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RSS2021 Vol. 45, No. 6
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2021, 45(6): 681-685.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.001
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Abstract:
In order to achieve high-precision interferometric measurement of physical quantities such as step height and absolute distance, etc, an optical fiber laser was constructed which includes multiple fiber laser resonators and can emit several wavelengths simultaneously. The erbium-doped fibers were used as gain material in each laser resonator, and the fiber Bragg gratings were employed as wavelength-choosing elements. By changing the Bragg wavelength of a fiber Bragg grating, the wavelength emitted from the corresponding resonator can be changed. Each of the cavities was independent and all of the cavities were overlapped each other. In the overlapped part, optical fiber couplers were used to configure sub-cavities and thus each resonator can emit single longitudinal mode laser. The experimental results show that each of the resonators can emit single longitudinal mode laser with stable power and stable wavelength. And the stability of each wavelength can be less than 0.01 nm within 4h. This design is helpful to the research of tunable single longitudinal mode multi wavelength fiber laser.
In order to achieve high-precision interferometric measurement of physical quantities such as step height and absolute distance, etc, an optical fiber laser was constructed which includes multiple fiber laser resonators and can emit several wavelengths simultaneously. The erbium-doped fibers were used as gain material in each laser resonator, and the fiber Bragg gratings were employed as wavelength-choosing elements. By changing the Bragg wavelength of a fiber Bragg grating, the wavelength emitted from the corresponding resonator can be changed. Each of the cavities was independent and all of the cavities were overlapped each other. In the overlapped part, optical fiber couplers were used to configure sub-cavities and thus each resonator can emit single longitudinal mode laser. The experimental results show that each of the resonators can emit single longitudinal mode laser with stable power and stable wavelength. And the stability of each wavelength can be less than 0.01 nm within 4h. This design is helpful to the research of tunable single longitudinal mode multi wavelength fiber laser.
2021, 45(6): 686-690.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.002
Abstract:
The imaging resolution of a conventional optical microscope is limited to 200nm by the diffraction in the visible spectrum. In order to overcome the resolution limit of the imaging, the microsphere combing with the traditional optical microscope was used to obtain the super-resolution imaging in far field. Firstly, the transport of the object light waves in the air was analyzed theoretically after the parallel light interacted with the micro-nano structure object, and the mechanism of the far-field super-resolution imaging was analyzed that the evanescent wave was converted into the transmission wave by the microsphere. Secondly, the photonic nanojet characteristics of the microspheres were researched. The results show that the radius of the photonic nanojet by the microsphere is less than half of the incident wavelength. Lastly, the blue-ray disc was used as the object, the experimental system of the super-resolution imaging based on the microsphere combining with traditional optical microscope was set up. The resolution of the imaging system is 100nm in the far-field. The results show that the imaging system can be used in the detection of the micro-nano structure. The results are helpful to the lithography, bio-medicine, etc.
The imaging resolution of a conventional optical microscope is limited to 200nm by the diffraction in the visible spectrum. In order to overcome the resolution limit of the imaging, the microsphere combing with the traditional optical microscope was used to obtain the super-resolution imaging in far field. Firstly, the transport of the object light waves in the air was analyzed theoretically after the parallel light interacted with the micro-nano structure object, and the mechanism of the far-field super-resolution imaging was analyzed that the evanescent wave was converted into the transmission wave by the microsphere. Secondly, the photonic nanojet characteristics of the microspheres were researched. The results show that the radius of the photonic nanojet by the microsphere is less than half of the incident wavelength. Lastly, the blue-ray disc was used as the object, the experimental system of the super-resolution imaging based on the microsphere combining with traditional optical microscope was set up. The resolution of the imaging system is 100nm in the far-field. The results show that the imaging system can be used in the detection of the micro-nano structure. The results are helpful to the lithography, bio-medicine, etc.
2021, 45(6): 691-696.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.003
Abstract:
In order to study the fatigue problem of laser melting deposition(LMD) high alloy steel, the fatigue crack growth path and residual life prediction of typical samples were analyzed by the extended finite element method and the direct cyclic. The parameters in Paris formula were obtained by the fatigue experiment of center crack tension(CCT)specimen, and then were used in the finite element simulation. The crack growth process of CCT and compact tension shear samples was studied by the finite element simulation and the experiment respectively. The results indicate that the crack growth path and fatigue life obtained by the finite element simulation are in good agreement with the experiment data. The error of deflection angle of crack propagation path is less than 16.54%, and the error of fatigue life is less than 2.72%. The results show that this method can predict the fatigue crack growth path and fatigue life of LMD high alloy steel components well, which has a certain engineering sense and practice value.
