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RSS2007 Vol. 31, No. 1
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2007, 31(1): 1-3,88.
[Abstract]
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Abstract:
To reduce the asymmetry of the output laser beam caused by the geometry of the conduct-cooled laser crystal in side pumped solid-state lasers,two pump modules were symmetrically placed and a semi-circumferentially mounted LD arrays were taken in each pump module.Numerical calculation and experiment were made,a maximum output power of 63.6mJ was gotten with 276mJ pump power at a frequency of 20Hz,the slope efficiency was 34%.Both numerical and experimental results prove the symmetrical geometry can effectively improve the beam quality and approximate symmetrical laser distribution can be obtained.
To reduce the asymmetry of the output laser beam caused by the geometry of the conduct-cooled laser crystal in side pumped solid-state lasers,two pump modules were symmetrically placed and a semi-circumferentially mounted LD arrays were taken in each pump module.Numerical calculation and experiment were made,a maximum output power of 63.6mJ was gotten with 276mJ pump power at a frequency of 20Hz,the slope efficiency was 34%.Both numerical and experimental results prove the symmetrical geometry can effectively improve the beam quality and approximate symmetrical laser distribution can be obtained.
2007, 31(1): 4-7.
Abstract:
Based on double-temperature equation,the temperature field of metal ablation by means of femtosecond,picosecond and nanosecond laser pulses is numerically calculated with finite-difference method to describe different laser pulses ablation on metal surface.The derived results are compared with those obtained with the approximate analytical expressions and simplified equations.Then the application range scope of the different simplified equations and the reasonability of simplification are discussed.The relationship between the electron heat flux expression and the laser intensity is also analyzed.The calculation shows that the results of the simplified equations are consistent with the numerical calculation results obtained with the double-temperature equation.It is proved that the temperature of the lattice can be treated as a constant and the double-temperature equation reduces to the electron temperature equation for femtosecond scale laser pulses,the system should be described by a complete double-temperature equation for picosecond laser pulses,and that the electron and lattice temperature are equal and the model is reduced to a heat conduction equation during for nanosecond laser pulses.
Based on double-temperature equation,the temperature field of metal ablation by means of femtosecond,picosecond and nanosecond laser pulses is numerically calculated with finite-difference method to describe different laser pulses ablation on metal surface.The derived results are compared with those obtained with the approximate analytical expressions and simplified equations.Then the application range scope of the different simplified equations and the reasonability of simplification are discussed.The relationship between the electron heat flux expression and the laser intensity is also analyzed.The calculation shows that the results of the simplified equations are consistent with the numerical calculation results obtained with the double-temperature equation.It is proved that the temperature of the lattice can be treated as a constant and the double-temperature equation reduces to the electron temperature equation for femtosecond scale laser pulses,the system should be described by a complete double-temperature equation for picosecond laser pulses,and that the electron and lattice temperature are equal and the model is reduced to a heat conduction equation during for nanosecond laser pulses.
2007, 31(1): 8-11.
Abstract:
For exploring the mechanism of formation of density solitons and self-generated magnetic field in laser plasma,their evolution is numerically simulated by using of nonlinear equation for density disturbance in axial-symmetric cylindrical coordinate.The simulation results show that laser with intensity of 4×1014W/cm2 irradiation on target produces solitons with density disturbance rate of 82%.At the same time,self-generated magnetic field about 30T along the propagation axes is induced.These results are consistent with observed results.
For exploring the mechanism of formation of density solitons and self-generated magnetic field in laser plasma,their evolution is numerically simulated by using of nonlinear equation for density disturbance in axial-symmetric cylindrical coordinate.The simulation results show that laser with intensity of 4×1014W/cm2 irradiation on target produces solitons with density disturbance rate of 82%.At the same time,self-generated magnetic field about 30T along the propagation axes is induced.These results are consistent with observed results.
2007, 31(1): 12-14,43.
Abstract:
To improve the sensitivity of temperature sensor and pressure sensor so that they are applicable,the fiber Bragg grating(FBG) temperature sensor and FBG pressure sensor are encapsulated.The temperature sensitivity of the FBG temperature sensor is(0.052nm/℃) and the pressure sensitivity of the FBG pressure sensor is 0.8208nm/MPa from the experimental results.The temperature sensitivity and pressure sensitivity is 5.2 times and 273 times of that of bare FBG.The temperature and pressure response curve of FBG sensor is linear with reflective wavelength of FBG.After the FBG sensing system is used to detect the temperature and pressure of oil in pipeline about half month,the experimental results are consistent with those of electric sensor.The FBG sensing system can be used in pipeline on-line measurement.
