Map
WeChat
Email alert
RSS2007 Vol. 31, No. 4
column
Display Method:
2007, 31(4): 337-340.
[Abstract]
[PDF 199KB]
Abstract:
In order to broaden the amplification bandwidth of conventional dispersion-shifted fiber(DSF) double-pumped fiber optical parametric amplifier(FOPA),a cascade configuration with periodic dispersion compensation composed of conventional DSF and single-mode fiber(SMF) was proposed.Utilizing the configuration,the phase-mismatch caused by the negative fourth-order dispersion of DSF can be reduced by the positive second-order dispersion of SMF,thus the amplification bandwidth can be broadened efficiently.Utilizing the four-wave-mixing coupling equations,the double FOPA was studied.Through simulation,a 69nm bandwidth after broadening was obtained.The results show,for a fixed DSF fiber length,using the optimal SMF length to compensate the dispersion,the phase-mismatch induced by the fourth-order dispersion of DSF can be efficiently reduced and the amplification bandwidth can be broadened.It further shows that a larger bandwidth can be obtained by using multi-segment compensation.
In order to broaden the amplification bandwidth of conventional dispersion-shifted fiber(DSF) double-pumped fiber optical parametric amplifier(FOPA),a cascade configuration with periodic dispersion compensation composed of conventional DSF and single-mode fiber(SMF) was proposed.Utilizing the configuration,the phase-mismatch caused by the negative fourth-order dispersion of DSF can be reduced by the positive second-order dispersion of SMF,thus the amplification bandwidth can be broadened efficiently.Utilizing the four-wave-mixing coupling equations,the double FOPA was studied.Through simulation,a 69nm bandwidth after broadening was obtained.The results show,for a fixed DSF fiber length,using the optimal SMF length to compensate the dispersion,the phase-mismatch induced by the fourth-order dispersion of DSF can be efficiently reduced and the amplification bandwidth can be broadened.It further shows that a larger bandwidth can be obtained by using multi-segment compensation.
2007, 31(4): 341-343.
Abstract:
The frequency-stabilized laser in 1.5μm region is vital for high capacity dense wavelength division multiplexing(DWDM).The acetylene saturated-absorption frequency stabilization can be used to stabilize the frequency of lasers in 1.5μm region.A fiber grating external cavity laser diode(ECLD) was designed according to the method of frequency stabilization,in which a step motor was used to strain the fiber grating to tune the wavelength,and the power of light was modulated by modulating the injecting current.The effect of frequency stabilization was authenticated by experiment.
The frequency-stabilized laser in 1.5μm region is vital for high capacity dense wavelength division multiplexing(DWDM).The acetylene saturated-absorption frequency stabilization can be used to stabilize the frequency of lasers in 1.5μm region.A fiber grating external cavity laser diode(ECLD) was designed according to the method of frequency stabilization,in which a step motor was used to strain the fiber grating to tune the wavelength,and the power of light was modulated by modulating the injecting current.The effect of frequency stabilization was authenticated by experiment.
2007, 31(4): 344-347.
Abstract:
In order to study the injection field of a chemical oxygen iodine laser(COIL),the injection flows in supersonic COIL were simulated by solving the Reynolds averaged Navier-Stokes equations and species continuity equations based on four-stage Runge-Kutta time-stepping scheme on structured viscous mesh.The simulations were carried out with AUSM+up scheme employing the k-ε turbulence model.The finite-rate reaction model was employed with thermodynamic perfect gas properties for chemical reaction.The stiffness problem of chemical source was overcome by a relaxation iterative scheme.Transverse He-I2 injection test case was simulated with this method.The results were in good agreement with the result of AeroSoft's GASP.The supersonic COIL flows with He-I2 injection were also simulated.The distribution of the mass fraction and averaged small signal gain were calculated.The results showed that the averaged small signal gain increased with the increasing of O2(1△) yields or with the decreasing of the water vapor.The averaged small signal gain of a COIL with two spouts is bigger than that of a COIL with one spout.
In order to study the injection field of a chemical oxygen iodine laser(COIL),the injection flows in supersonic COIL were simulated by solving the Reynolds averaged Navier-Stokes equations and species continuity equations based on four-stage Runge-Kutta time-stepping scheme on structured viscous mesh.The simulations were carried out with AUSM+up scheme employing the k-ε turbulence model.The finite-rate reaction model was employed with thermodynamic perfect gas properties for chemical reaction.The stiffness problem of chemical source was overcome by a relaxation iterative scheme.Transverse He-I2 injection test case was simulated with this method.The results were in good agreement with the result of AeroSoft's GASP.The supersonic COIL flows with He-I2 injection were also simulated.The distribution of the mass fraction and averaged small signal gain were calculated.The results showed that the averaged small signal gain increased with the increasing of O2(1△) yields or with the decreasing of the water vapor.The averaged small signal gain of a COIL with two spouts is bigger than that of a COIL with one spout.
2007, 31(4): 348-350.
