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ISSN1001-3806 CN51-1125/TN Map

2012 Vol. 36, No. 1

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Study on LiNbO3 electro-optical switches with low driving voltage
FU Bo, ZHANG Da-yong, LUO Yong-quan, LUO Fei, SHEN Zhi-xue
2012, 36(1): 1-4. doi: 10.3969/j.issn.1001-3806.2012.01.001
Abstract:
In order to reduce the driving voltage of an electro-optical switch,a LiNbO3 crystal was placed in a Fabry-Perot cavity and the transmissive characteristics of this Fabry-Perot electro-optical switch was investigated experimentally.The results showed that the driving voltage of the Fabry-Perot electro-optical switch was ~580V,which was much lower than the half-wave voltage of an electro-optical switch used as orthogonal polarizer,~2.1kV.Moreover,the rising time of the Fabry-Perot electro-optical switch,128μs,was shorter than that of a switch used as orthogonal polarizer,284μs.Theoretical analysis of transmitted characteristic dependence on driving voltage was performed,and the results were in accordance with the experimental results.
A common-path heterodyne interferometer technique for measurement of optical activity of liquid
LOU Ben-zhuo
2012, 36(1): 5-7,12. doi: 10.3969/j.issn.1001-3806.2012.01.002
Abstract:
In order to improve the detection sensitivity of optical activity,based on Zeeman effect,a common-path heterodyne interferometer was developed to measure the optical activity of liquid.In this heterodyne interferometer,a pair of correlated orthogonal linear polarized beam is emitted from a Zeeman He-Ne laser,which reduces the complexity of the optical system greatly.A balanced detector and a differential amplifier are integrated into this interferometer so as to reduce the excess noise induced by laser intensity fluctuation and external environments significantly.Thus,a shot-noise-limited detection of this interferometer can be achieved.The optical activity of glucose solution with concentration of(0~50)mg/dL was measured with this common-path heterodyne interferometer and the detection sensitivity was up to 2.3×10-5 degree.This simple heterodyne interferometer can be applied in the optical activity analysis of solid-state,liquid-state or gas-liquid material.
Self-similar pulse evolution in ytterbium doped fiber amplifiers
WANG Xu-de, ZHOU Zheng, LI Su-wen, JIANG En-hua
2012, 36(1): 8-12. doi: 10.3969/j.issn.1001-3806.2012.01.003
Abstract:
In order to study the evolvement and transmission of a self-similar pulse in a high power ultra-short pulse generation system,the self-similar solutions of the nonlinear Schrdinger equation in ytterbium doped fiber amplifiers were analyzed theoretically.The influence of the initial pulse shape,the initial pulse width as well as gain coefficient and gain dispersion on the pulse self-similar evolution were numerically studied.It is shown that when the dispersion length is close to fiber length,the initial pulse can evolve into a parabolic pulse.Different kinds of initial pulses are all evolved into parabolic profiles with different evolutionary process.Larger gain coefficient is beneficial to generate self-similar parabolic pulse with high power and wide frequency range.The gain dispersion plays an important role in frequency filtering.
Investigation on laser polishing of GaN film using deep ultraviolet laser
CHEN Sai-hua, DAI Yu-tang, XIAO Xiang, DING Li-yun
2012, 36(1): 13-15,36. doi: 10.3969/j.issn.1001-3806.2012.01.004
Abstract:
To study laser polishing performance of the 157nm deep ultraviolet(UV) laser,micro-surface laser etching of GaN semiconductor film was performed using a small laser-spot.After investigating the influencing relationships between the process parameters and the polishing quality,ideal process parameters were obtained.The results show that the etched surface roughness Ra gradually decreases with the speed of laser scan.When the scan speed is 0.014mm/s~0.015mm/s,the polishing quality of the etched surface is the best.With the decreasing of scan shift rate perpendicular to scan direction or with the increasing of laser repetition rate,the etched surface roughness would increase.As the laser repetition rate is 8Hz,the polishing effect is preferable and the surface roughness Ra is about 20nm.
