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RSS2012 Vol. 36, No. 5
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2012, 36(5): 577-581.
doi: 10.3969/j.issn.1001-3806.2012.05.001
[Abstract]
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Abstract:
In order to study effect of the align deviation value on welding property of automotive galvanized steel based on fiber laser welding,the orthogonal test was adopted to obtain the best ideal parameters without align deviation.Weld topography and cross section of different align deviation value were analyzed,micro-hardness,mechanical properties and micro-structure of weld were tested,and the effect of different butt joint gaps on the critical align deviation value was analyzed.The results show that when the align deviation value is less or equal to 0.30mm(about 17% of sheet thickness),the weld topography is even and continuous.Micro-hardness in the fusion zone and heat affected zone is higher than that in the base material,the tensile strength of fusion zone is better than that of the base material.The change of the align deviation value does not have much impact on the micro-structure of weld.The butt joint gap has obvious influence on the critical align deviation value.
In order to study effect of the align deviation value on welding property of automotive galvanized steel based on fiber laser welding,the orthogonal test was adopted to obtain the best ideal parameters without align deviation.Weld topography and cross section of different align deviation value were analyzed,micro-hardness,mechanical properties and micro-structure of weld were tested,and the effect of different butt joint gaps on the critical align deviation value was analyzed.The results show that when the align deviation value is less or equal to 0.30mm(about 17% of sheet thickness),the weld topography is even and continuous.Micro-hardness in the fusion zone and heat affected zone is higher than that in the base material,the tensile strength of fusion zone is better than that of the base material.The change of the align deviation value does not have much impact on the micro-structure of weld.The butt joint gap has obvious influence on the critical align deviation value.
2012, 36(5): 582-584.
doi: 10.3969/j.issn.1001-3806.2012.05.002
Abstract:
Using the optical nonlinear crystal materials as the guiding layer,symmetrical metal-cladding waveguide configuration was employed in the measurement of lateral shift of the laser beam.Due to the enhancement effect of Goos-Hänchen at the resonant condition,lateral shift of the laser beam can be controlled precisely by applying DC voltage on the guiding-layer.720μm maximum variation of the lateral shift was observed in the experiment and the measurement precision was 25nm.The experimental results are in agreement with the simulation.It is expected that this work will provide tools and resources of potential application in micro-fabrication.
Using the optical nonlinear crystal materials as the guiding layer,symmetrical metal-cladding waveguide configuration was employed in the measurement of lateral shift of the laser beam.Due to the enhancement effect of Goos-Hänchen at the resonant condition,lateral shift of the laser beam can be controlled precisely by applying DC voltage on the guiding-layer.720μm maximum variation of the lateral shift was observed in the experiment and the measurement precision was 25nm.The experimental results are in agreement with the simulation.It is expected that this work will provide tools and resources of potential application in micro-fabrication.
2012, 36(5): 585-588.
doi: 10.3969/j.issn.1001-3806.2012.05.003
Abstract:
In order to meet the requirement for electromagnetic rails,through presetting powder on pure copper surface,TiB2/Cu coatings with different proportion of TiB2 were prepared by means of laser cladding.The microstructure and phases were investigated with optical microscopy,scanning electron microscopy and X-ray diffraction.The coating composed of Cu and TiB2,when the mass fraction of TiB2 is 0.02,0.05 and 0.1,the micro-hardness of the coating is approximately 95HV0.1,105HV0.1and 152HV0.1,and the electrical conductivity is 22.9MS/m,20.4MS/m and 16.4MS/m respectively.The coating metallurgically bonded with the substrate,free of cracks,and some agglomerated TiB2 particles exist.The clad layer possesses the epitaxial growth of columnar crystal.The results show that with increase of TiB2 content,the micro-hardness of TiB2/Cu coatings increases,and the conductivity decreases.
In order to meet the requirement for electromagnetic rails,through presetting powder on pure copper surface,TiB2/Cu coatings with different proportion of TiB2 were prepared by means of laser cladding.The microstructure and phases were investigated with optical microscopy,scanning electron microscopy and X-ray diffraction.The coating composed of Cu and TiB2,when the mass fraction of TiB2 is 0.02,0.05 and 0.1,the micro-hardness of the coating is approximately 95HV0.1,105HV0.1and 152HV0.1,and the electrical conductivity is 22.9MS/m,20.4MS/m and 16.4MS/m respectively.The coating metallurgically bonded with the substrate,free of cracks,and some agglomerated TiB2 particles exist.The clad layer possesses the epitaxial growth of columnar crystal.The results show that with increase of TiB2 content,the micro-hardness of TiB2/Cu coatings increases,and the conductivity decreases.
2012, 36(5): 589-592.
doi: 10.3969/j.issn.1001-3806.2012.05.004
Abstract:
In order to measure the optical parameters of double layer films accurately,with an effective combination of advantages of the simulated annealing algorithm and the simplex algorithm,a simulated annealing-simplex hybrid algorithm was presented to deal with the ellipsometric data inversion of double layer films.In experiments of single wavelength measurement,any two optical parameters of double layer films can be extracted with a measurement of only one group of ellipsometric parameters.Likewise,two or more groups of known ellipsometric parameters can determine four optical parameters simultaneously.And the measured accuracies of refractive index and thickness of films are 0.0002 and 0.07nm respectively.Results of actual measurements show that using the hybrid algorithm to obtain the optical parameters of double layer film is feasible and reliable,and has strong flexibility for various samples.The algorithm is suitable to inversion and actual measurement of double layer films and multi-layer films by single wavelength ellipsometer.
In order to measure the optical parameters of double layer films accurately,with an effective combination of advantages of the simulated annealing algorithm and the simplex algorithm,a simulated annealing-simplex hybrid algorithm was presented to deal with the ellipsometric data inversion of double layer films.In experiments of single wavelength measurement,any two optical parameters of double layer films can be extracted with a measurement of only one group of ellipsometric parameters.Likewise,two or more groups of known ellipsometric parameters can determine four optical parameters simultaneously.And the measured accuracies of refractive index and thickness of films are 0.0002 and 0.07nm respectively.Results of actual measurements show that using the hybrid algorithm to obtain the optical parameters of double layer film is feasible and reliable,and has strong flexibility for various samples.The algorithm is suitable to inversion and actual measurement of double layer films and multi-layer films by single wavelength ellipsometer.
