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RSS2011 Vol. 35, No. 2
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2011, 35(2): 145-147,151.
doi: 10.3969/j.issn.1001-3806.2011.02.001
[Abstract]
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Abstract:
In order to meet the requirements of coherent detection,a high power,single frequency,1550nm pulsed fiber laser was studied based on all-fiber master oscillator power amplifier technique.A single mode pulsed laser was obtained with 400ns pulse duration,10kHz pulse repetition rate,148mW average power and 14μJ pulse energy.It was also found that the pulse shape was destroyed by the stimulated Brillouin scattering(SBS)resulting from the higher power density in the fiber.Then a way was put forward to suppress the SBS effect.The experimental results show that the SBS must be suppressed in order to improve the power.
In order to meet the requirements of coherent detection,a high power,single frequency,1550nm pulsed fiber laser was studied based on all-fiber master oscillator power amplifier technique.A single mode pulsed laser was obtained with 400ns pulse duration,10kHz pulse repetition rate,148mW average power and 14μJ pulse energy.It was also found that the pulse shape was destroyed by the stimulated Brillouin scattering(SBS)resulting from the higher power density in the fiber.Then a way was put forward to suppress the SBS effect.The experimental results show that the SBS must be suppressed in order to improve the power.
2011, 35(2): 148-151.
doi: 10.3969/j.issn.1001-3806.2011.02.002
Abstract:
Overhanging structure is an inherent geometric process limitation of selective laser melting(SLM),which would easily reduce the shape and dimension accuracy of built parts.To find the causes of defects in building overhanging surface, overhanging structure building experiments were carried out on 316L stainless steel at different inclined angle,scanning length and different speed.The results showed that at smaller inclined angle and the lower scanning speed,more serious warpage would happen,and the theoretical minimum building angle and reliable building angle fit with the experimental results at high and low scanning speed.High-speed scanning can build the overhanging surface with the minimum building angle,while low-speed scanning can only build the overhanging surface with a reliable building angle.Wrap of scanned overhanging surface would be more likely to happen along the long line direction.By control of local processing parameters,the quality of overhanging surface can be significantly improved.The basis for building overhanging surface by SLM was provided from the perspective of process and design,and the preliminary solution was proposed.
Overhanging structure is an inherent geometric process limitation of selective laser melting(SLM),which would easily reduce the shape and dimension accuracy of built parts.To find the causes of defects in building overhanging surface, overhanging structure building experiments were carried out on 316L stainless steel at different inclined angle,scanning length and different speed.The results showed that at smaller inclined angle and the lower scanning speed,more serious warpage would happen,and the theoretical minimum building angle and reliable building angle fit with the experimental results at high and low scanning speed.High-speed scanning can build the overhanging surface with the minimum building angle,while low-speed scanning can only build the overhanging surface with a reliable building angle.Wrap of scanned overhanging surface would be more likely to happen along the long line direction.By control of local processing parameters,the quality of overhanging surface can be significantly improved.The basis for building overhanging surface by SLM was provided from the perspective of process and design,and the preliminary solution was proposed.
2011, 35(2): 152-155.
doi: 10.3969/j.issn.1001-3806.2011.02.003
Abstract:
To deepen the understanding of laser welding of magnesium alloys,a high power CO2 laser was employed to join AZ31 magnesium alloy in 10mm thick.Its microstructure and tensile strength of laser welds were studied.Obvious concaves appeared on the welding surface because of serous burning-lost of magnesium at high temperature.Under the experimental conditions,the microstructure of the welding zone was equiaxed dendrites and the grains were refined with the decrease of the welding heat.The tensile test results showed surface concaves and porosities were two main factors affecting the tensile strength. The maximum tensile strength was only 74% of the substrate metal if the surface including concaves.However,it reached 91% of the substrate metal after surface concaves were eliminated by laser repair welding.Besides,the porosities were the main affecting factor inducing the tensile strength of laser repair weld is lower than that of the substrate metal.The results show it is necessary to eliminate the surface concaves and weld porosities in order to increase the mechanical property of laser welding joints.
To deepen the understanding of laser welding of magnesium alloys,a high power CO2 laser was employed to join AZ31 magnesium alloy in 10mm thick.Its microstructure and tensile strength of laser welds were studied.Obvious concaves appeared on the welding surface because of serous burning-lost of magnesium at high temperature.Under the experimental conditions,the microstructure of the welding zone was equiaxed dendrites and the grains were refined with the decrease of the welding heat.The tensile test results showed surface concaves and porosities were two main factors affecting the tensile strength. The maximum tensile strength was only 74% of the substrate metal if the surface including concaves.However,it reached 91% of the substrate metal after surface concaves were eliminated by laser repair welding.Besides,the porosities were the main affecting factor inducing the tensile strength of laser repair weld is lower than that of the substrate metal.The results show it is necessary to eliminate the surface concaves and weld porosities in order to increase the mechanical property of laser welding joints.
2011, 35(2): 156-159.
doi: 10.3969/j.issn.1001-3806.2011.02.004
Abstract:
For the wind measurement of the stratosphere,the principle of molecular Doppler wind lidar was introduced.The parameters of Fabry-Perot were designed in order that the measure error was least and the effect of the aerosol was eliminated. The structure of the molecular Doppler wind lidar receiver was designed,which could be placed on the mechanical etagere.The transmittance of the etalon and the wind profile were measured with this receiver used in the molecule wind lidar system.The results show that the measured transmittance of etalon agrees with the designed one approximately.The velocity sensitivity is lower than the designed one.The wind profile form is approximately in agreement with the American Goddard system.These indicate the receiver can be used for the wind measurement.
For the wind measurement of the stratosphere,the principle of molecular Doppler wind lidar was introduced.The parameters of Fabry-Perot were designed in order that the measure error was least and the effect of the aerosol was eliminated. The structure of the molecular Doppler wind lidar receiver was designed,which could be placed on the mechanical etagere.The transmittance of the etalon and the wind profile were measured with this receiver used in the molecule wind lidar system.The results show that the measured transmittance of etalon agrees with the designed one approximately.The velocity sensitivity is lower than the designed one.The wind profile form is approximately in agreement with the American Goddard system.These indicate the receiver can be used for the wind measurement.
2011, 35(2): 160-162.
doi: 10.3969/j.issn.1001-3806.2011.02.005
Abstract:
In the manufacture of a-Si:H thin film solar cell,sandblasting edge deletion has some disadvantages of pollution and poor conformity.Laser edge deletion was carried out with a 1064nm pulsed fiber laser under the conditions of 3500mm/s scan speed,30W output power,80kHz frequency and 0.05mm line space.The resistance of the specimen was larger than 1000MΩ. The best beam spot overlap ratio was acquired according to the experimental results,and the ratio in x and y direction was 0.83 and 0.88 respectively.It showed that beam spot overlap status influenced deletion efficiency and effect obviously with enough output power.Scan speed should match with frequency and line space to obtain the best processing effect with the optimal efficiency.
