreads to long wavelength and short wavelength simultaneously, and the anti-Stokes emission in output spectrum holds on dominant status gradually. When the average power of input pulses increases to 280 mW, the scope of spectrum increases no longer. Output spectrum about 20 dB from 560 nm to 960 nm has been obtained by ultra-short pulses transmiting in a normal dispersion nonlinear manufactured fiber..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1041 (2008)
Biomedical Photonics and Laser Medicine
Effects of the Reflection Losses and Nonnormal Incidence of Laser on the Eye’s Visual Quality after Refractive Procedure on a Cornea
Liu Yongji, Wang Zhaoq, iLü You, and Mu Guoguang
Based on the eye model of Kooijman, the effects of the reflection losses and nonnormal incidence of laser on the human eye’s visual quality after refractive procedure on a cornea were analyzed by comparing the J. R. Jimenez’s theory and Munnerlyn’s. The reflection losses and nonormal incidence on the anterior cornea leBased on the eye model of Kooijman, the effects of the reflection losses and nonnormal incidence of laser on the human eye’s visual quality after refractive procedure on a cornea were analyzed by comparing the J. R. Jimenez’s theory and Munnerlyn’s. The reflection losses and nonormal incidence on the anterior cornea lead to the under-correction of the post-surgery eye. With the 6 mm diameter of the optical zone, when the refractive error of the eye before surgery is -9D, the under-correction is only -0.6D. The corneal asphericity after refractive surgery increases for myopia. With the increase of the refractive error before refractive surgery, the asphericity of the anterior cornea changes from negative to positive, which leads to the increase of the spherical aberration. There is no large difference between the asphericities obtained by Munnerlyn’s theory and Jimenez’s. The diameter of the optical zone has little effect on the post-surgery p-value..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1101 (2008)
Ho∶YAG Laser Interaction with Bio-Tissue and Its Remained Thermal Effect
Qiu Yang, Li Shengwen, Zhang Yi, Li Hanming, Zhu Pengfei, Dong Quanli, Ruan Yingmao, Li Yingjun, Mao Lingtao, Wang Chao, and Zhang Jie
Medical laser has been applied more and more broadly in bio-tissue cutting, but the efficacy and the side effect have never been standardized at parameters level, depending highly on the experiences of the operator, which causes disadvantage for the spread of this technology; while the choice of the technical parameterMedical laser has been applied more and more broadly in bio-tissue cutting, but the efficacy and the side effect have never been standardized at parameters level, depending highly on the experiences of the operator, which causes disadvantage for the spread of this technology; while the choice of the technical parameters of the laser form a crucial factor in the developing of the product. To seek for the optimized parameters, we studied the interaction between the tissue such as the parenchyma of the dog′s kidney and Ho∶YAG laser at different energy densities (50～400 J/cm2), in a circumstance of operation simulated via some extra corporeal animal experiments. We got the statistical results of the interaction, the optical micrograph of the slice and the record of the remained thermal effects. We analyzed the influencing factors of the interaction and the evolution of the remained thermal effects. A peak-value exists at about 290 J/cm2 on the unified curve of the efficacy, which can be used as the recommended value in standardizing. The analysis of the influencing factors and the remained thermal effects brings reference to the improving on the medical laser devices..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1105 (2008)
Effect of NO on CO2 Laser Pretreatment Inducing Drought Tolerance in Wheat Seedlings
Qiu Zongbo, Li Fangmin, Liu Xiao, and Yue Ming
The wheat seeds are irridated by CO2 laser with power of 20.1 mW/mm2 for 3 min. When the wheat seeds grow about 12 days, the seedlings are treated with the 10% polyethyleneglycol 6000 (PEG6000) stress. And the effects of NO on the CO2 laser pretreatment inducing drought tolerance are studied through sodium nitroprussidThe wheat seeds are irridated by CO2 laser with power of 20.1 mW/mm2 for 3 min. When the wheat seeds grow about 12 days, the seedlings are treated with the 10% polyethyleneglycol 6000 (PEG6000) stress. And the effects of NO on the CO2 laser pretreatment inducing drought tolerance are studied through sodium nitroprusside and hemoglobin added with NO. The results show that laser pretreatment and NO donor sodium nitroprusside (SNP) could decrease the concentration of malondialdehyde (MDA) and increase the activities of superoxide dismutase (SOD), peroxidase(POD), catalase (CAT) and the concentration of chlorophyll a, chlorophyll b and root dry weight in the wheat seedlings with drought tolerance. But the promotive effect of laser pretreatment induced drought tolerance in wheat seedlings was not effectively reversed by the addition of hemoglobin (NO scavenger)..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1111 (2008)