2012, 36(5): 593-596.
doi: 10.3969/j.issn.1001-3806.2012.05.004
Abstract:
In order to study the combined characteristics of multi-channel spectral beam based on volume Bragg gratings (VBG),after building a model for the spectral combining system of multi-channel laser beam by reflective VBG,the diffraction efficiency curve of different beam spectral width was obtained,and the total combination efficiency curves affected by the absorption coefficient of VBG and the cross-talk between channels were also obtained respectively.Numerical results show that diffraction efficiency decreases with the increase of spectral width of beam under condition that the central frequency of the incident beam remains unchanged;diffraction efficiency decreases after increasing the offset between central frequency of incident beam and the central frequency of VBG;the diffraction efficiency of loss due to the cross-talk between neighboring channels should be considered under the condition that the spectral width of incident beam and the spectral selective width of VBG are approximately equal and the condition that the space between neighboring channels is smaller,with the increase of the combination channels,the effect of the absorption coefficient of the material on total combination efficiency gets larger,but the effect of the cross-talk is almost unchanged.
In order to study the combined characteristics of multi-channel spectral beam based on volume Bragg gratings (VBG),after building a model for the spectral combining system of multi-channel laser beam by reflective VBG,the diffraction efficiency curve of different beam spectral width was obtained,and the total combination efficiency curves affected by the absorption coefficient of VBG and the cross-talk between channels were also obtained respectively.Numerical results show that diffraction efficiency decreases with the increase of spectral width of beam under condition that the central frequency of the incident beam remains unchanged;diffraction efficiency decreases after increasing the offset between central frequency of incident beam and the central frequency of VBG;the diffraction efficiency of loss due to the cross-talk between neighboring channels should be considered under the condition that the spectral width of incident beam and the spectral selective width of VBG are approximately equal and the condition that the space between neighboring channels is smaller,with the increase of the combination channels,the effect of the absorption coefficient of the material on total combination efficiency gets larger,but the effect of the cross-talk is almost unchanged.
2012, 36(5): 597-601.
doi: 10.3969/j.issn.1001-3806.2012.05.006
Abstract:
In order to measure atmospheric aerosols and cloud optical properties quantitatively,a 607nm Raman lidar was developed.The methods for measuring optical properties of aerosols&cloud and detecting the interaction between aerosols and cloud by means of Raman lidar were discussed.The typical results of aerosol and cloud extinction coefficient were presented.A detailed study was performed for retrieval the aerosol optical parameters in the vicinity of clouds,which shows that a Raman lidar has the ability to detect the interaction of aerosols and clouds.Based on the result of the one-wavelength Raman lidar,a multiwavelength Raman lidar is under developing which should have more advantages in detecting the interaction of aerosols and clouds.
In order to measure atmospheric aerosols and cloud optical properties quantitatively,a 607nm Raman lidar was developed.The methods for measuring optical properties of aerosols&cloud and detecting the interaction between aerosols and cloud by means of Raman lidar were discussed.The typical results of aerosol and cloud extinction coefficient were presented.A detailed study was performed for retrieval the aerosol optical parameters in the vicinity of clouds,which shows that a Raman lidar has the ability to detect the interaction of aerosols and clouds.Based on the result of the one-wavelength Raman lidar,a multiwavelength Raman lidar is under developing which should have more advantages in detecting the interaction of aerosols and clouds.
2012, 36(5): 602-606.
doi: 10.3969/j.issn.1001-3806.2012.05.007
Abstract:
In order to realize coherent detection of speed of hard targets,a coherent system was designed with a balanced detector introduced to optimize the value of the local oscillator,and the speed of a diffusive hard target was detected.The result demonstrated that the signal to noise ratio of the system was efficiently improved with the balanced detector,the average speed accuracy of the hard target was about 0.49m/s,variance of detection was 0.91m/s,and this system made the coherent detection of the speed of a diffusive hard target.The outcome is useful for research of coherent wind lidar.
In order to realize coherent detection of speed of hard targets,a coherent system was designed with a balanced detector introduced to optimize the value of the local oscillator,and the speed of a diffusive hard target was detected.The result demonstrated that the signal to noise ratio of the system was efficiently improved with the balanced detector,the average speed accuracy of the hard target was about 0.49m/s,variance of detection was 0.91m/s,and this system made the coherent detection of the speed of a diffusive hard target.The outcome is useful for research of coherent wind lidar.
2012, 36(5): 607-611.
doi: 10.3969/j.issn.1001-3806.2012.05.008
Abstract:
In order to study the properties of linearly chirped fiber Bragg grating(LCFBG),and further use it in optical fiber lasers,the coupling theory of the LCFBG was introduced.By using four-order Runge-Kutta method,transfer matrix method and the control variable method,the dependence of reflectivity of the LCFBG on chirp coefficient,direct current index change spatially averaged over a grating period,and the dependence of full width at half maximum on the length of the LCFBG were simulated.The results show that linearly chirped fiber Bragg gratings can broaden the bandwidth.Based on this conclusion,the gratings are used as cavity mirrors of fiber lasers can expand the output spectrum,which can be used as a broadband light source.
In order to study the properties of linearly chirped fiber Bragg grating(LCFBG),and further use it in optical fiber lasers,the coupling theory of the LCFBG was introduced.By using four-order Runge-Kutta method,transfer matrix method and the control variable method,the dependence of reflectivity of the LCFBG on chirp coefficient,direct current index change spatially averaged over a grating period,and the dependence of full width at half maximum on the length of the LCFBG were simulated.The results show that linearly chirped fiber Bragg gratings can broaden the bandwidth.Based on this conclusion,the gratings are used as cavity mirrors of fiber lasers can expand the output spectrum,which can be used as a broadband light source.