To improve the sensitivity of temperature sensor and pressure sensor so that they are applicable,the fiber Bragg grating(FBG) temperature sensor and FBG pressure sensor are encapsulated.The temperature sensitivity of the FBG temperature sensor is(0.052nm/℃) and the pressure sensitivity of the FBG pressure sensor is 0.8208nm/MPa from the experimental results.The temperature sensitivity and pressure sensitivity is 5.2 times and 273 times of that of bare FBG.The temperature and pressure response curve of FBG sensor is linear with reflective wavelength of FBG.After the FBG sensing system is used to detect the temperature and pressure of oil in pipeline about half month,the experimental results are consistent with those of electric sensor.The FBG sensing system can be used in pipeline on-line measurement.
2007, 31(1): 15-17.
Abstract:
For quasi-soliton propagating steadily in standard monomode fiber,its transmission in a standard monomode fiber and dispersion compensation fiber is studied with the split-step Fourier method.The transmission characteristics in a standard monomode fiber and dispersion compensation fiber are obtained.The numerical analysis shows that its peak value descends and its width broadens when it propagates in a standard monomode fiber,so the quasi-soliton can't propagate steadily.When it propagates in a dispersion compensation system using dispersion compensation technique,its shape can be kept almost the original shape,so quasi-soliton propagation properties can be improved greatly than in a standard monomode fiber.
For quasi-soliton propagating steadily in standard monomode fiber,its transmission in a standard monomode fiber and dispersion compensation fiber is studied with the split-step Fourier method.The transmission characteristics in a standard monomode fiber and dispersion compensation fiber are obtained.The numerical analysis shows that its peak value descends and its width broadens when it propagates in a standard monomode fiber,so the quasi-soliton can't propagate steadily.When it propagates in a dispersion compensation system using dispersion compensation technique,its shape can be kept almost the original shape,so quasi-soliton propagation properties can be improved greatly than in a standard monomode fiber.
2007, 31(1): 18-21.
Abstract:
In order to the accurate single-layer depth to meet the technologic requirement of 3-D laser carving,experimental study of laser carving was carried out on the surface of Al2O3 ceramic with different laser processing parameters.The effects of parameters on single-layer depth,quality and the mechanisms of laser carving were described.The mathematical model of laser carving depth was established.Through experiments,it was found that the single-layer depth was nearly 0.1mm with a tolerance of less than three-thousandths when the laser power was 12.2A,the scanning speed was 25mm per second and the repeating frequency of laser pulse was 2kHz.At last,a 3-D solid was successfully carved on the surface of ceramic sample based on the experimental results.It was shown from the results that the layered-forming principle could be applied in the field of laser carving and the 3-D laser carving system could directly carve the real 3-D graphics on the surface of ceramic.
In order to the accurate single-layer depth to meet the technologic requirement of 3-D laser carving,experimental study of laser carving was carried out on the surface of Al2O3 ceramic with different laser processing parameters.The effects of parameters on single-layer depth,quality and the mechanisms of laser carving were described.The mathematical model of laser carving depth was established.Through experiments,it was found that the single-layer depth was nearly 0.1mm with a tolerance of less than three-thousandths when the laser power was 12.2A,the scanning speed was 25mm per second and the repeating frequency of laser pulse was 2kHz.At last,a 3-D solid was successfully carved on the surface of ceramic sample based on the experimental results.It was shown from the results that the layered-forming principle could be applied in the field of laser carving and the 3-D laser carving system could directly carve the real 3-D graphics on the surface of ceramic.
2007, 31(1): 25-28.
Abstract:
A new cavity-dumping RF excited waveguide CO2 laser which may be used in a heterodyne imaging lidar system is presented.The relationship between the fall delay of high voltage(HV) pulse and the width of cavity-dumping laser pulse is calculated theoretically.In our experiment,the width of cavity-dumping laser pulse could be controlled by adjusting the equivalent load parameters of HV pulse power supply.The cavity-dumping laser pulses with full width at half maximum(FWHM) about 30ns,peak power above(2kW),are obtained at the repetition rate up to 70kHz,which meet the requirement of the pulse heterodyne imaging lidar system.
A new cavity-dumping RF excited waveguide CO2 laser which may be used in a heterodyne imaging lidar system is presented.The relationship between the fall delay of high voltage(HV) pulse and the width of cavity-dumping laser pulse is calculated theoretically.In our experiment,the width of cavity-dumping laser pulse could be controlled by adjusting the equivalent load parameters of HV pulse power supply.The cavity-dumping laser pulses with full width at half maximum(FWHM) about 30ns,peak power above(2kW),are obtained at the repetition rate up to 70kHz,which meet the requirement of the pulse heterodyne imaging lidar system.