In order to study the fatigue problem of laser melting deposition(LMD) high alloy steel, the fatigue crack growth path and residual life prediction of typical samples were analyzed by the extended finite element method and the direct cyclic. The parameters in Paris formula were obtained by the fatigue experiment of center crack tension(CCT)specimen, and then were used in the finite element simulation. The crack growth process of CCT and compact tension shear samples was studied by the finite element simulation and the experiment respectively. The results indicate that the crack growth path and fatigue life obtained by the finite element simulation are in good agreement with the experiment data. The error of deflection angle of crack propagation path is less than 16.54%, and the error of fatigue life is less than 2.72%. The results show that this method can predict the fatigue crack growth path and fatigue life of LMD high alloy steel components well, which has a certain engineering sense and practice value.
2021, 45(6): 697-702.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.004
Abstract:
To realize the large area preparation and practical application of TiAl alloy coating on the surface of TC4 titanium alloy, a single and overlapped TiAl alloy coating was prepared on the titanium substrate by laser cladding. The cladding quality of the coating was analyzed by surface morphology and interface characteristics, the phase composition and microstructure of the coating were studied, and the hardness distribution between the interface of the cladding layer and the lap layer was measured. The results show that the coating is metallurgical, and there is no cracks and pores in the coating. The Ti/Al mainly exists in the form of TiAl(γ), Ti3Al(α2), and trace elements, and the coating is mainly composed of double-state structure and lamellar structure. The average hardness of single cladding coating and lap coating is more than 1.44 times that of substrate. The coating can carry out a wide range of multi-channel lap cladding, which proves the feasibility of the TiAl coating on the surface modification of the TC4 substrate. This study is of great significance for the practical application of the coating.
To realize the large area preparation and practical application of TiAl alloy coating on the surface of TC4 titanium alloy, a single and overlapped TiAl alloy coating was prepared on the titanium substrate by laser cladding. The cladding quality of the coating was analyzed by surface morphology and interface characteristics, the phase composition and microstructure of the coating were studied, and the hardness distribution between the interface of the cladding layer and the lap layer was measured. The results show that the coating is metallurgical, and there is no cracks and pores in the coating. The Ti/Al mainly exists in the form of TiAl(γ), Ti3Al(α2), and trace elements, and the coating is mainly composed of double-state structure and lamellar structure. The average hardness of single cladding coating and lap coating is more than 1.44 times that of substrate. The coating can carry out a wide range of multi-channel lap cladding, which proves the feasibility of the TiAl coating on the surface modification of the TC4 substrate. This study is of great significance for the practical application of the coating.
2021, 45(6): 703-708.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.005
Abstract:
In order to study the interference effect of multispectral CCD camera, both xenon lamp (white light) and laser with wavelength of 671nm, 473nm, and 532nm separatelywere used to interfere the multispectral CCD camera.The interference map of red, green and blue channels was extracted, and the interference effect was analyzed. Finally, the white light irradiation multispectral CCD was simulated by using the diffusion model of photo generated carriers. The results show that red, green, and blue channels will be interfered at the same time when white light irradiates the multispectral CCD camera, and the interference effect is obviously better than that of single wavelength.When the incident power of white light is 10.5μW, the saturation pixel number of white light irradiated multispectral CCD is 2382pixel.With the increase of incident power, the number of saturated pixels of multispectral CCD increases gradually.When the incident power of white light is 980μW, the saturation pixel number of white light irradiated multispectral CCD is stable at 320078pixel. The order of the response of multispectral CCD tosuccessive laser is white light, 532nm, 473nm, and 671nm.The simulated interference figure and the curve of the number of saturated pixels changing with the laser power are basically consistent with the experiment.The results are helpful to further study the interference mechanism of multispectral CCD camera.
In order to study the interference effect of multispectral CCD camera, both xenon lamp (white light) and laser with wavelength of 671nm, 473nm, and 532nm separatelywere used to interfere the multispectral CCD camera.The interference map of red, green and blue channels was extracted, and the interference effect was analyzed. Finally, the white light irradiation multispectral CCD was simulated by using the diffusion model of photo generated carriers. The results show that red, green, and blue channels will be interfered at the same time when white light irradiates the multispectral CCD camera, and the interference effect is obviously better than that of single wavelength.When the incident power of white light is 10.5μW, the saturation pixel number of white light irradiated multispectral CCD is 2382pixel.With the increase of incident power, the number of saturated pixels of multispectral CCD increases gradually.When the incident power of white light is 980μW, the saturation pixel number of white light irradiated multispectral CCD is stable at 320078pixel. The order of the response of multispectral CCD tosuccessive laser is white light, 532nm, 473nm, and 671nm.The simulated interference figure and the curve of the number of saturated pixels changing with the laser power are basically consistent with the experiment.The results are helpful to further study the interference mechanism of multispectral CCD camera.
