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RSS2016 Vol. 40, No. 6
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2016, 40(6): 779-781.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.001
Abstract:
In order to heighten the success probability of jamming interference and overcome the questions such as:interference signal offset and success probability were fixed substantially during synchronization interference and seeker had opportunity and conditions to take further anti-jamming measures when interfering signals and guided wave signals were in wave gate, a new jamming strategy based on wave gate decoy was put forward according to the principle of real-time wave gate. The method and key process of decoying wave gate were discussed and the tactics of jamming was studied. Taking repetition guided signal as example, the jamming signal based on interval modulation was designed, and the restriction of interference signal was gained. The joint distribution of wave gate and guided signal was derived. Through theory and simulation analysis, the results show that the wave gate isdecoyed and the success probability is promoted. The strategy is feasible and better. The jamming strategy is valuable for new jamming method research.
In order to heighten the success probability of jamming interference and overcome the questions such as:interference signal offset and success probability were fixed substantially during synchronization interference and seeker had opportunity and conditions to take further anti-jamming measures when interfering signals and guided wave signals were in wave gate, a new jamming strategy based on wave gate decoy was put forward according to the principle of real-time wave gate. The method and key process of decoying wave gate were discussed and the tactics of jamming was studied. Taking repetition guided signal as example, the jamming signal based on interval modulation was designed, and the restriction of interference signal was gained. The joint distribution of wave gate and guided signal was derived. Through theory and simulation analysis, the results show that the wave gate isdecoyed and the success probability is promoted. The strategy is feasible and better. The jamming strategy is valuable for new jamming method research.
2016, 40(6): 782-786.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.002
Abstract:
In order to achieve the shaping and control of infrared femtosecond pulse, 4f system phase control technology was used and pulse shaping device was set up by experiment. By using pulse shaping, coherent of population transfer of the excited double states in the rubidium atoms system was controlled. The results show that saturation population can be realized in excited double state by controlling the additional phase of pumping pulse. Population of the upper and lower excited state can be reversed by modifying the function of additional phase. Coherent control of population transfer by pulse shaping can also be applied in other atom and molecular systems.
In order to achieve the shaping and control of infrared femtosecond pulse, 4f system phase control technology was used and pulse shaping device was set up by experiment. By using pulse shaping, coherent of population transfer of the excited double states in the rubidium atoms system was controlled. The results show that saturation population can be realized in excited double state by controlling the additional phase of pumping pulse. Population of the upper and lower excited state can be reversed by modifying the function of additional phase. Coherent control of population transfer by pulse shaping can also be applied in other atom and molecular systems.
2016, 40(6): 787-790.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.003
Abstract:
In order to effectively solve the problem of signal modulation in THz communication systems affecting the performance of communication systems, a Terahertz communication system based on cascade Mach-Zehnder modulators was introduced. Pseudo random nonreturn to zero(NRZ) code and radio frequency local oscillator signal with frequency 10GHz were mixed into cascade Mach-Zehnder modulators. By adjusting the bias voltage of both modulators, they were biased at the maximum transmission point and the minimum transmission point respectively. The generated optical signal was amplified by erbium-doped optical fiber amplifier(EDFA), THz signal was generated by four-wave mixing effect in high nonlinear fiber and mode was selected by phase shifted fiber Bragg grating(FBG). Error rate of the transmission of terahertz communication system can be obtained by the recovery ofthe base band data after photoelectric conversion. The results show that THz signal is generated and modulated in the communication system based on cascade Mach-Zehnder modulators. The system has the significance of applications of THz communication systems.
In order to effectively solve the problem of signal modulation in THz communication systems affecting the performance of communication systems, a Terahertz communication system based on cascade Mach-Zehnder modulators was introduced. Pseudo random nonreturn to zero(NRZ) code and radio frequency local oscillator signal with frequency 10GHz were mixed into cascade Mach-Zehnder modulators. By adjusting the bias voltage of both modulators, they were biased at the maximum transmission point and the minimum transmission point respectively. The generated optical signal was amplified by erbium-doped optical fiber amplifier(EDFA), THz signal was generated by four-wave mixing effect in high nonlinear fiber and mode was selected by phase shifted fiber Bragg grating(FBG). Error rate of the transmission of terahertz communication system can be obtained by the recovery ofthe base band data after photoelectric conversion. The results show that THz signal is generated and modulated in the communication system based on cascade Mach-Zehnder modulators. The system has the significance of applications of THz communication systems.
ANSYS analysis of force-electric conversion of floating diaphragm for GaN-based micro-cavity sensors
2016, 40(6): 791-795.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.004
Abstract:
In order to figure out piezoelectric effect and mechanical properties of GaN film, a physics-based model was proposed in this study. Based on the theory that gas absorbed infrared directly, micro-cavity infrared sensor with GaN/AlGaN floating membrane was put as background and AlGaN/GaN floating membrane was put as sensitive element. After theoretical analysis and experimental verification of materials mechanics and piezoelectric effect by using finite element analysis software ANSYS 14.0, datas of the logical relationship between output voltage, membrane sensitivity and shapes, thickness, area were gotten, and the feasibility of membrane force-electric signal conversion mechanism was verified. The results show that GaN film has good piezoelectric performance and linearity which make a good contribution to forecast the sensor output signal accurately and make temperature compensation. The proposed model is useful to make a theoretical foundation for better design of micro cavity infrared sensor with good performance and high sensitivity.
In order to figure out piezoelectric effect and mechanical properties of GaN film, a physics-based model was proposed in this study. Based on the theory that gas absorbed infrared directly, micro-cavity infrared sensor with GaN/AlGaN floating membrane was put as background and AlGaN/GaN floating membrane was put as sensitive element. After theoretical analysis and experimental verification of materials mechanics and piezoelectric effect by using finite element analysis software ANSYS 14.0, datas of the logical relationship between output voltage, membrane sensitivity and shapes, thickness, area were gotten, and the feasibility of membrane force-electric signal conversion mechanism was verified. The results show that GaN film has good piezoelectric performance and linearity which make a good contribution to forecast the sensor output signal accurately and make temperature compensation. The proposed model is useful to make a theoretical foundation for better design of micro cavity infrared sensor with good performance and high sensitivity.
