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RSS2007 Vol. 31, No. 3
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2007, 31(3): 225-227.
[Abstract]
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Abstract:
For the propose of finding high energy mid-infrared laser output,a compound cavity kalium titanyl arsenate(KTA) optical parametric oscillator(OPO) pumped by an electro-optic Q-switched flash-lamp-pumped 1064nm Nd:YAG laser was experimentally studied.Single pulse energy of 36mJ of the OPO was obtained at a repetition rate of 1Hz,where the idler pulse energy was 11mJ at 3407nm wavelength with pulse width of 10ns.The pulse energy decreased with increasing the repetition rate within the range of 5Hz~40Hz.The experimental result shows that the compound cavity pumping technology has the advantage of enhancing conversion efficiency and reducing oscillator threshold.With a mid-infrared image apparatus illuminated by the OPO,the laser spot was observed from the monitor of the image system.This result is useful for mid-infrared laser study.
For the propose of finding high energy mid-infrared laser output,a compound cavity kalium titanyl arsenate(KTA) optical parametric oscillator(OPO) pumped by an electro-optic Q-switched flash-lamp-pumped 1064nm Nd:YAG laser was experimentally studied.Single pulse energy of 36mJ of the OPO was obtained at a repetition rate of 1Hz,where the idler pulse energy was 11mJ at 3407nm wavelength with pulse width of 10ns.The pulse energy decreased with increasing the repetition rate within the range of 5Hz~40Hz.The experimental result shows that the compound cavity pumping technology has the advantage of enhancing conversion efficiency and reducing oscillator threshold.With a mid-infrared image apparatus illuminated by the OPO,the laser spot was observed from the monitor of the image system.This result is useful for mid-infrared laser study.
2007, 31(3): 228-231,241.
Abstract:
For the purpose of evaluating the performance of combined optical diode lasers,two approaches estimating beam propagation factor were analyzed.One was similar to the approach used in the traditional diode stack,calculating the beam width based on the geometry optics,the other was based on the similar Gaussian model of the emitter calculating the beam width by the definition of the second order moment of intensity distribution.Finally the dependence of the M2 factor of the output beam on the number of the diode bars and the number of emitters per bar was deduced.An experiment on a three-bar combined optical diode laser was carried out,with output power of 120W,power density of 209W/cm2,average pitch of 1.1mm,and total beam propagation ratio M2=197.The two approaches were compared through the experiment.The analysis results show that both these approaches are available in estimating the output beam quality of the optical combination diode lasers.
For the purpose of evaluating the performance of combined optical diode lasers,two approaches estimating beam propagation factor were analyzed.One was similar to the approach used in the traditional diode stack,calculating the beam width based on the geometry optics,the other was based on the similar Gaussian model of the emitter calculating the beam width by the definition of the second order moment of intensity distribution.Finally the dependence of the M2 factor of the output beam on the number of the diode bars and the number of emitters per bar was deduced.An experiment on a three-bar combined optical diode laser was carried out,with output power of 120W,power density of 209W/cm2,average pitch of 1.1mm,and total beam propagation ratio M2=197.The two approaches were compared through the experiment.The analysis results show that both these approaches are available in estimating the output beam quality of the optical combination diode lasers.
2007, 31(3): 232-234,245.
Abstract:
The crystal-length and acceptance parameters of biaxial crystals KTP and LBO used to generate 589nm radiation by means of sum frequency generation(SFG) of 1064nm and 1319nm lasers is analyzed.According to the nonlinear wave-coupling equation of SFG,the exact solutions of low and high power conversion are derived and validated in SFG.On the basis of the solutions,the relationship between power density and crystal-length is given.Acceptance parameters of biaxial crystals are derived and validated from phase matching condition of SFG by means of Taylor expansion.The properties of non-critical phase matching(NCPM) is put forward.It can be seen that sum-frequency conversion efficiency could be increased with appropriate crystal-length,type-ⅠLBO and type-ⅡA KTP are much better and NCPM can be attained for LBO at 32.84℃.
The crystal-length and acceptance parameters of biaxial crystals KTP and LBO used to generate 589nm radiation by means of sum frequency generation(SFG) of 1064nm and 1319nm lasers is analyzed.According to the nonlinear wave-coupling equation of SFG,the exact solutions of low and high power conversion are derived and validated in SFG.On the basis of the solutions,the relationship between power density and crystal-length is given.Acceptance parameters of biaxial crystals are derived and validated from phase matching condition of SFG by means of Taylor expansion.The properties of non-critical phase matching(NCPM) is put forward.It can be seen that sum-frequency conversion efficiency could be increased with appropriate crystal-length,type-ⅠLBO and type-ⅡA KTP are much better and NCPM can be attained for LBO at 32.84℃.
