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RSS2023 Vol. 47, No. 6
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2023, 47(6): 729-735.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.001
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Abstract:
In order to increase the modulation bandwidth of frequency-modulated continuous wave (FMCW) light detection and ranging (LiDAR) for the high range resolution, with the use of external modulation mode based on dual-parallel Mach-Zehnder modulator (DPMZM), combined with the microwave photonic frequency multiplication technology where no optical filters were used, the broadband radio frequency(RF) modulated signal of 8 GHz was realized from a 1 GHz RF source. Furthermore, the effect of the variation of three parameters in the subsystem, namely extinction ratio, modulation index, and phase shift of phase shifter, on the performance of the built FMCW LiDAR system model was investigated. The results show that the extinction ratio of most commercial modulators can meet the requirements of use. When the modulation index is in the range of 2.385~2.425 or the electrical phase shifter error is not greater than 1.3°, the suppressed ratio of FMCW LiDAR detection signal peak power can be maintained above 20 dB. These researches provide theoretical support for the application of microwave photonic frequency multiplication technique in FMCW LiDAR and have certain reference significance for engineering implementation.
In order to increase the modulation bandwidth of frequency-modulated continuous wave (FMCW) light detection and ranging (LiDAR) for the high range resolution, with the use of external modulation mode based on dual-parallel Mach-Zehnder modulator (DPMZM), combined with the microwave photonic frequency multiplication technology where no optical filters were used, the broadband radio frequency(RF) modulated signal of 8 GHz was realized from a 1 GHz RF source. Furthermore, the effect of the variation of three parameters in the subsystem, namely extinction ratio, modulation index, and phase shift of phase shifter, on the performance of the built FMCW LiDAR system model was investigated. The results show that the extinction ratio of most commercial modulators can meet the requirements of use. When the modulation index is in the range of 2.385~2.425 or the electrical phase shifter error is not greater than 1.3°, the suppressed ratio of FMCW LiDAR detection signal peak power can be maintained above 20 dB. These researches provide theoretical support for the application of microwave photonic frequency multiplication technique in FMCW LiDAR and have certain reference significance for engineering implementation.
2023, 47(6): 736-741.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.002
Abstract:
In order to investigate the color-speckle characteristics in multi-primary laser display systems, the spatial distribution of color speckles was simulated by a Monte Carlo method. In the CIE-u′v′ chromaticity diagram, a simplified ellipse model of color speckles was defined to describe the spatial distribution of color speckles in the display system intuitively. The effects of the number and different wavelength combinations of primary colors on color speckles were analyzed. The results show that with the increase in the number of primary colors, the ellipse becomes smaller, and the color speckle is reduced. The ellipse area of the three-primary system is 16.0×10-4, while that of the six-primary system is 6.81×10-4. Especially, the green primary has the greatest effect on color speckles. In the multi-primary display system, the brightness ratio of each primary color is not unique for a given white point, so there is a tradeoff between the color performance and speckle phenomenon. When the brightness weight of the primary color with a large speckle contrast value is reduced, the color speckle phenomenon will be alleviated. This study can provide theoretical guidance for color speckle evaluation of multi-primary laser display systems.
In order to investigate the color-speckle characteristics in multi-primary laser display systems, the spatial distribution of color speckles was simulated by a Monte Carlo method. In the CIE-u′v′ chromaticity diagram, a simplified ellipse model of color speckles was defined to describe the spatial distribution of color speckles in the display system intuitively. The effects of the number and different wavelength combinations of primary colors on color speckles were analyzed. The results show that with the increase in the number of primary colors, the ellipse becomes smaller, and the color speckle is reduced. The ellipse area of the three-primary system is 16.0×10-4, while that of the six-primary system is 6.81×10-4. Especially, the green primary has the greatest effect on color speckles. In the multi-primary display system, the brightness ratio of each primary color is not unique for a given white point, so there is a tradeoff between the color performance and speckle phenomenon. When the brightness weight of the primary color with a large speckle contrast value is reduced, the color speckle phenomenon will be alleviated. This study can provide theoretical guidance for color speckle evaluation of multi-primary laser display systems.
2023, 47(6): 742-750.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.003
Abstract:
3 μm~5 μm is one of the transmission windows of the atmosphere, including many atoms or molecules' characteristic absorption peaks. 3 μm~5 μm laser souses have wide applications, such as medical diagnosis, environmental monitoring, spectral analysis, military countermeasure, and so on. In these application fields, light sources are often required to have narrow linewidth and wavelength tuning capability. Narrow-linewidth laser is an ideal light source for these applications due to its small spectrum range and concentrative energy. The technology of narrow-linewidth of 3 μm~5 μm laser were summarized, including the linewidth compression method of the Fe2+/Cr2+ ion-doped solid-state laser and fluoride fiber laser, and several methods of quantum cascade laser frequency stabilization were discussed. The compact and all-solid-state mid-infrared optical parametric oscillator was mainly introduced. And the related research work of our group on the narrow linewidth of an optical parametric oscillator was introduced. Finally, the research prospect of the narrow-linewidth mid-infrared laser has been prospected.
