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RSS2006 Vol. 30, No. 5
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2006, 30(5): 449-451.
[Abstract]
[PDF 122KB]
Abstract:
To solve the weak target detection under the clutter background,combined with dynamic chaotic model,the chaotic property of the laser echo signal is discussed and a novel algorithm is presented based on chaotic signal detection using neural network predictor.The weak signal in laser clutter background can be detected by means of the prediction error.The simulated results show the algorithm is effective.
To solve the weak target detection under the clutter background,combined with dynamic chaotic model,the chaotic property of the laser echo signal is discussed and a novel algorithm is presented based on chaotic signal detection using neural network predictor.The weak signal in laser clutter background can be detected by means of the prediction error.The simulated results show the algorithm is effective.
2006, 30(5): 452-454.
Abstract:
Considering the fact that power injection factor of the input signal is hard to evaluate when gain saturation is analyzed with existing rate equation models of vertical cavity semiconductor optical amplifier(VCSOA) according to the boundary condition of Fabry-Perot resonator,a gain model of VCSOA is established by using traveling-wave equation and position dependent carrier equation and employing gain enhancement factor which varies with axial position to describe the standing wave effect in a micro-cavity.After finding the self-consistent solution of equations based on the model,the distributions of carrier and photon in cavity are presented.Meanwhile,the reflection gain is investigated and agrees with the theoretical and experimental data.
Considering the fact that power injection factor of the input signal is hard to evaluate when gain saturation is analyzed with existing rate equation models of vertical cavity semiconductor optical amplifier(VCSOA) according to the boundary condition of Fabry-Perot resonator,a gain model of VCSOA is established by using traveling-wave equation and position dependent carrier equation and employing gain enhancement factor which varies with axial position to describe the standing wave effect in a micro-cavity.After finding the self-consistent solution of equations based on the model,the distributions of carrier and photon in cavity are presented.Meanwhile,the reflection gain is investigated and agrees with the theoretical and experimental data.
2006, 30(5): 455-457,461.
Abstract:
In order to study the characteristic signals according to the quality of the welding with dissimilar gaps,the self-made real-time monitoring system with coaxial sensors is applied to acquire and extract coaxial signal,and then the signals are analyzed with modes analysis,subsection power analysis and wavelet analysis.It is found that,the modes of coaxial optical emission of dissimilar gaps,clustering at distinct numerical range,can distinguish 1st,2nd and 3rd class welds of different welding quality effectively.The subsection power analysis of coaxial signals can reflect the welding changes obviously.The approximation signals on level 4 of the coaxial signals,after wavelet decomposing,can intuitionisticly distinguish the 1st class welds,while detail signals on level 3 and level 4 of coaxial optical emission can clearly identify the 2nd class welds.
In order to study the characteristic signals according to the quality of the welding with dissimilar gaps,the self-made real-time monitoring system with coaxial sensors is applied to acquire and extract coaxial signal,and then the signals are analyzed with modes analysis,subsection power analysis and wavelet analysis.It is found that,the modes of coaxial optical emission of dissimilar gaps,clustering at distinct numerical range,can distinguish 1st,2nd and 3rd class welds of different welding quality effectively.The subsection power analysis of coaxial signals can reflect the welding changes obviously.The approximation signals on level 4 of the coaxial signals,after wavelet decomposing,can intuitionisticly distinguish the 1st class welds,while detail signals on level 3 and level 4 of coaxial optical emission can clearly identify the 2nd class welds.
2006, 30(5): 458-461.
Abstract:
The UV optical probe at xingguang-Ⅱ laser installations is pumped by a sub-laser beam.A pulse of 800ps with 1054nm wavelength is converted into an output UV pulse with 1mJ energy,60ps pulse-width and 308nm wavelength through stimulated Raman frequency conversion.The obtained UV laser pulse can be used as the lamp-house for laser plasma diagnosis.The original optical probe can't run steady because of poor quality and structure instability.In order to enhance the quality and stability,engineering alteration is performed on the original system.Experiment results prove that the optical probe can output an uniform pulse with 1mJ energy 30ps pulse-width,and it can operate steadily with stabilization rate over 90%,which meets the requirement of the probe lamp-house for laser plasma diagnosis.
The UV optical probe at xingguang-Ⅱ laser installations is pumped by a sub-laser beam.A pulse of 800ps with 1054nm wavelength is converted into an output UV pulse with 1mJ energy,60ps pulse-width and 308nm wavelength through stimulated Raman frequency conversion.The obtained UV laser pulse can be used as the lamp-house for laser plasma diagnosis.The original optical probe can't run steady because of poor quality and structure instability.In order to enhance the quality and stability,engineering alteration is performed on the original system.Experiment results prove that the optical probe can output an uniform pulse with 1mJ energy 30ps pulse-width,and it can operate steadily with stabilization rate over 90%,which meets the requirement of the probe lamp-house for laser plasma diagnosis.
