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RSS2013 Vol. 37, No. 5
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2013, 37(5): 561-564.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.001
[Abstract]
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Abstract:
A novel method was put forward to measure the line width of stimulated Brillouin scattering(SBS) in water based on time-domain Fourier transform. The pulse duration and line width of SBS was studied over a temperature range of 5℃ to 40℃. Firstly, the pulse duration is measured with an oscilloscope, then the pulse duration at different temperature was obtained through Fourier transform and linewidth alignment. Experimental results and estimation of statistical error show that, this method possesses higher measurement accuracy(maximum error of measurement is less than 3.5%) and is a simple and feasible approach.
A novel method was put forward to measure the line width of stimulated Brillouin scattering(SBS) in water based on time-domain Fourier transform. The pulse duration and line width of SBS was studied over a temperature range of 5℃ to 40℃. Firstly, the pulse duration is measured with an oscilloscope, then the pulse duration at different temperature was obtained through Fourier transform and linewidth alignment. Experimental results and estimation of statistical error show that, this method possesses higher measurement accuracy(maximum error of measurement is less than 3.5%) and is a simple and feasible approach.
2013, 37(5): 571-576.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.003
Abstract:
In order to achieve accurate measurement of multiple optical-axis parallelism of an electro-optical sighting telescope, a detection system for multiple optical-axis parallelism was designed based on a large-calibre off-axis concave parabolic mirror. The whole system, including optical imaging system, controlling platform and image acquisition and processing system, was designed. Using discrete cosine transform coefficients as evaluation standard, high-precise auto-focusing was achieved. Using a large-calibre off-axis concave parabolic mirror, the demands of various kinds of electro-optical sighting telescopes measurement were meeted. The automatic measurement of optifcal-axis parallelism among light axis, far-infrared axis and near-infrared axis was achieved. The actual measurement was carried out for a certain electro-optical sighting telescope. When the deviation angle among multiple optical-axis was between 0.04mrad and 0.08mrad, the relative error was less than 13%, considered as the limit of system detection angle. The results showe that the detecting system decreases the error of human factor and is universal and high efficient. The accuracy of measurement also meet the requirements.
In order to achieve accurate measurement of multiple optical-axis parallelism of an electro-optical sighting telescope, a detection system for multiple optical-axis parallelism was designed based on a large-calibre off-axis concave parabolic mirror. The whole system, including optical imaging system, controlling platform and image acquisition and processing system, was designed. Using discrete cosine transform coefficients as evaluation standard, high-precise auto-focusing was achieved. Using a large-calibre off-axis concave parabolic mirror, the demands of various kinds of electro-optical sighting telescopes measurement were meeted. The automatic measurement of optifcal-axis parallelism among light axis, far-infrared axis and near-infrared axis was achieved. The actual measurement was carried out for a certain electro-optical sighting telescope. When the deviation angle among multiple optical-axis was between 0.04mrad and 0.08mrad, the relative error was less than 13%, considered as the limit of system detection angle. The results showe that the detecting system decreases the error of human factor and is universal and high efficient. The accuracy of measurement also meet the requirements.
2013, 37(5): 577-581.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.004
Abstract:
In order to overcome the known plaintext attack which the asymmetric optical image cryptosystem based on phase-truncated Fourier transforms can not resist, an encryption method based on phase-truncated Fourier transforms was proposed by employing the phase factor of the spherical wave under the spherical wave illumination. The theoretical analysis and experiment results indicate that the proposed encryption method can maintain the asymmetric characteristic of the cryptosystem and avoid various types of the currently existing attacks, especially the known plaintext attack, which the asymmetric cryptosystem based on phase-truncated Fourier transforms can not resist. The results are helpful for the security improvement of the asymmetric optical image cryptosystem based on phase-truncated Fourier transform.
In order to overcome the known plaintext attack which the asymmetric optical image cryptosystem based on phase-truncated Fourier transforms can not resist, an encryption method based on phase-truncated Fourier transforms was proposed by employing the phase factor of the spherical wave under the spherical wave illumination. The theoretical analysis and experiment results indicate that the proposed encryption method can maintain the asymmetric characteristic of the cryptosystem and avoid various types of the currently existing attacks, especially the known plaintext attack, which the asymmetric cryptosystem based on phase-truncated Fourier transforms can not resist. The results are helpful for the security improvement of the asymmetric optical image cryptosystem based on phase-truncated Fourier transform.
2013, 37(5): 679-681.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.025
Abstract:
To measure the pulse width of femtosecond laser rapidly and accurately, a measurement system was designed based on the second order autocorrelation principle. The results show that pulse width of the seed laser at 800nm was 199.51fs tested by the independently designed measurement system and was 217.6fs tested by the single pulse autocorrelation instrument of Coherent company. The error is only 0.43%. The results proved that this independent measurement system can test the femtosecond pulse width precisely.
To measure the pulse width of femtosecond laser rapidly and accurately, a measurement system was designed based on the second order autocorrelation principle. The results show that pulse width of the seed laser at 800nm was 199.51fs tested by the independently designed measurement system and was 217.6fs tested by the single pulse autocorrelation instrument of Coherent company. The error is only 0.43%. The results proved that this independent measurement system can test the femtosecond pulse width precisely.
2013, 37(5): 682-685.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.026
Abstract:
In order to suppress the influence of the environment on quantum teleportation, a scheme of quantum teleportation was presented based on decoherent-free subspace. In this scheme, a kind of disentanglement-free atomic six-bit state is taken as quantum entanglement channel, and the teleportated one logical qubit quantum information is encoded into three-bit atomic state which can avoid against influence of the environment. The properties of the quantum teleportation scheme and its experimental realization were analyzed. The result shows that the whole teleportation process is immune to amplitude-flip and phase-flip noises induced by the environment and the success probability for this scheme is 44%.