2021, 45(6): 709-714.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.006
Abstract:
In order to realize the additive preparation and surface repair of high strength bainitic steel parts, amedium-carbon high strength bainite steel was prepared by laser powder deposition and salt bath isothermal treatment with different process parameters. The alloy composition (mass fraction) was Fe-0.0029C-0.0150Si-0.0150Mn-0.0096Cr-0.0120Ni-0.0100Al-0.0050Mo.The microstructure of the steel wascharacterized by scanning electron microscope and X-ray diffraction, and the mechanical properties of steel were tested through tensile testing machine and Vicker's microhardness tester. The effect of isothermal temperature and isothermal time on microstructure and properties of the steel during salt bath isothermal process was analyzed. The best integrated mechanical properties were observed after deposition and salt bath isothermal at 280℃ for 5h, the average microhardness, tensile strength, yield strength, andelongationwas 494.5HV, 1248MPa, 1037MPa, and 14.5%, respectively. The results showe that the microstructure of the samples with different process parameters is composed of lath-like bainite and retained austenite, and the microstructure is uniform without defects such as carbide, segregation, pore and inclusion, but too low isothermal time or too high isothermal temperature would lead to the deterioration of the microstructure. This study provides a reference for the additive and repair of high strength parts.
In order to realize the additive preparation and surface repair of high strength bainitic steel parts, amedium-carbon high strength bainite steel was prepared by laser powder deposition and salt bath isothermal treatment with different process parameters. The alloy composition (mass fraction) was Fe-0.0029C-0.0150Si-0.0150Mn-0.0096Cr-0.0120Ni-0.0100Al-0.0050Mo.The microstructure of the steel wascharacterized by scanning electron microscope and X-ray diffraction, and the mechanical properties of steel were tested through tensile testing machine and Vicker's microhardness tester. The effect of isothermal temperature and isothermal time on microstructure and properties of the steel during salt bath isothermal process was analyzed. The best integrated mechanical properties were observed after deposition and salt bath isothermal at 280℃ for 5h, the average microhardness, tensile strength, yield strength, andelongationwas 494.5HV, 1248MPa, 1037MPa, and 14.5%, respectively. The results showe that the microstructure of the samples with different process parameters is composed of lath-like bainite and retained austenite, and the microstructure is uniform without defects such as carbide, segregation, pore and inclusion, but too low isothermal time or too high isothermal temperature would lead to the deterioration of the microstructure. This study provides a reference for the additive and repair of high strength parts.
2021, 45(6): 715-721.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.007
Abstract:
In order to study the coupling mechanism of butterfly optical communication lasers, a chip-lens-single mode fiber simulation model was established. Based on the coupling theory, the concept of tolerance was introduced, and the effect of space position error on coupling efficiency was analyzed. By comparing the tolerance that the lens and the fiber in each direction, combined with the offset phenomenon after welding, the packaging sequence that the lens first and then the fiber was proposed, and an experimental platform was built for verification. The results show that in the comparison experiment, the maximum power obtained by lens priority package is 1800μW, while the maximum power obtained by fiber priority package is only 1200μW. The effect of the offset after welding is better when the lens is encapsulated first. This research provides a reliable reference for the actual packaging and production of butterfly devices.
In order to study the coupling mechanism of butterfly optical communication lasers, a chip-lens-single mode fiber simulation model was established. Based on the coupling theory, the concept of tolerance was introduced, and the effect of space position error on coupling efficiency was analyzed. By comparing the tolerance that the lens and the fiber in each direction, combined with the offset phenomenon after welding, the packaging sequence that the lens first and then the fiber was proposed, and an experimental platform was built for verification. The results show that in the comparison experiment, the maximum power obtained by lens priority package is 1800μW, while the maximum power obtained by fiber priority package is only 1200μW. The effect of the offset after welding is better when the lens is encapsulated first. This research provides a reliable reference for the actual packaging and production of butterfly devices.
2021, 45(6): 722-728.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.008
Abstract:
In face detection, the small target face carries less feature information and is relatively fuzzy, which leads to higher detection difficulty. In order to solve this problem, a novel algorithm was designed. The network that combines the single shot scale-invariant face detector (S3FD) network with the channel and the spatial attention mechanism was used as the backbone, and the channel and the spatial establish the weight relationship between the features, which strengthens the feature extraction ability. Then, the receptive field of the original S3FD output feature map was expanded and then up-sampled, so that the output of the feature map of the previous layer includes the features of the feature map of the next layer. Result: The average precision (AP) values of this algorithm on the three different levels of widerface verification datasets are 95.0%, 93.7%, and 86.4%, respectively, which are increased by 1.3%, 1.2%, and 0.5% compared with the original S3FD. The algorithm proposed in this paper has a better detection effect in face detection.
In face detection, the small target face carries less feature information and is relatively fuzzy, which leads to higher detection difficulty. In order to solve this problem, a novel algorithm was designed. The network that combines the single shot scale-invariant face detector (S3FD) network with the channel and the spatial attention mechanism was used as the backbone, and the channel and the spatial establish the weight relationship between the features, which strengthens the feature extraction ability. Then, the receptive field of the original S3FD output feature map was expanded and then up-sampled, so that the output of the feature map of the previous layer includes the features of the feature map of the next layer. Result: The average precision (AP) values of this algorithm on the three different levels of widerface verification datasets are 95.0%, 93.7%, and 86.4%, respectively, which are increased by 1.3%, 1.2%, and 0.5% compared with the original S3FD. The algorithm proposed in this paper has a better detection effect in face detection.
