Journals >Chinese Journal of Lasers
Contents
2008
Volume: 35 Issue 1
31 Article(s)
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Research Article
Efficient High Power Diode-Side-Pumped Intracavity-Doubled Continuous Wave Green Laser
Zhang Huiyun, Zhang Yuping, Zhong Kai, Wang Peng, Li Xifu, and Yao Jianquan
Laser diode (LD) side-pumping and intracavity-doubling technology is an available method to achieve high power, high stability and low cost continuous wave (CW) green laser. To meet the demand in the fields of laser color display, laser processing, optical data storage, laser medical and scientific research, an efficieLaser diode (LD) side-pumping and intracavity-doubling technology is an available method to achieve high power, high stability and low cost continuous wave (CW) green laser. To meet the demand in the fields of laser color display, laser processing, optical data storage, laser medical and scientific research, an efficient high power diode-side-pumped intracavity-doubled CW green Nd:YAG/KTP laser has been developed successfully. By using plane-concave-plane resonator of three mirrors, and KTP of Ⅱ-type phase-matching for frequency doubling, a maximum of 18.7 W CW 532 nm green laser is obtained when the 808 nm pump laser power is 180 W, and the optical-to-optical conversion efficiency is 10.4%. The power stability of the laser is measured at output power of 15.4 W. During an hour measurement time, the output power instability is less than 0.5%. The output beam exhibits a smooth Gaussian-like profile in the far field and the beam transfer factor is measured to be less than 7 measured by knife-edge method at different output power..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 3 (2008)
Stimulated Raman Scattering and Stimulated Brillouin Scattering Effects in Ytterbium Doped Double Clad Fiber Laser
Hu Shuling, Zhang Chunxi, Gao Chunqing, Liu Huilan, Ou Pan, and Lü Fuyun
The double-clad ytterbium-doped fibers are the common gain material of high power fiber lasers. Because of the small core size, it is easy to arouse the stimulated Brillouin scattering and stimulated Raman scattering effects in the fiber resonator. Once the stimulated Brillouin scattering and stimulated Raman scatterinThe double-clad ytterbium-doped fibers are the common gain material of high power fiber lasers. Because of the small core size, it is easy to arouse the stimulated Brillouin scattering and stimulated Raman scattering effects in the fiber resonator. Once the stimulated Brillouin scattering and stimulated Raman scattering are taking place, the high intensity signals become the major noise source and play an important role on the lasers output characters. Experimental study on them is reported in this paper. The results are shown that the pump way, the output mirror reflectivity and stimulated Rayleigh scattering play important roles to them in the fiber laser resonators, especially stimulated Rayleigh scattering. Stimulated Rayleigh scattering provides additional feedback to fiber resonators, not only narrow the laser linewidth, but also make the threshold of stimulated Brillouin scattering decrease rapidly..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 6 (2008)
Stimulated Raman Scattering of GdVO4 Crystal
Hu Dawei, Wang Zhengping, Zhang Huaijin, Xu Xinguang, Wang Jiyang, and Shao Gongshu
By Czochralski method, high quality GdVO4 single crystals were grown out along a-axis and c-axis. The transmission spectrum of GdVO4 crystal was measured at room temperature. The ultra-violet cut-edge is 338 nm and the infrared cut-edge is larger than 3000 nm, so the transmission spectrum of GdVO4 crystal could cover tBy Czochralski method, high quality GdVO4 single crystals were grown out along a-axis and c-axis. The transmission spectrum of GdVO4 crystal was measured at room temperature. The ultra-violet cut-edge is 338 nm and the infrared cut-edge is larger than 3000 nm, so the transmission spectrum of GdVO4 crystal could cover the region from ultra-violet to part of mid- infrared, and it indicats that GdVO4 crystal could be used for Raman frequency shifting in a wide wavelength scope. The stimulated Raman scattering (SRS) excited by 532 nm and 355 nm pico-second pulses was investigated in GdVO4 crystal. With an ultra-cavity single-pass configuration, three Stokes lines (557.98 nm, 586.86 nm, 618.92 nm) and one anti-Stokes lines (508.01 nm) were observed. The steady-state Raman gain coefficient for the first Stokes line was calculated to be 26.6±0.2 cm/GW, the gain coefficient for the second Stokes line was calculated to be 14.0±0.2 cm/GW, and the total Raman conversion efficiency reached to 43%. For GdVO4 crystal, the SRS of 355 nm laser was reported. Two Stokes lines (365.9 nm, 378.1 nm) were observed, and in this condition the steady-state Raman gain coefficient for the first Stokes line was measured as high as 114±9 cm/GW..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 11 (2008)
Synthesis and Nonlinear Properties of Tetra-Tert-Butylnaphthalocyaninagallium Iodine
Liu Dajun, He Xingquan, Gao Zhengguo, Duan Qian, and Zhou Fenguo
The tetra-tert-butylnaphthalocyaninagallium iodine ((t-Bu)4NcGaI) was synthesized. The structure of the compound was tested by elementary analysis, infrared spectrum and hydrogen nuclear magnetic resonance spectrum. Q band of the compound is in the near infrared region (801 nm), red shift about 70 nm compared with phthThe tetra-tert-butylnaphthalocyaninagallium iodine ((t-Bu)4NcGaI) was synthesized. The structure of the compound was tested by elementary analysis, infrared spectrum and hydrogen nuclear magnetic resonance spectrum. Q band of the compound is in the near infrared region (801 nm), red shift about 70 nm compared with phthalocyanine. Z-scan curve of dichlromethane solution of the compound with the concentration of 1.22×104 mol/L was tested by using a frequency-doubled Q-switched Nd:YAG laser with 4.5 ns laser pulse, repeated frequency of 2 Hz and pulse energy of 39.8 μJ at the wavelength of 532 nm. The nonlinear refracting index, n2 and the third-order nonlinear polarizability, χ(3) were 2.54×10-11 esu and 9.51×10-12 esu, respectively, so the molecular polarizability γ′ of the compound was 3.3×10-29 esu..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 17 (2008)
