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RSS2013 Vol. 37, No. 4
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2013, 37(4): 417-420.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.001
[Abstract]
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Abstract:
In order to get high single pulse energy with 100ps pulse width, a mode-locked Yb-doped picosecond fiber laser was designed and 100ps laser pulse was output. Master oscillator power amplifier (MOPA) with two-stage all fiber structure was adopted. In the preamplifier, gain medium was double-clad Yb-doped fiber with 7m core diameter and average power of stable pulse output was 160mW. In the master amplifier, gain medium was double-clad Yb-doped fiber with 20m core diameter and its output power was 16.60W while pump power increased to 35.37W. The corresponding single pulse energy was 1.63J and peak power was 16.61kW. And then, output laser of master amplifier was injected into photonic crystal fiber of 4.6m core via a home-made mode field adapter. 2.85W output power of white light supercontinuum was obtained and the supercontinuum spectrum wavelength covered the measured range from 600nm to 1700nm. The results show that this laser can be used for the generation of supercontinuum spectrum sources.
In order to get high single pulse energy with 100ps pulse width, a mode-locked Yb-doped picosecond fiber laser was designed and 100ps laser pulse was output. Master oscillator power amplifier (MOPA) with two-stage all fiber structure was adopted. In the preamplifier, gain medium was double-clad Yb-doped fiber with 7m core diameter and average power of stable pulse output was 160mW. In the master amplifier, gain medium was double-clad Yb-doped fiber with 20m core diameter and its output power was 16.60W while pump power increased to 35.37W. The corresponding single pulse energy was 1.63J and peak power was 16.61kW. And then, output laser of master amplifier was injected into photonic crystal fiber of 4.6m core via a home-made mode field adapter. 2.85W output power of white light supercontinuum was obtained and the supercontinuum spectrum wavelength covered the measured range from 600nm to 1700nm. The results show that this laser can be used for the generation of supercontinuum spectrum sources.
2013, 37(4): 421-424.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.002
Abstract:
In order to study the effect of substrate diffraction on laser-focused Cr atom deposition, simulation and comparative analysis were performed based on the scalar optical diffraction theory under the presence and absence of substrate diffraction. The variation of stripe value of atomic wave-packet probability distribution which stands for the deposited lines with different atomic wave-packet velocities was focused. The results show that because of substrate diffraction, the max value of wave-packet probability distribution has 14.9% average increase and the full width of half maximum (FWHM) has 14.3% average decrease for different longitudinal most probable velocities when transverse velocity remains constant; the max value of wave-packet probability distribution has 14.5% average increase and the FWHM has 16.9% average decrease for different transverse velocities when the most probable longitudinal velocity remains constant. The research results provide a richer theoretical guidance for the experiment.
In order to study the effect of substrate diffraction on laser-focused Cr atom deposition, simulation and comparative analysis were performed based on the scalar optical diffraction theory under the presence and absence of substrate diffraction. The variation of stripe value of atomic wave-packet probability distribution which stands for the deposited lines with different atomic wave-packet velocities was focused. The results show that because of substrate diffraction, the max value of wave-packet probability distribution has 14.9% average increase and the full width of half maximum (FWHM) has 14.3% average decrease for different longitudinal most probable velocities when transverse velocity remains constant; the max value of wave-packet probability distribution has 14.5% average increase and the FWHM has 16.9% average decrease for different transverse velocities when the most probable longitudinal velocity remains constant. The research results provide a richer theoretical guidance for the experiment.
2013, 37(4): 425-430.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.003
Abstract:
In order to provide the theory basis to improve the surface quality, the main factors affecting the upper surface roughness of metal parts fabricated by selective laser melting(SLM)were studied. By studying the single track melting, the upper surface roughness of SLM parts was analyzed from the view of melting track lapping. The metal parts were fabricated by using the self-developed fabrication equipment Dimetal-280 and the measure roughness parameters were compared with the theoretical value. The theoretical value of arithmetical mean deviation of the profile Ra was 3.21m and the theoretical value of ten-point height of irregulartlies Rz was 12.79m. The actual value was Ra=7.36m and Rz=40.01m. After electrochemical polishing, the surface roughness was reduced to Ra=2.34m and Rz=10.86m. The results prove that upper surface roughness of the metal part was influenced by melting track width, scanning space and layer thickness altogether. The reason of the discrepancy between theoretical value and actual value was some defects such as instability in melting track, spheroidization on the surface and dust adhesiveness. The quality of surface roughness was greatly improved after electrochemical polishing. The metal parts processed by selective laser melting could obtain satisfied surface roughness in this experiment. The results provide guidance to surface research and industrial application in the future.
In order to provide the theory basis to improve the surface quality, the main factors affecting the upper surface roughness of metal parts fabricated by selective laser melting(SLM)were studied. By studying the single track melting, the upper surface roughness of SLM parts was analyzed from the view of melting track lapping. The metal parts were fabricated by using the self-developed fabrication equipment Dimetal-280 and the measure roughness parameters were compared with the theoretical value. The theoretical value of arithmetical mean deviation of the profile Ra was 3.21m and the theoretical value of ten-point height of irregulartlies Rz was 12.79m. The actual value was Ra=7.36m and Rz=40.01m. After electrochemical polishing, the surface roughness was reduced to Ra=2.34m and Rz=10.86m. The results prove that upper surface roughness of the metal part was influenced by melting track width, scanning space and layer thickness altogether. The reason of the discrepancy between theoretical value and actual value was some defects such as instability in melting track, spheroidization on the surface and dust adhesiveness. The quality of surface roughness was greatly improved after electrochemical polishing. The metal parts processed by selective laser melting could obtain satisfied surface roughness in this experiment. The results provide guidance to surface research and industrial application in the future.
