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RSS2022 Vol. 46, No. 6
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2022, 46(6): 713-721.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.001
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Abstract:
In order to study the effects of alkali vapor ionization on the scaling potential of diode pumped alkali lasers (DPAL), a photocurrent method suiting for measuring the ionization degree of alkali vapor that pumped by a short-pulse laser has been established. By using the photocurrent method, ionization degree of cesium vapor was measured versus different power density of pump laser, temperature of alkali cell, and repetition frequency of the pump laser. Experimental results show that the ionization degree of cesium vapor is merely around 1% even if the power density of the pump laser has reached 3×108W/cm2 in the case of temperature of alkali cell is around 150℃ and pressure of helium buffer gas is about 9.33×104Pa with no heat effects. Moreover, the variation of ionization degree of cesium vapor is minor relative to the obvious increase of the number density of cesium vapor when the temperature of alkali cell rises from 122℃ to 163℃. These results indicates important signification for cesium DPAL scaling by increasing the power density of pump laser and the temperature of alkali cell.
In order to study the effects of alkali vapor ionization on the scaling potential of diode pumped alkali lasers (DPAL), a photocurrent method suiting for measuring the ionization degree of alkali vapor that pumped by a short-pulse laser has been established. By using the photocurrent method, ionization degree of cesium vapor was measured versus different power density of pump laser, temperature of alkali cell, and repetition frequency of the pump laser. Experimental results show that the ionization degree of cesium vapor is merely around 1% even if the power density of the pump laser has reached 3×108W/cm2 in the case of temperature of alkali cell is around 150℃ and pressure of helium buffer gas is about 9.33×104Pa with no heat effects. Moreover, the variation of ionization degree of cesium vapor is minor relative to the obvious increase of the number density of cesium vapor when the temperature of alkali cell rises from 122℃ to 163℃. These results indicates important signification for cesium DPAL scaling by increasing the power density of pump laser and the temperature of alkali cell.
2022, 46(6): 722-728.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.002
Abstract:
The progress of quantum information technology depends to a large extent on the maturity and development of traditional materials. In recent years, lithium niobate has become an important building-block material for quantum devices, which have great application potential in the field of quantum science and technology. The technical progress of various lithium niobate quantum devices such as quantum emitters, quantum repeaters, and single photon detector prepared based on lithium niobate materials has been combed. The advantages and disadvantages of these devices were summarized, and their main development trends in the future were prospected. This study has a good guiding role for the practical application of quantum devices based on lithium niobate in quantum information technology.
The progress of quantum information technology depends to a large extent on the maturity and development of traditional materials. In recent years, lithium niobate has become an important building-block material for quantum devices, which have great application potential in the field of quantum science and technology. The technical progress of various lithium niobate quantum devices such as quantum emitters, quantum repeaters, and single photon detector prepared based on lithium niobate materials has been combed. The advantages and disadvantages of these devices were summarized, and their main development trends in the future were prospected. This study has a good guiding role for the practical application of quantum devices based on lithium niobate in quantum information technology.
2022, 46(6): 729-735.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.003
Abstract:
In order to investigate the influence of the nonlinear characteristics of thermal effects of optical components on the beam quality irradiated by high-power laser beam, based on the basic theories of heat conduction, thermoelasticity, and physical optics, etc., with the help of finite element analysis, the temperature field and displacement field of optical components irradiated by high-power continuous-wave laser (the power density is approximately 500kW/cm2) were presented. The influences of various parameters on the thermal effects of optical components were analyzed and compared. Moreover, the nonlinear thermal effects under different conditions were discussed. The results show that the thermal, mechanical, and optical absorption of optical components irradiated by high-power continuous-wave laser present nonlinear effects, and the strengths of these nonlinear effects depend on the materials of the optical components, and the spot shape of the laser beam. When fused silica sample is irradiated by Gaussian laser and the absorption rate is 100×10-6, the nonlinearity without the physical parameters and temperature boundary condition will cause 16% and 10% relative errors for the maximum surface temperature rise and the peak-to-valley surface deformation, respectively. The results presented in this paper is expected to provide some new clues for the related research.
In order to investigate the influence of the nonlinear characteristics of thermal effects of optical components on the beam quality irradiated by high-power laser beam, based on the basic theories of heat conduction, thermoelasticity, and physical optics, etc., with the help of finite element analysis, the temperature field and displacement field of optical components irradiated by high-power continuous-wave laser (the power density is approximately 500kW/cm2) were presented. The influences of various parameters on the thermal effects of optical components were analyzed and compared. Moreover, the nonlinear thermal effects under different conditions were discussed. The results show that the thermal, mechanical, and optical absorption of optical components irradiated by high-power continuous-wave laser present nonlinear effects, and the strengths of these nonlinear effects depend on the materials of the optical components, and the spot shape of the laser beam. When fused silica sample is irradiated by Gaussian laser and the absorption rate is 100×10-6, the nonlinearity without the physical parameters and temperature boundary condition will cause 16% and 10% relative errors for the maximum surface temperature rise and the peak-to-valley surface deformation, respectively. The results presented in this paper is expected to provide some new clues for the related research.