Influences of Characteristics of Pump Laser on Stimulated Brillouin Scattering Energy Reflectivity
Deng Shaoyong, Guo Shaofeng, Lu Qisheng, Chen Sui, Lin Wenxiong, and Lin Zongzhiz
Fused silica and K9 glasses were used for longitudinal stimulated Brillouin scattering (LSBS) instead of traditional medium of liquids or gases. A single longitudinal mode 1.064 μm laser which is electro-optical Q-modulation is used as pump laser. Influences of pulse duration, power and pulse repetition of pump laser oFused silica and K9 glasses were used for longitudinal stimulated Brillouin scattering (LSBS) instead of traditional medium of liquids or gases. A single longitudinal mode 1.064 μm laser which is electro-optical Q-modulation is used as pump laser. Influences of pulse duration, power and pulse repetition of pump laser on pulse compression of LSBS and energy reflectivity of scattering light were investigated. It is concluded that shorter pulse duration is with higher energy reflectivity and high pulse repetition gets higher energy reflectivity. At the same time, energy reflectivity of scattering in 300 mm K9 glass light is higher than that in 170 mm fused silica, when the focus length is 500 mm. And high energy reflectivity above 90% could be obtained in 170 mm fused silica long and 300 mm K9 glass when pump pulse repetition is 1 Hz. LSBS of pump laser with multi-longitudinal mode had been investigated in the experiments and it is proved that the optical breakdown could happen at the same time with SBS..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 21 (2008)
Temperature Characteristics of Volume Bragg Grating External Cavity Semiconductor Laser Working at Continuous Wave
Cheng Can, Xin Guofeng, Feng Huizhong, Fang Zujie, and Qu Ronghui
The wavelength stabilization of the external cavity semiconductor laser with volume Bragg grating (VBG) as wavelength selected element was studied experimentally, and the experimental results of a continuous wave semiconductor laser array whose output power is 43.5 W were reported. The results of wavelength stabilizatiThe wavelength stabilization of the external cavity semiconductor laser with volume Bragg grating (VBG) as wavelength selected element was studied experimentally, and the experimental results of a continuous wave semiconductor laser array whose output power is 43.5 W were reported. The results of wavelength stabilization with different heat sink temperature were given; it is shown that the temperature controlling pressure of the semiconductor laser could be reduced efficiently. The red shifting of the locked wavelength was observed at this experiment, due to the output power increasing caused by the driving current rising. When the output power is increased to 34.5 W from zero, the red shift is about 0.56 nm, which is in accordance with the measured temperature characteristic of the VBG. The effect of the laser should be considered in the design and applications of the high power external cavity semiconductor laser, which is working at continuous wave or high duty cycle..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 27 (2008)
An Invalidation Mechanism in Organic Light-Emitting Diodes
Zhong Gaoyu, Zhou Suyunz, Chen Guanyu, and Zhao Qing
Organic light-emitting diodes (OLEDs) with the structure of indium-tin-oxide (ITO)/NPB/inserting layer/Alq/LiF/Al have been fabricated. The electroluminescence (EL) spectra of devices with different driving voltage and the characteristics of voltage-current-luminance have been measured. It has been observed that an irrOrganic light-emitting diodes (OLEDs) with the structure of indium-tin-oxide (ITO)/NPB/inserting layer/Alq/LiF/Al have been fabricated. The electroluminescence (EL) spectra of devices with different driving voltage and the characteristics of voltage-current-luminance have been measured. It has been observed that an irreversible process on the EL performance, such as luminescence spectra, bright, efficiency, begin to occur instantly if the voltage increase to some value. The related mechanism has been analyzed. The nanometer-thick inserting layer near the recombination zone may lead to local accumulation of carriers or charges, and result in a local breakage or phase transition of the inserting thin layer. This study shows that a nanometer-thick organic layer should not be used in OLED for preventing this invalidation process..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 35 (2008)
Implementation of Coherent Array Beam Combination Using Two-Dimensional Sine Phase Grating
Wang Jingquan, Fang Liang, Zhang Zhiyou, Du Jinglei, and Guo Yongkang
Coherent beam combination is an effective method to get a high power beam. Two-dimensional (2D) sine phase grating of special design is a perfectly combining element. The design of 2D sine phase grating is introduced, and computational results indicate that the high splittering efficiencies are 81.1% and 73.1%, which iCoherent beam combination is an effective method to get a high power beam. Two-dimensional (2D) sine phase grating of special design is a perfectly combining element. The design of 2D sine phase grating is introduced, and computational results indicate that the high splittering efficiencies are 81.1% and 73.1%, which increase 37% and 26.9% compared with conventional Dammann gratings respectively in the case of 3×3 and 4×4 beam-splitting. The fabrication of 2D sine phase grating and errors are analyzed , and the results show that coupling efficiency of combination has a maximal value leading to greater error latitude for the fabrication of sine phase grating. Splittering and combination light field are different on phase grating surface. The coupling efficiency can be improved, if the phase grating is only used for combination..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 39 (2008)