2006, 30(5): 462-464,468.
Abstract:
It is studied the defect mode and bistability properties of a nonlinear medium sandwiched between Bragg reflectors composed of one-dimensional photonic crystal by numerical calculation and theoretical analysis.The influence of defect layer thickness and quasi-periodic Bragg reflectors on defect mode and bistability is discussed.It is revealed that the defect mode shift to lower frequency when the increasing thickness of defect layer or refractive index of Bragg reflectors.Hence microcavity resonant mode is superposition with incident wave mode at lower incident intensity,and produce the bistability with lower threshold.The numerical calculation results accord with theoretical analysis.It is significant for design of photonic crystal microcavity.
It is studied the defect mode and bistability properties of a nonlinear medium sandwiched between Bragg reflectors composed of one-dimensional photonic crystal by numerical calculation and theoretical analysis.The influence of defect layer thickness and quasi-periodic Bragg reflectors on defect mode and bistability is discussed.It is revealed that the defect mode shift to lower frequency when the increasing thickness of defect layer or refractive index of Bragg reflectors.Hence microcavity resonant mode is superposition with incident wave mode at lower incident intensity,and produce the bistability with lower threshold.The numerical calculation results accord with theoretical analysis.It is significant for design of photonic crystal microcavity.
2006, 30(5): 465-468.
Abstract:
In order to study uhe influence of elliptical birefringence on the polarization mode dispersion(PMD),the statistics of PMD with polarization dependent loss(PDL) is studied by using the polarization maintaining fiber(PMF) waveplate model and Monte Carlo simulations based on the elliptical birefringence.It is found that the elliptical birefringenceaffetcts the statistical distribution and mean values of PMD and the statistical distribution of PMD is the combination of Maxwell and Gaussian distribution.The obtained result is favor of the testing,compensation and system design of PMD.
In order to study uhe influence of elliptical birefringence on the polarization mode dispersion(PMD),the statistics of PMD with polarization dependent loss(PDL) is studied by using the polarization maintaining fiber(PMF) waveplate model and Monte Carlo simulations based on the elliptical birefringence.It is found that the elliptical birefringenceaffetcts the statistical distribution and mean values of PMD and the statistical distribution of PMD is the combination of Maxwell and Gaussian distribution.The obtained result is favor of the testing,compensation and system design of PMD.
2006, 30(5): 469-470,475.
Abstract:
The nonlinear optical properties of a novel dmit2- salt:(tetramethylammonium)bis(1,3-dithiole-2-thione-4,5-dithiolato) copper(abbreviated as MeCu) are studied with z-scan technique at 1064nm with 30ps laser duration.The nonlinear refraction coefficient n2 and the second hyperpolarizability γ have been determined to be -2.15×10-11 esu and 1.94×10-30 esu,respectively.No nonlinear absorption is observed under this condition.All the results show that MeCu is a potential material for nonlinear optical devices such as all-optical switches.
The nonlinear optical properties of a novel dmit2- salt:(tetramethylammonium)bis(1,3-dithiole-2-thione-4,5-dithiolato) copper(abbreviated as MeCu) are studied with z-scan technique at 1064nm with 30ps laser duration.The nonlinear refraction coefficient n2 and the second hyperpolarizability γ have been determined to be -2.15×10-11 esu and 1.94×10-30 esu,respectively.No nonlinear absorption is observed under this condition.All the results show that MeCu is a potential material for nonlinear optical devices such as all-optical switches.
2006, 30(5): 471-475.
Abstract:
The model for optimizing laser welding parameters of powder metallurgical material on back propagation(BP) artificial neural network was presented for laser welding application of thin-wall diamond core driller.The effects of laser welding parameters on porosity and welding strength were investigated with the model on the basis of one-side laser welding experiment by LSM240 auto-welding system.Laser welding parameters of thin-wall diamond core driller were optimized with the model,high quality laser welding seam with porosity defect are obtained.The results showed that the mathematic relation of the porosity with laser power and welding speed was power function and the mathematic relation of the welding strength with laser power and welding speed was Gaussian function.