2022, 46(6): 736-741.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.004
Abstract:
In order to evaluate the hole shape characteristics in femtosecond laser drilling of SiC/SiC composite, an experimental study has been conducted on 4mm thick specimen using beam concentric scanning mode. The effect of process parameters on entry diameter, hole depth, and hole taper has been analyzed. The results show that pulse energy, pulse frequency, line overlap ratio, and scanning speed have almost no influence on entry diameter. However, these factors significantly affect hole depth and hole taper. The pulse energy, pulse frequency, line overlap ratio, and scanning speed markedly influence energy density per unit area that during scanning of the laser beam. Higher energy density results in lower hole taper and greater hole depth. The experiment reached a minimum taper angle of 12.38° using the maximum pulse energy 130μJ, maximum repetition frequency 100kHz, minimum scanning speed 100mm/s, maximum line overlap 77% and minimum feed distance 0.1mm. It is concluded that the taper angle can hardly be controlled because the upper material will shelter part of the laser beam and there is difficulty to evacuate chips. This study can provide a reference for the future application of ultra-short pulse laser drilling of SiC/SiC composites.
In order to evaluate the hole shape characteristics in femtosecond laser drilling of SiC/SiC composite, an experimental study has been conducted on 4mm thick specimen using beam concentric scanning mode. The effect of process parameters on entry diameter, hole depth, and hole taper has been analyzed. The results show that pulse energy, pulse frequency, line overlap ratio, and scanning speed have almost no influence on entry diameter. However, these factors significantly affect hole depth and hole taper. The pulse energy, pulse frequency, line overlap ratio, and scanning speed markedly influence energy density per unit area that during scanning of the laser beam. Higher energy density results in lower hole taper and greater hole depth. The experiment reached a minimum taper angle of 12.38° using the maximum pulse energy 130μJ, maximum repetition frequency 100kHz, minimum scanning speed 100mm/s, maximum line overlap 77% and minimum feed distance 0.1mm. It is concluded that the taper angle can hardly be controlled because the upper material will shelter part of the laser beam and there is difficulty to evacuate chips. This study can provide a reference for the future application of ultra-short pulse laser drilling of SiC/SiC composites.
2022, 46(6): 742-748.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.005
Abstract:
In order to study the effect and mechanism of post-treatment on the microstructure and properties of medium entropy alloy in CoCrNi, the medium-entropy alloy in Co0.3288-Cr0.3288-Ni0.3288-Mo0.0136 was prepared by laser deposition. The microstructure and properties of medium-entropy alloy in CoCrNiMo0.0136 under laser deposition, hot forging and hot forging sandblasting were characterized by optical microscope, scanning electron microscope, X-ray diffractometer, electron backscatter diffraction, 3-D surface profilometer, and universal tensile testing machine. The results show that the medium-entropy alloy in laser deposited CoCrNiMo0.0136 has stable face-centered cubic structure after as-deposited, hot-forging, and hot-forging sandblasting. In the deposited state, the grain size of alloy is coarse, because of microsegregation, there is a substructure with uneven distribution of elements in the grain, and the strength of the alloy is low, but the plasticity is good. After hot forging treatment, the grain size of alloy is significantly refined, and more annealing twins can be observed. Compared with the laser deposited state, the yield strength is increased by 132.88%, the tensile strength is increased by 53.78%, and the elongation has no obvious change. After the hot forging sample was sandblasted, the surface of the sample showed a gradient nanostructure with a thickness of about 100μm, and there were a large number of nano-twins in the plastic deformation layer, the yield strength and tensile strength increased by 220.09% and 96.22% respectively, and the elongation did not change significantly. Through thermoplastic processing and preparation of nano-gradient surface structure, the static properties of medium-entropy alloy in Mo-doped CoCrNi can be effectively improved.
In order to study the effect and mechanism of post-treatment on the microstructure and properties of medium entropy alloy in CoCrNi, the medium-entropy alloy in Co0.3288-Cr0.3288-Ni0.3288-Mo0.0136 was prepared by laser deposition. The microstructure and properties of medium-entropy alloy in CoCrNiMo0.0136 under laser deposition, hot forging and hot forging sandblasting were characterized by optical microscope, scanning electron microscope, X-ray diffractometer, electron backscatter diffraction, 3-D surface profilometer, and universal tensile testing machine. The results show that the medium-entropy alloy in laser deposited CoCrNiMo0.0136 has stable face-centered cubic structure after as-deposited, hot-forging, and hot-forging sandblasting. In the deposited state, the grain size of alloy is coarse, because of microsegregation, there is a substructure with uneven distribution of elements in the grain, and the strength of the alloy is low, but the plasticity is good. After hot forging treatment, the grain size of alloy is significantly refined, and more annealing twins can be observed. Compared with the laser deposited state, the yield strength is increased by 132.88%, the tensile strength is increased by 53.78%, and the elongation has no obvious change. After the hot forging sample was sandblasted, the surface of the sample showed a gradient nanostructure with a thickness of about 100μm, and there were a large number of nano-twins in the plastic deformation layer, the yield strength and tensile strength increased by 220.09% and 96.22% respectively, and the elongation did not change significantly. Through thermoplastic processing and preparation of nano-gradient surface structure, the static properties of medium-entropy alloy in Mo-doped CoCrNi can be effectively improved.