Wavelength Locker of Pump Laser Based on Dual Fiber Bragg Grating
Hu Shuangshuang, Li Yi, Jiang Qunjie, and Wu Bin
The analytical expression of transmissivity and reflectivity of dual fiber Bragg grating (FBG) has been given based on the mode coupled theory, and the gain equations of the pump laser with dual FBG are also obtained. The characteristics of reflection and transmission for dual FBG were analyzed by relevant expression, The analytical expression of transmissivity and reflectivity of dual fiber Bragg grating (FBG) has been given based on the mode coupled theory, and the gain equations of the pump laser with dual FBG are also obtained. The characteristics of reflection and transmission for dual FBG were analyzed by relevant expression, and the effects of laser gain curve were studied. The dual FBG is composed of a pair of FBGs with the same structure and properties. The spacing of the two FBGs has been optimized to get the best mode-locking characteristics. The output spectral characteristics of the uncooled pump laser with dual FBG or single FBG wavelength locker are practically measured when the operating temperature are 0 ℃, 20 ℃, 70 ℃, respectively. The results show that the output spectral characteristics of the uncooled pump laser with dual FBG have been greatly improved. The uncooled pump laser can work steadily in the temperature range from 0 to 70 ℃. The wavelength shift is 0.2 nm. The side mode suppression ratio is more than 45 dB, and the spectral band width is less than 1.57 nm..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 44 (2008)
Design and Implementation of an Array Optical Receiver Device of Density Wavelength-Division Multiplexing-PIN-TIA for Wavelength-Division Multiplexing Passive Optical Networks
Li Wei, Chen Long, and Huang Dexiu
A kind of density wavelength-division multiplexing (DWDM) filter and PIN-TIA integrated optoelectrical device for upstream channels detection in wavelength-division multiplexing passive optical networks (WDM-PON) system is proposed. In order to achieve a parallel reflection beam for an efficient coupling and collimatioA kind of density wavelength-division multiplexing (DWDM) filter and PIN-TIA integrated optoelectrical device for upstream channels detection in wavelength-division multiplexing passive optical networks (WDM-PON) system is proposed. In order to achieve a parallel reflection beam for an efficient coupling and collimation to PIN-TIA, a novel structure design of a double single mode fiber core and self-focus lens is presented. Based on this device, a 32 channels array optical receiver module which can realize the demux and receiver performance in WDM-PON system is achieved. Through experiment, the responding bandwidth is from 100 Mbit/s to 1.25 Gbit/s, and the channel loss is from 0.3 dB to 6 dB..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 82 (2008)
High-Resolution Fiber Laser Sensor System
Xiao Hao, Li Fang, Wang Yongjie, Liu Lihui, and Liu Yuliang
A high-resolution fiber sensor system based on fiber Bragg grating (FBG) laser is proposed and demonstrated. The fiber laser sensor is made by writing Bragg grating into a section of high gain active fiber. Unmeasured singals applied on the fiber laser induce laser frequency shifts. And a polarization-insensitive unbalA high-resolution fiber sensor system based on fiber Bragg grating (FBG) laser is proposed and demonstrated. The fiber laser sensor is made by writing Bragg grating into a section of high gain active fiber. Unmeasured singals applied on the fiber laser induce laser frequency shifts. And a polarization-insensitive unbalanced Michelson fiber interferometer is employed to transpose the frequency shifts into phase shifts of the interferometer. After converting the output singals of the interferometer to electric signals, the signals are sampled and input into the computer. An improved normalized phase generated carrier (PGC) demodulation technique is used to achieve high resolution demodulation. Experiments demonstrate that the dynamic stain resolution of this system is 5.6×10-4 nε/Hz, and the system output is linear to the strain of the fiber laser sensor..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 87 (2008)
Beam Transmission
Theory Study on the Improved High-Power 19-Core Fiber Laser
Wang Chuncan, Zhang Fan, Tong Zhi, Ning Tigang, and Jian Shuisheng
To improve the ratio of the power of in-phase mode to the total power of output signal (Q) for the 19-core fiber laser, two improved methods are presented. In the first improved scheme, three pieces of undoped fiber, with the same structure and numerical aperture as the ytterbium-doped 19-core fiber, are introduced intTo improve the ratio of the power of in-phase mode to the total power of output signal (Q) for the 19-core fiber laser, two improved methods are presented. In the first improved scheme, three pieces of undoped fiber, with the same structure and numerical aperture as the ytterbium-doped 19-core fiber, are introduced into the Talbot cavity of the fiber laser. In the second improved scheme, the output beam from the single mode fiber laser is transformed to match the in-phase mode using the double convex lenses. The improved schemes are numerical simulated and analyzed based on a set of rate equations. The ratio Q and the output power of each mode are investigated for different parameters such as the distance between fiber ends (a), the power refraction factor of mirror on the signal output end (RM2), and the pump power. The quantitative analysis shows that, for the first scheme, the optimum distance a exists for the fixed RM2, and the Q can be increased from 79.06% to 88.25%; For the second scheme, the ratio Q can be increased to 95.74%, which ensures better beam quality..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 61 (2008)
