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RSS2020 Vol. 44, No. 2
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[Abstract]
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2020, 44(2): 143-147.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.001
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Abstract:
The spatial resolution of hyperspectral images was generally low. As a result, a large number of mixed pixels existed. It brought some difficulties to target detection. In order to realize target detection in hyperspectral images under complex background, a target detection method based on de-endmember was proposed. On the basis of spectral de-mixing technology, the spectral mixing model under complex background was established and improved. The method of removing endpoints many times was adopted. The hyperspectral image after simplified background was obtained. The results show that, compared with the traditional RX target detection algorithm, the proposed algorithm can significantly improve the performance of target detection. In practical military applications, it provides a train of thought for target recognition and camouflage exposure of large-scale images.
The spatial resolution of hyperspectral images was generally low. As a result, a large number of mixed pixels existed. It brought some difficulties to target detection. In order to realize target detection in hyperspectral images under complex background, a target detection method based on de-endmember was proposed. On the basis of spectral de-mixing technology, the spectral mixing model under complex background was established and improved. The method of removing endpoints many times was adopted. The hyperspectral image after simplified background was obtained. The results show that, compared with the traditional RX target detection algorithm, the proposed algorithm can significantly improve the performance of target detection. In practical military applications, it provides a train of thought for target recognition and camouflage exposure of large-scale images.
2020, 44(2): 148-155.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.002
Abstract:
In order to study the interaction mechanism between laser and spinel compounds in laser selective metallization technology, copper hydroxyphosphate (Cu2(OH)PO4), a cheap and high-quality photocatalyst with spinel structure, was selected as research object. The interaction mechanism between nanosecond pulsed fiber laser with 1064nm, continuous wave fiber laser and nanosecond pulsed ultraviolet laser with 355nm wavelength and copper hydroxyphosphate was discussed by using X-ray photoelectron spectroscopy. The results show that, all three lasers can reduce +2 copper element (Cu2+) in copper hydroxyphosphate to +1 copper element (Cu+). The original process varies with laser power (0.13W~3.89W) or laser energy density (2.76J/cm2~25.48J/cm2). Thermal properties and UV-visible absorption spectra of copper hydroxyphosphate were analyzed. In the above reduction process, photothermal and photochemical reactions may exist simultaneously by preliminary judgment. This study provides theoretical basis for copper hydroxyphosphate as new type of laser active material.
In order to study the interaction mechanism between laser and spinel compounds in laser selective metallization technology, copper hydroxyphosphate (Cu2(OH)PO4), a cheap and high-quality photocatalyst with spinel structure, was selected as research object. The interaction mechanism between nanosecond pulsed fiber laser with 1064nm, continuous wave fiber laser and nanosecond pulsed ultraviolet laser with 355nm wavelength and copper hydroxyphosphate was discussed by using X-ray photoelectron spectroscopy. The results show that, all three lasers can reduce +2 copper element (Cu2+) in copper hydroxyphosphate to +1 copper element (Cu+). The original process varies with laser power (0.13W~3.89W) or laser energy density (2.76J/cm2~25.48J/cm2). Thermal properties and UV-visible absorption spectra of copper hydroxyphosphate were analyzed. In the above reduction process, photothermal and photochemical reactions may exist simultaneously by preliminary judgment. This study provides theoretical basis for copper hydroxyphosphate as new type of laser active material.
2020, 44(2): 156-160.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.003
Abstract:
In order to solve the problem of particle contamination on the surface of optical elements, on the basis of single laser dry cleaning, laser cleaning assisted by air displacement system was proposed. Nd:YAG laser with 355nm wavelength was used. Typical SiO2 pollutant particulate with optical surface diameter of 1μm~50μm for sol-gel SiO2 thin film fused silica was theoretically analyzed and cleaning experiments were carried out. The process parameters for laser cleaning were obtained. The results show that, for single crystal laser dry cleaning of sol-gel membrane fused silica samples, optimum laser energy density is 2.29J/cm2. The process parameters of laser cleaning are different from those of uncoated quartz. Under the optimum technological parameters, the effect of single laser cleaning on SiO2 particles with particle size more than 1μm is obvious. The removal rate is 82.96%. Excessive contamination density will weaken the cleaning effect and damage the base. Laser cleaning assisted by air displacement system can further enhance the removal effect of particle contamination on optical surface. This research has important research significance and practical value for on-line cleaning of optical components and the design of cleaning equipment in large-scale high-power solid-state laser devices.
In order to solve the problem of particle contamination on the surface of optical elements, on the basis of single laser dry cleaning, laser cleaning assisted by air displacement system was proposed. Nd:YAG laser with 355nm wavelength was used. Typical SiO2 pollutant particulate with optical surface diameter of 1μm~50μm for sol-gel SiO2 thin film fused silica was theoretically analyzed and cleaning experiments were carried out. The process parameters for laser cleaning were obtained. The results show that, for single crystal laser dry cleaning of sol-gel membrane fused silica samples, optimum laser energy density is 2.29J/cm2. The process parameters of laser cleaning are different from those of uncoated quartz. Under the optimum technological parameters, the effect of single laser cleaning on SiO2 particles with particle size more than 1μm is obvious. The removal rate is 82.96%. Excessive contamination density will weaken the cleaning effect and damage the base. Laser cleaning assisted by air displacement system can further enhance the removal effect of particle contamination on optical surface. This research has important research significance and practical value for on-line cleaning of optical components and the design of cleaning equipment in large-scale high-power solid-state laser devices.