The model for optimizing laser welding parameters of powder metallurgical material on back propagation(BP) artificial neural network was presented for laser welding application of thin-wall diamond core driller.The effects of laser welding parameters on porosity and welding strength were investigated with the model on the basis of one-side laser welding experiment by LSM240 auto-welding system.Laser welding parameters of thin-wall diamond core driller were optimized with the model,high quality laser welding seam with porosity defect are obtained.The results showed that the mathematic relation of the porosity with laser power and welding speed was power function and the mathematic relation of the welding strength with laser power and welding speed was Gaussian function.
2006, 30(5): 476-478.
Abstract:
In order to make new optical devices with photonic crystal,three reflective phase compensators made of 1-D photonic crystals are investigated with transfer matrix method and numerical value calculation.Three different compensators are discussed respectively by means of both parameters of reflective amplitude coefficient ratio.The results show that these reflective phase compensators own some advantages of high-reflectivity,continuous tunable phase compensation etc.
In order to make new optical devices with photonic crystal,three reflective phase compensators made of 1-D photonic crystals are investigated with transfer matrix method and numerical value calculation.Three different compensators are discussed respectively by means of both parameters of reflective amplitude coefficient ratio.The results show that these reflective phase compensators own some advantages of high-reflectivity,continuous tunable phase compensation etc.
2006, 30(5): 479-482.
Abstract:
The aim of the paper is to study the effect of the quintic nonlinearity of an optical fiber on the propagation of optical pulses.Utilizing the cubic-quintic nonlinear Schrdinger equation in which the dispersion of optical fibers is neglected,the nonlinear phase shifts and frequency chirps of super-Gaussian optical pulses are calculated and investigated analytically.The power spectra of optical pulses are numerically simulated as well.The results show that the positive quintic nonlinear refractive index makes the nonlinear phase shifts and the maximum frequency chirps of optical pulses larger,the spectral width of unchirped optical pulses wider and the number of spectral peaks more than those of cubic nonlinear refractive index.The influence of initial chirps of Gaussian optical pulses on the spectra is similar to that of cubic nonlinear refractive index.In case of the negative quintic nonlinear refractive index,the nonlinear phase shifts and frequency chirps take on new characteristics.The negative quintic nonlinear refractive index also makes the width of unchirped optical pulses narrower and the number of spectral peaks less.
The aim of the paper is to study the effect of the quintic nonlinearity of an optical fiber on the propagation of optical pulses.Utilizing the cubic-quintic nonlinear Schrdinger equation in which the dispersion of optical fibers is neglected,the nonlinear phase shifts and frequency chirps of super-Gaussian optical pulses are calculated and investigated analytically.The power spectra of optical pulses are numerically simulated as well.The results show that the positive quintic nonlinear refractive index makes the nonlinear phase shifts and the maximum frequency chirps of optical pulses larger,the spectral width of unchirped optical pulses wider and the number of spectral peaks more than those of cubic nonlinear refractive index.The influence of initial chirps of Gaussian optical pulses on the spectra is similar to that of cubic nonlinear refractive index.In case of the negative quintic nonlinear refractive index,the nonlinear phase shifts and frequency chirps take on new characteristics.The negative quintic nonlinear refractive index also makes the width of unchirped optical pulses narrower and the number of spectral peaks less.
2006, 30(5): 483-485.
Abstract:
A new kind of real-time power control system of fast flow CO2 lasers is developed to improve the stability of laser power,which is composed of two parts:sampling unit and feedback control unit.In the sampling unit,an infrared detector is used to sample the laser power output from the rear mirror of the resonator.With an attenuator inserted between the detector and the rear mirror to prevent the detector from damage by the laser.In the feedback control system,the sampling signal is compared with the setting reference value,and the discharge current is automatically adjusted to make the output laser power stable around the setting power.The experimental results indicate that this system can automatically control the laser power on line,and greatly enhance the stability and accuracy of the laser power without any accessory inserted in the output laser path.This system has been successfully used in a 4kW fast-flow CO2 laser with much better output power stability of ±0.1%.
A new kind of real-time power control system of fast flow CO2 lasers is developed to improve the stability of laser power,which is composed of two parts:sampling unit and feedback control unit.In the sampling unit,an infrared detector is used to sample the laser power output from the rear mirror of the resonator.With an attenuator inserted between the detector and the rear mirror to prevent the detector from damage by the laser.In the feedback control system,the sampling signal is compared with the setting reference value,and the discharge current is automatically adjusted to make the output laser power stable around the setting power.The experimental results indicate that this system can automatically control the laser power on line,and greatly enhance the stability and accuracy of the laser power without any accessory inserted in the output laser path.This system has been successfully used in a 4kW fast-flow CO2 laser with much better output power stability of ±0.1%.
2006, 30(5): 486-489,493.
