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RSS2007 Vol. 31, No. 6
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2007, 31(6): 561-564.
[Abstract]
[PDF 197KB]
Abstract:
The technology of beam combination is an effective method to obtain high power and quality beams.Aiming at the demand of high power beams in the device of ICF in the future,an isosceles triangle phase grating was designed.Simulated and analyzed results indicated that the combination efficiency of four incident beams reached 90.2%,which was 22% higher than the efficiency of Dammann phase grating.Besides,the processing of the isosceles triangle phase grating was not difficult.So it is important and practical perspective in the future.
The technology of beam combination is an effective method to obtain high power and quality beams.Aiming at the demand of high power beams in the device of ICF in the future,an isosceles triangle phase grating was designed.Simulated and analyzed results indicated that the combination efficiency of four incident beams reached 90.2%,which was 22% higher than the efficiency of Dammann phase grating.Besides,the processing of the isosceles triangle phase grating was not difficult.So it is important and practical perspective in the future.
2007, 31(6): 565-567,580.
Abstract:
Numerical simulation for temperature field and crater on the laser ablation in laser micro-texture sculpt was performed by means of finite-difference method.Based on energy conservation equation,Gaussian distribution of the incident laser pulse was taken into account in the numerical model.The distribution of the temperature field of the target in the laser micro-texture sculpt was simulated and so were the depth and diameter of the crater.The simulated results were compared with the experiment before.The former accorded well with the latter.This study established the basic theory in laser micro-machining.
Numerical simulation for temperature field and crater on the laser ablation in laser micro-texture sculpt was performed by means of finite-difference method.Based on energy conservation equation,Gaussian distribution of the incident laser pulse was taken into account in the numerical model.The distribution of the temperature field of the target in the laser micro-texture sculpt was simulated and so were the depth and diameter of the crater.The simulated results were compared with the experiment before.The former accorded well with the latter.This study established the basic theory in laser micro-machining.
2007, 31(6): 568-570.
Abstract:
To obtain a narrow free-spectral range and controllable finesse,twin parallel channel waveguides are completely back coupled by a chirped Bragg grating,and cleaved facet mirrors are fabricated at the entrance of the coupling region.Thereby,the grating dispersion is introduced into the FabryPerot cavity,and the control of the cleaved facet mirrors on the finesse is maintained.The free-spectral range is determined not only by the cavity length,but also by the dispersion profile.A wide adjustment range of free-spectral range can be obtained by the adjustment of the grating profile.Numerical simulation and analyses show that the compression ratio of free-spectral range of the order of magnitude of 1000 can be obtained by this chirped Bragg grating F-P filter under the comparable device dimensions with conventional two-mirror F-P,and the free-spectral range will not be affected by the adjustment of finesse.
To obtain a narrow free-spectral range and controllable finesse,twin parallel channel waveguides are completely back coupled by a chirped Bragg grating,and cleaved facet mirrors are fabricated at the entrance of the coupling region.Thereby,the grating dispersion is introduced into the FabryPerot cavity,and the control of the cleaved facet mirrors on the finesse is maintained.The free-spectral range is determined not only by the cavity length,but also by the dispersion profile.A wide adjustment range of free-spectral range can be obtained by the adjustment of the grating profile.Numerical simulation and analyses show that the compression ratio of free-spectral range of the order of magnitude of 1000 can be obtained by this chirped Bragg grating F-P filter under the comparable device dimensions with conventional two-mirror F-P,and the free-spectral range will not be affected by the adjustment of finesse.
2007, 31(6): 571-574.
Abstract:
Based on many experiments of CO2 laser welding of zinc coated high strength steel to vehicle body,joint microstructure and stress-strain curve of specimen were acquired.In the course of experiments,the sort of welding protective gas was selected,the influence of technological parameter on material melting characteristic of deep penetration welding was analyzed.By adopting blowing side protective gas,the problem that gas hole was easy to form owed to evaporation of zinc and moisture of circumstances in laser welding was solved.The experimental result indicated that deep penetration laser welding could effectively avoid softening heat affecting zone,control the gas hole and restrain joint flaw of welding of zinc coated high strength steel by blowing side protective gas.
Based on many experiments of CO2 laser welding of zinc coated high strength steel to vehicle body,joint microstructure and stress-strain curve of specimen were acquired.In the course of experiments,the sort of welding protective gas was selected,the influence of technological parameter on material melting characteristic of deep penetration welding was analyzed.By adopting blowing side protective gas,the problem that gas hole was easy to form owed to evaporation of zinc and moisture of circumstances in laser welding was solved.The experimental result indicated that deep penetration laser welding could effectively avoid softening heat affecting zone,control the gas hole and restrain joint flaw of welding of zinc coated high strength steel by blowing side protective gas.
2007, 31(6): 575-577.
Abstract:
The effect of the technology parameters(laser current,laser pulse time and N2 pressure) for fluxless laser jet bumping on the bump's peel strength under N2 protecting conditions were investigated;the interfacial microstructure and composition of the intermetallic compound at bump(Sn63Pb37)/pad(Au/Ni/Cu) were analyzed in term of scanning electron microscopy and energy dispersive spectrometer.As the laser pulse time is constant,the peel strength decreases with increasing laser current;as the laser current is constant,the peel strength increases with increasing laser pulse time.In case of obtaining good bump's appearance,larger laser current along with shorter pulse time results in the decrease of bump's peel strength,smaller laser current along with longer pulse time increases bump's peel strength.Under existing test conditions,solder ball(Sn63Pb37) may wet the pad(Au/Ni/Cu) commendably.The continuous AuSn4 intermetallic compound layer is formed at the bump/pad interface and AuSn4 is detected in the solder pump near the interface.