2020, 44(2): 161-166.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.004
Abstract:
In order to solve the problems of poor cross-correlation stability and slow minimum mean square convergence in optical fiber vibration location algorithm, recursive least squares algorithm, moving average principle and early-late gate principle were adopted. A stable and fast response optical fiber vibration positioning system was designed. Optical path was based on double Mach-Zehnder interference structure. Hardware platform used high-speed acquisition board and field-programmable gate array to realize positioning. Repeated knocking experiments were carried out on 160m optical path. The obtained vibration data were computed separately in several segments. After removing the maximum and minimum values, the residual positioning results were averaged to improve the positioning accuracy. The results show that, as the number of iterations increases, recursive least squares method can stabilize the single positioning result without migration, compared with cross-correlation. Convergence rate is about 3 times of minimum mean square. At sampling rate of 10MHz, actual response time of the system is about 0.3s. The range of positioning error is ±6m. The positioning is stable and reliable. This research has positive significance for the improvement of location algorithm and positioning accuracy in optical fiber positioning system.
In order to solve the problems of poor cross-correlation stability and slow minimum mean square convergence in optical fiber vibration location algorithm, recursive least squares algorithm, moving average principle and early-late gate principle were adopted. A stable and fast response optical fiber vibration positioning system was designed. Optical path was based on double Mach-Zehnder interference structure. Hardware platform used high-speed acquisition board and field-programmable gate array to realize positioning. Repeated knocking experiments were carried out on 160m optical path. The obtained vibration data were computed separately in several segments. After removing the maximum and minimum values, the residual positioning results were averaged to improve the positioning accuracy. The results show that, as the number of iterations increases, recursive least squares method can stabilize the single positioning result without migration, compared with cross-correlation. Convergence rate is about 3 times of minimum mean square. At sampling rate of 10MHz, actual response time of the system is about 0.3s. The range of positioning error is ±6m. The positioning is stable and reliable. This research has positive significance for the improvement of location algorithm and positioning accuracy in optical fiber positioning system.
2020, 44(2): 167-172.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.005
Abstract:
In order to improve mechanical properties and corrosion resistance of brass surface, laser shock processing (LSP) of brass surface was achieved by nanosecond pulse laser (wavelength of 1064nm and pulse width of 7ns). The mechanical properties such as surface residual stress, cross section metallographic structure, hardness and surface morphology of LSP brass were analyzed. The effects of these properties on corrosion resistance were studied. The results show that, compared with brass samples without LSP treatment, the electrochemical corrosion potential of brass samples increases after LSP treatment. The quality of cavitation loss is reduced by only 1/4 of the original. The incubation period of cavitation erosion was prolonged by two times. The rate of cavitation erosion decreases. LSP treatment improves the corrosion resistance of brass samples. This study is helpful for the application of ordinary brass in corrosive working environment.
In order to improve mechanical properties and corrosion resistance of brass surface, laser shock processing (LSP) of brass surface was achieved by nanosecond pulse laser (wavelength of 1064nm and pulse width of 7ns). The mechanical properties such as surface residual stress, cross section metallographic structure, hardness and surface morphology of LSP brass were analyzed. The effects of these properties on corrosion resistance were studied. The results show that, compared with brass samples without LSP treatment, the electrochemical corrosion potential of brass samples increases after LSP treatment. The quality of cavitation loss is reduced by only 1/4 of the original. The incubation period of cavitation erosion was prolonged by two times. The rate of cavitation erosion decreases. LSP treatment improves the corrosion resistance of brass samples. This study is helpful for the application of ordinary brass in corrosive working environment.
2020, 44(2): 173-177.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.006
Abstract:
In order to study the expansion characteristics of laser-induced discharge plasma (LDP), a set of extreme ultraviolet source for tin target discharge plasma based on pulsed CO2 laser was established. The plume was photographed by intensified charge-coupled device. 1-D vacuum arc model was used to explain the experimental results. The time-resolved plume images under different conditions were obtained by changing the discharge voltage and laser energy. The results show that, under the condition of 140mJ laser energy and 10kV discharge voltage, a stable discharge plasma was obtained. There is a corresponding relationship between the plume morphology and the current. It has undergone different stages of formation, expansion, contraction, re-expansion and dissipation. Discharge voltage and induced laser energy have effects on plume size, stability and formation time. This study is helpful to improve the stability of LDP source and the output power of extreme ultraviolet light.
In order to study the expansion characteristics of laser-induced discharge plasma (LDP), a set of extreme ultraviolet source for tin target discharge plasma based on pulsed CO2 laser was established. The plume was photographed by intensified charge-coupled device. 1-D vacuum arc model was used to explain the experimental results. The time-resolved plume images under different conditions were obtained by changing the discharge voltage and laser energy. The results show that, under the condition of 140mJ laser energy and 10kV discharge voltage, a stable discharge plasma was obtained. There is a corresponding relationship between the plume morphology and the current. It has undergone different stages of formation, expansion, contraction, re-expansion and dissipation. Discharge voltage and induced laser energy have effects on plume size, stability and formation time. This study is helpful to improve the stability of LDP source and the output power of extreme ultraviolet light.