2021, 45(6): 729-734.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.009
Abstract:
In order to meet the requirements of objective, accurate, and high-precision measurement of laser damage threshold of thin films, the calibration technology of damage threshold was proposed. Firstly, the experimental calibration method of exchanging the positions of the two energy detectors was used to eliminate the error of the spectroscope and the measurement of the energy detector, so as to obtain the accurate irradiation energy. Then, the measurement method of adjusting the positions of two CCD devices to obtain the same spot size was used to calibrate the equivalence between the measured sample surface and the spot area measurement surface, and the non flat top part of the laser spot was eliminated, so as to obtain the accurate irradiation spot area. Finally, the least square method was used to fit the calculated energy density and the corresponding damage probability to obtain the damage threshold. The 1064nm laser irradiation experiment of TiO2/SiO2 high reflection film was carried out, and the laser damage threshold was 23.0164J/cm2. The results show that the measurement accuracy of laser damage threshold is increased by 9.26% by using calibration technology, which meets the high precision measurement requirements. This study is helpful for accurate calibration of laser damage threshold of thin films.
In order to meet the requirements of objective, accurate, and high-precision measurement of laser damage threshold of thin films, the calibration technology of damage threshold was proposed. Firstly, the experimental calibration method of exchanging the positions of the two energy detectors was used to eliminate the error of the spectroscope and the measurement of the energy detector, so as to obtain the accurate irradiation energy. Then, the measurement method of adjusting the positions of two CCD devices to obtain the same spot size was used to calibrate the equivalence between the measured sample surface and the spot area measurement surface, and the non flat top part of the laser spot was eliminated, so as to obtain the accurate irradiation spot area. Finally, the least square method was used to fit the calculated energy density and the corresponding damage probability to obtain the damage threshold. The 1064nm laser irradiation experiment of TiO2/SiO2 high reflection film was carried out, and the laser damage threshold was 23.0164J/cm2. The results show that the measurement accuracy of laser damage threshold is increased by 9.26% by using calibration technology, which meets the high precision measurement requirements. This study is helpful for accurate calibration of laser damage threshold of thin films.
2021, 45(6): 735-739.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.010
Abstract:
Thermal design is the key technology for a diode pump solid laser to keep high stability of the output energy. To solve the cooling problem of a solid laser, a 150mJ air cooled YAG laser with the repetition of 50Hz was systematically studied. The 3-D theoretical model of the diode-pumped laser and the cooling parts was constructed, and the generated heat of the laser was calculated. Further, the thermal management of the whole system was analyzed using the software of FloEFD, and the theoretical results were then discussed. Finally, the verified experiment was carried out. The results show that after three cycles, the laser output is 155mJ, 50Hz, the laser beam dispersion is 2.9mard, and the temperature of radiator is about 85℃, respectively. The thermal design in this study has high stability, with which the cooling problem of the laser can be perfectly solved to meet the final requirements of the system and guarantee the natural work of the laser. This study provides a reference for the further thermal design of laser.
Thermal design is the key technology for a diode pump solid laser to keep high stability of the output energy. To solve the cooling problem of a solid laser, a 150mJ air cooled YAG laser with the repetition of 50Hz was systematically studied. The 3-D theoretical model of the diode-pumped laser and the cooling parts was constructed, and the generated heat of the laser was calculated. Further, the thermal management of the whole system was analyzed using the software of FloEFD, and the theoretical results were then discussed. Finally, the verified experiment was carried out. The results show that after three cycles, the laser output is 155mJ, 50Hz, the laser beam dispersion is 2.9mard, and the temperature of radiator is about 85℃, respectively. The thermal design in this study has high stability, with which the cooling problem of the laser can be perfectly solved to meet the final requirements of the system and guarantee the natural work of the laser. This study provides a reference for the further thermal design of laser.
2021, 45(6): 740-744.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.011
Abstract:
In order to inspect the quality of the small-size parabolic mirrors, the focal length was measured by the parallel light focusing method, the eccentric angle was measured by rotating the measured mirror.The size of the dispersion spot was measured by combing with the image processing method, and a reduction measurement was proposed.Theoretical analysis and experimental verification of these measurement methods were carried out.The focal length, eccentric angle and size of the diffuse spot of the mirror under test were obtained. The results show that the relative error of the focal length is within 0.1%, the error of the eccentric angle is within 7%, the size of the dispersion spot is less than 0.2mm, and the measurement result is reliable. The design of this scheme provides a good idea for the detection of other small-caliber aspheric surfaces, and provides a good research method for reducing measurement errors and improving measurement accuracy.
