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RSS2012 Vol. 36, No. 4
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2012, 36(4): 433-437.
doi: 10.3969/j.issn.1001-806.2012.04.001
[Abstract]
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Abstract:
Based on both numerical simulation and experimental investigation,much research work has been done on on-line truing and dressing bronze-bonded diamond grinding wheel by acoustic-optic Q-switched YAG pulsed laser.A 3-D mathematical simulation model and a heat transfer model of single pulsed laser ablating the diamond abrasive was established by means of finite element method,where the process of diamond graphitization was taken into account.The removal depth of the diamond abrasive in different laser parameters(such as focal position,pulse width and laser power) was measured,and the relationship between them was analysed,which helped us to select optimal parameters.The results show that:the laser power,pulse width and the focal position are the direct effects of the removal depth of the diamond abrasive;it will increase along with the increase of laser power,and decrease along with the increase of pulse width and the focal position.The on-line grinding wheel dressing was achieved with closed-loop control,CCD and laser triangulation displacement measuring instrument which were used in control of Q-switch and the on-line monitoring of the circular run-out of the grinding wheel.After laser truing and dressing,the accuracy was further improved,the circular run-out error was reduced,and the surface topography was improved too.
Based on both numerical simulation and experimental investigation,much research work has been done on on-line truing and dressing bronze-bonded diamond grinding wheel by acoustic-optic Q-switched YAG pulsed laser.A 3-D mathematical simulation model and a heat transfer model of single pulsed laser ablating the diamond abrasive was established by means of finite element method,where the process of diamond graphitization was taken into account.The removal depth of the diamond abrasive in different laser parameters(such as focal position,pulse width and laser power) was measured,and the relationship between them was analysed,which helped us to select optimal parameters.The results show that:the laser power,pulse width and the focal position are the direct effects of the removal depth of the diamond abrasive;it will increase along with the increase of laser power,and decrease along with the increase of pulse width and the focal position.The on-line grinding wheel dressing was achieved with closed-loop control,CCD and laser triangulation displacement measuring instrument which were used in control of Q-switch and the on-line monitoring of the circular run-out of the grinding wheel.After laser truing and dressing,the accuracy was further improved,the circular run-out error was reduced,and the surface topography was improved too.
2012, 36(4): 438-440.
doi: 10.3969/j.issn.1001-806.2012.04.002
Abstract:
In order to get a high performance optical switch,a single channel optical switch was designed based on MachZehnder Interferometer,in which a fiber Bragg grating was connected with the end of the interferometer.The output spectrum at 1550nm wavelength was obtained.Theoretical and experiment results show that the single channel optical switch has characteristics of simple structure,easy feasibility and good performance.
In order to get a high performance optical switch,a single channel optical switch was designed based on MachZehnder Interferometer,in which a fiber Bragg grating was connected with the end of the interferometer.The output spectrum at 1550nm wavelength was obtained.Theoretical and experiment results show that the single channel optical switch has characteristics of simple structure,easy feasibility and good performance.
2012, 36(4): 441-444.
doi: 10.3969/j.issn.1001-806.2012.04.003
Abstract:
In order to study the influence of carbides produced by in situ synthesis of various chemical reactions or direct addition on wear resistance of carbide reinforced composite coatings,TiC reinforced Fe-based composite coatings were prepared on T10 steel substrate by laser alloying.Then their microstructures,phases,microhardness and wear properties were investigated and analyzed.Results showed that compact and non-defective alloy layers were obtained,consisting of γ-CrFe7C0.5 and submicron MC(M=Ti,Cr,W) particles.Austenite transformed into martensite in wear testing because of processing hardening.Wear weight loss of direct addition was 2 times to 3 times larger than that of in situ synthesis.The content of carbides produced through combination reaction between Ti and C was higher than that produced through reduction reaction between TiO2 and C,which led to a better tribological performance.The results can serve as a guide in selecting the best method of the ceramic phase introduction when preparing TiC reinforced Fe-based composite coatings.
In order to study the influence of carbides produced by in situ synthesis of various chemical reactions or direct addition on wear resistance of carbide reinforced composite coatings,TiC reinforced Fe-based composite coatings were prepared on T10 steel substrate by laser alloying.Then their microstructures,phases,microhardness and wear properties were investigated and analyzed.Results showed that compact and non-defective alloy layers were obtained,consisting of γ-CrFe7C0.5 and submicron MC(M=Ti,Cr,W) particles.Austenite transformed into martensite in wear testing because of processing hardening.Wear weight loss of direct addition was 2 times to 3 times larger than that of in situ synthesis.The content of carbides produced through combination reaction between Ti and C was higher than that produced through reduction reaction between TiO2 and C,which led to a better tribological performance.The results can serve as a guide in selecting the best method of the ceramic phase introduction when preparing TiC reinforced Fe-based composite coatings.
Effect of the o-polarized irradiation on the screening-photovoltaic photorefractive spatial solitons
2012, 36(4): 445-449.
doi: 10.3969/j.issn.1001-806.2012.04.004
Abstract:
In order to study effect of the o-polarized irradiation on the screening-photovoltaic spatial solitons,the theory of screening-photovoltaic spatial solitons was established based on the one-photon photorefractive effect.The optical circuit includes a divider resistance and an o-polarized uniform background beam.The numerical results show that the dark solitons can be obtained for the proper values of biased field and photovoltaic field and the bright solitons can also be obtained by only changing the value of effective glass coefficient between o-background beam and soliton beam while the other parameters remain unchanged.The intensity full width at half maximum(FWHM)of solitons increases with the increase of the ratio of the o-background beam intensity to the dark-irradiation intensity.Similarly,the FWHM of solitons will also increase with the ratio of cross section of the o-background beam to that of the soliton beam.The paper gives a new scheme of the transformation of a dark soliton into a bright soliton in photorefractive crystal.