2022, 46(6): 749-754.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.006
Abstract:
Water-laser coupling transmission efficiency is the premise and efficiency guarantee of water-jet guided laser machinability. In order to study the law of water-laser coupling energy transmission in water-jet guided laser, and to obtain high laser power transmission efficiency and uniform laser power density distribution in water beam, by using ray tracing theory and physical optics propagation method, the simulation analysis of the focused beam characteristics at 1064nm and the speckle beam pattern after coupling were carried out. And the laser power transmission efficiency under different water beam length, the distribution of laser power density under different power, pressure and water beam length were tested and analyzed systematically. The results show that the power transmission efficiency of 1064nm laser increases with the decrease of the water beam length, and the power transmission efficiency can reach 63.6% when the water beam length is 20mm. The variation of laser power has the greatest influence on the distribution of laser power density in water beam. When the laser power is constant, the increase of water pressure is beneficial to the uniform distribution of laser power density in the stable length of water beam, and the decrease of coupled water beam length can improve laser transmission efficiency. The research results provide some guidance for improving the energy utilization rate of water guided laser.
Water-laser coupling transmission efficiency is the premise and efficiency guarantee of water-jet guided laser machinability. In order to study the law of water-laser coupling energy transmission in water-jet guided laser, and to obtain high laser power transmission efficiency and uniform laser power density distribution in water beam, by using ray tracing theory and physical optics propagation method, the simulation analysis of the focused beam characteristics at 1064nm and the speckle beam pattern after coupling were carried out. And the laser power transmission efficiency under different water beam length, the distribution of laser power density under different power, pressure and water beam length were tested and analyzed systematically. The results show that the power transmission efficiency of 1064nm laser increases with the decrease of the water beam length, and the power transmission efficiency can reach 63.6% when the water beam length is 20mm. The variation of laser power has the greatest influence on the distribution of laser power density in water beam. When the laser power is constant, the increase of water pressure is beneficial to the uniform distribution of laser power density in the stable length of water beam, and the decrease of coupled water beam length can improve laser transmission efficiency. The research results provide some guidance for improving the energy utilization rate of water guided laser.
2022, 46(6): 755-759.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.007
Abstract:
In order to improve the performance of the He-Ne laser in the laser feedback measurement system, and solve the technical problem that the frequency cannot be stabilized by traditional methods when the laser feedback mirror is constantly moving, a closed-loop passive frequency stabilization system method based on temperature feedback was adopted to control the temperature of the laser tube, and the theoretical analysis and experimental verification was conducted. The stability of the system under different stabilization temperature and ambient temperature difference was studied. The experimental results show that the best temperature difference of the system is 25.6℃. After frequency stabilization under this temperature difference, the He-Ne laser's wavelength fluctuation range is 10-4, that is, the frequency stability reaches 1.61×10-7, and power drift is less that 3.20%. The system can adjust the frequency stabilization temperature point according to the change of the ambient temperature, and the frequency stabilization structure is simple, meet the requirements of laser feedback for general application system stability.
In order to improve the performance of the He-Ne laser in the laser feedback measurement system, and solve the technical problem that the frequency cannot be stabilized by traditional methods when the laser feedback mirror is constantly moving, a closed-loop passive frequency stabilization system method based on temperature feedback was adopted to control the temperature of the laser tube, and the theoretical analysis and experimental verification was conducted. The stability of the system under different stabilization temperature and ambient temperature difference was studied. The experimental results show that the best temperature difference of the system is 25.6℃. After frequency stabilization under this temperature difference, the He-Ne laser's wavelength fluctuation range is 10-4, that is, the frequency stability reaches 1.61×10-7, and power drift is less that 3.20%. The system can adjust the frequency stabilization temperature point according to the change of the ambient temperature, and the frequency stabilization structure is simple, meet the requirements of laser feedback for general application system stability.
2022, 46(6): 760-766.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.008
Abstract:
Fiber optic sensing technology is a kind of sensing technology emerging in recent years, which has received extensive attention and research in many fields. The main progress of optical fiber shape sensing technology was summarized, and the basic principle of fiber shape sensing technology based on fiber grating sensing and distributed sensing was discussed. The theoretical framework of shape reconstruction (Frenet-Serret formula) was introduced, and the key problems in the research of distributed fiber shape sensing technology were summarized and discussed. On this basis, the research prospect of distributed fiber shape sensing technology is prospected.