2007, 31(1): 29-30.
Abstract:
A method for measuring diffusivity of nanometer material by means of laser photothermal displacement technique is presented,which measures the phase of thermal displacement in different frequencies and gives the diffusivity of material by fitted curves of phase.Experimental results of the diffusivity of nanometer TiO2 at different annealing temperatures are given and the results indicate that the diffusivity of nanometer TiO2 decreases while the annealing temperature rises.
A method for measuring diffusivity of nanometer material by means of laser photothermal displacement technique is presented,which measures the phase of thermal displacement in different frequencies and gives the diffusivity of material by fitted curves of phase.Experimental results of the diffusivity of nanometer TiO2 at different annealing temperatures are given and the results indicate that the diffusivity of nanometer TiO2 decreases while the annealing temperature rises.
2007, 31(1): 35-36,70.
Abstract:
Using color reversal film as record medium,the radius of the Bessel beam central spot is measured through the analysis of the digital image by film-scanning.The experimental result 16.77μm±0.01μm is consisted well with the theory result 15.16μm.The result also indicates that the film-scanning method shows some advantages in lower cost,higher accuracy and larger measurable scale.Furthermore,this measurement is superior to the expensive laser beam parameter analyzer in measuring the beam size on micrometer magnitude of 1Hz ultrashort pulse.
Using color reversal film as record medium,the radius of the Bessel beam central spot is measured through the analysis of the digital image by film-scanning.The experimental result 16.77μm±0.01μm is consisted well with the theory result 15.16μm.The result also indicates that the film-scanning method shows some advantages in lower cost,higher accuracy and larger measurable scale.Furthermore,this measurement is superior to the expensive laser beam parameter analyzer in measuring the beam size on micrometer magnitude of 1Hz ultrashort pulse.
2007, 31(1): 37-40,46.
Abstract:
Aspheric surface testing technique with radial shearing interferometer has been developed.The principle of the measurement is based on the radial shearing interference in which the measuring wavefront from the entire mirror surface under test is referred to that of the central part.The compact and low-cost radial shearing interferometer is constructed with two Fresnel zone plates,which are designed and fabricated by photographic processing.Radial shearing interferogram is detected by a CCD camera and processed by a computer.Fringe phase of shearing interferogram is evaluated by fast Fourier transform(FFT) algorithm and testing wavefront is reconstructed.The measurement for standard lens show the accuracy to be around λ/5 P-V and λ/10 RMS.The experiments show that this stable interferometer can be applicable to the in-process measurement for aspheric lens.
Aspheric surface testing technique with radial shearing interferometer has been developed.The principle of the measurement is based on the radial shearing interference in which the measuring wavefront from the entire mirror surface under test is referred to that of the central part.The compact and low-cost radial shearing interferometer is constructed with two Fresnel zone plates,which are designed and fabricated by photographic processing.Radial shearing interferogram is detected by a CCD camera and processed by a computer.Fringe phase of shearing interferogram is evaluated by fast Fourier transform(FFT) algorithm and testing wavefront is reconstructed.The measurement for standard lens show the accuracy to be around λ/5 P-V and λ/10 RMS.The experiments show that this stable interferometer can be applicable to the in-process measurement for aspheric lens.
2007, 31(1): 41-43.
Abstract:
Serratia Marcescens GT596 was isolated from soil and brought to mutation by CO2 laser irradiation.The radiation duration was 30s with distance of 23cm and the flash beam diameter was 0.4cm.High chondrotinase producing strain mutant GT596 was obtained after screening culture.The GT596 was found to have chondrotinase stable producing activity in descendant cultures.
Serratia Marcescens GT596 was isolated from soil and brought to mutation by CO2 laser irradiation.The radiation duration was 30s with distance of 23cm and the flash beam diameter was 0.4cm.High chondrotinase producing strain mutant GT596 was obtained after screening culture.The GT596 was found to have chondrotinase stable producing activity in descendant cultures.
2007, 31(1): 44-46.