2013, 37(4): 431-436.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.004
Abstract:
In order to revise the light-route deviation of a laser autocollimator, a fast reflector control system of fast reflector in laser autocollimator control was designed. By adopting a step motor as power element, the movement of fast reflector in 2-D way was controlled, the light-route deviation of laser was eliminated and the light route of laser could be controlled accurately. The hardware and software of the fast reflector control system were expatiated exactly. Using hardware such as the laser autocollimator control box, the hardware and software design of laser autocollimator control system were validated. The experimental results show that root-mean-square of both azimuth errors and elevation direction errors are less than 1 when the working range of the fast reflector system is small, that is to say, the precision of fast reflector control system is less than 1. Fast reflector control system can control the movement of fast reflector in 2-D way exactly. The hardware and software of the design is correct and reliable. The fast reflector control system can satisfy the demand of the laser autocollimator control system.
In order to revise the light-route deviation of a laser autocollimator, a fast reflector control system of fast reflector in laser autocollimator control was designed. By adopting a step motor as power element, the movement of fast reflector in 2-D way was controlled, the light-route deviation of laser was eliminated and the light route of laser could be controlled accurately. The hardware and software of the fast reflector control system were expatiated exactly. Using hardware such as the laser autocollimator control box, the hardware and software design of laser autocollimator control system were validated. The experimental results show that root-mean-square of both azimuth errors and elevation direction errors are less than 1 when the working range of the fast reflector system is small, that is to say, the precision of fast reflector control system is less than 1. Fast reflector control system can control the movement of fast reflector in 2-D way exactly. The hardware and software of the design is correct and reliable. The fast reflector control system can satisfy the demand of the laser autocollimator control system.
2013, 37(4): 437-440.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.005
Abstract:
In order to achieve the conversion from the sunlight to the laser, two-level aggregation experimental system was designed and built. By choosing a Fresnel lens as the first level of aggregation system, the diffuse reflectance tapered cavity as the second level of aggregation system and Nd:YAG as the working substance, the experimental maximum power output was 13.3W available, when the sunlight incident power was about 950W/m2. In order to optimize the experimental system and improve the power output, the resonant cavity was simulated by LASCAD software. The temperature distribution and the refractive index distribution during the working of the crystal rod were obtained. The system was optimized by changing the parameters. The variation of the output power along with the cavity length and the output mirror reflectivity, the best cavity length of 142mm and the output mirror reflectivity of 91% were obtained. The results show that the output power of the laser pumped by sunlight directly can be improved effectively by adjusting the cavity length and the output mirror reflectivity and the best value can be achieved.
In order to achieve the conversion from the sunlight to the laser, two-level aggregation experimental system was designed and built. By choosing a Fresnel lens as the first level of aggregation system, the diffuse reflectance tapered cavity as the second level of aggregation system and Nd:YAG as the working substance, the experimental maximum power output was 13.3W available, when the sunlight incident power was about 950W/m2. In order to optimize the experimental system and improve the power output, the resonant cavity was simulated by LASCAD software. The temperature distribution and the refractive index distribution during the working of the crystal rod were obtained. The system was optimized by changing the parameters. The variation of the output power along with the cavity length and the output mirror reflectivity, the best cavity length of 142mm and the output mirror reflectivity of 91% were obtained. The results show that the output power of the laser pumped by sunlight directly can be improved effectively by adjusting the cavity length and the output mirror reflectivity and the best value can be achieved.
2013, 37(4): 441-444.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.006
Abstract:
To obtain high beam quality pump sources for mid-infrared lasers, a Nd:YAG pulsed solid-state laser was designed with positive branch confocal unstable resonator. Under the influence of thermal effect, parameters of the positive branch confocal unstable resonator were optimized after numerical simulation and experimental verification. Single pulse energy of 260mJ, pulse width of 9.7ns and beam parameter product of 3.5mmmrad were achieved at 10Hz. After amplification and pumping MgO:LiNbO3 crystal, single pulse energy of 104mJ at 3.85m was obtained with pulse width of 8ns, and its optical-optical conversion efficiency gets up to 12.5%. The results demonstrate that beam quality of laser pump source meets the requirements of the mid-infrared optical parametric oscillation laser. The research lays the technical foundation for its application in the field of optoelectronic countermeasures.
To obtain high beam quality pump sources for mid-infrared lasers, a Nd:YAG pulsed solid-state laser was designed with positive branch confocal unstable resonator. Under the influence of thermal effect, parameters of the positive branch confocal unstable resonator were optimized after numerical simulation and experimental verification. Single pulse energy of 260mJ, pulse width of 9.7ns and beam parameter product of 3.5mmmrad were achieved at 10Hz. After amplification and pumping MgO:LiNbO3 crystal, single pulse energy of 104mJ at 3.85m was obtained with pulse width of 8ns, and its optical-optical conversion efficiency gets up to 12.5%. The results demonstrate that beam quality of laser pump source meets the requirements of the mid-infrared optical parametric oscillation laser. The research lays the technical foundation for its application in the field of optoelectronic countermeasures.
2013, 37(4): 445-448.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.007
Abstract:
In order to study high precise orientation of the aerial digital images, the geographical relationship model was derived with aerial digital images and virtual ground control points from airborne LiDAR point clouds. Both the self-calibration geographical model and error equations were built based on the principle thatall corresponding image rays intersect with one ground point which was captured on multi images. The high precise orientation data of aerial images was obtained by solving the algorithm equation. The results show that the effect of self-calibration of exterior orientation parameters without ground control points is achieved.