Abstract:
Because of the need for broad bandwidth of optical materials with the development of optical communication,the spectral properties,the fusion properties and the structure of erbium doped bismuth phosphate glass were studied,and the spectrum was calculated based on the Judd-Ofelt theory.A suitable material for optical amplifiers was obtainedwith refractive index of 1.778,half of the fluorescence width of 54nm,the emission cross section of 0.6×10-20cm2 and the fluorescence lifetime of 8ms.The results show that erbium ytterbium co-doped bismuth phosphate glass is a good material for broad bandwidth amplifiers.
Because of the need for broad bandwidth of optical materials with the development of optical communication,the spectral properties,the fusion properties and the structure of erbium doped bismuth phosphate glass were studied,and the spectrum was calculated based on the Judd-Ofelt theory.A suitable material for optical amplifiers was obtainedwith refractive index of 1.778,half of the fluorescence width of 54nm,the emission cross section of 0.6×10-20cm2 and the fluorescence lifetime of 8ms.The results show that erbium ytterbium co-doped bismuth phosphate glass is a good material for broad bandwidth amplifiers.
2007, 31(4): 351-353.
Abstract:
In order to study the optical parametric characteristics of KBe2BO3F2,according to dispersion equation of nonlinear crystal,momentum and energy conservation,the angle tuning curves and range of wavelength in type-Ⅰ and type-Ⅱ were obtained through numerical simulation,which were compared with those of CsLiB6O10.It can be seen that KBe2BO3F2 is an excellent nonlinear crystal to obtain ultraviolet continuous tunable output and the shortest wavelength 220nm can be obtained when the pump wavelength is 213nm in type-Ⅰ.
In order to study the optical parametric characteristics of KBe2BO3F2,according to dispersion equation of nonlinear crystal,momentum and energy conservation,the angle tuning curves and range of wavelength in type-Ⅰ and type-Ⅱ were obtained through numerical simulation,which were compared with those of CsLiB6O10.It can be seen that KBe2BO3F2 is an excellent nonlinear crystal to obtain ultraviolet continuous tunable output and the shortest wavelength 220nm can be obtained when the pump wavelength is 213nm in type-Ⅰ.
2007, 31(4): 354-357.
Abstract:
For improving the quality of the reconstructed image calculated from the hologram,a 3-D object digital hologram was successfully recorded by using single exposure method and 3-D object holographic optical setup based on Mach-Zehnder interferometer.The quality of the reconstructed image directly calculated from the recorded hologram was unsatisfactory because of the presence of the zero-order diffraction and the speckle noise.A set of digital image processing algorithms was then proposed to process the digital hologram and the reconstructed image with multi-filtering technique.The method synthetizing the wavelet filtering and the contracted weighted mean filtering is capable to eliminate the zero-order diffraction component and reduce the speckle noise to obtain realistic reconstructed image.The experimental result shows that this simple method is very effective for improving the quality of the reconstructed image.For recording hologram only once,it is convenient for application in the real time image processing fields.
For improving the quality of the reconstructed image calculated from the hologram,a 3-D object digital hologram was successfully recorded by using single exposure method and 3-D object holographic optical setup based on Mach-Zehnder interferometer.The quality of the reconstructed image directly calculated from the recorded hologram was unsatisfactory because of the presence of the zero-order diffraction and the speckle noise.A set of digital image processing algorithms was then proposed to process the digital hologram and the reconstructed image with multi-filtering technique.The method synthetizing the wavelet filtering and the contracted weighted mean filtering is capable to eliminate the zero-order diffraction component and reduce the speckle noise to obtain realistic reconstructed image.The experimental result shows that this simple method is very effective for improving the quality of the reconstructed image.For recording hologram only once,it is convenient for application in the real time image processing fields.
2007, 31(4): 358-359,363.
Abstract:
In order to measure the variation of birefringence varying with temperature when incident wavelength is fixed,firstly,the formula of the birefringence of a single axis crystal varying with temperature was deduced according to the theory of polarized light interference.Then an experimental system with double beam paths was set up for comparing measurement.With this system,a sample of quartz was measured and the curve of birefringence vs.temperature was drawn.After analyzing the test results,a formula of birefringence vs.temperature was obtained.The results indicate that,when the incident wavelength is fixed,the relationship between birefringence and temperature is linear.In the experimental process,if the instrument is regulated well and the temperature is contorlled properly,the test result is reliable.
In order to measure the variation of birefringence varying with temperature when incident wavelength is fixed,firstly,the formula of the birefringence of a single axis crystal varying with temperature was deduced according to the theory of polarized light interference.Then an experimental system with double beam paths was set up for comparing measurement.With this system,a sample of quartz was measured and the curve of birefringence vs.temperature was drawn.After analyzing the test results,a formula of birefringence vs.temperature was obtained.The results indicate that,when the incident wavelength is fixed,the relationship between birefringence and temperature is linear.In the experimental process,if the instrument is regulated well and the temperature is contorlled properly,the test result is reliable.
2007, 31(4): 360-363.