3 μm~5 μm is one of the transmission windows of the atmosphere, including many atoms or molecules' characteristic absorption peaks. 3 μm~5 μm laser souses have wide applications, such as medical diagnosis, environmental monitoring, spectral analysis, military countermeasure, and so on. In these application fields, light sources are often required to have narrow linewidth and wavelength tuning capability. Narrow-linewidth laser is an ideal light source for these applications due to its small spectrum range and concentrative energy. The technology of narrow-linewidth of 3 μm~5 μm laser were summarized, including the linewidth compression method of the Fe2+/Cr2+ ion-doped solid-state laser and fluoride fiber laser, and several methods of quantum cascade laser frequency stabilization were discussed. The compact and all-solid-state mid-infrared optical parametric oscillator was mainly introduced. And the related research work of our group on the narrow linewidth of an optical parametric oscillator was introduced. Finally, the research prospect of the narrow-linewidth mid-infrared laser has been prospected.
2023, 47(6): 751-756.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.004
Abstract:
By combining theoretical derivation and experimental verification, research was conducted on how optical parameters affected the coherence efficiency of wind light detection and ranging (LiDAR). According to the superposition principle of optical fields, the influence of local oscillator waist and fiber coupler diameter and optical aberrations on coherent efficiency was discussed. Experiment of atmospheric turbulence effect was conducted, and the system signal-to-noise ratio with different optical parameters was measured under typical weather conditions. The consequence indicate that if the pupil aperture and F number are 100 mm and 2, the optimal beam waist and receive fiber diameter are 3.3 μm and 9 μm, and root mean square of the optical wavefront aberration is less than 0.06λ. Under strong turbulence, when the visibility is less than 5 km, the radar detection distance decreases by 60%. It has special significance for optimizing optical parameters to promote the study.
By combining theoretical derivation and experimental verification, research was conducted on how optical parameters affected the coherence efficiency of wind light detection and ranging (LiDAR). According to the superposition principle of optical fields, the influence of local oscillator waist and fiber coupler diameter and optical aberrations on coherent efficiency was discussed. Experiment of atmospheric turbulence effect was conducted, and the system signal-to-noise ratio with different optical parameters was measured under typical weather conditions. The consequence indicate that if the pupil aperture and F number are 100 mm and 2, the optimal beam waist and receive fiber diameter are 3.3 μm and 9 μm, and root mean square of the optical wavefront aberration is less than 0.06λ. Under strong turbulence, when the visibility is less than 5 km, the radar detection distance decreases by 60%. It has special significance for optimizing optical parameters to promote the study.
2023, 47(6): 757-765.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.005
Abstract:
Spectral detection was a crucial method for identifying the types and compositions of the substance. The concave grating was the key element of a spectrograph when a concave grating was used as an element of a spectrograph. The detection results of the imaging quality are directly influenced by the concave grating. The methods of affecting the image quality were named aberration correction and resolution improvement, respectively. The research progress of the aberration correction and the resolution improvement in spectrograph manufacture is stated. For each scheme of the aberration correction and the resolution improvement, the skills and characteristics are summarized, and the conditions for the aberration correction and the resolution improvement are pointed out. Finally, the possible development directions of spectral detection based on the concave grating in the future prospect.
Spectral detection was a crucial method for identifying the types and compositions of the substance. The concave grating was the key element of a spectrograph when a concave grating was used as an element of a spectrograph. The detection results of the imaging quality are directly influenced by the concave grating. The methods of affecting the image quality were named aberration correction and resolution improvement, respectively. The research progress of the aberration correction and the resolution improvement in spectrograph manufacture is stated. For each scheme of the aberration correction and the resolution improvement, the skills and characteristics are summarized, and the conditions for the aberration correction and the resolution improvement are pointed out. Finally, the possible development directions of spectral detection based on the concave grating in the future prospect.
2023, 47(6): 766-771.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.006
Abstract:
In order to solve the problem of silver-based contacts in low-voltage devices, which were prone to fusion and ablation, leading to insufficient electrical life, a new graphene/silver-based composite contact was prepared by the laser method. A fully covered graphene film was prepared on the surface of commercial AgNi15 contacts by laser cladding technology as a stand-alone coating to resist environmental damage. Theoretical analysis and experimental verification were carried out to obtain the optimal process conditions and corresponding performance data. The results demonstrate that the hardness of graphene/silver composite contact is 104.05 HV, the density is 9.15 g/cm3, and the contact resistance is 0.016 Ω. The new solution protocol and experimental bases have been provided for the fabrication of high-performance low-pressure contacts in this study.
In order to solve the problem of silver-based contacts in low-voltage devices, which were prone to fusion and ablation, leading to insufficient electrical life, a new graphene/silver-based composite contact was prepared by the laser method. A fully covered graphene film was prepared on the surface of commercial AgNi15 contacts by laser cladding technology as a stand-alone coating to resist environmental damage. Theoretical analysis and experimental verification were carried out to obtain the optimal process conditions and corresponding performance data. The results demonstrate that the hardness of graphene/silver composite contact is 104.05 HV, the density is 9.15 g/cm3, and the contact resistance is 0.016 Ω. The new solution protocol and experimental bases have been provided for the fabrication of high-performance low-pressure contacts in this study.