Fiber optic sensing technology is a kind of sensing technology emerging in recent years, which has received extensive attention and research in many fields. The main progress of optical fiber shape sensing technology was summarized, and the basic principle of fiber shape sensing technology based on fiber grating sensing and distributed sensing was discussed. The theoretical framework of shape reconstruction (Frenet-Serret formula) was introduced, and the key problems in the research of distributed fiber shape sensing technology were summarized and discussed. On this basis, the research prospect of distributed fiber shape sensing technology is prospected.
2022, 46(6): 767-772.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.009
Abstract:
In order to investigate the process law and material removal mechanism of 266nm nanosecond solid-state laser drilling on CH film, the single-pulse and multi-pulse drilling experiments were carried out by adopting the single-factor control variable method. The removal mechanism of CH film material by 266nm nanosecond solid-state laser was analyzed. The data of the influence of laser pulse energy and pulse number on the diameter and depth of micropores were obtained. The results show that: when the CH film material is drilled by a single pulse with energy of 0.014mJ, the micropore with the smallest diameter and depth is obtained; when the laser pulse energy is 0.326mJ, the micropore with the largest diameter and depth is obtained. Both the diameter and depth of a micropore increases with the increase of laser pulse energy. When the CH film material is drilled by multiple pulses with low pulse energy, the single pulse ablation rate of laser on CH film is about 0.56μm/pulse. When the laser pulse energy is high, the single pulse ablation rate of laser on CH film is about 1μm/pulse. The diameter and depth of a micropore increase with the increase of laser pulse number. When 266nm nanosecond solid-state laser is used as the drilling source on the CH film, the micropores are regular in shape and uniform in size. There are no residues and debris around the micropores, and there is no heat affected zone at the edge. It can be inferred that the material removal mechanism is mainly "photochemical removal". The research has certain reference significance for the application of 266nm nanosecond solid-state laser processing CH film.
In order to investigate the process law and material removal mechanism of 266nm nanosecond solid-state laser drilling on CH film, the single-pulse and multi-pulse drilling experiments were carried out by adopting the single-factor control variable method. The removal mechanism of CH film material by 266nm nanosecond solid-state laser was analyzed. The data of the influence of laser pulse energy and pulse number on the diameter and depth of micropores were obtained. The results show that: when the CH film material is drilled by a single pulse with energy of 0.014mJ, the micropore with the smallest diameter and depth is obtained; when the laser pulse energy is 0.326mJ, the micropore with the largest diameter and depth is obtained. Both the diameter and depth of a micropore increases with the increase of laser pulse energy. When the CH film material is drilled by multiple pulses with low pulse energy, the single pulse ablation rate of laser on CH film is about 0.56μm/pulse. When the laser pulse energy is high, the single pulse ablation rate of laser on CH film is about 1μm/pulse. The diameter and depth of a micropore increase with the increase of laser pulse number. When 266nm nanosecond solid-state laser is used as the drilling source on the CH film, the micropores are regular in shape and uniform in size. There are no residues and debris around the micropores, and there is no heat affected zone at the edge. It can be inferred that the material removal mechanism is mainly "photochemical removal". The research has certain reference significance for the application of 266nm nanosecond solid-state laser processing CH film.
2022, 46(6): 773-778.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.010
Abstract:
In order to solve the problems of high cost, complex system, poor practicability, and slow response speed in common non-contact temperature measurement systems, multi-spectral temperature measurement and fast-response photoelectric detection technology were adopted, and a low-cost and high-speed multi-spectral radiation temperature measurement system was designed. By using the high-speed weak optical signal acquisition module, high-speed analog-to-digital conversion chip, high-performance field-programmable gate array, and synchronous dynamic random-access memory, ensures the high-speed conversion, synchronous acquisition, large-capacity buffering of weak optical signals and the ability to measure temperature field changes in nanoseconds can be obtained. The results show that, temperature measurement error is less than ±1% and time resolution can reach 50ns. This result is helpful for the measurement of rapidly changing temperature field.
In order to solve the problems of high cost, complex system, poor practicability, and slow response speed in common non-contact temperature measurement systems, multi-spectral temperature measurement and fast-response photoelectric detection technology were adopted, and a low-cost and high-speed multi-spectral radiation temperature measurement system was designed. By using the high-speed weak optical signal acquisition module, high-speed analog-to-digital conversion chip, high-performance field-programmable gate array, and synchronous dynamic random-access memory, ensures the high-speed conversion, synchronous acquisition, large-capacity buffering of weak optical signals and the ability to measure temperature field changes in nanoseconds can be obtained. The results show that, temperature measurement error is less than ±1% and time resolution can reach 50ns. This result is helpful for the measurement of rapidly changing temperature field.