2007, 31(3): 235-237.
Abstract:
In order to study the characteristics of superimposed multi-wavelength fiber Bragg gratings,the coupled-mode theory of the superimposed multi-wavelength fiber Bragg gratings was presented and the numerical analysis result about the reflected spectra and time delay of 4 and 8 wavelengths superimposed FBG whose wavelength gap equals to 1.6nm was obtained.The reflected spectra of 8 wavelength superimposed FBG whose wavelength gap equal to 0.4nm is designed.The numerical result was in good agreement with the experimental results.The result show that the coupled-mode theory of the superimposed multi-wavelength fiber Bragg gratings is reliable,which can be used to analyze the characteristics of superimposed multi-wavelength fiber Bragg gratings and is conducive to the design and fabrication of superimposed multi-wavelength fiber Bragg gratings.
In order to study the characteristics of superimposed multi-wavelength fiber Bragg gratings,the coupled-mode theory of the superimposed multi-wavelength fiber Bragg gratings was presented and the numerical analysis result about the reflected spectra and time delay of 4 and 8 wavelengths superimposed FBG whose wavelength gap equals to 1.6nm was obtained.The reflected spectra of 8 wavelength superimposed FBG whose wavelength gap equal to 0.4nm is designed.The numerical result was in good agreement with the experimental results.The result show that the coupled-mode theory of the superimposed multi-wavelength fiber Bragg gratings is reliable,which can be used to analyze the characteristics of superimposed multi-wavelength fiber Bragg gratings and is conducive to the design and fabrication of superimposed multi-wavelength fiber Bragg gratings.
2007, 31(3): 238-241.
Abstract:
In order to calculate the accurate temperature distribution of a side-pumping laser rod,a nonuniform heat generation model of quasi-gaussian profile is proposed.Approximate analytical expression of the temperature distribution of the laser rod is derived.This model is more practical than the uniform model reported before and it can meet a wide situation of the diode side-pumped laser system.With this model,the thermal stress,thermal lens,and other thermal effects in a laser rod can be easily calculated.
In order to calculate the accurate temperature distribution of a side-pumping laser rod,a nonuniform heat generation model of quasi-gaussian profile is proposed.Approximate analytical expression of the temperature distribution of the laser rod is derived.This model is more practical than the uniform model reported before and it can meet a wide situation of the diode side-pumped laser system.With this model,the thermal stress,thermal lens,and other thermal effects in a laser rod can be easily calculated.
2007, 31(3): 242-245.
Abstract:
In order to break through the power restriction in IOC(intersatellite optical communication),the electrodes of MgO:LiNbO3 was optimally designed based on quasistatic conformal transformation theory in the background of IOC.The propagation of optical field with high input power was simulated.The effect of nonlinearity on modulator was analyzed and finally the maximum input power was determined.The research is significative for high power laser modulation field,such as IOC.
In order to break through the power restriction in IOC(intersatellite optical communication),the electrodes of MgO:LiNbO3 was optimally designed based on quasistatic conformal transformation theory in the background of IOC.The propagation of optical field with high input power was simulated.The effect of nonlinearity on modulator was analyzed and finally the maximum input power was determined.The research is significative for high power laser modulation field,such as IOC.
2007, 31(3): 246-249.
Abstract:
To study the efficient broadband third-harmonic generation(THG) technology,the process in CsLiB6O10(CLBO) crystals was studied through numerical simulation based on split-step Fourier transformation and the fourth-order Runge-Kutta method.The dependence of conversion efficiency on input intensity and bandwidth of 1ω waves was analyzed in type-Ⅰ/type-Ⅱ and type-Ⅰ/type-Ⅱ/type-Ⅰ quadrature schemes respectively.As a comparison,broadband THG in KDP crystals was also investigated.Conversion efficiency up to 60% with a bandwidth of 650GHz was achieved in the type-Ⅰ/type-Ⅱ/type-Ⅰ quadrature scheme while the temporal profile of 1ω was assumed to be super-Gaussian(40,exponent) with an intensity of 3GW/cm2.An increase of 250GHz was accomplished in CLBO crystals compared with that in KDP crystals.The obtained results show that broadband THG conversion efficiency can be improved availably in the type-Ⅰ/type-Ⅱ/type-Ⅰ quadrature scheme with CLBO crystals.