Polarization Properties of Partially Coherent Electromagnetic Hermite-Gaussian Beams in Atmospheric Turbulence
Ji Xiaoling, Chen Senhui, and Li Xiaoqing
Based on the unified theory of coherence and polarization, the expression for the degree of polarization of partially coherent electromagnetic Hermite-Gaussian (EHG) beams in atmospheric turbulence is derived, and the conditions for keeping polarization invariance are also given. It is shown that the degree of polarizaBased on the unified theory of coherence and polarization, the expression for the degree of polarization of partially coherent electromagnetic Hermite-Gaussian (EHG) beams in atmospheric turbulence is derived, and the conditions for keeping polarization invariance are also given. It is shown that the degree of polarization of partially coherent EHG beams in atmospheric turbulence at the observation point (x,y,z) depends on refraction index structure constant of turbulence, coherence length of the source, order numbers of Hermite polynomial, and constant associated with the degree of polarization of the source. However, after a long-propagation distance, the degree of polarization in turbulence tends to the value at the source plane. The result is independent of coherent length and order number of Hermite polynomial, and the strength of turbulence. The change in the polarization of electromagnetic Gaussian Schell-model (EGSM) beams is just a special case of the obtained results..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 67 (2008)
Biomedical Photonics and Laser Medicine
Effects of He-Ne Laser Irradiation on Vascular Endothelial Cell Growth Factor R-2 Expression in Periodontium of Tooth Movement in Rabbits
Fu Chunmao, and Sun Xinhua
To study the mechanism of helium neon laser promoting blood vessel rebuilds in periodontium of rabbits experimental tooth movement in rabbits, He-Ne laser with the wavelength of 632.8 nm and power of 20 mW was used to irradiate periodontium of experimental tooth movement of rabbits. The result was analysised by immunohTo study the mechanism of helium neon laser promoting blood vessel rebuilds in periodontium of rabbits experimental tooth movement in rabbits, He-Ne laser with the wavelength of 632.8 nm and power of 20 mW was used to irradiate periodontium of experimental tooth movement of rabbits. The result was analysised by immunohistochemistry dyeing and image analysis. The experiment show that the vascular endothelial cell growth factor (VEGF) R-2 expression where the low level laser irradiation, regardless of comparison in the pressure zone or the tension area, appears earlier, have higher peak power and longer time than it does in side irradiating. After stopping the irradiation, the expression level of the irradiation side of the VEGFR-2 is still higher than the comparison side. It shows that the biologic effect still continue after stopping the low level laser irradiation. The result indicates that the low level laser irradiation can promote the VEGFR-2 expression effectively, thus promotes the vascularization of orthodontic dental capsule and the rebuilding of bone..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 156 (2008)
Laser Manufacturing
Fluorescence Discrimination Technology for the Red Tide Algae by Spectra Similarity Index
Hu Xupeng, Su Rongguo, Zhang Chuansong, and Wang Xiulin
Prorocentrum dentatum, Gymnodinium stein and Skeletonema costatum are the main algae which frequently cause red tide. In this paper in vivo fluorescence excitation spectra were measured and the discrimination method of the red tide algae was established by the similarity index of spectra. The results show that the in vProrocentrum dentatum, Gymnodinium stein and Skeletonema costatum are the main algae which frequently cause red tide. In this paper in vivo fluorescence excitation spectra were measured and the discrimination method of the red tide algae was established by the similarity index of spectra. The results show that the in vivo fluorescence excitation spectra were well reproduced (RSD≤5%) and the spectra precision was very high (RSD≤3%). The similarity index between the standard spectra of one algae species and hypothetical mixed spectra of algae and spectra of mixed algae assemblage was calculated. There is a linear relationship between the similarity index and the relative content of the algae. So the red tide algae can be discriminated by calculating the similarity index between fluorescence spectra of mixed algae and their standard fluorescence spectra, and the relative content of the red tide algae can also be detected semi-quantitatively. There is almost no influence of noise on the discrimination of red tide algae when noise is lower than 25%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 115 (2008)
Experimental Study of Laser-Generated Surface Acoustic Waves in Laser Shock Hardening Metals
Yuan Ling, Ren Xudong, Yan Gang, Shen Zhonghua, Ni Xiaowu, Lu Jian, and Zhang Yongkang