2016, 40(6): 796-800.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.005
Abstract:
In order to improve the beam quality of traditional spherical mirror cavity in 3kW radio frequency slab CO2 laser, a new negative branch unstable-waveguide hybrid resonator with parabolic mirrors was designed. Based on Rayleigh-Sommerfeld diffraction theory for scalar beam, the influence of mirror type on optical field transmission characteristics of unstable hybrid waveguide cavity in the condition of large Fresnel number was studied. Based on rectangular waveguide theory and 1-D approximation, the waveguide propagation loss and polarization were analyzed. The research shows that, in the unstable direction, rear mirror and output mirror with paraboloid of curvature radius R1=951.32mm, R2=1088.68mm can avoid light leak of rear mirror and effectively improve the mode identification characteristic. Among common waveguide electrode coating materials, aluminum electrode can supply minimum waveguide propagation loss and transmission optical field is x polarization EH1 mode. Using unstable-waveguide hybrid resonator with parabolic mirrors whose electrodes are coated with aluminum can reduce loss and improve beam quality.
In order to improve the beam quality of traditional spherical mirror cavity in 3kW radio frequency slab CO2 laser, a new negative branch unstable-waveguide hybrid resonator with parabolic mirrors was designed. Based on Rayleigh-Sommerfeld diffraction theory for scalar beam, the influence of mirror type on optical field transmission characteristics of unstable hybrid waveguide cavity in the condition of large Fresnel number was studied. Based on rectangular waveguide theory and 1-D approximation, the waveguide propagation loss and polarization were analyzed. The research shows that, in the unstable direction, rear mirror and output mirror with paraboloid of curvature radius R1=951.32mm, R2=1088.68mm can avoid light leak of rear mirror and effectively improve the mode identification characteristic. Among common waveguide electrode coating materials, aluminum electrode can supply minimum waveguide propagation loss and transmission optical field is x polarization EH1 mode. Using unstable-waveguide hybrid resonator with parabolic mirrors whose electrodes are coated with aluminum can reduce loss and improve beam quality.
2016, 40(6): 801-805.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.006
Abstract:
In order to obtain the frequency information of remote object's micron vibration, the remote detection technique of micro vibration information bases on laser speckle interferometer was used. The CW laser of 532nm wavelength was used as light source to light the to-be-detected object surface 50m away. A high speed camera was used as speckle image acquisition system. At first, telephoto lens was used to do the appropriate defocus processing of remote speckle image. Then, the changing information of speckle was obtained from the vector size between the peak value of correlation and the origin point. At the same time, the vibration frequency information in a certain wide frequency range was extracted. The results show that, extraction accuracy of remote micro vibration frequency by laser speckle is up to 99.22%. The study can provide some argumentation basis for acoustic vibration based on laser speckle.
In order to obtain the frequency information of remote object's micron vibration, the remote detection technique of micro vibration information bases on laser speckle interferometer was used. The CW laser of 532nm wavelength was used as light source to light the to-be-detected object surface 50m away. A high speed camera was used as speckle image acquisition system. At first, telephoto lens was used to do the appropriate defocus processing of remote speckle image. Then, the changing information of speckle was obtained from the vector size between the peak value of correlation and the origin point. At the same time, the vibration frequency information in a certain wide frequency range was extracted. The results show that, extraction accuracy of remote micro vibration frequency by laser speckle is up to 99.22%. The study can provide some argumentation basis for acoustic vibration based on laser speckle.
2016, 40(6): 806-809.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.007
Abstract:
In order to study the effect of laser power on performance of dissimilar lap joints of austenite stainless steel and Cu-Ni coated low carbon steel, Nd:YAG laser with 300W power was used to weld stainless steel and Cu-Ni coated low carbon steel. Optical microscope was adopted to observe the joint and measure the size of weld spot, and universal tensile machine was used to test the bond strength. The results indicate that the size of cross section of weld spot increases with the increase of laser power. The variation of laser power has no influence on the concentration of copper within weld joint which leads to the formation of weld crack. The increasing laser power leads to the transition of laser welding mode from conduction to keyhole. The transition causes the significant growth of weld size and the improvement of bond strength. The research is useful for studying the influence of laser power on laser welding between Cu-Ni coated low carbon steel and stainless steel.
In order to study the effect of laser power on performance of dissimilar lap joints of austenite stainless steel and Cu-Ni coated low carbon steel, Nd:YAG laser with 300W power was used to weld stainless steel and Cu-Ni coated low carbon steel. Optical microscope was adopted to observe the joint and measure the size of weld spot, and universal tensile machine was used to test the bond strength. The results indicate that the size of cross section of weld spot increases with the increase of laser power. The variation of laser power has no influence on the concentration of copper within weld joint which leads to the formation of weld crack. The increasing laser power leads to the transition of laser welding mode from conduction to keyhole. The transition causes the significant growth of weld size and the improvement of bond strength. The research is useful for studying the influence of laser power on laser welding between Cu-Ni coated low carbon steel and stainless steel.
2016, 40(6): 810-813.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.008
Abstract:
In order to resolve the difficulty of massive laser target signal channels during testing barrage weapons dispersion, a modularized system connected with parallel data acquisition scheme based on field-programmable gate array (FPGA) and central processing unit was presented. Trajectory parameter, data acquisition speed and storing velocity of the measured projectile were analyzed. Coordinate measuring principle of parallel line laser detector array was given and photoelectric detection circuit with brief and high reliability was designed. Adjustment method of circuit sensitivity was derived and data acquisition was verified by experiment. The results show that this acquisition system is easy to install and debug, and has high functionality reliability. Acquisition speed and storing velocity can meet the demand of barrage weapons dispersion measuerment.