2012, 36(5): 612-616.
doi: 10.3969/j.issn.1001-3806.2012.05.009
Abstract:
In order to calculate temperature field and thermal distortion field of laser diode end-pumped Nd:YAG crystal,the temperature thermal model of the crystal was built under the condition of thermal isolation of the end face and constant peripheral temperature.Based on the function of temperature of the Nd:YAG crystal depending upon the thermal conductivity and thermal distortion coefficient,after the thermal model of heat conduction equations were solved by means of the Newton tangent method,the general equations of the temperature field and thermal distortion field of the end-pumped rectangular cross section Nd:YAG crystal with variable thermal conductivity and thermal distortion coefficient were obtained.Then the internal temperature field distribution and thermal distortion field were calculated under different of pump power and pump spot size.Results show that under the condition of 0.01 Nd ion mass fraction,60W pump power and 450μm pump spot radius,the maximum temperature rise on the end face of the Nd:YAG crystal in 3mm×3mm×8mm was 55.7℃,and the maximum thermal distortion was 2.85μm. However,traditionally the thermal conductivity and thermal distortion coefficient were taken as constant,the maximum temperature rise on the end face of the Nd:YAG crystal was 43.4℃and the maximum thermal distortion was 2.84μm.
In order to calculate temperature field and thermal distortion field of laser diode end-pumped Nd:YAG crystal,the temperature thermal model of the crystal was built under the condition of thermal isolation of the end face and constant peripheral temperature.Based on the function of temperature of the Nd:YAG crystal depending upon the thermal conductivity and thermal distortion coefficient,after the thermal model of heat conduction equations were solved by means of the Newton tangent method,the general equations of the temperature field and thermal distortion field of the end-pumped rectangular cross section Nd:YAG crystal with variable thermal conductivity and thermal distortion coefficient were obtained.Then the internal temperature field distribution and thermal distortion field were calculated under different of pump power and pump spot size.Results show that under the condition of 0.01 Nd ion mass fraction,60W pump power and 450μm pump spot radius,the maximum temperature rise on the end face of the Nd:YAG crystal in 3mm×3mm×8mm was 55.7℃,and the maximum thermal distortion was 2.85μm. However,traditionally the thermal conductivity and thermal distortion coefficient were taken as constant,the maximum temperature rise on the end face of the Nd:YAG crystal was 43.4℃and the maximum thermal distortion was 2.84μm.
2012, 36(5): 617-619.
doi: 10.3969/j.issn.1001-3806.2012.05.010
Abstract:
In order to carry out deep research in square ring laser gyro,it is necessary to understand its beam characteristics.Taking advantage of the transmission matrix,the steady condition of a square ring laser gyro was obtained.The electric field distribution in the cavity was obtained by numerical calculation.It is pointed out that there are two Gaussian beams in the cavity,which are combined together at the two curved mirrors.The spot radius will increase with the increase of the curved mirror radii,and the beam will become flatter.
In order to carry out deep research in square ring laser gyro,it is necessary to understand its beam characteristics.Taking advantage of the transmission matrix,the steady condition of a square ring laser gyro was obtained.The electric field distribution in the cavity was obtained by numerical calculation.It is pointed out that there are two Gaussian beams in the cavity,which are combined together at the two curved mirrors.The spot radius will increase with the increase of the curved mirror radii,and the beam will become flatter.
2012, 36(5): 620-622.
doi: 10.3969/j.issn.1001-3806.2012.05.011
Abstract:
In order to measure the surface roughness,based on laser speckle,the parameters of laser speckles were analyzed by means of gray level co-occurrence matrix least squares method.The measurement system of laser speckle was set up,and the images at different incident angles were compared.The results showed that the contrast of the laser speckles was best when the incident angle was 60°.
In order to measure the surface roughness,based on laser speckle,the parameters of laser speckles were analyzed by means of gray level co-occurrence matrix least squares method.The measurement system of laser speckle was set up,and the images at different incident angles were compared.The results showed that the contrast of the laser speckles was best when the incident angle was 60°.
2012, 36(5): 623-623.
Abstract:
In order to study the rest time and the reducing rate of liquid level on thickness and uniformity of polystyrene（C8H8）filters, C8H8 filters are made by dip-coating and measured by Vecco Dektak6.0 Stylus Profiler. The interpolation fitting method is introduced to research the relation of C8H8 filters with the rest time and the reducing rate of liquid level. It’s finding that the rest time and the reducing rate of liquid level have great influence on uniformity of C8H8 filter. With the shorter rest time and the smaller the reducing rate of liquid level, C8H8 filters have better uniformity.
In order to study the rest time and the reducing rate of liquid level on thickness and uniformity of polystyrene（C8H8）filters, C8H8 filters are made by dip-coating and measured by Vecco Dektak6.0 Stylus Profiler. The interpolation fitting method is introduced to research the relation of C8H8 filters with the rest time and the reducing rate of liquid level. It’s finding that the rest time and the reducing rate of liquid level have great influence on uniformity of C8H8 filter. With the shorter rest time and the smaller the reducing rate of liquid level, C8H8 filters have better uniformity.
2012, 36(5): 632-635.
doi: 10.3969/j.issn.1001-3806.2012.05.014
Abstract:
In order to improve the reconstructed image quality of off-axis digital hologram,an elimination method of zero-order image and conjugate image of off-axis digital hologram was presented.Based on reference light with a π phase shift and recording two holograms,Fourier transform was made for two subtracted holograms.Combined with spectral filtering method,the associated spatial frequencies was filtered out with rectangular window function.Then digital reconstruction was made.Experiments show that the method can eliminate the zero-order image and conjugate image even in the case that the zero-order image and others images overlap seriously,so the method can effectively improve the quality of reconstructed image in digital holography.
In order to improve the reconstructed image quality of off-axis digital hologram,an elimination method of zero-order image and conjugate image of off-axis digital hologram was presented.Based on reference light with a π phase shift and recording two holograms,Fourier transform was made for two subtracted holograms.Combined with spectral filtering method,the associated spatial frequencies was filtered out with rectangular window function.Then digital reconstruction was made.Experiments show that the method can eliminate the zero-order image and conjugate image even in the case that the zero-order image and others images overlap seriously,so the method can effectively improve the quality of reconstructed image in digital holography.