Laser shock hardening is a well-known method for prolonging the fatigue life of metals components by introducing near-surface compressive residual stresses. The surface acoustic wave can disperse when the material properties of near-surface change. The near-surface properties, such as elastic properties, residual stresLaser shock hardening is a well-known method for prolonging the fatigue life of metals components by introducing near-surface compressive residual stresses. The surface acoustic wave can disperse when the material properties of near-surface change. The near-surface properties, such as elastic properties, residual stresses, can be analyzed by the phase velocity dispersion. An experiment method is presented to detect laser surface acoustic wave (SAW) of Al alloy by laser shock. Based on the advantage of broad bandwidth generation and detection, the experiment use laser excitating and polyvinylindene fluoride (PVDF) as transducer. The SAW signals in aluminum alloy material under different conditions by laser shock hardening were detected. The signals spectrum and phase velocity dispersive curves were obtained and analyzed. The SAW velocity dispersion is mainly caused by the near-surface grain reorientation and the increasing of dislocation density..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 120 (2008)
Laser and Plasma Nitriding of Titanium Using Continuous Wave-CO2 Laser in Atmosphere Environment
Sun Fengjiu, Yu Hanjiang, and Zhang Jun
In the atmosphere environment, laser combined with plasma stream technique was used to process industrially pure titanium surface, and film of titanium nitride was formed on the titanium surface. Microstructure and phase formation of the nitrided sample surface were analyzed using scanning electron microscopy (SEM) (wiIn the atmosphere environment, laser combined with plasma stream technique was used to process industrially pure titanium surface, and film of titanium nitride was formed on the titanium surface. Microstructure and phase formation of the nitrided sample surface were analyzed using scanning electron microscopy (SEM) (with energy dispersive spectrometer (EDS)) and X-ray diffraction (XRD) techniques. It was found that under proper conditions, the satisfactory nitriding results were obtained. In the range of laser power density between 2.0×105 and 1.0×106 W/cm2, scanning velocity between 200 and 1000 mm/min, the nitride effect was best when laser power is 1.0×106 W/cm2 and scanning velocity is 200 mm/min.The best nitride depth of the industrially pure titanium sample was 80 μm. In the effective nitriding area, with the increasing of the depth, the nitrogen content decreased quickly, while the nitrogen content decreased slowly in the transition area..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 125 (2008)
Technique of Three-Dimensional Laser Forming of Thin Square Metal Sheet to Spherical Dome
Yang Lijun, and Wang Yang
Laser forming is a technique of using the energy from a laser beam to modify and adjust the curvature of sheet metals or hard materials. In order to explore the mechanism and physical process of three-dimensional (3D) laser forming of square sheet, spider scanning path was used to transform the thin square 1Cr18Ni9Ti sLaser forming is a technique of using the energy from a laser beam to modify and adjust the curvature of sheet metals or hard materials. In order to explore the mechanism and physical process of three-dimensional (3D) laser forming of square sheet, spider scanning path was used to transform the thin square 1Cr18Ni9Ti sheet to the spherical dome by 3D laser forming. And dynamic analysis on 3D laser forming was studied. On the base of temperature gradient mechanism of two-dimensional (2D) laser forming, depending on the geometry and the thermo-physical properties of stainless steel 1Cr18Ni9Ti, the mechanism for 3D laser forming of thin square sheet to the spherical dome was developed. This paper discusses the interaction between the moving laser beam and the sheet, the temperature field on the sheet, and the step transition of strain, stress, acceleration, velocity and deformation of the nodes in laser forming. The temperature of the whole sheet is increasing during laser scanning. The heat at any time or position can cause the change of stress which shapes the circles line. But the deformation of the four corners are different from the scanning difference..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 131 (2008)
Analysis of Densification Rate of Fe-C Mixture Powder Forming with Laser Sintering
Fan Chunhua, Kong Lihua, and Huang Kaixu
Densification mechanism of metal powder sintered with selective laser was studied. Different parameters were used in the laser sintering of Fe-C mixed powder experiments. The densification mechanism of metal powder was analyzed by observing the microstructure of sintered part. Based on experiment, the relationship betwDensification mechanism of metal powder sintered with selective laser was studied. Different parameters were used in the laser sintering of Fe-C mixed powder experiments. The densification mechanism of metal powder was analyzed by observing the microstructure of sintered part. Based on experiment, the relationship between the densification rate and forming parameters was studied and its mathematical model was established. The results show that part of powder melts into liquid phase by low power laser and the densification is caused by powders rearrangement, dissolution and deposition participated in the liquid phase. The affect of laser process parameters on densification rate is decided by the amount of liquid phase produced during laser sintering. With the increase of laser power, the decrease of scanning interval, scanning speed and piece thickness, the densification is improved..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 137 (2008)
Effect of Laser Remelting on Microstructure and Properties of Nanocrystalline Nickel Coating Prepared by Jet Electrodepositing
Wang Dongsheng, Huang Yinhui, Tian Zongjun, Liu Zhidong, Zhu Jun, and Chen Jingsong