In order to resolve the difficulty of massive laser target signal channels during testing barrage weapons dispersion, a modularized system connected with parallel data acquisition scheme based on field-programmable gate array (FPGA) and central processing unit was presented. Trajectory parameter, data acquisition speed and storing velocity of the measured projectile were analyzed. Coordinate measuring principle of parallel line laser detector array was given and photoelectric detection circuit with brief and high reliability was designed. Adjustment method of circuit sensitivity was derived and data acquisition was verified by experiment. The results show that this acquisition system is easy to install and debug, and has high functionality reliability. Acquisition speed and storing velocity can meet the demand of barrage weapons dispersion measuerment.
2016, 40(6): 814-819.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.009
Abstract:
In traditional shape context, the calculation complexity was high in traversing the contour sampling points to calculate the histogram similarity and it can not meet the industrial real-time requirements. In order to solve the problem, a fast stereo matching algorithm of workpiece images based on the improved shape context was proposed. In the disparity constraints of stereo image centroid, by using the histogram distribution of shape context, candidate matching points set were obtained and the calculation complexity was greatly reduced. To increase the discrimination between the matching points and non-matching points, the similarity measurement of shape context was weighted by the weighted coefficient. During the matching period, the improved shape context was combined with the histograms of oriented gradients of the corresponding contour feature points in 33 neighborhood to acquire the initial matching point set. At last, the false matching points were eliminated by random sample consensus algorithm. Theoretical analysis and experimental verification were applied to workpiece images, and the corresponding experimental comparison was presented. The experiment results show that this improved algorithm has higher precision, faster matching speed and high robustness.
In traditional shape context, the calculation complexity was high in traversing the contour sampling points to calculate the histogram similarity and it can not meet the industrial real-time requirements. In order to solve the problem, a fast stereo matching algorithm of workpiece images based on the improved shape context was proposed. In the disparity constraints of stereo image centroid, by using the histogram distribution of shape context, candidate matching points set were obtained and the calculation complexity was greatly reduced. To increase the discrimination between the matching points and non-matching points, the similarity measurement of shape context was weighted by the weighted coefficient. During the matching period, the improved shape context was combined with the histograms of oriented gradients of the corresponding contour feature points in 33 neighborhood to acquire the initial matching point set. At last, the false matching points were eliminated by random sample consensus algorithm. Theoretical analysis and experimental verification were applied to workpiece images, and the corresponding experimental comparison was presented. The experiment results show that this improved algorithm has higher precision, faster matching speed and high robustness.
2016, 40(6): 820-824.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.010
Abstract:
In order to measure phase distribution of phase object, a method based on optical scanning holography was proposed. Different from traditional methods greatly, optical scanning holography based on coherent mode was adopted. By using pinhole detector, the phase information of the measured phase object was recorded. And then, the object's phase information can be reconstructed by inversion reconstruction algorithm. The working principle and reconstruction result were demonstrated theoretically and simulated numerically. The influence of pinhole on measurements of phase distribution was analyzed in detail, when non-ideal pinhole was used in recording and reconstruction stages. The results show the validity and correctness of the method proposed, and reasonable measuring results have been achieved.
In order to measure phase distribution of phase object, a method based on optical scanning holography was proposed. Different from traditional methods greatly, optical scanning holography based on coherent mode was adopted. By using pinhole detector, the phase information of the measured phase object was recorded. And then, the object's phase information can be reconstructed by inversion reconstruction algorithm. The working principle and reconstruction result were demonstrated theoretically and simulated numerically. The influence of pinhole on measurements of phase distribution was analyzed in detail, when non-ideal pinhole was used in recording and reconstruction stages. The results show the validity and correctness of the method proposed, and reasonable measuring results have been achieved.
2016, 40(6): 825-829.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.011
Abstract:
In order to research the process of laser scanner welding, the laser scanner welding process of 0.7mm galvanized sheet and 0.8mm cold-rolled sheet(SPCC)with a 4kW fiber laser was analyzed in theory and verified in experiments. The influence of the gap between the sheets, laser power and scanning speed on macro-morphology and strength were obtained. The results show that the welded seams achieved by laser parameters of plate gap 0.1mm~0.2mm, laser power 3kW~4kW and welding speed 3m/min have the strength higher than the base metal, and can satisfy the C-class of electron and laser beam welded joints (levels guidance for quality imperfaction). Laser scanner welding can get a high quality welding seam without shielding gas when selecting right parameters.
In order to research the process of laser scanner welding, the laser scanner welding process of 0.7mm galvanized sheet and 0.8mm cold-rolled sheet(SPCC)with a 4kW fiber laser was analyzed in theory and verified in experiments. The influence of the gap between the sheets, laser power and scanning speed on macro-morphology and strength were obtained. The results show that the welded seams achieved by laser parameters of plate gap 0.1mm~0.2mm, laser power 3kW~4kW and welding speed 3m/min have the strength higher than the base metal, and can satisfy the C-class of electron and laser beam welded joints (levels guidance for quality imperfaction). Laser scanner welding can get a high quality welding seam without shielding gas when selecting right parameters.
2016, 40(6): 830-833.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.012
Abstract:
In order to evaluate the laser warning device in different background light, the study of laser warning probability curve based on different background sunlight was presented. Firstly, the complex light environment for laser warning device was analyzed. Then, preliminary study results of laser warning probability curve variation were obtained by theoretical research and experimental verification. Finally, a calculating method of laser warning probability curve from typical to different intensity irradiance background sunlight was introduced. The results indicate that the background sunlight has a big influence on the performance of the laser warning device, and the warning threshold increases with the increasing of the intensity of sunlight irradiance. The results will be helpful for effect evaluation of laser warning.