In order to suppress the influence of the environment on quantum teleportation, a scheme of quantum teleportation was presented based on decoherent-free subspace. In this scheme, a kind of disentanglement-free atomic six-bit state is taken as quantum entanglement channel, and the teleportated one logical qubit quantum information is encoded into three-bit atomic state which can avoid against influence of the environment. The properties of the quantum teleportation scheme and its experimental realization were analyzed. The result shows that the whole teleportation process is immune to amplitude-flip and phase-flip noises induced by the environment and the success probability for this scheme is 44%.
2013, 37(5): 690-695.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.028
Abstract:
In order to overcome the defects of fuzzy detection, low recognition rate and poor real-time of traditional fusion methods used in precision-guided weapons systems, a new image fusion algorithm was proposed combining wavelet transform with Canny operator. Firstly, the source image was decomposed into 3 layers in vertical and horizontal directions, which are suitable for image reconstruction; then due to its own characteristics of the different frequency components, an unique fusion rule was used to change wavelet coefficients of images, that is, for the low frequency components, the weighted average fusion algorithm was adopted, and for the high-frequency components, wavelet coefficients were changed using Canny operator and the local area variance criteria method. Finally, images were reconstructed using the inverse wavelet transform for different components. Results show the improved method not only reduces the fuzziness of edge, highlights target color, gets better visual effects, but also makes computational efficiency high, real-time good, particularly can detect and recognize pretend targets. It has better theoretical research and application value.
In order to overcome the defects of fuzzy detection, low recognition rate and poor real-time of traditional fusion methods used in precision-guided weapons systems, a new image fusion algorithm was proposed combining wavelet transform with Canny operator. Firstly, the source image was decomposed into 3 layers in vertical and horizontal directions, which are suitable for image reconstruction; then due to its own characteristics of the different frequency components, an unique fusion rule was used to change wavelet coefficients of images, that is, for the low frequency components, the weighted average fusion algorithm was adopted, and for the high-frequency components, wavelet coefficients were changed using Canny operator and the local area variance criteria method. Finally, images were reconstructed using the inverse wavelet transform for different components. Results show the improved method not only reduces the fuzziness of edge, highlights target color, gets better visual effects, but also makes computational efficiency high, real-time good, particularly can detect and recognize pretend targets. It has better theoretical research and application value.
2013, 37(5): 565-570.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.002
Abstract:
In order to obtain the influence rule of laser cutting parameters on carbon fiber reinforced polymer(CFRP), CFRPs were cut with a 500W millisecond pulsed Nd:YAG laser in air and under the water respectively. The relationships of pulse energy, frequency, cutting speed, gas pressure with the cutting quality were investigated by means of the one-factor experimental design. The influence of the laser cutting parameters on kerf width, fiber pull out at the beam entrance, fiber pull out at the beam exit and taper angle were obtained. The laser cutting mechanism was also analyzed and studied. The research shows that the laser cutting under the water can greatly reduce the heat affected zone generated by the laser cutting, which provides some reference for the further research of the laser cutting CFRP under the water.
In order to obtain the influence rule of laser cutting parameters on carbon fiber reinforced polymer(CFRP), CFRPs were cut with a 500W millisecond pulsed Nd:YAG laser in air and under the water respectively. The relationships of pulse energy, frequency, cutting speed, gas pressure with the cutting quality were investigated by means of the one-factor experimental design. The influence of the laser cutting parameters on kerf width, fiber pull out at the beam entrance, fiber pull out at the beam exit and taper angle were obtained. The laser cutting mechanism was also analyzed and studied. The research shows that the laser cutting under the water can greatly reduce the heat affected zone generated by the laser cutting, which provides some reference for the further research of the laser cutting CFRP under the water.
2013, 37(5): 582-586.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.005
Abstract:
In order to meet the demand of fabrication and application of 2N optical power splitters, theoretical and experimental researches were carried out for broadband integrated 22 3dB couplers. The traditional asymmetric X-junction was improved by using three-dimension beam propagation method, through simulation and design,22 3dB couplers with low loss and wide operating bandwidth were obtained. Considering characteristics of asymmetric X-junction, the broadband 22 3dB coupler was successfully made by using Ag+-Na+ ion-exchange in glass. The measurement of light spectrum, using two broadband light source with wavelength respectively in 1260nm~1360nm and 1460nm~1600nm, showed that the insertion loss was less than 4.0dB in the broadband range, wavelength response was relatively flat and wavelength insensitive, uniformity was less than 0.5dB. The results prove that, using the improved asymmetric X-junction combined with ion-exchange technique, broadband 22 3dB couplers with good performance can be fabricated in glass, which lays good foundation for further optimization of the device performance and successful development of its valuable application.
In order to meet the demand of fabrication and application of 2N optical power splitters, theoretical and experimental researches were carried out for broadband integrated 22 3dB couplers. The traditional asymmetric X-junction was improved by using three-dimension beam propagation method, through simulation and design,22 3dB couplers with low loss and wide operating bandwidth were obtained. Considering characteristics of asymmetric X-junction, the broadband 22 3dB coupler was successfully made by using Ag+-Na+ ion-exchange in glass. The measurement of light spectrum, using two broadband light source with wavelength respectively in 1260nm~1360nm and 1460nm~1600nm, showed that the insertion loss was less than 4.0dB in the broadband range, wavelength response was relatively flat and wavelength insensitive, uniformity was less than 0.5dB. The results prove that, using the improved asymmetric X-junction combined with ion-exchange technique, broadband 22 3dB couplers with good performance can be fabricated in glass, which lays good foundation for further optimization of the device performance and successful development of its valuable application.