In order to study effect of the o-polarized irradiation on the screening-photovoltaic spatial solitons,the theory of screening-photovoltaic spatial solitons was established based on the one-photon photorefractive effect.The optical circuit includes a divider resistance and an o-polarized uniform background beam.The numerical results show that the dark solitons can be obtained for the proper values of biased field and photovoltaic field and the bright solitons can also be obtained by only changing the value of effective glass coefficient between o-background beam and soliton beam while the other parameters remain unchanged.The intensity full width at half maximum(FWHM)of solitons increases with the increase of the ratio of the o-background beam intensity to the dark-irradiation intensity.Similarly,the FWHM of solitons will also increase with the ratio of cross section of the o-background beam to that of the soliton beam.The paper gives a new scheme of the transformation of a dark soliton into a bright soliton in photorefractive crystal.
2012, 36(4): 450-452.
doi: 10.3969/j.issn.1001-806.2012.04.005
Abstract:
Si-based optoelectronic integration technology is one of the main study topics and development directions for the high-speed information.New Si-based luminescent materials were developed to break the limits of Nd:YAG solid laser material,which was confined by two main solid states:single crystal and transparent ceramics.Nd:YAG thin film was prepared on Si(100) substrates by electron beam evaporation deposition.The surface morphology,crystalline phase and optical properties of Nd:YAG thin film were characterized by X-ray diffraction,scanning electron microscopy and spectrophotometer.The crystallization of Nd:YAG thin film was improved after annealing at 1100℃ for 1h in the vacuum,photoluminescent spectra of Nd:YAG thin film were measured at room temperature,with 808nm radiation from a Ti:sapphire laser,and photoluminescent spectrum in the region of 1064nm peak was detected by a liquid nitrogen cooled InGaAs detector array.The results showed that Nd:YAG crystalline thin film was grown on Si substrates for the first time by means of electron beam evaporation deposition and subsequent high temperature annealing process.
Si-based optoelectronic integration technology is one of the main study topics and development directions for the high-speed information.New Si-based luminescent materials were developed to break the limits of Nd:YAG solid laser material,which was confined by two main solid states:single crystal and transparent ceramics.Nd:YAG thin film was prepared on Si(100) substrates by electron beam evaporation deposition.The surface morphology,crystalline phase and optical properties of Nd:YAG thin film were characterized by X-ray diffraction,scanning electron microscopy and spectrophotometer.The crystallization of Nd:YAG thin film was improved after annealing at 1100℃ for 1h in the vacuum,photoluminescent spectra of Nd:YAG thin film were measured at room temperature,with 808nm radiation from a Ti:sapphire laser,and photoluminescent spectrum in the region of 1064nm peak was detected by a liquid nitrogen cooled InGaAs detector array.The results showed that Nd:YAG crystalline thin film was grown on Si substrates for the first time by means of electron beam evaporation deposition and subsequent high temperature annealing process.
2012, 36(4): 453-458.
doi: 10.3969/j.issn.1001-806.2012.04.006
Abstract:
In order to study the welding process of 5052 aluminum alloy,5052 aluminum alloy plates in 1.5mm thick were welded with pulsed and continuous laser respectively,then the process parameters were improved.After comparing their microstructures,tensile strength and micro hardness,it can be seen that pulsed laser welding is more ideal for control the porosity of welding joint,its welding quality is more excellent,and that the tensile strength of the welding joint is increased by 10%.The results show that both pulsed laser welding and continuous laser welding can make welded samples obtain ideal welds morphology and high tensile strength.
In order to study the welding process of 5052 aluminum alloy,5052 aluminum alloy plates in 1.5mm thick were welded with pulsed and continuous laser respectively,then the process parameters were improved.After comparing their microstructures,tensile strength and micro hardness,it can be seen that pulsed laser welding is more ideal for control the porosity of welding joint,its welding quality is more excellent,and that the tensile strength of the welding joint is increased by 10%.The results show that both pulsed laser welding and continuous laser welding can make welded samples obtain ideal welds morphology and high tensile strength.
2012, 36(4): 459-462.
doi: 10.3969/j.issn.1001-806.2012.04.007
Abstract:
In order to realize nondestructive test of the chlorophyll content,the optical characteristic parameters of wheat leaves were measured with laser backscatter images.Firstly,the laser backscatter images of wheat leaves were obtained with 670nm and 970nm of semiconductor lasers and a video imaging system.Secondly,based on the diffuse theory,diffusive light distribution of the leaf surface was analyzed,and the laser backscatter images of green leaves,yellow leaves and dry leaves were compared at both the above wavelengths.The optical characteristic parameter data(the reduced scattering and absorption coefficient) were obtained,and the function corresponding to the relative contents of chlorophyll was established.The results show the optical characteristic parameters of wheat leaves and are linear with the relative contents of chlorophyll.In the model predicting the relative contents of chlorophyll value based on the scattering coefficients,the correlation coefficient prediction samples is set 0.9095,prediction root mean square error(RMSE) is 5.9.In the model predicting the relative contents of chlorophyll value based on the absorption coefficients,the correlation coefficient prediction samples is set 0.8366,prediction RMSE is 7.5.The results show that it is feasible to detect plant chlorophyll content and diagnose the crop growth conditions with laser backscatter image technology.