In order to evaluate the laser warning device in different background light, the study of laser warning probability curve based on different background sunlight was presented. Firstly, the complex light environment for laser warning device was analyzed. Then, preliminary study results of laser warning probability curve variation were obtained by theoretical research and experimental verification. Finally, a calculating method of laser warning probability curve from typical to different intensity irradiance background sunlight was introduced. The results indicate that the background sunlight has a big influence on the performance of the laser warning device, and the warning threshold increases with the increasing of the intensity of sunlight irradiance. The results will be helpful for effect evaluation of laser warning.
2016, 40(6): 834-839.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.013
Abstract:
In order to design coordinate measuring system of laser radar precisely, based on the measuring principle and structure of laser radar coordinate measuring system, a angel measuring error model was built with three main system errors of peipendicularity error of pitch axis and azimuth axis, tilt error of reflector and tilt error of incident laser beam. After theoretical analysis, the maximum error values of single point coordinate measurement from 10m, were 124.1m, 447.9m and 242.4m. The results show that, in the design of laser radar coordinate measuring system, it is necessary to strictly control system error parameters like peipendicularity error of pitch axis and azimuth axis, tilt error of reflector and tilt error of incident laser beam in order that the measuring system has high measurement accuracy when measuring in large space. Besides, parameter calibration and error compensation are required to improve the measurement accuracy.
In order to design coordinate measuring system of laser radar precisely, based on the measuring principle and structure of laser radar coordinate measuring system, a angel measuring error model was built with three main system errors of peipendicularity error of pitch axis and azimuth axis, tilt error of reflector and tilt error of incident laser beam. After theoretical analysis, the maximum error values of single point coordinate measurement from 10m, were 124.1m, 447.9m and 242.4m. The results show that, in the design of laser radar coordinate measuring system, it is necessary to strictly control system error parameters like peipendicularity error of pitch axis and azimuth axis, tilt error of reflector and tilt error of incident laser beam in order that the measuring system has high measurement accuracy when measuring in large space. Besides, parameter calibration and error compensation are required to improve the measurement accuracy.
2016, 40(6): 840-842.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.014
Abstract:
In order to get hundred picosecond laser at 2m band, by using an acousto-optic modulator and Tm:YLF laser as the pump source, an actively continuous wave mode-locked Ho:YAG solid-state laser was obtained at room temperature. The output characteristics of active mode-locked laser were studied. After experimental verification, the parameters of laser were obtained, such as mode-locked pulse repetition frequency of 82.75MHz, the maximal average output power of 1W, wavelength center of 2097.25nm, slope efficiency of 13.3%, and pulse width of about 86.6ps. The results show that mode-locked Ho-doped laser with 100ps pulse width could be obtained by the method of active mode-locked technology.
In order to get hundred picosecond laser at 2m band, by using an acousto-optic modulator and Tm:YLF laser as the pump source, an actively continuous wave mode-locked Ho:YAG solid-state laser was obtained at room temperature. The output characteristics of active mode-locked laser were studied. After experimental verification, the parameters of laser were obtained, such as mode-locked pulse repetition frequency of 82.75MHz, the maximal average output power of 1W, wavelength center of 2097.25nm, slope efficiency of 13.3%, and pulse width of about 86.6ps. The results show that mode-locked Ho-doped laser with 100ps pulse width could be obtained by the method of active mode-locked technology.
2016, 40(6): 843-847.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.015
Abstract:
In order to investigate splitting properties of YVO4 Wollaston prisms, by analysis of wave propagation in the prism, the formulas of o beam and e beam at normal incidence were obtained. The curve of splitting properties of the prism changing with wavelength and structure angle was obtained by MATLAB software. The results show that for the prism with the given structure angles, the dispersion property of splitting angle is evident. The shorter the wavelength, the greater the splitting angle, the faster the change. In infrared region, the effect of incident wavelength on splitting angle reduces and splitting angle is stable. The effects of wavelength changes on the symmetry of splitting angle are so little that they can be ignored in the application. The structure angles of the prism and the incident light wavelength have effects on the transmission ratio of prism. For the given structure angles of prism, transmission ratio changes with the wavelength of incident light oscillatory. Spectral effects of o light transmission ratio are more obvious. The research provides an important and valuable reference to the design and application of YVO4 prisms.
In order to investigate splitting properties of YVO4 Wollaston prisms, by analysis of wave propagation in the prism, the formulas of o beam and e beam at normal incidence were obtained. The curve of splitting properties of the prism changing with wavelength and structure angle was obtained by MATLAB software. The results show that for the prism with the given structure angles, the dispersion property of splitting angle is evident. The shorter the wavelength, the greater the splitting angle, the faster the change. In infrared region, the effect of incident wavelength on splitting angle reduces and splitting angle is stable. The effects of wavelength changes on the symmetry of splitting angle are so little that they can be ignored in the application. The structure angles of the prism and the incident light wavelength have effects on the transmission ratio of prism. For the given structure angles of prism, transmission ratio changes with the wavelength of incident light oscillatory. Spectral effects of o light transmission ratio are more obvious. The research provides an important and valuable reference to the design and application of YVO4 prisms.
2016, 40(6): 848-852.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.016
Abstract:
When adopting traditional hyperspectral ground objects identification method, the error of spectral matching became big because of the difference of absorption peak number. In order to solve the problem, an optional algorithm based on hyperspectral absorption peak characteristics was brought out, and then spectral matching according to the selected absorption was carried out. At beginning, the continuum removal in spectral curve and the extraction of spectral characteristic parameters matrix were made. And then the matching vertor of absorption peak was searched gradually according to the cosine distance-Euclidian distance of every vertor from the standard characteristic parameter matrix and the to-be-detected characteristic parameter matrix. After theoretical analysis and experimental verification of the selected absorption peak characteristic parameters matrix, the results show that this algorithm can get the best characteristic parameters vector, to realize the selection of absorption peak and make the hyperspectra matching with the selected absorption peak characteristic parameters matrix. The study is helpful for the decrease of the error of spectral matching.