2013, 37(5): 587-591.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.006
Abstract:
In order to study the influence of laser power density on crystallization effect in continuous laser crystallization of amorphous silicon thin film, amorphous silicon thin films were prepared by means of magnetron sputtering and then crystallized by continuous Ar+Kr+laser. Crystallization effect was studied by means of micro-Raman spectroscopic measurement and field emission scanning electron microscope under the fixed time 5ms and different laser power density. The difference of crystal growth process on two different substrates-common glass substrate and quartz substrate was compared.It was shown that within the limit of 27.1kW/cm2 the amorphous Si films were able to be crystallized at laser power densities above 15.1kW/cm2 on common glass substrate, crystallization effect became better first and then worse with the increase of laser power density, large area of scattered apple shape polysilicon particles of crystal size around 478nm can be obtained at 24.9kW/cm2. An intermediate laser power density value exists to make the crystallization effect best. Films deposited on quartz substrate present a different crystallization growth process, large spherical polysilicon particles emerged as the energy density reaches to 19.7kW/cm2,with the increase of energy density, the particle size got larger and the maximum size 5.38m was obtained at 27.1kW/cm2. These results play a positive role in studying preparing poly-Si thin film by means of continuous laser crystallizing.
In order to study the influence of laser power density on crystallization effect in continuous laser crystallization of amorphous silicon thin film, amorphous silicon thin films were prepared by means of magnetron sputtering and then crystallized by continuous Ar+Kr+laser. Crystallization effect was studied by means of micro-Raman spectroscopic measurement and field emission scanning electron microscope under the fixed time 5ms and different laser power density. The difference of crystal growth process on two different substrates-common glass substrate and quartz substrate was compared.It was shown that within the limit of 27.1kW/cm2 the amorphous Si films were able to be crystallized at laser power densities above 15.1kW/cm2 on common glass substrate, crystallization effect became better first and then worse with the increase of laser power density, large area of scattered apple shape polysilicon particles of crystal size around 478nm can be obtained at 24.9kW/cm2. An intermediate laser power density value exists to make the crystallization effect best. Films deposited on quartz substrate present a different crystallization growth process, large spherical polysilicon particles emerged as the energy density reaches to 19.7kW/cm2,with the increase of energy density, the particle size got larger and the maximum size 5.38m was obtained at 27.1kW/cm2. These results play a positive role in studying preparing poly-Si thin film by means of continuous laser crystallizing.
2013, 37(5): 592-595.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.007
Abstract:
In order to satisfy the requirements of coatings of deep ultraviolet(DUV) lithography objective lens and obtain coatings with low optical losses, high stability and long lifetimes, a deposition method should be confirmed first. LaF3 single layers were deposited upon fused silica by ion beam sputtering(IBS), boat and electron beam evaporation with optimized process parameters respectively. Firstly, based on spectrophotometry, the refractive index n and extinction coefficients k in 185nm~800nm of the LaF3 layer deposited with three methods were obtained. Secondly, the surface roughness of LaF3 layers was measured by means of atomic-force microscope(AFM). Finally, X-ray diffraction(XRD) was used to investigate the microstructure of LaF3 layer. Experimental results indicate that, LaF3 layer deposited by IBS has the highest refractive index and the lowest surface roughness but the highest extinction coefficients; for LaF3 layer deposited by electron beam, although its extinction coefficients is low, but the refractive index and surface roughness doesn't seem good; as for thermal boat, all parameters discussed here is intermediate between that of LaF3 layer deposited by IBS and electron beam. Finally,based on consideration with every factors, thermal boat evaporation method is most suitable for depositing DUV LaF3 film.
In order to satisfy the requirements of coatings of deep ultraviolet(DUV) lithography objective lens and obtain coatings with low optical losses, high stability and long lifetimes, a deposition method should be confirmed first. LaF3 single layers were deposited upon fused silica by ion beam sputtering(IBS), boat and electron beam evaporation with optimized process parameters respectively. Firstly, based on spectrophotometry, the refractive index n and extinction coefficients k in 185nm~800nm of the LaF3 layer deposited with three methods were obtained. Secondly, the surface roughness of LaF3 layers was measured by means of atomic-force microscope(AFM). Finally, X-ray diffraction(XRD) was used to investigate the microstructure of LaF3 layer. Experimental results indicate that, LaF3 layer deposited by IBS has the highest refractive index and the lowest surface roughness but the highest extinction coefficients; for LaF3 layer deposited by electron beam, although its extinction coefficients is low, but the refractive index and surface roughness doesn't seem good; as for thermal boat, all parameters discussed here is intermediate between that of LaF3 layer deposited by IBS and electron beam. Finally,based on consideration with every factors, thermal boat evaporation method is most suitable for depositing DUV LaF3 film.
2013, 37(5): 596-600.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.008
Abstract:
The phase accuracy of numerically reconstructed images directly affects the result of the digital holographic measurement. How to find the phase distortion and adopt corresponding method to automatically correct the distortion is challenging. The phase correction problem of lensless Fourier transform digital holographic was analyzed. When reconstruct the numerical wave surface by means of single Fourier transform, there is an additional quadratic phase factor inducing the phase distortion of reconstructed images. The digital phase mask was calculated based on multiple-profile calculation by means of the least square method for curve fitting, the phase distribution was corrected. The theoretical analysis and experimental prove that it is better to correct phase distortion compared with frequently-used two-profile method, the result is helpful for the study of phase correction.
The phase accuracy of numerically reconstructed images directly affects the result of the digital holographic measurement. How to find the phase distortion and adopt corresponding method to automatically correct the distortion is challenging. The phase correction problem of lensless Fourier transform digital holographic was analyzed. When reconstruct the numerical wave surface by means of single Fourier transform, there is an additional quadratic phase factor inducing the phase distortion of reconstructed images. The digital phase mask was calculated based on multiple-profile calculation by means of the least square method for curve fitting, the phase distribution was corrected. The theoretical analysis and experimental prove that it is better to correct phase distortion compared with frequently-used two-profile method, the result is helpful for the study of phase correction.