Influence of Different Defocus Conditions on Bone Hard Tissue Ablation with Pulsed CO2 Laser
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
This paper evaluates the influence of different defocus irradiation conditions on bone hard tissue ablation by pulsed CO2 laser. Bovine shank bones in vitro were used in this experiment which were put on a PC-controlled motorized linear drive stage and moved repeatedly through the focused beam. Work distance was adjustThis paper evaluates the influence of different defocus irradiation conditions on bone hard tissue ablation by pulsed CO2 laser. Bovine shank bones in vitro were used in this experiment which were put on a PC-controlled motorized linear drive stage and moved repeatedly through the focused beam. Work distance was adjusted to obtain a beam spot size of about 510 μm on tissue sample before and after focus plane respectively. The wavelength of pulse CO2 laser was 10.64 μm, pulse repetition rate was 60 Hz, and the energy density is 5～45 J/cm2. The moving speed of the stage was 20 mm/s, scanning times was 6. After irradiation, the incision morphology was observed by naked eye and confocal microscopy. The geometry measurement of the incision was also taken. It was showed that pulsed CO2 laser can be used to cut hard bone tissue, and the defocus irradiation condition has an important influence on ablation effect. In order to obtain a narrow-and-deep incision and high ablation rate, one can locate the beam focus slightly under the bone surface..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1116 (2008)
Holography and Information Processing
Optimization of Nonvolatile Holographic Recording in LiNbO3:Ce:Cu with Green Light
Dai Cuixia, Yu Yingjie, Liu De’an, and Liu Liren
In order to optimize the nonvolatile holographic recording in LiNbO3:Ce:Cu crystal with green light, we solved the joint two-center material equations and the coupled wave equations. Variations of parameters were analyzed, such as average space charge field (SCF) and the diffraction efficiency with the crystal annealinIn order to optimize the nonvolatile holographic recording in LiNbO3:Ce:Cu crystal with green light, we solved the joint two-center material equations and the coupled wave equations. Variations of parameters were analyzed, such as average space charge field (SCF) and the diffraction efficiency with the crystal annealing state, the intensity ratio of green-to-ultraviolet (UV), and the concentration of shallow and deep traps in oxidized LiNbO3:Ce:Cu crystal. The results show that strong photorefractive grating with the averaged space-charge field as high as 107 V/m and 80% high fixed diffraction efficiency can be obtained in LiNbO3:Ce:Cu with green light recording. And much better performance can be obtained by changing the corresponding parameters..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1045 (2008)
Laser Manufacturing
Experimental Research of Laser Shock Strengthening AM50 Magnesium Alloy
Zhang Yongkang, Chen Jufang, and Xu Renjun
In order to study the effect of laser shock processing (LSP) on the properties of magnesium alloy, an AM50 magnesium alloy sample was processed with Nd∶glass laser with the wavelength of 1054 nm and pulse width of 23 ns, and its surface figure, microstructure, micro-hardness and residual stress were examined and analyzIn order to study the effect of laser shock processing (LSP) on the properties of magnesium alloy, an AM50 magnesium alloy sample was processed with Nd∶glass laser with the wavelength of 1054 nm and pulse width of 23 ns, and its surface figure, microstructure, micro-hardness and residual stress were examined and analyzed. The experimental results show that a bright dense shallow dent forms in the laser shocked area with laser power density of 3.1 GW/cm2, and the dent depth is about 27 μm. Ultrahigh strain rate plastic deformation takes place in the surface layer and results in extensive formation of dislocations and twins, and the depth of strengthening layer is about 0.8 mm. Laser shock processing improves hardness and residual stress of AM50 magnesium alloy significantly, surface micro-hardness increases by up to 58% and the compressive residual stress on the surface of laser shocked area reaches up to -146 MPa. The experiment results show that the effect of laser shock evidently strengthens the magnesium alloy..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1068 (2008)
Fatigue Performance of Laser Cladding on LY12CZ
Sun Fujuan, Hu Fangyou, Huang Xuren, Wang Bin, Lu Changliang, and Hu Bin
In order to find a good method to repair the corrosion damage of LY12CZ, laser cladding Al-Y (4%Y) and Al-Si (12%Si) powder on LY12CZ was studied by changing the technological parameters of the YAG pulsed laser, such as current, pulse width, frequency, spot diameter and scanning velocity. Through studing the fatigue teIn order to find a good method to repair the corrosion damage of LY12CZ, laser cladding Al-Y (4%Y) and Al-Si (12%Si) powder on LY12CZ was studied by changing the technological parameters of the YAG pulsed laser, such as current, pulse width, frequency, spot diameter and scanning velocity. Through studing the fatigue test, analyzing the fatigue fracture and metallic phase, the result shows that the fatigue life of the laser cladding Al-Y is 339% of the cladding Al-Si alloy specimens. There was little pore and impurity in the Al-Y layer which joins with the substrate firmly. There is fatigue ribbon and fatigue setback in the expansion region of the crack. There are many holes in the Al-Si layer which does not appear the low-cycle fatigue characteristic..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1073 (2008)