The effect of the technology parameters(laser current,laser pulse time and N2 pressure) for fluxless laser jet bumping on the bump's peel strength under N2 protecting conditions were investigated;the interfacial microstructure and composition of the intermetallic compound at bump(Sn63Pb37)/pad(Au/Ni/Cu) were analyzed in term of scanning electron microscopy and energy dispersive spectrometer.As the laser pulse time is constant,the peel strength decreases with increasing laser current;as the laser current is constant,the peel strength increases with increasing laser pulse time.In case of obtaining good bump's appearance,larger laser current along with shorter pulse time results in the decrease of bump's peel strength,smaller laser current along with longer pulse time increases bump's peel strength.Under existing test conditions,solder ball(Sn63Pb37) may wet the pad(Au/Ni/Cu) commendably.The continuous AuSn4 intermetallic compound layer is formed at the bump/pad interface and AuSn4 is detected in the solder pump near the interface.
2007, 31(6): 578-580.
Abstract:
In order to quantify the heat affected zone(HAZ) of femtosecond machining.Based on a two-dimensional model of the two temperature model(TTM),the radial heat affected zone of femtosecond laser ablation on nickel was simulated numerically with finite-difference method.The radial HAZ was defined as two parts,one was the melting and resolidification zone(between melting temperature and phase explosion temperature) and the other was thermal activation zone(between thermal activation temperature and melting temperature).The evolution of the temperature as a function of time was studied,leading to a radial HAZ width of 160nm for 500nm thick Ni samples,which showed that the heat affected zone of femtosecond machining is very small.Besides,the effects of the thermal conductivity and the specific heat of the electron on the radial HAZ were analyzed.
In order to quantify the heat affected zone(HAZ) of femtosecond machining.Based on a two-dimensional model of the two temperature model(TTM),the radial heat affected zone of femtosecond laser ablation on nickel was simulated numerically with finite-difference method.The radial HAZ was defined as two parts,one was the melting and resolidification zone(between melting temperature and phase explosion temperature) and the other was thermal activation zone(between thermal activation temperature and melting temperature).The evolution of the temperature as a function of time was studied,leading to a radial HAZ width of 160nm for 500nm thick Ni samples,which showed that the heat affected zone of femtosecond machining is very small.Besides,the effects of the thermal conductivity and the specific heat of the electron on the radial HAZ were analyzed.
2007, 31(6): 581-583.
Abstract:
Because of the cloud barrier in a remote sensing image,the information couldn't be captured.Based on spline curve,a proposed method kept the continuity between inner and outer edge of cloud and captures more details in the remote sensing image without previous information.Firstly,the brightness in the cloud region was stretched.Secondly,the more details in the cloud region was exposed after the convolution between the cloud region and a high pass filter.Thirdly,the brightness of the pixels in the cloud region was improved with histogram stretching method.The results show the more details,such as the wall of dam,water stream can be exposed in a remote sensing image in which over a quarter of whole size was covered black cloud,which means the image enhancement technology is multiformity.
Because of the cloud barrier in a remote sensing image,the information couldn't be captured.Based on spline curve,a proposed method kept the continuity between inner and outer edge of cloud and captures more details in the remote sensing image without previous information.Firstly,the brightness in the cloud region was stretched.Secondly,the more details in the cloud region was exposed after the convolution between the cloud region and a high pass filter.Thirdly,the brightness of the pixels in the cloud region was improved with histogram stretching method.The results show the more details,such as the wall of dam,water stream can be exposed in a remote sensing image in which over a quarter of whole size was covered black cloud,which means the image enhancement technology is multiformity.
2007, 31(6): 584-586.
Abstract:
In order to study the damping characteristics of the liquid surface waves,the relation between the liquid surface wave amplitude and the spreading distance was testified experimentally and analyzed theoretically by means of laser diffraction.The experimental results indicated that the liquid surface wave amplitude declined exponentially with the spreading distance and the damping coefficient,which varied lineally with frequency,has dispersive characteristics.The conclusion is valuable for liquid surface wave detecting and application.
In order to study the damping characteristics of the liquid surface waves,the relation between the liquid surface wave amplitude and the spreading distance was testified experimentally and analyzed theoretically by means of laser diffraction.The experimental results indicated that the liquid surface wave amplitude declined exponentially with the spreading distance and the damping coefficient,which varied lineally with frequency,has dispersive characteristics.The conclusion is valuable for liquid surface wave detecting and application.
2007, 31(6): 587-589,592.
Abstract:
A simple method which can measure the chirp of femtosecond laser pulses was described.Modified spectrum autointerferometric correlation(MOSAIC) uses spectral filtering of the interferometric autocorrelation(IAC) to render a waveform that is highly sensitive to chirp.The Gaussian intensity of femto-second chirped pulses was numerically calculated.The peak of the MOSAIC minima envelope as a function of the normalized mean chirp for different orders of chirp and MOSAIC peak number corresponding to the first-and second-order chirps were obtained.Low chirp of femto-second laser pulses can be determined accurately with the MOSAIC.
A simple method which can measure the chirp of femtosecond laser pulses was described.Modified spectrum autointerferometric correlation(MOSAIC) uses spectral filtering of the interferometric autocorrelation(IAC) to render a waveform that is highly sensitive to chirp.The Gaussian intensity of femto-second chirped pulses was numerically calculated.The peak of the MOSAIC minima envelope as a function of the normalized mean chirp for different orders of chirp and MOSAIC peak number corresponding to the first-and second-order chirps were obtained.Low chirp of femto-second laser pulses can be determined accurately with the MOSAIC.
2007, 31(6): 590-592.