To improve the properties of nanocrystalline nickel coating prepared by jet electrodepositing, laser remelting experiment was carried out and the effects of laser remelting on microsturcture and properties on coating were researched. The surface morphology, microstructure and microhardness of coatings were investigatedTo improve the properties of nanocrystalline nickel coating prepared by jet electrodepositing, laser remelting experiment was carried out and the effects of laser remelting on microsturcture and properties on coating were researched. The surface morphology, microstructure and microhardness of coatings were investigated using scanning electron microscopy (SEM), X-ray diffractometry (XRD) and microhardness measurement. Meanwhile, the corrosion behavior was studied. The results showed that the nickel coatings prepared by pulse jet electrodepositing owned a fine-grained structure (average grain size is 13.7 nm) with a smooth surface and high density under the optimum processing parameters. However, there were still some pores and other defects. After laser remelting, the grain size of coating was greatly diminished, the density of coating was also improved and the bonding state between the coating and substrate became metallurgical combination from mechanical combination. So the laser remelting sample had higher hardness, better corrosion resistance than jet electrodepositing coating did..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 142 (2008)
Synthesis of SiC/Ni Composite Coatings by Laser Cladding and Property of Erosion Resistance
Xu Bin, Lou Baiyang, Bai Wanjin, and Dong Gang
Ni60A and SiC/Ni60A coatings had been synthesized by laser cladding on 45# steel substrate. Optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to analyse the microstructure and metallographic. The microhardness and erosion resistance performance had also been investigated.Ni60A and SiC/Ni60A coatings had been synthesized by laser cladding on 45# steel substrate. Optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to analyse the microstructure and metallographic. The microhardness and erosion resistance performance had also been investigated. Results reveal that SiC can easily be dissolved in alloy coatings due to its low heat of formation. The phase of coatings is mainly composed of γ(Ni-Cr-Fe) solid solution, Fe7C3 and Fe0.79C0.12Si0.09. As the coaction of solution strengthening, second-phase strengthening and fine-crystal strengthening, the erosion performance of SiC/Ni60A composite coatings has been significantly increased and the microhardness has also been evidently raised..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 147 (2008)
Measurement of Interaction Potential between Colloidal Particles Using Dual Optical Tweezers
Ren Hongliang, Zhuang Lihui, and Li Yinmei
Based on the analyses of the Brownian motion of two interactive colloidal particles, the experimental method for measuring the interaction potential between two micro-scale colloidal particles was studied by making a micro observation of Brownian motion of particles. The measuring system was constructed by dual opticalBased on the analyses of the Brownian motion of two interactive colloidal particles, the experimental method for measuring the interaction potential between two micro-scale colloidal particles was studied by making a micro observation of Brownian motion of particles. The measuring system was constructed by dual optical tweezers and a synchronized chopper. This method was used to measure the interaction potential of a pair of 1μm diameter polystyrene spheres. The consistency between the measured result and the DLVO (Derjagin-Landau-Verwey-Overbeek) theory provides direct microscopic experimental evidence to the theory. Some parameters deciding the experimetal precision and efficiency, such as the switching time, the duration of the on and the off state of the optical tweezers, the distance between the sample particles and the bottom of the sample cell, and the precision of experimental measuring interval, were discussed. The apparatus and method provide an effective technique for measuring the interaction potential between particles of different colloid system and getting an insight into the microscopic foundation for the macroscopic properties of colloids..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 151 (2008)
Laser Physics
Numerical Analysis of Air-Breathing Mode Laser Propulsion
Shi Lei, Zhao Shanghonh, Zhou Wanyin, Li Yongjun, Xu Jie, and Fang Shaoqiang
The laser induced air-breakdown and propagation mechanism of laser sustained plasma detonation (LSD) were analyzed in detail. Based on Navier-Stokes equations, the analysis models considering turbulence and plasma irradiation were established for flow field. And the evolvement of plasma shock wave in thruster was systeThe laser induced air-breakdown and propagation mechanism of laser sustained plasma detonation (LSD) were analyzed in detail. Based on Navier-Stokes equations, the analysis models considering turbulence and plasma irradiation were established for flow field. And the evolvement of plasma shock wave in thruster was systematically analyzed by the finite volume method. The effects of single pulse energy and width on propulsion performance were described also. The production and transmission process of Mach cone observed in many experiments has been captured in this numerical simulation. The relation between thrust, impulse coupling coefficient and one pulse laser energy, pulse width were gained, which agreed well with the experimental results by Germany Space Center. These numerical results can provide some reference for the pulse laser choice and pulse parameters optimization..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 49 (2008)
Numerical Simulations of Pr3+:ZBLAN Upconversion Ultraviolet Fiber Laser Based on 1S0 Level
Luo Tao, and Dai Zhenwen