2022, 46(6): 779-783.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.011
Abstract:
To study the 3-D trajectory and spatial radiation characteristics of collisional moving electrons of closely focused circularly polarized Gaussian pulses with different collision centers, a numerical simulation within the framework of laser-electron interaction and nonlinear Thomson scattering was performed. The results show that, the amplitude of the motion trajectory reaches to the peak value of 0.151752λ0(λ0=1μm) at the position of λ0, whereas the valley value is 0.151662λ0 at the position of -λ0, presenting a asymmetry. Through visual display and numerical results, the law of the maximum radiation angle and radiation intensity of electron radiation changing with the collision center was described. Finally, the variation of radiation pulses was studied. The pulse with a primary peak and a sub peak over time was discovered. This research provides a rationale for the building of new generations of X-ray detectors.
To study the 3-D trajectory and spatial radiation characteristics of collisional moving electrons of closely focused circularly polarized Gaussian pulses with different collision centers, a numerical simulation within the framework of laser-electron interaction and nonlinear Thomson scattering was performed. The results show that, the amplitude of the motion trajectory reaches to the peak value of 0.151752λ0(λ0=1μm) at the position of λ0, whereas the valley value is 0.151662λ0 at the position of -λ0, presenting a asymmetry. Through visual display and numerical results, the law of the maximum radiation angle and radiation intensity of electron radiation changing with the collision center was described. Finally, the variation of radiation pulses was studied. The pulse with a primary peak and a sub peak over time was discovered. This research provides a rationale for the building of new generations of X-ray detectors.
2022, 46(6): 784-787.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.012
Abstract:
In order to choose a better input coupler, the conversion efficiency of the frequency doubling cavity were studied in the case of the transmittance of the input coupler to the fundamental light of 5% and 10%, respectively. 447.3nm blue light was obtained by external-cavity frequency doubling of a tapered amplifier-boosted continuous-wave diode laser at cesium D1 line. The frequency doubling cavity consists of a two-mirror standing wave cavity with a periodically poled KTiOPO4 (PPKTP) crystal inside. With a maximum fundamental power around 350mW, the frequency doubling cavity with a 5% transmittance input coupler generate 178mW blue light, corresponding to a conversion efficiency of 50.8%. With the input coupler with a 10% transmittance at the fundamental wavelength, 131mW of blue light is obtained, and the corresponding conversion efficiency is 37.4%. With a maximum input fundamental power, the output blue power was measured for 0.5h. In the frequency doubling cavity with 5% transmittance input coupler, the root mean square fluctuation is 1.4%, while the other is 0.7%. The result shows that the input coupler with 5% transmittance is better. This research is helpful for preparing high quality pump light resources to generate nonclassical light at cesium D1 line.
In order to choose a better input coupler, the conversion efficiency of the frequency doubling cavity were studied in the case of the transmittance of the input coupler to the fundamental light of 5% and 10%, respectively. 447.3nm blue light was obtained by external-cavity frequency doubling of a tapered amplifier-boosted continuous-wave diode laser at cesium D1 line. The frequency doubling cavity consists of a two-mirror standing wave cavity with a periodically poled KTiOPO4 (PPKTP) crystal inside. With a maximum fundamental power around 350mW, the frequency doubling cavity with a 5% transmittance input coupler generate 178mW blue light, corresponding to a conversion efficiency of 50.8%. With the input coupler with a 10% transmittance at the fundamental wavelength, 131mW of blue light is obtained, and the corresponding conversion efficiency is 37.4%. With a maximum input fundamental power, the output blue power was measured for 0.5h. In the frequency doubling cavity with 5% transmittance input coupler, the root mean square fluctuation is 1.4%, while the other is 0.7%. The result shows that the input coupler with 5% transmittance is better. This research is helpful for preparing high quality pump light resources to generate nonclassical light at cesium D1 line.
2022, 46(6): 788-795.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.013
Abstract:
In order to solve the shortcomings of using the extreme learning machine (ELM) neural network to position indoor visible light, such as large error, long network model training time and poor stability of results, multi-objective momentum particle swarm optimization (MMPSO)-ELM scheme was formed by using sparse training fingerprint database, MMPSO and ELM indoor visible light positioning method. Momentum factor was introduced to avoid excessive oscillation during iteration and speed up the system convergence. Training data was set randomly in different positioning spaces. When the number of test points is different, the scheme of MMPSO-ELM was compared with back propagation, ELM and PSO-ELM. The simulation results show that, under the condition of 20 groups of training data and 80 points to be located, the maximum positioning error is 0.0225m, the minimum error is 0.00093mm and the average positioning error is as low as 0.00143m. The positioning performance is less affected by the size of the positioning space. MMPSO-ELM visible light positioning scheme has the advantages of high positioning accuracy, fast speed and strong generalization. This research provides theoretical support for fast and accurate positioning in indoor places.