2013, 37(5): 601-604.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.009
Abstract:
In order to eliminate geometric distortion error of marking point caused by 2-D galvanometer scan before the objective in laser marking system, the causes of the distortion was analyzed in detail. On the basis of the ideal formula of galvanometer deflection angle (,), using the least squares curve fitting method, a fitting polynomial for compensating the errors of (,) with the marking point coordinates (x,y) was obtained and the distortion error of the galvanometer laser marking point was corrected. After correction, the maximum geometric distortion error of the laser marking point can be reduced from 3.2mm down to less than 20m with smaller amount of calculation and faster speed. The results show that this error correction algorithm can meet the requirements of high-speed, high-precision laser marking. At the same time, new compensation formula can be calculated by changing the objective lens focal length to be applied to the different parameters laser marking system.
In order to eliminate geometric distortion error of marking point caused by 2-D galvanometer scan before the objective in laser marking system, the causes of the distortion was analyzed in detail. On the basis of the ideal formula of galvanometer deflection angle (,), using the least squares curve fitting method, a fitting polynomial for compensating the errors of (,) with the marking point coordinates (x,y) was obtained and the distortion error of the galvanometer laser marking point was corrected. After correction, the maximum geometric distortion error of the laser marking point can be reduced from 3.2mm down to less than 20m with smaller amount of calculation and faster speed. The results show that this error correction algorithm can meet the requirements of high-speed, high-precision laser marking. At the same time, new compensation formula can be calculated by changing the objective lens focal length to be applied to the different parameters laser marking system.
2013, 37(5): 605-609.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.010
Abstract:
In order to improve the complex structure of the receiver and the transmitter and the unfixed rate of the modulator while pulse position modulation (PPM) needed symbol synchronization and digital pulse interval modulation(DPIM), dual-header pulse interval modulation(DHPIM), multilevel digital pulse interval modulation(MDPIM) had unfixed symbol length, fixed-length digital pulse interval modulation (FDPIM) used in underwater wireless optical communication system was put forward. Bandwidth requirement and transmission capacity were analyzed, compared with on-off keying(OOK), PPM, DPIM and MDPIM. Based on the model of underwater wireless optical communication channel, packet error rate (PER) of FDPIM for this channel was presented. The results show that FDPIM is suitable for underwater optical wireless communication system
In order to improve the complex structure of the receiver and the transmitter and the unfixed rate of the modulator while pulse position modulation (PPM) needed symbol synchronization and digital pulse interval modulation(DPIM), dual-header pulse interval modulation(DHPIM), multilevel digital pulse interval modulation(MDPIM) had unfixed symbol length, fixed-length digital pulse interval modulation (FDPIM) used in underwater wireless optical communication system was put forward. Bandwidth requirement and transmission capacity were analyzed, compared with on-off keying(OOK), PPM, DPIM and MDPIM. Based on the model of underwater wireless optical communication channel, packet error rate (PER) of FDPIM for this channel was presented. The results show that FDPIM is suitable for underwater optical wireless communication system
2013, 37(5): 610-617.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.011
Abstract:
In order to study the generation of high coherent supercontinuum and pulse compression in an all-normal dispersion photonic crystal fiber, the nonlinear propagation of an ultrashort pulse and supercontinuum generation in an all-normal dispersion photonic crystal fiber were simulated with the standard split-step Fourier algorithm. The impact of center wavelength and input peak power of the pump pulse on the coherence properties of supercontinuum was simulated and analyzed. It is found the weaker the dispersion effect is, the more advantageous to the high coherent supercontinuum generation. A high coherent supercontinuum with band width of 587nm and flatness of less 7dB can be obtained by pumping the fiber under which the dispersion effect is small. It is also found the higher the coherence properties of supercontinuum is, the more advantageous to the supercontinuum pulse compression. An ultrashort pulse with pulse duration of 8.4fs and compression quality factor of 88.88% can be obtained by using a grating pair compressor to compress the high coherent supercontinuum pulse. Therefore, the high coherent supercontinuum and high quality pulse compression can be obtained by using the effect of self phase modulation and suppressing the dispersion effect.
In order to study the generation of high coherent supercontinuum and pulse compression in an all-normal dispersion photonic crystal fiber, the nonlinear propagation of an ultrashort pulse and supercontinuum generation in an all-normal dispersion photonic crystal fiber were simulated with the standard split-step Fourier algorithm. The impact of center wavelength and input peak power of the pump pulse on the coherence properties of supercontinuum was simulated and analyzed. It is found the weaker the dispersion effect is, the more advantageous to the high coherent supercontinuum generation. A high coherent supercontinuum with band width of 587nm and flatness of less 7dB can be obtained by pumping the fiber under which the dispersion effect is small. It is also found the higher the coherence properties of supercontinuum is, the more advantageous to the supercontinuum pulse compression. An ultrashort pulse with pulse duration of 8.4fs and compression quality factor of 88.88% can be obtained by using a grating pair compressor to compress the high coherent supercontinuum pulse. Therefore, the high coherent supercontinuum and high quality pulse compression can be obtained by using the effect of self phase modulation and suppressing the dispersion effect.
2013, 37(5): 618-621.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.012
Abstract:
In order to achieve high-quality hologram reconstruction based on digital micro-mirror device(DMD), gray scale adjustment characteristics and Fresnel diffraction characteristics of DMDs were described in detail. Then, the principle of holographic display based on DMD was analyzed. Finally, high-quality hologram was reconstructed. The results demonstrate holographic display was improved obviously after gray scale adjustment. The results are helpful for the display of computer generated hologram based on digital micro-mirror device.