To study the efficient broadband third-harmonic generation(THG) technology,the process in CsLiB6O10(CLBO) crystals was studied through numerical simulation based on split-step Fourier transformation and the fourth-order Runge-Kutta method.The dependence of conversion efficiency on input intensity and bandwidth of 1ω waves was analyzed in type-Ⅰ/type-Ⅱ and type-Ⅰ/type-Ⅱ/type-Ⅰ quadrature schemes respectively.As a comparison,broadband THG in KDP crystals was also investigated.Conversion efficiency up to 60% with a bandwidth of 650GHz was achieved in the type-Ⅰ/type-Ⅱ/type-Ⅰ quadrature scheme while the temporal profile of 1ω was assumed to be super-Gaussian(40,exponent) with an intensity of 3GW/cm2.An increase of 250GHz was accomplished in CLBO crystals compared with that in KDP crystals.The obtained results show that broadband THG conversion efficiency can be improved availably in the type-Ⅰ/type-Ⅱ/type-Ⅰ quadrature scheme with CLBO crystals.
2007, 31(3): 250-252,256.
Abstract:
To study the influence of the different CuO concentration rates on the resonance angle,a novel surface plasmon resonance(SPR) optical sensor coated a combined Ag and SnO2(dropped by CuO) film is proposed.Four-layer films Ag(50nm),SnO2(50nm),CuO and SnO2(50nm) were prepared deposition on rutile prism in turn by means of RF-reactive-sputtering,and the thickness of the CuO was various with the concentration rate,and the combined film was formed after being annealed.The SPR experiments show that,when the concentration rates of the CuO are 0,0.01 and 0.05,the resonance angles are 59.61°,60.52°和61.3°,respectively.The faster concentration rate of the CuO,the larger of the resonance angle.
To study the influence of the different CuO concentration rates on the resonance angle,a novel surface plasmon resonance(SPR) optical sensor coated a combined Ag and SnO2(dropped by CuO) film is proposed.Four-layer films Ag(50nm),SnO2(50nm),CuO and SnO2(50nm) were prepared deposition on rutile prism in turn by means of RF-reactive-sputtering,and the thickness of the CuO was various with the concentration rate,and the combined film was formed after being annealed.The SPR experiments show that,when the concentration rates of the CuO are 0,0.01 and 0.05,the resonance angles are 59.61°,60.52°和61.3°,respectively.The faster concentration rate of the CuO,the larger of the resonance angle.
2007, 31(3): 253-256.
Abstract:
To get higher laser output,the temperature distribution of a pulsed 2kJ high energy Nd:glass solid-state laser was numerically studied by means of finite difference under two thermal management methods,i.e.,the traditional method with a fixed cooling water temperature,and the novel method with an altering water temperature.It is shown that the temperature gradient in the laser rod can be limited to a low level and higher energy could be outputted if the novel thermal management method employed.
To get higher laser output,the temperature distribution of a pulsed 2kJ high energy Nd:glass solid-state laser was numerically studied by means of finite difference under two thermal management methods,i.e.,the traditional method with a fixed cooling water temperature,and the novel method with an altering water temperature.It is shown that the temperature gradient in the laser rod can be limited to a low level and higher energy could be outputted if the novel thermal management method employed.
2007, 31(3): 257-261.
Abstract:
Based on the impulse coupling process between laser and target,a new method of combining pendulum with light electric tachometer was presented,which was adopted in the experiment of impulse coupling between laser supported detonation wave and aluminum target.Considering the air buoyancy,air friction and the pendulum line weight,the actual kinetic equation of pendulum was deduced from the principle of work and power and the rotation theory when the reasonable model of air friction was found.Furthermore,the precision of the kinetic equation of pendulum was checked.Finally,after comparison,the experimental result with the new methodwas in agreement with the experimental result from other methods.
Based on the impulse coupling process between laser and target,a new method of combining pendulum with light electric tachometer was presented,which was adopted in the experiment of impulse coupling between laser supported detonation wave and aluminum target.Considering the air buoyancy,air friction and the pendulum line weight,the actual kinetic equation of pendulum was deduced from the principle of work and power and the rotation theory when the reasonable model of air friction was found.Furthermore,the precision of the kinetic equation of pendulum was checked.Finally,after comparison,the experimental result with the new methodwas in agreement with the experimental result from other methods.
2007, 31(3): 262-264.
Abstract:
In the process of excimer ablation,the template in different sizes should be changed to get different structure,which not only interrupts the continuity of the experiment but also disturbs the results if other equipments are touched when changing the templates.In order not to change the template time and again and reduce the influence to ensure the continuity and the reliability,a zoom lens was designed with the software of ZEMAX based on the zoom lens theory and was introduced to the machining system instead of normal lens.At last its imaging quality was analyzed.The simulation result proved that the system could get satisfactory results and its minification could be changed continuosly from 0.15 to 0.24.In this case many structures were obtained in this range at the same status and the other templates were not needed.Because the templates are not need to be displaced time and again,the results in the experiment are reliable.The technology using zoom lens instead of normal lens in the ablation by excimer laser is of great feasible.