Study on effect of incident angles on the confined state for PQW structure
CHEN Hai-bo, HU Su-mei, GAO Ying-jun
2012, 36(1): 16-18. doi: 10.3969/j.issn.1001-3806.2012.01.005
Abstract:
In order to study effect of incident angles on the optical transmission properties of photonic quantum well(PQW)structure,the optical transmission properties at different incident angles were studied based on the optical transfer matrix.A conclusion can be drawn that PQW structure can be applied to multi-channeled filters and orientation switching.The calculation results show that the frequency is quantized by confined effect.The frequency of confined state can be changed by changing the incident angles.The dependence of the change of confined frequency for PQW structure on each incident angle is third-order relationship.The results might be used to multi-channeled filters and orientation switching.It provides theoretical basis for obtaining the desired frequency of confined state.
Zirconia single crystal fiber generation based on new laser heating pedestal growth
WANG Nan-nan, WANG Gao, LI Yang-jun, WANG Xiao-yan, ZHAO Hui
2012, 36(1): 19-21. doi: 10.3969/j.issn.1001-3806.2012.01.006
Abstract:
WANG Nan-nan,WANG Gao,LI Yang-jun,WANG Xiao-yan,ZHAO Hui(National Key Laboratory For Electronic Measurement Technology,North University of China,Taiyuan 030051,China) In order to produce zirconia crystal optical fibers,a pulling single crystal fiber system was put forward based on the method of laser heating pedestal growth(LHPG).Based on original LHPG,a circular focused laser heating system was designed and its optical system was improved and optimized.Making use of both focal points in an ellipsoidal mirror,a focused circular heating source was formed at one of the focal points to melt the crystal and produce fibers.Optical simulation was carried out with ZEMAX software.The simulation results indicate that a high quality circular heating source can be formed at the focal point of the optical system.The system has incomparable advantages comparing with other laser pedestal heating optical systems.The system has good application in the production of zirconia and other high temperature single-crystal optical fibers.
Algorithm and simulation of downward velocity azimuth display of airborne wind lidars
HUANG Min, WANG Yu-lan, WANG Na, CHEN Yong, ZHOU Ding-fu, SHI Xiao-ding, FENG Li-tian
2012, 36(1): 22-25,41. doi: 10.3969/j.issn.1001-3806.2012.01.007
Abstract:
In order to study how to detect three-dimension wind field under an airplane,a model for wind field was built based on ground-based wind lidars,and the radial velocity was optimized by means of Levenber-Marquardt(LM) least square method.It was compared with the traditional algorithms.The working mechanism and scanning modes for airborne lidars are similar with ground-based lidars.On the contrary,it is more difficult to retrieve the wind field because of its own flying speed,instability of flight status,the curvature of the earth,the strong ground scattering echo and ground clutter;the LM least square method is able to converge rapidly and accurately because it has the advantages of fast convergence features of the Newton-Gaussian least square method and the ensuring convergence features of the gradient descent method.The results provide references for the optimization of lidars.
Research of computer-generated hologram based on FPGA technology
JIAN Xian-zhong, ZHANG Han, FAN Jian-peng, ZHOU Zhi-gang
2012, 36(1): 26-28,32. doi: 10.3969/j.issn.1001-3806.2012.01.008
Abstract:
A method based on parallel processing of field programmable gate array(FPGA)technology was put forward to accelerate the computation speed of computer-generated hologram(CGH).Its Fresnel CGH of a point and two-dimension images were produced particularly and the numerical reconstruction of CGH was realized.The experimental results show that the computational speed of a resolution of 50×50 hologram based on FPGA is 165-fold of traditional MATLAB implementation.The study is helpful for implementing real-time CGH.
Tiny vibration measurement based on all-fiber self-mixing interference
LIU Sheng-gang, LIU Qiao, LI Ze-ren
2012, 36(1): 29-32. doi: 10.3969/j.issn.1001-3806.2012.01.009
Abstract:
In order to overcome disadvantages of a free-space self-mixing system,such as short working distance and susceptivity to the environment,an all-fiber self-mixing interference system was designed using a fiber to transmit light and a gradient refractive index(GRIN)lens to collect feedback light.The collection efficiency model of the GRIN lens with a mirror reflecting surface was built.Then the feasibility of an all-fiber self-mixing interference system was theoretically proved.Finally,the experimental facility was established.Experiments were carried out with aluminous foil as reflecting surface.The experimental results show that this new instrument can acquire fine signal and it also has the ability of remote measurement.