Abstract:
The development of laser welding diamond saw blade including backing layer composition,welding process and welding product test is reviewed.The backing layer composition is consisted of single element such as Co and Ni,or two elements such as FeCo,FeNi,CoNi,FeCu,or three elements such as FeCoNi and FeCoCu,and the backing layer including Co element is suitable for the laser welding.The laser welding process of diamond saw blade is advanced.The welding products should be tested especially for welding strength.The current problems are lacking in the mechanism and numerical model of laser welding,the pre-alloyed powder of backing layer and the online quality test technique.The above problems should be focused on in the future study.
The development of laser welding diamond saw blade including backing layer composition,welding process and welding product test is reviewed.The backing layer composition is consisted of single element such as Co and Ni,or two elements such as FeCo,FeNi,CoNi,FeCu,or three elements such as FeCoNi and FeCoCu,and the backing layer including Co element is suitable for the laser welding.The laser welding process of diamond saw blade is advanced.The welding products should be tested especially for welding strength.The current problems are lacking in the mechanism and numerical model of laser welding,the pre-alloyed powder of backing layer and the online quality test technique.The above problems should be focused on in the future study.
2006, 30(5): 490-493.
Abstract:
Laser double texturing of metal and non-metal substrate disks is introduced.The difference between the laser and traditional technique,application,process and mechanism are also introduced.This technique employs Nd:YVO4 or CO2 laser to provide a high repetition rate short-pulsed laser acting on the inner circle substrate surface of the disk,change the surface topographical feature and create a great number of bumps with rounded protrusions.The laser texture zone provides a precision contact start/stop zone for the contacting slider.
Laser double texturing of metal and non-metal substrate disks is introduced.The difference between the laser and traditional technique,application,process and mechanism are also introduced.This technique employs Nd:YVO4 or CO2 laser to provide a high repetition rate short-pulsed laser acting on the inner circle substrate surface of the disk,change the surface topographical feature and create a great number of bumps with rounded protrusions.The laser texture zone provides a precision contact start/stop zone for the contacting slider.
2006, 30(5): 494-497.
Abstract:
In the field of laser radiation protection and photoelectric countermeasure,it is important to find out the laser damaged characteristics of photovoltaic detectors.Considering the damaged area and the open circuit voltage,different performance of pulse laser induced damage to photovoltaic detectors in vacuum and atmosphere environments is investigated.The measuring object is uncovered 2CR 10×2.5 four-quadrant silicon photo cell and the irradiation source is 1064nm wavelength pulsed solid-state Nd:YAG laser.In both vacuum and atmosphere,the damage threshold and damage spot appearance of the photovoltaic detector are discussed under single pulse or multi-pulse laser irradiation.The difference of the damage area and their influence on the photovoltaic detector are compared experimentally in both environments.The results show that the laser induced damage threshold in vacuum is obviously lower than that in atmosphere.It is about forty percent of that in atmosphere under the experimental condition.
In the field of laser radiation protection and photoelectric countermeasure,it is important to find out the laser damaged characteristics of photovoltaic detectors.Considering the damaged area and the open circuit voltage,different performance of pulse laser induced damage to photovoltaic detectors in vacuum and atmosphere environments is investigated.The measuring object is uncovered 2CR 10×2.5 four-quadrant silicon photo cell and the irradiation source is 1064nm wavelength pulsed solid-state Nd:YAG laser.In both vacuum and atmosphere,the damage threshold and damage spot appearance of the photovoltaic detector are discussed under single pulse or multi-pulse laser irradiation.The difference of the damage area and their influence on the photovoltaic detector are compared experimentally in both environments.The results show that the laser induced damage threshold in vacuum is obviously lower than that in atmosphere.It is about forty percent of that in atmosphere under the experimental condition.
2006, 30(5): 498-500,506.
Abstract:
In order to understand the mechanism and effect factors of laser-arc hybrid welding,hybrid welding combining CO2 laser and pulsed metal active gas(MAG) arc are taken to weld mild steels,and the effect of various parameters on the welding penetration depth and quality is studied.Laser and arc can be coupled to enhance welding quality if using suitable parameters.Compared with laser welding and MAG welding respectively,hybrid welding penetration can be increased by 1.6 and 2.2 times,while hybrid welding speed can increase 2.7 times that of laser welding.
In order to understand the mechanism and effect factors of laser-arc hybrid welding,hybrid welding combining CO2 laser and pulsed metal active gas(MAG) arc are taken to weld mild steels,and the effect of various parameters on the welding penetration depth and quality is studied.Laser and arc can be coupled to enhance welding quality if using suitable parameters.Compared with laser welding and MAG welding respectively,hybrid welding penetration can be increased by 1.6 and 2.2 times,while hybrid welding speed can increase 2.7 times that of laser welding.