2023, 47(6): 772-777.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.007
Abstract:
In order to obtain a larger color gamut in the green region and broader gamut coverage with Rec. 2020, 532 nm laser light was adopted as the fourth primary. The color gamut volume, gamut coverage with Rec. 2020, gamut enhancement in the green region, and gamut coverage in the yellow region of RGGB(red, green, green, blue) wavelength set 660 nm, 532 nm, 520 nm, 465 nm was simulated and analyzed in CIEL*a*b* uniform color space. The result shows that the maximum color gamut volume is 2218900, the maximum gamut coverage with Rec. 2020 standard is 97.51%, and the maximum gamut enhancement in the yellow region and green region is 29.75% and 9.58%, respectively. This RGGB system has excellent performance when compared with RGB three-primary system and RGBY four-primary system, and the luminance ratio can be adjusted according to the actual requirements. This research provides another feasible idea for the construction of a four-primary color display system.
In order to obtain a larger color gamut in the green region and broader gamut coverage with Rec. 2020, 532 nm laser light was adopted as the fourth primary. The color gamut volume, gamut coverage with Rec. 2020, gamut enhancement in the green region, and gamut coverage in the yellow region of RGGB(red, green, green, blue) wavelength set 660 nm, 532 nm, 520 nm, 465 nm was simulated and analyzed in CIEL*a*b* uniform color space. The result shows that the maximum color gamut volume is 2218900, the maximum gamut coverage with Rec. 2020 standard is 97.51%, and the maximum gamut enhancement in the yellow region and green region is 29.75% and 9.58%, respectively. This RGGB system has excellent performance when compared with RGB three-primary system and RGBY four-primary system, and the luminance ratio can be adjusted according to the actual requirements. This research provides another feasible idea for the construction of a four-primary color display system.
2023, 47(6): 778-785.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.008
Abstract:
In order to explore the height variation characteristics of the boundary layer over Guanghan Airport, the carrier noise ratio data of Doppler light detection and ranging (LiDAR) was used to invert the boundary layer height over the airport by gradient method, wavelet covariance method, and standard variance method. The calculated data through these methods was then compared with that of the L-band sounding and aircraft detection data. The results show that boundary layer information can be captured well by these methods, and good consistency in the recognition of convective boundary pause can be observed. However, the gradient method shows obvious advantages in accuracy, continuity and stability in the recognition of residual layer pause and stable boundary top layer. During the observation period, the height of the convective boundary layer and the residual layer is about 2000 m, and the height of the stable boundary layer is between 100 m~200 m. The boundary layer height of LiDAR inversion was verified by aircraft detection data and sonde data. Due to the turbulence in the boundary layer, the material boundary layer and the thermal boundary layer were significantly different at certain times. The study can provide early warning information for flight training and better ensure flight safety.
In order to explore the height variation characteristics of the boundary layer over Guanghan Airport, the carrier noise ratio data of Doppler light detection and ranging (LiDAR) was used to invert the boundary layer height over the airport by gradient method, wavelet covariance method, and standard variance method. The calculated data through these methods was then compared with that of the L-band sounding and aircraft detection data. The results show that boundary layer information can be captured well by these methods, and good consistency in the recognition of convective boundary pause can be observed. However, the gradient method shows obvious advantages in accuracy, continuity and stability in the recognition of residual layer pause and stable boundary top layer. During the observation period, the height of the convective boundary layer and the residual layer is about 2000 m, and the height of the stable boundary layer is between 100 m~200 m. The boundary layer height of LiDAR inversion was verified by aircraft detection data and sonde data. Due to the turbulence in the boundary layer, the material boundary layer and the thermal boundary layer were significantly different at certain times. The study can provide early warning information for flight training and better ensure flight safety.
2023, 47(6): 786-794.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.009
Abstract:
To study the effect of water-mist on laser processing of carbon fiber reinforced plastic (CFRP). A method was used to process CFRP with a water-mist assisted laser. Theoretical analysis and experimental verification were carried out by orthogonal experiment, multiple linear regression analysis, and optical instruments. The effect of water-mist on the laser processing of CFRP was obtained, and the process parameters were optimized. The results show that the spot diameter of the laser gradually decreases with the increase of nozzle height, nozzle angle, and the decrease in gas pressure. As the nozzle angle increases and the gas pressure decreases, the laser loss rate decreases gradually. The nozzle height has little effect on laser power. When the nozzle angle is 50°, the gas pressure is 0.2 MPa, and the nozzle height is 30 mm, a depth-width ratio up to 5.303 can be obtained, and the laser loss rate is 1.473%. The internal characteristics of the kerf can be predicted by establishing empirical formulas between the water-mist parameters and the machining quality. Finally, compared with the gas-assisted laser processing of CFRP, smaller cross-section heat-affected zone and larger groove depth can be obtained by the water-mist-assisted laser processing of CFRP. This study provides a reference for laser low-damage processing of CFRP.
To study the effect of water-mist on laser processing of carbon fiber reinforced plastic (CFRP). A method was used to process CFRP with a water-mist assisted laser. Theoretical analysis and experimental verification were carried out by orthogonal experiment, multiple linear regression analysis, and optical instruments. The effect of water-mist on the laser processing of CFRP was obtained, and the process parameters were optimized. The results show that the spot diameter of the laser gradually decreases with the increase of nozzle height, nozzle angle, and the decrease in gas pressure. As the nozzle angle increases and the gas pressure decreases, the laser loss rate decreases gradually. The nozzle height has little effect on laser power. When the nozzle angle is 50°, the gas pressure is 0.2 MPa, and the nozzle height is 30 mm, a depth-width ratio up to 5.303 can be obtained, and the laser loss rate is 1.473%. The internal characteristics of the kerf can be predicted by establishing empirical formulas between the water-mist parameters and the machining quality. Finally, compared with the gas-assisted laser processing of CFRP, smaller cross-section heat-affected zone and larger groove depth can be obtained by the water-mist-assisted laser processing of CFRP. This study provides a reference for laser low-damage processing of CFRP.