In order to study high precise orientation of the aerial digital images, the geographical relationship model was derived with aerial digital images and virtual ground control points from airborne LiDAR point clouds. Both the self-calibration geographical model and error equations were built based on the principle thatall corresponding image rays intersect with one ground point which was captured on multi images. The high precise orientation data of aerial images was obtained by solving the algorithm equation. The results show that the effect of self-calibration of exterior orientation parameters without ground control points is achieved.
2013, 37(4): 449-454.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.008
Abstract:
In order to study effect of different surface textures on the friction characteristics of no-match friction-pairs, according to the frictional characteristics of no-match friction-pair, micro-pit network was produced on the specimen surface with continuous wave laser, then, the surface textures, friction and wear were measured for different macro-pit diameters, share ratio of processing area and mean depth. The conclusion reveals that the coefficient of surface friction gradually rises with the increase of micro-pit's depth, but the share ratio of microstructure area has no significant influence on the coefficient of friction.
In order to study effect of different surface textures on the friction characteristics of no-match friction-pairs, according to the frictional characteristics of no-match friction-pair, micro-pit network was produced on the specimen surface with continuous wave laser, then, the surface textures, friction and wear were measured for different macro-pit diameters, share ratio of processing area and mean depth. The conclusion reveals that the coefficient of surface friction gradually rises with the increase of micro-pit's depth, but the share ratio of microstructure area has no significant influence on the coefficient of friction.
2013, 37(4): 455-459.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.009
Abstract:
In order to load laser energy reasonably in the laser ultrasonic testing under the ablation mechanism and obtain large amplitude of ultrasonic signal without damaging the detected material, temperature rise and laser ablation of material surface irradiated by laser were analyzed. Theory model of laser irradiating material surface was established and laser was loaded on the material surface by the form of heat flux. By combining heat conduction differential equation with the boundary condition of convective heat transfer and radiation heat transfer, the latent heat in the material surface during the heating process was dealt with effectively and numerical simulation of temperature field of material surface irradiated by laser was made. The program flow of laser ablating material finite element analysis was given out. Taking 45# billet for example, laser irradiation simulation was made. The temperature rise law of the nodes of the irradiated area, of the lower area and near the boundary was analyzed. Contrasting with the actual ablation by laser irradiation and collecting the laser ultrasonic signal, the verification was made. The results show that numerical simulation provides the basis for the load during the finite element thermal stress analysis and the reference for the loading of the laser energy during the laser ultrasonic test.
In order to load laser energy reasonably in the laser ultrasonic testing under the ablation mechanism and obtain large amplitude of ultrasonic signal without damaging the detected material, temperature rise and laser ablation of material surface irradiated by laser were analyzed. Theory model of laser irradiating material surface was established and laser was loaded on the material surface by the form of heat flux. By combining heat conduction differential equation with the boundary condition of convective heat transfer and radiation heat transfer, the latent heat in the material surface during the heating process was dealt with effectively and numerical simulation of temperature field of material surface irradiated by laser was made. The program flow of laser ablating material finite element analysis was given out. Taking 45# billet for example, laser irradiation simulation was made. The temperature rise law of the nodes of the irradiated area, of the lower area and near the boundary was analyzed. Contrasting with the actual ablation by laser irradiation and collecting the laser ultrasonic signal, the verification was made. The results show that numerical simulation provides the basis for the load during the finite element thermal stress analysis and the reference for the loading of the laser energy during the laser ultrasonic test.
2013, 37(4): 460-463.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.010
Abstract:
When processing far-field spot images with the commonly used laser spot image processing algorithm based on Gaussian beam characteristics, the data about lower energy is lost so that the processing accuracy of spot energy density at lower-end can not reach 0.01J/cm2 in demand. In order to get more accurate far-field laser spot data, an automatic threshold processing algorithm was proposed based on noise characteristics of the laser spot image. After analyzing the noise characteristics, the image extraction threshold was determined based on the 3 principles and the light spot image was processed. Experiments show that the algorithm can effectively restrain system noise, improve the light spot image processing quality, restore missing data information of the spot image, and make spot energy density low enough meet detection requirements. The results show that, the processing algorithm of light spot images based on the noise characteristics can effectively improve the processing accuracy of the far field laser facula, and is more suitable for the far field laser spot image processing.
When processing far-field spot images with the commonly used laser spot image processing algorithm based on Gaussian beam characteristics, the data about lower energy is lost so that the processing accuracy of spot energy density at lower-end can not reach 0.01J/cm2 in demand. In order to get more accurate far-field laser spot data, an automatic threshold processing algorithm was proposed based on noise characteristics of the laser spot image. After analyzing the noise characteristics, the image extraction threshold was determined based on the 3 principles and the light spot image was processed. Experiments show that the algorithm can effectively restrain system noise, improve the light spot image processing quality, restore missing data information of the spot image, and make spot energy density low enough meet detection requirements. The results show that, the processing algorithm of light spot images based on the noise characteristics can effectively improve the processing accuracy of the far field laser facula, and is more suitable for the far field laser spot image processing.
2013, 37(4): 464-468.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.011
Abstract:
In order to improve focus depth of digital grayscale lithography, an optimization method of pupil coding was studied based on the stabilization of point spread function. A digital grayscale lithography system with 1m resolution, long focus depth and five-zone phase pupil filter was designed by using MAPLE and ZEMAX software. The results show that system modulation transfer function has defocus invariance. Under the premise of image resolution stability, the focus depth of the system is extended 2.5 times more than the original focus depth. And then, the system performance within the space of the entire focus depth is consistent with the system performance at the focal point. Thereby, the tolerance of lithography system is increased. The experimental result is the same as the theoretical analysis and the design is feasible.