In order to realize nondestructive test of the chlorophyll content,the optical characteristic parameters of wheat leaves were measured with laser backscatter images.Firstly,the laser backscatter images of wheat leaves were obtained with 670nm and 970nm of semiconductor lasers and a video imaging system.Secondly,based on the diffuse theory,diffusive light distribution of the leaf surface was analyzed,and the laser backscatter images of green leaves,yellow leaves and dry leaves were compared at both the above wavelengths.The optical characteristic parameter data(the reduced scattering and absorption coefficient) were obtained,and the function corresponding to the relative contents of chlorophyll was established.The results show the optical characteristic parameters of wheat leaves and are linear with the relative contents of chlorophyll.In the model predicting the relative contents of chlorophyll value based on the scattering coefficients,the correlation coefficient prediction samples is set 0.9095,prediction root mean square error(RMSE) is 5.9.In the model predicting the relative contents of chlorophyll value based on the absorption coefficients,the correlation coefficient prediction samples is set 0.8366,prediction RMSE is 7.5.The results show that it is feasible to detect plant chlorophyll content and diagnose the crop growth conditions with laser backscatter image technology.
2012, 36(4): 463-466.
doi: 10.3969/j.issn.1001-806.2012.04.008
Abstract:
An all fiber,compact high power tunable laser source for atmospheric CO2 measurement was investigated.Based on the ultra precise atmospheric CO2 absorption spectrum,a tunable seed laser was designed with the peak absorption around 1572nm,and then its output power was amplified to the order of watt level with an Er-Yb double cladding fiber amplifier.The experimental results show that the laser can provide 10dBm output power with 50dB side mode suppression,500kHz linewidth;the max gain of the fiber amplifier is 25.13dB,output power is 1W.This laser possesses a small size,low power consumption and low cost it builds a steady foundation for the wider range of Atmospheric CO2 measurements.
An all fiber,compact high power tunable laser source for atmospheric CO2 measurement was investigated.Based on the ultra precise atmospheric CO2 absorption spectrum,a tunable seed laser was designed with the peak absorption around 1572nm,and then its output power was amplified to the order of watt level with an Er-Yb double cladding fiber amplifier.The experimental results show that the laser can provide 10dBm output power with 50dB side mode suppression,500kHz linewidth;the max gain of the fiber amplifier is 25.13dB,output power is 1W.This laser possesses a small size,low power consumption and low cost it builds a steady foundation for the wider range of Atmospheric CO2 measurements.
2012, 36(4): 467-470.
doi: 10.3969/j.issn.1001-806.2012.04.009
Abstract:
In order to apply laser micro-forming planar array in engineering,the processing process of planar array was studied based on a novel laser surface texturing technology,so-called "single pulse one time,repeating at intervals".A new scanning strategy was provided to optimize the path of the old processing method.Because high positioning accuracy was demanded for the starting processing point when the new scanning strategy was applied,the location problem of the workbench was studied and the accurate positioning flow chart was provided.Finally,the programming method of the new scanning strategy was studied,and the processing flow chart was given.The results show that the scanning strategy meets the requirements of the novel processing process and better micro-morphology and surface quality can be obtained.
In order to apply laser micro-forming planar array in engineering,the processing process of planar array was studied based on a novel laser surface texturing technology,so-called "single pulse one time,repeating at intervals".A new scanning strategy was provided to optimize the path of the old processing method.Because high positioning accuracy was demanded for the starting processing point when the new scanning strategy was applied,the location problem of the workbench was studied and the accurate positioning flow chart was provided.Finally,the programming method of the new scanning strategy was studied,and the processing flow chart was given.The results show that the scanning strategy meets the requirements of the novel processing process and better micro-morphology and surface quality can be obtained.
2012, 36(4): 471-474.
doi: 10.3969/j.issn.1001-806.2012.04.010
Abstract:
In order to obtain the accurate diffraction efficiency of gratings,the diffraction mechanism of volume Bragg gratings was established and the diffraction efficiency was calculated with the rigorous coupled-wave method.The first-order coupled Maxwell's equations was solved in terms of Legendre polynomials,and the diffraction efficiency of volume Bragg gratings was obtained.The simulation results were consistent with theoretical calculation results.This method converges faster than the matrix method,and is more precise than the Kogelnik coupling wave theory.
In order to obtain the accurate diffraction efficiency of gratings,the diffraction mechanism of volume Bragg gratings was established and the diffraction efficiency was calculated with the rigorous coupled-wave method.The first-order coupled Maxwell's equations was solved in terms of Legendre polynomials,and the diffraction efficiency of volume Bragg gratings was obtained.The simulation results were consistent with theoretical calculation results.This method converges faster than the matrix method,and is more precise than the Kogelnik coupling wave theory.
2012, 36(4): 480-484.
doi: 10.3969/j.issn.1001-806.2012.04.011
Abstract:
In order to obtain a new flattened dispersion photonic crystal fiber with high nonlinearity,a novel octagonal photonic crystal fiber(O-PCF) with three-cladding structure was designed.The effect of the hole size and hole space on the nonlinearity and dispersion of the PCF was analyzed by means of the multi-pole method.The result shows that the dispersion and the nonlinearity coefficient of O-PCF decrease with the increasing of the diameter of inner air hole.With the increasing of the diameter of the third air hole,the dispersion increases.Meanwhile,the nonlinearity coefficient almost remains constant.The dispersion and nonlinearity coefficient is affected little by the diameter of the second layer and peripheral air hole.By optimizing the diameters of the O-PCF holes and the hole pitch,an O-PCF with high flattened dispersion and nonlinearity was achieved.At the wavelength range of 1.46μm~1.73μm,the dispersion coefficient is merely changed within ±0.5ps/(km·nm),and the nonlinearity coefficient is merely changed from 42.5W-1·km-1 to 50W-1·km-1 at 1.5μm to 1.65μm.These results offer theoretical references for designing the photonic crystal fiber with some specific function.