2006, 30(5): 501-503.
Abstract:
A gain-switched Cr4+:Mg2SiO4 laser pumped by a 1.06μm Q-switched laser pulse with lower energy is investigated.By numerically solving the rate equations and choosing the suitable initial conditions,the temporal profile of the(1.22μm) laser pulse is obtained.Simultaneously the relations of the buildup time and the pulse-duration of the 1.22μm laser with the pump energy are achieved respectively and the theoretical and experimental results basically coincide with each other.When the energy and the pulse-duration of the pump laser pulse are 45mJ and 30ns respectively,a 1.22μm laser pulse is achieved with the energy of 7mJ and the pulse-duration of 8.2ns.The pulse-duration of the output laser is nearly a quarter of that of the pump laser and the transfer efficiency is 15.5%.The numerical calculation and the experimental results show that both the buildup time and pulse-duration decreased as the pump energy increasing.
A gain-switched Cr4+:Mg2SiO4 laser pumped by a 1.06μm Q-switched laser pulse with lower energy is investigated.By numerically solving the rate equations and choosing the suitable initial conditions,the temporal profile of the(1.22μm) laser pulse is obtained.Simultaneously the relations of the buildup time and the pulse-duration of the 1.22μm laser with the pump energy are achieved respectively and the theoretical and experimental results basically coincide with each other.When the energy and the pulse-duration of the pump laser pulse are 45mJ and 30ns respectively,a 1.22μm laser pulse is achieved with the energy of 7mJ and the pulse-duration of 8.2ns.The pulse-duration of the output laser is nearly a quarter of that of the pump laser and the transfer efficiency is 15.5%.The numerical calculation and the experimental results show that both the buildup time and pulse-duration decreased as the pump energy increasing.
2006, 30(5): 504-506.
Abstract:
Photonic crystals were the new artificial complex media during the last decades,however its transmission property might change a lot if new material with negative refraction index are inserted.The main properties of the band gap and dispersion structure of the one-dimensional photonic crystal,whose each period consisting of one layer of a usual material and one layer of negative refractive material,are studied based on Maxwell equation and Bloch theory.Our analysis results show it possible to make the band gap of the periodically-layered photonic crystals wider than the usual material,which offers a possibility to design photonic band gap structure with wide stop bands.
Photonic crystals were the new artificial complex media during the last decades,however its transmission property might change a lot if new material with negative refraction index are inserted.The main properties of the band gap and dispersion structure of the one-dimensional photonic crystal,whose each period consisting of one layer of a usual material and one layer of negative refractive material,are studied based on Maxwell equation and Bloch theory.Our analysis results show it possible to make the band gap of the periodically-layered photonic crystals wider than the usual material,which offers a possibility to design photonic band gap structure with wide stop bands.
2006, 30(5): 507-510.
Abstract:
The influence of laser shock of Ni-Co sample on plasticity deformation,hardness,stress and life is studied experimentally and simulated by ABAQUS.The results indicate that laser shock can make shock area produce residual pressure stress and hardness of shock area be enhanced.By test on an automobile,the average life of the impacted spark plug is testified to be enhanced by almost one times than the crude spark plug.The results prove that the laser impact strengthening technology is a prospective measure for enhancing the lifespan of the spark plug.
The influence of laser shock of Ni-Co sample on plasticity deformation,hardness,stress and life is studied experimentally and simulated by ABAQUS.The results indicate that laser shock can make shock area produce residual pressure stress and hardness of shock area be enhanced.By test on an automobile,the average life of the impacted spark plug is testified to be enhanced by almost one times than the crude spark plug.The results prove that the laser impact strengthening technology is a prospective measure for enhancing the lifespan of the spark plug.
2006, 30(5): 511-513.
Abstract:
In order to study the effect on the properties of laser peened brass,a brass sample is processed with Nd:YAG lasers and its hardness,residual stress,roughness and texture are examined and analyzed.The experimental results show that its hardness can be improved up to 25% and the compressive residual stress can reach-200MPa～-250MPa.On the other hand,compared with the unshocked area,the surface smoothness and the microstructure have no remarkable change.
In order to study the effect on the properties of laser peened brass,a brass sample is processed with Nd:YAG lasers and its hardness,residual stress,roughness and texture are examined and analyzed.The experimental results show that its hardness can be improved up to 25% and the compressive residual stress can reach-200MPa～-250MPa.On the other hand,compared with the unshocked area,the surface smoothness and the microstructure have no remarkable change.