In order to improve focus depth of digital grayscale lithography, an optimization method of pupil coding was studied based on the stabilization of point spread function. A digital grayscale lithography system with 1m resolution, long focus depth and five-zone phase pupil filter was designed by using MAPLE and ZEMAX software. The results show that system modulation transfer function has defocus invariance. Under the premise of image resolution stability, the focus depth of the system is extended 2.5 times more than the original focus depth. And then, the system performance within the space of the entire focus depth is consistent with the system performance at the focal point. Thereby, the tolerance of lithography system is increased. The experimental result is the same as the theoretical analysis and the design is feasible.
2013, 37(4): 469-472.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.012
Abstract:
In order to meet the needs of vibration signal monitoring on various occasions, based on long-period grating edge filtering principle, a fiber Bragg grating vibration sensor demodulation system with simple structure and low cost was designed. Dual optical path structure and low noise photoelectric conversion circuit were used in the hardware part. Demodulation system and display software were based on LabVIEW platform. After the testing on a tunable vibration bench, the demodulation of vibration signal frequency was obtained in the available range (0Hz~300Hz)of vibration sensors. The error was less than 3%. The results show that vibration acceleration analog signal volt value is a linear relationship, the fitting scale factor of the system is 0.94, the fitting extent is 0.9752 and vibration acceleration demodulation can be realized in the range of 0~4.7g of the acceleration of vibration signal.
In order to meet the needs of vibration signal monitoring on various occasions, based on long-period grating edge filtering principle, a fiber Bragg grating vibration sensor demodulation system with simple structure and low cost was designed. Dual optical path structure and low noise photoelectric conversion circuit were used in the hardware part. Demodulation system and display software were based on LabVIEW platform. After the testing on a tunable vibration bench, the demodulation of vibration signal frequency was obtained in the available range (0Hz~300Hz)of vibration sensors. The error was less than 3%. The results show that vibration acceleration analog signal volt value is a linear relationship, the fitting scale factor of the system is 0.94, the fitting extent is 0.9752 and vibration acceleration demodulation can be realized in the range of 0~4.7g of the acceleration of vibration signal.
2013, 37(4): 473-477.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.013
Abstract:
To control the bias of dual-electrode Mach-Zehnder electro-optic modulators automatically,an adjustable phase shifter was introduced based on closed-loop control method so that the error signal remained the same at different direct-current(DC)bias points. The relationship between phase shift of the adjustable shifter and DC bias phase was derived by theoretical analysis. Simulation showed that,the drift of DC bias phase in the range of -0.15rad~0.08rad with the added phase drift caused by the phase shifter in the range of -0.55rad~0.55rad could be suppressed to -3.010-4rad~1.710-4rad at different DC bias points. The results show that the automatic bias control of an electro-optic modulator at any DC bias points is effectively achieved.
To control the bias of dual-electrode Mach-Zehnder electro-optic modulators automatically,an adjustable phase shifter was introduced based on closed-loop control method so that the error signal remained the same at different direct-current(DC)bias points. The relationship between phase shift of the adjustable shifter and DC bias phase was derived by theoretical analysis. Simulation showed that,the drift of DC bias phase in the range of -0.15rad~0.08rad with the added phase drift caused by the phase shifter in the range of -0.55rad~0.55rad could be suppressed to -3.010-4rad~1.710-4rad at different DC bias points. The results show that the automatic bias control of an electro-optic modulator at any DC bias points is effectively achieved.
2013, 37(4): 478-482.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.014
Abstract:
Micromaching by ultrashort laser pulse-train can effectively improve femtosecond laser ablation of metal, which are important both theoretically and practically in micro/nano-laser fabrication applications. In order to study the effect of separation of pulse on the accuracy of laser ablation, the phenomena and process of laser ablation with different separation of pulse train were studied in detail by combining the molecular dynamic simulation and two-temperature model, the electron and lattice temperatures of the layers next to dynamic film surfaces and the snapshots of nickel thin films irradiated by the femtosecond laser pulse trains were obtained. The result is that,within a certain range, as the increase of the separation of pulse, femtosecond pulse train laser ablation of Ni films can apparently cause more flat ablation plane, slower initial melting speed, smaller and more uniform nanoparticles, smaller ablation ratio,which can effectively improve femtosecond laser ablation of metal.
Micromaching by ultrashort laser pulse-train can effectively improve femtosecond laser ablation of metal, which are important both theoretically and practically in micro/nano-laser fabrication applications. In order to study the effect of separation of pulse on the accuracy of laser ablation, the phenomena and process of laser ablation with different separation of pulse train were studied in detail by combining the molecular dynamic simulation and two-temperature model, the electron and lattice temperatures of the layers next to dynamic film surfaces and the snapshots of nickel thin films irradiated by the femtosecond laser pulse trains were obtained. The result is that,within a certain range, as the increase of the separation of pulse, femtosecond pulse train laser ablation of Ni films can apparently cause more flat ablation plane, slower initial melting speed, smaller and more uniform nanoparticles, smaller ablation ratio,which can effectively improve femtosecond laser ablation of metal.
2013, 37(4): 483-486.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.015
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 grayscale-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 grayscale-adjustment. The results are helpful for the display of computer generated hologram based on digital micro-mirror device.