In order to obtain a new flattened dispersion photonic crystal fiber with high nonlinearity,a novel octagonal photonic crystal fiber(O-PCF) with three-cladding structure was designed.The effect of the hole size and hole space on the nonlinearity and dispersion of the PCF was analyzed by means of the multi-pole method.The result shows that the dispersion and the nonlinearity coefficient of O-PCF decrease with the increasing of the diameter of inner air hole.With the increasing of the diameter of the third air hole,the dispersion increases.Meanwhile,the nonlinearity coefficient almost remains constant.The dispersion and nonlinearity coefficient is affected little by the diameter of the second layer and peripheral air hole.By optimizing the diameters of the O-PCF holes and the hole pitch,an O-PCF with high flattened dispersion and nonlinearity was achieved.At the wavelength range of 1.46μm~1.73μm,the dispersion coefficient is merely changed within ±0.5ps/(km·nm),and the nonlinearity coefficient is merely changed from 42.5W-1·km-1 to 50W-1·km-1 at 1.5μm to 1.65μm.These results offer theoretical references for designing the photonic crystal fiber with some specific function.
2012, 36(4): 485-489.
doi: 10.3969/j.issn.1001-806.2012.04.012
Abstract:
With laser beam propagating over a long distance through even weak atmospheric turbulence,significant turbulence effect might happen so that a continuous phase function does not exist in general owing to the presence of branch points in phase.Branch points could induce degradation of the performance of a standard adaptive optics system when it is used to compensate atmospheric turbulence.The generation and development,the optical properties and topological characteristics of branch points in the atmosphere were introduced.The study of phase discontinuity of laser propagation through atmosphere was reviewed so as to provide a reference for further study of laser propagation through atmosphere and adaptive optics system.
With laser beam propagating over a long distance through even weak atmospheric turbulence,significant turbulence effect might happen so that a continuous phase function does not exist in general owing to the presence of branch points in phase.Branch points could induce degradation of the performance of a standard adaptive optics system when it is used to compensate atmospheric turbulence.The generation and development,the optical properties and topological characteristics of branch points in the atmosphere were introduced.The study of phase discontinuity of laser propagation through atmosphere was reviewed so as to provide a reference for further study of laser propagation through atmosphere and adaptive optics system.
2012, 36(4): 490-492.
doi: 10.3969/j.issn.1001-806.2012.04.013
Abstract:
According to the theory of Fresnel diffraction,a continuous land model was established for natural terrain like desert and grass land,a method of gridding partition was developed to simulate the effect of average surficial height and height mean square error on the properties of return signal,including waveform,power and pulse width.The results show that height mean square error determines the properties of return signal,while the change of terrain mean height cause no difference in return signal in the case of fixed height mean square error.
According to the theory of Fresnel diffraction,a continuous land model was established for natural terrain like desert and grass land,a method of gridding partition was developed to simulate the effect of average surficial height and height mean square error on the properties of return signal,including waveform,power and pulse width.The results show that height mean square error determines the properties of return signal,while the change of terrain mean height cause no difference in return signal in the case of fixed height mean square error.
2012, 36(4): 493-496.
doi: 10.3969/j.issn.1001-806.2012.04.014
Abstract:
For analyzing the influence of multiple scattering on measuring beam attenuation in bubble wakes,the correction coefficient was introduced which denotes the extent of multiple scattering,and its theoretical formulations was derived by means of a narrow angle approximation solution to the radiation transfer equation.Given a typical bubbles size distribution function and number density in bubbles wakes,the relation among the correction coefficient and detector field of view(FOV),wake optical depth,beam size,received section size were analyzed by numerical calculation.Analysis shows that the influence of FOV in forward small angle on the correction coefficient is great,but it has a little change when the FOV is wide;and the impact of optical depth on the correction coefficient is prominent,besides the impact is more prominent when the optical depth is less than 1;and the effect of received section size on the correction coefficient is very little when depth is less than 1,but it becomes visible as the optical depth increase;the influence of beam size on the correction coefficient is comparatively less,further the correction coefficient almost keeps changeless when the beam size is large.The research proposes a theoretical foundation for choice and optimization of conditions during measuring beam attenuation in bubble wakes.
For analyzing the influence of multiple scattering on measuring beam attenuation in bubble wakes,the correction coefficient was introduced which denotes the extent of multiple scattering,and its theoretical formulations was derived by means of a narrow angle approximation solution to the radiation transfer equation.Given a typical bubbles size distribution function and number density in bubbles wakes,the relation among the correction coefficient and detector field of view(FOV),wake optical depth,beam size,received section size were analyzed by numerical calculation.Analysis shows that the influence of FOV in forward small angle on the correction coefficient is great,but it has a little change when the FOV is wide;and the impact of optical depth on the correction coefficient is prominent,besides the impact is more prominent when the optical depth is less than 1;and the effect of received section size on the correction coefficient is very little when depth is less than 1,but it becomes visible as the optical depth increase;the influence of beam size on the correction coefficient is comparatively less,further the correction coefficient almost keeps changeless when the beam size is large.The research proposes a theoretical foundation for choice and optimization of conditions during measuring beam attenuation in bubble wakes.