Abstract:
In order to analyze the intensity and position of the diffraction pattern from the liquid surface wave,a low-frequency signal generator was used to produce a sinusoidal output at low frequency,which was then used to drive the surface acoustic wave(SAW)exciter.A laser beam was directly incident upon the water surface where the SAW was excited and diffracted.Thus,a technique for low-frequency SAW visualization was developed based on the light diffration.The intensity curve was draun and the intensity and position of each-order diffraction spots were obtained.The asymmetrical position and intensity were also discovered.The dependence of the diffraction intensity on the liquid surface waves was theoretically derived.The approximate conditions of the surface wave diffraction and the half angular width were analyzed,respectively.When laser was at normal incidence,the symmetrical distribution was theoretically derived.The theoretical and experimental results are in good agreement.
In order to analyze the intensity and position of the diffraction pattern from the liquid surface wave,a low-frequency signal generator was used to produce a sinusoidal output at low frequency,which was then used to drive the surface acoustic wave(SAW)exciter.A laser beam was directly incident upon the water surface where the SAW was excited and diffracted.Thus,a technique for low-frequency SAW visualization was developed based on the light diffration.The intensity curve was draun and the intensity and position of each-order diffraction spots were obtained.The asymmetrical position and intensity were also discovered.The dependence of the diffraction intensity on the liquid surface waves was theoretically derived.The approximate conditions of the surface wave diffraction and the half angular width were analyzed,respectively.When laser was at normal incidence,the symmetrical distribution was theoretically derived.The theoretical and experimental results are in good agreement.
2007, 31(6): 593-595,599.
Abstract:
To research the transmission characteristic of low power signal optical pulse outside the stop band of uniform periodic structure,the theory analysis was run by the numerical result of the nonlinear Schrdinger equation.The relation curve of pulse width and peak power against the transmission,and the slow light delay of pulse with difference frequency deturning were shown.Results show:pulse waveform will experience a very remarkably evolution,and the peak power of output pulse will hold comparative to that of the incident pulse when the incident pulse has appropriate initial chirp parameter.The theory results obtained will produce importance reference value in experiment.
To research the transmission characteristic of low power signal optical pulse outside the stop band of uniform periodic structure,the theory analysis was run by the numerical result of the nonlinear Schrdinger equation.The relation curve of pulse width and peak power against the transmission,and the slow light delay of pulse with difference frequency deturning were shown.Results show:pulse waveform will experience a very remarkably evolution,and the peak power of output pulse will hold comparative to that of the incident pulse when the incident pulse has appropriate initial chirp parameter.The theory results obtained will produce importance reference value in experiment.
2007, 31(6): 596-599.
Abstract:
In order to realize the automation of the container yard work,a fast and accurate chassis positioning system is needed urgently.A 3-D laser radar scanning system,which was made up of a motion control card,a stepper motor and a 2-D laser radar,was designed to satisfy the requirement.On this foundation,more than one 3-D laser radar system work way and improved ICP algorithm which adapts with 3-D laser radar system data processing and gradually localization method were applied in the chassis positioning system.The result of industry tries indicates that the loading efficiency achieved 80TEU/h and the control precision was less than 5mm.It is the first time that pilotless rail mounted gantry RMG is used to locate the container truck fast and accurately.This system also has much significance on other large-scale part examination and localization.
In order to realize the automation of the container yard work,a fast and accurate chassis positioning system is needed urgently.A 3-D laser radar scanning system,which was made up of a motion control card,a stepper motor and a 2-D laser radar,was designed to satisfy the requirement.On this foundation,more than one 3-D laser radar system work way and improved ICP algorithm which adapts with 3-D laser radar system data processing and gradually localization method were applied in the chassis positioning system.The result of industry tries indicates that the loading efficiency achieved 80TEU/h and the control precision was less than 5mm.It is the first time that pilotless rail mounted gantry RMG is used to locate the container truck fast and accurately.This system also has much significance on other large-scale part examination and localization.
The spectroscopic property of erbium ytterbium co-doped alumina material prepared by sol-gel process
2007, 31(6): 600-602,606.
Abstract:
The alumina powder co-doped with different ratio of Yb3+Er3+ was prepared with an advanced sol-gel method as batter material used for Er3+ doped waveguide amplifier.The absorption and emission spectra ware measured and analysed.The result indicated that the incorporation of Yb3+ could enhance the absorption of 980nm exciting light,for the Er3+ and Yb3+ co-doped alumina power,the photoluminescence peak intensity at 1533nm was increased by a factor of about 6.3 compared with that of the Er3+ doped alumina powders.And optimum ratio of the Yb3+:Er3+ was 6:1 for this method.The X-ray diffraction spectra show that the best thermal treatment temperature was 900℃,and the incorporation of Yb3+could postponed the forming of γ-phase at 900℃ thermal treatment condition.The result is helpful for making more effective Er3+ doped waveguide amplifier.
The alumina powder co-doped with different ratio of Yb3+Er3+ was prepared with an advanced sol-gel method as batter material used for Er3+ doped waveguide amplifier.The absorption and emission spectra ware measured and analysed.The result indicated that the incorporation of Yb3+ could enhance the absorption of 980nm exciting light,for the Er3+ and Yb3+ co-doped alumina power,the photoluminescence peak intensity at 1533nm was increased by a factor of about 6.3 compared with that of the Er3+ doped alumina powders.And optimum ratio of the Yb3+:Er3+ was 6:1 for this method.The X-ray diffraction spectra show that the best thermal treatment temperature was 900℃,and the incorporation of Yb3+could postponed the forming of γ-phase at 900℃ thermal treatment condition.The result is helpful for making more effective Er3+ doped waveguide amplifier.
2007, 31(6): 603-606.