2012, 36(5): 636-638.
doi: 10.3969/j.issn.1001-3806.2012.05.015
Abstract:
In order to find out the forward and backward splitting angles of a Wollaston prism and their symmetry,satisfactory data were obtained by combining mathematical calculations and experimental test.Analysis shows that the main reason of the symmetry difference of the splitting angles is that the o light incident on the first prism becomes e light on the second prism and then does not parallel to the optical axis of the crystal,no longer is caused by the principal refractive indices.The results demonstrate that the splitting angles becomes slightly larger when it is used positively than negatively.Moreover,the wavelength gets more and more shorter as long as the angle of the prism's structure became larger.Besides,the difference value between forward and backward splitting angles will get larger too.
In order to find out the forward and backward splitting angles of a Wollaston prism and their symmetry,satisfactory data were obtained by combining mathematical calculations and experimental test.Analysis shows that the main reason of the symmetry difference of the splitting angles is that the o light incident on the first prism becomes e light on the second prism and then does not parallel to the optical axis of the crystal,no longer is caused by the principal refractive indices.The results demonstrate that the splitting angles becomes slightly larger when it is used positively than negatively.Moreover,the wavelength gets more and more shorter as long as the angle of the prism's structure became larger.Besides,the difference value between forward and backward splitting angles will get larger too.
2012, 36(5): 639-641.
doi: 10.3969/j.issn.1001-3806.2012.05.016
Abstract:
As one of the core parts of a radar system,high-power kHz laser is extremely important in the study of atmospheric science.It is one of the feasible ways to achieve high-power kHz laser master oscillator power amplifier.In order to get the narrow pulse width,high beam quality kHz master oscillator laser,a diode end-pumped kHz electro-optic Q-switched Nd:YAG laser was used in experiments.A laser at 1064nm was obtained with repetition rate of 1kHz,pulse width of 5ns,pulse energy of 2.7mJ,optical-optical efficiency of 40%,M2=1.2.The results show that this laser provides a qualified seed source for 1kHz,500W,10ns green master oscillator power amplifiers.
As one of the core parts of a radar system,high-power kHz laser is extremely important in the study of atmospheric science.It is one of the feasible ways to achieve high-power kHz laser master oscillator power amplifier.In order to get the narrow pulse width,high beam quality kHz master oscillator laser,a diode end-pumped kHz electro-optic Q-switched Nd:YAG laser was used in experiments.A laser at 1064nm was obtained with repetition rate of 1kHz,pulse width of 5ns,pulse energy of 2.7mJ,optical-optical efficiency of 40%,M2=1.2.The results show that this laser provides a qualified seed source for 1kHz,500W,10ns green master oscillator power amplifiers.
2012, 36(5): 642-644.
doi: 10.3969/j.issn.1001-3806.2012.05.017
Abstract:
In order to effectively restrain the interference of bias light from the surrounding environment for the spectral nonimaging pulse laser alarm device,after eliminating the bias light noise through light filtering,circuit filtering,comparator's threshold restrictions,aiming at the existence of huge energy background flash interference,according to the difference of the time length between background flash and pulse laser,calculating the incident light time of the alarm device based on complex programmable logic device and doing a judgment,the background flash interference can be eliminated.During the actual test,the false-alarm number of the alarm device caused by sunlight was 0 in 12h,and no false alarm happened in various simulating close and huge energy background flash interference situation.The result shows that the project can provides a good example and experimental scheme for resolving the false alarm problem cause by bias light of a laser warning device,the circuit hardware is highly integrated for judging time with only one complex programmable logic device chip,its program is short,and the method has good application value.
In order to effectively restrain the interference of bias light from the surrounding environment for the spectral nonimaging pulse laser alarm device,after eliminating the bias light noise through light filtering,circuit filtering,comparator's threshold restrictions,aiming at the existence of huge energy background flash interference,according to the difference of the time length between background flash and pulse laser,calculating the incident light time of the alarm device based on complex programmable logic device and doing a judgment,the background flash interference can be eliminated.During the actual test,the false-alarm number of the alarm device caused by sunlight was 0 in 12h,and no false alarm happened in various simulating close and huge energy background flash interference situation.The result shows that the project can provides a good example and experimental scheme for resolving the false alarm problem cause by bias light of a laser warning device,the circuit hardware is highly integrated for judging time with only one complex programmable logic device chip,its program is short,and the method has good application value.
2012, 36(5): 645-648.
doi: 10.3969/j.issn.1001-3806.2012.05.018
Abstract:
In order to test deflection wavefront of liquid-crystal grating phased array,a key component in phased array laser radar,and monitor and evaluate the quality of radar scanning beams,a radial shearing interference measurement technology with direction changing function was adopted and theoretical analysis and experimental verification about this method were carried out.Test data were obtained with a 10mm×10mm aperture deflection wavefront tester and a commercial WYKO interferometer respectively.The difference of test results is less than λ/20 for peak-valley value and less than λ/200 for root mean square(RMS)value for the same plane optical element.Deflection wavefront of liquid-crystal grating phased array was measured.The experimental results show that this method can measure deflection wavefront of the liquid-crystal grating phased array with high precision.
In order to test deflection wavefront of liquid-crystal grating phased array,a key component in phased array laser radar,and monitor and evaluate the quality of radar scanning beams,a radial shearing interference measurement technology with direction changing function was adopted and theoretical analysis and experimental verification about this method were carried out.Test data were obtained with a 10mm×10mm aperture deflection wavefront tester and a commercial WYKO interferometer respectively.The difference of test results is less than λ/20 for peak-valley value and less than λ/200 for root mean square(RMS)value for the same plane optical element.Deflection wavefront of liquid-crystal grating phased array was measured.The experimental results show that this method can measure deflection wavefront of the liquid-crystal grating phased array with high precision.
2012, 36(5): 649-652.
doi: 10.3969/j.issn.1001-3806.2012.05.019
Abstract:
In order to improve the efficiency of wavelet transform in laser velocity interferometers,computing course of wavelet transform was analyzed,two kinds of fast wavelet algorithms were put forward.After comparing both the different methods,one was chosen to analyze the all fiber displacement interferometer system for any reflector signals.Signals were processed by means of general wavelet transform and fast wavelet algorithm based on fast Fourier transforamation under the same conditions.Simulation results show that signal processed with the fast wavelet algorithm was not degraded with much faster computation efficiency.It is effective that the fast method can be used to process the all fiber displacement interferometer system for any reflector signals and it can increase the speed of signal processing,which is available in engineering field.