Abstract:
To find out the optical limiting mechanism of carbon nanotube suspension,the scattered and transmitted energy for the carbon nanotube suspension,as a function of incident fluence,is measured.The angular scattering profile at different incident fluences for 10 ns,1064nm linearly polarized light parallel to the scattering plane is obtained and pump-probe time-resolved experiments also performed.Based on Mie theory,the scattering energy distribution and scattering cross-section varying with carbon vapour bubble radius is calculated,which qualitatively agree with experiment results.The results indicate that the optical limiting mechanism of carbon nanotube suspension probably originated from the nonlinear scattering of carbon vapour bubble formed by light Absorption.
To find out the optical limiting mechanism of carbon nanotube suspension,the scattered and transmitted energy for the carbon nanotube suspension,as a function of incident fluence,is measured.The angular scattering profile at different incident fluences for 10 ns,1064nm linearly polarized light parallel to the scattering plane is obtained and pump-probe time-resolved experiments also performed.Based on Mie theory,the scattering energy distribution and scattering cross-section varying with carbon vapour bubble radius is calculated,which qualitatively agree with experiment results.The results indicate that the optical limiting mechanism of carbon nanotube suspension probably originated from the nonlinear scattering of carbon vapour bubble formed by light Absorption.
2007, 31(1): 47-49,53.
Abstract:
In order to improve the precision of a 3bit variable optical fiber delay line,a new technology using a tunable laser as the lighting source of the delay system is proposed based on the characteristics of optical fiber's material dispersion that the refraction index of optical fiber changes along with the difference of transmitting wavelength.At the same time,the period of optical signal storage in delay lines is also altered and the delay precision of optical fiber delay lines is improved.The simulation results indicate the mean delay error decreases from 4.1ps to 1.3ps,and the delay precision of the 3bit optical fiber delay line is remarkably improved by using this new technology.
In order to improve the precision of a 3bit variable optical fiber delay line,a new technology using a tunable laser as the lighting source of the delay system is proposed based on the characteristics of optical fiber's material dispersion that the refraction index of optical fiber changes along with the difference of transmitting wavelength.At the same time,the period of optical signal storage in delay lines is also altered and the delay precision of optical fiber delay lines is improved.The simulation results indicate the mean delay error decreases from 4.1ps to 1.3ps,and the delay precision of the 3bit optical fiber delay line is remarkably improved by using this new technology.
2007, 31(1): 50-53.
Abstract:
In order to investigate the gain and noise characteristics of double cladding ytterbium-doped fiber amplifiers at different pump modes,numerical analysis of 910nm ytterbium-doped fiber amplifiers is performed.The results show that pump mode has less effect on gain than noise figure,and the fiber amplifier has low noise under forward and bi-direction pumping schemes at optimal fiber length.The results are useful for experimental design.
In order to investigate the gain and noise characteristics of double cladding ytterbium-doped fiber amplifiers at different pump modes,numerical analysis of 910nm ytterbium-doped fiber amplifiers is performed.The results show that pump mode has less effect on gain than noise figure,and the fiber amplifier has low noise under forward and bi-direction pumping schemes at optimal fiber length.The results are useful for experimental design.
2007, 31(1): 54-56,60.
Abstract:
In the adaptive optical systems,the precision of Hartmann-Shack wavefront sensor relies on the centroid detecting accuracy,but the noise in the light spot image lead to centroid detecting error.So the noise should be inhibited before estimating centroid.According to analyzing five kinds of common filtering methods by computer simulation and experiment,the two nonlinear filtering algorithms are showed to be the optimal selection.The study will offer valuable reference in enhancement of the precision of wavefront measurement.
In the adaptive optical systems,the precision of Hartmann-Shack wavefront sensor relies on the centroid detecting accuracy,but the noise in the light spot image lead to centroid detecting error.So the noise should be inhibited before estimating centroid.According to analyzing five kinds of common filtering methods by computer simulation and experiment,the two nonlinear filtering algorithms are showed to be the optimal selection.The study will offer valuable reference in enhancement of the precision of wavefront measurement.
2007, 31(1): 57-60.
Abstract:
Three-position-pumped double-clad fiber lasers are the simplest and essential forms of multi-position-pumped ones with side-pump technologies.In order to obtain higher laser output power under the same pump powers,the optimization of the pump parameters was studied.Firstly,the rate equations of Yb-doped double-clad fiber lasers are applied to acquire the expression of total lost pump power.Secondly,the optimum design model,the analytical expression for choosing the optimum side-pumping position,was obtained based on the principle of minimal total lost pump power for the three-position-pumped double-clad fiber lasers.The simulation results showed that the output power of the optimized double-clad fiber lasers was higher than that of the original ones,especially for the double-clad fibers with large total lost pump powers.The optimization methods are valuable,from which the optimum design for multi-position-pumped double-clad fiber lasers can be derived.