In the manufacture of a-Si:H thin film solar cell,sandblasting edge deletion has some disadvantages of pollution and poor conformity.Laser edge deletion was carried out with a 1064nm pulsed fiber laser under the conditions of 3500mm/s scan speed,30W output power,80kHz frequency and 0.05mm line space.The resistance of the specimen was larger than 1000MΩ. The best beam spot overlap ratio was acquired according to the experimental results,and the ratio in x and y direction was 0.83 and 0.88 respectively.It showed that beam spot overlap status influenced deletion efficiency and effect obviously with enough output power.Scan speed should match with frequency and line space to obtain the best processing effect with the optimal efficiency.
2011, 35(2): 163-166.
doi: 10.3969/j.issn.1001-3806.2011.02.006
Abstract:
Ni-based alloy coating was prepared on the Q235 steel by thermal spraying and laser remelting process at different scanning speeds,in order to study the effect of laser scanning speeds on the microstructure and corrosion resistance of laser cladding layers.The surface macro-morphology and microstructure were observed with an optical microscope(OM)and a scanning electronic microscope(SEM),and the micro-hardness and corrosion resistance were measured and analyzed with the hardness tester and electrochemical corrosion method.The results show that the microstructure becomes dense and even and the grains become tiny,while the amount of the white-bright dendrites increase and the eutectic compounds between the dendrites reduce with laser scanning speeds increasing.In addition,the micro-hardness and corrosion resistance greatly increase due to grain refinement and so on.As a result,the optimum technological parameters are 3kW in laser power,6mm/s in laser scanning speed and 3mm in beam diameter for the Ni-based alloy cladding layer preparation.The result is expected to provide practical value for selecting reasonable laser cladding technological parameters to achieve optimal performance of the cladding layer.
Ni-based alloy coating was prepared on the Q235 steel by thermal spraying and laser remelting process at different scanning speeds,in order to study the effect of laser scanning speeds on the microstructure and corrosion resistance of laser cladding layers.The surface macro-morphology and microstructure were observed with an optical microscope(OM)and a scanning electronic microscope(SEM),and the micro-hardness and corrosion resistance were measured and analyzed with the hardness tester and electrochemical corrosion method.The results show that the microstructure becomes dense and even and the grains become tiny,while the amount of the white-bright dendrites increase and the eutectic compounds between the dendrites reduce with laser scanning speeds increasing.In addition,the micro-hardness and corrosion resistance greatly increase due to grain refinement and so on.As a result,the optimum technological parameters are 3kW in laser power,6mm/s in laser scanning speed and 3mm in beam diameter for the Ni-based alloy cladding layer preparation.The result is expected to provide practical value for selecting reasonable laser cladding technological parameters to achieve optimal performance of the cladding layer.
2011, 35(2): 167-169,181.
doi: 10.3969/j.issn.1001-3806.2011.02.007
Abstract:
In order to alleviate the thermal lens effect effectively,based on the matrix optics,thermal lens effect in a flashpumped long-pulse green laser was analyzed with matrix transformation of Gaussian beam and a V-type cavity insensitive to thermal lens was designed.It was analyzed in theory and verified in experiments.The results show that it is reasonable to select parameters according to the matrix transformation of the Gaussian beams and the analytical simulation.This result is helpful for the alleviation of thermal lens effect and the improvement in performance of high energy medical lasers.
In order to alleviate the thermal lens effect effectively,based on the matrix optics,thermal lens effect in a flashpumped long-pulse green laser was analyzed with matrix transformation of Gaussian beam and a V-type cavity insensitive to thermal lens was designed.It was analyzed in theory and verified in experiments.The results show that it is reasonable to select parameters according to the matrix transformation of the Gaussian beams and the analytical simulation.This result is helpful for the alleviation of thermal lens effect and the improvement in performance of high energy medical lasers.
2011, 35(2): 173-176.
doi: 10.3969/j.issn.1001-3806.2011.02.009
Abstract:
In order to study the diffraction effect of the tunable phase modulation grating,steady and explicit diffraction patterns were obtained with the low-frequency generator driving the exciter to generate the low-frequency liquid surface wave (LFLSW).The distance between the diffraction patterns was variable with the frequency of the surface wave.Furthermore,the diffraction order might disappear at certain amplitude of the LFLSW.According to the physical optics theory,the periodical modulated LSW can be regarded as a phase modulated grating.The corresponding analytic expression of intensity distribution of diffraction patterns was derived,which explained the experimental phenomenon well.And the diffracted effect of the LSW was compared with that of the plane scotch grating.The results show that the LSW gives better diffracted effect.
In order to study the diffraction effect of the tunable phase modulation grating,steady and explicit diffraction patterns were obtained with the low-frequency generator driving the exciter to generate the low-frequency liquid surface wave (LFLSW).The distance between the diffraction patterns was variable with the frequency of the surface wave.Furthermore,the diffraction order might disappear at certain amplitude of the LFLSW.According to the physical optics theory,the periodical modulated LSW can be regarded as a phase modulated grating.The corresponding analytic expression of intensity distribution of diffraction patterns was derived,which explained the experimental phenomenon well.And the diffracted effect of the LSW was compared with that of the plane scotch grating.The results show that the LSW gives better diffracted effect.
2011, 35(2): 177-181.
doi: 10.3969/j.issn.1001-3806.2011.02.010
Abstract:
In order to develop special cladding powder for laser direct writing signs,and obtain convex shaped logo on weathering steel Q450NQR1 used in railway freight cars,based on uniform design and optimization,the composition of alloy powder was analyzed in theory and confirmed in experiments,and the data of appearance,hardness,corrosion weight loss and corrosion loss rate were obtained for different component.The results indicate that when the mass fraction of alloy composition is w(Ni)=0.20～0.22,w(Cr)=0.14～0.155,w(Si)=0.01～0.015,w(B)=0.005～0.006,and Fe as the remainder,the obtained cladding layer has beautiful appearance,metallurgical bonding with the substrate,and better atmospheric corrosion resistance than the base metal.The result is helpful for application of the system of laser direct writing signs on railway wagons industry.
In order to develop special cladding powder for laser direct writing signs,and obtain convex shaped logo on weathering steel Q450NQR1 used in railway freight cars,based on uniform design and optimization,the composition of alloy powder was analyzed in theory and confirmed in experiments,and the data of appearance,hardness,corrosion weight loss and corrosion loss rate were obtained for different component.The results indicate that when the mass fraction of alloy composition is w(Ni)=0.20～0.22,w(Cr)=0.14～0.155,w(Si)=0.01～0.015,w(B)=0.005～0.006,and Fe as the remainder,the obtained cladding layer has beautiful appearance,metallurgical bonding with the substrate,and better atmospheric corrosion resistance than the base metal.The result is helpful for application of the system of laser direct writing signs on railway wagons industry.