2023, 47(6): 795-802.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.010
Abstract:
In order to improve the accuracy and efficiency of line structure light plane calibration and the universality of the calibration method, a line structure light plane calibration method based on a 2-D circular target was proposed. The subpixel coordinates of the center point of the light strip irradiated at any position of the 2-D circular calibration target were obtained by the light strip extraction algorithm. All the points on the light strip were fitted into a straight line, and the lines connecting each column of the circular calibration target intersected at one point. After obtaining the intersection point of each column of the calibration target line and the fitted light strip center line, a line connecting the intersection point and the camera optical center was formed. By setting up the equation of the line and the equations of two intersecting lines in the pixel coordinate system, and the equation of the plane where the 2-D circular calibration target was located, the coordinates of each intersection point in the camera coordinate system are solved. Finally, the plane fitting algorithm of least squares was used to obtain the equation of the light plane. The basic principle and implementation process of the calibration method was introduced, and the validity of the method was verified by setting up the experimental system. The results show that the average measurement error of the light plane obtained by this method can reach 2.36737 mm, which has high robustness, and the calibration process is very simple and suitable for general engineering applications and machining processes. This study provides a reference for the light plane calibration of line structure light sensors.
In order to improve the accuracy and efficiency of line structure light plane calibration and the universality of the calibration method, a line structure light plane calibration method based on a 2-D circular target was proposed. The subpixel coordinates of the center point of the light strip irradiated at any position of the 2-D circular calibration target were obtained by the light strip extraction algorithm. All the points on the light strip were fitted into a straight line, and the lines connecting each column of the circular calibration target intersected at one point. After obtaining the intersection point of each column of the calibration target line and the fitted light strip center line, a line connecting the intersection point and the camera optical center was formed. By setting up the equation of the line and the equations of two intersecting lines in the pixel coordinate system, and the equation of the plane where the 2-D circular calibration target was located, the coordinates of each intersection point in the camera coordinate system are solved. Finally, the plane fitting algorithm of least squares was used to obtain the equation of the light plane. The basic principle and implementation process of the calibration method was introduced, and the validity of the method was verified by setting up the experimental system. The results show that the average measurement error of the light plane obtained by this method can reach 2.36737 mm, which has high robustness, and the calibration process is very simple and suitable for general engineering applications and machining processes. This study provides a reference for the light plane calibration of line structure light sensors.
2023, 47(6): 803-810.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.011
Abstract:
In order to study the compression characteristics of the self-similar pulse in the Mach-Zehnder interferometer(MZI), the evolution and compression of the self-similar pulse were simulated by using the nonlinear Schrödinger equation. The influence of the fiber parameters on pulse compression of the MZI based on the cascade single-mode fiber was analyzed. The results show that without considering the high-order dispersion, when the length of the two single-mode fibers in the upper arm is 8.16 m and 2.16 m, respectively, and the length of the single-mode fiber in the lower arm is 8.16 m, the optimal compression pulse is obtained with the full width at half maximum of 27.85 fs, peak power of 1860.59 W and the pedestal energy ratio is 10.241%. When high-order dispersion is considered, it is found that pulse transmission in single-mode fiber presents the phenomenon of the peak power increase and the pedestal energy ratio increase, and the right shift of pulse is not favorable to output compression pulse with a small pedestal. When the third-order dispersion is less than 0.001 ps3/km, femtosecond pulses of good quality can be obtained by using MZI compression. The result of this study has certain reference values for self-similar pulse compression research.
In order to study the compression characteristics of the self-similar pulse in the Mach-Zehnder interferometer(MZI), the evolution and compression of the self-similar pulse were simulated by using the nonlinear Schrödinger equation. The influence of the fiber parameters on pulse compression of the MZI based on the cascade single-mode fiber was analyzed. The results show that without considering the high-order dispersion, when the length of the two single-mode fibers in the upper arm is 8.16 m and 2.16 m, respectively, and the length of the single-mode fiber in the lower arm is 8.16 m, the optimal compression pulse is obtained with the full width at half maximum of 27.85 fs, peak power of 1860.59 W and the pedestal energy ratio is 10.241%. When high-order dispersion is considered, it is found that pulse transmission in single-mode fiber presents the phenomenon of the peak power increase and the pedestal energy ratio increase, and the right shift of pulse is not favorable to output compression pulse with a small pedestal. When the third-order dispersion is less than 0.001 ps3/km, femtosecond pulses of good quality can be obtained by using MZI compression. The result of this study has certain reference values for self-similar pulse compression research.