2013, 37(4): 487-492.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.016
Abstract:
In order to obtain accurate light scattering information of red blood cell in the fluid flow, the scattering model of red blood cell in the fluid flow was constructed based on the anomalous diffraction approximation and the oblate ellipsoid. The effect of the variety of body, volume, relative refractive index and orientation angle on the scattering amplitude was studied. The simulation data indicate that the volume and relative refractive index of different red blood cell has the prominent effect on the scattering information at small orientation angles. The model was proved by experiments. This result is helpful for measuring red blood cell fast and accurately and the precise measurement of the cell measurement instrument such as flow cytometer.
In order to obtain accurate light scattering information of red blood cell in the fluid flow, the scattering model of red blood cell in the fluid flow was constructed based on the anomalous diffraction approximation and the oblate ellipsoid. The effect of the variety of body, volume, relative refractive index and orientation angle on the scattering amplitude was studied. The simulation data indicate that the volume and relative refractive index of different red blood cell has the prominent effect on the scattering information at small orientation angles. The model was proved by experiments. This result is helpful for measuring red blood cell fast and accurately and the precise measurement of the cell measurement instrument such as flow cytometer.
2013, 37(4): 493-497.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.017
Abstract:
In order to reduce the bandwidth of tunable optical filters, a continuous tunable optical filter with ultra-narrow bandwidth wavelength was designed by using double gratings and mirror of micro-electromechanical system. Through theoretical analysis and experimental verification, filter bandwidth less than 0.4nm was obtained. The results show that an optical filter with double gratings has high stability and excellent repeatability. This scheme can reduce the filter bandwidth, which meets the bandwidth demand.
In order to reduce the bandwidth of tunable optical filters, a continuous tunable optical filter with ultra-narrow bandwidth wavelength was designed by using double gratings and mirror of micro-electromechanical system. Through theoretical analysis and experimental verification, filter bandwidth less than 0.4nm was obtained. The results show that an optical filter with double gratings has high stability and excellent repeatability. This scheme can reduce the filter bandwidth, which meets the bandwidth demand.
2013, 37(4): 498-502.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.018
Abstract:
When using tunable diode laser absorption spectroscopy(TDLAS) for gas detection, modulation phase difference would make the result different. In order to improve harmonic wave detection sensitivity, frequency modulation and amplitude modulation were simultaneously chosen to analyze and extract the second harmonic wave signal. The functional relationship expression between the phase difference and the photo-electron current of the second harmonic wave and the residual amplitude modulation noise was also derived. From the simulation experiments, the variation trend of the second harmonic wave signal and the residual amplitude modulation noise with the phase difference were obtained. And then, the effect of phase difference on signal-to-noise ratio(SNR) was analyzed. The results show that the phase difference between amplitude modulation and frequency modulation has a significant impact on SNR. The largest drop is 59.18% when compared with the typical value of phase difference of /2. Modulation phase difference is another important affecting factor of SNR besides residual amplitude modulation.
When using tunable diode laser absorption spectroscopy(TDLAS) for gas detection, modulation phase difference would make the result different. In order to improve harmonic wave detection sensitivity, frequency modulation and amplitude modulation were simultaneously chosen to analyze and extract the second harmonic wave signal. The functional relationship expression between the phase difference and the photo-electron current of the second harmonic wave and the residual amplitude modulation noise was also derived. From the simulation experiments, the variation trend of the second harmonic wave signal and the residual amplitude modulation noise with the phase difference were obtained. And then, the effect of phase difference on signal-to-noise ratio(SNR) was analyzed. The results show that the phase difference between amplitude modulation and frequency modulation has a significant impact on SNR. The largest drop is 59.18% when compared with the typical value of phase difference of /2. Modulation phase difference is another important affecting factor of SNR besides residual amplitude modulation.
2013, 37(4): 503-505.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.019
Abstract:
In order to generate the third harmonic in AgGaSe2 crystals, Ⅰand Ⅱ phase-match were applied for the second and third harmonics of CO2 laser respectively. In the experiment, output wavelength of CO2 laser was 9.6m. The peak power of the second-harmonic at 4.8m was 88kW and the peak power of the third-harmonic at 3.2m was 4kW respectively. The phase-matching acceptance angle was measured. The results show that the second-harmonic wave and the third-harmonic wave are acquired effectively and peak power of the second-harmonic wave and third-harmonic wave increase rapidly with the increase of input power of CO2 laser.
In order to generate the third harmonic in AgGaSe2 crystals, Ⅰand Ⅱ phase-match were applied for the second and third harmonics of CO2 laser respectively. In the experiment, output wavelength of CO2 laser was 9.6m. The peak power of the second-harmonic at 4.8m was 88kW and the peak power of the third-harmonic at 3.2m was 4kW respectively. The phase-matching acceptance angle was measured. The results show that the second-harmonic wave and the third-harmonic wave are acquired effectively and peak power of the second-harmonic wave and third-harmonic wave increase rapidly with the increase of input power of CO2 laser.
2013, 37(4): 506-510.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.020
Abstract:
In order to eliminate dispersion in a fiber communication system,based on the finite element method and perfectly matched boundary layers,an octagonal dispersion compensation fiber was proposed. The guiding properties such as fundamental mode,dispersion,confinement loss and nonlinear coefficient were obtained. Besides,it was shown that the negative dispersion over 200nm bandwidth was obtained (the minimum value was -1500ps/(nmkm) at =1.55m). Meanwhile,the fiber exhibited low confinement loss less than 3.3dB/km at 1.55m in the entire E+S+C band. Also,the nonlinear effect was eliminated effectively because of the low nonlinear coefficient.