In order to improve the efficiency of wavelet transform in laser velocity interferometers,computing course of wavelet transform was analyzed,two kinds of fast wavelet algorithms were put forward.After comparing both the different methods,one was chosen to analyze the all fiber displacement interferometer system for any reflector signals.Signals were processed by means of general wavelet transform and fast wavelet algorithm based on fast Fourier transforamation under the same conditions.Simulation results show that signal processed with the fast wavelet algorithm was not degraded with much faster computation efficiency.It is effective that the fast method can be used to process the all fiber displacement interferometer system for any reflector signals and it can increase the speed of signal processing,which is available in engineering field.
2012, 36(5): 653-656.
doi: 10.3969/j.issn.1001-3806.2012.05.020
Abstract:
In order to study effect of Compton scattering on protons accelerated along the normal direction of the target back side in the plasma,based on the model of multi-photon nonlinear Compton scattering and plasma particle-in cell simulation,the accelerated protons were analyzed and simulated,and a new mechanism of protons accelerated by the electrostatic field formed by incident laser and Compton scattering on the plasma face was put forward,then some important data were given out.The results show that the energetic electron numbers induced by Compton scattering in plasma are increased so that the electrostatic field on the target face of the energetic electrons is increased,and higher accelerated energy is absorbed by the protons.The proton gets the accelerated energy from the plasma of the gradual density scale length by Compton scattering higher than the energy getting from the plasma of the steep density scale length,and the key cause is that the effect of the electrostatic field increased by Compton scattering effectively compensates the loss energy of the electron in the transporting energy to the plasma as the increasing of the laser modulation instability taking place under Compton scattering.Therefore,it is perfect to accelerate protons with plasma of the gradual density scale length under Compton scattering.
In order to study effect of Compton scattering on protons accelerated along the normal direction of the target back side in the plasma,based on the model of multi-photon nonlinear Compton scattering and plasma particle-in cell simulation,the accelerated protons were analyzed and simulated,and a new mechanism of protons accelerated by the electrostatic field formed by incident laser and Compton scattering on the plasma face was put forward,then some important data were given out.The results show that the energetic electron numbers induced by Compton scattering in plasma are increased so that the electrostatic field on the target face of the energetic electrons is increased,and higher accelerated energy is absorbed by the protons.The proton gets the accelerated energy from the plasma of the gradual density scale length by Compton scattering higher than the energy getting from the plasma of the steep density scale length,and the key cause is that the effect of the electrostatic field increased by Compton scattering effectively compensates the loss energy of the electron in the transporting energy to the plasma as the increasing of the laser modulation instability taking place under Compton scattering.Therefore,it is perfect to accelerate protons with plasma of the gradual density scale length under Compton scattering.
2012, 36(5): 657-661.
doi: 10.3969/j.issn.1001-3806.2012.05.021
Abstract:
In order to study the dependence of the focus on the quality of the femtosecond laser beam,the tighten focusing of the femtosecond laser beam reflected by a 90°off-axis parabolic mirror was studied experimentally and theoretically trough the classical geometrical optical model.The obtained theoretical and experimental results indicate that the peak power density of the laser spot will reduce by half when the declination reaches 3mrad.Simultaneously the optical path difference resulted from incident angle causes time broadening of the spot on the target surface and impairs the focal spot intensity to some degrees.A3TW Ti:sapphire laser system was adopted in the present work.The best focal spot obtained in the present work with an ƒ/1 off-axis parabolic mirror is 5.6μm×5.4μm and the peak power density is 3.83×1017W/cm2and 1.23×1019W/cm2for 3mJ and 96mJ ultra-short pulse laser separately.The study of the tighten focusing for ultra-short laser pulse reflected by 90°off-axis parabolic mirror.This research provides important information for the study on the interactions between the femtosecond laser pulses and solid,gas,clusters and so on.
In order to study the dependence of the focus on the quality of the femtosecond laser beam,the tighten focusing of the femtosecond laser beam reflected by a 90°off-axis parabolic mirror was studied experimentally and theoretically trough the classical geometrical optical model.The obtained theoretical and experimental results indicate that the peak power density of the laser spot will reduce by half when the declination reaches 3mrad.Simultaneously the optical path difference resulted from incident angle causes time broadening of the spot on the target surface and impairs the focal spot intensity to some degrees.A3TW Ti:sapphire laser system was adopted in the present work.The best focal spot obtained in the present work with an ƒ/1 off-axis parabolic mirror is 5.6μm×5.4μm and the peak power density is 3.83×1017W/cm2and 1.23×1019W/cm2for 3mJ and 96mJ ultra-short pulse laser separately.The study of the tighten focusing for ultra-short laser pulse reflected by 90°off-axis parabolic mirror.This research provides important information for the study on the interactions between the femtosecond laser pulses and solid,gas,clusters and so on.
2012, 36(5): 662-664.
doi: 10.3969/j.issn.1001-3806.2012.05.022
Abstract:
A measuring method based on white-light spectral-domain optical coherence tomography was used to measure thin film thickness.The theory was analyzed and the experiment was done.The single-layer and multi-layer thin film on glass substrate was used for imaging experiments respectively and 2-D cross-sectional images were obtained.The experiment shows that system can not only measure the inner microstructure of the film,but also measure the film thickness of single-layer and multi-layer film in 68μm and 30μm respectively.The measured value is the same as the theoretical value,which verifies the validity of the theory.The system has high imaging speed and resolution,and can meet the industrial measurement.
A measuring method based on white-light spectral-domain optical coherence tomography was used to measure thin film thickness.The theory was analyzed and the experiment was done.The single-layer and multi-layer thin film on glass substrate was used for imaging experiments respectively and 2-D cross-sectional images were obtained.The experiment shows that system can not only measure the inner microstructure of the film,but also measure the film thickness of single-layer and multi-layer film in 68μm and 30μm respectively.The measured value is the same as the theoretical value,which verifies the validity of the theory.The system has high imaging speed and resolution,and can meet the industrial measurement.