Abstract:
In order to measure the mass concentration of particulate matter,according to Mie scattering theory,the relationship between scattered light flux and spherical particle diameter was discussed under the condition of polarized light input,then the formula was attained for calculating particle mass concentration by means of optical particle counter.And particle size distribution was considered using the formula to calculate mass concentration.The experimental results indicate that,in the range of 0.001mg/m3~2mg/m3,calculated mass concentration by the formula and measured mass concentration by a photometer (TSI SIDEPAK AM510) are highly correlated,the correlation coefficient is 0.9953.
In order to measure the mass concentration of particulate matter,according to Mie scattering theory,the relationship between scattered light flux and spherical particle diameter was discussed under the condition of polarized light input,then the formula was attained for calculating particle mass concentration by means of optical particle counter.And particle size distribution was considered using the formula to calculate mass concentration.The experimental results indicate that,in the range of 0.001mg/m3~2mg/m3,calculated mass concentration by the formula and measured mass concentration by a photometer (TSI SIDEPAK AM510) are highly correlated,the correlation coefficient is 0.9953.
2007, 31(4): 364-366,377.
Abstract:
In order to investigate the effect of the high-order dispersion on the gain spectra of cross-phase modulation(XPM) instability under different incident optical power,starting from the coupled nonlinear Schrdinger equations of two optical waves in an optical fiber and utilizing the linearorder stability analysis,the gain spectra of cross-phase modulation instability varying with the incident optical power was calculated when the second-order and the fourth-order dispersion coefficients have the same,opposite signs and when the second-order dispersion coefficients was equal to zero,respectively.The mechanism behind these diverse spectra was analyzed in detail.The results show that,when the second-order and the fourth-order dispersion coefficients have the same sign,with the increase of the incident optical power,the gain spectrum which consists of two separated regions first,will broaden and combine to one region.When the second-order and the fourth-order dispersion coefficients have the opposite signs and the second-order dispersions are equal to zero,the gain spectrum consists of only the first spectral region near the zero point.Moreover,the width and the peak value of the gain spectrum will increase with the incident optical power.The investigation can be a theory guidance to generate ultrashort optical pulse chains with high repetition rate to some extent.
In order to investigate the effect of the high-order dispersion on the gain spectra of cross-phase modulation(XPM) instability under different incident optical power,starting from the coupled nonlinear Schrdinger equations of two optical waves in an optical fiber and utilizing the linearorder stability analysis,the gain spectra of cross-phase modulation instability varying with the incident optical power was calculated when the second-order and the fourth-order dispersion coefficients have the same,opposite signs and when the second-order dispersion coefficients was equal to zero,respectively.The mechanism behind these diverse spectra was analyzed in detail.The results show that,when the second-order and the fourth-order dispersion coefficients have the same sign,with the increase of the incident optical power,the gain spectrum which consists of two separated regions first,will broaden and combine to one region.When the second-order and the fourth-order dispersion coefficients have the opposite signs and the second-order dispersions are equal to zero,the gain spectrum consists of only the first spectral region near the zero point.Moreover,the width and the peak value of the gain spectrum will increase with the incident optical power.The investigation can be a theory guidance to generate ultrashort optical pulse chains with high repetition rate to some extent.
2007, 31(4): 367-369.
Abstract:
In order to study the effect of metal fabric and distortion of work piece in tungsten inert gas(TIG) welding rapid prototyping and obtain the height and variety range of metal parts,the method of the laser vision detecting was used to establish a detecting system to analyze the obtained image.After comparing the detecting result and the actual height of metal parts,it showed that the detecting error was in the nature figuration error range of one welding seam.Results prove that this method can be used to detect the height and distortion of work piece effectively.
In order to study the effect of metal fabric and distortion of work piece in tungsten inert gas(TIG) welding rapid prototyping and obtain the height and variety range of metal parts,the method of the laser vision detecting was used to establish a detecting system to analyze the obtained image.After comparing the detecting result and the actual height of metal parts,it showed that the detecting error was in the nature figuration error range of one welding seam.Results prove that this method can be used to detect the height and distortion of work piece effectively.
2007, 31(4): 370-373.
Abstract:
Several preparation methods were used to synthenize fluorinated polyimide with bigger molecular weight so that a better preparation was found after the structure of the fluorinated polyimide was tested by IR absorbing spectrum.Based on thermogravimetric analysis and differential scanning calorimetry,it was proved that the material might decompose at 530℃ with high thermal stability and have wave-guide thermal character.Finally the linearity relations of refractive index and temperature or refractive index and content of fluorin were proved through measurement of the material.
Several preparation methods were used to synthenize fluorinated polyimide with bigger molecular weight so that a better preparation was found after the structure of the fluorinated polyimide was tested by IR absorbing spectrum.Based on thermogravimetric analysis and differential scanning calorimetry,it was proved that the material might decompose at 530℃ with high thermal stability and have wave-guide thermal character.Finally the linearity relations of refractive index and temperature or refractive index and content of fluorin were proved through measurement of the material.
2007, 31(4): 374-377.