2011, 35(2): 182-184,188.
doi: 10.3969/j.issn.1001-3806.2011.02.011
Abstract:
In order to study the effect of annealing temperature on the stress,optical constants and surface roughness of HfO2 film,the film specimen was fabricated with electron beam evaporation method,then annealed at different temperatures.The film specimen was tested with interferometer,UV-3101PC spectrophotometer,X-ray diffraction instrument and emission scanning electron microscopy.The experimental results show that the HfO2 film is amorphous under the experimental conditions.The residual stress is tensile stress,first decreases and then increases with annealing temperature,and achieve to the minimum at 300℃.The refractive index increases with annealing temperature,however the dispersion decreases with the annealing temperature.The film roughness annealing at low temperature is smaller than that at high temperature.These results can provide reference for the preparation of high-quality HfO2 films.
In order to study the effect of annealing temperature on the stress,optical constants and surface roughness of HfO2 film,the film specimen was fabricated with electron beam evaporation method,then annealed at different temperatures.The film specimen was tested with interferometer,UV-3101PC spectrophotometer,X-ray diffraction instrument and emission scanning electron microscopy.The experimental results show that the HfO2 film is amorphous under the experimental conditions.The residual stress is tensile stress,first decreases and then increases with annealing temperature,and achieve to the minimum at 300℃.The refractive index increases with annealing temperature,however the dispersion decreases with the annealing temperature.The film roughness annealing at low temperature is smaller than that at high temperature.These results can provide reference for the preparation of high-quality HfO2 films.
2011, 35(2): 185-188.
doi: 10.3969/j.issn.1001-3806.2011.02.012
Abstract:
In order to prepare Ni-based amorphous coatings,Ni60.5Zr19.63Nb18.07Al1.8 amorphous composite coating was prepared on 45 steel substrate by means of laser cladding.Then the microstructure and phase of the coating were analyzed and the parameters characterizing the mechanical and corrosion resistance were measured.The results show that a great deal of dendritic and cystiform crystal phases exist in the coating.X-ray diffraction analysis reveals that amorphous,intermetallic compound such as NiZr2,Ni8 Nb,Al2O3 and Fe-Ni,and some other phases present in the coating.Content of white amorphous phase is up to maximum at the power of 3600W,and microstructure is most fine;hardness reaches maximum at the power of 3000W and can be up to 2399.9HK at topmost surface,while surface wear weight loss is 0.5921 mg·mm-2;coating corrosion resistance is the best at the power of 3600W.The minimum obtuse current density is 3.05mA/m2,and passive potential widest range is 1170mV;Ni60.5Zr19.63Nb18.07Al1.8 designed according to the new criterion has strong glass forming ability.
In order to prepare Ni-based amorphous coatings,Ni60.5Zr19.63Nb18.07Al1.8 amorphous composite coating was prepared on 45 steel substrate by means of laser cladding.Then the microstructure and phase of the coating were analyzed and the parameters characterizing the mechanical and corrosion resistance were measured.The results show that a great deal of dendritic and cystiform crystal phases exist in the coating.X-ray diffraction analysis reveals that amorphous,intermetallic compound such as NiZr2,Ni8 Nb,Al2O3 and Fe-Ni,and some other phases present in the coating.Content of white amorphous phase is up to maximum at the power of 3600W,and microstructure is most fine;hardness reaches maximum at the power of 3000W and can be up to 2399.9HK at topmost surface,while surface wear weight loss is 0.5921 mg·mm-2;coating corrosion resistance is the best at the power of 3600W.The minimum obtuse current density is 3.05mA/m2,and passive potential widest range is 1170mV;Ni60.5Zr19.63Nb18.07Al1.8 designed according to the new criterion has strong glass forming ability.
2011, 35(2): 189-192.
doi: 10.3969/j.issn.1001-3806.2011.02.013
Abstract:
In order to measure inhomogeneity of optic material accurately,an optical wedge was prepared at a small angle less than 0.117°.Then its inhomogeneity was measured with a Fizeu interferometer.This method was proved to be correct by simulation and experiments in which the inhomogeneity of fused silica was measured,and the peak to valley value of fused silica was 4.33×10-6,and the root mean square value was 0.862×10-6,and the accuracy of this method was less than 4.8×10-7. The results show that the light reflected either from the front surface or from the near surface can be distinguished with this method.
In order to measure inhomogeneity of optic material accurately,an optical wedge was prepared at a small angle less than 0.117°.Then its inhomogeneity was measured with a Fizeu interferometer.This method was proved to be correct by simulation and experiments in which the inhomogeneity of fused silica was measured,and the peak to valley value of fused silica was 4.33×10-6,and the root mean square value was 0.862×10-6,and the accuracy of this method was less than 4.8×10-7. The results show that the light reflected either from the front surface or from the near surface can be distinguished with this method.
2011, 35(2): 193-195,209.
doi: 10.3969/j.issn.1001-3806.2011.02.014
Abstract:
In order to study the feasibility of Cr,Nd:YAG ceramic used for solar-pumped lasers,the absorption spectra of Cr,Nd:YAG ceramic and solar spectrum were measured with a fiber optic spectrometer actually,the absorption coefficient curve was calculated,the percentage of the solar energy which could be absorbed by Cr,Nd:YAG ceramics was calculated.In an assumed condition,the threshold of pumped power density of the medium was calculated.The results show that the Cr,Nd:YAG ceramic have broad absorption bands at visible light and near-infrared band and the matching degree reached 38.44%,so Cr,Nd:YAG ceramic can be chosen as the most suitable medium for solar-pumped lasers.
In order to study the feasibility of Cr,Nd:YAG ceramic used for solar-pumped lasers,the absorption spectra of Cr,Nd:YAG ceramic and solar spectrum were measured with a fiber optic spectrometer actually,the absorption coefficient curve was calculated,the percentage of the solar energy which could be absorbed by Cr,Nd:YAG ceramics was calculated.In an assumed condition,the threshold of pumped power density of the medium was calculated.The results show that the Cr,Nd:YAG ceramic have broad absorption bands at visible light and near-infrared band and the matching degree reached 38.44%,so Cr,Nd:YAG ceramic can be chosen as the most suitable medium for solar-pumped lasers.
2011, 35(2): 196-198.
doi: 10.3969/j.issn.1001-3806.2011.02.015
Abstract:
In order to study the chaos complexity degree and bandwidth of mutually coupled semiconductor lasers, numerical analysis was carried out based on their rate equations.The results indicate that the chaotic bandwidth enhances with the increase of injection coefficient,and chaos turns more complicated.The higher the current biases,the larger chaotic bandwidth turns and the more complex the chaos wave is.These results provide theoretic guidance to realize broad bandwidth complex chaos.