In the process of excimer ablation,the template in different sizes should be changed to get different structure,which not only interrupts the continuity of the experiment but also disturbs the results if other equipments are touched when changing the templates.In order not to change the template time and again and reduce the influence to ensure the continuity and the reliability,a zoom lens was designed with the software of ZEMAX based on the zoom lens theory and was introduced to the machining system instead of normal lens.At last its imaging quality was analyzed.The simulation result proved that the system could get satisfactory results and its minification could be changed continuosly from 0.15 to 0.24.In this case many structures were obtained in this range at the same status and the other templates were not needed.Because the templates are not need to be displaced time and again,the results in the experiment are reliable.The technology using zoom lens instead of normal lens in the ablation by excimer laser is of great feasible.
2007, 31(3): 265-267,280.
Abstract:
Light transmitted properties of chicken muscle tissue are experimentally measured under the condition of far field.And the results show that slice muscle tissue can make the incident laser beam generate obvious diffraction phenomena.In order to interpret the experimental results,the radiative transfer theory is modified and the diffraction effects are considered in the modified theory.According to the modified model,theoretical calculation is executed for light transmitted properties of chicken muscle tissues and the result is well matched with the experimental results.
Light transmitted properties of chicken muscle tissue are experimentally measured under the condition of far field.And the results show that slice muscle tissue can make the incident laser beam generate obvious diffraction phenomena.In order to interpret the experimental results,the radiative transfer theory is modified and the diffraction effects are considered in the modified theory.According to the modified model,theoretical calculation is executed for light transmitted properties of chicken muscle tissues and the result is well matched with the experimental results.
2007, 31(3): 268-270,273.
Abstract:
A theoretical investigation with the method of splitstep Fourier was presented on the propagation of a picosecond pulse in photonic crystal fibers.The effect of initial chirp and power on pulse compression was simulated and analyzed.It was found that the compression factor and the compression quality factor increased with initial chirp and power,but optimum fiber length decreased.When the values of initial chirp and power were small,the compression factor and the compression quality factor didn't simultaneously achieve the optimum value.If an appropriate optical fiber length and initial peak power was selected,efficient pulse compression could be attained in photonic crystal fibers.
A theoretical investigation with the method of splitstep Fourier was presented on the propagation of a picosecond pulse in photonic crystal fibers.The effect of initial chirp and power on pulse compression was simulated and analyzed.It was found that the compression factor and the compression quality factor increased with initial chirp and power,but optimum fiber length decreased.When the values of initial chirp and power were small,the compression factor and the compression quality factor didn't simultaneously achieve the optimum value.If an appropriate optical fiber length and initial peak power was selected,efficient pulse compression could be attained in photonic crystal fibers.
2007, 31(3): 271-273.
Abstract:
In order to discuss the influence of the nonlinear gain saturation on the ultrashort pulses generated from self mode-locked lasers,the differential equations describing the output of this kind of lasers were analyzed by means of Liapunov linear stability theory.It was found that two stationary self mode-locked states appear simultaneously in the laser when the gain saturation energy is lower than a critical value.Only the state with lower energy is stable.With the gain saturation energy increasing,the energy of the stable stationary state increase and its pulse width is shortened,and it should be the working state of the self mode-locked lasers.
In order to discuss the influence of the nonlinear gain saturation on the ultrashort pulses generated from self mode-locked lasers,the differential equations describing the output of this kind of lasers were analyzed by means of Liapunov linear stability theory.It was found that two stationary self mode-locked states appear simultaneously in the laser when the gain saturation energy is lower than a critical value.Only the state with lower energy is stable.With the gain saturation energy increasing,the energy of the stable stationary state increase and its pulse width is shortened,and it should be the working state of the self mode-locked lasers.
2007, 31(3): 274-276.
Abstract:
In order to obtain more exact analytical solution to study the output characteristics of double-clad fiber lasers,according to the continuous-wave rate equations of fiber lasers,using typical parameters of double-clad fiber lasers(DCFLs),the contribution of the re-emission effect arising from the interaction between the upper-level atoms and pump light was estimated.Taking into account the predominant part of the re-emission to improve the accuracy of the integration approximated rate equations,the integration of the product of the loss and radiation should be found and explicit analytical expressions for the output of the DCFLs and gradient efficiency of the pump radiation,were deduced,and certain issues of concern were discussed.As an example,for laser wavelength 1090nm,if the pump wavelength is 915nm,920nm,and 975nm,respectively,the gradient efficiency of 975nm is the maximum and it is about 87%.The result shows that the analytical solutions are fit to investigate the output characteristics of fiber lasers extending the application range.
