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RSS2017 Vol. 41, No. 5
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2017, 41(5): 619-625.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.001
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Abstract:
Laser induced breakdown spectroscopy (LIBS) is an element analysis technique based on atomic emission spectroscopy and an important research method in the field of elemental analysis. As the excitation source of LIBS analysis, ultra-violet(UV) laser has the advantages of high photon energy and high spatial resolution, so it can effectively improve the ablation efficiency, reduce the fractionation effect and has good application prospects in geological and biological medicine detection. UV laser can also effectively enhance the effect of elemental analysis, and expand the application scope of LIBS technology. The principle and characteristics of ultraviolet LIBS technology were introduced. The application of ultraviolet LIBS technology at home and abroad was discussed. The development trend of ultraviolet LIBS technology was summarized.
Laser induced breakdown spectroscopy (LIBS) is an element analysis technique based on atomic emission spectroscopy and an important research method in the field of elemental analysis. As the excitation source of LIBS analysis, ultra-violet(UV) laser has the advantages of high photon energy and high spatial resolution, so it can effectively improve the ablation efficiency, reduce the fractionation effect and has good application prospects in geological and biological medicine detection. UV laser can also effectively enhance the effect of elemental analysis, and expand the application scope of LIBS technology. The principle and characteristics of ultraviolet LIBS technology were introduced. The application of ultraviolet LIBS technology at home and abroad was discussed. The development trend of ultraviolet LIBS technology was summarized.
2017, 41(5): 626-631.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.002
Abstract:
In order to solve the problem of high pressure loss and low heat transfer efficiency of fin-and-tube heat exchangers in a high power axial flow fast CO2 laser in the thick plate cutting field, computational fluid dynamics software ANSYS was used to analyze the heat transfer characteristics of 3 kinds of vortex generators. The shape, length, height and angle of trapezoidal winglet vortex generator with better heat transfer performance were optimized. The reliability of the numerical simulation data was verified through an open loop wind tunnel experimental platform. The results show that the optimum heat transfer performance is gotten with trapezoidal winglet vortex generator of 11mm length, 2.6mm height and 30° angle of attack which is gradually reduced. Compared with the generator without installing vortex, the heat transfer performance of trapezoidal winglet vortex generator Nu is increased by 8%~22%, and the friction factor is increased by 16%~27%, in Reynolds number of 600~1600. Test results of CP4000 series axial fast flow CO2 laser show that the stable output power of 8h is 4216W, 5.4% higher than the rated output power. The study improves the plate cutting capacity of CP4000 series lasers.
In order to solve the problem of high pressure loss and low heat transfer efficiency of fin-and-tube heat exchangers in a high power axial flow fast CO2 laser in the thick plate cutting field, computational fluid dynamics software ANSYS was used to analyze the heat transfer characteristics of 3 kinds of vortex generators. The shape, length, height and angle of trapezoidal winglet vortex generator with better heat transfer performance were optimized. The reliability of the numerical simulation data was verified through an open loop wind tunnel experimental platform. The results show that the optimum heat transfer performance is gotten with trapezoidal winglet vortex generator of 11mm length, 2.6mm height and 30° angle of attack which is gradually reduced. Compared with the generator without installing vortex, the heat transfer performance of trapezoidal winglet vortex generator Nu is increased by 8%~22%, and the friction factor is increased by 16%~27%, in Reynolds number of 600~1600. Test results of CP4000 series axial fast flow CO2 laser show that the stable output power of 8h is 4216W, 5.4% higher than the rated output power. The study improves the plate cutting capacity of CP4000 series lasers.
2017, 41(5): 632-636.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.003
Abstract:
In order to study damage effect of interline-transfer color CCD under millisecond pulsed laser irradiation, theoretical analysis and experimental study were carried out. The center temperature, damage area and depth on the CCD surface, the internal reset clock signal and impedance value of the CCD were measured under the action of laser beam with different energy densities. Combined with non-recoverable focal spot and black-white snowflake phenomena in the CCD output images, the damage effect of color plane array CCD irradiated by millisecond pulse laser was analyzed. The results show that the internal structure of the interline transfer color array CCD is damaged to different extents under the irradiation of millisecond pulsed laser. The ablation depth is direct to the basement layer with laser power intensity of 23.49J/cm2 so that the internal signal transmission channel of CCD is cut off and the leakage current is increased, and then, there is no signal output from the CCD, and the CCD is completely damaged. The study is helpful to study the damage effect of CCD detectors under intense laser.