When adopting traditional hyperspectral ground objects identification method, the error of spectral matching became big because of the difference of absorption peak number. In order to solve the problem, an optional algorithm based on hyperspectral absorption peak characteristics was brought out, and then spectral matching according to the selected absorption was carried out. At beginning, the continuum removal in spectral curve and the extraction of spectral characteristic parameters matrix were made. And then the matching vertor of absorption peak was searched gradually according to the cosine distance-Euclidian distance of every vertor from the standard characteristic parameter matrix and the to-be-detected characteristic parameter matrix. After theoretical analysis and experimental verification of the selected absorption peak characteristic parameters matrix, the results show that this algorithm can get the best characteristic parameters vector, to realize the selection of absorption peak and make the hyperspectra matching with the selected absorption peak characteristic parameters matrix. The study is helpful for the decrease of the error of spectral matching.
2016, 40(6): 853-859.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.017
Abstract:
In order to investigate the mechanism of laser welding of carbon fiber reinforced plastics(CFRP)and stainless steel, and find out the effect of different process parameters on welding quality, a 3-D finite element model based on heat conduction welding was built by ANSYS. The distributions of temperature field and stress field were calculated by ANSYS. The effect of process parameters, including laser power, scanning welding and spot diameter, on welding width and welding depth was investigated. And the influence of welding residual stress on the quality of welding was also investigated. The results show that temperature field and residual stress distributions can be rapidly and effectively simulated by the proposed finite element model. Welding width and depth are affected by laser power, scanning welding and spot diameter. The calculated distribution and the theoretical distribution of residual stress agree well. The result confirms that the model is reliable. The result is helpful to obtain high quality welded joints of CFRP-stainless steel.
In order to investigate the mechanism of laser welding of carbon fiber reinforced plastics(CFRP)and stainless steel, and find out the effect of different process parameters on welding quality, a 3-D finite element model based on heat conduction welding was built by ANSYS. The distributions of temperature field and stress field were calculated by ANSYS. The effect of process parameters, including laser power, scanning welding and spot diameter, on welding width and welding depth was investigated. And the influence of welding residual stress on the quality of welding was also investigated. The results show that temperature field and residual stress distributions can be rapidly and effectively simulated by the proposed finite element model. Welding width and depth are affected by laser power, scanning welding and spot diameter. The calculated distribution and the theoretical distribution of residual stress agree well. The result confirms that the model is reliable. The result is helpful to obtain high quality welded joints of CFRP-stainless steel.
2016, 40(6): 860-865.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.018
Abstract:
In order to develop a practical all-optical polarization control tool, according to vector stimulated Raman scattering theory and random birefringence effect of optical fibers, a scheme of all-optical polarization control was proposed based on bi-propagating dual-order Raman pump. After the establishment of the theoretical model solved by rigorous numerical method, the optimal design of the polarization control scheme was completed. The results show that when signal wavelength is 1550nm, signal power is 0.1mW, pump light P1 and P2 power are 1W and 4W, and their polarization states are (0, 1, 0), fiber length is 3km, the degree of polarization of signal light could be more than 0.85, and the intensity fluctuations of signal light are less than 35%. The proposed method is effective to reduce the power of the interacting light wave, weaken the intensity noise of output optical signal and improve the degree of polarization of optical signals.
In order to develop a practical all-optical polarization control tool, according to vector stimulated Raman scattering theory and random birefringence effect of optical fibers, a scheme of all-optical polarization control was proposed based on bi-propagating dual-order Raman pump. After the establishment of the theoretical model solved by rigorous numerical method, the optimal design of the polarization control scheme was completed. The results show that when signal wavelength is 1550nm, signal power is 0.1mW, pump light P1 and P2 power are 1W and 4W, and their polarization states are (0, 1, 0), fiber length is 3km, the degree of polarization of signal light could be more than 0.85, and the intensity fluctuations of signal light are less than 35%. The proposed method is effective to reduce the power of the interacting light wave, weaken the intensity noise of output optical signal and improve the degree of polarization of optical signals.
2016, 40(6): 866-870.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.019
Abstract:
In order to operate 3-D measurement efficiently and accurately, a vision measurement method correlation was proposed based on Bayesian model and digital image. Digital image correlation was used to match the rectified images, which had the ability to improve the accuracy of traditional stereo matching method. The iterative initial disparity of digital image correlation was determined by Bayesian model to overcome the disadvantages of coarse-fine search. Based on the projecting relationship between the rectified image and the raw image, 3-D coordinates of the matched point were then calculated by the least square method. The results show that the proposed vision measurement method based on Bayesian model and digital image correlation has high accuracy and efficiency of 3-D vision measurement.
In order to operate 3-D measurement efficiently and accurately, a vision measurement method correlation was proposed based on Bayesian model and digital image. Digital image correlation was used to match the rectified images, which had the ability to improve the accuracy of traditional stereo matching method. The iterative initial disparity of digital image correlation was determined by Bayesian model to overcome the disadvantages of coarse-fine search. Based on the projecting relationship between the rectified image and the raw image, 3-D coordinates of the matched point were then calculated by the least square method. The results show that the proposed vision measurement method based on Bayesian model and digital image correlation has high accuracy and efficiency of 3-D vision measurement.
2016, 40(6): 871-875.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.020
Abstract:
In order to reduce the vibration sensitivity of ultra-stable optical cavity, a new parameter was defined to characterize the vibration sensitivity of optical cavity by considering the displacement and rotation of mirrors. Based on the finite element analysis method, a typical vertical ultra-stable optical cavity was optimized by using the defined single parameter. In the optimization process, the key geometric parameters, including the cavity diameter, position and depth of supporting hole were took into account. The results show that the optimized cavity structure and support method could obviously reduce the vibration sensitivity of ultra-stable cavity. The stability of cavity was 1.5 times higher than that before optimization. The optimization method with good feasibility could improve the efficiency of simulation and design of ultra-stable cavities.