2012, 36(4): 497-500.
doi: 10.3969/j.issn.1001-806.2012.04.015
Abstract:
The protective gas plays an important role in the CO2 laser metal intertia gas(MIG)hybrid welding of aluminum alloy.The laser-MIG hybrid welding was carried out on 5052 Al alloy plates at different flow rates of He,Ar mixed protective gas,and the data about penetration depth and welding voltages were obtained.The results show when He is added to protective gas,the arc voltage of MIG will increase,and Arc stability reduces so that the weld penetration is affected by the pure He protective gas.The surface quality and the arc stability are improved when a little Ar gas is mixed with He protective gas,and the weld penetration is added.When the ratio of V(Ar):V(He)=5:25,the weld penetration is maximum.When a great amount of Ar is added to He protective gas,the weld penetration is decreased,even the deep penetration of laser welding is prevented.When using pure Ar gas,although the weld appearance is beautiful,but the weld penetration is very small.The results have an important role in the weld quality of the CO2 laser-MIG arc hybrid welding aluminum.
The protective gas plays an important role in the CO2 laser metal intertia gas(MIG)hybrid welding of aluminum alloy.The laser-MIG hybrid welding was carried out on 5052 Al alloy plates at different flow rates of He,Ar mixed protective gas,and the data about penetration depth and welding voltages were obtained.The results show when He is added to protective gas,the arc voltage of MIG will increase,and Arc stability reduces so that the weld penetration is affected by the pure He protective gas.The surface quality and the arc stability are improved when a little Ar gas is mixed with He protective gas,and the weld penetration is added.When the ratio of V(Ar):V(He)=5:25,the weld penetration is maximum.When a great amount of Ar is added to He protective gas,the weld penetration is decreased,even the deep penetration of laser welding is prevented.When using pure Ar gas,although the weld appearance is beautiful,but the weld penetration is very small.The results have an important role in the weld quality of the CO2 laser-MIG arc hybrid welding aluminum.
2012, 36(4): 501-503.
doi: 10.3969/j.issn.1001-806.2012.04.016
Abstract:
In order to study the growth mechanism of a zinc oxide nanorod.Firstly,thin zinc oxide film was deposited on a glass substrate as a seed layer by pulsed laser deposition.Then,well-aligned zinc oxide nanorod arrays were synthesized with hydrothermal method.Effects of growth time on structure,morphology and photoluminescent properties of zinc oxide nanorods were investigated.The results show that zinc oxide nanorods are hexagonal wurtzite structures and grow along the c-axis.Homogenization,compactness,orientation of zinc oxide nanorods are improved with the growth time.The photoluminescent intensity of defect luminescence is enhanced while the excitation photoluminescence is weakened.
In order to study the growth mechanism of a zinc oxide nanorod.Firstly,thin zinc oxide film was deposited on a glass substrate as a seed layer by pulsed laser deposition.Then,well-aligned zinc oxide nanorod arrays were synthesized with hydrothermal method.Effects of growth time on structure,morphology and photoluminescent properties of zinc oxide nanorods were investigated.The results show that zinc oxide nanorods are hexagonal wurtzite structures and grow along the c-axis.Homogenization,compactness,orientation of zinc oxide nanorods are improved with the growth time.The photoluminescent intensity of defect luminescence is enhanced while the excitation photoluminescence is weakened.
2012, 36(4): 508-511.
doi: 10.3969/j.issn.1001-806.2012.04.018
Abstract:
In order to study the properties of the complete bandgap of 2-D columnar photonic crystal in square lattice,two types of 2-D photonic crystals were studied based on the plane wave expansion method.The dependence of the complete bandgap on the variation of column radius and the refractive index was studied for a fixed lattice constant.Results show that when the radius of dielectric rods increases,the width of the complete photonic bandgap of photonic crystal composed of Ge cylinders in air background firstly increased,then declined and disappeared at last.When the filling fraction was 38.3%,as the dielectric constant of dielectric rods increased,the obtained maximum complete photonic band gap was 0.02754(ωa/(2πc)) when the refractive index was 4.2.It was also found that the bandgap frequency increased when the radius of air rods in Ge background increased.When the filling fraction was 48.3%,as the dielectric constant increased in the background,three complete bandgaps could be found,and the width of the largest complete bandgap was 0.02922(ωa/(2πc)) when the background index was 6.2.The photonic band structure was also shown by the frequency analysis of TE/TM.These results provide theoretical instructions for 2-D square photonic crystals with big photonic bandgap.
In order to study the properties of the complete bandgap of 2-D columnar photonic crystal in square lattice,two types of 2-D photonic crystals were studied based on the plane wave expansion method.The dependence of the complete bandgap on the variation of column radius and the refractive index was studied for a fixed lattice constant.Results show that when the radius of dielectric rods increases,the width of the complete photonic bandgap of photonic crystal composed of Ge cylinders in air background firstly increased,then declined and disappeared at last.When the filling fraction was 38.3%,as the dielectric constant of dielectric rods increased,the obtained maximum complete photonic band gap was 0.02754(ωa/(2πc)) when the refractive index was 4.2.It was also found that the bandgap frequency increased when the radius of air rods in Ge background increased.When the filling fraction was 48.3%,as the dielectric constant increased in the background,three complete bandgaps could be found,and the width of the largest complete bandgap was 0.02922(ωa/(2πc)) when the background index was 6.2.The photonic band structure was also shown by the frequency analysis of TE/TM.These results provide theoretical instructions for 2-D square photonic crystals with big photonic bandgap.