Three-position-pumped double-clad fiber lasers are the simplest and essential forms of multi-position-pumped ones with side-pump technologies.In order to obtain higher laser output power under the same pump powers,the optimization of the pump parameters was studied.Firstly,the rate equations of Yb-doped double-clad fiber lasers are applied to acquire the expression of total lost pump power.Secondly,the optimum design model,the analytical expression for choosing the optimum side-pumping position,was obtained based on the principle of minimal total lost pump power for the three-position-pumped double-clad fiber lasers.The simulation results showed that the output power of the optimized double-clad fiber lasers was higher than that of the original ones,especially for the double-clad fibers with large total lost pump powers.The optimization methods are valuable,from which the optimum design for multi-position-pumped double-clad fiber lasers can be derived.
2007, 31(1): 65-67.
Abstract:
The flexible coating is an energy conversion body that consists of confinement layer and Absorbing layer,so that laser shock processing(LSP) can be applied in engineering.For the sake of resolving original problem of bad shocking effect,the crylic acid synthetic resin and polyving 1 chloride(PVC) glue were used to replace silicone jelly.The result indicated:the materials hardness after laser shocking all exceeded 33HV and maximum residual stress approximately achieved 60MPa,which are comparative level with K9 optical glass(hardness and residual stress are 34HV and 70MPa separately).Flexible coating based on macromolecule materials can become the better energy conversion body that make LSP more practical.
The flexible coating is an energy conversion body that consists of confinement layer and Absorbing layer,so that laser shock processing(LSP) can be applied in engineering.For the sake of resolving original problem of bad shocking effect,the crylic acid synthetic resin and polyving 1 chloride(PVC) glue were used to replace silicone jelly.The result indicated:the materials hardness after laser shocking all exceeded 33HV and maximum residual stress approximately achieved 60MPa,which are comparative level with K9 optical glass(hardness and residual stress are 34HV and 70MPa separately).Flexible coating based on macromolecule materials can become the better energy conversion body that make LSP more practical.
2007, 31(1): 68-70.
Abstract:
In order to optical response in nonlinear material,considering the general problem of electronmagnetic wave propagation through one-dimensional photonic crystal heterjunction structure with a nonlinear defect,an expression for the optical response of such dielectric superlattice is obtained when the nonlinear impurity dielectric constant is in δ function approximation.The simulation results show that once the nonlinear medium sandwiched between two photonic crystals and the system exhibits bistability and multistability.Then the conditions for the onset of bistability and multistability are discussed.Comparison proves the δ function approximation and the nonlinear layer of finite width displays qualitatively similar behavior,which might supply a beneficial reference for the design zero threshold laser and nonlinear optical elements.
In order to optical response in nonlinear material,considering the general problem of electronmagnetic wave propagation through one-dimensional photonic crystal heterjunction structure with a nonlinear defect,an expression for the optical response of such dielectric superlattice is obtained when the nonlinear impurity dielectric constant is in δ function approximation.The simulation results show that once the nonlinear medium sandwiched between two photonic crystals and the system exhibits bistability and multistability.Then the conditions for the onset of bistability and multistability are discussed.Comparison proves the δ function approximation and the nonlinear layer of finite width displays qualitatively similar behavior,which might supply a beneficial reference for the design zero threshold laser and nonlinear optical elements.
2007, 31(1): 74-76,101.
Abstract:
In order to find a more effective and sensitive waveguide sensor,a new kind of structure of anti-resonant reflecting optical waveguide(ARROW) based on the traditional ARROW is proposed.Its reflectivity and transmitted loss are simulated and its sensitivity is calculated.Comparing with traditional surface homogenous sensing ARROW sensors,as waveguide is directly constructed by the sample and a periodic structure is adopted,the beam is mostly confined in the waveguide and the transmitted loss is effectively deduced,then,the sensitivity is greatly improved.
In order to find a more effective and sensitive waveguide sensor,a new kind of structure of anti-resonant reflecting optical waveguide(ARROW) based on the traditional ARROW is proposed.Its reflectivity and transmitted loss are simulated and its sensitivity is calculated.Comparing with traditional surface homogenous sensing ARROW sensors,as waveguide is directly constructed by the sample and a periodic structure is adopted,the beam is mostly confined in the waveguide and the transmitted loss is effectively deduced,then,the sensitivity is greatly improved.
2007, 31(1): 77-79.