In order to inspect the quality of the small-size parabolic mirrors, the focal length was measured by the parallel light focusing method, the eccentric angle was measured by rotating the measured mirror.The size of the dispersion spot was measured by combing with the image processing method, and a reduction measurement was proposed.Theoretical analysis and experimental verification of these measurement methods were carried out.The focal length, eccentric angle and size of the diffuse spot of the mirror under test were obtained. The results show that the relative error of the focal length is within 0.1%, the error of the eccentric angle is within 7%, the size of the dispersion spot is less than 0.2mm, and the measurement result is reliable. The design of this scheme provides a good idea for the detection of other small-caliber aspheric surfaces, and provides a good research method for reducing measurement errors and improving measurement accuracy.
2021, 45(6): 745-750.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.012
Abstract:
Carbon fiber reinforced plastics (CFRP) is prone to defects such as uneven heat-affected zone and fiber damage during the laser surface ablation and epoxy removal process. In order to solve this problem, a laser stripping process algorithm based on CFRP fiber woven grid block scanning was proposed and implemented. Theoretical analysis and experimental verification were carried out by single-factor experiment method, and the influence of different laser scanning surface filling algorithms on the resin removal rate and fiber damage degree of CFRP surface were obtained. The laser ablation mechanism was also analyzed and studied. The result shows that the processed samples have better process effects such as fiber integrity and less thermal damage undertheconditions ofaverage power 24W, repetition rate 20kHz, scanning speed 1000mm/s, defocus length 5mm, which is helpful for the research of CFRP laser resin removal.
Carbon fiber reinforced plastics (CFRP) is prone to defects such as uneven heat-affected zone and fiber damage during the laser surface ablation and epoxy removal process. In order to solve this problem, a laser stripping process algorithm based on CFRP fiber woven grid block scanning was proposed and implemented. Theoretical analysis and experimental verification were carried out by single-factor experiment method, and the influence of different laser scanning surface filling algorithms on the resin removal rate and fiber damage degree of CFRP surface were obtained. The laser ablation mechanism was also analyzed and studied. The result shows that the processed samples have better process effects such as fiber integrity and less thermal damage undertheconditions ofaverage power 24W, repetition rate 20kHz, scanning speed 1000mm/s, defocus length 5mm, which is helpful for the research of CFRP laser resin removal.
2021, 45(6): 751-755.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.013
Abstract:
The calculation of fog attenuation empirical model is an important method to predict fog attenuation. In order to apply the fog attenuation empirical model to practice for applicability analysis, based on Mie scattering theory, the attenuation of the laser under different visibility in the Kruse model, Kim model and Ijaz model was calculated using theoretical derivation and simulation analysis methods. The difference between the three models in calculating the attenuation coefficient was analyzed, and the experimental results were compared with the simulation results by building a free-space optical communication experimental platform. The results show that the attenuation results of the 650nm wavelength laser in the fog attenuation channel are closer to the Kim attenuation model. This research conclusion provides a reference for the analysis of the fog attenuation coefficient of the free space optical communication system in Xi'an.
The calculation of fog attenuation empirical model is an important method to predict fog attenuation. In order to apply the fog attenuation empirical model to practice for applicability analysis, based on Mie scattering theory, the attenuation of the laser under different visibility in the Kruse model, Kim model and Ijaz model was calculated using theoretical derivation and simulation analysis methods. The difference between the three models in calculating the attenuation coefficient was analyzed, and the experimental results were compared with the simulation results by building a free-space optical communication experimental platform. The results show that the attenuation results of the 650nm wavelength laser in the fog attenuation channel are closer to the Kim attenuation model. This research conclusion provides a reference for the analysis of the fog attenuation coefficient of the free space optical communication system in Xi'an.
2021, 45(6): 756-761.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.014
Abstract:
In order to improve the absorption efficiency of sapphire for ordinary infrared lasers, a metal oxide coating was used to assist 1064nm infrared fiber laser to etch sapphire. Through the single factor research method, the groove threshold of different metal oxide coatings and the influence of laser energy and metal oxide coating on the etching rate were studied. The theoretical analysis and experimental verification of the different reasons and mechanisms of the six metal oxide coatings assisted laser etching were carried out. The results show that the minimum groove threshold of TiO2 coating is about 8.5J/cm2, and the highest etching rate of TiO2 coating is about 107.3×104μm3/s when the laser energy is 77.7J/cm2; the etching rate first increases with the increase of laser energy and then tends to be gentle and decreases. The groove threshold and the etching rate are mainly related to the laser absorption ability, thermal conductivity and melting boiling point of the coating, and the laser absorption ability and melting boiling point of the coating are more affected. This research result provides a certain technical basis for the industrial application of laser processing sapphire.