In order to achieve high-quality hologram reconstruction based on digital micro-mirror device(DMD), gray scale adjustment characteristics and Fresnel diffraction characteristics of DMDs were described in detail. Then, the principle of holographic display based on DMD was analyzed. Finally, high-quality hologram was reconstructed. The results demonstrate holographic display was improved obviously after gray scale adjustment. The results are helpful for the display of computer generated hologram based on digital micro-mirror device.
2013, 37(5): 622-626.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.013
Abstract:
A method for conveniently measuring the size distribution of hydrogen-bubbles in water electrolysis was presented based on micrograph, image proceeding and statistical analysis. Firstly, pictures of hydrogen-bubbles produced by water electrolysis in the same space and at different time were taken by an optical microscopy apparatus. Secondly, image enhancement, image segmentation, morphological transformation and particle measurements were adopted to get number and size micro-bubbles in each picture. Finally, based on ergodicity of the amount of micro-bubbles in measuring space, the size distribution of bubbles in the whole bubble-producing space was obtained by substituting statistical size distribution in time sequence for spatial size distribution. The experimental results show that the hydrogen-bubbles' size distribution in water electrolysis quite fits Gaussian function and the square correlative coefficients are all beyond 0.95 under three electrolytic currents, and the larger electrolytic current is, the more dispersive the size distribution is, but the influence of electrolytic current on average size of hydrogen-bubbles is little. Analysis and experiment make sure that the presented method can measure the size distribution effectively.
A method for conveniently measuring the size distribution of hydrogen-bubbles in water electrolysis was presented based on micrograph, image proceeding and statistical analysis. Firstly, pictures of hydrogen-bubbles produced by water electrolysis in the same space and at different time were taken by an optical microscopy apparatus. Secondly, image enhancement, image segmentation, morphological transformation and particle measurements were adopted to get number and size micro-bubbles in each picture. Finally, based on ergodicity of the amount of micro-bubbles in measuring space, the size distribution of bubbles in the whole bubble-producing space was obtained by substituting statistical size distribution in time sequence for spatial size distribution. The experimental results show that the hydrogen-bubbles' size distribution in water electrolysis quite fits Gaussian function and the square correlative coefficients are all beyond 0.95 under three electrolytic currents, and the larger electrolytic current is, the more dispersive the size distribution is, but the influence of electrolytic current on average size of hydrogen-bubbles is little. Analysis and experiment make sure that the presented method can measure the size distribution effectively.
2013, 37(5): 627-630.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.014
Abstract:
In order to study the characteristics of relativistic Langmuir solitons, the control equations of relativistic strong Langmuir turbulence in ultrapowerful laser plasma were obtained from momentum theory. And then, theoretical analysis was made. The research shows that half-width of wave-packet will become narrower and the total energy and momentum of solitons will become bigger with the increasing of average Lorentz factor of electrons and turbulence parameter of field. The relativistic effect of electrons affects the total energy and momentum of the solitons much larger in the nonlinear part than in the linear part. The results will provide the theoretical reference on the nonlinear phenomenon in ultrapowerful laser plasma.
In order to study the characteristics of relativistic Langmuir solitons, the control equations of relativistic strong Langmuir turbulence in ultrapowerful laser plasma were obtained from momentum theory. And then, theoretical analysis was made. The research shows that half-width of wave-packet will become narrower and the total energy and momentum of solitons will become bigger with the increasing of average Lorentz factor of electrons and turbulence parameter of field. The relativistic effect of electrons affects the total energy and momentum of the solitons much larger in the nonlinear part than in the linear part. The results will provide the theoretical reference on the nonlinear phenomenon in ultrapowerful laser plasma.
2013, 37(5): 631-635.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.015
Abstract:
In order to realize dual beam formation and 2-D scan in optical phased array, choosing glass as substrate material and liquid crystal as phase-shifting medium, using the electric control phase-shifting characteristics of liquid crystal, double beam formation and phase control spatial scanning of incident light were gotten. Wave control data were transmitted to LCD driver chip by FPGA chip and the liquid crystal phase shifting array was driven by voltage, and beam scanning function was controlled, so a single transmissive-type liquid crystal optical phased-control array assembly was developed. Therefore, based on beam scanning function of the assembly, a liquid crystal optical phased array was developed by cascading multiple-assembly to realize dual beam formation and 2-D scan. The results show that the cascading system has the ability to achieve double beam independent deflection control and high precision 2-D deflection.
In order to realize dual beam formation and 2-D scan in optical phased array, choosing glass as substrate material and liquid crystal as phase-shifting medium, using the electric control phase-shifting characteristics of liquid crystal, double beam formation and phase control spatial scanning of incident light were gotten. Wave control data were transmitted to LCD driver chip by FPGA chip and the liquid crystal phase shifting array was driven by voltage, and beam scanning function was controlled, so a single transmissive-type liquid crystal optical phased-control array assembly was developed. Therefore, based on beam scanning function of the assembly, a liquid crystal optical phased array was developed by cascading multiple-assembly to realize dual beam formation and 2-D scan. The results show that the cascading system has the ability to achieve double beam independent deflection control and high precision 2-D deflection.
2013, 37(5): 636-641.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.016
Abstract:
In order to study the evolution of laser-induced plasma and obtain the properties of plasma, transversely excited atmospheric CO2 laser was focused by a parabolic reflector to generate air breakdown plasma. Based on the imaging spectrometer system and intensified CCD detector, time-space resolution of laser-induced air plasma were investigated and the time evolution spectra and the space resolution spectra of plasma were obtained. Electron temperature of about 4104K and electron density of 1018cm-3 were calculated respectively by using the ratio of oxygen line spectrum and continuous spectrum and full width at half maximum of spectral line. The results show high-energy laser-induced plasma spectra radiate the intense continuous spectra outward, comparing with low-energy laser-induced plasma spectra. At the same time, laser-induced air plasma expands outward rapidly with the way of the laser-supported detonation wave. Due to the shielding effect of laser power, laser-induced air plasma shows the behavior of spatial separation. The results are useful for understanding the interaction between plasma and high-energy laser.