Abstract:
In order to obtain 1.444μm Nd:YAG pulsed laser,the theoretical model of the 1.444μm Nd:YAG pulsed laser system was build up according to the rate equation theory and the laser producing condition of other spectrum with high cross section was analyzed.The output of double wavelength laser of 1.444μm and 1.064μm was calculated in pulsed pump condition.The numerical results indicated that the low 1.064μm laser emission had not obvious effecton the 1.444μm laser output.The amplified spontaneous emission(ASE) effect on the laser output was calculated by one-dimension numerical model.The ASE effect was less than 2% and might be neglected in the ideal condition that there was no reflection on the crystal surface.
In order to obtain 1.444μm Nd:YAG pulsed laser,the theoretical model of the 1.444μm Nd:YAG pulsed laser system was build up according to the rate equation theory and the laser producing condition of other spectrum with high cross section was analyzed.The output of double wavelength laser of 1.444μm and 1.064μm was calculated in pulsed pump condition.The numerical results indicated that the low 1.064μm laser emission had not obvious effecton the 1.444μm laser output.The amplified spontaneous emission(ASE) effect on the laser output was calculated by one-dimension numerical model.The ASE effect was less than 2% and might be neglected in the ideal condition that there was no reflection on the crystal surface.
2007, 31(4): 378-380,383.
Abstract:
The sensitivity of a bulk type optical current sensor(OCS) was compared with that of a point type OCS.Based on Jones matrix,the factors affecting the bulk type OCS's sensitivity,such as linear birefringence in horizontal path,angle tolerance and elliptical polarization in vertical cantlet were analyzed and the effect of only elliptical polarization in vertical cantlet on the sensitiveity was deduced.When all the factors act together,a calibrating factor is necessary.This factor was simulated quantitatively.The comparison result shows that the linear birefringence existing in the material is the most important factor affecting the sensitivity and that the sensitivity of a point type OCS decrease little when linear birefringence of unit length increases.Even when it exceeds a specific value,the sensitivity of a point type can be greater than that of a bulk type.
The sensitivity of a bulk type optical current sensor(OCS) was compared with that of a point type OCS.Based on Jones matrix,the factors affecting the bulk type OCS's sensitivity,such as linear birefringence in horizontal path,angle tolerance and elliptical polarization in vertical cantlet were analyzed and the effect of only elliptical polarization in vertical cantlet on the sensitiveity was deduced.When all the factors act together,a calibrating factor is necessary.This factor was simulated quantitatively.The comparison result shows that the linear birefringence existing in the material is the most important factor affecting the sensitivity and that the sensitivity of a point type OCS decrease little when linear birefringence of unit length increases.Even when it exceeds a specific value,the sensitivity of a point type can be greater than that of a bulk type.
2007, 31(4): 381-383.
Abstract:
A simple method was used to study the initiative time of the thin film irradiated by laser,in which adopting 1.06μm,1.315μm CW laser and 1.06μm single pulse to irradiate typical optical film elements,laser reflex from the surfaces of film elements was measured reflected signal happened to change in a certain time,which is in accordance with time of film damaged by laser.The damaged time was 0.8s and 0.4s when 1.06μm CW laser density was 7133W/cm2 and 11776W/cm2 respectively.The damage time was 3.63ns,2.727ns and 1.09ns when 1.06μm single pulse laser energy was 48.725mJ,97.45mJ,194.9mJ respectively.The damaged time was 3.44s and 1.44s when 1.315μm CW laser density was 2743W/cm2and 4128W/cm2 respectively.Result shows the method of measuring reflected signal of damaged thin films can obtain damaged time of film and it is hepful for improving the laser-resistance of film.
A simple method was used to study the initiative time of the thin film irradiated by laser,in which adopting 1.06μm,1.315μm CW laser and 1.06μm single pulse to irradiate typical optical film elements,laser reflex from the surfaces of film elements was measured reflected signal happened to change in a certain time,which is in accordance with time of film damaged by laser.The damaged time was 0.8s and 0.4s when 1.06μm CW laser density was 7133W/cm2 and 11776W/cm2 respectively.The damage time was 3.63ns,2.727ns and 1.09ns when 1.06μm single pulse laser energy was 48.725mJ,97.45mJ,194.9mJ respectively.The damaged time was 3.44s and 1.44s when 1.315μm CW laser density was 2743W/cm2and 4128W/cm2 respectively.Result shows the method of measuring reflected signal of damaged thin films can obtain damaged time of film and it is hepful for improving the laser-resistance of film.
2007, 31(4): 384-386,390.
Abstract:
In order to measure an object with some breaks precisely and in real-time,the two-frequency grating was created with VC++ first,and then the grating was projected on the surface of the object by LCD projector,so that the phase difference could be calculated by means of Fourier transform profilometry(FTP) from only one image,and the shape of the object could recur.Experiments indicate that this method is simple,exact and in real-time,it greatly promotes the development of FTP by two-frequency grating.
In order to measure an object with some breaks precisely and in real-time,the two-frequency grating was created with VC++ first,and then the grating was projected on the surface of the object by LCD projector,so that the phase difference could be calculated by means of Fourier transform profilometry(FTP) from only one image,and the shape of the object could recur.Experiments indicate that this method is simple,exact and in real-time,it greatly promotes the development of FTP by two-frequency grating.
2007, 31(4): 387-390.