In order to improve the absorption efficiency of sapphire for ordinary infrared lasers, a metal oxide coating was used to assist 1064nm infrared fiber laser to etch sapphire. Through the single factor research method, the groove threshold of different metal oxide coatings and the influence of laser energy and metal oxide coating on the etching rate were studied. The theoretical analysis and experimental verification of the different reasons and mechanisms of the six metal oxide coatings assisted laser etching were carried out. The results show that the minimum groove threshold of TiO2 coating is about 8.5J/cm2, and the highest etching rate of TiO2 coating is about 107.3×104μm3/s when the laser energy is 77.7J/cm2; the etching rate first increases with the increase of laser energy and then tends to be gentle and decreases. The groove threshold and the etching rate are mainly related to the laser absorption ability, thermal conductivity and melting boiling point of the coating, and the laser absorption ability and melting boiling point of the coating are more affected. This research result provides a certain technical basis for the industrial application of laser processing sapphire.
2021, 45(6): 762-767.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.015
Abstract:
In order to study the effect of aperture reception on the bit error rate of underwater wireless optical communication (UWOC) system under the condition of anisotropic ocean turbulence, Gaussian beam transmission was adopted to pass through an anisotropic ocean turbulence channel under pulse position modulation.The signal was then received though the apertureby the acceptor, the effects of ocean turbulence parameters, transmission distance, average gain of avalanche photodiode (APD), and modulation order on the bit error rate of the system under different receiving aperture and anisotropy factor were numerically simulatedby introducing the anisotropic ocean turbulence structure constant and analyzing the formation principle of scintillation and scintillation index under the condition of anisotropic ocean turbulence. The results show that under the same anisotropy factor and ocean turbulence parameters, the bit error rate performance of the system can be effectively improved by large aperture receiver. The larger the anisotropy factor, the better the system communication performance for the same aperture diameter and ocean turbulence parameters. The bit error rate performance of the system becomes better when the ratios of mean square temperature dissipation rate, temperature, and salinity contribution to the variation of ocean power spectrum are smaller, while the turbulent kinetic energy dissipation rate and kinetic viscosity are larger and the transmission distance is shorter. The performance of system communication is optimal when the APD gain is 100 or 150. The optimal system communication performance is achieved when the modulation order M=8, and the degree of system bit error rate variation is almost saturated when M>64. This study provides a reference for UWOC system platform construction and performance estimation.
In order to study the effect of aperture reception on the bit error rate of underwater wireless optical communication (UWOC) system under the condition of anisotropic ocean turbulence, Gaussian beam transmission was adopted to pass through an anisotropic ocean turbulence channel under pulse position modulation.The signal was then received though the apertureby the acceptor, the effects of ocean turbulence parameters, transmission distance, average gain of avalanche photodiode (APD), and modulation order on the bit error rate of the system under different receiving aperture and anisotropy factor were numerically simulatedby introducing the anisotropic ocean turbulence structure constant and analyzing the formation principle of scintillation and scintillation index under the condition of anisotropic ocean turbulence. The results show that under the same anisotropy factor and ocean turbulence parameters, the bit error rate performance of the system can be effectively improved by large aperture receiver. The larger the anisotropy factor, the better the system communication performance for the same aperture diameter and ocean turbulence parameters. The bit error rate performance of the system becomes better when the ratios of mean square temperature dissipation rate, temperature, and salinity contribution to the variation of ocean power spectrum are smaller, while the turbulent kinetic energy dissipation rate and kinetic viscosity are larger and the transmission distance is shorter. The performance of system communication is optimal when the APD gain is 100 or 150. The optimal system communication performance is achieved when the modulation order M=8, and the degree of system bit error rate variation is almost saturated when M>64. This study provides a reference for UWOC system platform construction and performance estimation.
2021, 45(6): 768-775.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.016
Abstract:
When a ship is sailing, its huge body and superstructure will cause great interference to the distribution of atmospheric flow field around the ship. The application of lidar to obtain high spatial-temporal resolution information of atmospheric flow field around the ship can improve the safe take-off and landing ability of ship aircraft under terrible ocean environment. The application mode and data requirements of shipborne lidar in marine environmentwas analyzed in this paper.The working principle of shipborne lidar and its development at home and abroadwas respectively introduced. Then, the related key technologies of radar was analyzed.Finally, the development trend of shipborne 3-D high spatial-temporal resolution wind field measurement technology was prospected.
When a ship is sailing, its huge body and superstructure will cause great interference to the distribution of atmospheric flow field around the ship. The application of lidar to obtain high spatial-temporal resolution information of atmospheric flow field around the ship can improve the safe take-off and landing ability of ship aircraft under terrible ocean environment. The application mode and data requirements of shipborne lidar in marine environmentwas analyzed in this paper.The working principle of shipborne lidar and its development at home and abroadwas respectively introduced. Then, the related key technologies of radar was analyzed.Finally, the development trend of shipborne 3-D high spatial-temporal resolution wind field measurement technology was prospected.