Micromachining System Based on Photonic Crystal Fiber Femtosecond Laser Amplifier
Wu Yinzhong, Liu Bowen, Song Youjian, Hu Minglie, Jia Wei, and Wang Qingyue
A compact and stable femtosecond laser micromachining system was founded based on Yb-doped large-mode-area photonic crystal fiber (PCF) femtosecond laser amplifier, which outputs pulse with 1040 nm center wavelength, 50 MHz repetiton rate, 100 fs pulse width, 16 W maximal average power and 85 fs pulse duration after coA compact and stable femtosecond laser micromachining system was founded based on Yb-doped large-mode-area photonic crystal fiber (PCF) femtosecond laser amplifier, which outputs pulse with 1040 nm center wavelength, 50 MHz repetiton rate, 100 fs pulse width, 16 W maximal average power and 85 fs pulse duration after compressed by grating. Fabrication of micropatterns on silicon and metallic thin film (Cr, Al) was demonstrated by the system and the obtained micropatterns were compared with those fabricated by solid-state Ti∶sappire femtosecond laser amplifier with 1 kHz repetition rate. It shows that due to the lower and easily adjusted single pulse energy of our high repetition rate femtosecond laser, the proposed system can effectively control the morphologies of micropatterns, and avoid contamination during micromachining, herein, protect the substrates. The characteristics of high repetition rate and high average power for the founded system are revealed to be advantageous for femtosecond micromachining in aspects of improving the fabrication outcome and promoting the efficiency..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1078 (2008)
WC Particulate Reinforced Metal Matrix Composites Layers Produced by Laser Melt Injection
Liu Dejian, Chen Yanbin, Li Fuquan, and Li Liqun
Laser melt injection (LMI) was used to produce WC particulate reinforced metal matrix composites (MMC) layers on Q235 steel. Based on the analysis of the LMI process characteristic and the macrostructure of the MMC layer, the MMC layer was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The rLaser melt injection (LMI) was used to produce WC particulate reinforced metal matrix composites (MMC) layers on Q235 steel. Based on the analysis of the LMI process characteristic and the macrostructure of the MMC layer, the MMC layer was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that WC particles can be injected into the whole region of the melted pool and distribute uniformly in the MMC layer. New phase of Fe3W3C is observed in the MMC layer due to the injection of WC particles. The microstructure of the MMC layer is quite complicated and can roughly be divided into two regions: the top part and the bottom part. The microstructure in the top part is characterized by many Fe3W3C dendrites surrounded by few interdendrite eutectics. In the bottom, the amount of Fe3W3C dendrites decreases while eutectics increase obviously. The size and morphology of reaction layers around different WC particles inside the MMC layer exhibit obvious difference. Moreover, the particle injection position plays a critical role in the thickness of the reaction layer..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1083 (2008)
Effect of Heating Position on Deformation of Plate in Laser Forming
Shi Yongjun, Liu Feng, Qi Yaoguang, and Yao Zhenqiang
To obtain the desirable shape for the complicated curve surface forming, it is necessary to place the laser scanning lines on different positions of metal plate. However, the deformation of plate is different when the heating position varies. In this paper, effect of the heating position on deformation behavior of the To obtain the desirable shape for the complicated curve surface forming, it is necessary to place the laser scanning lines on different positions of metal plate. However, the deformation of plate is different when the heating position varies. In this paper, effect of the heating position on deformation behavior of the plate is discussed under the temperature gradient mechanism and the buckling mechanism in order to optimize the process parameters in industrial applications. The results suggest that under the temperature gradient mechanism the heating position has a little effect on the bending angle of the plate when the laser scanning line is far away from the fixing edge, while the effect of the heating position on the bending angle is great when the laser scanning line is close to the fixing edge. Under the buckling mechanism, the heating position has an effect not only on the bending angle of the plate, but also on the bending direction of the plate. Therefore, to acquire more precise parameters for the complicated curve surface process planning, the effect of the heating position on the deformation must be considered when building the basic relationship database between process parameters and plate deformation..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1087 (2008)