In order to study the evolution of laser-induced plasma and obtain the properties of plasma, transversely excited atmospheric CO2 laser was focused by a parabolic reflector to generate air breakdown plasma. Based on the imaging spectrometer system and intensified CCD detector, time-space resolution of laser-induced air plasma were investigated and the time evolution spectra and the space resolution spectra of plasma were obtained. Electron temperature of about 4104K and electron density of 1018cm-3 were calculated respectively by using the ratio of oxygen line spectrum and continuous spectrum and full width at half maximum of spectral line. The results show high-energy laser-induced plasma spectra radiate the intense continuous spectra outward, comparing with low-energy laser-induced plasma spectra. At the same time, laser-induced air plasma expands outward rapidly with the way of the laser-supported detonation wave. Due to the shielding effect of laser power, laser-induced air plasma shows the behavior of spatial separation. The results are useful for understanding the interaction between plasma and high-energy laser.
2013, 37(5): 642-646.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.017
Abstract:
In order to measure the evolution of gas temperature during self-sustained volume discharge, the second positive spectra of nitrogen was analyzed using fitting spectra method. Plasma time-domain resolution molecular spectra of two transversely excited atmospheric(TEA)gas laser discharge systems (excimer laser fast discharge system and TEA CO2 laser slow discharge system) were measured. Gas rotational temperature was fitted to obtain the data of gas temperature evolution of two discharge structures. The results show that the rising temperature is 92K while the total of inject energy density is 1.3105 J/m3 of excimer laser fast discharge system and the rising temperature is 50K while the total of inject energy density is 7104 J/m3 of TEA CO2 laser slow discharge system. The ratio of the rising temperature of these two systems is proportional to the raio of the inject energy density of these two systems. These results are helpful to study self-sustained volume discharge mechanism and improve discharge stability.
In order to measure the evolution of gas temperature during self-sustained volume discharge, the second positive spectra of nitrogen was analyzed using fitting spectra method. Plasma time-domain resolution molecular spectra of two transversely excited atmospheric(TEA)gas laser discharge systems (excimer laser fast discharge system and TEA CO2 laser slow discharge system) were measured. Gas rotational temperature was fitted to obtain the data of gas temperature evolution of two discharge structures. The results show that the rising temperature is 92K while the total of inject energy density is 1.3105 J/m3 of excimer laser fast discharge system and the rising temperature is 50K while the total of inject energy density is 7104 J/m3 of TEA CO2 laser slow discharge system. The ratio of the rising temperature of these two systems is proportional to the raio of the inject energy density of these two systems. These results are helpful to study self-sustained volume discharge mechanism and improve discharge stability.
2013, 37(5): 647-650.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.018
Abstract:
All solid-state lasers have many applications. The thermal effect of laser crystal is one of the main factors affecting the performance of laser. Usually, the temperature field distribution in crystal is found, and then the thermal distortion of laser crystal is calculated. This process is tediously long and includes some repetition. In order to simplify the solution finding process for analyzing the influence of pumping light distribution on thermal distortion, a simplified method was proposed to compute the thermal distortion of laser crystal with circular cross-section taking the pumping as super-Gaussian beam. It is found that because of thermal distortion, the pumped end of laser crystal becomes a rotational curved surface with power 3. As the rank of pumping super-Gaussian beam increases, the thermal distortion of crystal pumped-end decreases. The result is helpful for solid-state laser design.
All solid-state lasers have many applications. The thermal effect of laser crystal is one of the main factors affecting the performance of laser. Usually, the temperature field distribution in crystal is found, and then the thermal distortion of laser crystal is calculated. This process is tediously long and includes some repetition. In order to simplify the solution finding process for analyzing the influence of pumping light distribution on thermal distortion, a simplified method was proposed to compute the thermal distortion of laser crystal with circular cross-section taking the pumping as super-Gaussian beam. It is found that because of thermal distortion, the pumped end of laser crystal becomes a rotational curved surface with power 3. As the rank of pumping super-Gaussian beam increases, the thermal distortion of crystal pumped-end decreases. The result is helpful for solid-state laser design.
2013, 37(5): 651-655.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.019
Abstract:
In order to improve the tracking accuracy of acquisition, tracking, pointing(ATP) control system for space optical communication, a novel two degree-of-freedom Smith predictive control was presented. Firstly, the ATP servo control system and novel two degree-of-freedom Smith predictive control system were analyzed. Then the simulation model was established by discussing the transfer function. Simulation was carried out with MATLAB software. Finally, the obtained result was compared with that of some conventional proportion-integral-derivative(PID)controllers, and the anti-interference and robustness of the method were measured. The simulation results show that the novel control method not only has the advantage of Smith predictor delay effective control,but also show the good match effect of incomplete derivative forward PID control and proportion-integral(PI) control. This method is a good solution to the instability caused by pure time delay, it also has better robustness and immunity.
In order to improve the tracking accuracy of acquisition, tracking, pointing(ATP) control system for space optical communication, a novel two degree-of-freedom Smith predictive control was presented. Firstly, the ATP servo control system and novel two degree-of-freedom Smith predictive control system were analyzed. Then the simulation model was established by discussing the transfer function. Simulation was carried out with MATLAB software. Finally, the obtained result was compared with that of some conventional proportion-integral-derivative(PID)controllers, and the anti-interference and robustness of the method were measured. The simulation results show that the novel control method not only has the advantage of Smith predictor delay effective control,but also show the good match effect of incomplete derivative forward PID control and proportion-integral(PI) control. This method is a good solution to the instability caused by pure time delay, it also has better robustness and immunity.