2021, 45(6): 776-781.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.017
Abstract:
In order to explore the generation conditions and change factors of the vortex hollow beam in the end-pumped Nd∶YVO4 microchip laser, a new method of generating ring pump light based on the axicon-lens group was constructed. The pump light was simulated and analyzed by ZEMAX, and the mode matching calculation was performed based on the thermal effect analysis. The output of the ring pump light and the ring hollow laser were successfully obtained through the experiment, and the output light was verified by the experiment as the first-order vortex light. The results show that the method can generate 808nm pump light with controllable beam size, and its spot radius can change rapidly with the relative position of the axicon tip and the focal plane of the lens. At the same time, the pump lightgenerated by this method can make the microchip laser with a cavity length of 300μm output a stable 1064nm first-order Laguerre-Gaussian vortex hollow beam. This research result has important guiding significance for the establishment of the actual method of microchip laser output vortex hollow beam.
In order to explore the generation conditions and change factors of the vortex hollow beam in the end-pumped Nd∶YVO4 microchip laser, a new method of generating ring pump light based on the axicon-lens group was constructed. The pump light was simulated and analyzed by ZEMAX, and the mode matching calculation was performed based on the thermal effect analysis. The output of the ring pump light and the ring hollow laser were successfully obtained through the experiment, and the output light was verified by the experiment as the first-order vortex light. The results show that the method can generate 808nm pump light with controllable beam size, and its spot radius can change rapidly with the relative position of the axicon tip and the focal plane of the lens. At the same time, the pump lightgenerated by this method can make the microchip laser with a cavity length of 300μm output a stable 1064nm first-order Laguerre-Gaussian vortex hollow beam. This research result has important guiding significance for the establishment of the actual method of microchip laser output vortex hollow beam.
2021, 45(6): 782-787.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.018
Abstract:
To improve the automation degree and provide a novel real-time, in situ measurement methods of optimizing real boiler control, tunable diode absorption spectroscopy (TDLAS) combined with computed tomography reconstruction was proposed by theoretical analysis and experimental validation. It was proved by simulation that the peak location could be reconstructed and the relative values could be distinguished in case of only two projections. Six measuring grid was arranged to obtain the reconstructed 2-D temperature distribution. The result showes that the correlation coefficient between the averaged temperature and load is 0.91. Linear regression analysis showes that the coefficient of determination is 0.88. The averaged temperature could represent the real-time total radiation, which can be used to avoid over adjusting and obtain the heat value. The 2-D temperature distribution can be used to leveling the boiler. It was concluded that this method provides important support to the non-intrusive in-situ temperature measurement and study of optimizing combustion control.
To improve the automation degree and provide a novel real-time, in situ measurement methods of optimizing real boiler control, tunable diode absorption spectroscopy (TDLAS) combined with computed tomography reconstruction was proposed by theoretical analysis and experimental validation. It was proved by simulation that the peak location could be reconstructed and the relative values could be distinguished in case of only two projections. Six measuring grid was arranged to obtain the reconstructed 2-D temperature distribution. The result showes that the correlation coefficient between the averaged temperature and load is 0.91. Linear regression analysis showes that the coefficient of determination is 0.88. The averaged temperature could represent the real-time total radiation, which can be used to avoid over adjusting and obtain the heat value. The 2-D temperature distribution can be used to leveling the boiler. It was concluded that this method provides important support to the non-intrusive in-situ temperature measurement and study of optimizing combustion control.
2021, 45(6): 788-793.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.019
Abstract:
In order to study the influence of process parameters on crack and thickness of Ni60 laser cladding, the orthogonal experiment was designed by laser cladding Ni60 powder on the surface of 45# steel. The primary and secondary factors affecting the crack formation and coating thickness were analyzed, then, the range analysis method was carried out to obtain the optimal process parameters with the least cracks.The result showesthat the affecting order of crack is that scanning speed > powder feeding rate > laser power; and the process parameters with the least cracks areas follows: Laser power is 1400W, scanning speed is 4.0mm/s, powder feeding rate is 1.0r/min, and thereis only a short crack at the initial position of cladding by using the process parameter. The order of influence on coating thickness is as follows: powder feeding rate > scanning speed. Through microhardness test, the hardness of cladding layer is 3.3 times of that of substrate. Through scanning electron microscope analysis, the grain structure of cladding layer is uniform, and a good metallurgical combination with substrateis formed, which provided a reference for the engineering application of Ni60 alloy powder laser cladding.
In order to study the influence of process parameters on crack and thickness of Ni60 laser cladding, the orthogonal experiment was designed by laser cladding Ni60 powder on the surface of 45# steel. The primary and secondary factors affecting the crack formation and coating thickness were analyzed, then, the range analysis method was carried out to obtain the optimal process parameters with the least cracks.The result showesthat the affecting order of crack is that scanning speed > powder feeding rate > laser power; and the process parameters with the least cracks areas follows: Laser power is 1400W, scanning speed is 4.0mm/s, powder feeding rate is 1.0r/min, and thereis only a short crack at the initial position of cladding by using the process parameter. The order of influence on coating thickness is as follows: powder feeding rate > scanning speed. Through microhardness test, the hardness of cladding layer is 3.3 times of that of substrate. Through scanning electron microscope analysis, the grain structure of cladding layer is uniform, and a good metallurgical combination with substrateis formed, which provided a reference for the engineering application of Ni60 alloy powder laser cladding.