In order to obtain more exact analytical solution to study the output characteristics of double-clad fiber lasers,according to the continuous-wave rate equations of fiber lasers,using typical parameters of double-clad fiber lasers(DCFLs),the contribution of the re-emission effect arising from the interaction between the upper-level atoms and pump light was estimated.Taking into account the predominant part of the re-emission to improve the accuracy of the integration approximated rate equations,the integration of the product of the loss and radiation should be found and explicit analytical expressions for the output of the DCFLs and gradient efficiency of the pump radiation,were deduced,and certain issues of concern were discussed.As an example,for laser wavelength 1090nm,if the pump wavelength is 915nm,920nm,and 975nm,respectively,the gradient efficiency of 975nm is the maximum and it is about 87%.The result shows that the analytical solutions are fit to investigate the output characteristics of fiber lasers extending the application range.
2007, 31(3): 277-280.
Abstract:
The transfer matrix method was used to simulate the transmission characteristics of 1-D photonic crystal.Furthermore,it was also studied how the defect layer thickness affects the defect mode polarization properties.The results shew that the variance of incident angle had significant influence on the forbidden band and defect mode of 1-D photonic crystal,both of which shifted in the direction of high frequency(low wavelength) with the incident angle increasing.The forbidden band width of s polarization increased gradually but that of p polarization changed little.The defect mode frequency of p polarization shifted a little more than that of s polarization.When the incident angle increased,the defect mode of s polarization became narrow more and more and its quality factor increases gradually,nevertheless,the defect mode of p polarization changes the other way round.
The transfer matrix method was used to simulate the transmission characteristics of 1-D photonic crystal.Furthermore,it was also studied how the defect layer thickness affects the defect mode polarization properties.The results shew that the variance of incident angle had significant influence on the forbidden band and defect mode of 1-D photonic crystal,both of which shifted in the direction of high frequency(low wavelength) with the incident angle increasing.The forbidden band width of s polarization increased gradually but that of p polarization changed little.The defect mode frequency of p polarization shifted a little more than that of s polarization.When the incident angle increased,the defect mode of s polarization became narrow more and more and its quality factor increases gradually,nevertheless,the defect mode of p polarization changes the other way round.
2007, 31(3): 281-284,329.
Abstract:
The laser-induced cavitation bubble collapse sound waves during the high-power laser and matter interaction in liquid were experimentally investigated.Laser-induced cavitation bubble collapse sound waves at different conditions were measured with a piezoelectric transducer hydrophone in the experiments,and the signals of sound waves were analyzed based on fast Fourier transform.The investigation results showed the frequency varied with the radius of laser-generated bubble,i.e,the bigger the radius,and the lower the frequency.The results are valuable for theoretical and practical research in cavitation noise.
The laser-induced cavitation bubble collapse sound waves during the high-power laser and matter interaction in liquid were experimentally investigated.Laser-induced cavitation bubble collapse sound waves at different conditions were measured with a piezoelectric transducer hydrophone in the experiments,and the signals of sound waves were analyzed based on fast Fourier transform.The investigation results showed the frequency varied with the radius of laser-generated bubble,i.e,the bigger the radius,and the lower the frequency.The results are valuable for theoretical and practical research in cavitation noise.
2007, 31(3): 285-287.
Abstract:
In order to modify the deviation angle of ultraviolet polarizing prism of iceland crystal and barium fluoride,a new design was given by changing the structure angle of the iceland crystal.The relation between modified angle and structure angle was given at 303nm,and the relation of the deviation angle with wavelength was also investigated.The results obtained by the mathematical software ORIGIN 7.0 indicated that the deviation angle was less than 0.04° in the range of 240nm~410nm.
In order to modify the deviation angle of ultraviolet polarizing prism of iceland crystal and barium fluoride,a new design was given by changing the structure angle of the iceland crystal.The relation between modified angle and structure angle was given at 303nm,and the relation of the deviation angle with wavelength was also investigated.The results obtained by the mathematical software ORIGIN 7.0 indicated that the deviation angle was less than 0.04° in the range of 240nm~410nm.
2007, 31(3): 288-290,294.