2012, 36(5): 665-669.
doi: 10.3969/j.issn.1001-3806.2012.05.023
Abstract:
Dissimilar metal plates welding between galvanized steel and carbon steel was investigated experimentally.The fiber laser and equipped robot were used in the experiment.The microstructure and mechanical properties of joints were analyzed.Based on the experiment,the influence of parameters variation such as laser beam power,welding speed and defocusing distance on the width and depth of welding seam was studied.The experimental results indicate that the width and depth of welding seam are inclined to be higher with the increase of laser beam power and the decrease of welding speed,and the surface hardness in the welded joint and heat affected zone are higher than that of base materials,and the tensile strength of the welded joint is reasonable equal to that of the carbon steel under the experimental condition.It is advisible that laser beam center offset a bit to the carbon steel side so as to prevent the uncoinciding between the centerline of joint and butt caused by the material physical properties difference,and to keep the continuity of strength and performance in the joint during the laser welding dissimilar materials between galvanized steel and carbon steel.
Dissimilar metal plates welding between galvanized steel and carbon steel was investigated experimentally.The fiber laser and equipped robot were used in the experiment.The microstructure and mechanical properties of joints were analyzed.Based on the experiment,the influence of parameters variation such as laser beam power,welding speed and defocusing distance on the width and depth of welding seam was studied.The experimental results indicate that the width and depth of welding seam are inclined to be higher with the increase of laser beam power and the decrease of welding speed,and the surface hardness in the welded joint and heat affected zone are higher than that of base materials,and the tensile strength of the welded joint is reasonable equal to that of the carbon steel under the experimental condition.It is advisible that laser beam center offset a bit to the carbon steel side so as to prevent the uncoinciding between the centerline of joint and butt caused by the material physical properties difference,and to keep the continuity of strength and performance in the joint during the laser welding dissimilar materials between galvanized steel and carbon steel.
2012, 36(5): 670-673.
doi: 10.3969/j.issn.1001-3806.2012.05.024
Abstract:
When tunable diode laser absorption spectroscopy gas sensor is used in open optical path gas measurement,the laser absorption signal can be influenced by atmospheric turbulence.The amplitude of absorption signal varies with the fluctuation of atmospheric turbulence so that the obtained gas absorption spectrum signal is deformed and the measurement accuracy is affected.In order to improve laser absorption spectrum signal quality impacted by atmospheric turbulence and measurement sensitivity,a method,changing the scan frequency of laser wavelength,was put forward.The variance of average signal between adjacent periods of absorption spectrum was less than 0.1 when the scan frequency of laser wavelength was 2kHz.This method effectively improved the laser absorption spectrum signal quality impacted by atmospheric turbulence.
When tunable diode laser absorption spectroscopy gas sensor is used in open optical path gas measurement,the laser absorption signal can be influenced by atmospheric turbulence.The amplitude of absorption signal varies with the fluctuation of atmospheric turbulence so that the obtained gas absorption spectrum signal is deformed and the measurement accuracy is affected.In order to improve laser absorption spectrum signal quality impacted by atmospheric turbulence and measurement sensitivity,a method,changing the scan frequency of laser wavelength,was put forward.The variance of average signal between adjacent periods of absorption spectrum was less than 0.1 when the scan frequency of laser wavelength was 2kHz.This method effectively improved the laser absorption spectrum signal quality impacted by atmospheric turbulence.
2012, 36(5): 674-676.
doi: 10.3969/j.issn.1001-3806.2012.05.025
Abstract:
In order to study the dependence of the effective index and the coupling constant on the radii and refractive index of the fiber core and cladding,the relation between the structural parameters and the change of the resonance wave of the transmission spectra was obtained by means of theoretical analysis and the numerical simulation.The results show when the radii a1,a2and refractive index of fiber core and cladding n1,n2increase,the resonance wavelengths shift towards shorter wavelengths;when the grating period Λ increases,the resonance wavelengths shift towards longer wavelengths.The conclusion can be used for reference in the design of long period fiber gratings.
In order to study the dependence of the effective index and the coupling constant on the radii and refractive index of the fiber core and cladding,the relation between the structural parameters and the change of the resonance wave of the transmission spectra was obtained by means of theoretical analysis and the numerical simulation.The results show when the radii a1,a2and refractive index of fiber core and cladding n1,n2increase,the resonance wavelengths shift towards shorter wavelengths;when the grating period Λ increases,the resonance wavelengths shift towards longer wavelengths.The conclusion can be used for reference in the design of long period fiber gratings.
2012, 36(5): 677-681.
doi: 10.3969/j.issn.1001-3806.2012.05.026
Abstract:
In order to study effect of modal overlap coefficients on conversion efficiency in lithium niobate waveguide,propagation modes and difference frequency generation conversion efficiency were studied with finite difference method.The mode field distributions of 1560nm and 780nm waves and the modified wavelength conversion introduced by mode overlap coefficients were obtained.The modified theoretical results were consistent with the experimental ones and the optimal ridge waveguide size was achieved.The calculated results can provide guide for design of direct bonded periodically poled lithium niobate ridge waveguide with nonlinear interaction.
In order to study effect of modal overlap coefficients on conversion efficiency in lithium niobate waveguide,propagation modes and difference frequency generation conversion efficiency were studied with finite difference method.The mode field distributions of 1560nm and 780nm waves and the modified wavelength conversion introduced by mode overlap coefficients were obtained.The modified theoretical results were consistent with the experimental ones and the optimal ridge waveguide size was achieved.The calculated results can provide guide for design of direct bonded periodically poled lithium niobate ridge waveguide with nonlinear interaction.
2012, 36(5): 682-685.
doi: 10.3969/j.issn.1001-3806.2012.05.027
Abstract:
In order to improve the measurement accuracy of the miniature fiber spectrometer,a complete calibration scheme was obtained based on the standard emission spectrum of mercury and argon lamp and three-order linear fitting of the least squares.Calibration results show that the arithmetic mean error is less than 0.167nm,standard deviation is less than 0.217nm and the fitting related degree is high.Test results show that after calibration the wavelength uncertainty is better than the 0.11nm,the error is less than 0.15nm,and the wavelength repeatability can reach 0.01nm.This result is beneficial for improving the measurement precision of spectrometers in the practical applications.