2021, 45(6): 794-798.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.020
Abstract:
In order to solve the problem of missed detection easily caused in dense multi-target detection, an infrared small target detection algorithm based on double neighborhood contrast measure was proposed. First, the peak search algorithm was used to screen out the candidate targets; then the candidate targets were traversed through a single-scale three-layer double neighborhood window; finally the dual-neighbor contrast model was used to calculate the minimum gray contrast of the candidate target area, and the contrast and suppresses clutter were enhanced by the diagonal gradient. The results show that compared with the five comparison methods, the background suppression factor and contrast gain of this method are increased by 4.7 times and 1.8 times on average, respectively, which effectively suppresses clutter and enhances the target. This research can accurately detect multiple targets that are close to each other, which is helpful to improve the accuracy of multi-target detection in complex backgrounds.
In order to solve the problem of missed detection easily caused in dense multi-target detection, an infrared small target detection algorithm based on double neighborhood contrast measure was proposed. First, the peak search algorithm was used to screen out the candidate targets; then the candidate targets were traversed through a single-scale three-layer double neighborhood window; finally the dual-neighbor contrast model was used to calculate the minimum gray contrast of the candidate target area, and the contrast and suppresses clutter were enhanced by the diagonal gradient. The results show that compared with the five comparison methods, the background suppression factor and contrast gain of this method are increased by 4.7 times and 1.8 times on average, respectively, which effectively suppresses clutter and enhances the target. This research can accurately detect multiple targets that are close to each other, which is helpful to improve the accuracy of multi-target detection in complex backgrounds.
2021, 45(6): 806-810.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.022
Abstract:
In order to speedup the reconstruction of particle hologram, a fast reconstruction method based on two-level parallel framework was proposed. The framework combines open multi-processing(OpenMP) and compute unified device architecture(CUDA). The image level parallelism was realized by OpenMP, and the pixel level was realized by CUDA. The parallel computation was carried out on each reconstruction plane and pixel. Taking the coal particle hologram as the test object, the single thread reconstruction program and the two-level parallel reconstruction program were used to reconstruct the hologram at the same time. The reconstruction results and time consumption of the two methods were compared. The experimental results show that the results of two-level parallel reconstruction are consistent with those of single thread reconstruction, and the time consumption can be greatly reduced. For a high-resolution 5000×5000 hologram, the speedup ratio is up to 48.3 with 40 reconstruted planes.This computing framework has a good application prospect in the real-time and on-line holographic diagnosis of particle field.
In order to speedup the reconstruction of particle hologram, a fast reconstruction method based on two-level parallel framework was proposed. The framework combines open multi-processing(OpenMP) and compute unified device architecture(CUDA). The image level parallelism was realized by OpenMP, and the pixel level was realized by CUDA. The parallel computation was carried out on each reconstruction plane and pixel. Taking the coal particle hologram as the test object, the single thread reconstruction program and the two-level parallel reconstruction program were used to reconstruct the hologram at the same time. The reconstruction results and time consumption of the two methods were compared. The experimental results show that the results of two-level parallel reconstruction are consistent with those of single thread reconstruction, and the time consumption can be greatly reduced. For a high-resolution 5000×5000 hologram, the speedup ratio is up to 48.3 with 40 reconstruted planes.This computing framework has a good application prospect in the real-time and on-line holographic diagnosis of particle field.
2021, 45(6): 811-816.
doi: 10.7510/jgjs.issn.1001-3806.2021.06.023
Abstract:
In order to improve the adaptability of complex logic decision-making in the tracking mode of the compound seeker, a mode decision network was constructed using random forest. The model error compensation was combined to optimize the traditional manual condition interpretation process, and the classification accuracy of the model was improved at the same time. The proposed method was added to the compound seeker for theoretical analysis and simulation verification. The results show that the classification accuracy of tracking mode is about 100%, and the running speed increased by 16%, the amount of code was reduced by 3 times. The optimized tracking mode decision process, which based on random forest and error compensation, can good adapt to the seeker tracking mode decision, efficiently implement the autonomous decision of tracking mode. This research algorithm provides a reference for the efficient realization of seeker tracking mode decision-making.
In order to improve the adaptability of complex logic decision-making in the tracking mode of the compound seeker, a mode decision network was constructed using random forest. The model error compensation was combined to optimize the traditional manual condition interpretation process, and the classification accuracy of the model was improved at the same time. The proposed method was added to the compound seeker for theoretical analysis and simulation verification. The results show that the classification accuracy of tracking mode is about 100%, and the running speed increased by 16%, the amount of code was reduced by 3 times. The optimized tracking mode decision process, which based on random forest and error compensation, can good adapt to the seeker tracking mode decision, efficiently implement the autonomous decision of tracking mode. This research algorithm provides a reference for the efficient realization of seeker tracking mode decision-making.