2023, 47(6): 811-815.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.012
Abstract:
A pre-amending method was studied and implemented to the fast steering mirror (FSM) execute component to improve the dynamic response characteristics of an opto-electronic fine tracking system based on voice coil actuator(VCA) FSM. A feedforward adjusting step was additionally applied for optimizing the control of the FSM according to the target position variation obtained by a target detection and recognition component. The configuration and principle of the opto-electronic fine tracking system based on FSM were described, and the control of the VCA driven fast steering mirror was modeled. Further, the feedforward-feedback control method was implemented. An experimental system consisting of a target simulation part, a target imaging and detection part, and a target tracking part was constructed to test and verify the method. The results show that the delay of the system is shortened from 2.9 ms to 0.8 ms, and the dynamic response bandwidth is improved from 20 Hz to 45 Hz. The pre-amending control method can significantly reduce the phase lag of the opto-electronic fine tracking system and improve the systematic response characteristic.
A pre-amending method was studied and implemented to the fast steering mirror (FSM) execute component to improve the dynamic response characteristics of an opto-electronic fine tracking system based on voice coil actuator(VCA) FSM. A feedforward adjusting step was additionally applied for optimizing the control of the FSM according to the target position variation obtained by a target detection and recognition component. The configuration and principle of the opto-electronic fine tracking system based on FSM were described, and the control of the VCA driven fast steering mirror was modeled. Further, the feedforward-feedback control method was implemented. An experimental system consisting of a target simulation part, a target imaging and detection part, and a target tracking part was constructed to test and verify the method. The results show that the delay of the system is shortened from 2.9 ms to 0.8 ms, and the dynamic response bandwidth is improved from 20 Hz to 45 Hz. The pre-amending control method can significantly reduce the phase lag of the opto-electronic fine tracking system and improve the systematic response characteristic.
2023, 47(6): 816-823.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.013
Abstract:
To improve the efficiency and detail performance of the Poisson surface reconstruction algorithm's reconstruction results, a point cloud search method based on a hybrid tree balances the conflict between time complexity and space complexity of octree and binary tree technology. In the point cloud search stage, the density evaluation and filtering of the point cloud were used by introducing multiple energy terms, and adaptive point cloud up sampling was used for the sparse part of the point cloud to ensure the details and accuracy of the reconstructed model. The results show that the speed of the hybrid tree reconstruction algorithm increased by 33% and 15% on average compared with the Poisson surface reconstruction algorithm and the screened Poisson surface reconstruction algorithm. In addition, the details of the reconstructed model can be better maintained to obtain the minimum error. This study provides a reference for the surface reconstruction of point clouds.
To improve the efficiency and detail performance of the Poisson surface reconstruction algorithm's reconstruction results, a point cloud search method based on a hybrid tree balances the conflict between time complexity and space complexity of octree and binary tree technology. In the point cloud search stage, the density evaluation and filtering of the point cloud were used by introducing multiple energy terms, and adaptive point cloud up sampling was used for the sparse part of the point cloud to ensure the details and accuracy of the reconstructed model. The results show that the speed of the hybrid tree reconstruction algorithm increased by 33% and 15% on average compared with the Poisson surface reconstruction algorithm and the screened Poisson surface reconstruction algorithm. In addition, the details of the reconstructed model can be better maintained to obtain the minimum error. This study provides a reference for the surface reconstruction of point clouds.
2023, 47(6): 824-830.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.014
Abstract:
In order to investigate the process of molten material ejection during nanosecond laser ablation of mono-crystalline silicon, simulation and experimental investigation on nanosecond laser ablation of silicon under different environments were carried out. Simulation on the material ejection during nanosecond laser ablation of silicon under air, water, and vacuum environments with simulation software was carried out based on the Level-Set method. The effects of the temperature field and velocity field on surface sputtering under different environments were investigated. Experiments on laser ablation of mono-crystalline silicon using a wavelength of 266 nm, a pulse width of 30 ns, and a frequency of 50 Hz were done to verify the simulation results. The ablation results were observed by atomic force microscopy and digital microscopy. The results show that the spatter velocity under the air environment is 14.1 m/s at t=30 ns, and the molten material ejectes the ablated holes outwards due to the action of vapor pressure in the ablated area. Under the water environment, the spatter velocity is 1.68 m/s at t=30 ns, much lower than that in air conditions. Under the vacuum environment, the material is vaporized for a short time, and the spatter velocity of the molten material is 18.4 m/s at t=30 ns. The molten materials eject productively due to the high spatter velocity. The adhesion of molten material on the surface is improved. The processing environment has a strong influence on the material ejection during the nanosecond laser ablation of silicon. The investigation provides a reference for improving the quality during nanosecond laser micro-machining.
In order to investigate the process of molten material ejection during nanosecond laser ablation of mono-crystalline silicon, simulation and experimental investigation on nanosecond laser ablation of silicon under different environments were carried out. Simulation on the material ejection during nanosecond laser ablation of silicon under air, water, and vacuum environments with simulation software was carried out based on the Level-Set method. The effects of the temperature field and velocity field on surface sputtering under different environments were investigated. Experiments on laser ablation of mono-crystalline silicon using a wavelength of 266 nm, a pulse width of 30 ns, and a frequency of 50 Hz were done to verify the simulation results. The ablation results were observed by atomic force microscopy and digital microscopy. The results show that the spatter velocity under the air environment is 14.1 m/s at t=30 ns, and the molten material ejectes the ablated holes outwards due to the action of vapor pressure in the ablated area. Under the water environment, the spatter velocity is 1.68 m/s at t=30 ns, much lower than that in air conditions. Under the vacuum environment, the material is vaporized for a short time, and the spatter velocity of the molten material is 18.4 m/s at t=30 ns. The molten materials eject productively due to the high spatter velocity. The adhesion of molten material on the surface is improved. The processing environment has a strong influence on the material ejection during the nanosecond laser ablation of silicon. The investigation provides a reference for improving the quality during nanosecond laser micro-machining.