2020, 44(2): 178-182.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.007
Abstract:
In order to study the influence of laser power on the formation of laser-metal inert-gas composite welding seam of ship steel, joint test of 7mm AH36 ship steel plate with different laser powers, microstructure observation and mechanical properties test were carried out. Theoretical analysis and experimental verification were carried out. The optimum technological parameters of weld forming, microstructures and mechanical properties of different regions of weld joints were obtained. The results show that, at laser power of 6kW, current of 220A and welding rate of 1.2m/min, weld forming is the best. The structure of weld zone is lath martensite and a little ferrite. Its tensile strength is 545MPa. The mechanical properties meet the requirements of national standards and China Classification Society specifications. This has certain guiding significance for laser hybrid welding of ship steel.
In order to study the influence of laser power on the formation of laser-metal inert-gas composite welding seam of ship steel, joint test of 7mm AH36 ship steel plate with different laser powers, microstructure observation and mechanical properties test were carried out. Theoretical analysis and experimental verification were carried out. The optimum technological parameters of weld forming, microstructures and mechanical properties of different regions of weld joints were obtained. The results show that, at laser power of 6kW, current of 220A and welding rate of 1.2m/min, weld forming is the best. The structure of weld zone is lath martensite and a little ferrite. Its tensile strength is 545MPa. The mechanical properties meet the requirements of national standards and China Classification Society specifications. This has certain guiding significance for laser hybrid welding of ship steel.
2020, 44(2): 183-189.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.008
Abstract:
In order to know the variation of rail gauge in real time, a real-time on-line gauge monitoring system was developed. Position sensitive detector and laser emitter was used as measuring elements for real-time acquisition of gauge change information. Mathematical model was established to calculate the offset of the gauge. The offset of two rails after moving was calculated by the combination algorithm. The position sensitive detector was compensated by quadratic interpolation algorithm to improve the accuracy and accuracy of position sensitive detector. The gauge change information in certain area was sent to the monitoring center for display by using controller area network bus and general packet radio service communication technology. The same simulation track was measured by the existing two-stage gauge gauge. The results show that, measurement accuracy of the system is 0.32mm. It meets the precision requirement of 1mm stipulated by track inspection industry at present.
In order to know the variation of rail gauge in real time, a real-time on-line gauge monitoring system was developed. Position sensitive detector and laser emitter was used as measuring elements for real-time acquisition of gauge change information. Mathematical model was established to calculate the offset of the gauge. The offset of two rails after moving was calculated by the combination algorithm. The position sensitive detector was compensated by quadratic interpolation algorithm to improve the accuracy and accuracy of position sensitive detector. The gauge change information in certain area was sent to the monitoring center for display by using controller area network bus and general packet radio service communication technology. The same simulation track was measured by the existing two-stage gauge gauge. The results show that, measurement accuracy of the system is 0.32mm. It meets the precision requirement of 1mm stipulated by track inspection industry at present.
2020, 44(2): 190-195.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.009
Abstract:
In order to extract the center of laser stripe accurately in noisy environment, the improved gray-scale weight model was adopted to extract subpixel centers of laser fringes. The image acquired by 3-D laser imaging system was processed by means of mean threshold method and the improved gray weight model. The method was compared with the traditional algorithm. The results show that, the algorithm can extract laser fringe region more completely. The average fitting correlation coefficient is 0.9809 (closest to 1). The maximum difference of average column coordinates is 0.4518pixel (closest to 0). The average coefficient of variation is 0.0062 (closest to 0). Compared with other methods, it has better results. It can suppress the influence of multi-noise environment on laser stripe extraction and extract subpixel centers of laser fringes accurately. It has good robustness. The algorithm provides a reference for extracting the center of laser fringes accurately.
In order to extract the center of laser stripe accurately in noisy environment, the improved gray-scale weight model was adopted to extract subpixel centers of laser fringes. The image acquired by 3-D laser imaging system was processed by means of mean threshold method and the improved gray weight model. The method was compared with the traditional algorithm. The results show that, the algorithm can extract laser fringe region more completely. The average fitting correlation coefficient is 0.9809 (closest to 1). The maximum difference of average column coordinates is 0.4518pixel (closest to 0). The average coefficient of variation is 0.0062 (closest to 0). Compared with other methods, it has better results. It can suppress the influence of multi-noise environment on laser stripe extraction and extract subpixel centers of laser fringes accurately. It has good robustness. The algorithm provides a reference for extracting the center of laser fringes accurately.