In order to reduce the vibration sensitivity of ultra-stable optical cavity, a new parameter was defined to characterize the vibration sensitivity of optical cavity by considering the displacement and rotation of mirrors. Based on the finite element analysis method, a typical vertical ultra-stable optical cavity was optimized by using the defined single parameter. In the optimization process, the key geometric parameters, including the cavity diameter, position and depth of supporting hole were took into account. The results show that the optimized cavity structure and support method could obviously reduce the vibration sensitivity of ultra-stable cavity. The stability of cavity was 1.5 times higher than that before optimization. The optimization method with good feasibility could improve the efficiency of simulation and design of ultra-stable cavities.
Quantitative analysis of composition in molten steel by LIBS based on improved partial least squares
2016, 40(6): 876-881.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.021
Abstract:
In order to study the effect of laser induced breakdown spectroscopy (LIBS) matrix effect on measurement accuracy, the improved partial least squares (PLS)was used to forecast the data and reduce the influence of matrix effect on the to-be-detected parameters. The comparative study with univariate calibration and partial least squares model calibration shows that the fitting degree of calibration curves of Mn and Si improve from 0.991 and 0.993 to 0.996 and 0.997, and the relative error of prediction for validation samples were decreased from 6.231%, 6.912% to 5.510%, 6.125%.The above results show that the improved PSL can reduce matrix effects and improve the calibration accuracy. The analysis of performance has been improved significantly.
In order to study the effect of laser induced breakdown spectroscopy (LIBS) matrix effect on measurement accuracy, the improved partial least squares (PLS)was used to forecast the data and reduce the influence of matrix effect on the to-be-detected parameters. The comparative study with univariate calibration and partial least squares model calibration shows that the fitting degree of calibration curves of Mn and Si improve from 0.991 and 0.993 to 0.996 and 0.997, and the relative error of prediction for validation samples were decreased from 6.231%, 6.912% to 5.510%, 6.125%.The above results show that the improved PSL can reduce matrix effects and improve the calibration accuracy. The analysis of performance has been improved significantly.
2016, 40(6): 882-887.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.022
Abstract:
In order to reduce the broadening of output beam line width in negative-branch off-axis unstable resonator laser, the function relationship between the two main parameters of effective Fresnel number Neff and geometry magnification M and excess noise factor K of output mode was analyzed. From negative branch structure, excess noise factor was firstly presented as functional distribution of transverse mode in output plane based on classical wave equation theory. By using the edge wave method, output transverse mode was approximated as a function of Neff and M. And then, the dependence of K on Neff and M were numerical calculated. The results indicate that K changes quasi-periodically with Neff. The cyclical peak is presented at Neffs+0.85 (s is a positive integer). Output line width is broadened nearly 2000 times of the natural line width. The study is useful for the research of output loss of unstable resonator and provides reference for practical laser designs.
In order to reduce the broadening of output beam line width in negative-branch off-axis unstable resonator laser, the function relationship between the two main parameters of effective Fresnel number Neff and geometry magnification M and excess noise factor K of output mode was analyzed. From negative branch structure, excess noise factor was firstly presented as functional distribution of transverse mode in output plane based on classical wave equation theory. By using the edge wave method, output transverse mode was approximated as a function of Neff and M. And then, the dependence of K on Neff and M were numerical calculated. The results indicate that K changes quasi-periodically with Neff. The cyclical peak is presented at Neffs+0.85 (s is a positive integer). Output line width is broadened nearly 2000 times of the natural line width. The study is useful for the research of output loss of unstable resonator and provides reference for practical laser designs.
2016, 40(6): 888-891.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.023
Abstract:
In order to study the characteristics and the evolution of laser-induced liquid droplet jet flow plasma, the behaviors of laser-induced liquid droplet plasma were investigated by the shadow method based on laser-droplet interaction system. Time-series images of CO2 laser-induced plasma with liquid droplet were captured. The evolution of air shock wave was obtained and the energy of shockwaves was estimated by theoretical model. The results show that air shock wave occurrs with laser-induced plasma and the radial expansion of shockwaves increases linearly under current time range. In addition, laser energy dissipated in the droplet was estimated to 32% for generating air shockwaves. The characteristics and the evolution of shockwaves generated by laser-induced droplet could provide a reference for laser induced fuel spray ignition.
In order to study the characteristics and the evolution of laser-induced liquid droplet jet flow plasma, the behaviors of laser-induced liquid droplet plasma were investigated by the shadow method based on laser-droplet interaction system. Time-series images of CO2 laser-induced plasma with liquid droplet were captured. The evolution of air shock wave was obtained and the energy of shockwaves was estimated by theoretical model. The results show that air shock wave occurrs with laser-induced plasma and the radial expansion of shockwaves increases linearly under current time range. In addition, laser energy dissipated in the droplet was estimated to 32% for generating air shockwaves. The characteristics and the evolution of shockwaves generated by laser-induced droplet could provide a reference for laser induced fuel spray ignition.
2016, 40(6): 892-896.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.024
Abstract:
In order to retain more detail information and reduce the algorithm complexity when fusing the infrared and visible light images, a fusion algorithm based on non-subsampled shearlet transform (NSST) and improved fuzzy logic was proposed to decompose source images sparsely on multi-direction and multi-scale. Low-frequency subband coeffients and high-frequency subband coeffients were obtained. The improved average fusion method of fuzzy Cauchy membership function was adopted in low-frequency subband coeffients. The fusion rule of the combination of energy compatibility and visual sensitivity coefficient was used in high-frequency subband coeffients. Finally, fusion image was obtained after NSST inverse transformation. Experimental results show that the fusion method can not only guarantee the definition of fused image, but also shorten the running time of algorithm.
In order to retain more detail information and reduce the algorithm complexity when fusing the infrared and visible light images, a fusion algorithm based on non-subsampled shearlet transform (NSST) and improved fuzzy logic was proposed to decompose source images sparsely on multi-direction and multi-scale. Low-frequency subband coeffients and high-frequency subband coeffients were obtained. The improved average fusion method of fuzzy Cauchy membership function was adopted in low-frequency subband coeffients. The fusion rule of the combination of energy compatibility and visual sensitivity coefficient was used in high-frequency subband coeffients. Finally, fusion image was obtained after NSST inverse transformation. Experimental results show that the fusion method can not only guarantee the definition of fused image, but also shorten the running time of algorithm.