Abstract:
New binary joint transform correlator(BJTC) based on differential operation was proposed.It can well resolve the disadvantages about the bottleneck of real-time processing and thresholding selection in BJTC.The unwanted term in joint power spectrum(JPS) varies slowly compared with wanted term.It is reasonable to use differential operation to improve JTC's contrast by depressing the auto-correlate peak and enhancing the cross-correlate peak.Then the differential JPS was binarized to only two values at Fourier plane before inverse Fourier transform.Then higher cross-correlate output between references and object image can be obtained.Simulation results show the proposed JTC can well weakens auto-correlation peak and enhances cross-correlation peak.It also has better robustness.The proposed method can avoid computing or pre-setup threshold.Furthermore,it's quite simple differential operation and binarization require far fewer digital computations than does the BJTC.
New binary joint transform correlator(BJTC) based on differential operation was proposed.It can well resolve the disadvantages about the bottleneck of real-time processing and thresholding selection in BJTC.The unwanted term in joint power spectrum(JPS) varies slowly compared with wanted term.It is reasonable to use differential operation to improve JTC's contrast by depressing the auto-correlate peak and enhancing the cross-correlate peak.Then the differential JPS was binarized to only two values at Fourier plane before inverse Fourier transform.Then higher cross-correlate output between references and object image can be obtained.Simulation results show the proposed JTC can well weakens auto-correlation peak and enhances cross-correlation peak.It also has better robustness.The proposed method can avoid computing or pre-setup threshold.Furthermore,it's quite simple differential operation and binarization require far fewer digital computations than does the BJTC.
2007, 31(6): 607-609,612.
Abstract:
In order to realize the monomode output in large core multimode double-clad fiber laser to suppress the nonlinear effects in high power double-clad fiber lasers,mode selection by bending the large core multimode double-clad fiber to a suitable radius was used.Theoretical analysis and experiments about mode selection in large core multimode double-clad fiber laser were demonstrated in this paper.Factors that influence the laser bending loss and output mode,such as inner-clad refractive index,core radius,laser wavelength,bending radius,were obtained.Monomode output was obtained from multimode double-clad fiber laser by bending the homemade Yb3+-doped large core multimode fiber.The laser has a fundamental mode output with power of 9W,conversion efficiency of 17.3%.The research is useful in mode selection from large core multimode double-clad fiber laser.
In order to realize the monomode output in large core multimode double-clad fiber laser to suppress the nonlinear effects in high power double-clad fiber lasers,mode selection by bending the large core multimode double-clad fiber to a suitable radius was used.Theoretical analysis and experiments about mode selection in large core multimode double-clad fiber laser were demonstrated in this paper.Factors that influence the laser bending loss and output mode,such as inner-clad refractive index,core radius,laser wavelength,bending radius,were obtained.Monomode output was obtained from multimode double-clad fiber laser by bending the homemade Yb3+-doped large core multimode fiber.The laser has a fundamental mode output with power of 9W,conversion efficiency of 17.3%.The research is useful in mode selection from large core multimode double-clad fiber laser.
2007, 31(6): 610-612.
Abstract:
The experimental study of ultrashort pulse Yb3+-doped fiber ring laser was reported.The Yb3+-doped fiber laser was pumped by two 976nm semiconductor lasers.Self-starting mode-locking of the fiber laser was demonstrated by employing the polarization additive pulse mode-locking.Wavelength tuning of the short pulse was carried out by changing the length of the Yb3+-doped fiber and the position of the polarization controllers.When the Yb3+-doped fiber length was 1.6m,the laser oscillate at 1053nm with 9.5mW maximum output power and 23.7MHz repetition frequency,corresponding to ～6nm spectrum width.The result shows:the wavelength-tunable fiber laser of ultrashort pulse is achieved by changing the length of the Yb3+-doped fiber and the position of the polarization controller.
The experimental study of ultrashort pulse Yb3+-doped fiber ring laser was reported.The Yb3+-doped fiber laser was pumped by two 976nm semiconductor lasers.Self-starting mode-locking of the fiber laser was demonstrated by employing the polarization additive pulse mode-locking.Wavelength tuning of the short pulse was carried out by changing the length of the Yb3+-doped fiber and the position of the polarization controllers.When the Yb3+-doped fiber length was 1.6m,the laser oscillate at 1053nm with 9.5mW maximum output power and 23.7MHz repetition frequency,corresponding to ～6nm spectrum width.The result shows:the wavelength-tunable fiber laser of ultrashort pulse is achieved by changing the length of the Yb3+-doped fiber and the position of the polarization controller.
2007, 31(6): 613-615,619.
Abstract:
To study the generation of ultrashort pulse in Er3+-doped fiber laser,the fiber laser was composed of a gain-flattened erbium doped fiber amplifier(EDFA),two polarization controllers(PCs) and three couplers.A nonlinear optical loop mirror was used for mode-locking.By adjusting the position of PCs,the pulse at 1561nm at a repetition rate 1.1MHz was obtained.The maximum output power of the pulse was 0.6mW with 434ps pulse width and 9nm spectrum width.After amplified by EDFA,the maximum power of the output pulse is 10.8mW and the center wavelength did not change,the spectrum width became slightly narrow,the output power increases greatly and the pulse width of the amplified pulse was 495ps.The experimental results show that:the ultrashort pulse could be generated by the Er3+-doped fiber laser using a commercial EDFA.The self-starting of the mode-locked fiber laser can be achieved easily and the mode-locked operation can be hardly influenced by the experimental environment.
To study the generation of ultrashort pulse in Er3+-doped fiber laser,the fiber laser was composed of a gain-flattened erbium doped fiber amplifier(EDFA),two polarization controllers(PCs) and three couplers.A nonlinear optical loop mirror was used for mode-locking.By adjusting the position of PCs,the pulse at 1561nm at a repetition rate 1.1MHz was obtained.The maximum output power of the pulse was 0.6mW with 434ps pulse width and 9nm spectrum width.After amplified by EDFA,the maximum power of the output pulse is 10.8mW and the center wavelength did not change,the spectrum width became slightly narrow,the output power increases greatly and the pulse width of the amplified pulse was 495ps.The experimental results show that:the ultrashort pulse could be generated by the Er3+-doped fiber laser using a commercial EDFA.The self-starting of the mode-locked fiber laser can be achieved easily and the mode-locked operation can be hardly influenced by the experimental environment.