2013, 37(5): 656-659.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.020
Abstract:
In order to study the suppression effect of side lobes of volume Bragg gratings(VBG) and the characteristics of the spectral beam combining with apodized VBG, the side-lobe of VBG was suppressed by means of Gaussian apodization. The diffraction characteristics of the Gaussian-apodized Bragg grating were analyzed based on the chain matrix method. Then the function of the combining efficiency with apodized grating was given, and the effect of apodized grating on the combining efficiency was analyzed. The results show that the peaks of the first four side-lobe are reduced from 73%,47%,31%,22% to 11%,20%,10%,7%, respectively. The combining efficiency decreases as the diffraction loss increases, when the number and the spectral width of combining beam are limited. Therefore, the diffraction loss between the combined beams is suppressed well after using the Gaussian-apodized grating that suppress the side-lobe of the VBG, and the combining efficiency increases.
In order to study the suppression effect of side lobes of volume Bragg gratings(VBG) and the characteristics of the spectral beam combining with apodized VBG, the side-lobe of VBG was suppressed by means of Gaussian apodization. The diffraction characteristics of the Gaussian-apodized Bragg grating were analyzed based on the chain matrix method. Then the function of the combining efficiency with apodized grating was given, and the effect of apodized grating on the combining efficiency was analyzed. The results show that the peaks of the first four side-lobe are reduced from 73%,47%,31%,22% to 11%,20%,10%,7%, respectively. The combining efficiency decreases as the diffraction loss increases, when the number and the spectral width of combining beam are limited. Therefore, the diffraction loss between the combined beams is suppressed well after using the Gaussian-apodized grating that suppress the side-lobe of the VBG, and the combining efficiency increases.
2013, 37(5): 660-663.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.021
Abstract:
To reduce fluctuation of discharging time of both the cavity in a master oscillator power amplifier(MOPA)excimer laser and obtain stable laser output energy, a high precision voltage control scheme was designed based on a closed loop controlling circuit. i.e., monitoring the voltage across the energy storage capacitor, when the capacitor voltage is larger than the objective voltage, the voltage discharging circuit discharges capacitance voltage to the objective voltage for getting a precision charging voltage. The results show that the fluctuation of charging voltage was reduced from 1.67 to 0.83 by using the voltage control scheme. The precision of the voltage across the energy-storage capacitor in a resonance power supply can be improved; the relative jitter of the discharge time for both the laser cavities can be reduced by means of this method. It lays a good foundation for stable laser energy output.
To reduce fluctuation of discharging time of both the cavity in a master oscillator power amplifier(MOPA)excimer laser and obtain stable laser output energy, a high precision voltage control scheme was designed based on a closed loop controlling circuit. i.e., monitoring the voltage across the energy storage capacitor, when the capacitor voltage is larger than the objective voltage, the voltage discharging circuit discharges capacitance voltage to the objective voltage for getting a precision charging voltage. The results show that the fluctuation of charging voltage was reduced from 1.67 to 0.83 by using the voltage control scheme. The precision of the voltage across the energy-storage capacitor in a resonance power supply can be improved; the relative jitter of the discharge time for both the laser cavities can be reduced by means of this method. It lays a good foundation for stable laser energy output.
2013, 37(5): 664-667.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.022
Abstract:
In order to measure the structure of V-shaped silicon grooves, a thermal light spectral-domain optical coherence tomography was introduced. After the theoretical analysis and the experimental verification, 1-D depth image and 2-D cross-sectional image of V-shaped silicon grooves were obtained. Depth of 145.38m, top width of 212m and bottom width of 32m were gotten. The measured data was the same as the measured result of scanning electron microscope. The results are helpful for the measurement of micro-electromechanical system.
In order to measure the structure of V-shaped silicon grooves, a thermal light spectral-domain optical coherence tomography was introduced. After the theoretical analysis and the experimental verification, 1-D depth image and 2-D cross-sectional image of V-shaped silicon grooves were obtained. Depth of 145.38m, top width of 212m and bottom width of 32m were gotten. The measured data was the same as the measured result of scanning electron microscope. The results are helpful for the measurement of micro-electromechanical system.
2013, 37(5): 668-671.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.023
Abstract:
A new laser focusing method was proposed to reduce the nonlinear optical effect for the measurement of damage threshold on optical material surfaces. The focus is located by utilizing the plasma beam as the reference object which is emitted by the air ionization. In the focusing process, an image is formed by a plasma luminous point which is formed by the air ionization. Based on the mirror image principle, the sample surface is in the middle of the luminous point and the image, the focusing process is completed when the luminous point and the image coincide. In conclusion, the method is simple operation and high precision, it is important to the measurement of damage threshold on optical material surfaces.
A new laser focusing method was proposed to reduce the nonlinear optical effect for the measurement of damage threshold on optical material surfaces. The focus is located by utilizing the plasma beam as the reference object which is emitted by the air ionization. In the focusing process, an image is formed by a plasma luminous point which is formed by the air ionization. Based on the mirror image principle, the sample surface is in the middle of the luminous point and the image, the focusing process is completed when the luminous point and the image coincide. In conclusion, the method is simple operation and high precision, it is important to the measurement of damage threshold on optical material surfaces.
2013, 37(5): 672-678.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.024
Abstract:
To study the degree of polarization of partially coherent elegant Laguerre-Gaussian (PCELG) beam propagating through a circular aperture in turbulent atmosphere, based on extended Huygens-Fresnel principle, the formulas for the degree of polarization of PCELG beam were derived via theoretical calculation and the corresponding numerical calculation was carried out. The results indicate that the aperture diffraction effect will result in increasing oscillations of the polarization of PCELG beam. In turbulent atmosphere or in free space, the transverse degree of polarization near to the axis has a dramatic oscillation while the degree of polarization far from the axis approaches to 1. The further the propagation distance is, the larger the off-axis distance is. After propagating for a sufficiently long distance through the circular aperture in free space, the degree of polarization of PCELG beam approaches a value different from the initial one. However, it tends to the initial value in turbulent atmosphere. The results are useful for beam propagation and applications in atmosphere.