2016, 40(6): 897-901.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.025
Abstract:
To solve the problem of long-distance pipeline safety monitoring, a 3-D long-distance early warning system combined with geographic information system based on Sagnac optical fiber interference was proposed. By using digital filtering and wavelet analysis, the system positioning accuracy reached to 25m in a laboratory environment of 60km long and one meter underground. The system was also tested in a real pipeline of 211km, and alarm report was gotted successfully with positioning accuracy under 150m when excavating about 1m around optics fiber cable. Both false positive rate and negative rate of alarm system were less than 5%. The test proves that the system is applicable in terms of long-distance oil and gas pipeline safety warning.
To solve the problem of long-distance pipeline safety monitoring, a 3-D long-distance early warning system combined with geographic information system based on Sagnac optical fiber interference was proposed. By using digital filtering and wavelet analysis, the system positioning accuracy reached to 25m in a laboratory environment of 60km long and one meter underground. The system was also tested in a real pipeline of 211km, and alarm report was gotted successfully with positioning accuracy under 150m when excavating about 1m around optics fiber cable. Both false positive rate and negative rate of alarm system were less than 5%. The test proves that the system is applicable in terms of long-distance oil and gas pipeline safety warning.
2016, 40(6): 902-906.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.026
Abstract:
In order to improve evaluation effect of structural similarity index image, the traditional window selection criterion was improved. By contrasting the window evaluation value before and after improvement, the best window for different databases and different types of distortion was obtained. The results show that the traditional single window does not get the best evaluation result, and the widely-used Gaussian weighted window with standard deviation of 1.5 does not better than the ordinary square window. The optimal windows of different types of image distortion are also different. From the experimental results, for luminance window W1, the bigger the window, the better the evaluation result. And for contrast and structure window W2, the evaluation result is best when W2=7. The results play an important role on optimizing the evaluation method of structural similarity index.
In order to improve evaluation effect of structural similarity index image, the traditional window selection criterion was improved. By contrasting the window evaluation value before and after improvement, the best window for different databases and different types of distortion was obtained. The results show that the traditional single window does not get the best evaluation result, and the widely-used Gaussian weighted window with standard deviation of 1.5 does not better than the ordinary square window. The optimal windows of different types of image distortion are also different. From the experimental results, for luminance window W1, the bigger the window, the better the evaluation result. And for contrast and structure window W2, the evaluation result is best when W2=7. The results play an important role on optimizing the evaluation method of structural similarity index.
2016, 40(6): 907-911.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.027
Abstract:
In order to improve the laser absorption rate of metal surface and processing surface quality of laser micro-dimple,W-71s type spray gun was used to spray black paint, water glass and yellow material on the surface of samples, respectively. Then, the samples were processed by Nd:YAG laser. Compared with the uncoated specimens, the dimple volume increased and slag volume decreased respectively, around the dimples of specimen surface coated with water glass and yellow material. Dimple volume of the sample coated with yellow material increased by 29.4%. On the basis, the influence of thickness and formula of water glass and yellow material on dimple volume and slag volume of laser processing surface were discussed by orthogonal experimental method. The results show that when the thickness of absorb light coating is about 0.1mm, the content of yellow material is 17% and the content of water glass is 18%, the coating formulation is optimal. Compared with the uncoated sample, dimple volume of the best sample in orthogonal table increased by 70.6% and the corresponding slag volume around the dimple decreased by 16.2%. The study indicates that laser absorption rate and laser processing quality on the surface can be significantly improved.
In order to improve the laser absorption rate of metal surface and processing surface quality of laser micro-dimple,W-71s type spray gun was used to spray black paint, water glass and yellow material on the surface of samples, respectively. Then, the samples were processed by Nd:YAG laser. Compared with the uncoated specimens, the dimple volume increased and slag volume decreased respectively, around the dimples of specimen surface coated with water glass and yellow material. Dimple volume of the sample coated with yellow material increased by 29.4%. On the basis, the influence of thickness and formula of water glass and yellow material on dimple volume and slag volume of laser processing surface were discussed by orthogonal experimental method. The results show that when the thickness of absorb light coating is about 0.1mm, the content of yellow material is 17% and the content of water glass is 18%, the coating formulation is optimal. Compared with the uncoated sample, dimple volume of the best sample in orthogonal table increased by 70.6% and the corresponding slag volume around the dimple decreased by 16.2%. The study indicates that laser absorption rate and laser processing quality on the surface can be significantly improved.
2016, 40(6): 912-915.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.028
Abstract:
For the existing measurement system of lens center thickness based on optical confocal technology, refraction and reflection of incident light affected the measuring accuracy. In order to solve this problems, based on confocal technology, the modified measurement system of lens center thickness was designed with the method of double-side optical confocal measurement. After theoretical analysis, error analysis and experimental verification, the results show that the measurement range of the system reaches 30mm and the measurement accuracy is 2m. The system can get the high-speed untouched measurement of center thickness and satisfy the demands of actual measurement.
For the existing measurement system of lens center thickness based on optical confocal technology, refraction and reflection of incident light affected the measuring accuracy. In order to solve this problems, based on confocal technology, the modified measurement system of lens center thickness was designed with the method of double-side optical confocal measurement. After theoretical analysis, error analysis and experimental verification, the results show that the measurement range of the system reaches 30mm and the measurement accuracy is 2m. The system can get the high-speed untouched measurement of center thickness and satisfy the demands of actual measurement.