Abstract:
The dynamics characteristics of a mode-locking laser using a gain-flattened erbium doped fiber amplifier are reported.Based on polarization additive pulse mode locking technique,a self-starting mode-locking of the fiber laser was demonstrated with a gain-flattened erbium doped fiber amplifier,fiber polarization controllers and a polarization dependent isolator.The stable optical pulses train at 1560nm center wavelength and 6.495MHz repetition rate was generated,with 1.5ps pulse width and 0.7nJ pulse energy.Mode locked pulses with dual peak-wavelengths at 1557nm and 1570nm were also observed.The results of the experiment indicate that higher energy of the pulses can be generated by the fiber laser with a gain-switched erbium doped fiber amplifier than that with a general erbium doped fiber.The mode-locked pulse spectrum of the fiber laser with a gain-flattened erbium doped fiber amplifier could show dual peak structure.It's valuable to the design and practicability of the ultra-short fiber lasers.
The dynamics characteristics of a mode-locking laser using a gain-flattened erbium doped fiber amplifier are reported.Based on polarization additive pulse mode locking technique,a self-starting mode-locking of the fiber laser was demonstrated with a gain-flattened erbium doped fiber amplifier,fiber polarization controllers and a polarization dependent isolator.The stable optical pulses train at 1560nm center wavelength and 6.495MHz repetition rate was generated,with 1.5ps pulse width and 0.7nJ pulse energy.Mode locked pulses with dual peak-wavelengths at 1557nm and 1570nm were also observed.The results of the experiment indicate that higher energy of the pulses can be generated by the fiber laser with a gain-switched erbium doped fiber amplifier than that with a general erbium doped fiber.The mode-locked pulse spectrum of the fiber laser with a gain-flattened erbium doped fiber amplifier could show dual peak structure.It's valuable to the design and practicability of the ultra-short fiber lasers.
2007, 31(1): 80-82,85.
Abstract:
Based on the theory of the Stokes vector and Muller matrix,the Muller matrix expression of a refraction polarizer is deduced.Then the Stokes vector formula and polarization formula of the transmitted light are discussed when the natural light is incident the refraction polarizer at an arbitrary angle.Finally the relation curve among the polarization degree and the refractive index and layer number of the medium is drawn when the light is incident the polarizer at Brewster angle.Results show it is easy to obtain higher polarization degree if the medium's refractive index or the number of the medium layer is increased when the natural light is incident at Brewster angle.The study results are applicable for other multilayer medium membrane device.
Based on the theory of the Stokes vector and Muller matrix,the Muller matrix expression of a refraction polarizer is deduced.Then the Stokes vector formula and polarization formula of the transmitted light are discussed when the natural light is incident the refraction polarizer at an arbitrary angle.Finally the relation curve among the polarization degree and the refractive index and layer number of the medium is drawn when the light is incident the polarizer at Brewster angle.Results show it is easy to obtain higher polarization degree if the medium's refractive index or the number of the medium layer is increased when the natural light is incident at Brewster angle.The study results are applicable for other multilayer medium membrane device.
2007, 31(1): 83-85.
Abstract:
With 0.8MeV electron irradiating the passivation film with three different thickness of SiO2 at 4 radiation dosages(1013cm-2~1014 cm-2),the radiation hardness of the passivation film was studied through comparing the photocurrent and dark current of the photodiode.It is found after radiation,the characteristics of the photodiodes degrade to some extent.The photocurrent decreases at short and long wavelength,never decrease at middle wavelength(600nm~800nm).On the other hand,the dark current increases with radiation dosage.When the radiation is 1×1014cm-2,the photocurrent is only 80% of that before radiation and the dark current is 40 times of that before radiation.In addition,for photodiodes passivated with thin SiO2,photocurrent decreases slightly,however dark current increases remarkably.Results show that the radiation effect has a relationship with device structure and technics of the film.
With 0.8MeV electron irradiating the passivation film with three different thickness of SiO2 at 4 radiation dosages(1013cm-2~1014 cm-2),the radiation hardness of the passivation film was studied through comparing the photocurrent and dark current of the photodiode.It is found after radiation,the characteristics of the photodiodes degrade to some extent.The photocurrent decreases at short and long wavelength,never decrease at middle wavelength(600nm~800nm).On the other hand,the dark current increases with radiation dosage.When the radiation is 1×1014cm-2,the photocurrent is only 80% of that before radiation and the dark current is 40 times of that before radiation.In addition,for photodiodes passivated with thin SiO2,photocurrent decreases slightly,however dark current increases remarkably.Results show that the radiation effect has a relationship with device structure and technics of the film.