To study the degree of polarization of partially coherent elegant Laguerre-Gaussian (PCELG) beam propagating through a circular aperture in turbulent atmosphere, based on extended Huygens-Fresnel principle, the formulas for the degree of polarization of PCELG beam were derived via theoretical calculation and the corresponding numerical calculation was carried out. The results indicate that the aperture diffraction effect will result in increasing oscillations of the polarization of PCELG beam. In turbulent atmosphere or in free space, the transverse degree of polarization near to the axis has a dramatic oscillation while the degree of polarization far from the axis approaches to 1. The further the propagation distance is, the larger the off-axis distance is. After propagating for a sufficiently long distance through the circular aperture in free space, the degree of polarization of PCELG beam approaches a value different from the initial one. However, it tends to the initial value in turbulent atmosphere. The results are useful for beam propagation and applications in atmosphere.
2013, 37(5): 686-689.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.027
Abstract:
In order to detect the low-frequency underwater acoustic signal at tens of hertz, an optical measurement method was put forward and a measurement system was developed. The clear and high stable diffraction pattern was observed experimentally when laser beam illuminates on the liquid surface modulated by underwater acoustic signal. The diffraction fringes were asymmetric. The expressions of the diffraction intensity were derived theoretically. The asymmetric distribution of position and diffraction intensity with laser oblique incidence was explained and the symmetric distribution of diffraction intensity with laser normal incidence was explained. Theoretical results were in good agreement with experimental ones. The results show that the position and diffraction intensity with laser oblique incidence has asymmetric distribution.
In order to detect the low-frequency underwater acoustic signal at tens of hertz, an optical measurement method was put forward and a measurement system was developed. The clear and high stable diffraction pattern was observed experimentally when laser beam illuminates on the liquid surface modulated by underwater acoustic signal. The diffraction fringes were asymmetric. The expressions of the diffraction intensity were derived theoretically. The asymmetric distribution of position and diffraction intensity with laser oblique incidence was explained and the symmetric distribution of diffraction intensity with laser normal incidence was explained. Theoretical results were in good agreement with experimental ones. The results show that the position and diffraction intensity with laser oblique incidence has asymmetric distribution.
Research of surface micro-structure and anti-coagulant property of pyrolytic carbon induced by laser
2013, 37(5): 696-699.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.029
Abstract:
In order to study the effect of the micro-structure of the material surface on its anti-coagulant characteristics, the micro-structures were fabricated on pyrolytic carbon, the most popular material of heart valves, with nanosecond laser. The micro-structures coated with silylation were periodic micro-holes and micro-gratings. The topographies were characterized by scanning electron mircoscopy, the surface chemical composition was characterized by X-ray diffraction, the surface energy was characterized by contact angle machine, and the anti-coagulant characteristics were measured. The results show that the chemical composition is the same between the micro-structure surfaces and the smooth surfaces, the micro-structure surfaces have the super hydrophobicity and the low surface energy. Comparing with the smooth surface, the micro-structure surface has less platelet adhesion, fewer clusters, fewer deformation and better anti-coagulant property. The results are helpful to improve the anti-thrombotic characteristics of the artificial heart valves by surface modification.
In order to study the effect of the micro-structure of the material surface on its anti-coagulant characteristics, the micro-structures were fabricated on pyrolytic carbon, the most popular material of heart valves, with nanosecond laser. The micro-structures coated with silylation were periodic micro-holes and micro-gratings. The topographies were characterized by scanning electron mircoscopy, the surface chemical composition was characterized by X-ray diffraction, the surface energy was characterized by contact angle machine, and the anti-coagulant characteristics were measured. The results show that the chemical composition is the same between the micro-structure surfaces and the smooth surfaces, the micro-structure surfaces have the super hydrophobicity and the low surface energy. Comparing with the smooth surface, the micro-structure surface has less platelet adhesion, fewer clusters, fewer deformation and better anti-coagulant property. The results are helpful to improve the anti-thrombotic characteristics of the artificial heart valves by surface modification.
2013, 37(5): 700-704.
doi: 10.7510/jgjs.issn.1001-3806.2013.05.030
Abstract:
In order to analyze the laser butt welding process of Ti6Al4V(TC4)alloy sheet, a nonlinear transient heat conduction model was established by means of the finite element analysis and the distribution of the 3-D transient temperature was calculated with ANSYS. In the process, it was taken into account that the material thermophysical properties varied with temperature, and the loading and moving of the Gaussian heat source were realized using the APDL programming languages. The results show that the temperature field changes from non-steady state to state, and eventually present a stable meteor-shape distribution, the isotherms are dense near the weld and the heat affected zone is narrow. The simulated weld profile matches well with the experiment result. According to the simulation results, the dimension of the area where temperature is above 400℃ is 42.00mm10.56mm. The study proved the correctness of the simulation method, and provided references for the design of welding protection device.
In order to analyze the laser butt welding process of Ti6Al4V(TC4)alloy sheet, a nonlinear transient heat conduction model was established by means of the finite element analysis and the distribution of the 3-D transient temperature was calculated with ANSYS. In the process, it was taken into account that the material thermophysical properties varied with temperature, and the loading and moving of the Gaussian heat source were realized using the APDL programming languages. The results show that the temperature field changes from non-steady state to state, and eventually present a stable meteor-shape distribution, the isotherms are dense near the weld and the heat affected zone is narrow. The simulated weld profile matches well with the experiment result. According to the simulation results, the dimension of the area where temperature is above 400℃ is 42.00mm10.56mm. The study proved the correctness of the simulation method, and provided references for the design of welding protection device.