2023, 47(6): 831-840.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.015
Abstract:
For the purpose of enhancing the precision of 3-D reconstruction based on the structured light method, the regression model in machine learning was used to measure the 3-D topography of objects. The light intensity information cluster samples in different directions of object height points were obtained monocular as the training set of the regression model. After the regression model was trained, the mapping function relationship between the illumination intensity information distribution of the modulation diagram and the height of the object can be directly established to complete the three-dimensional measurement of the object. The numerical information of modulated fringe light was introduced into the regression model in the form of characteristics. 3-D surface of the object was accurately reconstructed, and the purpose of obtaining the height information from end to end was realized. The feasibility of the neural network regression model based on machine learning in 3-D surface reconstruction was verified. The results show that the model can reconstruct the 3-D surface accurately even when the projection features are fuzzy or the noise is large. The average reconstruction error is 1.40×10-4 mm, which is better than the data of the general reconstruction method. This study provides a reference for the high-precision 3-D surface reconstruction of monocular objects under strong interference conditions, effectively simplifies the tedious calculation and measurement process, and improves measurement accuracy.
For the purpose of enhancing the precision of 3-D reconstruction based on the structured light method, the regression model in machine learning was used to measure the 3-D topography of objects. The light intensity information cluster samples in different directions of object height points were obtained monocular as the training set of the regression model. After the regression model was trained, the mapping function relationship between the illumination intensity information distribution of the modulation diagram and the height of the object can be directly established to complete the three-dimensional measurement of the object. The numerical information of modulated fringe light was introduced into the regression model in the form of characteristics. 3-D surface of the object was accurately reconstructed, and the purpose of obtaining the height information from end to end was realized. The feasibility of the neural network regression model based on machine learning in 3-D surface reconstruction was verified. The results show that the model can reconstruct the 3-D surface accurately even when the projection features are fuzzy or the noise is large. The average reconstruction error is 1.40×10-4 mm, which is better than the data of the general reconstruction method. This study provides a reference for the high-precision 3-D surface reconstruction of monocular objects under strong interference conditions, effectively simplifies the tedious calculation and measurement process, and improves measurement accuracy.
Fabrication and temperature characteristics of erbium-doped fiber based on chemical vapor deposition
2023, 47(6): 841-845.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.016
Abstract:
In order to develop erbium-doped fibers with temperature stability to achieve the requirements of super-fluorescent light sources for medium and high precision fiber optic gyroscopes, two types of erbium-doped fibers, Al-Er co-doped and Al-Ge-Er co-doped were prepared by a chelate vapour deposition method. The absorption coefficients and background losses of the two fibers were measured, and the temperature stability of the Al-Ge-Er co-doped fibers was verified experimentally by building a test platform for the super fluorescent light source. The study shows that the Al-Er co-doped fibers have higher absorption coefficients but worse background losses when they are fabricated with an equal volume of erbium chelate. The absorption coefficients of the two fibers are 35.6 dB/m and 20.0 dB/m at 1530 nm, and the background losses are 31.7 dB/km and 6.3 dB/km at 1200 nm. In the temperature range of -45.0 ℃~ 70.0 ℃, the spontaneous emission spectrum mean wavelength variation of the Al-Ge-Er co-doped fiber fabricated by chelate vapor deposition method is about 6.52×10-7 nm/℃ at the central wavelength of 1560.84 nm with the bandwidth of 10.51 nm. This fiber can achieve the requirements of a super-fluorescent light source for high precision fiber optic gyroscope. And this study provides a reference for the development of erbium-doped optical fibers.
In order to develop erbium-doped fibers with temperature stability to achieve the requirements of super-fluorescent light sources for medium and high precision fiber optic gyroscopes, two types of erbium-doped fibers, Al-Er co-doped and Al-Ge-Er co-doped were prepared by a chelate vapour deposition method. The absorption coefficients and background losses of the two fibers were measured, and the temperature stability of the Al-Ge-Er co-doped fibers was verified experimentally by building a test platform for the super fluorescent light source. The study shows that the Al-Er co-doped fibers have higher absorption coefficients but worse background losses when they are fabricated with an equal volume of erbium chelate. The absorption coefficients of the two fibers are 35.6 dB/m and 20.0 dB/m at 1530 nm, and the background losses are 31.7 dB/km and 6.3 dB/km at 1200 nm. In the temperature range of -45.0 ℃~ 70.0 ℃, the spontaneous emission spectrum mean wavelength variation of the Al-Ge-Er co-doped fiber fabricated by chelate vapor deposition method is about 6.52×10-7 nm/℃ at the central wavelength of 1560.84 nm with the bandwidth of 10.51 nm. This fiber can achieve the requirements of a super-fluorescent light source for high precision fiber optic gyroscope. And this study provides a reference for the development of erbium-doped optical fibers.