The theory of population rate equations was used to investigate the kinetics of upconversion ultraviolet laser based on the highest level 1S0 of 4f configuration in Pr3+:ZBLAN fiber. 586 nm and 335 nm pumping lasers are used to populate 1S0 level through stepwise two-photon absorption, and 250 nm ultraviolet (UV) contiThe theory of population rate equations was used to investigate the kinetics of upconversion ultraviolet laser based on the highest level 1S0 of 4f configuration in Pr3+:ZBLAN fiber. 586 nm and 335 nm pumping lasers are used to populate 1S0 level through stepwise two-photon absorption, and 250 nm ultraviolet (UV) continuous wave (CW) laser can be achieved by laser transition from 1S0 to 3F4. The threshold pump powers, output power, slope efficiency and optimum cavity length are calculated. The results show that the threshold pump power increases with the fiber length, and slope efficiency decreases with the increase of fiber length. Higher output power cannot be obtained in a short fiber. Moreover, higher doping concentration makes laser oscillate with lower threshold pump powers but higher slope efficiency. The best slope efficiency is 16.7% in the conditions taken in this paper..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 55 (2008)
Materials and Thin Films
Study on Trap States in Photorefractive Polymer of Polyvinylcarbazole
Wang Xuan, He Lijuan, Zhang Wenlong, and Lei Qingquan
The measurement of thermally stimulated current (TSC) spectrum was completed in photorefractive polymer of polyvinylcarbazole (PVK). The active energy of the thermally stimulated relaxation process in PVK was obtained. The results show that there are two peaks in TSC spectrum of PVK, the low-temperature peak at 338 K hThe measurement of thermally stimulated current (TSC) spectrum was completed in photorefractive polymer of polyvinylcarbazole (PVK). The active energy of the thermally stimulated relaxation process in PVK was obtained. The results show that there are two peaks in TSC spectrum of PVK, the low-temperature peak at 338 K has 0.6 eV active energy, while the high-temperature peak at 417 K has the active energy ranging from 0.53 to 1.00 eV, and the distribution was similar to Gauss law with a 0.77 eV maximum. The maximum of trap density is 5.7×1013 cm-3. Meanwhile, it is proved that the low-temperature originates from the reorientation relaxation of carbazole group and the high-temperature peak originates from the thermo-release of holes in the trap states..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 111 (2008)
Measurement and Metrology
New Frequency Discriminating Circuit of Laser Doppler Vibration Signal
Shang Jianhua, He Yan, Zang Huaguo, Cui Xuemei, and Chen Weibiao
According to the principle of the acousto-optic communication with the technique of laser Doppler vibration, a novel and compact circuit of frequency discrimination for laser Doppler vibration signal is proposed. Based on the principle of heterodyne detection, one signal is produced by the local oscillator signal mixinAccording to the principle of the acousto-optic communication with the technique of laser Doppler vibration, a novel and compact circuit of frequency discrimination for laser Doppler vibration signal is proposed. Based on the principle of heterodyne detection, one signal is produced by the local oscillator signal mixing with the detected signal and the other signal is produced by 90° phase-shifted local oscillator signal mixing with the detected signal. These two signals are used to acquire the Doppler shift and the sound source frequency. The measurable vibration frequency range can be up from 300 Hz to 10 kHz with the simulating acoustic sound source, and it can be used for the acousto-optic communication..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 92 (2008)
Automatic Measurement of the Linewidth Enhancement Factor Based on Moderate Optical Feedback
Yu Yanguang, and Yuan Xiujuan
The basic principle of measuring the linewidth enhancement factor (LEF) using optical feedback self-mixing interference (OFSMI) method is introduced. The theoretical errors are analyzed at different parameters, and the optimal measurement conditions and stripe positions are given. Based on the charcteristics of opticalThe basic principle of measuring the linewidth enhancement factor (LEF) using optical feedback self-mixing interference (OFSMI) method is introduced. The theoretical errors are analyzed at different parameters, and the optimal measurement conditions and stripe positions are given. Based on the charcteristics of optical feedback self-mixing interfence signal, an automatic measurement algorithm is developed. The algorithm can automatically identify and extract all eigenvalues of optical feedback self-mixing interference signal in one vibrant period, and the accurate estimation linewidth enhancement factor can be obtained by the eigenvalues at the optimal measurement stripe position. The simulative data have verified the effectiveness of automatic measurement algorithm. The experimental results show that the accuracy of measuring paramters is better in processing data, and the relative standard error of linewidth enhancement factor is 3.26% when peak-peak value of self-mixing signal is 1.75 V..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 97 (2008)
Measuring the Quality of Milk Using Low-Coherence Dynamic Light Scattering
Xia Hui, Huang Shengxiang, and Li Hongjian