2020, 44(2): 196-201.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.010
Abstract:
In order to develop fluorescent microscope that can simultaneously take into account super-resolution, fast imaging and field of view, and promote its application in imaging of living cells or micro-dynamic processes, the compressed sensing was applied to super-resolution fluorescence microscopy. The algorithm of gradient projection for sparse reconstruction was used to reconstruct single fluorescence wide field image. Theoretical analysis, simulation and experimental verification were carried out. The results show that, this method can break through the optical diffraction limit. The imaging resolution is 180nm. Compared with the diffraction limit, it is 1.8 times higher. Compressed sensing can realize single-frame wide-field super-resolution fluorescence microscopy imaging. Compared with the existing methods, the imaging speed has been greatly improved.
In order to develop fluorescent microscope that can simultaneously take into account super-resolution, fast imaging and field of view, and promote its application in imaging of living cells or micro-dynamic processes, the compressed sensing was applied to super-resolution fluorescence microscopy. The algorithm of gradient projection for sparse reconstruction was used to reconstruct single fluorescence wide field image. Theoretical analysis, simulation and experimental verification were carried out. The results show that, this method can break through the optical diffraction limit. The imaging resolution is 180nm. Compared with the diffraction limit, it is 1.8 times higher. Compressed sensing can realize single-frame wide-field super-resolution fluorescence microscopy imaging. Compared with the existing methods, the imaging speed has been greatly improved.
2020, 44(2): 202-205.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.011
Abstract:
In order to study the forming mechanism of molten pool and heat-affected zone in the preparation of amorphous alloys by laser additive manufacturing, finite element software ANSYS was used. The thermal effect of laser rapid melting Zr65Al7.5Ni10Cu17.5 amorphous alloy was numerically simulated and analyzed. The simulation results show that, average cooling rate of molten pool is 6.3×104K/s when laser solidification is carried out at single point. Average cooling rate in heat affected zone is 1.4×104K/s, much higher than 1.5K/s of critical cooling rate of Zr65Al7.5Ni10Cu17.5 amorphous alloy. The thermal change of single-point laser melting meets the growth conditions of amorphous alloys. In the process of single-channel laser melting, average cooling rate of molten pool is 2.11×102K/s, still relatively high. However, average cooling rate of heat affected zone is 74K/s and low. In addition, relaxation accumulation occurs in the heat-affected zone. It may cause a certain degree of crystallization. This study provides theoretical basis for thermal effect of amorphous alloys prepared by laser additive manufacturing.
In order to study the forming mechanism of molten pool and heat-affected zone in the preparation of amorphous alloys by laser additive manufacturing, finite element software ANSYS was used. The thermal effect of laser rapid melting Zr65Al7.5Ni10Cu17.5 amorphous alloy was numerically simulated and analyzed. The simulation results show that, average cooling rate of molten pool is 6.3×104K/s when laser solidification is carried out at single point. Average cooling rate in heat affected zone is 1.4×104K/s, much higher than 1.5K/s of critical cooling rate of Zr65Al7.5Ni10Cu17.5 amorphous alloy. The thermal change of single-point laser melting meets the growth conditions of amorphous alloys. In the process of single-channel laser melting, average cooling rate of molten pool is 2.11×102K/s, still relatively high. However, average cooling rate of heat affected zone is 74K/s and low. In addition, relaxation accumulation occurs in the heat-affected zone. It may cause a certain degree of crystallization. This study provides theoretical basis for thermal effect of amorphous alloys prepared by laser additive manufacturing.
2020, 44(2): 206-211.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.012
Abstract:
In order to study effect of fluorescence decay of ethyl acetate in the simulated liquor environment, the steady-state and time-resolved fluorescence spectra of ethyl acetate ethanol aqueous solution with different volume fractions were measured. Combined with quantum chemical calculation, experimental measurements and theoretical analysis were carried out. The results show that, for ethyl and acetate, there are two fluorescence peaks at 407nm and 431nm, respectively. Fluorescence lifetime is about 1.4ns. There are two fluorescence lifetimes in the decay process of ethyl acetate ethanol aqueous solution with different volume fractions. The short-life component is ethyl acetate. The long-life component is polymer structure formed by ethyl acetate, ethanol and water molecules. Intermolecular interaction in the structure of the polymer improves the planarity of ethyl acetate. This is conducive to radiation transition. Water molecules connect ethyl acetate and ethanol through hydrogen bonds and van der Waals forces to form layered structures, block the movement of the fluorescent body, reduce non-radiative transitions, and prolong fluorescence lifetime. This result is helpful to enrich the detection methods of organic compounds in liquor. It is also helpful to study the changes of molecular conformation and spectral characteristics in solvent environment.
In order to study effect of fluorescence decay of ethyl acetate in the simulated liquor environment, the steady-state and time-resolved fluorescence spectra of ethyl acetate ethanol aqueous solution with different volume fractions were measured. Combined with quantum chemical calculation, experimental measurements and theoretical analysis were carried out. The results show that, for ethyl and acetate, there are two fluorescence peaks at 407nm and 431nm, respectively. Fluorescence lifetime is about 1.4ns. There are two fluorescence lifetimes in the decay process of ethyl acetate ethanol aqueous solution with different volume fractions. The short-life component is ethyl acetate. The long-life component is polymer structure formed by ethyl acetate, ethanol and water molecules. Intermolecular interaction in the structure of the polymer improves the planarity of ethyl acetate. This is conducive to radiation transition. Water molecules connect ethyl acetate and ethanol through hydrogen bonds and van der Waals forces to form layered structures, block the movement of the fluorescent body, reduce non-radiative transitions, and prolong fluorescence lifetime. This result is helpful to enrich the detection methods of organic compounds in liquor. It is also helpful to study the changes of molecular conformation and spectral characteristics in solvent environment.