2012, 36(4): 512-515.
doi: 10.3969/j.issn.1001-806.2012.04.019
Abstract:
In order to obtain the analytic expression for CO2 laser power distribution,the power distribution of a CO2 laser was measured with thermal paper at the different heights and output power.The experiment images of the laser spot were processed with MATLAB,and a numerical model of laser power distribution was built up and compared with the experimental spot.The obtained analytic expression was verified with the measurement results in laser heat treatment experiments and calculation results of temperature field.The experimental results were in good agreement with the theoretical calculation.The results show that it is feasible to measure the laser power distribution with thermal paper,and it is practical to calculate the power distribution based on the analytic expressions.
In order to obtain the analytic expression for CO2 laser power distribution,the power distribution of a CO2 laser was measured with thermal paper at the different heights and output power.The experiment images of the laser spot were processed with MATLAB,and a numerical model of laser power distribution was built up and compared with the experimental spot.The obtained analytic expression was verified with the measurement results in laser heat treatment experiments and calculation results of temperature field.The experimental results were in good agreement with the theoretical calculation.The results show that it is feasible to measure the laser power distribution with thermal paper,and it is practical to calculate the power distribution based on the analytic expressions.
2012, 36(4): 516-519.
doi: 10.3969/j.issn.1001-806.2012.04.020
Abstract:
For the sake of understanding the carrier-envelope-phase dependence of the two single-attosecond-pulse generation techniques,i.e.,amplitude gating and polarization gating,the influence of carrier-envelope phase of the driving field on the generation of extreme ultraviolet single attosecond pulse with either of the basic techniques was analyzed based on its principle and the three-step scenario of high-harmonic generation.It indicates that the optimal carrier-envelope phases for amplitude gating and polarization gating are 0 and 0.5π respectively,whose difference was induced by the close dependence of high-harmonic generation on the polarization feature of driving field.The results are of great significance to the generation and its related applications of extreme ultraviolet attosecond pulses with narrow pulse duration.
For the sake of understanding the carrier-envelope-phase dependence of the two single-attosecond-pulse generation techniques,i.e.,amplitude gating and polarization gating,the influence of carrier-envelope phase of the driving field on the generation of extreme ultraviolet single attosecond pulse with either of the basic techniques was analyzed based on its principle and the three-step scenario of high-harmonic generation.It indicates that the optimal carrier-envelope phases for amplitude gating and polarization gating are 0 and 0.5π respectively,whose difference was induced by the close dependence of high-harmonic generation on the polarization feature of driving field.The results are of great significance to the generation and its related applications of extreme ultraviolet attosecond pulses with narrow pulse duration.
2012, 36(4): 527-531.
doi: 10.3969/j.issn.1001-806.2012.04.023
Abstract:
Based on the real condition that laser quenching steel substrate could improve the service life of chromium-plated gun bore,the interfacial shear strengths of Cr-plating coating on laser re-quenching substrate and laser non-treating one were measured by multi-cracks tensile method respectively.The experimental results show that the interfacial shear strength is increased by 77.7% through laser re-quenching steel substrate.The analysis of interface structure between substrate and Cr-coating shows that the interface of laser pretreatment is a continuous transition,while there is an over-layer on the original interface.The mechanical model analysis shows that the compressive residual stress in the laser processing zone could increases fracture stress of chromium coating and the improvement of substrate surface hardness decreases maximum crack spacing.The synthetic result of above two effecting factors is that the interfacial shear strength is increased by laser re-quenching substrate.
Based on the real condition that laser quenching steel substrate could improve the service life of chromium-plated gun bore,the interfacial shear strengths of Cr-plating coating on laser re-quenching substrate and laser non-treating one were measured by multi-cracks tensile method respectively.The experimental results show that the interfacial shear strength is increased by 77.7% through laser re-quenching steel substrate.The analysis of interface structure between substrate and Cr-coating shows that the interface of laser pretreatment is a continuous transition,while there is an over-layer on the original interface.The mechanical model analysis shows that the compressive residual stress in the laser processing zone could increases fracture stress of chromium coating and the improvement of substrate surface hardness decreases maximum crack spacing.The synthetic result of above two effecting factors is that the interfacial shear strength is increased by laser re-quenching substrate.
2012, 36(4): 532-535.
doi: 10.3969/j.issn.1001-806.2012.04.025
Abstract:
In order to study the spectral properties of J0-correlated partially coherent flat-topped beam in turbulent atmosphere,the analytical spectrum expression of J0-correlated partially coherent flat-topped beam was derived based on extended Huygens-Fresnel principle.The effect of structure constant,central frequency,spectrum width,coherence parameter and orders of flat-topped beams on the spectral shift was discussed.Results show that the above parameters have great effect on the value of the frequency shift.Furthermore,the spectral shift decreases with the increase of turbulence.In free space,the higher order of flat-top beam,the greater impact of the spectral shift,but the order has little effect on the spectral shift in turbulent atmosphere.
In order to study the spectral properties of J0-correlated partially coherent flat-topped beam in turbulent atmosphere,the analytical spectrum expression of J0-correlated partially coherent flat-topped beam was derived based on extended Huygens-Fresnel principle.The effect of structure constant,central frequency,spectrum width,coherence parameter and orders of flat-topped beams on the spectral shift was discussed.Results show that the above parameters have great effect on the value of the frequency shift.Furthermore,the spectral shift decreases with the increase of turbulence.In free space,the higher order of flat-top beam,the greater impact of the spectral shift,but the order has little effect on the spectral shift in turbulent atmosphere.