In order to improve the measurement accuracy of the miniature fiber spectrometer,a complete calibration scheme was obtained based on the standard emission spectrum of mercury and argon lamp and three-order linear fitting of the least squares.Calibration results show that the arithmetic mean error is less than 0.167nm,standard deviation is less than 0.217nm and the fitting related degree is high.Test results show that after calibration the wavelength uncertainty is better than the 0.11nm,the error is less than 0.15nm,and the wavelength repeatability can reach 0.01nm.This result is beneficial for improving the measurement precision of spectrometers in the practical applications.
2012, 36(5): 686-688.
doi: 10.3969/j.issn.1001-3806.2012.05.028
Abstract:
In order to save the rare iceland and output two parallel polarized beams,a new type of bireflective parallel beam splitter combined of iceland and glass was designed.Two main parts of the prism are made of iceland and optical glass,and the glue is bromonaphthalene.The theoretical analysis shows that the suitable choices of structural angles can guarantee that two polarized beams whose directions of electric vector are orthogonal can escape vertically to the same exit widow after their total reflection on cemented surface and back surface respectively.The experiments indicate that the transmittance of the prism is more than 80%,the extinction ratio of o light is better than 10－5,and that of e light is better than 10－3.Therefore,that the prism still has good performance on the premise of the less iceland and it will have more chance to be applied.
In order to save the rare iceland and output two parallel polarized beams,a new type of bireflective parallel beam splitter combined of iceland and glass was designed.Two main parts of the prism are made of iceland and optical glass,and the glue is bromonaphthalene.The theoretical analysis shows that the suitable choices of structural angles can guarantee that two polarized beams whose directions of electric vector are orthogonal can escape vertically to the same exit widow after their total reflection on cemented surface and back surface respectively.The experiments indicate that the transmittance of the prism is more than 80%,the extinction ratio of o light is better than 10－5,and that of e light is better than 10－3.Therefore,that the prism still has good performance on the premise of the less iceland and it will have more chance to be applied.
2012, 36(5): 689-692.
doi: 10.3969/j.issn.1001-3806.2012.05.029
Abstract:
In order to realize wind field multipoint and remote sensing,make it convenient to monitor wind speed and set up the internet of thing of wind field velocity,an all-fiber wind velocity sensor fabric was introduced with a wind-cup to modulate fiber Bragg grating wavelength,so that the wind velocity can be obtained based on the wavelength changing frequency.Design scheme was described in detail.Fabrication process of the probe was introduced emphatically and some experimental data were also presented.The results show that the system works stably and reliably.The system can achieve a location precision of 0.16m/s and this system is very suitable for large wind power generation in consideration of its large-capacity.
In order to realize wind field multipoint and remote sensing,make it convenient to monitor wind speed and set up the internet of thing of wind field velocity,an all-fiber wind velocity sensor fabric was introduced with a wind-cup to modulate fiber Bragg grating wavelength,so that the wind velocity can be obtained based on the wavelength changing frequency.Design scheme was described in detail.Fabrication process of the probe was introduced emphatically and some experimental data were also presented.The results show that the system works stably and reliably.The system can achieve a location precision of 0.16m/s and this system is very suitable for large wind power generation in consideration of its large-capacity.
2012, 36(5): 693-695.
doi: 10.3969/j.issn.1001-3806.2012.05.030
Abstract:
In order to design a simulation system for shooting training of small arms,based on laser modulation technology,a simulation target was designed with TSOP34838 chip as optical receiving device.A filter membrane was used to solve the problem that ordinary laser spot is too large,the hardware was simplified with array multi-channel signals detection method,multi-channel data were collected quickly and easily.This system can identifying off-target situation,and increase the fidelity by setting the vibration sensor.The simulation system uses wireless communication,has advantages of simple operation,high stability,properly handling details and practicality.
In order to design a simulation system for shooting training of small arms,based on laser modulation technology,a simulation target was designed with TSOP34838 chip as optical receiving device.A filter membrane was used to solve the problem that ordinary laser spot is too large,the hardware was simplified with array multi-channel signals detection method,multi-channel data were collected quickly and easily.This system can identifying off-target situation,and increase the fidelity by setting the vibration sensor.The simulation system uses wireless communication,has advantages of simple operation,high stability,properly handling details and practicality.
2012, 36(5): 696-699.
doi: 10.3969/j.issn.1001-3806.2012.05.031
Abstract:
In order to study the conversion efficiency of monocrystalline silicon solar cell under laser irradiation,a method to calculate the efficiency of ideal solar cells under laser light was put forward based on the method usually used under solar spectrum.Analytical expressions and experimental measurements were used to describe the relation between the conversion efficiency and laser wavelength,incident intensity and ambient temperature,etcetera.Research shows that,under the laser light conversion efficiency will be improved obviously,the maximum conversion efficiency is up to 27.7%.All of these have certain reference value to the application of laser power transmission.
In order to study the conversion efficiency of monocrystalline silicon solar cell under laser irradiation,a method to calculate the efficiency of ideal solar cells under laser light was put forward based on the method usually used under solar spectrum.Analytical expressions and experimental measurements were used to describe the relation between the conversion efficiency and laser wavelength,incident intensity and ambient temperature,etcetera.Research shows that,under the laser light conversion efficiency will be improved obviously,the maximum conversion efficiency is up to 27.7%.All of these have certain reference value to the application of laser power transmission.