2023, 47(6): 846-853.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.017
Abstract:
In order to realize dual-band perfect absorption in the infrared wavelength range, single-layer black phosphorus ribbons were arranged in parallel with alternating carrier doping concentration. Theoretical analysis and optical simulation were performed to get absorption spectra and sensing characteristics of the device in the infrared wavelength range. The results show the proposed device can achieve dual-band perfect absorption (>99.9% absorption efficiency) in the 2 μm~5 μm infrared wavelength range. The high absorption is caused by the critical coupling of incident light to the device, and instructive resonance is formed; the on-resonance light is restricted around black phosphorus; the dual-band absorption characteristic of the metamaterial makes it an ideal sensor with high reliability and accuracy; shift of absorption peaks is almost in a linear relationship with change of refractive index of cladding material. The margin of error between the calculated and actual refractive index is within 1%. The simple structure and reasonable tolerance in dimension deviation make the proposed metamaterial a good candidate for applications such as multiple-band absorption and sensing in the infrared wavelength range.
In order to realize dual-band perfect absorption in the infrared wavelength range, single-layer black phosphorus ribbons were arranged in parallel with alternating carrier doping concentration. Theoretical analysis and optical simulation were performed to get absorption spectra and sensing characteristics of the device in the infrared wavelength range. The results show the proposed device can achieve dual-band perfect absorption (>99.9% absorption efficiency) in the 2 μm~5 μm infrared wavelength range. The high absorption is caused by the critical coupling of incident light to the device, and instructive resonance is formed; the on-resonance light is restricted around black phosphorus; the dual-band absorption characteristic of the metamaterial makes it an ideal sensor with high reliability and accuracy; shift of absorption peaks is almost in a linear relationship with change of refractive index of cladding material. The margin of error between the calculated and actual refractive index is within 1%. The simple structure and reasonable tolerance in dimension deviation make the proposed metamaterial a good candidate for applications such as multiple-band absorption and sensing in the infrared wavelength range.
2023, 47(6): 854-859.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.018
Abstract:
To achieve single wavelength output, a single wavelength fiber laser based on a single-mode quartz-erbium-doped single-mode quartz hybrid fiber interferometer (HFI) was proposed. Based on the optical field interference principle and optical waveguide theory in hybrid dielectric fiber waveguides, the mode interference theory of HFI was analyzed, and the variation of the interference optical characteristics in HFI with the length and dislocation amount of the intermediate erbium-doped fiber (EDF) was studied. HFI was prepared using a melt dislocation method, which optimized the length of the EDF and the offset between the single-mode fiber and the EDF. The results show that, the optimal EDF length is 15 mm, and the optimal offset between the single-mode fiber and the EDF is 7.9 μm. Selecting an EDF HFI with a length of 15 mm as a mode selector for the resonator of a ring fiber laser can achieve a relatively stable single wavelength fiber laser output. This result is helpful for the application of the laser in optical fiber sensing and communication systems.
To achieve single wavelength output, a single wavelength fiber laser based on a single-mode quartz-erbium-doped single-mode quartz hybrid fiber interferometer (HFI) was proposed. Based on the optical field interference principle and optical waveguide theory in hybrid dielectric fiber waveguides, the mode interference theory of HFI was analyzed, and the variation of the interference optical characteristics in HFI with the length and dislocation amount of the intermediate erbium-doped fiber (EDF) was studied. HFI was prepared using a melt dislocation method, which optimized the length of the EDF and the offset between the single-mode fiber and the EDF. The results show that, the optimal EDF length is 15 mm, and the optimal offset between the single-mode fiber and the EDF is 7.9 μm. Selecting an EDF HFI with a length of 15 mm as a mode selector for the resonator of a ring fiber laser can achieve a relatively stable single wavelength fiber laser output. This result is helpful for the application of the laser in optical fiber sensing and communication systems.
2023, 47(6): 860-865.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.019
Abstract:
In order to discuss the influence of different laser energy on the transformation mechanism of graphite into nano-diamond in a 1-D microscale heat conduction model, optimized graphite structure was simulated by molecular dynamics method based on density functional theory(DFT). The temperature distribution of graphite surface irradiated by laser was calculated by the finite difference method. Based on the sp3 bond that can make a distinction between diamond and graphite was discussed especially, the carbon atom bonding condition was studied according to the band gap of the density of states(DOS) obtained by energy coupling. The results show that a small number of sp3 hybrid carbon atoms can be formed only when the laser energy reaches 5 J, and with the increase of laser energy, the temperature of the irradiated graphite surface in the liquid phase increases, the free electrons in the carbon atoms can be easier to move to a bonding molecular orbital, and the electronegativity of the electrons will be enhanced, which boosts the sp3 bond polarity and helps to transform sp2 bond into sp3 bond. This study has important practical significance in improving the preparation efficiency of nano-diamond under laser irradiation in the liquid phase and exploring the preparation mechanism of nano-diamond.