2012, 36(4): 540-543.
doi: 10.3969/j.issn.1001-806.2012.04.027
Abstract:
For studying the optical filtering of Gaussian beam passing through diffractive gratings,the Fraunhofer diffraction equation of Gaussian beam was deduced based on scalar diffraction theory,and then the filtering characteristics of multi-wavelength Gaussian beam was analyzed,which were compared with those of parallel plane light.It was found that the optical intensity distribution for a single wavelength Gaussian beam was related to the factor T,and the band-width for multi-wavelength Gaussian beam was narrowed.This theory is helpful for optical filter design and optimization.
For studying the optical filtering of Gaussian beam passing through diffractive gratings,the Fraunhofer diffraction equation of Gaussian beam was deduced based on scalar diffraction theory,and then the filtering characteristics of multi-wavelength Gaussian beam was analyzed,which were compared with those of parallel plane light.It was found that the optical intensity distribution for a single wavelength Gaussian beam was related to the factor T,and the band-width for multi-wavelength Gaussian beam was narrowed.This theory is helpful for optical filter design and optimization.
2012, 36(4): 544-547.
doi: 10.3969/j.issn.1001-806.2012.04.028
Abstract:
In order to eliminate the effect of amplified spontaneous emission(ASE) noise of Er-doped fiber amplifiers(EDFA)on the temperature measuring precision of distributed optical fiber temperature sensors,a precise modified formula is an effective means.Firstly,the influence of ASE noise in EDFA was analyzed,and then the temperature demodulation formula was modified with intermediate calculation results.Secondly,based on the theoretical and modified formula,the temperature was tested,and the results were compared.Analysis results indicate that the modified temperature demodulation formula can efficiently compensate errors due to ASE noise and improve the signal-to-noise ratio of the system and measurement precision of the temperature obviously.The experimental results show that the temperature precision is raised to 1℃ ~2℃ by using the modified formula.Moreover,amplified Raman spontaneous scattering is also observed in multimode fibers as the same as in single mode fibers and causes amplified Raman spontaneous scattering curve distortion.However,amplified Raman spontaneous scattering exhibits ideal temperature effect.
In order to eliminate the effect of amplified spontaneous emission(ASE) noise of Er-doped fiber amplifiers(EDFA)on the temperature measuring precision of distributed optical fiber temperature sensors,a precise modified formula is an effective means.Firstly,the influence of ASE noise in EDFA was analyzed,and then the temperature demodulation formula was modified with intermediate calculation results.Secondly,based on the theoretical and modified formula,the temperature was tested,and the results were compared.Analysis results indicate that the modified temperature demodulation formula can efficiently compensate errors due to ASE noise and improve the signal-to-noise ratio of the system and measurement precision of the temperature obviously.The experimental results show that the temperature precision is raised to 1℃ ~2℃ by using the modified formula.Moreover,amplified Raman spontaneous scattering is also observed in multimode fibers as the same as in single mode fibers and causes amplified Raman spontaneous scattering curve distortion.However,amplified Raman spontaneous scattering exhibits ideal temperature effect.
2012, 36(4): 548-552.
doi: 10.3969/j.issn.1001-806.2012.04.029
Abstract:
In order to detect the size and depth of an internal deep flaw in materials,combining out-of-plane displacement digital speckle pattern interferometry(DSPI) with elasticity theory,the out-of-plane displacement distribution of a plate with an internal flaw was analyzed.Then it was verified by numerical simulation and DSPI.The out-of-plane displacement curves and its first-order derivative curves obtained by the above three methods were compared with each other.It was shown that results obtained from these three methods were in good agreement.The experimental error was analyzed.Finally,the flaw size was calculated from the first-order derivate of the out-of-plane displacement.Both the errors of the experimental and theoretical results were in the acceptable range.The results show that DSPI is suit for detection of internal deep flaws with high accuracy.
In order to detect the size and depth of an internal deep flaw in materials,combining out-of-plane displacement digital speckle pattern interferometry(DSPI) with elasticity theory,the out-of-plane displacement distribution of a plate with an internal flaw was analyzed.Then it was verified by numerical simulation and DSPI.The out-of-plane displacement curves and its first-order derivative curves obtained by the above three methods were compared with each other.It was shown that results obtained from these three methods were in good agreement.The experimental error was analyzed.Finally,the flaw size was calculated from the first-order derivate of the out-of-plane displacement.Both the errors of the experimental and theoretical results were in the acceptable range.The results show that DSPI is suit for detection of internal deep flaws with high accuracy.
2012, 36(4): 553-556.
doi: 10.3969/j.issn.1001-806.2012.04.030
Abstract:
For extracting feature points and feature lines of the building,this paper adopted plain fitting algorithm and theoretically analyzed and experimentally proved it,then obtained feature points and feature lines of the building and constructed boundary frame of it eventually.The result demonstrated that,which is significant for building digital city,with processing of point cloud acquired by terrestrial laser scanning technique,boundaries of buildings can be extracted.
For extracting feature points and feature lines of the building,this paper adopted plain fitting algorithm and theoretically analyzed and experimentally proved it,then obtained feature points and feature lines of the building and constructed boundary frame of it eventually.The result demonstrated that,which is significant for building digital city,with processing of point cloud acquired by terrestrial laser scanning technique,boundaries of buildings can be extracted.