Abstract:
In order to improve quality of reconstructed images,the common algorithms used to reconstruct digital holograms was studied by means of comparison.According to the theorems of holography and linear system,the reconstructing methods of the off-axis lens-less Fourier transform hologram by Fresnel diffraction formula and by the convolution method based on Rayleigh-Sommerfeld diffraction integral were studied through simulation.The results show that Fresnel diffraction formula is still correct within very short recording distance,although the traditional Fresnel approximate condition isn't fulfilled.The characters of the fast Fourier transform of the free space impulse response are different at different distance,so the quality of the reconstructed image by the convolution isn't perfect.For the microscopy by off-axis lensless Fourier transform holography,Fresnel reconstructing method is better than the convolution method.
In order to improve quality of reconstructed images,the common algorithms used to reconstruct digital holograms was studied by means of comparison.According to the theorems of holography and linear system,the reconstructing methods of the off-axis lens-less Fourier transform hologram by Fresnel diffraction formula and by the convolution method based on Rayleigh-Sommerfeld diffraction integral were studied through simulation.The results show that Fresnel diffraction formula is still correct within very short recording distance,although the traditional Fresnel approximate condition isn't fulfilled.The characters of the fast Fourier transform of the free space impulse response are different at different distance,so the quality of the reconstructed image by the convolution isn't perfect.For the microscopy by off-axis lensless Fourier transform holography,Fresnel reconstructing method is better than the convolution method.
2007, 31(3): 291-294.
Abstract:
The correlative experimental techniques of SESAM mode-locked OP-VECSELS were analyzed,and the latest results of relevant researches were introduced.
The correlative experimental techniques of SESAM mode-locked OP-VECSELS were analyzed,and the latest results of relevant researches were introduced.
2007, 31(3): 295-297,305.
Abstract:
In order to validate the approximate algorithm of Collins' formula,the diffraction images for a light wave that passes a thin lens from a quadrate aperture were evaluated numerically and compared with the experimental results.It is shown that the experimental results are in agreement with the computation results.Therefore,this approximate method is applied to the measurement of the lens focus,and the focus error between the approximate method and traditional method is less than 1%.
In order to validate the approximate algorithm of Collins' formula,the diffraction images for a light wave that passes a thin lens from a quadrate aperture were evaluated numerically and compared with the experimental results.It is shown that the experimental results are in agreement with the computation results.Therefore,this approximate method is applied to the measurement of the lens focus,and the focus error between the approximate method and traditional method is less than 1%.
2007, 31(3): 298-300,321.
Abstract:
Based on the numerical simulation method for solving the steady-state rate equations that describe the pump,laser and Stokes waves,the dependence of Raman effects on the parameter of high power Yb3+-doped double-clad fiber laser was investigated.The distribution of laser power and Stokes power along the fiber,and the relation between the threshold pump power for the generation of the stimulated Raman scattering(SRS) and the parameter of fiber laser were obtained.Numerical results show that the threshold pump power for the generation of SRS can be improved,and the Raman effects can be effectively suppressed by using large mode area fiber,shortening the cavity length,reducing the emission cross-section of Yb3+ at the Stokes wavelength and adopting a longer lasing wavelength.
Based on the numerical simulation method for solving the steady-state rate equations that describe the pump,laser and Stokes waves,the dependence of Raman effects on the parameter of high power Yb3+-doped double-clad fiber laser was investigated.The distribution of laser power and Stokes power along the fiber,and the relation between the threshold pump power for the generation of the stimulated Raman scattering(SRS) and the parameter of fiber laser were obtained.Numerical results show that the threshold pump power for the generation of SRS can be improved,and the Raman effects can be effectively suppressed by using large mode area fiber,shortening the cavity length,reducing the emission cross-section of Yb3+ at the Stokes wavelength and adopting a longer lasing wavelength.
2007, 31(3): 301-305.
Abstract:
The development of cleaning tiny particle technology by short-pulsed laser is reviewed.At first its research background and basic theoretical model are introduced.Then its applications such as the dry laser cleaning and the steam laser cleaning are described and the influence factors on the cleaning effect are summed up.Finally some predictions of its future development are presented.
The development of cleaning tiny particle technology by short-pulsed laser is reviewed.At first its research background and basic theoretical model are introduced.Then its applications such as the dry laser cleaning and the steam laser cleaning are described and the influence factors on the cleaning effect are summed up.Finally some predictions of its future development are presented.
2007, 31(3): 306-310,313.
Abstract:
The principle of laser ignition,the basic setup and recent progress of laser ignition system were summarized.All the major factors affecting laser ignition were discussed.Then a framework of a minimized multiple-point laser ignition system is presented,and microdectromc machine system(MEMS) device were introduced into laser ignition system,such as MEMS optical switches and MEMS optical splitters,which could enhance the safety and reduce the system size.Finally,all the difficulties and problems involved in laser ignition were offered.A conclusion was made that the future research work should be focused on the theory study of ignition process and the methods to decrease the ignition energy threshold.