Study on machinability for laser-assisted machining of hydraulic carbon-graphite seal rings
BO Ji-kang, ZHANG Hai-ying
2012, 36(1): 33-36. doi: 10.3969/j.issn.1001-3806.2012.01.010
Abstract:
To perform high efficient turning of hydraulic carbon-graphite seal rings,the laser-assisted machining of the material of carbon-graphite seal ring was conducted using laser pre-heating.The material of carbon-graphite seal rings has the characteristics of high strength and high hardness,and is typical non-metallic difficult-to-machine material.The laser-assisted machining heats the workpiece using laser beam,improving machining efficiency as well as reducing cutting force and tool wear.The turning process of carbon-graphite M104 seal ring was focused on,and the conventional machining was compared with the laser-assisted machining.The experimental process of laser-assisted machining was designed and reasonable process parameters were selected.A high cutting efficiency was obtained.The main cutting force and radial force decreased by 23.5% and 19.9% compared with conventional machining.The temperature distribution in the cutting zone of laser-assisted machining is similar to conventional machining.The laser-assisted machining has less tool wear and can get a better surface quality.
Error simulation of Ronchi gratings
YANG Ren-fu, ZHU Xiao-li, CHEN Jun-ning
2012, 36(1): 37-41. doi: 10.3969/j.issn.1001-3806.2012.01.011
Abstract:
In order to study the effect of grating manufacturing error on the accuracy of Moiré metrology,a transmittance function for Moiré fringes was built based on Fourier optical theory and coordinate conversion.The grating error function was simulated by means of linear superimposition.The grating errors were simulated based on previously received moiré fringe models.The Moiré fringe waveform caused by the short-period errors and long-period errors were obtained.Simulation results were analyzed and verified.Although short-period grating error induces high-order harmonics of Moiré fringe signal,its effect on measurement accuracy can be effectively removed after digital filtering.The long-period grating error can affect the accuracy of a grating test system.
Application of off-axis parabolic mirrors in temperature sensor calibration systems
JIANG Lian-yong, HAO Xiao-jian, ZHOU Han-chang
2012, 36(1): 42-44. doi: 10.3969/j.issn.1001-3806.2012.01.012
Abstract:
In order to improve focusing effect of the crystalline lens on the laser beam in a temperature sensor dynamic calibration system,a 90° off-axis parabolic mirror was used instead of the crystalline lens.The influence of the misalignment angle of the 90° off-axis parabolic mirror on the focused laser spot was studied according to geometrical optics.Utilizing the improved system,the CHAL-010-type thermocouple' s time constant at step temperature around 242℃ was tested and the dynamic calibration experiment was carried out.The results show that the new system reconstructed with the 90° off-axis parabolic mirror can fulfill the dynamic calibration of temperature sensors.
Finite element analysis on residual stress field for laser shock processing AM50 magnesium alloy
SHEN Lai-di, CHEN Ju-fang, LI Xing-cheng, LI Ren-xing
2012, 36(1): 45-49. doi: 10.3969/j.issn.1001-3806.2012.01.013
Abstract:
In order to study the characteristics of the residual stress field in the laser shocked area,the residual stress was studied with finite element analysis method.With a Nd: glass pulse laser shocking the surface of AM50 magnesium alloy in experiments,when the laser power density was about 3GW/cm2,the compressive residual stress on the surface of laser shocked area reached-146MPa,and the depth of the compressive residual stress layer was about 0.8mm.Numerical analysis was done with finite element software ABAQUS.The numerical analysis results showed that when the laser power density was over 0.49GW/cm2,there was compressive residual stress in the shocked area,as the laser power density increased,the residual compressive stress also increased and when the laser power density was between 1.95GW/cm2 and 3.06GW/cm2,the residual compressive stress reached saturation.The results show that the calculation results conforms to the experimental data,the numerical results can be used as theoretical basis for optimizing the process parameters in laser shock processing.
A new fast algorithm for gyrator transform
LIN Rui, LIU Qi-neng, ZHANG Cui-ling
2012, 36(1): 50-53. doi: 10.3969/j.issn.1001-3806.2012.01.014
Abstract:
In order to study the application of gyrator transform in optical information processing,a new fast algorithm for calculating gyrator transform was proposed based on twice fast Fourier transform algorithm.Under the condition of dimensional normalization,the discretization of the gyrator transform was studied and the sampling intervals were obtained in space domain,Fourier transform domain and gyrator transform domain respectively.Thus,this new algorithm could avoid scale transform.Some numerical simulation experiments were carried out based on the algorithm and the simulation results were consistent with those reported in the corresponding references.This algorithm can be applied to study gyrator transform.