Study on Microstructure of In-situ Synthesis of TiC-Cr7C3-Ti-Ni Metal-Ceramics Composite Coating
Zhang Weiping, and Liu Zhonghua
In-situ synthesized TiC-Cr7C3-Ti-Ni multiphase metal-ceramics composite coating has been fabricated on Ti-6Al-4V surface by laser cladding in order to improve the comprehensive properties of the material. Composite coating were studied by means of X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispIn-situ synthesized TiC-Cr7C3-Ti-Ni multiphase metal-ceramics composite coating has been fabricated on Ti-6Al-4V surface by laser cladding in order to improve the comprehensive properties of the material. Composite coating were studied by means of X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and electron probe microanalyzer (EPMA). Results show that main phase in the coating is β-Ti and γ-Ni solid solution dendrite with eutectic structure of Ti/TiC or Ti/ Cr7C3 distributing in intergranular. Among the crystal structure is β-Ti solid solution which is poor Ni and C, Ti/TiC or Ti/ Cr7C3 distributes in intergranular which is rich Ti and C. The amount of reinforcement phase varies with chemical composition of the coating, the form of crystal in the coating transfers from network to dendrite and equiaxial crystals. The microhardness of the coating increases prominently compares with the matrix..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1091 (2008)
Characteristics of Deformation of Plate by Laser Peening under the Elastic Pre-Loading Condition
Zhang Xingquan, Zhang Yongkang, Zhou Jianzhong, Gu Yongyu, and Wang Zheng
Laser peening forming is a novel technology, which employes the residual stress induced by high-power repetition laser to form plate. The mechanism of laser peening forming under elastic pre-loading condition was analyzed and the feature of deformation was tested by experiments. In the experiments, the parameters of laLaser peening forming is a novel technology, which employes the residual stress induced by high-power repetition laser to form plate. The mechanism of laser peening forming under elastic pre-loading condition was analyzed and the feature of deformation was tested by experiments. In the experiments, the parameters of laser were as follows: the wavelength is 1.054 μm, the pulse duration is 23 ns, and the power dsnsity is 109 W/cm2. The material of sample was LY12CZ aeronautic aluminum alloy. The experimetal results show that the flexural moment of the sample in the prebending direction is far bigger than that in the vertical direction to pre-bending and the spherical shape can be conquered during pre-loading laser peening forming to a great extent. Under the same conditions, curvature of workpiece after the pre-loading laser peening is two to three times than that after laser peening without pre-loading, and the surface roughness can be improved by one to two grade. So the laser peening forming during pre-loading is superior to the laser peening without pre-loading..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1095 (2008)
Measurement and Metrology
High-Speed Flyer Velocity Measurement System Based on Laser Scattering
Jia Zhexin, Gong Ke, He Shufang, and Huo Yujing
High-speed flyer velocity measurement is one of the key technologies in simulating impact of space flyer driven by ground-based system. A non-contact velocity measurement system for high-speed flyer is developed, and the sources of measurement error and the way to improve the measurement accuracy are also analyzed. A hHigh-speed flyer velocity measurement is one of the key technologies in simulating impact of space flyer driven by ground-based system. A non-contact velocity measurement system for high-speed flyer is developed, and the sources of measurement error and the way to improve the measurement accuracy are also analyzed. A high-power laser diode module is used as the light source, and a PIN photodiode is used as the photo-detector. This system utilizes lateral scattering light as the start and the end signal to measure the average velocity of flyers. Experimental results show that this system is adequate to measure the flyers lager than 100 μm, with the velocity varying from 1 km/s to 10 km/s. And its accuracy is higher than 1.8%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1050 (2008)
Wavefront Sensing Technology of High Repetition Rate Heat Capacity Master Oscillator Power Amplifier System
Deng Zewei, Ma Xiuhua, and Shi Xiangchun