In order to study the chaos complexity degree and bandwidth of mutually coupled semiconductor lasers, numerical analysis was carried out based on their rate equations.The results indicate that the chaotic bandwidth enhances with the increase of injection coefficient,and chaos turns more complicated.The higher the current biases,the larger chaotic bandwidth turns and the more complex the chaos wave is.These results provide theoretic guidance to realize broad bandwidth complex chaos.
2011, 35(2): 199-201,205.
doi: 10.3969/j.issn.1001-3806.2011.02.016
Abstract:
In order to measure the phase displacement of a heterodyne interferometer,namely Doppler frequency shift,an interpolation processing method of the heterodyne interferometer based on field programmable gate array(FPGA)was introduced. Based on zero-crossing detection,it starts to interpolate pulses at the rising edges of measurement and reference signals respectively and the phase displacement can be calculated by counting the interpolated pulses.In the experiment,the light source is He-Ne laser with beat frequency of 2.2MHz,measurement device is Michelson's interferometer,and the inserting pulse frequency is 100MHz.The following calculating work,such as counting,multiplication and division,was accomplished by FPGA.From theoretical analysis,the measurement resolution can achieve,(11)/(1000)λ,about 6.9608nm.The result indicates that is of high value for practical application.
In order to measure the phase displacement of a heterodyne interferometer,namely Doppler frequency shift,an interpolation processing method of the heterodyne interferometer based on field programmable gate array(FPGA)was introduced. Based on zero-crossing detection,it starts to interpolate pulses at the rising edges of measurement and reference signals respectively and the phase displacement can be calculated by counting the interpolated pulses.In the experiment,the light source is He-Ne laser with beat frequency of 2.2MHz,measurement device is Michelson's interferometer,and the inserting pulse frequency is 100MHz.The following calculating work,such as counting,multiplication and division,was accomplished by FPGA.From theoretical analysis,the measurement resolution can achieve,(11)/(1000)λ,about 6.9608nm.The result indicates that is of high value for practical application.
2011, 35(2): 202-205.
doi: 10.3969/j.issn.1001-3806.2011.02.017
Abstract:
In order to realize low loss fusion splicing between photonic crystal fiber(PCFs)and conventional fibers,after optimizing the splicer parameters and gradually decreasing the air hole collapse of PCFs,the main source of fusion splicing loss between PCFs and conventional fibers and rules of choosing parameters of arc fusion splicer were discussed in detail.Then some experiments splicing PCFs and conventional fibers were carried out with matched and mismatched mode field diameters,and very low loss(less than 0.2dB and 0.3dB respectively)was obtained.In conclusion,low loss splicing can be achieved by optimizing the splicer parameters for matched mode field diameters,however for much mismatched mode field diameters,low splicing loss can be obtained through controlling air hole collapse of PCFs.
In order to realize low loss fusion splicing between photonic crystal fiber(PCFs)and conventional fibers,after optimizing the splicer parameters and gradually decreasing the air hole collapse of PCFs,the main source of fusion splicing loss between PCFs and conventional fibers and rules of choosing parameters of arc fusion splicer were discussed in detail.Then some experiments splicing PCFs and conventional fibers were carried out with matched and mismatched mode field diameters,and very low loss(less than 0.2dB and 0.3dB respectively)was obtained.In conclusion,low loss splicing can be achieved by optimizing the splicer parameters for matched mode field diameters,however for much mismatched mode field diameters,low splicing loss can be obtained through controlling air hole collapse of PCFs.
2011, 35(2): 206-209.
doi: 10.3969/j.issn.1001-3806.2011.02.018
Abstract:
In order to obtain the hardening depth that treated with laser surface hardening simply and immediately,the process of laser surface hardening was analyzed and an analytical equation was concluded based on the semi-infinite surface point heat thermal diffusion equation,at the same time the experiment was conducted and ideal results were obtained.The method is right and efficient verified by the experimental results under existing experimental conditions.
In order to obtain the hardening depth that treated with laser surface hardening simply and immediately,the process of laser surface hardening was analyzed and an analytical equation was concluded based on the semi-infinite surface point heat thermal diffusion equation,at the same time the experiment was conducted and ideal results were obtained.The method is right and efficient verified by the experimental results under existing experimental conditions.
2011, 35(2): 210-213.
doi: 10.3969/j.issn.1001-3806.2011.02.019
Abstract:
Fiber yellow lasers are more compact and insensitive to alignment than their bulk laser counterparts.Because of the heat-dissipation characteristics of fibers and the excellent spatial mode characteristics,fiber yellow lasers are preferred candidates for various applications such as modern medicine,material processing,high-resolution spectroscopy,military applications and laser guided stars.Resent progress in fiber yellow lasers were reviewed.Key techniques and methods to realize fiber yellow lasers were analyzed and discussed.
Fiber yellow lasers are more compact and insensitive to alignment than their bulk laser counterparts.Because of the heat-dissipation characteristics of fibers and the excellent spatial mode characteristics,fiber yellow lasers are preferred candidates for various applications such as modern medicine,material processing,high-resolution spectroscopy,military applications and laser guided stars.Resent progress in fiber yellow lasers were reviewed.Key techniques and methods to realize fiber yellow lasers were analyzed and discussed.
2011, 35(2): 214-217.
doi: 10.3969/j.issn.1001-3806.2011.02.020
Abstract:
For the purpose of dealing with low-resolution interferograms acquired by large-diameter interferometer,a method was presented including homogenization and ternary and so on.The acquired interferograms,which couldn't be processed by interferometers,were filtered and the 3-D surfaces were restored.Compared with the traditional Goldstein filter method,the results show that this method enhances the restoration possibility of low resolution interferogram,and paves the way for its latter process.
For the purpose of dealing with low-resolution interferograms acquired by large-diameter interferometer,a method was presented including homogenization and ternary and so on.The acquired interferograms,which couldn't be processed by interferometers,were filtered and the 3-D surfaces were restored.Compared with the traditional Goldstein filter method,the results show that this method enhances the restoration possibility of low resolution interferogram,and paves the way for its latter process.
2011, 35(2): 218-221,225.
doi: 10.3969/j.issn.1001-3806.2011.02.021
Abstract:
In order to analyze the influence of Q-switch in a laser on the output signal pulse in wireless optical communication,on the basis of the rate equations,under different Q-switch function models,the power and waveform characteristics of the output signal were theoretically analyzed and simulated.Then the obtained data were compared with the raised cosine roll-off signal.The results indicate that the output pulse of a Q-switch laser has excellent power and waveform characteristics,which make it suitable for long distance wireless optical communication,restraining code intercross and reducing the bit error rate effectively.