2016, 40(6): 916-920.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.029
Abstract:
In order to satisfy the applications with high quality beams and fast scanning, the formation of single flat-top and multiple flat-top beams were simulated by digital micromirror device and error diffusion method. An experimental setup with 680nm laser was built to validate the model. The beam shaping result was evaluated by using beam fill factor, light field modulation factor, root mean square error as parameters, and the energy utilization rate of beam shaping based on digital micromirror array was measured and analyzed. The results show that beam fill factors increase from 36.1% to 62.3%(single),56.7%(multiple) respectively, while light field modulation factors decrease from 73.3% to 25.6%(single),30.3%(multiple) respectively. Spatial shaping results show that the multiple flat-top beams are valuable in high quality beams and fast scanning.
In order to satisfy the applications with high quality beams and fast scanning, the formation of single flat-top and multiple flat-top beams were simulated by digital micromirror device and error diffusion method. An experimental setup with 680nm laser was built to validate the model. The beam shaping result was evaluated by using beam fill factor, light field modulation factor, root mean square error as parameters, and the energy utilization rate of beam shaping based on digital micromirror array was measured and analyzed. The results show that beam fill factors increase from 36.1% to 62.3%(single),56.7%(multiple) respectively, while light field modulation factors decrease from 73.3% to 25.6%(single),30.3%(multiple) respectively. Spatial shaping results show that the multiple flat-top beams are valuable in high quality beams and fast scanning.
2016, 40(6): 921-925.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.030
Abstract:
In order to analysis the characteristics and differences of photoacoustic imaging signal under different wavelengths in time domain and frequency domain, multi-wavelength photoacoustic imaging experiment with different targets including graphite phantom, pork and pig blood phantom was designed. The results show that the performance of different targets was quite different in time domain and frequency domain. The acoustic spectrum of photoacoustic signals for different targets was unique. Frequencies corresponded to the peaks of acoustic spectrum were same. The performance can be utilized for tissue characterization description and component identification. The research is helpful for organizational recognization by using photoacoustic imaging. And it will be the fundamental research for further frequency-domain analysis and study of multispectral photoacoustic imaging.
In order to analysis the characteristics and differences of photoacoustic imaging signal under different wavelengths in time domain and frequency domain, multi-wavelength photoacoustic imaging experiment with different targets including graphite phantom, pork and pig blood phantom was designed. The results show that the performance of different targets was quite different in time domain and frequency domain. The acoustic spectrum of photoacoustic signals for different targets was unique. Frequencies corresponded to the peaks of acoustic spectrum were same. The performance can be utilized for tissue characterization description and component identification. The research is helpful for organizational recognization by using photoacoustic imaging. And it will be the fundamental research for further frequency-domain analysis and study of multispectral photoacoustic imaging.
2016, 40(6): 926-929.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.031
Abstract:
In the product delivery process, deviation between the laser divergence angled calculated by hole-set method and CCD imaging method is usually large. In order to find the reason, theoretical analysis was carried out by ZEMAX simulaiton and experimental verification was done. The results show that:when using CCD imaging method to measure the laser spot size in white CCD sighting system, due to optical path difference between white light and laser, the influence of image error caused by optical path difference on the calculation of laser divergence angle should be eliminated. Laser spot size and distance are in accordance with the law of hyperbolic variation. In the near field conditions, there is not the linear relationship. Laser spot image measured by CCD imaging method is large and the calculated laser divergence angle is far more than the angle measured by hole-set method. In the far field conditions, there is approximately the linear relationship. The values of laser divergence angles calculated by hole-set method and CCD imaging method are in consistence. The study can eliminate the influence of optical path difference on divergence angle of laser beam and improve the measurement accuracy according to design parameters of the products.
In the product delivery process, deviation between the laser divergence angled calculated by hole-set method and CCD imaging method is usually large. In order to find the reason, theoretical analysis was carried out by ZEMAX simulaiton and experimental verification was done. The results show that:when using CCD imaging method to measure the laser spot size in white CCD sighting system, due to optical path difference between white light and laser, the influence of image error caused by optical path difference on the calculation of laser divergence angle should be eliminated. Laser spot size and distance are in accordance with the law of hyperbolic variation. In the near field conditions, there is not the linear relationship. Laser spot image measured by CCD imaging method is large and the calculated laser divergence angle is far more than the angle measured by hole-set method. In the far field conditions, there is approximately the linear relationship. The values of laser divergence angles calculated by hole-set method and CCD imaging method are in consistence. The study can eliminate the influence of optical path difference on divergence angle of laser beam and improve the measurement accuracy according to design parameters of the products.
2016, 40(6): 930-934.
doi: 10.7510/jgjs.issn.1001-3806.2016.06.032
Abstract:
In order to realize the desired shaping precision of fiber laser online-selective shaping diamond wheel, a fiber laser online shaping diamond wheel system was built by utilizing the computer, charge coupled device(CCD) sensor, PCIe-6361 data acquisition card as the main hardwares and LabVIEW software as the computer development tools. The system can not only realize diamond wheel shaping with laser on line, but also achieve high precision measurement on the surface profile of the grinding wheel and data storage in a short time. Experimental results show that, after the measurement of wheel contour, when the system of fiber laser shaping diamond grinding wheel is set with diamond wheel shaping threshold of 38.23m, power of 35W, repetition frequency of 50kHz, the maximum height of wheel after shaping is under 38m. The system design can meet the shaping requirements of diamond wheel.
In order to realize the desired shaping precision of fiber laser online-selective shaping diamond wheel, a fiber laser online shaping diamond wheel system was built by utilizing the computer, charge coupled device(CCD) sensor, PCIe-6361 data acquisition card as the main hardwares and LabVIEW software as the computer development tools. The system can not only realize diamond wheel shaping with laser on line, but also achieve high precision measurement on the surface profile of the grinding wheel and data storage in a short time. Experimental results show that, after the measurement of wheel contour, when the system of fiber laser shaping diamond grinding wheel is set with diamond wheel shaping threshold of 38.23m, power of 35W, repetition frequency of 50kHz, the maximum height of wheel after shaping is under 38m. The system design can meet the shaping requirements of diamond wheel.