The operating time of high repetition rate heat capacity master oscillator power amplifier (MOPA) laser usually lasts for only several seconds or tens of seconds. During this time, the wavefront distortion of the output beam is changing all the time. A method of sensing the wavefront of high repetition rate heat capaciThe operating time of high repetition rate heat capacity master oscillator power amplifier (MOPA) laser usually lasts for only several seconds or tens of seconds. During this time, the wavefront distortion of the output beam is changing all the time. A method of sensing the wavefront of high repetition rate heat capacity MOPA system by a cyclic radial wavefront shearing interferometer (CRWSI) was proposed. The main structure of this system has been designed. A simplified experimental system was established. A plano-concave lens instead of the optical amplifier was used to generate wavefront distortion. Based on this system, the measurement accuracy of CRWSI was certified. The results show that the difference between the experimental result and the theoretical result is 7.8% (0.02λ)..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1055 (2008)
A Novel Method for Dynamically Measuring Diameters of Train Wheels Using Laser Displacement Transducers
Feng Qibo, Zhang Zhifeng, Chen Shiqian, Gao Yan, and Cui Jianying
With the continuous increase of the rail vehicle’s speed, the wear of wheel is becoming more and more serious, thus accelerating the changes of wheels’ diameters, which will certainly bring potential safety hazard to the operation of railway. A new laser dynamic measurement method was put forward, and the principles foWith the continuous increase of the rail vehicle’s speed, the wear of wheel is becoming more and more serious, thus accelerating the changes of wheels’ diameters, which will certainly bring potential safety hazard to the operation of railway. A new laser dynamic measurement method was put forward, and the principles for measuring diameters by using both one and two laser displacement sensors were introduced. The main factors that influence the accuracy for measuring diameter of wheel were theoretically analyzed and simulated. The results show that adopting two laser sensors can greatly reduce diameter measurement errors caused by the positioning errors when the train moves. A system based on this laser method was built and put into use in a railway site. The experimental results show that the measurement accuracy of using two laser transducers is ±0.38 mm(σ), which can meet the needs of site measurements. And the measurement apparatus can be used in the railway site for dynamically measuring the diameters of wheels..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1059 (2008)
Determining the Orbital Angular Momentum of Vortex Beam by Young’s Double-Slit Interference Experiment
Chen Ziyang, Zhang Guowen, Rao Lianzhou, and Pu Jixiong
The distribution of interference pattern in Young’s double-slit experiment of vortex beam, which was generated by passing a plane beam through a spiral phase plate, was investigated. It is found that topological charge of vortex beam influences the interference pattern, i.e., by compared with the straight interference The distribution of interference pattern in Young’s double-slit experiment of vortex beam, which was generated by passing a plane beam through a spiral phase plate, was investigated. It is found that topological charge of vortex beam influences the interference pattern, i.e., by compared with the straight interference pattern of plane wave, the interference pattern of vortex beam is shifted in the transverse direction as we look from the top of the interference to the bottom, and the magnitude and direction of shift are related to the topological charge. The topological charge of vortex beam can be derived from the interference pattern. Vortex beams carrying orbital angular momentum may find applications in information encoding and transmission. Therefore our research results may be applied to this new kind of information encoding and transmission..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 1063 (2008)
Reviews
Non-Imaging Optics and Its Application in Solid State Lighting
Luo Yi, Zhang Xianpeng, Wang Lin, Yang Yi, Hu Fei, Qian Keyuan, Han Yanjun, Lee William, Zhang Oceam, and Deng Guoqiang
Solid state lighting sources based on GaN-based high power light emitting diodes (LEDs) have been considered as one of the most valuable light sources in 21th century due to its many unparalleled advantages over other conventional lighting sources. It is a sensible strategy choice to promote the developments of solid sSolid state lighting sources based on GaN-based high power light emitting diodes (LEDs) have been considered as one of the most valuable light sources in 21th century due to its many unparalleled advantages over other conventional lighting sources. It is a sensible strategy choice to promote the developments of solid state lighting industrial progress by making a breakthrough at some high class solid state lighting products, which can utilize the advantages of high power LEDs through introducing revolutionary design ideas based on non-imaging optics. In this paper, the history and development of non-imaging optics and its application in solid state lighting are reviewed. Then, the non-imaging optical system design principles and practical solutions are given through a few samples including optical system design of bundles-coupling, two-dimentional (2D) prescribed light distribution and 3-dimentional prescribed light distribution problems based on LEDs..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 7, 963 (2008)
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