Abstract:
In order to achieve fast and high precision,a dynamic laser flying marking system equipped on product line was introduced based on digital signal processing(DSP) and complex programmable logic device(CPLD)'s dynamic tracing technology so that the problems in the course of laser process on product line,such as metamorphosis,dislocation,distortion was solved,and the labor degree of workers was decreased than the static marking system.Applying the software developed by ourselves,with the laser parameters'setting marking on the same object,it can be seen that the efficiency of laser marking was enhanced with a velocity up to 2000byte/s and the marking line and silhouette were very clear.To the same marking result was achieved on both the dynamic and the static marking systems.
In order to achieve fast and high precision,a dynamic laser flying marking system equipped on product line was introduced based on digital signal processing(DSP) and complex programmable logic device(CPLD)'s dynamic tracing technology so that the problems in the course of laser process on product line,such as metamorphosis,dislocation,distortion was solved,and the labor degree of workers was decreased than the static marking system.Applying the software developed by ourselves,with the laser parameters'setting marking on the same object,it can be seen that the efficiency of laser marking was enhanced with a velocity up to 2000byte/s and the marking line and silhouette were very clear.To the same marking result was achieved on both the dynamic and the static marking systems.
2007, 31(4): 391-393.
Abstract:
In order to obtain an elliptically polarized light,whose ellipticity angle to be invariable and the elliptical azimuth may continuously change,or the ellipticity angle may continuously change and the elliptical azimuth invariable,the polarization is analyzed based on the matrix optics method when the linearly polarized light transits the λ/4 and λ/2 wave-plates,which are placed according to the certain azimuth,the reliable data are obtained.The results indicate our theoretical analysis is correct and it is helpful to the path of rays adjustment and the polarization condition transition.
In order to obtain an elliptically polarized light,whose ellipticity angle to be invariable and the elliptical azimuth may continuously change,or the ellipticity angle may continuously change and the elliptical azimuth invariable,the polarization is analyzed based on the matrix optics method when the linearly polarized light transits the λ/4 and λ/2 wave-plates,which are placed according to the certain azimuth,the reliable data are obtained.The results indicate our theoretical analysis is correct and it is helpful to the path of rays adjustment and the polarization condition transition.
2007, 31(4): 394-396,430.
Abstract:
In order to decrease the thermal stress during process,based on the "element life and death" technique of finite element method(FEM),detailed numerical simulation of 3-D multi-track and multi-layer temperature field during laser metal deposition Shaping(LMDS) process was conducted with ANSYS parametric design language(APDL).Through those simulation,the dynamic variation of temperature in model reappeared,and the distribution rule of temperature and temperature gradient was obtained.The calculated results show that although the nodes on longitudinal section have different activated time,they have similar temperature variation history;the temperature gradients in sample are mainly along z direction,and the temperature gradients in substrate are mainly parallel to substrate.Under the same conditions,the SEM photos of samples tallies closely with the simulations results.
In order to decrease the thermal stress during process,based on the "element life and death" technique of finite element method(FEM),detailed numerical simulation of 3-D multi-track and multi-layer temperature field during laser metal deposition Shaping(LMDS) process was conducted with ANSYS parametric design language(APDL).Through those simulation,the dynamic variation of temperature in model reappeared,and the distribution rule of temperature and temperature gradient was obtained.The calculated results show that although the nodes on longitudinal section have different activated time,they have similar temperature variation history;the temperature gradients in sample are mainly along z direction,and the temperature gradients in substrate are mainly parallel to substrate.Under the same conditions,the SEM photos of samples tallies closely with the simulations results.
2007, 31(4): 397-399,444.
Abstract:
In order to study the relationship between optical signal and cutting quality,an on-line monitoring system with cut front radiation as the criterion for laser cutting was built up.The signal was studied in time-domain and frequency-domain.The analysis in time-domain shows that there is little fluctuation for free defect,while the reverse for the defects.The analysis in frequency-domain shows that when the cutting speed is slower than that of combustion reaction,the dominant frequency relates to the waviness frequency of cut front.The combustion cycle is the main reason of both cutting waviness and main frequency of optical signal.
In order to study the relationship between optical signal and cutting quality,an on-line monitoring system with cut front radiation as the criterion for laser cutting was built up.The signal was studied in time-domain and frequency-domain.The analysis in time-domain shows that there is little fluctuation for free defect,while the reverse for the defects.The analysis in frequency-domain shows that when the cutting speed is slower than that of combustion reaction,the dominant frequency relates to the waviness frequency of cut front.The combustion cycle is the main reason of both cutting waviness and main frequency of optical signal.
2007, 31(4): 400-402,411.
Abstract:
For studying the beam stability of high power solid-state lasers,drift error of main beam was analyzed on the basis of shooting error budget of prototype facility.The drift angle of main laser must be less than 10.6μrad.In 37 minutes,144 frames of far-field images were collected.Two kinds of methods,threshold and gravity model,were used in far-field image processing with MATLAB.The drift was calculated separately in x direction and y direction.The drift of x direction was 3.47μrad and y direction was 4.09μrad.Results indicate that requirement of the main laser stability is met and the requirement of practical shooting is also met.