In order to analyze the influence of Q-switch in a laser on the output signal pulse in wireless optical communication,on the basis of the rate equations,under different Q-switch function models,the power and waveform characteristics of the output signal were theoretically analyzed and simulated.Then the obtained data were compared with the raised cosine roll-off signal.The results indicate that the output pulse of a Q-switch laser has excellent power and waveform characteristics,which make it suitable for long distance wireless optical communication,restraining code intercross and reducing the bit error rate effectively.
2011, 35(2): 222-225.
doi: 10.3969/j.issn.1001-3806.2011.02.022
Abstract:
In order to prevent laser sending a long "0" or "1" signal list,avoid communication system making infinite bit errors in underwater wireless optical communication systems,a new convolution encoding scheme was adopted.The encoding method was designed and Viterbi decoding theory was analyzed.The simulative demonstration of bit error rate performance was carried out.The field programmable gate array(FPGA)design of encoder was implemented with VHDL language.The bit error rates of encoded and uncoded system,the signal noise ratio demanded to attain the same bit error rate was received.The result show that this code can reduce the bit error rate of the system,improve communication reliability,and reduce the need of the signal noise ratio in underwater wireless optical communication systems.
In order to prevent laser sending a long "0" or "1" signal list,avoid communication system making infinite bit errors in underwater wireless optical communication systems,a new convolution encoding scheme was adopted.The encoding method was designed and Viterbi decoding theory was analyzed.The simulative demonstration of bit error rate performance was carried out.The field programmable gate array(FPGA)design of encoder was implemented with VHDL language.The bit error rates of encoded and uncoded system,the signal noise ratio demanded to attain the same bit error rate was received.The result show that this code can reduce the bit error rate of the system,improve communication reliability,and reduce the need of the signal noise ratio in underwater wireless optical communication systems.
2011, 35(2): 226-229,259.
doi: 10.3969/j.issn.1001-3806.2011.02.023
Abstract:
In order to both reduce the number of scanning frames and ensure the image quality,a variable step scanning method was put forward for range-gated underwater laser imaging.Firstly,the focal length,focal position of the receiver lens and the system scanning scope were defined based on both radiation detection theory and the principle of depth of field.Then the step size of delay and the width of the gated pulse were calculated according to the time-domain broadening of underwater laser pulses. Finally,the simulation and experiments were conducted.The experimental results show that the range-gated imaging system based on the proposed scan method can scan over the scope from 15m to 48.6m with 7 pulses imaging,and the image quality is kept at the same time.This proves the validity of this method,and provides an attempt for the actual application of range-gated technique in underwater imaging.
In order to both reduce the number of scanning frames and ensure the image quality,a variable step scanning method was put forward for range-gated underwater laser imaging.Firstly,the focal length,focal position of the receiver lens and the system scanning scope were defined based on both radiation detection theory and the principle of depth of field.Then the step size of delay and the width of the gated pulse were calculated according to the time-domain broadening of underwater laser pulses. Finally,the simulation and experiments were conducted.The experimental results show that the range-gated imaging system based on the proposed scan method can scan over the scope from 15m to 48.6m with 7 pulses imaging,and the image quality is kept at the same time.This proves the validity of this method,and provides an attempt for the actual application of range-gated technique in underwater imaging.
2011, 35(2): 230-233,263.
doi: 10.3969/j.issn.1001-3806.2011.02.024
Abstract:
In order to enhance mixing effect,two novel styles of triplet impingement injectors were presented by changing middle jet orifice or the other two jet orifices into cone-shaped orifices.Flow field characteristics of above-mentioned two kinds of injectors and traditional injectors with triple straight-wall jet orifices under conditions of fuel-oxidizer-fuel triplet arrangement were analyzed based on 3-D computational fluid dynamic methods.The numerical simulation results demonstrate that mixing of triplet impingement injectors is principally accelerated by transverse vortices.For the injector with cone-shaped oxidizer jet orifice,the vertex intensity of flow field is lower than that of the injector with triple straight-wall jet orifices.For the injector with cone-shaped fuel jet orifices,there is a definite increase of the vertex intensity of flow field.Mass-weighted average unmixedness was introduced to evaluate the mixing performances of three kinds of injectors.It is indicated that the mixing effect of injector with cone-shaped fuel jet orifices is better than that of injector with triple straight-wall jet orifices and the injector with cone-shaped oxidizer jet orifice is the worst of three.For injector design of chemical laser combustors,oxidizer and fuel jet orifices adopt different styles,for example,the injector with cone-shaped fuel jet orifices,which helps improve mixing effect of oxidizer flow and fuel flow further.
In order to enhance mixing effect,two novel styles of triplet impingement injectors were presented by changing middle jet orifice or the other two jet orifices into cone-shaped orifices.Flow field characteristics of above-mentioned two kinds of injectors and traditional injectors with triple straight-wall jet orifices under conditions of fuel-oxidizer-fuel triplet arrangement were analyzed based on 3-D computational fluid dynamic methods.The numerical simulation results demonstrate that mixing of triplet impingement injectors is principally accelerated by transverse vortices.For the injector with cone-shaped oxidizer jet orifice,the vertex intensity of flow field is lower than that of the injector with triple straight-wall jet orifices.For the injector with cone-shaped fuel jet orifices,there is a definite increase of the vertex intensity of flow field.Mass-weighted average unmixedness was introduced to evaluate the mixing performances of three kinds of injectors.It is indicated that the mixing effect of injector with cone-shaped fuel jet orifices is better than that of injector with triple straight-wall jet orifices and the injector with cone-shaped oxidizer jet orifice is the worst of three.For injector design of chemical laser combustors,oxidizer and fuel jet orifices adopt different styles,for example,the injector with cone-shaped fuel jet orifices,which helps improve mixing effect of oxidizer flow and fuel flow further.
2011, 35(2): 234-237,241.
doi: 10.3969/j.issn.1001-3806.2011.02.025
Abstract:
In order to study the effect of laser speckle on target detection,according to the extended Huygens-Fresnel principle,statistical properties of the speckle scattered from the rough surfaces in the far field were analyzed in double transmission.Analytical expressions for the correlation function and covariance of the speckle intensity were derived under the illumination of focused beam and coUimated beam.The results indicate that under the illumination of focused beam,the speckle intensity correlation function of the receiver surface is decreased fast with the laser beam waist and transmission distance decreasing.However,under the illumination of collimated beam,the speckle intensity correlation function of the receiver surface is decreased fast with the laser beam waist and transmission distance increasing.In the whole,it decreased fast under the coUimated illumination than focused illumination.The change rule of intensity covariance is identical with the speckle intensity correlation function.