In order to solve the shortcomings of using the extreme learning machine (ELM) neural network to position indoor visible light, such as large error, long network model training time and poor stability of results, multi-objective momentum particle swarm optimization (MMPSO)-ELM scheme was formed by using sparse training fingerprint database, MMPSO and ELM indoor visible light positioning method. Momentum factor was introduced to avoid excessive oscillation during iteration and speed up the system convergence. Training data was set randomly in different positioning spaces. When the number of test points is different, the scheme of MMPSO-ELM was compared with back propagation, ELM and PSO-ELM. The simulation results show that, under the condition of 20 groups of training data and 80 points to be located, the maximum positioning error is 0.0225m, the minimum error is 0.00093mm and the average positioning error is as low as 0.00143m. The positioning performance is less affected by the size of the positioning space. MMPSO-ELM visible light positioning scheme has the advantages of high positioning accuracy, fast speed and strong generalization. This research provides theoretical support for fast and accurate positioning in indoor places.
2022, 46(6): 796-801.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.014
Abstract:
To solve the anti-oil deposition problem of switch panel, femtosecond laser was used to prepare micro/nano composite surface of the switch panel. And superhydrophobicity can be achieved, and then the adhesion of oil deposition can be reduced. In this paper, the laser ablation threshold, micro-nano structure design, and the influence of different laser process parameters and micro-nano structure on the surface wettability of polycarbonate (PC) switch panel were studied. The experimental results show that the ablation threshold of PC switch panel is 1.66μJ at 515nm. When the laser energy is 1.6μJ, the scanning speed is 200mm/s, and the overlapping ratio is 1/3 of the line width, the droplet contact angle is 161°, the superhydrophobicity is observed. PC panel with superhydro-phobicity can achieve surface self-cleaning effect, showing a huge market potential.
To solve the anti-oil deposition problem of switch panel, femtosecond laser was used to prepare micro/nano composite surface of the switch panel. And superhydrophobicity can be achieved, and then the adhesion of oil deposition can be reduced. In this paper, the laser ablation threshold, micro-nano structure design, and the influence of different laser process parameters and micro-nano structure on the surface wettability of polycarbonate (PC) switch panel were studied. The experimental results show that the ablation threshold of PC switch panel is 1.66μJ at 515nm. When the laser energy is 1.6μJ, the scanning speed is 200mm/s, and the overlapping ratio is 1/3 of the line width, the droplet contact angle is 161°, the superhydrophobicity is observed. PC panel with superhydro-phobicity can achieve surface self-cleaning effect, showing a huge market potential.
2022, 46(6): 802-807.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.015
Abstract:
In order to solve the problem that the output pulse laser energy of the laser target echo simulator can not be calibrated in the field, the analog integral principle was adopted, the energy calibration device of laser target echo simulator was established through the parameter optimization design of the photoelectric detection module and the circuit structure design of the integral module, and the corresponding experiments were designed to verify the measurement ability of the calibration device. The results show that, the energy calibration device of the laser target echo simulator can accurately measure the laser energy when the pulse width is 10ns~100ns and the energy measurement range is 10fJ~1pJ. The measurement uncertainty is 13.8% when the inclusion factor k is 2. It can fully meet the requirements of the output pulse laser energy measurement and calibration of the laser target echo simulator.
In order to solve the problem that the output pulse laser energy of the laser target echo simulator can not be calibrated in the field, the analog integral principle was adopted, the energy calibration device of laser target echo simulator was established through the parameter optimization design of the photoelectric detection module and the circuit structure design of the integral module, and the corresponding experiments were designed to verify the measurement ability of the calibration device. The results show that, the energy calibration device of the laser target echo simulator can accurately measure the laser energy when the pulse width is 10ns~100ns and the energy measurement range is 10fJ~1pJ. The measurement uncertainty is 13.8% when the inclusion factor k is 2. It can fully meet the requirements of the output pulse laser energy measurement and calibration of the laser target echo simulator.
2022, 46(6): 808-816.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.016
Abstract:
In order to solve the problem that reduction of the subsequent classification accuracy in the hyperspectral image classification algorithm based on supervised learning due to the presence of noise labels in the training samples, a false label detection algorithm based on low rank sparse representation and improved spectral angle mapping (SAM) was adopted. Firstly, the signal subspace of hyperspectral image was predicted, and the original hyperspectral image was reconstructed and denoised according to the predicted subspace. Next, the normalized spectral angle mapping algorithm was used to obtain the distance information between each class of samples, and the spectral similarity between each class of samples was obtained. Then, the density peak clustering algorithm was used to get the local density of each training sample. Support vector machine was used to verify the results on two real datasets. The experimental results show that the overall accuracy is improved by 1.91% compared with the advanced hierarchical structure of hyperspectral image false label detection algorithm. This result is helpful for hyperspectral image classification.