2007, 31(6): 616-619.
Abstract:
In order to study the threshold characteristics of coupled-cavity vertical-cavity surface emitting lasers(CC-VCSELs),the threshold carrier density of CC-VCSELs was calculated based on transfer matrix method.Then the threshold current was discussed with the carrier rate equation based on threshold carrier density.The curve of "Double Threshold" point(1mA,0.75mA) and threshold currents curve was obtained.Numerical calculated shows that the results obtained by transfer matrix and carrier rate equation are better than those obtained by rate equation,and the calculation result agreed with the experiment.
In order to study the threshold characteristics of coupled-cavity vertical-cavity surface emitting lasers(CC-VCSELs),the threshold carrier density of CC-VCSELs was calculated based on transfer matrix method.Then the threshold current was discussed with the carrier rate equation based on threshold carrier density.The curve of "Double Threshold" point(1mA,0.75mA) and threshold currents curve was obtained.Numerical calculated shows that the results obtained by transfer matrix and carrier rate equation are better than those obtained by rate equation,and the calculation result agreed with the experiment.
2007, 31(6): 620-623.
Abstract:
In order to simplify the complicated theory and calculation about arrayed wave-guide gratings(AWG),a simple analysis theory method is provided for the design of AWG,in which the gaussian approximation of the field distribution of the mode in an wave-guide,effective index method and Marcatili method were adopted to analyze the optical wave-guides,without regard to the dispersion of the slab wave-guides.Based on the above approximation,a simple and practical AWG calculation method is obtained.
In order to simplify the complicated theory and calculation about arrayed wave-guide gratings(AWG),a simple analysis theory method is provided for the design of AWG,in which the gaussian approximation of the field distribution of the mode in an wave-guide,effective index method and Marcatili method were adopted to analyze the optical wave-guides,without regard to the dispersion of the slab wave-guides.Based on the above approximation,a simple and practical AWG calculation method is obtained.
2007, 31(6): 624-626,629.
Abstract:
To describe ultrashort laser ablation on semiconductor surface,numerical simulation of the double-temperature equation is performed by finite-difference method.The temperature fields of femtosecond,picosecond pulses laser ablation on semiconductor are showed.The results indicate that metal and semiconductor have the same time of the couple with carrier temperature and lattice temperature.Laser pulse power density is the main factors affecting temperature of carrier,the simulation results are accorded with the experiment reported by others.
To describe ultrashort laser ablation on semiconductor surface,numerical simulation of the double-temperature equation is performed by finite-difference method.The temperature fields of femtosecond,picosecond pulses laser ablation on semiconductor are showed.The results indicate that metal and semiconductor have the same time of the couple with carrier temperature and lattice temperature.Laser pulse power density is the main factors affecting temperature of carrier,the simulation results are accorded with the experiment reported by others.
2007, 31(6): 627-629.
Abstract:
In order to solve the problem that power spectral density function(PSD) is only an evaluation guideline to specify large aperture optical components' quality of laser system and can't provide effective guidance for eliminating certain frequency segment error,a wavelet method was used to analysis the optical surface errors.Firstly,PSD character curve was used to find the unqualified frequency range;secondly,two-dimensional continuous wavelet transform was used to find the corresponding region of this frequency segment,which can use as feedback to a machining process.The experiments' results show the use of wavelet can find the corresponding region of certain frequency segment effectively.
In order to solve the problem that power spectral density function(PSD) is only an evaluation guideline to specify large aperture optical components' quality of laser system and can't provide effective guidance for eliminating certain frequency segment error,a wavelet method was used to analysis the optical surface errors.Firstly,PSD character curve was used to find the unqualified frequency range;secondly,two-dimensional continuous wavelet transform was used to find the corresponding region of this frequency segment,which can use as feedback to a machining process.The experiments' results show the use of wavelet can find the corresponding region of certain frequency segment effectively.
2007, 31(6): 630-633.
Abstract:
In order to study the gain and wavelength tunable property of MEMS-based tunable vertical cavity semiconductor optical amplifiers at reflection mode,transfer matrix method was used.Unlike the previous coupling cavity method,the transfer matrix method avoids calculating the effective cavity length and gain-enhancement factor and its calculated result is corresponded directly with the physical structure of the device.The change of the gain and peak wavelength depending on the shift of empty cavity length and the variation of position of the quantum well stacks were obtained,and the calculation result was agreement with the experiment.
In order to study the gain and wavelength tunable property of MEMS-based tunable vertical cavity semiconductor optical amplifiers at reflection mode,transfer matrix method was used.Unlike the previous coupling cavity method,the transfer matrix method avoids calculating the effective cavity length and gain-enhancement factor and its calculated result is corresponded directly with the physical structure of the device.The change of the gain and peak wavelength depending on the shift of empty cavity length and the variation of position of the quantum well stacks were obtained,and the calculation result was agreement with the experiment.
2007, 31(6): 636-638.
Abstract:
La1-XCaXMnO(LCMO),La1-XPbXMnO(LPMO) and La1-XSrXCoO(LSCO) thin films were prepared with laser pulse deposition technique in order to investigate the laser induced thermoelectric voltage signal which affected by temperature.The laser induced thermoelectric voltage signals of La1-XCaXMnO3(LCMO),La1-XPbXMnO3(LPMO) and La1-XSr-XCoO3(LSCO) thin films were measured at 290K～340K temperature range by using lock-in amplifier.The signal-temperature coefficients(STC) of three CMR thin films were defined and compared.It was found that the LSCO demonstrated positive and smallest STC,while LCMO showed largest and negative STC.