Screening-photovoltaic spatial solitons illuminated by e-polarized incoherent uniform background irradiation with a divider resistance
JI Xuan-mang, JIANG Qi-chang, LIU Jin-song
2012, 36(1): 54-58. doi: 10.3969/j.issn.1001-3806.2012.01.015
Abstract:
In order to obtain a divider resistance and e-polarized incoherent uniform background irradiation effect on the screening-photovoltaic spatial solitons,a universal spatial soliton theory in photovoltaic photorefractive crystals illuminated by e-polarized incoherent uniform background irradiation with a divider resistance was put forward.The effect of a divider resistance and e-polarized incoherent uniform background irradiation on the full width of half maximum(FWHM) of solitons were simulated.The numerical results show that the FWHM of the solitons decreases with increasing of divider coefficient.The background irradiation has a paltry influence on the solitons when the ratio of the intensity of the e-polarized background irradiation to dark irradiance is small.The FWHM of solitons increases with increasing of the intensity of background irradiation when the ratio is bigger.All kinds of the spatial soliton can be obtained from this theory by adjusting the value of the divider resistance,e-polarized background irradiation,the biased electric field and photovoltaic electric field.
Temperature field of nonlinear crystal eccentric-radiated by intra-cavity multi-mode beam
LIU Xiao-jian, LI Long, DU Chang-long, SHI Xia, SHI Peng, GAN An-sheng
2012, 36(1): 59-63. doi: 10.3969/j.issn.1001-3806.2012.01.016
Abstract:
In order to improve the frequency doubling conversion efficiency of nonlinear crystal influenced by non-uniform temperature rise in high power green lasers,the temperature performance of nonlinear crystal with intracavity multi-mode frequency doubling was analytically investigated.According to the actual characteristics of nonlinear crystal with intra-cavity frequency doubling,based on the heat conduction equation,a general analytical expression of temperature field in nonlinear crystal eccentric-radiated by multi-mode fundamental wave was obtained.The result shows that when the waist spot radius of multi-mode light beam is 200μm,the power of fundamental wave is 500W,and the maximum temperature rise of KTP crystal eccentric-radiated(eccentric degree ξ=0.33)by fundamental harmonic is 79.80℃,4.0% lower than the maximum temperature rise 83.14℃ of KTP crystal center-radiated by fundamental harmonic with other conditions keeping the same.When the radiation eccentricity increases,the maximum temperature rise of KTP crystal can be effectively reduced.The thermal model of nonlinear crystal meets the actual requirement of green lasers,which will play an instructive role in elimination of nonlinear crystal heating effect and improvement of the harmonic conversion efficiency of nonlinear crystal.
A method for improving precision of hydroxyl tagging velocimetry
YE Jing-feng, HU Zhi-yun, ZHANG Zhen-rong, WANG Sheng, LIU Jing-ru
2012, 36(1): 64-66. doi: 10.3969/j.issn.1001-3806.2012.01.017
Abstract:
In order to increase the velocity measurement precision of hydroxyl tagging velocimetry(HTV),experimental data were fitted with Gaussian function because the intensity of the tagging lines is in Gaussian distribution along width direction.Then the fitted peak position was regarded as the center position of the tagging lines.Finally with the center position as reference position,typical measurement data for hydorxyl tagging velocity were processed.The results show that the precision of velocity can be improved distinctly by means of this algorithm.
Performance comparison of various pulse position modulation in wireless laser communication
KE Xi-zheng, CHEN Jin-ni
2012, 36(1): 67-76. doi: 10.3969/j.issn.1001-3806.2012.01.018
Abstract:
In order to compare the performance of various types of pulse position modulation,the coding structure,average transmitted power,bandwidth requirements,transmission rate,power spectral density and channel capacity were compared.Their characteristics and application fields were analyzed.The results show that,on off keying is easy to implement,but power utilization ratio is too low;pulse position modulation improves power utilization ratio but bandwidth availability ratio is low and it need symbol synchronization;digital pulse interval modulation shortens the length of the symbols,it has high bandwidth availability ratio and does not need symbol synchronization,but it is too complex;dual header pulse interval modulation improves the bandwidth efficiency and transmission capacity and do not need symbol synchronization,greatly simplify the complexity of the system implementation.