In order to study the effect of laser speckle on target detection,according to the extended Huygens-Fresnel principle,statistical properties of the speckle scattered from the rough surfaces in the far field were analyzed in double transmission.Analytical expressions for the correlation function and covariance of the speckle intensity were derived under the illumination of focused beam and coUimated beam.The results indicate that under the illumination of focused beam,the speckle intensity correlation function of the receiver surface is decreased fast with the laser beam waist and transmission distance decreasing.However,under the illumination of collimated beam,the speckle intensity correlation function of the receiver surface is decreased fast with the laser beam waist and transmission distance increasing.In the whole,it decreased fast under the coUimated illumination than focused illumination.The change rule of intensity covariance is identical with the speckle intensity correlation function.
2011, 35(2): 238-241.
doi: 10.3969/j.issn.1001-3806.2011.02.026
Abstract:
In order to increase the etching depth with one laser pulse and promote the production efficiency,the effect of laser parameters on the etching depth was studied by means of double acousto-optic modulation technique after comparing the laser pulse etching crater morphology under different pulse energy density and two different lasers.The results showed:when the pulse energy density was 20.21 J/cm2,the etching crater depth reached the maximum,and when continuing to increase the energy density,the crater depth would be reduced;compared with single-cavity laser,the crater depth with two-cavities laser increased from 5μm to 10μm,and the crater diameter reduced from 161 μm to 134μm.
In order to increase the etching depth with one laser pulse and promote the production efficiency,the effect of laser parameters on the etching depth was studied by means of double acousto-optic modulation technique after comparing the laser pulse etching crater morphology under different pulse energy density and two different lasers.The results showed:when the pulse energy density was 20.21 J/cm2,the etching crater depth reached the maximum,and when continuing to increase the energy density,the crater depth would be reduced;compared with single-cavity laser,the crater depth with two-cavities laser increased from 5μm to 10μm,and the crater diameter reduced from 161 μm to 134μm.
2011, 35(2): 242-244.
doi: 10.3969/j.issn.1001-3806.2011.02.027
Abstract:
In order to study the birefringence effect of liquid crystal in communication,the transmission of liquid crystal electric-dependent was analyzed by means of the polarized light interference method and tested with a UV-3101PC spectral photometer at room temperature 20℃.The electro-optic effect of liquid crystal was studied by altering voltages at wavelengths of 1300nm and 1550nm.The result showed that there was a high transmission bandwidth nearby 1550nm when the voltage was 2V of the liquid crystal,and there was a high transmission bandwidth nearby 1300nm when the voltage was 2.3V of the liquid crystal. The conclusion is helpful for designing of liquid crystal device in communication.
In order to study the birefringence effect of liquid crystal in communication,the transmission of liquid crystal electric-dependent was analyzed by means of the polarized light interference method and tested with a UV-3101PC spectral photometer at room temperature 20℃.The electro-optic effect of liquid crystal was studied by altering voltages at wavelengths of 1300nm and 1550nm.The result showed that there was a high transmission bandwidth nearby 1550nm when the voltage was 2V of the liquid crystal,and there was a high transmission bandwidth nearby 1300nm when the voltage was 2.3V of the liquid crystal. The conclusion is helpful for designing of liquid crystal device in communication.
2011, 35(2): 245-248.
doi: 10.3969/j.issn.1001-3806.2011.02.028
Abstract:
Particle contaminations on the optical surfaces limit the operation of optical systems.In order to solve the pollution problem,laser plasma shockwave was utilized to remove the SiO2 particles on the surface of K9 glass.The laser cleaning effect was studied in the scanning mode.In case of single pulse laser cleaning,the effect of several parameters,such as particle position,separation distance and laser energy,on the cleaning result was simulated and demonstrated in experiments.The results show that Nd:YAG laser can remove the SiO2 particles effectively if properly controlling the laser parameters.The simulation results are consistent with the experimental ones in case of single pulse laser cleaning.
Particle contaminations on the optical surfaces limit the operation of optical systems.In order to solve the pollution problem,laser plasma shockwave was utilized to remove the SiO2 particles on the surface of K9 glass.The laser cleaning effect was studied in the scanning mode.In case of single pulse laser cleaning,the effect of several parameters,such as particle position,separation distance and laser energy,on the cleaning result was simulated and demonstrated in experiments.The results show that Nd:YAG laser can remove the SiO2 particles effectively if properly controlling the laser parameters.The simulation results are consistent with the experimental ones in case of single pulse laser cleaning.
2011, 35(2): 249-251.
doi: 10.3969/j.issn.1001-3806.2011.02.029
Abstract:
In order to solve multi-signal processing simultaneously in an optical coherent receiver system,a frequency measurement system that employs acousto-optic deflection technology and fiber-based coherent optical detection was designed based on acousto-optic deflection principle and characteristics of multiple signals co-existing and transmitting in the complex and dense electromagnetic environment.The acousto-optic interaction and beam deflection of different frequency signals were analyzed in theory.Through numerical simulation of multi-frequency intermodulation,the solution of reducing intermodulation of multiple signals was obtained.An experimental platform for handling multiple signals was constructed with space light injecting into fiber. Experimental result shows that real-time signal capture capability of the system is very strong and carrier frequency measurement of multi-signal can be realized in the system bandwidth.The test data displays that the frequency resolution is less than 0.1 MHz and the interception rate is up to 100%.
In order to solve multi-signal processing simultaneously in an optical coherent receiver system,a frequency measurement system that employs acousto-optic deflection technology and fiber-based coherent optical detection was designed based on acousto-optic deflection principle and characteristics of multiple signals co-existing and transmitting in the complex and dense electromagnetic environment.The acousto-optic interaction and beam deflection of different frequency signals were analyzed in theory.Through numerical simulation of multi-frequency intermodulation,the solution of reducing intermodulation of multiple signals was obtained.An experimental platform for handling multiple signals was constructed with space light injecting into fiber. Experimental result shows that real-time signal capture capability of the system is very strong and carrier frequency measurement of multi-signal can be realized in the system bandwidth.The test data displays that the frequency resolution is less than 0.1 MHz and the interception rate is up to 100%.
2011, 35(2): 255-259.
doi: 10.3969/j.issn.1001-3806.2011.02.031
Abstract:
A synthetic aperture lidar is a new imaging system in combination of synthetic aperture signal processing and laser techniques.Firstly,the principle of a synthetic aperture lidar was introduced.And then,some good domestic and foreign experiment results of were described.After analysis of these successful experiments,the key techniques,which are needed to be overcome to make synthetic aperture come into practice were reviewed.Finally,the perspective in military,scientific research and inspection of disaster and environment were put forward.