The principle of laser ignition,the basic setup and recent progress of laser ignition system were summarized.All the major factors affecting laser ignition were discussed.Then a framework of a minimized multiple-point laser ignition system is presented,and microdectromc machine system(MEMS) device were introduced into laser ignition system,such as MEMS optical switches and MEMS optical splitters,which could enhance the safety and reduce the system size.Finally,all the difficulties and problems involved in laser ignition were offered.A conclusion was made that the future research work should be focused on the theory study of ignition process and the methods to decrease the ignition energy threshold.
2007, 31(3): 311-313.
Abstract:
To cancel the negative influence of the polarization variety of the incident light on a coherent system because,one of the effective methods is to depolarize the incident light.Making use of the characteristic of liquid crystal whose refractive index n along z is various with the deflection orientation of the liquid crystal element,the polarization of the liquid crystal can be arbitrarily controlled by changing the voltage of the liquid crystal and the light can propagate at arbitrary polarization.A new depolarizer composed of two liquid crystal was proposed in the paper.Experimental results show that the liquid crystal depolarizer is insensitive to the polarization state of the incident light and can totally depolarize CW or pulsed monochromatic light with arbitrary polarization states.The depolarizer has the potential to keep the polarization state of the fiber injection laser system of the ICF driver.
To cancel the negative influence of the polarization variety of the incident light on a coherent system because,one of the effective methods is to depolarize the incident light.Making use of the characteristic of liquid crystal whose refractive index n along z is various with the deflection orientation of the liquid crystal element,the polarization of the liquid crystal can be arbitrarily controlled by changing the voltage of the liquid crystal and the light can propagate at arbitrary polarization.A new depolarizer composed of two liquid crystal was proposed in the paper.Experimental results show that the liquid crystal depolarizer is insensitive to the polarization state of the incident light and can totally depolarize CW or pulsed monochromatic light with arbitrary polarization states.The depolarizer has the potential to keep the polarization state of the fiber injection laser system of the ICF driver.
2007, 31(3): 314-316.
Abstract:
In order to find an effectual method of polychromatic light depolarizer and the development of polarization detecting technology,based on wave plate and revolver,the multiplex depolarizer effect on polychromatic light was analyzed by means of Stokes vector and Mueller matrix,the matrix presentation of Stokes vector was obtained.Then the depolarizing mechanism of polychromatic light was represented.The effect of polarized direction of the polarized light and rotation angle of revolver on depolarization was discussed through detailed calculation.The obtained results are useful for design and study about depolarizer device.
In order to find an effectual method of polychromatic light depolarizer and the development of polarization detecting technology,based on wave plate and revolver,the multiplex depolarizer effect on polychromatic light was analyzed by means of Stokes vector and Mueller matrix,the matrix presentation of Stokes vector was obtained.Then the depolarizing mechanism of polychromatic light was represented.The effect of polarized direction of the polarized light and rotation angle of revolver on depolarization was discussed through detailed calculation.The obtained results are useful for design and study about depolarizer device.
2007, 31(3): 317-321.
Abstract:
In order to generate 2μm laser,a novel method was presented with kalium titanyl arsenate(KTA) as a nonlinear crystal in optical parametric oscillators.It was proved feasible by comparing the nonlinear parameters between KTA and KTP crystal.The graph of the relationship between the wavelength and the tunable-angle was drawn based on Sellmeier equation and refractive index ellipsoid of KTA.After compareson it was found that the crystal has better nonlinear characteristic at cut angles of φ=0°,θ=48.37°.Then the walk-off angle,acceptance angle and bandwidth were calculated.The basic problems on the design of KTA-OPO were solved and the study foundation was built up for the future experiments.
In order to generate 2μm laser,a novel method was presented with kalium titanyl arsenate(KTA) as a nonlinear crystal in optical parametric oscillators.It was proved feasible by comparing the nonlinear parameters between KTA and KTP crystal.The graph of the relationship between the wavelength and the tunable-angle was drawn based on Sellmeier equation and refractive index ellipsoid of KTA.After compareson it was found that the crystal has better nonlinear characteristic at cut angles of φ=0°,θ=48.37°.Then the walk-off angle,acceptance angle and bandwidth were calculated.The basic problems on the design of KTA-OPO were solved and the study foundation was built up for the future experiments.
2007, 31(3): 322-325,332.