Study on transmission properties of 2-D super-lattice photonic crystals
YAN Ming-bao, FU Zhen-tang, WANG Wei-yu
2012, 36(1): 77-79,110. doi: 10.3969/j.issn.1001-3806.2012.01.019
Abstract:
The finite difference time domain method was used to calculate the transmission characteristics of 2-D super-lattice photonic crystal formed by cylinders and elliptic rods or cylinders and composite medium rods.It is shown that the width of the band gap becomes lager and the central frequency becomes higher with increase of the sectional area of elliptical rods for the cylinder-elliptical rods super-lattice.As to the case of composite medium rods super-lattice,the thicker the nested elliptical rod,the narrower the band gap is and the lower the central frequency is when the long axis is along the direction of incident wave.However,the wider band gap appeared in the range of high frequency band and in the low frequency band the band gap vanished when the long axis direction is perpendicular to the incident wave.The study provides the theory of the manufacture of photonic crystals.
Design of constant-current source for high power semiconductor laser diode
ZHANG Rui-feng, KONG Ling-hang
2012, 36(1): 80-83. doi: 10.3969/j.issn.1001-3806.2012.01.020
Abstract:
In order to satisfy high power and high stability requirements of the laser K98SA3F-30.00W-R(operating current 12A,ripple coefficient requirement 0.05%),a constant-current source circuit was designed.Its output current can realize high efficiency,high precision and high stability by the chip LTC1625,LT1620,MOSFET IRF7811,digital potentiometers AD5231 and a π-type filter.The LTC1625 is a current mode synchronous step-down switching regulator and the LT1620 is a current sense amplifier.The simulation results given by LTspice Ⅳ show that,when working in constant-current mode,the output current can be changed continuously from zero to 20A,the minimum variable stepping current value is 0.061A,the output current ripple coefficient of the circuit can be less than 0.001%.Results indicate the circuit can meet the application requirements of the semiconductor laser diode K98SA3F-30.00W-R.
Study on high power green lasers with unstable resonators
OU Tian-you, ZHANG Ning, PANG Qing-sheng, LI Gang
2012, 36(1): 87-89,137. doi: 10.3969/j.issn.1001-3806.2012.01.022
Abstract:
In order to improve its laser beam quality,obtain collimated laser beam and provide an excellent high-power green laser source to pump Ti:sapphire,a diode-side-pumped acoustic-optic Q-switched intra-cavity frequency doubling Nd:YAG laser was studied.In the experiment,a convex-plane unstable resonator was adopted assuming the convex mirrors and gain medium thermal lens as a telescope system.Experimental results show that a convex-plane unstable resonator has lager mode volume and better stability.Using a second type phase-matched KTP(KTiOPO4) for intra-cavity frequency doubling,with 200W pump power,42W green laser was output with 109ns pulse width,9.3kHz pulse repetition frequency,less than 2mrad divergent angle,21% optical-optical conversion efficiency and instability less than 2% during 24h work.It is proven that an effective output of green laser can be achieved with an unstable resonator and side pump module.
Research of dispersion characteristics of square-lattice all solid photonic bandgap fibers
HE Feng-liang, LIU Min, DONG Chuan-pei, ZHANG Min, MA Ling-fang
2012, 36(1): 90-92,102. doi: 10.3969/j.issn.1001-3806.2012.01.023
Abstract:
In order to study the dispersion characteristics of square-lattice all solid photonic bandgap fibers,the dispersion characteristics were simulated by means of full-vector finite element method.After changing the structure parameters of a square-lattice all solid photonic bandgap fiber,its dispersion characteristics were analyzed.Finally,an all solid photonic bandgap fiber with zero dispersion wavelength at 1.55μm was proposed.The analytical results demonstrate that an all solid square-lattice photonic bandgap fiber has three zero wavelengths,the dispersion characteristic curves shift to the longer wavelength as the hole diameter d becomes larger and the dispersion slope becomes more flattened with the decrease of the hole pitch Λ.It provides a theoretical evidence to design and fabricate all solid photonic bandgap fibers.