2020, 44(2): 212-216.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.013
Abstract:
In order to improve the surface corrosion resistance of AISI430 ferritic stainless steel, laser shock peening(LSP) was used to strengthen AISI430 ferritic stainless steel. Polarization curves and electrochemical impedance spectroscopy were used to study the effect of laser shock processing on corrosion resistance of AISI430 ferritic stainless steel, combined with surface residual stress and corrosion morphology of the specimens. The results show that, residual compressive stress layer appears on specimens surface after strengthening treatment. The maximum residual stress is -339MPa. The depth direction is extended to 900μm in a nearly decreasing manner. Self corrosion potential of the sample in NaCl solution increases from -251mV to -192mV. Corrosion current density can be reduced by 28.18μA/cm-2 at most. It enlarges the radius of capacitive arc of impedance spectrum. Corrosion pits and strip corrosion are reduced. LSP strengthens corrosion resistance of AISI430 ferritic stainless steel in NaCl solution.
In order to improve the surface corrosion resistance of AISI430 ferritic stainless steel, laser shock peening(LSP) was used to strengthen AISI430 ferritic stainless steel. Polarization curves and electrochemical impedance spectroscopy were used to study the effect of laser shock processing on corrosion resistance of AISI430 ferritic stainless steel, combined with surface residual stress and corrosion morphology of the specimens. The results show that, residual compressive stress layer appears on specimens surface after strengthening treatment. The maximum residual stress is -339MPa. The depth direction is extended to 900μm in a nearly decreasing manner. Self corrosion potential of the sample in NaCl solution increases from -251mV to -192mV. Corrosion current density can be reduced by 28.18μA/cm-2 at most. It enlarges the radius of capacitive arc of impedance spectrum. Corrosion pits and strip corrosion are reduced. LSP strengthens corrosion resistance of AISI430 ferritic stainless steel in NaCl solution.
2020, 44(2): 217-220.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.014
Abstract:
Raman spectroscopy was nondestructive and rapid method for the determination of substance composition. In order to improve the sensitivity of monitoring, the cavity-enhanced spontaneous Raman scattering of 408nm band semiconductor laser was studied. 408nm semiconductor laser with output power of 500mW and linewidth of 0.9nm was used as excitation light. The laser was coupled into confocal spherical mirror cavity. The reflectivity of two-sided confocal spherical mirrors was 96.5% and 99.5%, respectively. Some lasers returned to the semiconductor laser to form optical feedback. Semiconductor laser resonated with confocal cavity. The optical feedback process of the device was discussed. The mode matching and frequency matching of the external cavity were analyzed respectively. The results show that, the power in the confocal cavity reaches 15W. The power is increased by 30 times. Raman signals are collected with 90° probe configuration. Air Raman signal detection has been completed. 900 counts of N2 signal are obtained in 1s integration time. The results show that the resonance enhanced cavity greatly enhances the Raman scattering signal and has the potential to be used in the on-line detection or high-sensitivity detection of a variety of gases.
Raman spectroscopy was nondestructive and rapid method for the determination of substance composition. In order to improve the sensitivity of monitoring, the cavity-enhanced spontaneous Raman scattering of 408nm band semiconductor laser was studied. 408nm semiconductor laser with output power of 500mW and linewidth of 0.9nm was used as excitation light. The laser was coupled into confocal spherical mirror cavity. The reflectivity of two-sided confocal spherical mirrors was 96.5% and 99.5%, respectively. Some lasers returned to the semiconductor laser to form optical feedback. Semiconductor laser resonated with confocal cavity. The optical feedback process of the device was discussed. The mode matching and frequency matching of the external cavity were analyzed respectively. The results show that, the power in the confocal cavity reaches 15W. The power is increased by 30 times. Raman signals are collected with 90° probe configuration. Air Raman signal detection has been completed. 900 counts of N2 signal are obtained in 1s integration time. The results show that the resonance enhanced cavity greatly enhances the Raman scattering signal and has the potential to be used in the on-line detection or high-sensitivity detection of a variety of gases.
2020, 44(2): 221-225.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.015
Abstract:
In order to realize the accurate and continuous detection of SO2 in air by SO2 analyzer, and solve the problems of weak light convergence effect, large aberration and longer optical path of fluorescence acquisition due to the lengthening of focal length of lens in traditional sulfur dioxide detector when fluorescence converges, on the basis of traditional instruments, the optical path of fluorescence acquisition was redesigned and optimized. The method of decomposition of light focus was used to improve the spherical aberration of the system. Theoretical analysis and experimental verification were carried out. After the improvement, ZEMAX simulation was carried out and orthogonal method was used to correct the new optical path. By simulating the non-sequential structured shadow model of two light paths, the illumination map of the detection viewer and the point chart, experimental data of light intensity and spot diameter were obtained. The results show that, the peak-to-radial intensity of the optimized optical system reaches 219.41W/cm2. The diameter of the speckle is reduced by 17%. This scheme can effectively solve the shortcomings of traditional optical path and the imaging quality is better.