2007, 31(1): 86-88.
Abstract:
The circular harmonic Mellin filter is proposed in pattern recognition to obtain the characters of invariable rotation and scale.The circular harmonic transform and Mellin transform are combined to form the circular harmonic Mellin transform.Simulation results show the rotation and scale of the filterkeeps constant.It can pick up the inflexion and edge of the object and the structure of edge is judged by the correlation peaks of inflexions.
The circular harmonic Mellin filter is proposed in pattern recognition to obtain the characters of invariable rotation and scale.The circular harmonic transform and Mellin transform are combined to form the circular harmonic Mellin transform.Simulation results show the rotation and scale of the filterkeeps constant.It can pick up the inflexion and edge of the object and the structure of edge is judged by the correlation peaks of inflexions.
2007, 31(1): 92-94,97.
Abstract:
The performances of dual-header pulse interval modulation(DH-PIM) and digital pulse interval modulation(DPIM) are analyzed for the high packet error rate and low information transmission rate of optical wireless communication modulations presently.After discussing their symbol structures,their packet error rates and information transmission rates are compared based on the given model.The simulation results show that DH-PIM with higher information transmission rate is fit for real-time transmission systems,while DPIM is fit for lower power or higher reliability systems for it's lower average power and packet error rate.
The performances of dual-header pulse interval modulation(DH-PIM) and digital pulse interval modulation(DPIM) are analyzed for the high packet error rate and low information transmission rate of optical wireless communication modulations presently.After discussing their symbol structures,their packet error rates and information transmission rates are compared based on the given model.The simulation results show that DH-PIM with higher information transmission rate is fit for real-time transmission systems,while DPIM is fit for lower power or higher reliability systems for it's lower average power and packet error rate.
2007, 31(1): 95-97.
Abstract:
To characterize beam quality in high power SILEX-Ⅰ ultra-short pulse Ti:sapphire laser system,experiments on wavefront measurement are performed.Using Shack-Hartmann wavefront sensor manufactured by Institute of Laser and Information Technology of the Russian Academy of Science,experiments at different positions are completed.The results show that the beam quality of this facility is very good,the P-V is 0.13λ,the RMS is 0.02λ before the compressor,and the P-V is 0.63λ,the RMS is 0.09λ after the compressor.The experimental results show that the system has good beam quality,and the wavefront aberration mainly come from the compressor.
To characterize beam quality in high power SILEX-Ⅰ ultra-short pulse Ti:sapphire laser system,experiments on wavefront measurement are performed.Using Shack-Hartmann wavefront sensor manufactured by Institute of Laser and Information Technology of the Russian Academy of Science,experiments at different positions are completed.The results show that the beam quality of this facility is very good,the P-V is 0.13λ,the RMS is 0.02λ before the compressor,and the P-V is 0.63λ,the RMS is 0.09λ after the compressor.The experimental results show that the system has good beam quality,and the wavefront aberration mainly come from the compressor.
2007, 31(1): 98-101.
Abstract:
The high-speed modulated semiconductor lasers are the key devices in the system of high-speed fiber communication and phase control radar systems,etc.The parasitic capacitance of the high speed laser is one of those factors which affect the modulation bandwidth.In order to reduce it,the capacitance of the ridge waveguide structure was analyzed and tested,computer simulation was performed.A conclusion is made that capacitance's value is related to not only the eroded depth of the insulation channel but also the area of the metallization,which is important for the realization of the high-speed modulation of the laser.
The high-speed modulated semiconductor lasers are the key devices in the system of high-speed fiber communication and phase control radar systems,etc.The parasitic capacitance of the high speed laser is one of those factors which affect the modulation bandwidth.In order to reduce it,the capacitance of the ridge waveguide structure was analyzed and tested,computer simulation was performed.A conclusion is made that capacitance's value is related to not only the eroded depth of the insulation channel but also the area of the metallization,which is important for the realization of the high-speed modulation of the laser.
2007, 31(1): 102-105.
Abstract:
In order to obtain the effect of temperature on the separate spatial soliton pairs in an unbiased series photorefractive crystal,the low-amplitude bright-dark separate spatial soliton pairs in an unbiased series photorefractive crystal circuit are investigated theoretically.The analytical solutions for both bright and the dark low-amplitude separate spatial soliton in series photorefractive crystal circuit are obtained.The effect of temperature on the soliton property is analyzed.The result shows that the dynamical evolution of bright soliton in one crystal can be modulated by changing the temperature of the other crystal in which the dark soliton is supported.The dynamical evolution of the bright-dark separate spatial soliton pair is investigated by numerical simulation.Potential application in thermo-control optical devices is discussed.