2012, 36(4): 557-561.
doi: 10.3969/j.issn.1001-806.2012.04.031
Abstract:
In order to explore the ability for a dispersion managed soliton(DMS) system to resist smaller fluctuation,firstly,starting from the analysis of its modulation instability(MI),on the base of nonlinear soliton transfer equation,the expression for the gain spectrum of MI in DMS was deduced.Secondly,the gain curve of each order MI was presented,and then conditions of the fundamental MI playing a leading role were analyzed.Finally,the influence of average dispersion and dispersion depth on MI was discussed.The results show that in negative average dispersion region as the average dispersion becomes larger and dispersion fluctuates smaller,and influence of fundamental MI becomes smaller,so it is more favorable to suppress MI.However,MI gain spectrum appears side-lobe phenomenon,when the average dispersion becomes very small.
In order to explore the ability for a dispersion managed soliton(DMS) system to resist smaller fluctuation,firstly,starting from the analysis of its modulation instability(MI),on the base of nonlinear soliton transfer equation,the expression for the gain spectrum of MI in DMS was deduced.Secondly,the gain curve of each order MI was presented,and then conditions of the fundamental MI playing a leading role were analyzed.Finally,the influence of average dispersion and dispersion depth on MI was discussed.The results show that in negative average dispersion region as the average dispersion becomes larger and dispersion fluctuates smaller,and influence of fundamental MI becomes smaller,so it is more favorable to suppress MI.However,MI gain spectrum appears side-lobe phenomenon,when the average dispersion becomes very small.
2012, 36(4): 565-567.
doi: 10.3969/j.issn.1001-806.2012.04.033
Abstract:
In order to improve the precision of rhomb-type achromatic retarders,according to the optical refraction rule and based on that the sum of the angle of total reflection θ and the reflection angle r is constant,dual-wavelength design was analyzed for two different wavelength beams incident on the retarder.Since the delay errors were the positive and negative,retardation was 90° at two wavelengths in the whole region of spectrum.Simultaneously,achromatic precision of the λ/4 retarder was enhanced greatly after optimum design for two wavelengths.The maximal delay error was smaller than 0.02° for a λ/4 retarder designed with LaK2 glass within the range of 360nm~1160nm.Compared with other two designing methods,the new designed retarder not only simplifies the designing theory,but also has higher achromatic precision,and the results are helpful to the design of high precision rhomb-type achromatic retarders.
In order to improve the precision of rhomb-type achromatic retarders,according to the optical refraction rule and based on that the sum of the angle of total reflection θ and the reflection angle r is constant,dual-wavelength design was analyzed for two different wavelength beams incident on the retarder.Since the delay errors were the positive and negative,retardation was 90° at two wavelengths in the whole region of spectrum.Simultaneously,achromatic precision of the λ/4 retarder was enhanced greatly after optimum design for two wavelengths.The maximal delay error was smaller than 0.02° for a λ/4 retarder designed with LaK2 glass within the range of 360nm~1160nm.Compared with other two designing methods,the new designed retarder not only simplifies the designing theory,but also has higher achromatic precision,and the results are helpful to the design of high precision rhomb-type achromatic retarders.
2012, 36(4): 568-571.
doi: 10.3969/j.issn.1001-806.2012.04.034
Abstract:
In order to study how to obtain the beam that meets the need of laser applications including such as beam pattern,spot size and intensity distribution,the formula for the diffraction transform of Gaussian beam throughout a micro-circular aperture was deduced based on Kirchhoff diffraction formula.The beam pattern change and its influencing factors of Fresnel diffraction transformation of Gaussian beam throughout the micro-circular aperture were discussed.The simulations carried out with the MATLAB software show that this kind of method is reliable and feasible.This is conductive to the application of laser in the laser engineering,micro-optics and micro-opto-electro-mechaning system.
In order to study how to obtain the beam that meets the need of laser applications including such as beam pattern,spot size and intensity distribution,the formula for the diffraction transform of Gaussian beam throughout a micro-circular aperture was deduced based on Kirchhoff diffraction formula.The beam pattern change and its influencing factors of Fresnel diffraction transformation of Gaussian beam throughout the micro-circular aperture were discussed.The simulations carried out with the MATLAB software show that this kind of method is reliable and feasible.This is conductive to the application of laser in the laser engineering,micro-optics and micro-opto-electro-mechaning system.
2012, 36(4): 572-576.
doi: 10.3969/j.issn.1001-806.2012.04.035
Abstract:
In order to study effect of Compton scattering on the modulation instability in the un-magnetized plasma,the modulation instability of the un-magnetized plasma under Compton scattering was analyzed and simulated based on the model of the multi-photon nonlinear Compton scattering.Some important data about effect of Compton scattering on the time rise rate of the modulation instability,the nonlinear dispersion and control were obtained,and a new mechanism of the modulation instability formed by the incident light and the Compton scattering was put forward.The result shows that the maximum time rise rate of the modulation instability and laser self-focusing in the un-magnetized laser-plasma becomes smaller than before the Compton scattering,and the time rise rate of the modulation instability in the vicinity of the laser-plasma surface is increased.
In order to study effect of Compton scattering on the modulation instability in the un-magnetized plasma,the modulation instability of the un-magnetized plasma under Compton scattering was analyzed and simulated based on the model of the multi-photon nonlinear Compton scattering.Some important data about effect of Compton scattering on the time rise rate of the modulation instability,the nonlinear dispersion and control were obtained,and a new mechanism of the modulation instability formed by the incident light and the Compton scattering was put forward.The result shows that the maximum time rise rate of the modulation instability and laser self-focusing in the un-magnetized laser-plasma becomes smaller than before the Compton scattering,and the time rise rate of the modulation instability in the vicinity of the laser-plasma surface is increased.