In order to realize the accurate and continuous detection of SO2 in air by SO2 analyzer, and solve the problems of weak light convergence effect, large aberration and longer optical path of fluorescence acquisition due to the lengthening of focal length of lens in traditional sulfur dioxide detector when fluorescence converges, on the basis of traditional instruments, the optical path of fluorescence acquisition was redesigned and optimized. The method of decomposition of light focus was used to improve the spherical aberration of the system. Theoretical analysis and experimental verification were carried out. After the improvement, ZEMAX simulation was carried out and orthogonal method was used to correct the new optical path. By simulating the non-sequential structured shadow model of two light paths, the illumination map of the detection viewer and the point chart, experimental data of light intensity and spot diameter were obtained. The results show that, the peak-to-radial intensity of the optimized optical system reaches 219.41W/cm2. The diameter of the speckle is reduced by 17%. This scheme can effectively solve the shortcomings of traditional optical path and the imaging quality is better.
2020, 44(2): 226-231.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.016
Abstract:
In order to study the characteristics of magneto-optical imaging of laser welding cracks under rotating magnetic field excitation in frequency domain, the method of 2-D discrete Fourier transform for magneto-optical image of laser welding crack was adopted. Theoretical analysis and experimental verification were carried out. Spectrum data of laser welding crack under different excitation intensities of rotating magnetic field were obtained. Combining spatial characteristics of crack magneto-optic maps, statistical analysis was carried out on the points whose gray value of crack spectrum was 255. The results show that, frequency domain characteristics of magneto-optic image of laser welding crack have a certain corresponding relationship with spatial domain characteristics. During a period of change (885 frames of magneto-optic map), the corresponding spectrum map will be a process of first decreasing, then enlarging, then decreasing, then enlarging or the opposite, and finally returning to the initial state. The results verify the correctness of magneto-optical imaging law of cracks under rotating magnetic field. It is helpful for non-destructive detection of laser welding defects.
In order to study the characteristics of magneto-optical imaging of laser welding cracks under rotating magnetic field excitation in frequency domain, the method of 2-D discrete Fourier transform for magneto-optical image of laser welding crack was adopted. Theoretical analysis and experimental verification were carried out. Spectrum data of laser welding crack under different excitation intensities of rotating magnetic field were obtained. Combining spatial characteristics of crack magneto-optic maps, statistical analysis was carried out on the points whose gray value of crack spectrum was 255. The results show that, frequency domain characteristics of magneto-optic image of laser welding crack have a certain corresponding relationship with spatial domain characteristics. During a period of change (885 frames of magneto-optic map), the corresponding spectrum map will be a process of first decreasing, then enlarging, then decreasing, then enlarging or the opposite, and finally returning to the initial state. The results verify the correctness of magneto-optical imaging law of cracks under rotating magnetic field. It is helpful for non-destructive detection of laser welding defects.
2020, 44(2): 232-236.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.017
Abstract:
In quantitative analysis of carbon content in coal samples, matrix effect has great influence and prediction accuracy is low. In order to solve this problem, under the optimum experimental conditions, spectral data of 14 standard coal samples after laser-induced breakdown spectroscopy (LIBS) test were obtained. C Ⅰ 193.09nm wavelength with good independence and without interference from adjacent spectral lines was selected. Integral strength was taken as input variable. Basic curve calibration method and neural network calibration method were used to carry out quantitative analysis of coal samples. The results show that, when basic calibration curve method is used, it is greatly affected by noise interference and matrix effect. Average relative error is 15.39%. When neural network calibration method is used, relative error of the validated samples decreases by 7.54% on average. Neural network calibration method can effectively reduce the quantitative analysis error and improve the ability of LIBS to predict carbon content in coal. This study can provide guidance for quantitative analysis of carbon content in coal.
In quantitative analysis of carbon content in coal samples, matrix effect has great influence and prediction accuracy is low. In order to solve this problem, under the optimum experimental conditions, spectral data of 14 standard coal samples after laser-induced breakdown spectroscopy (LIBS) test were obtained. C Ⅰ 193.09nm wavelength with good independence and without interference from adjacent spectral lines was selected. Integral strength was taken as input variable. Basic curve calibration method and neural network calibration method were used to carry out quantitative analysis of coal samples. The results show that, when basic calibration curve method is used, it is greatly affected by noise interference and matrix effect. Average relative error is 15.39%. When neural network calibration method is used, relative error of the validated samples decreases by 7.54% on average. Neural network calibration method can effectively reduce the quantitative analysis error and improve the ability of LIBS to predict carbon content in coal. This study can provide guidance for quantitative analysis of carbon content in coal.