For studying the beam stability of high power solid-state lasers,drift error of main beam was analyzed on the basis of shooting error budget of prototype facility.The drift angle of main laser must be less than 10.6μrad.In 37 minutes,144 frames of far-field images were collected.Two kinds of methods,threshold and gravity model,were used in far-field image processing with MATLAB.The drift was calculated separately in x direction and y direction.The drift of x direction was 3.47μrad and y direction was 4.09μrad.Results indicate that requirement of the main laser stability is met and the requirement of practical shooting is also met.
2007, 31(4): 403-405,441.
Abstract:
For the sake of evaluating the effect of laser processing parameters on the shaping accuracy of laser freeform fabricating for solid metallic parts;the experiment was arranged by means of orthogonal design.With the aid of CNC continuous interpolation model endowed with velocity prospecting,the problem of too large laser heat input on the sectional contour-path during fabricating of thin-wall metallic sample was solved.The metallic samples which in good shape were fabricated by means of laser freeform fabrication.The result shows that transverse velocity and laser power were the two major factors affecting the shaping accuracy and the effect of the former was more remarkable.
For the sake of evaluating the effect of laser processing parameters on the shaping accuracy of laser freeform fabricating for solid metallic parts;the experiment was arranged by means of orthogonal design.With the aid of CNC continuous interpolation model endowed with velocity prospecting,the problem of too large laser heat input on the sectional contour-path during fabricating of thin-wall metallic sample was solved.The metallic samples which in good shape were fabricated by means of laser freeform fabrication.The result shows that transverse velocity and laser power were the two major factors affecting the shaping accuracy and the effect of the former was more remarkable.
2007, 31(4): 406-407,448.
Abstract:
In order to study adjustable-bandwidth optical filters,the variation of Bragg reflection bandwidth induced by electric field in cholesteric liquid crystal(CLC) was measured and analyzed.Experimental results showed that field-induced reorientation might happen when the applied electric field reached a threshold value.The pitch of CLC became gradient along the axis under the combine restriction of applied electric field and boundary condition of liquid crystal cell and the bandwidth was broadened with the input voltage,based which adjustable optical filter can be manufactured.
In order to study adjustable-bandwidth optical filters,the variation of Bragg reflection bandwidth induced by electric field in cholesteric liquid crystal(CLC) was measured and analyzed.Experimental results showed that field-induced reorientation might happen when the applied electric field reached a threshold value.The pitch of CLC became gradient along the axis under the combine restriction of applied electric field and boundary condition of liquid crystal cell and the bandwidth was broadened with the input voltage,based which adjustable optical filter can be manufactured.
2007, 31(4): 408-411.
Abstract:
In order to improve the ranging accuracy of a lidar,the effect of amplitude and width of the echo signal on the ranging accuracy of a lidar with bell-type laser pulses in temporal domain and Gaussian pulses in spatial domain,was studied under the condition of constant-voltage-amplitude discrimination.For different discrimination level,the range error induced by the variation of amplitude and width of echo signal exhibited reverse variant tendency.As a result,the concept of optimum signal threshold ratio was proposed to improve the ranging accuracy of the lidar and its computational formula was also presented in this paper.Further more,the existence of the optimum signal threshold ratio was verified through experiments under different signal threshold ratio and the experiments showed that the optimum signal threshold ratio of our lidar was about 1.8.The study results provide the basis for the reasomable selection of the lidar to identify the level under different application conditions.
In order to improve the ranging accuracy of a lidar,the effect of amplitude and width of the echo signal on the ranging accuracy of a lidar with bell-type laser pulses in temporal domain and Gaussian pulses in spatial domain,was studied under the condition of constant-voltage-amplitude discrimination.For different discrimination level,the range error induced by the variation of amplitude and width of echo signal exhibited reverse variant tendency.As a result,the concept of optimum signal threshold ratio was proposed to improve the ranging accuracy of the lidar and its computational formula was also presented in this paper.Further more,the existence of the optimum signal threshold ratio was verified through experiments under different signal threshold ratio and the experiments showed that the optimum signal threshold ratio of our lidar was about 1.8.The study results provide the basis for the reasomable selection of the lidar to identify the level under different application conditions.
2007, 31(4): 416-418.
Abstract:
The laser diode-coupling unit is an important part of an intersatellite optical communication system.In terms of the requirement of the intersatellite optical communication system,a new coupling method was proposed,in which an aspherical cylindrical lens,whose front cylindrical lens is orthonormal to its back cylindrical lens,was used to collimate the laser beam,and then the beam was focused by a GRIN lens and coupled to a single-mode fiber.How the coupling efficiency changing with the fiber position displacement and fiber axial angle variation was studied,and it was found that the coupling efficiency was insensitive to both the above parameters.Furthermore,the optical power versus the driver current at the end of the fiber was tested,and 80mW output power was obtained,which showed the optical unit satisfied the designed request.