Effect of assembling error in LD array on homogeneity of hollow ducts
JIA Wen-wu, WANG Yue-feng, LEI Cheng-qiang, HUANG Feng
2012, 36(1): 93-98. doi: 10.3969/j.issn.1001-3806.2012.01.024
Abstract:
In order to improve the performance of a hollow duct pumping system,how assembling error of a laser diode(LD) array affects the homogeneity of hollow ducts was studied by means of theoretical analysis and ZEMAX simulation.The result shows that the more each beamlet in a LD array is segmented,the less homogeneity is affected by beam direction error in LD array.Based on the above,collimating principle of LD beam in a hollow duct pumping system was proposed.That is,the collimated divergence of a LD array in fast and slow direction should be in a certain value to make sure that each beamlet can reflect several times in both directions.This can help to get a high coupling efficiency and make it insensitive to assembling error in LD array.This research is valuable for designing such kind of LD pumping systems.
Variable gain amplifiers in underwater optical wireless communication systems
WANG Feng, RAO Jiong-hui
2012, 36(1): 99-102. doi: 10.3969/j.issn.1001-3806.2012.01.025
Abstract:
A variable gain amplifier can be used to reduce the dynamic range of the received signal in an underwater optical wireless communication system.Two methods based on digital to analog converter and digital potentiometer,were discussed in detail.Both the methods can be used to control the amplification gain.Simulation was carried out for the method based on digital potentiometer.The results show that the signal dynamic range is effectively compressed and tends to be stable.
Photonic band gap properties of magnetized plasma photonic crystals under Compton scattering
HAO Xiao-fei, LI Hu-yong, HAO Dong-shan
2012, 36(1): 107-110. doi: 10.3969/j.issn.1001-3806.2012.01.027
Abstract:
For studying effect of multi-photon nonlinear Compton scattering on photonic band gap properties of magnetized plasma photonic crystals under the transverse magneto-optical effect,it was analyzed based on the multi-photon nonlinear Compton scattering model and finite difference time domain algorithm.Some important data on the crystal dispersion and modulation instability and photonic band width were obtained.A new dispersion mechanism of magnetized plasma photonic crystals formed by incident light and scattered optical was put forward.The results show that the plasma dispersion can be increased by the multi-photon nonlinear Compton scattering,and the narrower conduct band of electromagnetic wave and wider forbidden band than before Compton scattering are formed,therefore,the instability of the cross phase modulation in electromagnetic wave propagation is decreased,and that the propagation probability of electromagnetic wave is decreased at lower frequency than plasma.
Mode field and dispersion analysis of photonic crystal fiber based on finite element method
SONG De-jun, XIE Kang, XIAO Jun
2012, 36(1): 111-113,117. doi: 10.3969/j.issn.1001-3806.2012.01.028
Abstract:
In order to obtain ultra-smooth dispersion characteristics,a large mode area and a smaller limitation loss,starting from the Maxwell equations,taking into account the dispersion of pure quartz themselves,the mode field distribution of the photonic crystal fibers,effective index of fundamental modes and dispersion coefficient were calculated with the finite element method.With the fiber dispersion within ±1.0ps·km-1·nm-1,the mode area was larger than 40μm2,and the confinement loss was less than 0.2dB/km.The results show that the dispersion and mode field area of photonic crystal fibers can be controlled by adjusting the air hole diameter,the pitch size of the cladding air holes,and the media filling ratio.
Optical design of a detection device for hard disk platter surface defects
SUN Hao, TANG Yong, LI Jing-zhan, JIA Tian-xiang, YANG Ming, ZHANG Yuan-jian, CHAI Li-fei, CHEN Bao-ying
2012, 36(1): 118-119,123. doi: 10.3969/j.issn.1001-3806.2012.01.030
Abstract:
In order to detect whether the surface defect grade of a hard disk platter meet the standard,a detection device was designed according to scattering theory of light,experimental result and roughness grade of the hard disk platter surface defects.Four models of surface scattering were discussed based on scattering phenomenon when light incident on rough surfaces,scattering property and model constitution of scattering objects.With the help of an optical design software,the optical system of detection device was designed based on mixed scattering model.The results indicated scattering angle and scattering power density of mixed type was maximum,so it was optimum to reflect scattering phenomenon of the hard disk platter surface defects.