Abstract:
In order to study binary error diffusion algorithm,computer simulation is used to form grating templates which are used in the phase measuring profilometry.The influence of error distributing coefficients and the number of error diffusion points on the precision of encoding and phase measurement is discussed.The results indicate that with the three familiar kinds of error distributing coefficients,the three corresponding sinusoidal structured illumination formed all have relatively high measurement precision and there isn't obvious diversity among them.The influence of diffusion points number on the precision of encoding and phase measurement is relatively small.According to the experiment,the general error of the system can be controlled within 1% of the equivalent wavelength.As a result,the feasibility and accuracy of binary error diffusion method are proved.
In order to study binary error diffusion algorithm,computer simulation is used to form grating templates which are used in the phase measuring profilometry.The influence of error distributing coefficients and the number of error diffusion points on the precision of encoding and phase measurement is discussed.The results indicate that with the three familiar kinds of error distributing coefficients,the three corresponding sinusoidal structured illumination formed all have relatively high measurement precision and there isn't obvious diversity among them.The influence of diffusion points number on the precision of encoding and phase measurement is relatively small.According to the experiment,the general error of the system can be controlled within 1% of the equivalent wavelength.As a result,the feasibility and accuracy of binary error diffusion method are proved.
2007, 31(3): 326-329.
Abstract:
In order to reduce the deformation of welding parts,optimize welding technics,it is necessary to forecast the thermal field of welding process.It is proved the finite element analysis(FEA) is a good method to resolve the problem.After reviewing the present research of the finite element simulation and theoretical calculation of the laser welding,a physical model for plate welding was built and its temperature field was simulated based on ABAQUS,the modeling and meshing method,boundary conditions and the simulation result were discussed.The simulation results can tell us the temperature of any point of the workpiece at any time.For a 2mm thick A3 steel plate,the simulation results are the highest temperature is 3100℃,the temperature of the point A 4mm distant from the center point of the plate is 150℃ under the condition of 2000W laser power and 20mm/s welding speed,which are in good agreement with experimental results and prove that the FEA can be used to forecast the temperature field of welding process precisely.
In order to reduce the deformation of welding parts,optimize welding technics,it is necessary to forecast the thermal field of welding process.It is proved the finite element analysis(FEA) is a good method to resolve the problem.After reviewing the present research of the finite element simulation and theoretical calculation of the laser welding,a physical model for plate welding was built and its temperature field was simulated based on ABAQUS,the modeling and meshing method,boundary conditions and the simulation result were discussed.The simulation results can tell us the temperature of any point of the workpiece at any time.For a 2mm thick A3 steel plate,the simulation results are the highest temperature is 3100℃,the temperature of the point A 4mm distant from the center point of the plate is 150℃ under the condition of 2000W laser power and 20mm/s welding speed,which are in good agreement with experimental results and prove that the FEA can be used to forecast the temperature field of welding process precisely.
2007, 31(3): 330-332.
Abstract:
In order to repair the clear defects of photomask,a 355nm UV laser with the intensity of 1.3×108W/cm2 is used to induce hexacarbonyls chrome photolysis in the open air,and get the Cr film with good adhesion and extinction on transparent substrate.Results show that,in the open air,the method with high intensity and short radiation time can get high quality film.
In order to repair the clear defects of photomask,a 355nm UV laser with the intensity of 1.3×108W/cm2 is used to induce hexacarbonyls chrome photolysis in the open air,and get the Cr film with good adhesion and extinction on transparent substrate.Results show that,in the open air,the method with high intensity and short radiation time can get high quality film.
2007, 31(3): 333-336.
Abstract:
After analyzing the resources of the system aberration in a four-pass amplification system,it was found that some aberrations which have main influenceon the energy concertration in the far field were caused by the off-axis transmission and tilt of lens.Firstly the influence of the lens tilt at different positions on the system aberration was analyzed with the commercial ZEMAX software.It concludes that the four-pass lens has main influence.Secondly the relation between the tilted angle of this lens and the aberration components was analyzed and compared based on the Fringe-Zernike polynomial.Finally experiments were performed to prove the study reasonable.The conclusion provides guidance to control the wave-front distortion of the output beams and optimize the design of the similar systems.
After analyzing the resources of the system aberration in a four-pass amplification system,it was found that some aberrations which have main influenceon the energy concertration in the far field were caused by the off-axis transmission and tilt of lens.Firstly the influence of the lens tilt at different positions on the system aberration was analyzed with the commercial ZEMAX software.It concludes that the four-pass lens has main influence.Secondly the relation between the tilted angle of this lens and the aberration components was analyzed and compared based on the Fringe-Zernike polynomial.Finally experiments were performed to prove the study reasonable.The conclusion provides guidance to control the wave-front distortion of the output beams and optimize the design of the similar systems.