In order to solve the problem that reduction of the subsequent classification accuracy in the hyperspectral image classification algorithm based on supervised learning due to the presence of noise labels in the training samples, a false label detection algorithm based on low rank sparse representation and improved spectral angle mapping (SAM) was adopted. Firstly, the signal subspace of hyperspectral image was predicted, and the original hyperspectral image was reconstructed and denoised according to the predicted subspace. Next, the normalized spectral angle mapping algorithm was used to obtain the distance information between each class of samples, and the spectral similarity between each class of samples was obtained. Then, the density peak clustering algorithm was used to get the local density of each training sample. Support vector machine was used to verify the results on two real datasets. The experimental results show that the overall accuracy is improved by 1.91% compared with the advanced hierarchical structure of hyperspectral image false label detection algorithm. This result is helpful for hyperspectral image classification.
2022, 46(6): 823-828.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.018
Abstract:
To produce the harmonic spectra with high conversion efficiency and high photon energy, the effect of the multi-color chirp waveform on the harmonic spectra was theoretically studied by solving the Schrödinger equation. The results show that, under the fixed laser intensity, the harmonic cutoff energy can be effectively extended by the best 3-color chirp waveform. The harmonic intensity can be enhanced by the best 4-color chirp waveform. Finally, the isolated attosecond pulses of 42as can be obtained by superposition of the harmonic spectrum of the best 3-color and 4-color combined waveforms. The results are helpful for the generation of ultra-short attosecond pulses.
To produce the harmonic spectra with high conversion efficiency and high photon energy, the effect of the multi-color chirp waveform on the harmonic spectra was theoretically studied by solving the Schrödinger equation. The results show that, under the fixed laser intensity, the harmonic cutoff energy can be effectively extended by the best 3-color chirp waveform. The harmonic intensity can be enhanced by the best 4-color chirp waveform. Finally, the isolated attosecond pulses of 42as can be obtained by superposition of the harmonic spectrum of the best 3-color and 4-color combined waveforms. The results are helpful for the generation of ultra-short attosecond pulses.
2022, 46(6): 829-834.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.019
Abstract:
In order to realize the online monitoring of carbon monoxide gas generated by overheating or discharge failure of insulating paperboard in transformers, a detection technology of carbon monoxide gas dissolved in oil based on optical fiber photoacoustic sensing was proposed. Combining photoacoustic spectroscopy, optical fiber sensing, and membrane separation technology, a fiber optic photoacoustic sensing probe that integrates oil and gas separation and gas detection functions was designed. The carbon monoxide gas dissolved in the oil enters the miniature air cavity in the optical fiber probe through the oil and gas separation membrane. Two optical fibers were used to connect the probe to the demodulation instrument, and transmit near-infrared excitation light and probe light respectively. The photoacoustic signal generated by the absorption of light energy by the gas was detected by the optical fiber Fabry-Perot sensor and processed by the designed optical fiber photoacoustic demodulator. The detection sensitivity of the system for volume fraction of carbon monoxide gas was 0.345pm/10-6. The experimental results show that the designed optical fiber sensing system has a detection limit of 5×10-6 for the volume fraction of dissolved carbon monoxide gas in oil. This research has the advantages of high accuracy, anti-electromagnetic interference, and simple degassing, and provides a new method for detecting carbon monoxide gas dissolved in transformer oil.
In order to realize the online monitoring of carbon monoxide gas generated by overheating or discharge failure of insulating paperboard in transformers, a detection technology of carbon monoxide gas dissolved in oil based on optical fiber photoacoustic sensing was proposed. Combining photoacoustic spectroscopy, optical fiber sensing, and membrane separation technology, a fiber optic photoacoustic sensing probe that integrates oil and gas separation and gas detection functions was designed. The carbon monoxide gas dissolved in the oil enters the miniature air cavity in the optical fiber probe through the oil and gas separation membrane. Two optical fibers were used to connect the probe to the demodulation instrument, and transmit near-infrared excitation light and probe light respectively. The photoacoustic signal generated by the absorption of light energy by the gas was detected by the optical fiber Fabry-Perot sensor and processed by the designed optical fiber photoacoustic demodulator. The detection sensitivity of the system for volume fraction of carbon monoxide gas was 0.345pm/10-6. The experimental results show that the designed optical fiber sensing system has a detection limit of 5×10-6 for the volume fraction of dissolved carbon monoxide gas in oil. This research has the advantages of high accuracy, anti-electromagnetic interference, and simple degassing, and provides a new method for detecting carbon monoxide gas dissolved in transformer oil.
2022, 46(6): 835-840.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.020
Abstract:
In order to obtain the physical mechanism of the enhanced spectral performance of the combined pulse laser-induced plasma, the effects of pre-pulse parameters on the spatial and temporal distribution of parameters of the combined pulse laser-induced aluminum plasma were simulated based on the FLASH program. The spatial evolution of electron temperature, electron density, and ablative mass of aluminum plasma under different prepulse wavelength and different pre-pulse delay was obtained. The numerical simulation results show that the space range of helium plasma plume increases from 0.7cm to 3.0cm with the change of pre-pulse wavelength from 0.266μm to 1.064μm when the total energy of the pre-pulse is the same, but the ablation efficiency of the combined pulse on the target decreases seriously. During this period, the maximum electron temperature of the aluminum plasma remains stable. In addition, the combined pulse time delay should be less than 100ns. This study can provide a theoretical reference for combined pulsed laser-induced breakdown plasma spectral enhancement technology.