Simulation and structure design of a high power laser mirror with self-compensation of thermal distortion
PENG Yu-feng, WU Ding-yun, ZHANG Yi, CHENG Zu-hai
2012, 36(1): 120-123. doi: 10.3969/j.issn.1001-3806.2012.01.031
Abstract:
A high-power laser mirror with self-compensation for thermal distortion was presented and numerically simulated on the basis of its thermal deformation behavior after optimizing its substrate structure.When 7kW laser was input in 17cm diameter,and the reflectivity of the mirror was 98%,the difference between central maximum thermal distortion and boundary thermal distortion within laser radiation region on the mirror surface for the general silicon substrate(peak valley values) was 0.167μm,0.174μm and 0.172μm respectively,under the radiation time of 2s,4s and 10s.However,the thermal distortion difference(peak valley values) of the laser mirror with self-compensation of thermal distortions was 0.092μm,0.052μm,0.027μm,respectively.The study results are useful for improving the heat-effective stability and beam quality.
2-D nonlinear corretion in an improved BP neural network
LIN Qing-song, YANG Xiao-jing, WANG Jun-xiao, ZHANG Ju-wei
2012, 36(1): 124-126,130. doi: 10.3969/j.issn.1001-3806.2012.01.032
Abstract:
In order to reduce the effect of nonlinearity of a position sensitive detector(PSD),after analyzing its working principle and the reasons of nonlinearity formation,nonlinearity correction was carried out in an improved back propagation(BP)neural network based on Levenberg-Morquardt algorithm.MATLAB simulation results show that the improved BP neural network can reduce nonlinearity more effectively,and converge faster than a traditional BP neural network.After revision the PSD obtains approximate linearity in non-linear area within the linear area.This result is helpful for PSD application.
Extraction and optimization of marking path in laser marking systems
KUANG Yan, WU Yun-feng, WU Bo, WU Jian-ping
2012, 36(1): 131-133. doi: 10.3969/j.issn.1001-3806.2012.01.034
Abstract:
In order to meet the accuracy of a laser marking system,after analyzing the PLT file's format,the vector graphics in the PLT file was correctly parsed based on the Visual C++ development platform and the original marking path was extracted.Traditional linear interpolation algorithm was improved because the curves in the vector graphics were approximated to straight lines.Analytical and experimental results show that the algorithm can well resolve the problem how to achieve the marking path by setting an appropriate step length.
Ultra-short blue laser generation by sum-frequency of two lasers with different pulse width
KONG Yan, CHEN Xian-feng, ZHU Tuo, GAO Shu-mei
2012, 36(1): 134-137. doi: 10.3969/j.issn.1001-3806.2012.01.035
Abstract:
In order to get new femtosec;ond-laser an aperiodic; poled optical superlattic;e was employed during the sum-frequency generation process.The optimized structure of the quasi-phase matching optical superlattic;e was studied by means of the genetic; algorithm.Femtosec;ond blue-light laser at 457nm c;an he generated through femtosec;ond pulse mixed with top-hat pump pulse in the aperiodic; optical superlattice.The simulation results indicate that this technique give a new scheme for generating a new ultra}hort laser through nonlinear frequency conversion.
Simulation and measurement of scattering laser energy distribution in extinctive chambers
XU Cheng-wei, YAO Mei, XU Zhen-ling, ZHANG Wen-pan, HU Xin, WANG Jun, LIU Yan-fang
2012, 36(1): 141-144. doi: 10.3969/j.issn.1001-3806.2012.01.037
Abstract:
To simulate the scattering laser energy distribution of 1.06μm pulsed laser reflected multiple times by the inner wall of an extinctive chamber,after analyzing the laser scattering characteristics,a neural network superposition algorithm was put forward and the mathematical model for energy distribution was created.The laser energy distribution pattern under was simulated with 1J 1.06μm laser incident in the chamber.In some reflection area,the reflectance was high with maximal energy of 3.5×10-4J.Actual measurement and theoretical calculation were carried out respectively.Theoretical and measurement results were compared,the maximal and minimum relative error of actual and theoretical value was 10.7% and 1.3%,and both were in the consistent changing rule.All the results show the precision of model can meet the practical requirements of infield simulation tests.