A synthetic aperture lidar is a new imaging system in combination of synthetic aperture signal processing and laser techniques.Firstly,the principle of a synthetic aperture lidar was introduced.And then,some good domestic and foreign experiment results of were described.After analysis of these successful experiments,the key techniques,which are needed to be overcome to make synthetic aperture come into practice were reviewed.Finally,the perspective in military,scientific research and inspection of disaster and environment were put forward.
2011, 35(2): 260-263.
doi: 10.3969/j.issn.1001-3806.2011.02.032
Abstract:
Considering the relationship between the average photon and the input signal power,the output tune characteristics were analyzed and simulated based on the carrier density rate equation.The relationship between the cavity reflective index and carrier density was also taken into account.The bistable phenomena was obtained at certain input optical power and wavelength.The bistability loop width first increases and then discreases with input optical power.The bistability loop width increases versus pump optical power.The gain is magnified at certain area when the wavelength is bigger than center wavelength.
Considering the relationship between the average photon and the input signal power,the output tune characteristics were analyzed and simulated based on the carrier density rate equation.The relationship between the cavity reflective index and carrier density was also taken into account.The bistable phenomena was obtained at certain input optical power and wavelength.The bistability loop width first increases and then discreases with input optical power.The bistability loop width increases versus pump optical power.The gain is magnified at certain area when the wavelength is bigger than center wavelength.
2011, 35(2): 264-267,271.
doi: 10.3969/j.issn.1001-3806.2011.02.033
Abstract:
In order to transmit wire and wireless signals simultaneously,a hybrid network was constructed with both the signals transmitted in the two orthogonal polarization respectively,in which wireless millimeter-wave was generated by a nonsymmetrical input dual Mach-Zehnder modulator in a wireless link,while wire signal was generated with a phase modulator to achieve differential phase-shift key modulation format and realize carrier reuse in uplink,then both the orthogonal polarization signals modulated respectively were coupled into the same optical wavelength and transmitted to the base station through the fiber. Both the orthogonal polarization signals were separated in the base station,the optical carrier modulatedby wireless signal was detected by a photodiode and amplified,then transmitted by the antenna.On the other hand,the optical signal carrying wire signal was divided into two signals,one was injected to the balanced detector to achieve wire signal,and the other was used as optical carrier in uplink.After simulation with OPTICSYSTEM software,the eye diagrams of 10Gbit/s wire signal and 60GHz wireless signal were obtained after transmission 50km in optical fiber.The results show that this method is very effective in transmission.
In order to transmit wire and wireless signals simultaneously,a hybrid network was constructed with both the signals transmitted in the two orthogonal polarization respectively,in which wireless millimeter-wave was generated by a nonsymmetrical input dual Mach-Zehnder modulator in a wireless link,while wire signal was generated with a phase modulator to achieve differential phase-shift key modulation format and realize carrier reuse in uplink,then both the orthogonal polarization signals modulated respectively were coupled into the same optical wavelength and transmitted to the base station through the fiber. Both the orthogonal polarization signals were separated in the base station,the optical carrier modulatedby wireless signal was detected by a photodiode and amplified,then transmitted by the antenna.On the other hand,the optical signal carrying wire signal was divided into two signals,one was injected to the balanced detector to achieve wire signal,and the other was used as optical carrier in uplink.After simulation with OPTICSYSTEM software,the eye diagrams of 10Gbit/s wire signal and 60GHz wireless signal were obtained after transmission 50km in optical fiber.The results show that this method is very effective in transmission.
2011, 35(2): 268-271.
doi: 10.3969/j.issn.1001-3806.2011.02.034
Abstract:
In order to detect the helium density in thermosphere with a laser radar,after theoretical analysis and computer simulation,the atmospheric absorption coefficients for the three resonance lines making up metastable He 1083nm emission line were calculated,and the atmospheric absorption coefficient was found at the order of magnitude of 10-3.The results show that for the same spectral line,the atmospheric absorption coefficient is proportional to the concentrate of atoms and the fourth root of the temperature,however it is inversely proportional to the pressure.For different spectral lines,the atmospheric absorption coefficients are proportional to the central wave length.In the half width of the spectral line,the average atmospheric absorption coefficient is proportional to the atmospheric absorption coefficient at the line center.Finally,the application of atmospheric absorption coefficient in spectrum analysis was pointed out.This calculation has some reference significance to realize the detection of the helium density in thermosphere.
In order to detect the helium density in thermosphere with a laser radar,after theoretical analysis and computer simulation,the atmospheric absorption coefficients for the three resonance lines making up metastable He 1083nm emission line were calculated,and the atmospheric absorption coefficient was found at the order of magnitude of 10-3.The results show that for the same spectral line,the atmospheric absorption coefficient is proportional to the concentrate of atoms and the fourth root of the temperature,however it is inversely proportional to the pressure.For different spectral lines,the atmospheric absorption coefficients are proportional to the central wave length.In the half width of the spectral line,the average atmospheric absorption coefficient is proportional to the atmospheric absorption coefficient at the line center.Finally,the application of atmospheric absorption coefficient in spectrum analysis was pointed out.This calculation has some reference significance to realize the detection of the helium density in thermosphere.
2011, 35(2): 272-274,277.
doi: 10.3969/j.issn.1001-3806.2011.02.035
Abstract:
In order to study the effect of sampling point number on fitting precision when fitting wave front by Zernike polynomials,it was analyzed by means of the method of inadequate induction,and then the change law of sampling point number and fitting precision of dozens of different test functions was obtained.The results reveal that all test functions follow the same law that fitting precision has little change when sampling point number reach a certain number.In addition,the change law of sampling point number and Zernike polynomials term number was obtained by calculation.Thus,the experiential formula to determinate sampling point number are found,which is of great practical instructional significance in wave front fitting with Zernike polynomials.
In order to study the effect of sampling point number on fitting precision when fitting wave front by Zernike polynomials,it was analyzed by means of the method of inadequate induction,and then the change law of sampling point number and fitting precision of dozens of different test functions was obtained.The results reveal that all test functions follow the same law that fitting precision has little change when sampling point number reach a certain number.In addition,the change law of sampling point number and Zernike polynomials term number was obtained by calculation.Thus,the experiential formula to determinate sampling point number are found,which is of great practical instructional significance in wave front fitting with Zernike polynomials.
2011, 35(2): 275-277.
doi: 10.3969/j.issn.1001-3806.2011.02.036
Abstract:
In order to improve precision of rhomb-type achromatic A/4 phase retarders,based on the positive and negative delay error of A/4 phase retarders and larger refractive index,high precision retarders were designed.The retarder was analyzed and validated in experiments,and the data of high precision λ/4 phase retarder were obtained.It is shown at the retardation curve within the range of 350nm to 2000nm that retardation is 90°at two wavelengths and the maximal retardance error is smaller than 0.04°.Comparing with conventional retarders,the new retarder not only extends achromatic range,but also improves achromatic precision.The results are helpful to design high precision λ/4 phase retarders.