A new method measuring the quality of dairy products is proposed. The low-coherence dynamic light scattering setup consists of the combination of the low-coherence source and Michelson interferometer and the traditional dynamic light scattering technology. By detecting the variation of the field autocorrelation functioA new method measuring the quality of dairy products is proposed. The low-coherence dynamic light scattering setup consists of the combination of the low-coherence source and Michelson interferometer and the traditional dynamic light scattering technology. By detecting the variation of the field autocorrelation function of the single backscattered light, the deterioration of the milk can be discriminated on-line. The autocorrelation function of the single backscattered light field intensity from milk saved in refrigerator and room temperture was dectected, and the CONTIN algorithm was used to analyze the experimental data. The experimetnal results show that the autocorrelation function of the single backscattered light field intensity from milk saved in room temperture did not change in the anterior five days, but the autocorrelation function varied violently in posterior two days, indicating that the milk is deterioration and the particle size distribution is wider. It proves that the method can measure the quality of dairy products..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 102 (2008)
Laser Radar Target Detection Based on Fractional Brownian Motion Model
Ping Qingwei, and Xia Guifen
The fractal characteristics of the laser radar′s echo and clutter are researched and analyzed. Based on the fraction Brownian motion (FBM) model and analysis of different signal-to-noise ratio (SNR) of the laser radar echo, it proves that the laser radar echo data can be processed has the characteristic of Brownian motThe fractal characteristics of the laser radar′s echo and clutter are researched and analyzed. Based on the fraction Brownian motion (FBM) model and analysis of different signal-to-noise ratio (SNR) of the laser radar echo, it proves that the laser radar echo data can be processed has the characteristic of Brownian motion. Because the clutter of the laser radar has increment self-similar characteristic of Brownian motion, it can match the fractal Brownian motion. So the laser radar echo data can be processed by adopting the Brownian motion model. When the SNR of the target echo is small, the fractal dimension of the clutter and target echo is similar. The target can not be detected by the single fractal dimension. But the fractal dimension of the clutter and target is different in the different fractal scale. A method to detect the target by the characteristic of the different fractal dimension of the target and the clutter is advised. This method is called target detect algorithm based on multi fractal dimension. The theory and experiment result shows that this algorithm is reliable and accurate..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 106 (2008)
Optical Communication
Millimeter-Wave Generation Utilizing One Phase Modulator
Huang Cheng, Chen Lin, Yu Jianjun, and Wen Shuangchun
A scheme of millimeter (mm)-wave generation utilizing one phase modulator (PM) has been proposed experimentally. To generate a mixing signal, the baseband signal is mixed with the radio frequency (RF) signal using an electric mixer. And the double-sideband (DSB) signal generated from phase modulator which is drived by A scheme of millimeter (mm)-wave generation utilizing one phase modulator (PM) has been proposed experimentally. To generate a mixing signal, the baseband signal is mixed with the radio frequency (RF) signal using an electric mixer. And the double-sideband (DSB) signal generated from phase modulator which is drived by the mixing signal is transmitted to base station along an optical fiber. The central carrier and the first-order sideband are separated by an optical interleaver (IL) at base station. The first-order sideband signals are beaten to generate the mm-wave with a double repetitive frequency of the RF signal when they are detected by an optical receiver, and the central optical carrier can be reused as carrier for uplink connection. The transmission performance of the mm-wave is analyzed. The duty cycle of the code decreases as the transmission distance increases because of the different delay of the first-order sidebands caused by fiber dispersion. And it limits the lagest transmission distance of the mm-wave. In the experiment, the 20 GHz RF signal generates 40 GHz mm-wave and 2.5 Gbit/s non-return-zero (NRZ) is carried by mm-wave. For downlink connection, the power penalty is 0.2 dBm after data transmit over 20 km dispersive fiber..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 73 (2008)
Wavelength Division Multiplexing/Optical Code Divison Multiplexing System Based on Supercontinuum and Supersturctured Fiber Bragg Grating
Chen Xiaogang, Huang Dexiu, Yuan Xiuhua, and Xia Ge
Wavelength division multiplexing/optical code division multiplexing (WDM/OCDM) system based on supercontinuum (SC) and superstructured fiber Bragg grating (SSFBG) is experimentally demonstrated, simultaneous dual-wavelength optical encoding of a single supercontinuum source using SSFBG is achieved. Under the impact of Wavelength division multiplexing/optical code division multiplexing (WDM/OCDM) system based on supercontinuum (SC) and superstructured fiber Bragg grating (SSFBG) is experimentally demonstrated, simultaneous dual-wavelength optical encoding of a single supercontinuum source using SSFBG is achieved. Under the impact of the interchannel interference and noise of the WDM/OCDM system, the degradation of the pulse waveform is obvious, the width of the main peak is broadened to 8.2 ps and the sidelobe of the auto-correlation trace is increasing apparently. In the receiver, a nonlinear amplifying loop mirror (NALM) is introduced to improve the system performance, both the sidelobe and the pedestal are reduced, the waveform quality of decoded output signal is enhanced, and the auto-correlation peak of decoded output pulse is compressed to 4.8 ps. The peak power of the input signal in the NALM is about 8 mW..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 35, Issue 1, 77 (2008)
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