In order to obtain the physical mechanism of the enhanced spectral performance of the combined pulse laser-induced plasma, the effects of pre-pulse parameters on the spatial and temporal distribution of parameters of the combined pulse laser-induced aluminum plasma were simulated based on the FLASH program. The spatial evolution of electron temperature, electron density, and ablative mass of aluminum plasma under different prepulse wavelength and different pre-pulse delay was obtained. The numerical simulation results show that the space range of helium plasma plume increases from 0.7cm to 3.0cm with the change of pre-pulse wavelength from 0.266μm to 1.064μm when the total energy of the pre-pulse is the same, but the ablation efficiency of the combined pulse on the target decreases seriously. During this period, the maximum electron temperature of the aluminum plasma remains stable. In addition, the combined pulse time delay should be less than 100ns. This study can provide a theoretical reference for combined pulsed laser-induced breakdown plasma spectral enhancement technology.
2022, 46(6): 841-849.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.021
Abstract:
To solve the problem that the mechanical bruise of nectarine is difficult to be effectively detected due to the complex color features of nectarine skin, a polarization imaging technology was introduced into the mechanical bruise detection of nectarines. A pixel-level bruise classification model based on polarization imaging technology was proposed. In the experiment, the division of focal plane (DoFP) polarization camera was utilized to capture the degree of polarization images in the four polarization directions respectively. Firstly, bilinear interpolation was utilized to reduce the dimension of the polarization image cube to improve the operation speed of the whole algorithm, and low-light image enhancement (LIME) was utilized to compensate for the shape of nectarine fruit and to improve the light intensity of nectarine edge area, so as to reduce the influence of fruit curvature change. Secondly, the color features and gray-level co-occurrence matrix (GLCM) features of positive (bruised) and negative (non-bruised) pixels in the preprocessed image were extracted. Then, two least squares support vector machine (LSSVM) classifiers were trained independently based on the two features. Finally, two classifiers (color-LSSVM model and GLCM-LSSVM model) were connected in series to realize bruise detection. Results show that: Two independent classifiers with radial basis function (RBF) as kernel function were used in series (color-LSSVM→GLCM-LSSVM model) with the precision of 95.68% and the recall of 93.29%. This study proves that DoFP polarization imaging technology has a prosperous application prospect in the field of non-destructive detection of mechanical bruises of dark fruits.
To solve the problem that the mechanical bruise of nectarine is difficult to be effectively detected due to the complex color features of nectarine skin, a polarization imaging technology was introduced into the mechanical bruise detection of nectarines. A pixel-level bruise classification model based on polarization imaging technology was proposed. In the experiment, the division of focal plane (DoFP) polarization camera was utilized to capture the degree of polarization images in the four polarization directions respectively. Firstly, bilinear interpolation was utilized to reduce the dimension of the polarization image cube to improve the operation speed of the whole algorithm, and low-light image enhancement (LIME) was utilized to compensate for the shape of nectarine fruit and to improve the light intensity of nectarine edge area, so as to reduce the influence of fruit curvature change. Secondly, the color features and gray-level co-occurrence matrix (GLCM) features of positive (bruised) and negative (non-bruised) pixels in the preprocessed image were extracted. Then, two least squares support vector machine (LSSVM) classifiers were trained independently based on the two features. Finally, two classifiers (color-LSSVM model and GLCM-LSSVM model) were connected in series to realize bruise detection. Results show that: Two independent classifiers with radial basis function (RBF) as kernel function were used in series (color-LSSVM→GLCM-LSSVM model) with the precision of 95.68% and the recall of 93.29%. This study proves that DoFP polarization imaging technology has a prosperous application prospect in the field of non-destructive detection of mechanical bruises of dark fruits.
2022, 46(6): 850-854.
doi: 10.7510/jgjs.issn.1001-3806.2022.06.022
Abstract:
In order to investigate the propagation dynamics of vortex Airy beams passing through the negative index medium(NIM), the propagation dynamics equation was obtained based on the Collins formula. The intensity, vortex, and phase were studied by using the equation. The results show that it is possible to controlling the center lobe, superimposition position, and the intensity by adjusting the parameters of the negative index medium. All these properties of the propagation of the beam in NIM may have applications in areas such as optical micromanipulation and optical sorting.
In order to investigate the propagation dynamics of vortex Airy beams passing through the negative index medium(NIM), the propagation dynamics equation was obtained based on the Collins formula. The intensity, vortex, and phase were studied by using the equation. The results show that it is possible to controlling the center lobe, superimposition position, and the intensity by adjusting the parameters of the negative index medium. All these properties of the propagation of the beam in NIM may have applications in areas such as optical micromanipulation and optical sorting.