In order to eliminate dispersion in a fiber communication system,based on the finite element method and perfectly matched boundary layers,an octagonal dispersion compensation fiber was proposed. The guiding properties such as fundamental mode,dispersion,confinement loss and nonlinear coefficient were obtained. Besides,it was shown that the negative dispersion over 200nm bandwidth was obtained (the minimum value was -1500ps/(nmkm) at =1.55m). Meanwhile,the fiber exhibited low confinement loss less than 3.3dB/km at 1.55m in the entire E+S+C band. Also,the nonlinear effect was eliminated effectively because of the low nonlinear coefficient.
2013, 37(4): 511-514.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.021
Abstract:
In order to quickly determine reasonable lidar ratiothe key parameter in the inversion of lidar geometric form factor,a simple and convenient method was presented to determine the lidar ratio for the geometrical form factor is a constant as 1 in lidar full zone. This method is theoretically deduced and verified with actual lidar data. The retrieved geometric form factor does not appear increasing or decreasing monotonously in full zone,which shows that this method is reasonable and effective,avoiding a large of qualitative analysis which is tedious and time consuming. It is useful to get lidar geometric form factor and obtain the surface aerosol important information.
In order to quickly determine reasonable lidar ratiothe key parameter in the inversion of lidar geometric form factor,a simple and convenient method was presented to determine the lidar ratio for the geometrical form factor is a constant as 1 in lidar full zone. This method is theoretically deduced and verified with actual lidar data. The retrieved geometric form factor does not appear increasing or decreasing monotonously in full zone,which shows that this method is reasonable and effective,avoiding a large of qualitative analysis which is tedious and time consuming. It is useful to get lidar geometric form factor and obtain the surface aerosol important information.
2013, 37(4): 515-518.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.022
Abstract:
In order to study the effect of Compton scattering on TE wave prohibited band gaps of 1-D ternary un-magnetized plasma photonic crystals,based on the model of Compton scattering and transfer matrix method,some important data was obtained after the theoretical analysis and experimental verification. The broadening width of prohibited band gap of the left circle polarization wave and the right circle polarization wave were decreased 0.09GHz along with the increasing of plasma frequency after Compton scattering. The movement from the central frequency area of prohibited band gap to the high frequency area was increased 0.48GHz. The change of prohibited band gaps widths of the left circle polarization wave and the right circle polarization wave happened along with the increasing of plasma collision frequency. The significant tuning effect of prohibited band gaps of the left circle polarization wave and the right circle polarization wave was induced by Compton scattering along with the increasing of plasma circle frequency,filling index,light incident angle and relative dielectric constant. The result is helpful for the application of the plasma photonic crystals.
In order to study the effect of Compton scattering on TE wave prohibited band gaps of 1-D ternary un-magnetized plasma photonic crystals,based on the model of Compton scattering and transfer matrix method,some important data was obtained after the theoretical analysis and experimental verification. The broadening width of prohibited band gap of the left circle polarization wave and the right circle polarization wave were decreased 0.09GHz along with the increasing of plasma frequency after Compton scattering. The movement from the central frequency area of prohibited band gap to the high frequency area was increased 0.48GHz. The change of prohibited band gaps widths of the left circle polarization wave and the right circle polarization wave happened along with the increasing of plasma collision frequency. The significant tuning effect of prohibited band gaps of the left circle polarization wave and the right circle polarization wave was induced by Compton scattering along with the increasing of plasma circle frequency,filling index,light incident angle and relative dielectric constant. The result is helpful for the application of the plasma photonic crystals.
2013, 37(4): 519-522.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.023
Abstract:
In order to improve the quality of image segmentation, two-dimensional maximum entropy optimal threshold (TDMEOT) method was used. Firstly, 2-D random vector of the domain pixels was defined through the gray region and TDMEOT value was gotten by the criterion function. Secondly, calculation data of 2-D maximum entropy threshold were optimized through the recursive optimization and the repetitive data calculation was reduced. Finally, based on the maximum mutual information criterion between the segmentation image area and the target space position and choosing error segmentation function as the segmentation standard, the algorithm flow and the image segmentation results of different algorithms were given after experimental simulation. The results show that this method has higher precision of image segmentation and has no residual background noise, and retains the image information with fast speed, good segmentation visual and minimum segmentation error. The research is helpful to improve the efficiency of image segmentation.
In order to improve the quality of image segmentation, two-dimensional maximum entropy optimal threshold (TDMEOT) method was used. Firstly, 2-D random vector of the domain pixels was defined through the gray region and TDMEOT value was gotten by the criterion function. Secondly, calculation data of 2-D maximum entropy threshold were optimized through the recursive optimization and the repetitive data calculation was reduced. Finally, based on the maximum mutual information criterion between the segmentation image area and the target space position and choosing error segmentation function as the segmentation standard, the algorithm flow and the image segmentation results of different algorithms were given after experimental simulation. The results show that this method has higher precision of image segmentation and has no residual background noise, and retains the image information with fast speed, good segmentation visual and minimum segmentation error. The research is helpful to improve the efficiency of image segmentation.
2013, 37(4): 523-528.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.024
Abstract:
In order to solve the problems of the large field of view,high-precision and non-contact 3-D measurement in the complex environment,a trinocular measuring system was put forward,in which the 3-D coordinates of the measured point were measured by analyzing target images. When under the measurement,the camera captured images of the measurement target,while the computer obtained the 3-D coordinates of the mark points in the measurement target by means of image processing,and an optimized method for solving the measured points was proposed based on the distance between the measured points and mark points,as well as linear constraint. The measurement target can be moved with the platform of the high precision grating ruler and measurement can be carried out. As shown in the experiment,the 3-D measurement system has a greater improvement in the field range,measurement accuracy,operation flexibility and so on. Its measurement accuracy is higher than 0.2mm in the depth of field ranging from 2m to 5m within the viewing field.