In order to obtain the effect of temperature on the separate spatial soliton pairs in an unbiased series photorefractive crystal,the low-amplitude bright-dark separate spatial soliton pairs in an unbiased series photorefractive crystal circuit are investigated theoretically.The analytical solutions for both bright and the dark low-amplitude separate spatial soliton in series photorefractive crystal circuit are obtained.The effect of temperature on the soliton property is analyzed.The result shows that the dynamical evolution of bright soliton in one crystal can be modulated by changing the temperature of the other crystal in which the dark soliton is supported.The dynamical evolution of the bright-dark separate spatial soliton pair is investigated by numerical simulation.Potential application in thermo-control optical devices is discussed.
2007, 31(1): 106-108.
Abstract:
The fast Fourier transform method is used to study the mode field distribution for high-energy CO2 laser induced by the resonator mirror tilt,centre thermal distortion at the mirror and inhomogeneous gain resulting from transverse flow of gain medium.The simulation results indicate that all the above factors influence affect the mode field distribution.However the effect can be reduced by cooling resonator mirrors,adopting new mirror substrate materials,improving the reflective rate of mirror and arranging mirror tilt.
The fast Fourier transform method is used to study the mode field distribution for high-energy CO2 laser induced by the resonator mirror tilt,centre thermal distortion at the mirror and inhomogeneous gain resulting from transverse flow of gain medium.The simulation results indicate that all the above factors influence affect the mode field distribution.However the effect can be reduced by cooling resonator mirrors,adopting new mirror substrate materials,improving the reflective rate of mirror and arranging mirror tilt.
2007, 31(1): 109-112.
Abstract:
Based on a CCD-imaging tracking system with a laser range-finder,the laser echo rate and the distribution of laser missing detection is studied.Under the direction of satisfactory theory,a satisfactory predictive gain design method with prescribed performance specifications of estimation error variance,regional polar and stochastic passage characteristics,is proposed by solving bilinear matrix inequalities.The proposed filter can guarantee the echo rate of the laser range-finder being large,and distribution of missing detection period being uniform,so that the flight path detected by the tracking system is to be stationary and continuous to the expected extent.Numerical example indicates a satisfactory performance of the proposed gain.
Based on a CCD-imaging tracking system with a laser range-finder,the laser echo rate and the distribution of laser missing detection is studied.Under the direction of satisfactory theory,a satisfactory predictive gain design method with prescribed performance specifications of estimation error variance,regional polar and stochastic passage characteristics,is proposed by solving bilinear matrix inequalities.The proposed filter can guarantee the echo rate of the laser range-finder being large,and distribution of missing detection period being uniform,so that the flight path detected by the tracking system is to be stationary and continuous to the expected extent.Numerical example indicates a satisfactory performance of the proposed gain.
2007, 31(1): 71-73.
Abstract:
In order to improve the measuring accuracy of the intelligence high extinction ratio measuring system,the polarization interference principle is used to study and design an attenuator used in the system,and the attenuator's principle is analyzed carefully.The attenuator is consisted of three polarization prisms,one λ/4 wave-plate(λ=632.8nm),and two stepper motors.It can continuously adjust intensity of light within the range of about 0~60dB and the insertion lossof less than 1.5dB,so the aberration generated by changing attenuator with fixing attenuation value can be canceled effectively.If the attenuator is used to measure the extinction,the extinction ratio better than 10-7 can be obtained.The attenuator can be used not only in the high extinction ratio measuring system,but also in other optical measuring systems.The attenuator can adjust kinds of wavelength lights with achromatic plate in place of λ/4 wave-plate,so the useful range can be expanded.
In order to improve the measuring accuracy of the intelligence high extinction ratio measuring system,the polarization interference principle is used to study and design an attenuator used in the system,and the attenuator's principle is analyzed carefully.The attenuator is consisted of three polarization prisms,one λ/4 wave-plate(λ=632.8nm),and two stepper motors.It can continuously adjust intensity of light within the range of about 0~60dB and the insertion lossof less than 1.5dB,so the aberration generated by changing attenuator with fixing attenuation value can be canceled effectively.If the attenuator is used to measure the extinction,the extinction ratio better than 10-7 can be obtained.The attenuator can be used not only in the high extinction ratio measuring system,but also in other optical measuring systems.The attenuator can adjust kinds of wavelength lights with achromatic plate in place of λ/4 wave-plate,so the useful range can be expanded.