2012, 36(5): 700-703.
doi: 10.3969/j.issn.1001-3806.2012.05.032
Abstract:
In order to analyze the spectral propagating properties of laser beam,spectral propagation equations of Gaussian beam propagating through free space and turbulent atmosphere were derived according to the extended Huygens-Fresnel formula,and then numerical simulation was carried out for the beam with center frequency 1.78×1015rad/s and bandwidth 8.39×1013rad/s.Results indicate that when Gaussian beam propagating through free space and turbulent atmosphere,spectrum blue-shifted exists at the scopes of near-axis and red-shifted happens if the distance from z-axis increases to a critical value.Turbulent atmosphere has the ability to reduce spectrum shift for off-axis scope,and increase of spectrum bandwidth in source can make spectrum shift phenomena more obvious.Intensity distribution vertical to z-axis at 5000m for Gaussian beams with frequency 1.78×1015rad/s and 1.75×1015rad/s shows that,for a fixed position light intensity of center frequency becomes weaker than intensity of some other frequency,and this can leads to spectral shift,besides,the phenomena of spectral changing with some parameters can be explained with the theories of Gaussian beam propagation and turbulent atmosphere beam width-spreading effect.
In order to analyze the spectral propagating properties of laser beam,spectral propagation equations of Gaussian beam propagating through free space and turbulent atmosphere were derived according to the extended Huygens-Fresnel formula,and then numerical simulation was carried out for the beam with center frequency 1.78×1015rad/s and bandwidth 8.39×1013rad/s.Results indicate that when Gaussian beam propagating through free space and turbulent atmosphere,spectrum blue-shifted exists at the scopes of near-axis and red-shifted happens if the distance from z-axis increases to a critical value.Turbulent atmosphere has the ability to reduce spectrum shift for off-axis scope,and increase of spectrum bandwidth in source can make spectrum shift phenomena more obvious.Intensity distribution vertical to z-axis at 5000m for Gaussian beams with frequency 1.78×1015rad/s and 1.75×1015rad/s shows that,for a fixed position light intensity of center frequency becomes weaker than intensity of some other frequency,and this can leads to spectral shift,besides,the phenomena of spectral changing with some parameters can be explained with the theories of Gaussian beam propagation and turbulent atmosphere beam width-spreading effect.
2012, 36(5): 704-707.
doi: 10.3969/j.issn.1001-3806.2012.05.033
Abstract:
To realize the electromechanical integration of the laser and operating platform and bring convenience to the user,a design of computerized numerical control system for laser peening based on motion control card was presented.PC achieved the control to the core part of system,the motion control card and the single-chip microcomputer achieved the control to the details.Then the structure of the hardware and the partition of the software were reviewed.The system is proved to be flexible,open and easy for expansion by experiments.
To realize the electromechanical integration of the laser and operating platform and bring convenience to the user,a design of computerized numerical control system for laser peening based on motion control card was presented.PC achieved the control to the core part of system,the motion control card and the single-chip microcomputer achieved the control to the details.Then the structure of the hardware and the partition of the software were reviewed.The system is proved to be flexible,open and easy for expansion by experiments.
2012, 36(5): 708-712.
doi: 10.3969/j.issn.1001-3806.2012.05.034
Abstract:
Based on the quantum theory and numerical calculation,the fidelities of quantum states were investigated in intensity-dependent Jaynes-Cummings model containing atomic motion under the interaction of coherent field.The analytical expressions of the fidelities of quantum states were derived and simulation results were obtained.In addition,the influence of atomic motion and the field mode structure on the fidelities of quantum states of the system in different atomic initial states was discussed.The results indicate that both the atomic motion and the field mode structure can modulate the fidelities of quantum states in the system of interaction.The greater the velocities of atomic motion,the higher the fidelities of the three systems are.On the other hand,the larger the field mode structures,the higher fidelity of the three systems.The results are meaningful for the development of quantum communication and quantum calculation.
Based on the quantum theory and numerical calculation,the fidelities of quantum states were investigated in intensity-dependent Jaynes-Cummings model containing atomic motion under the interaction of coherent field.The analytical expressions of the fidelities of quantum states were derived and simulation results were obtained.In addition,the influence of atomic motion and the field mode structure on the fidelities of quantum states of the system in different atomic initial states was discussed.The results indicate that both the atomic motion and the field mode structure can modulate the fidelities of quantum states in the system of interaction.The greater the velocities of atomic motion,the higher the fidelities of the three systems are.On the other hand,the larger the field mode structures,the higher fidelity of the three systems.The results are meaningful for the development of quantum communication and quantum calculation.
2012, 36(5): 627-631.
doi: 10.3969/j.issn.1001-3806.2012.05.013
Abstract:
The VC-WxC particulate reinforced Ni-based coating was successfully in-situ synthesized by laser cladding on steel 45# substrates.The micro-structural and metallographic analyses were performed with a scanning electron microscopy,energy-dispersive spectrometer and X-ray diffractometer.The microhardness and wear-resistance of the coatings were investigated.It is indicated that a good finish VC-WxC reinforced composite coating can be reached at a suitable processing parameters.The microstructure at the bottom of the cladding layer mainly consists of oriented dendrites of γ(NiFe),and the microstructure at the center and upper zones contains VC,W2C,WC and Cr3C2 phase dispersed in the matrix of γ(NiFe)solid solution.The in-situ synthesized VC-WxC reinforced Ni-based coating gives very high hardness of HV0.3 1400 and excellent wear resistance,which is six times as that of Ni60 coatings.The results show that the improvement in hardness and wear resistance of the layer is due to the in-situ synthesis of VC,W2C,WC and Cr3C2,its homogenous distribution in the clad layer.
The VC-WxC particulate reinforced Ni-based coating was successfully in-situ synthesized by laser cladding on steel 45# substrates.The micro-structural and metallographic analyses were performed with a scanning electron microscopy,energy-dispersive spectrometer and X-ray diffractometer.The microhardness and wear-resistance of the coatings were investigated.It is indicated that a good finish VC-WxC reinforced composite coating can be reached at a suitable processing parameters.The microstructure at the bottom of the cladding layer mainly consists of oriented dendrites of γ(NiFe),and the microstructure at the center and upper zones contains VC,W2C,WC and Cr3C2 phase dispersed in the matrix of γ(NiFe)solid solution.The in-situ synthesized VC-WxC reinforced Ni-based coating gives very high hardness of HV0.3 1400 and excellent wear resistance,which is six times as that of Ni60 coatings.The results show that the improvement in hardness and wear resistance of the layer is due to the in-situ synthesis of VC,W2C,WC and Cr3C2,its homogenous distribution in the clad layer.