In order to solve the problems of the large field of view,high-precision and non-contact 3-D measurement in the complex environment,a trinocular measuring system was put forward,in which the 3-D coordinates of the measured point were measured by analyzing target images. When under the measurement,the camera captured images of the measurement target,while the computer obtained the 3-D coordinates of the mark points in the measurement target by means of image processing,and an optimized method for solving the measured points was proposed based on the distance between the measured points and mark points,as well as linear constraint. The measurement target can be moved with the platform of the high precision grating ruler and measurement can be carried out. As shown in the experiment,the 3-D measurement system has a greater improvement in the field range,measurement accuracy,operation flexibility and so on. Its measurement accuracy is higher than 0.2mm in the depth of field ranging from 2m to 5m within the viewing field.
2013, 37(4): 529-532.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.025
Abstract:
In order to adjust the gain automatically under different environmental conditions, an erbium-doped fiber amplifier (EDFA) with mid-stage access was introduced, which had two amplifier stages and variable gain within a certain range. To achieve the purpose of automatic gain adjustment, the method of automatic gain calibration was adopted. After theoretical analysis and experimental verification, the data of gain calibration and verification of the EDFA with mid-stage access were obtained. The results show that the data of automatic calibration has high accuracy. This research is helpful for EDFA to achieve automatic gain control rapidly and exactly.
In order to adjust the gain automatically under different environmental conditions, an erbium-doped fiber amplifier (EDFA) with mid-stage access was introduced, which had two amplifier stages and variable gain within a certain range. To achieve the purpose of automatic gain adjustment, the method of automatic gain calibration was adopted. After theoretical analysis and experimental verification, the data of gain calibration and verification of the EDFA with mid-stage access were obtained. The results show that the data of automatic calibration has high accuracy. This research is helpful for EDFA to achieve automatic gain control rapidly and exactly.
2013, 37(4): 533-536.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.026
Abstract:
Transmission characteristics of terahertz (THz) wave through a slit with parallel grooves on both sides were analyzed numerically by means of the finite element method (FEM). Simulation results show that the transmissivity peak blue shifts firstly and then red shifts with the increase of groove width,red shifts with the increase of periodicity,slit width and groove depth. With each geometrical parameters increasing,the transmissivity peak increases firstly and then decreases,which is up to 0.95. 3dB bandwidth broadens with the increase of slit width and groove depth,compresses with the increase of slit width and periodicity. Compared with the conventional optical filter,the Thz filter possesses high selectivity and high center transmissivity.
Transmission characteristics of terahertz (THz) wave through a slit with parallel grooves on both sides were analyzed numerically by means of the finite element method (FEM). Simulation results show that the transmissivity peak blue shifts firstly and then red shifts with the increase of groove width,red shifts with the increase of periodicity,slit width and groove depth. With each geometrical parameters increasing,the transmissivity peak increases firstly and then decreases,which is up to 0.95. 3dB bandwidth broadens with the increase of slit width and groove depth,compresses with the increase of slit width and periodicity. Compared with the conventional optical filter,the Thz filter possesses high selectivity and high center transmissivity.
2013, 37(4): 537-540.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.027
Abstract:
In order to find the optimal parameters of laser processing,the micro-structures were fabricated on pyrolytic carbon of the artificial heart valves with nanosecond laser. Effects of pulse energy, scanning times, pulse width, scanning speed and scanning gap on the melt rules of the pyrolytic carbon were analyzed. Three kinds of micro-structures were fabricated according to the melt rules of pyrolytic carbon. The conditions of superhydrophobicity were analyzed according to Cassie theory. When the percentage of pyrolytic carbon surface micro-structures to the total area in the unit area is less than 20%, the surface becomes superhydrophobic. Choosing contact angle as test index, the experimental program was optimized according to orthogonal design. Micro-structures of pit array, parallel grating and mastoid were fabricated successfully on the surface of pyrolytic carbon under six kinds of experimental programs. The testing results of contact angle show that the six kinds of micro-structures surfaces have the superhydrophobicity after silanization. The results are helpful for the fabrication of the artifical heart valves of anticooagulant property.
In order to find the optimal parameters of laser processing,the micro-structures were fabricated on pyrolytic carbon of the artificial heart valves with nanosecond laser. Effects of pulse energy, scanning times, pulse width, scanning speed and scanning gap on the melt rules of the pyrolytic carbon were analyzed. Three kinds of micro-structures were fabricated according to the melt rules of pyrolytic carbon. The conditions of superhydrophobicity were analyzed according to Cassie theory. When the percentage of pyrolytic carbon surface micro-structures to the total area in the unit area is less than 20%, the surface becomes superhydrophobic. Choosing contact angle as test index, the experimental program was optimized according to orthogonal design. Micro-structures of pit array, parallel grating and mastoid were fabricated successfully on the surface of pyrolytic carbon under six kinds of experimental programs. The testing results of contact angle show that the six kinds of micro-structures surfaces have the superhydrophobicity after silanization. The results are helpful for the fabrication of the artifical heart valves of anticooagulant property.