La1-XCaXMnO(LCMO),La1-XPbXMnO(LPMO) and La1-XSrXCoO(LSCO) thin films were prepared with laser pulse deposition technique in order to investigate the laser induced thermoelectric voltage signal which affected by temperature.The laser induced thermoelectric voltage signals of La1-XCaXMnO3(LCMO),La1-XPbXMnO3(LPMO) and La1-XSr-XCoO3(LSCO) thin films were measured at 290K～340K temperature range by using lock-in amplifier.The signal-temperature coefficients(STC) of three CMR thin films were defined and compared.It was found that the LSCO demonstrated positive and smallest STC,while LCMO showed largest and negative STC.
2007, 31(6): 639-641,645.
Abstract:
Laser punching technique is a new idea about hole-forming of sheet metal which is based on the effects of shock waves induced by laser and the high speed punching process.The theoretical minimum movement velocity for the sheet to be punched by laser shock waves was deduced.Also,the mechanism and the punching properties was analyzed on the basis of laser shock forming technology.To test the feasibility of laser punching,a corresponding experiment was designed.In the experiment,a neodymium glass high-power laser was adopted to irradiate the black coating painted on the surface of the 0.4mm thick aluminum sheet through the overlay-K9 glass,and the coating was gasified immediately into high-pressure plasma to generate a hole in the sample.The experimental results show there is no obvious distortion around the hole;the edge of hole is smooth;and the size of hole is dependent on the concave die.So,the laser punching technique can be used as an effective method for hole-forming.
Laser punching technique is a new idea about hole-forming of sheet metal which is based on the effects of shock waves induced by laser and the high speed punching process.The theoretical minimum movement velocity for the sheet to be punched by laser shock waves was deduced.Also,the mechanism and the punching properties was analyzed on the basis of laser shock forming technology.To test the feasibility of laser punching,a corresponding experiment was designed.In the experiment,a neodymium glass high-power laser was adopted to irradiate the black coating painted on the surface of the 0.4mm thick aluminum sheet through the overlay-K9 glass,and the coating was gasified immediately into high-pressure plasma to generate a hole in the sample.The experimental results show there is no obvious distortion around the hole;the edge of hole is smooth;and the size of hole is dependent on the concave die.So,the laser punching technique can be used as an effective method for hole-forming.
2007, 31(6): 642-645.
Abstract:
In order to analyze image singularity and the features of the different sections,a new multifractal algorithm based on sub-pixel edge measure is proposed.The greylevel gradient area density function and edge-measure of random subsets(radii can reach the precision of sub-pixel) were obtained by the square aperture sampling law on the position of sub-pixel.Utilized the multifractal frame,the image could be segmented into a series of fractal sets of the different singularity exponents.At the same time,the reconstruction algorithm was presented by using the different information content of multifractal subset.So the image could be divided from texture to edge precisely.At last,the algorithm was analyzed and examined.The data showed that the reconstruction PSNR was 14.76dB from the edge extracted by 3×3 sub-pixels method.The results show that the peak signal-to-noise ratio of the reconstruction image depends on the extracted image edge quality and the coefficient ratio of the reconstruction and the information of the different layers of the image are identical with the important information from the human visual reception.
In order to analyze image singularity and the features of the different sections,a new multifractal algorithm based on sub-pixel edge measure is proposed.The greylevel gradient area density function and edge-measure of random subsets(radii can reach the precision of sub-pixel) were obtained by the square aperture sampling law on the position of sub-pixel.Utilized the multifractal frame,the image could be segmented into a series of fractal sets of the different singularity exponents.At the same time,the reconstruction algorithm was presented by using the different information content of multifractal subset.So the image could be divided from texture to edge precisely.At last,the algorithm was analyzed and examined.The data showed that the reconstruction PSNR was 14.76dB from the edge extracted by 3×3 sub-pixels method.The results show that the peak signal-to-noise ratio of the reconstruction image depends on the extracted image edge quality and the coefficient ratio of the reconstruction and the information of the different layers of the image are identical with the important information from the human visual reception.
2007, 31(6): 646-648.
Abstract:
The whole ablation process of target ZnO heated by pulsed laser was studied.The ablating model of a bulk target irradiated by a pulse laser was set up.Under the appropriate dynamic boundary conditions,the heat flow equation with heat generation term,and the temperature distribution of target before and after the melting were studied in detail.The results showed that before the melting,at a fixed location,the temperature increased with the ablation time.The less the heat diffusion distance was,the faster the variety rate of the temperature was.At the same time,in different location,the temperature decreased gradually along with the increase of the heat diffusion distance.Using the combination of analytical method and integral-approximation method,and solving the heat flow equation,the temperature distribution of solid and liquid phases's functions of time and location were obtained.The temperature grad of liquid phases decreased with the increase of the heat diffusion distance.Within 0.5 micron distance from the ablation surface,the temperature grad of liquid phases was great;beyond 0.5 micron,the variety rate of the temperature became very slow;while the temperature distribution of solid phases was more complex.
The whole ablation process of target ZnO heated by pulsed laser was studied.The ablating model of a bulk target irradiated by a pulse laser was set up.Under the appropriate dynamic boundary conditions,the heat flow equation with heat generation term,and the temperature distribution of target before and after the melting were studied in detail.The results showed that before the melting,at a fixed location,the temperature increased with the ablation time.The less the heat diffusion distance was,the faster the variety rate of the temperature was.At the same time,in different location,the temperature decreased gradually along with the increase of the heat diffusion distance.Using the combination of analytical method and integral-approximation method,and solving the heat flow equation,the temperature distribution of solid and liquid phases's functions of time and location were obtained.The temperature grad of liquid phases decreased with the increase of the heat diffusion distance.Within 0.5 micron distance from the ablation surface,the temperature grad of liquid phases was great;beyond 0.5 micron,the variety rate of the temperature became very slow;while the temperature distribution of solid phases was more complex.