The laser diode-coupling unit is an important part of an intersatellite optical communication system.In terms of the requirement of the intersatellite optical communication system,a new coupling method was proposed,in which an aspherical cylindrical lens,whose front cylindrical lens is orthonormal to its back cylindrical lens,was used to collimate the laser beam,and then the beam was focused by a GRIN lens and coupled to a single-mode fiber.How the coupling efficiency changing with the fiber position displacement and fiber axial angle variation was studied,and it was found that the coupling efficiency was insensitive to both the above parameters.Furthermore,the optical power versus the driver current at the end of the fiber was tested,and 80mW output power was obtained,which showed the optical unit satisfied the designed request.
2007, 31(4): 419-422.
Abstract:
Porosity formation in high power laser welding,which is related to the characteristics of high power laser welding,is an important problem of welding quality.The pulsed CO2 laser welding was employed to prevent porosity in partial penetration.The experimental results reveal that the porosity ratio decrease with increasing pulse frequency when the pulse frequency is below 50Hz,and is nearly kept constant in the range of 50Hz~200Hz.Moderate increase of the duty ratio is benefit to the reduction of porosity.
Porosity formation in high power laser welding,which is related to the characteristics of high power laser welding,is an important problem of welding quality.The pulsed CO2 laser welding was employed to prevent porosity in partial penetration.The experimental results reveal that the porosity ratio decrease with increasing pulse frequency when the pulse frequency is below 50Hz,and is nearly kept constant in the range of 50Hz~200Hz.Moderate increase of the duty ratio is benefit to the reduction of porosity.
2007, 31(4): 423-426.
Abstract:
In order to study the energy distribution and other parameters of 1.06μm and 10.6μm lasers in the laser semi-active guidance,a new measurement was put forward based on gray photograph.The influence of laser on the target temperature distribution and the receiving property of infrared video camera was discussed in detail.A mathematical model from optical signal to electric signal to image signal is built up.For a certain 10.6μm laser guided-instrument,its output was simulated according to the model.The obtained result was similar to the actual outcome and the 2-demension correlative coefficient was 0.88995.The result shows that the model is correct and it can be used to test the 1.06μm and 10.6μm lasers.
In order to study the energy distribution and other parameters of 1.06μm and 10.6μm lasers in the laser semi-active guidance,a new measurement was put forward based on gray photograph.The influence of laser on the target temperature distribution and the receiving property of infrared video camera was discussed in detail.A mathematical model from optical signal to electric signal to image signal is built up.For a certain 10.6μm laser guided-instrument,its output was simulated according to the model.The obtained result was similar to the actual outcome and the 2-demension correlative coefficient was 0.88995.The result shows that the model is correct and it can be used to test the 1.06μm and 10.6μm lasers.
2007, 31(4): 427-430.
Abstract:
In order to investigate the effects of glass heated by CO2 laser and the difference between using TEM00 and TEM11 to preheat quartz glass,the temperature field and thermal stress field of quartz glass were obtained through numerical computation.The results show that it is better to use TEM11 laser beam to preheat quartz glass than to use TEM00 laser beam.
In order to investigate the effects of glass heated by CO2 laser and the difference between using TEM00 and TEM11 to preheat quartz glass,the temperature field and thermal stress field of quartz glass were obtained through numerical computation.The results show that it is better to use TEM11 laser beam to preheat quartz glass than to use TEM00 laser beam.
2007, 31(4): 431-434.
Abstract:
Based on rate equations,changing doping concentration and cladding size of the Er3+/Yb3+ co-doped double-cladding fiber laser,the effect of the doping concentration and cladding sizeon the performance of the Er3+/Yb3+ co-doped double-cladding fiber laser was studied.Analysis results show:when Er3+-concentration is stable,the output power will be increased efficiently with Yb3+-concentration increase;when Yb3+-concentration is stable,the output power will be increased too with Er3+-concentration increase,but the change is not obvious;the optimal fiber length of the laser becomes shorter when the inner cladding size becomes smaller.
Based on rate equations,changing doping concentration and cladding size of the Er3+/Yb3+ co-doped double-cladding fiber laser,the effect of the doping concentration and cladding sizeon the performance of the Er3+/Yb3+ co-doped double-cladding fiber laser was studied.Analysis results show:when Er3+-concentration is stable,the output power will be increased efficiently with Yb3+-concentration increase;when Yb3+-concentration is stable,the output power will be increased too with Er3+-concentration increase,but the change is not obvious;the optimal fiber length of the laser becomes shorter when the inner cladding size becomes smaller.
2007, 31(4): 435-437.
Abstract:
In order to study the large energy pulse atom iodine laser,a set of xenon light pumped photolytic iodine laser with C3F7I as working substance was built up and the relative experiment was performanced.About 700mJ of pulse laser energy was obtained.The working principle and technical routine of this kind of laser was introduced and experimental resultswere analyzed.The experimental results show that this kind of laser has the characters of simple structure and large energy output capability and is suitable for the application in industry and technology.
In order to study the large energy pulse atom iodine laser,a set of xenon light pumped photolytic iodine laser with C3F7I as working substance was built up and the relative experiment was performanced.About 700mJ of pulse laser energy was obtained.The working principle and technical routine of this kind of laser was introduced and experimental resultswere analyzed.The experimental results show that this kind of laser has the characters of simple structure and large energy output capability and is suitable for the application in industry and technology.