In order to improve precision of rhomb-type achromatic A/4 phase retarders,based on the positive and negative delay error of A/4 phase retarders and larger refractive index,high precision retarders were designed.The retarder was analyzed and validated in experiments,and the data of high precision λ/4 phase retarder were obtained.It is shown at the retardation curve within the range of 350nm to 2000nm that retardation is 90°at two wavelengths and the maximal retardance error is smaller than 0.04°.Comparing with conventional retarders,the new retarder not only extends achromatic range,but also improves achromatic precision.The results are helpful to design high precision λ/4 phase retarders.
Propagation characteristics of ultrashort optical pulse passing through distributed fiber amplifiers
2011, 35(2): 278-281.
doi: 10.3969/j.issn.1001-3806.2011.02.037
Abstract:
In order to discuss the propagation and amplification characteristics of ultrashort optical pulse in distributed fiber amplifiers and the influencing factors,its basic propagation equation was established.Taking an ytterbium-doped fiber amplifier as example,the evolution of optical pulse in the amplifier was simulated by means of split-step Fourier transform method.Then the effect of initial chirp and gain dispersion were discussed.The results show that when the optical pulse propagates in a distributed optical fiber amplifier,dispersion and nonlinear effect of the fiber will affect pulse profile and frequency spectrum, and initial chirp also influence the propagation state of optical pulse.For wide-spectrum optical pulse,gain dispersion is equivalent to a loss mechanism,so its influence should be considered.Relevant results have certain reference value to the system design and optimization of optical fiber amplifiers.
In order to discuss the propagation and amplification characteristics of ultrashort optical pulse in distributed fiber amplifiers and the influencing factors,its basic propagation equation was established.Taking an ytterbium-doped fiber amplifier as example,the evolution of optical pulse in the amplifier was simulated by means of split-step Fourier transform method.Then the effect of initial chirp and gain dispersion were discussed.The results show that when the optical pulse propagates in a distributed optical fiber amplifier,dispersion and nonlinear effect of the fiber will affect pulse profile and frequency spectrum, and initial chirp also influence the propagation state of optical pulse.For wide-spectrum optical pulse,gain dispersion is equivalent to a loss mechanism,so its influence should be considered.Relevant results have certain reference value to the system design and optimization of optical fiber amplifiers.
2011, 35(2): 282-284.
doi: 10.3969/j.issn.1001-3806.2011.02.038
Abstract:
The results of numerical calculation of photon acceleration(photon frequency up shift)in the plasma wakefield driven by asymmetric laser pulses were presented.It is found that the maximum frequency up shift of the accelerated photons depends on the pulse shape and pulse width.There is an optimum pulse width and pulse rising width.There also exists an upper limit on plasma electron density to get the maximum photon frequency up shift.This will be helpful for further study about laser-plasma particle acceleration mechanism.
The results of numerical calculation of photon acceleration(photon frequency up shift)in the plasma wakefield driven by asymmetric laser pulses were presented.It is found that the maximum frequency up shift of the accelerated photons depends on the pulse shape and pulse width.There is an optimum pulse width and pulse rising width.There also exists an upper limit on plasma electron density to get the maximum photon frequency up shift.This will be helpful for further study about laser-plasma particle acceleration mechanism.
2011, 35(2): 285-288.
doi: 10.3969/j.issn.1001-3806.2011.02.039
Abstract:
In order to study the laser-induced damage mechanism in inertial confinement fusion system,temperature and thermal stress distributions in the fused silica,heated by repetition frequency laser,were given by means of finite element methods.The simulated results indicate the temperature of the contaminations rise to 2800K during the pulse laser irradiation, but the fused silica's temperature mainly rise from 300K to 2200K in 100μs after irradiation,and damage induced by the thermal stress occurs.The strong compressive in the damage region is about 30.73MPa.The highest stress outside the damage region is deviatoric hoop stress.The damage morphologies were tested by means of optical microscopy.The simulated outcomes correspond to the experiment result.
In order to study the laser-induced damage mechanism in inertial confinement fusion system,temperature and thermal stress distributions in the fused silica,heated by repetition frequency laser,were given by means of finite element methods.The simulated results indicate the temperature of the contaminations rise to 2800K during the pulse laser irradiation, but the fused silica's temperature mainly rise from 300K to 2200K in 100μs after irradiation,and damage induced by the thermal stress occurs.The strong compressive in the damage region is about 30.73MPa.The highest stress outside the damage region is deviatoric hoop stress.The damage morphologies were tested by means of optical microscopy.The simulated outcomes correspond to the experiment result.
2011, 35(2): 170-172,176.
doi: 10.3969/j.issn.1001-3806.2011.02.008
Abstract:
In order to control the voltage of each electrode of a liquid-crystal-based phased array independently,based on field programmable gate array,the voltage of electrodes of the liquid-crystal-based phased array was driven to regulate phase distribution of electrodes.Analytical and experimental results show that periodic phase distribution of the electrodes can modulate the phase of an optical beam,i.e.,scan can be accomplished.This conclusion is helpful for adjusting phase of the electrodes of a liquid-crystal-based phased array.
In order to control the voltage of each electrode of a liquid-crystal-based phased array independently,based on field programmable gate array,the voltage of electrodes of the liquid-crystal-based phased array was driven to regulate phase distribution of electrodes.Analytical and experimental results show that periodic phase distribution of the electrodes can modulate the phase of an optical beam,i.e.,scan can be accomplished.This conclusion is helpful for adjusting phase of the electrodes of a liquid-crystal-based phased array.
2011, 35(2): 252-254.
doi: 10.3969/j.issn.1001-3806.2011.02.030
Abstract:
In order to study temperature characteristics of the transmission spectra of long period fiber gratings,simulation was carried out based on the three-layer fiber model,and the change rule of transmission spectra was obtained in the case of coupling between lowest-order cladding modes and the fundamental core mode.It is shown that the depth of harmonic wave is almost independent of temperature within the low temperature range.Different harmonic wave has different temperature sensitivity,the bigger the order,the higher the temperature sensitivity,K7=0.04951 nm/℃,K3=0.04246nm/℃.But the response the same harmonic wave is linear with temperature.
In order to study temperature characteristics of the transmission spectra of long period fiber gratings,simulation was carried out based on the three-layer fiber model,and the change rule of transmission spectra was obtained in the case of coupling between lowest-order cladding modes and the fundamental core mode.It is shown that the depth of harmonic wave is almost independent of temperature within the low temperature range.Different harmonic wave has different temperature sensitivity,the bigger the order,the higher the temperature sensitivity,K7=0.04951 nm/℃,K3=0.04246nm/℃.But the response the same harmonic wave is linear with temperature.