2007, 31(6): 649-652.
Abstract:
In order to study the propagation of partially coherent modified Bessel-Gaussian beams passing through a paraxial ABCD optical system with hard-edge aperture,the approximate analytical propagation equation was derived with the hard-edged aperture function expanded into a finite sum of complex Gaussian functions.As an application example,numerical calculation was performed for partially coherent modified Bessel-Gaussian beams propagating in free space with hard-edge aperture,and the computation errors and application ranges of those analytical equations were discussed.The results show that the method provides the advantage of reduction of computing time and analyzing the propagation property of partially coherent modified Bessel-Gaussian beams through the circular aperture optical systems.The influence of Fressnel number and the truncation parameter on the intensity distributions was also analyzed.
In order to study the propagation of partially coherent modified Bessel-Gaussian beams passing through a paraxial ABCD optical system with hard-edge aperture,the approximate analytical propagation equation was derived with the hard-edged aperture function expanded into a finite sum of complex Gaussian functions.As an application example,numerical calculation was performed for partially coherent modified Bessel-Gaussian beams propagating in free space with hard-edge aperture,and the computation errors and application ranges of those analytical equations were discussed.The results show that the method provides the advantage of reduction of computing time and analyzing the propagation property of partially coherent modified Bessel-Gaussian beams through the circular aperture optical systems.The influence of Fressnel number and the truncation parameter on the intensity distributions was also analyzed.
2007, 31(6): 653-655.
Abstract:
In order to study the effects of laser shock forming on the surface roughness,metal sheet of aluminum and 304 stainless steel of 0.5mm thickness are used as samples of laser shock forming,and laser beams with radius of 0.4mm,wavelength of 1054nm and pulse width of 23ns was applied in laser shock forming,while the energy for aluminum sheet was 15.4J and for 304 stainless steel was 18.92J.The measurement results after laser shock forming show that laser shock forming may improve the surface roughness to two roughness rank.There are two reasons for surface roughness improvement.On the one hand,it will generate a series of trasmission wasves and reflection waves when the stress wave spreads in tiny peak of sheet surface,and the tiny peak would rupture if the strength of reflection tensile wave is beyond the tensile strength of targets.On the other hand,a high pressure zone is formed in the air because of high speed motion of sheet,and plastic deformation of tiny peak would take place if the pressure of air acted on the back of sheet is greater than the dynamic bend intensity.So the altitude of tiny peak is decreased by the rupture and plastic deformation of tiny peak and it results in improvement of the surface roughness.
In order to study the effects of laser shock forming on the surface roughness,metal sheet of aluminum and 304 stainless steel of 0.5mm thickness are used as samples of laser shock forming,and laser beams with radius of 0.4mm,wavelength of 1054nm and pulse width of 23ns was applied in laser shock forming,while the energy for aluminum sheet was 15.4J and for 304 stainless steel was 18.92J.The measurement results after laser shock forming show that laser shock forming may improve the surface roughness to two roughness rank.There are two reasons for surface roughness improvement.On the one hand,it will generate a series of trasmission wasves and reflection waves when the stress wave spreads in tiny peak of sheet surface,and the tiny peak would rupture if the strength of reflection tensile wave is beyond the tensile strength of targets.On the other hand,a high pressure zone is formed in the air because of high speed motion of sheet,and plastic deformation of tiny peak would take place if the pressure of air acted on the back of sheet is greater than the dynamic bend intensity.So the altitude of tiny peak is decreased by the rupture and plastic deformation of tiny peak and it results in improvement of the surface roughness.
2007, 31(6): 656-658,662.
Abstract:
The process parameters in laser peen forming(LPF) have great impact on the forming shape of the processed metal sheet.In order to gain desired deformation volume and certain deep of residual stress,it is essential to optimize and control these parameters.In this paper,the orthogonal layout was used to design the main parameters of laser and the sheet.And all the situation was simulated by the ANSYS/LS-DYNA.The numeral result was studied by range analysis method.It was indicated that the optimum design of the parameters in laser peening process by orthogonal method can effectively control the residual stress modality and constructively conduct the experiments.
The process parameters in laser peen forming(LPF) have great impact on the forming shape of the processed metal sheet.In order to gain desired deformation volume and certain deep of residual stress,it is essential to optimize and control these parameters.In this paper,the orthogonal layout was used to design the main parameters of laser and the sheet.And all the situation was simulated by the ANSYS/LS-DYNA.The numeral result was studied by range analysis method.It was indicated that the optimum design of the parameters in laser peening process by orthogonal method can effectively control the residual stress modality and constructively conduct the experiments.
2007, 31(6): 659-662.
Abstract:
The dependence of the mechanics effect to the target induced by laser on laser intensity was reported.The experiments were performed by focusing output pulses of the Nd:YAG laser(10ns pulse width at 1.06 μm wavelength and 42mJ～320mJ pulse energy) on aluminum targets mounted on a ballistic pendulum.The data showed that there were different optimum intensities which gave a maximum Cm at different extant of depart from the focus(χ).And the impulse coupling coefficients(Cm) was determined by similar functions of intensity in the different χ.The Cm increases slowly with the increasing of laser intensity and decreases after it gets maximum quantity.According to the absorption of the plasma and the different laser-target interaction mechanisms at the different χ,the results show that there is the maximum Cm because of the plasma shielding effect;the optimum intensity is largest at the focus because of the effect caused by the rare faction wave and the maximum Cm at χ0 is smaller than the others due to the energy consuming of the air breakdown at the focus.