In order to discuss the influence of different laser energy on the transformation mechanism of graphite into nano-diamond in a 1-D microscale heat conduction model, optimized graphite structure was simulated by molecular dynamics method based on density functional theory(DFT). The temperature distribution of graphite surface irradiated by laser was calculated by the finite difference method. Based on the sp3 bond that can make a distinction between diamond and graphite was discussed especially, the carbon atom bonding condition was studied according to the band gap of the density of states(DOS) obtained by energy coupling. The results show that a small number of sp3 hybrid carbon atoms can be formed only when the laser energy reaches 5 J, and with the increase of laser energy, the temperature of the irradiated graphite surface in the liquid phase increases, the free electrons in the carbon atoms can be easier to move to a bonding molecular orbital, and the electronegativity of the electrons will be enhanced, which boosts the sp3 bond polarity and helps to transform sp2 bond into sp3 bond. This study has important practical significance in improving the preparation efficiency of nano-diamond under laser irradiation in the liquid phase and exploring the preparation mechanism of nano-diamond.
2023, 47(6): 866-871.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.020
Abstract:
For the purpose of studying the optical constants of CsPbBr3 films prepared by the multi-step spin coating method, CsPbBr3 films were prepared on silicon and SnO2∶F (FTO) substrates by the multi-step spin-coating with lead bromide and cesium bromide as raw materials. The ellipsometric spectrum of films on silicon substrate was achieved by a photoelastic modulating ellipsometry spectrometer. The parameters of the ellipsometric spectrum were fitted by using the combination model of Tanguy and Tauc-Lorentz three oscillators, and the dispersion relationship of the optical constants of thin films in the range of 1.00 eV~5.00 eV was obtained. Fluorescence emission spectra and absorption spectra were used to verify the ellipsometry fitting results. The results show that the optical constants of CsPbBr3 films prepared by the multi-step spin coating method are different from those of other methods, and the refractive index may be negatively correlated with the surface roughness of the films. The band gap obtained by ellipsometry fitting is 2.3 eV, which verifies the results of fluorescence spectra and absorption spectra. This study provides a reference for the fitting analysis of the ellipsometry spectra of CsPbBr3 films prepared by multi-step spin coating.
For the purpose of studying the optical constants of CsPbBr3 films prepared by the multi-step spin coating method, CsPbBr3 films were prepared on silicon and SnO2∶F (FTO) substrates by the multi-step spin-coating with lead bromide and cesium bromide as raw materials. The ellipsometric spectrum of films on silicon substrate was achieved by a photoelastic modulating ellipsometry spectrometer. The parameters of the ellipsometric spectrum were fitted by using the combination model of Tanguy and Tauc-Lorentz three oscillators, and the dispersion relationship of the optical constants of thin films in the range of 1.00 eV~5.00 eV was obtained. Fluorescence emission spectra and absorption spectra were used to verify the ellipsometry fitting results. The results show that the optical constants of CsPbBr3 films prepared by the multi-step spin coating method are different from those of other methods, and the refractive index may be negatively correlated with the surface roughness of the films. The band gap obtained by ellipsometry fitting is 2.3 eV, which verifies the results of fluorescence spectra and absorption spectra. This study provides a reference for the fitting analysis of the ellipsometry spectra of CsPbBr3 films prepared by multi-step spin coating.
2023, 47(6): 872-880.
doi: 10.7510/jgjs.issn.1001-3806.2023.06.021
Abstract:
In order to solve the problems of food production and processing sites, such as the unfixed location of health inspection and the great influence of environmental factors on the inspection effect, according to the characteristics of different kinds of food residues under ultraviolet irradiation, a handheld fluorescence imaging device was developed by using fluorescence imaging technology and block Otsu algorithm, which can assist field inspectors in carrying out visual health inspection. The equipment detected milk powder (the volume fractions are 50%, 33%, 20%, 10%, and 2%) and spinach residue (the volume fractions are 50%, 33%, 25%, 20%, and 10%) on the surface of three common materials (wooden board, stainless steel board, polyethylene board). The results show that the system can assist inspectors in carrying out health and safety inspections. The detection rate of spinach residue with different volume fractions on the surface of the three materials is 100%, the detection rate of milk powder residue with different volume fractions on the surface of the wooden board and the stainless steel board is 100%, and on the surface of polyethylene plastic plate, except for the residual part of milk powder with the volume fractions of 2%, the remaining volume fraction of milk powder residue can be effectively detected. This study provides a reference for the development of handheld sanitary inspection equipment in food processing places.
In order to solve the problems of food production and processing sites, such as the unfixed location of health inspection and the great influence of environmental factors on the inspection effect, according to the characteristics of different kinds of food residues under ultraviolet irradiation, a handheld fluorescence imaging device was developed by using fluorescence imaging technology and block Otsu algorithm, which can assist field inspectors in carrying out visual health inspection. The equipment detected milk powder (the volume fractions are 50%, 33%, 20%, 10%, and 2%) and spinach residue (the volume fractions are 50%, 33%, 25%, 20%, and 10%) on the surface of three common materials (wooden board, stainless steel board, polyethylene board). The results show that the system can assist inspectors in carrying out health and safety inspections. The detection rate of spinach residue with different volume fractions on the surface of the three materials is 100%, the detection rate of milk powder residue with different volume fractions on the surface of the wooden board and the stainless steel board is 100%, and on the surface of polyethylene plastic plate, except for the residual part of milk powder with the volume fractions of 2%, the remaining volume fraction of milk powder residue can be effectively detected. This study provides a reference for the development of handheld sanitary inspection equipment in food processing places.