2013, 37(4): 541-546.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.028
Abstract:
A high stability and continuously adjustable 1310nm/1550nm semiconductor laser power supply was designed for accurate and rapid measurement of the optical fiber. The laser power supply uses precision constant current source to drive the semiconductor laser diodes by applying the current negative feedback control technology and constant temperature control circuit to drive thermoelectric coolers, and ensures the stability of the laser output power. The contrdler area network bus circuit realizes continuous power adjustment and laser source selection, and variable integration proportion-integration-differentiation algorithm eliminates the integral saturation and accelerates the system temperature stability. The laser power supply works reliably and stably under laser protection and soft-start circuit. The experimental results show that the system has stability of temperature of 0.01℃ and the long-term output power stability of 0.018dB when the laser works at room temperature 25℃. Compared with the traditional 1310nm/1550nm laser power supply, the system has high and fast stability, small size and facilitates the optical fiber online measurement.
A high stability and continuously adjustable 1310nm/1550nm semiconductor laser power supply was designed for accurate and rapid measurement of the optical fiber. The laser power supply uses precision constant current source to drive the semiconductor laser diodes by applying the current negative feedback control technology and constant temperature control circuit to drive thermoelectric coolers, and ensures the stability of the laser output power. The contrdler area network bus circuit realizes continuous power adjustment and laser source selection, and variable integration proportion-integration-differentiation algorithm eliminates the integral saturation and accelerates the system temperature stability. The laser power supply works reliably and stably under laser protection and soft-start circuit. The experimental results show that the system has stability of temperature of 0.01℃ and the long-term output power stability of 0.018dB when the laser works at room temperature 25℃. Compared with the traditional 1310nm/1550nm laser power supply, the system has high and fast stability, small size and facilitates the optical fiber online measurement.
2013, 37(4): 547-550.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.029
Abstract:
In order to analyze the rules of temperature field and molten pool crystalline diversification during the preset powder Ni-based alloy cladding process, a 3-D model of laser cladding was made with finite element method. Taking consideration of the impact of temperature changes on the thermal physical parameters and the effects of heat convection and radiation heat, temperature field and solidification and crystallization of laser cladding process were analyzed and verified by SYSWELD software. The results show that the highest temperature is at the spot center, the isothermal line is almost elliptical and the temperature declines gradually along the radius of the spot center. Thermal cycle peak temperature at a certain point on the coating reduced significantly as the heat source was away. The temperature increased from the room temperature at the first pass to 730℃ at the final pass. Shape factor is reduced from 1.9109℃smm-2 of bonding surface to 0.7109℃smm-2 of cladding surface. At the same time, secondary dendrite spacing is the biggest at the bonding surface and the smallest at the cladding surface. The calculation results are perfectly matched with metallographic microstructure and solidification and crystallization theory. The results provide theoretical guidance for the optimization of laser cladding
In order to analyze the rules of temperature field and molten pool crystalline diversification during the preset powder Ni-based alloy cladding process, a 3-D model of laser cladding was made with finite element method. Taking consideration of the impact of temperature changes on the thermal physical parameters and the effects of heat convection and radiation heat, temperature field and solidification and crystallization of laser cladding process were analyzed and verified by SYSWELD software. The results show that the highest temperature is at the spot center, the isothermal line is almost elliptical and the temperature declines gradually along the radius of the spot center. Thermal cycle peak temperature at a certain point on the coating reduced significantly as the heat source was away. The temperature increased from the room temperature at the first pass to 730℃ at the final pass. Shape factor is reduced from 1.9109℃smm-2 of bonding surface to 0.7109℃smm-2 of cladding surface. At the same time, secondary dendrite spacing is the biggest at the bonding surface and the smallest at the cladding surface. The calculation results are perfectly matched with metallographic microstructure and solidification and crystallization theory. The results provide theoretical guidance for the optimization of laser cladding
2013, 37(4): 551-555.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.030
Abstract:
In order to collimate and shape the LD beam with astigmatism, the mathematic condition for LD beam shaping with a cylindrical gradient-index lens was introduced applying ABCD law. Based on this, a system with good effect was got through software simulation. After collimation and beam shaping, the beam in fast and slow axis has the same divergence angle which is less than 0.7mrad and the beam waist difference in z axis is less than 2.8mm. The result shows a good effect was obtained with a cylindrical gradient-index lens in this system. Under the condition of beam shaping and collimation, the LD beam has the characteristics of small divergence angle and rotationally symmetry.
In order to collimate and shape the LD beam with astigmatism, the mathematic condition for LD beam shaping with a cylindrical gradient-index lens was introduced applying ABCD law. Based on this, a system with good effect was got through software simulation. After collimation and beam shaping, the beam in fast and slow axis has the same divergence angle which is less than 0.7mrad and the beam waist difference in z axis is less than 2.8mm. The result shows a good effect was obtained with a cylindrical gradient-index lens in this system. Under the condition of beam shaping and collimation, the LD beam has the characteristics of small divergence angle and rotationally symmetry.
2013, 37(4): 556-560.
doi: 10.7510/jgjs.issn.1001-3806.2013.04.031
Abstract:
In order to evaluate the countermeasure effect of the electro-optical countermeasure equipment in the electronic base,the quadrant detector (QD) model was established,which is the sub-model of a certain type laser seeker, and simulated. The spot quadrant energy division model compensates the deficiency of the traditional sum-and-difference circuit method. The simulation result shows that the QD model can imitate the process of the QD, and it has advantages of feasibility and fast computation, which improves the credibility and reality of this type of laser seeker, and the real-time simulation speed as well.
In order to evaluate the countermeasure effect of the electro-optical countermeasure equipment in the electronic base,the quadrant detector (QD) model was established,which is the sub-model of a certain type laser seeker, and simulated. The spot quadrant energy division model compensates the deficiency of the traditional sum-and-difference circuit method. The simulation result shows that the QD model can imitate the process of the QD, and it has advantages of feasibility and fast computation, which improves the credibility and reality of this type of laser seeker, and the real-time simulation speed as well.