2020, 44(2): 237-243.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.018
Abstract:
In order to study the effective evaluation of speckle image quality in digital image correlation method, the quality of speckle pattern was effectively evaluated by means of the second derivative of average gray level of quality characterization parameter of speckle pattern. By analyzing the relationship between image interpolation error and the distribution of image gray information, the relationship between the second derivative of average gray level of speckle pattern and the distribution form of gray level information of speckle pattern was pointed out. In order to verify the validity of the quality characterization parameters of the speckle pattern, Fourier transform was used to translate the speckle pattern. The sub-pixel displacement of speckle pattern before and after translation was calculated by Newton-Raphson method. According to the displacement calculation results, speckle pattern with low average gray second derivative corresponded to small displacement measurement error. The results show that, the second derivative of average gray level is effective in the quality evaluation of speckle pattern. In practical application, the quality of speckle pattern should be evaluated comprehensively and effectively by combining the second derivative of average gray level and average gray gradient of speckle pattern. This study provides a reference for the preparation and selection of high quality speckle patterns.
In order to study the effective evaluation of speckle image quality in digital image correlation method, the quality of speckle pattern was effectively evaluated by means of the second derivative of average gray level of quality characterization parameter of speckle pattern. By analyzing the relationship between image interpolation error and the distribution of image gray information, the relationship between the second derivative of average gray level of speckle pattern and the distribution form of gray level information of speckle pattern was pointed out. In order to verify the validity of the quality characterization parameters of the speckle pattern, Fourier transform was used to translate the speckle pattern. The sub-pixel displacement of speckle pattern before and after translation was calculated by Newton-Raphson method. According to the displacement calculation results, speckle pattern with low average gray second derivative corresponded to small displacement measurement error. The results show that, the second derivative of average gray level is effective in the quality evaluation of speckle pattern. In practical application, the quality of speckle pattern should be evaluated comprehensively and effectively by combining the second derivative of average gray level and average gray gradient of speckle pattern. This study provides a reference for the preparation and selection of high quality speckle patterns.
2020, 44(2): 244-249.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.019
Abstract:
In order to solve the problem that point clouds of intersecting and crossing lines may be difficult to deal with, insulator point clouds are difficult to be segmented, and the existing algorithm models are incomplete, fast extraction and reconstruction method of power line based on point cloud data features was adopted. Firstly, fast rough classification of point clouds was carried out based on voxel grid elevation characteristics of transmission lines. Then point cloud was refined rapidly by using random consistency algorithm. Point cloud of power line was extracted efficiently and accurately by filtering algorithm taking into account cross-line. In view of local linear model of power line, insulators were segmented. Finally, the local weighted centroid method was used to extract the key points of power line. Fast reconstruction of power line was realized. Theoretical analysis and experimental verification were carried out. Good experimental results were obtained. The results show that, overall accuracy of power line extraction and reconstruction is 95.3%. Total time consumed is less than 2.5s. The speed, accuracy and robustness of the algorithm are verified. This result is helpful to extract and reconstruct point cloud of power line.
In order to solve the problem that point clouds of intersecting and crossing lines may be difficult to deal with, insulator point clouds are difficult to be segmented, and the existing algorithm models are incomplete, fast extraction and reconstruction method of power line based on point cloud data features was adopted. Firstly, fast rough classification of point clouds was carried out based on voxel grid elevation characteristics of transmission lines. Then point cloud was refined rapidly by using random consistency algorithm. Point cloud of power line was extracted efficiently and accurately by filtering algorithm taking into account cross-line. In view of local linear model of power line, insulators were segmented. Finally, the local weighted centroid method was used to extract the key points of power line. Fast reconstruction of power line was realized. Theoretical analysis and experimental verification were carried out. Good experimental results were obtained. The results show that, overall accuracy of power line extraction and reconstruction is 95.3%. Total time consumed is less than 2.5s. The speed, accuracy and robustness of the algorithm are verified. This result is helpful to extract and reconstruct point cloud of power line.
2020, 44(2): 250-254.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.020
Abstract:
In order to study thermodynamic effect of 1070nm continwous wave fiber laser on three-junction GaAs solar cells, physical model was built by COMSOL software and numerical simulation was carried out. Thermal stress fields under different laser power densities were obtained. In order to verify the correctness of thermal stress calculation method, surface deformation of batteries under laser irradiation with power of 16.7W, irradiation radius of 1mm and irradiation time of 10s was measured by grating projection method. The simulation results show that, when irradiation radius is 1.5cm and power density is 16.7W/cm2, laser irradiation time is 20s, central temperature of bottom battery is just above service temperature of the battery. Equivalent stress in the center of bottom battery is 96.6MPa. It just exceeds the yield limit of bottom battery material. According to this result, it can be inferred that the failure of battery is related to the structural damage caused by thermal stress. The experimental results are in good agreement with the simulation results. The numerical simulation results and experimental results provide theoretical basis for the study of thermal effects of laser irradiated solar cells.
In order to study thermodynamic effect of 1070nm continwous wave fiber laser on three-junction GaAs solar cells, physical model was built by COMSOL software and numerical simulation was carried out. Thermal stress fields under different laser power densities were obtained. In order to verify the correctness of thermal stress calculation method, surface deformation of batteries under laser irradiation with power of 16.7W, irradiation radius of 1mm and irradiation time of 10s was measured by grating projection method. The simulation results show that, when irradiation radius is 1.5cm and power density is 16.7W/cm2, laser irradiation time is 20s, central temperature of bottom battery is just above service temperature of the battery. Equivalent stress in the center of bottom battery is 96.6MPa. It just exceeds the yield limit of bottom battery material. According to this result, it can be inferred that the failure of battery is related to the structural damage caused by thermal stress. The experimental results are in good agreement with the simulation results. The numerical simulation results and experimental results provide theoretical basis for the study of thermal effects of laser irradiated solar cells.