2007, 31(4): 438-441.
Abstract:
In order to clarify the impact of cavity length change on measurement,taking the laser's line-width into account,the influence of cavity length change on the measurement of cavity ring-down in two limiting cases was analyzed and simulated by using cavity ring-down and multiple-beam interferometry theory,hereby the general cases were discussed.Analyses showed the instability chiefly changed resonant frequency of ring-down cavity,then varied the emergent light power and the feature of ring-down signal,which shouled bring serious measurement error.All of these will provide theory direction to measurement error analysis and improve measurement accuracy.
In order to clarify the impact of cavity length change on measurement,taking the laser's line-width into account,the influence of cavity length change on the measurement of cavity ring-down in two limiting cases was analyzed and simulated by using cavity ring-down and multiple-beam interferometry theory,hereby the general cases were discussed.Analyses showed the instability chiefly changed resonant frequency of ring-down cavity,then varied the emergent light power and the feature of ring-down signal,which shouled bring serious measurement error.All of these will provide theory direction to measurement error analysis and improve measurement accuracy.
2007, 31(4): 442-444.
Abstract:
Based on the finite-difference format of Helmholz equation,the normal cutoff wavelength of the dominant mode in the ridge-trough rectangle waveguide is calculated under the condition that physical dimensions of the ridge and the trough vary continuously in the middle of the waveguide while the ratio of short side to long side is 0.45 and ration of the height of the trough to the short side is 0.4.Then the normal cutoff wavelength of the single-ridge waveguide is calculated,which is considered as the ridge of the ridge-trough rectangle waveguide disappear for the width of the ridge equals to 0,the space length equals to the short side plus the height of the trough.A conclusion is made that the cutoff characteristic of the ridge-trough waveguide is better than that of a single ridge waveguide or a single-trough wavegide.
Based on the finite-difference format of Helmholz equation,the normal cutoff wavelength of the dominant mode in the ridge-trough rectangle waveguide is calculated under the condition that physical dimensions of the ridge and the trough vary continuously in the middle of the waveguide while the ratio of short side to long side is 0.45 and ration of the height of the trough to the short side is 0.4.Then the normal cutoff wavelength of the single-ridge waveguide is calculated,which is considered as the ridge of the ridge-trough rectangle waveguide disappear for the width of the ridge equals to 0,the space length equals to the short side plus the height of the trough.A conclusion is made that the cutoff characteristic of the ridge-trough waveguide is better than that of a single ridge waveguide or a single-trough wavegide.
2007, 31(4): 445-448.
Abstract:
Thermoelectric cooler(TEC) behaves approximately as a two-pole system,acting as the most important component to regulate operating temperature of the laser diode(LD).In order to research the influence of thermoelectric cooler module on stability of a temperature control system for a laser diode module,an analog proportional-integral-differential(PID) network was adopted as the system controller.By adjusting the PID control network,the response of TEC was optimized.For unit-step input,the stable state error and stability was studied.A conclusion can be made that the system takes on the better instantaneity and stability.
Thermoelectric cooler(TEC) behaves approximately as a two-pole system,acting as the most important component to regulate operating temperature of the laser diode(LD).In order to research the influence of thermoelectric cooler module on stability of a temperature control system for a laser diode module,an analog proportional-integral-differential(PID) network was adopted as the system controller.By adjusting the PID control network,the response of TEC was optimized.For unit-step input,the stable state error and stability was studied.A conclusion can be made that the system takes on the better instantaneity and stability.
2007, 31(4): 412-415.
Abstract:
In optical monitor system(OMS) for thin film deposition,the film thickness is insensitive to the monitor signal when the signal is near the peak.The accuracy of the monitor system is limited by the noise of the signal.A generalized Kalman filter(KF) was applied to process the monitor signal.Based on nonlinearity of OMS,mathematical model and arithmetic of extend KF was constituted.An ideal monitor curve of 4-layer AR film was generated by TFCalc and mixed with a Gaussian noise.As a result,the signal-to-noise improvement of monitor signal after KF reached 16dB with excellent dynamic tracking characteristic and the delay time was less than 1s.By comparing the theoretic peak coordinates and zero coordinates of first derivative after KF,the calculated thickness error was less than 4nm.The study improves the accuracy of the film thickness detection.
In optical monitor system(OMS) for thin film deposition,the film thickness is insensitive to the monitor signal when the signal is near the peak.The accuracy of the monitor system is limited by the noise of the signal.A generalized Kalman filter(KF) was applied to process the monitor signal.Based on nonlinearity of OMS,mathematical model and arithmetic of extend KF was constituted.An ideal monitor curve of 4-layer AR film was generated by TFCalc and mixed with a Gaussian noise.As a result,the signal-to-noise improvement of monitor signal after KF reached 16dB with excellent dynamic tracking characteristic and the delay time was less than 1s.By comparing the theoretic peak coordinates and zero coordinates of first derivative after KF,the calculated thickness error was less than 4nm.The study improves the accuracy of the film thickness detection.