The dependence of the mechanics effect to the target induced by laser on laser intensity was reported.The experiments were performed by focusing output pulses of the Nd:YAG laser(10ns pulse width at 1.06 μm wavelength and 42mJ～320mJ pulse energy) on aluminum targets mounted on a ballistic pendulum.The data showed that there were different optimum intensities which gave a maximum Cm at different extant of depart from the focus(χ).And the impulse coupling coefficients(Cm) was determined by similar functions of intensity in the different χ.The Cm increases slowly with the increasing of laser intensity and decreases after it gets maximum quantity.According to the absorption of the plasma and the different laser-target interaction mechanisms at the different χ,the results show that there is the maximum Cm because of the plasma shielding effect;the optimum intensity is largest at the focus because of the effect caused by the rare faction wave and the maximum Cm at χ0 is smaller than the others due to the energy consuming of the air breakdown at the focus.
2007, 31(6): 663-664,583.
Abstract:
In the retardation measurement of wave plate,the accuracy is often influenced by the fluctuation of the light source.If the fluctuation of the light intensity is avoided,the measurement system will become simple,and the measurement accuracy will be improved.A new measurement system with a polarization apparatus was built,which is composed of two λ/4 wave plates and the measured wave plate.In the system,angle measurement substitutes direct light intensity measarement,which can effectively avoid fluctuation of the light intensity.The measurement accuracy can reach 0.5°.Compared with traditional measurement methods,it is a handy method with simpler system and higher accuracy.
In the retardation measurement of wave plate,the accuracy is often influenced by the fluctuation of the light source.If the fluctuation of the light intensity is avoided,the measurement system will become simple,and the measurement accuracy will be improved.A new measurement system with a polarization apparatus was built,which is composed of two λ/4 wave plates and the measured wave plate.In the system,angle measurement substitutes direct light intensity measarement,which can effectively avoid fluctuation of the light intensity.The measurement accuracy can reach 0.5°.Compared with traditional measurement methods,it is a handy method with simpler system and higher accuracy.
2007, 31(6): 665-667,670.
Abstract:
In order to get shorter pulse width to improve time resolution,femtosecond pulse was compressed by using two prisms and a reflective mirror.Femtosecond pulse was measured with a home-made second-harmonic generation frequency-resolved optical gating.The temporal width of input pulse was 89fs,the time-bandwidth product was 0.9096,the minimum error was 2.4‰ and the average power of the input light was about 480mW.The width of compressed pulse was 22fs,the time-bandwidth product was 0.44203,the minimum error was 1.1‰ and the average power of the output light was about 250mW.The compression ratio was 4:1,which was higher than that in the related report.The experimental results indicate that the compressing device is valid and the result is useful for getting shorter pulses.
In order to get shorter pulse width to improve time resolution,femtosecond pulse was compressed by using two prisms and a reflective mirror.Femtosecond pulse was measured with a home-made second-harmonic generation frequency-resolved optical gating.The temporal width of input pulse was 89fs,the time-bandwidth product was 0.9096,the minimum error was 2.4‰ and the average power of the input light was about 480mW.The width of compressed pulse was 22fs,the time-bandwidth product was 0.44203,the minimum error was 1.1‰ and the average power of the output light was about 250mW.The compression ratio was 4:1,which was higher than that in the related report.The experimental results indicate that the compressing device is valid and the result is useful for getting shorter pulses.
2007, 31(6): 668-670.
Abstract:
In order to make the Wollaston prisms get better transmitting performance,the influence of the refractive index of optical cement used in Wollaston prisms on the splitting ratio and the transmission was analyzed in this paper.The relationship formula about the refractive index of optical cement and the splitting ratio and the transmission was worked out,and besides,the relationship curves were fitted by computer.The result indicates that the refractive index of optical cement used in Wollaston prisms can influence both the splitting ratio and the transmission;and especially when the value of the splitting ratio is 1 and the value of total transmission reaches the maximum,the value of refractive index of optical cement is the same.If the wavelength of the light is 633nm,the value of the index is 1.570.The result is very helpful for optimizing the transmitting performance of Wollaston prisms.
In order to make the Wollaston prisms get better transmitting performance,the influence of the refractive index of optical cement used in Wollaston prisms on the splitting ratio and the transmission was analyzed in this paper.The relationship formula about the refractive index of optical cement and the splitting ratio and the transmission was worked out,and besides,the relationship curves were fitted by computer.The result indicates that the refractive index of optical cement used in Wollaston prisms can influence both the splitting ratio and the transmission;and especially when the value of the splitting ratio is 1 and the value of total transmission reaches the maximum,the value of refractive index of optical cement is the same.If the wavelength of the light is 633nm,the value of the index is 1.570.The result is very helpful for optimizing the transmitting performance of Wollaston prisms.
2007, 31(6): 671-672.
Abstract:
In order to get a symmetric beam splitting prism,the conventional Wollaston prism was modified,i.e.to modify the surface of o light and get symmetric beam splitting.The relation between the correction angle and prism's structure angle was given.Taking 632.8nm for example,the relation curve between the correction angle and prism's structure angle was obtained.Furthermore,the relation curve between the correction angle and wavelength was also obtained.The results indicate that this design can get symmetric beam splitting and it is simple and easy to process.
In order to get a symmetric beam splitting prism,the conventional Wollaston prism was modified,i.e.to modify the surface of o light and get symmetric beam splitting.The relation between the correction angle and prism's structure angle was given.Taking 632.8nm for example,the relation curve between the correction angle and prism's structure angle was obtained.Furthermore,the relation curve between the correction angle and wavelength was also obtained.The results indicate that this design can get symmetric beam splitting and it is simple and easy to process.