2020, 44(2): 255-260.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.021
Abstract:
In order to analyze and accurately predict the performance of semiconductor optical amplifiers, an effective mathematical model of InP-InGaAsP uniformly buried semiconductor optical amplifier was established. Considering the relationship between spontaneous and stimulated radiation, the effects of bias current and input power on gain and noise index were analyzed by real-time simulation. The results show that, when the bias current is 120mA and the input power is -10dBm, semiconductor optical amplifier has the best performance. The model can provide some reference for the design of semiconductor optical amplifier.
In order to analyze and accurately predict the performance of semiconductor optical amplifiers, an effective mathematical model of InP-InGaAsP uniformly buried semiconductor optical amplifier was established. Considering the relationship between spontaneous and stimulated radiation, the effects of bias current and input power on gain and noise index were analyzed by real-time simulation. The results show that, when the bias current is 120mA and the input power is -10dBm, semiconductor optical amplifier has the best performance. The model can provide some reference for the design of semiconductor optical amplifier.
2020, 44(2): 261-265.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.022
Abstract:
In visible light communications, multipath effects and channel attenuation in traditional orthogonal frequency division multiplexing (OFDM) systems can generate intersymbol interference and reduce system reliability. In order to guarantee the quality of communication, OFDM system with cyclic prefix was used to resist the symbolic interference caused by multipath effect. In order to reduce bit error rate(BER) and peak-to-average power ratio(PAPR) of the system, Haar wavelet was used to optimize the performance of system parameters such as validity, reliability and PAPR. Monte Carlo method was used to verify the simulation results. The results show that, when bit error rate of the system is 10-4, BER performance of discrete wavelet transform OFDM system is about 5dB higher than that of fast Fourier transform OFDM (FFT-OFDM) system. Communication efficiency has been improved by about 11%. When PAPR of the system is 5dB, complementary cumulative distribution function (CCDF) of FFT-OFDM system is close to 10-2. CCDF value of DWT-OFDM system is 0. This study provides a reference for OFDM communication based on visible light wavelet transform.
In visible light communications, multipath effects and channel attenuation in traditional orthogonal frequency division multiplexing (OFDM) systems can generate intersymbol interference and reduce system reliability. In order to guarantee the quality of communication, OFDM system with cyclic prefix was used to resist the symbolic interference caused by multipath effect. In order to reduce bit error rate(BER) and peak-to-average power ratio(PAPR) of the system, Haar wavelet was used to optimize the performance of system parameters such as validity, reliability and PAPR. Monte Carlo method was used to verify the simulation results. The results show that, when bit error rate of the system is 10-4, BER performance of discrete wavelet transform OFDM system is about 5dB higher than that of fast Fourier transform OFDM (FFT-OFDM) system. Communication efficiency has been improved by about 11%. When PAPR of the system is 5dB, complementary cumulative distribution function (CCDF) of FFT-OFDM system is close to 10-2. CCDF value of DWT-OFDM system is 0. This study provides a reference for OFDM communication based on visible light wavelet transform.
2020, 44(2): 266-270.
doi: 10.7510/jgjs.issn.1001-3806.2020.02.023
Abstract:
In order to meet the requirement of low volume fraction SO2 gas detection in grid atmospheric monitoring, aiming at the key problem of optical path in modular application of ultraviolet fluorescence method, object telecentric optical system was combined with double-plane-convex optical system to apply the excitation and acquisition paths of SO2 detection module. Theoretical analysis and experimental verification were carried out by complementary advantages of multi-optical systems. Through the establishment of the model, the influence of optical system on signal-to-noise ratio of reaction chamber was analyzed. Combining ZEMAX software simulation, Monte Carlo tolerance evaluation analysis and indirect experimental verification of the whole optical system, the application of the optimized optical system was achieved. The results show that, the square of correlation coefficient of instrument linearity can reach 0.9999. The optical system has strong application value. It can provide theoretical basis and experimental data support for the design of modular optical system of ultraviolet fluorescence method.
In order to meet the requirement of low volume fraction SO2 gas detection in grid atmospheric monitoring, aiming at the key problem of optical path in modular application of ultraviolet fluorescence method, object telecentric optical system was combined with double-plane-convex optical system to apply the excitation and acquisition paths of SO2 detection module. Theoretical analysis and experimental verification were carried out by complementary advantages of multi-optical systems. Through the establishment of the model, the influence of optical system on signal-to-noise ratio of reaction chamber was analyzed. Combining ZEMAX software simulation, Monte Carlo tolerance evaluation analysis and indirect experimental verification of the whole optical system, the application of the optimized optical system was achieved. The results show that, the square of correlation coefficient of instrument linearity can reach 0.9999. The optical system has strong application value. It can provide theoretical basis and experimental data support for the design of modular optical system of ultraviolet fluorescence method.