In order to study damage effect of interline-transfer color CCD under millisecond pulsed laser irradiation, theoretical analysis and experimental study were carried out. The center temperature, damage area and depth on the CCD surface, the internal reset clock signal and impedance value of the CCD were measured under the action of laser beam with different energy densities. Combined with non-recoverable focal spot and black-white snowflake phenomena in the CCD output images, the damage effect of color plane array CCD irradiated by millisecond pulse laser was analyzed. The results show that the internal structure of the interline transfer color array CCD is damaged to different extents under the irradiation of millisecond pulsed laser. The ablation depth is direct to the basement layer with laser power intensity of 23.49J/cm2 so that the internal signal transmission channel of CCD is cut off and the leakage current is increased, and then, there is no signal output from the CCD, and the CCD is completely damaged. The study is helpful to study the damage effect of CCD detectors under intense laser.
2017, 41(5): 637-643.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.004
Abstract:
In order to improve coupling efficiency of laser energy of monocrystalline silicon in laser processing, a short laser pulse and a long laser pulse were used to form a combined pulse to irradiate the monocrystalline silicon. The process was simulated by using COMSOL software. The influences of the delay time of combination laser and the laser energy density of long pulse on the process effect were obtained. The effect was compared with that of individual action millisecond laser under the equal total energy. The measured damage morphologies of monocrystalline silicon irradiated by lasers with different power intensities were in agreement with the trend of numerical results. The results show that the combined laser can improve the coupling efficiency of laser. The different delay time would affect the process effect of the combined laser. The optimum delay time is 0.1ms. When the ratio of the millisecond laser energy density in the combined laser is relatively low, the effect is obvious. With the increase of the ratio of the millisecond laser energy density, the enhancement of the effect is relatively slow. The research results can provide theoretical and experimental basis for the application of combined laser.
In order to improve coupling efficiency of laser energy of monocrystalline silicon in laser processing, a short laser pulse and a long laser pulse were used to form a combined pulse to irradiate the monocrystalline silicon. The process was simulated by using COMSOL software. The influences of the delay time of combination laser and the laser energy density of long pulse on the process effect were obtained. The effect was compared with that of individual action millisecond laser under the equal total energy. The measured damage morphologies of monocrystalline silicon irradiated by lasers with different power intensities were in agreement with the trend of numerical results. The results show that the combined laser can improve the coupling efficiency of laser. The different delay time would affect the process effect of the combined laser. The optimum delay time is 0.1ms. When the ratio of the millisecond laser energy density in the combined laser is relatively low, the effect is obvious. With the increase of the ratio of the millisecond laser energy density, the enhancement of the effect is relatively slow. The research results can provide theoretical and experimental basis for the application of combined laser.
2017, 41(5): 644-648.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.005
Abstract:
In order to study characteristics of metasurface array of discontinuous phase L-shaped antenna in the 1st and 2nd order modes, by using the theory of scattering field with anomalous transmission, a L-shaped antenna structure was designed. By controlling the geometric parameters of the antenna and selecting the array element group, the coverage phase exceeded 2π. According to different topological charges, the vortex phase plates of the 1st order and the 2nd order were designed to produce different order vortex beams. The simulation results show that the simulation efficiency of the vertical polarization direction of the antenna element is about 55% when the incident wave is polarized vertically. When the phase covered 0~2π and 0~4π, the anomalous transmission angles of the linear array are different, -14.7° and -30° respectively. The results are consistent with the generalized Fresnel theory. This study has the important application value in the research of terahertz vortex beam devices.
In order to study characteristics of metasurface array of discontinuous phase L-shaped antenna in the 1st and 2nd order modes, by using the theory of scattering field with anomalous transmission, a L-shaped antenna structure was designed. By controlling the geometric parameters of the antenna and selecting the array element group, the coverage phase exceeded 2π. According to different topological charges, the vortex phase plates of the 1st order and the 2nd order were designed to produce different order vortex beams. The simulation results show that the simulation efficiency of the vertical polarization direction of the antenna element is about 55% when the incident wave is polarized vertically. When the phase covered 0~2π and 0~4π, the anomalous transmission angles of the linear array are different, -14.7° and -30° respectively. The results are consistent with the generalized Fresnel theory. This study has the important application value in the research of terahertz vortex beam devices.
2017, 41(5): 649-653.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.006
Abstract:
In order to realize rapid annealing of fiber Bragg gratings, high temperature arc plasma heat treatment method was adopted. The related experiments were designed for verification. A fiber Bragg grating (FBG) with transmission spectrum depth of 23dB, central wavelength of 1552.09nm and 3dB bandwidth of 0.2784nm was scanned by arc plasma discharging. The results show that the transmission spectrum depth is reduced, the 3dB bandwidth is narrowed and the central wavelength shows blue shift. The variation trend of each parameter is slowed down with the increasing of the repetitive scanning times. Finally, the transmission spectrum depth is reduced by 13dB, the central wavelength is shifted blue by 0.84nm and the 3dB bandwidth is narrowed by 0.1013nm. After fiber grating is annealed in a high temperature furnace for 24h, the transmission spectrum depth, central wavelength and 3dB bandwidth remain the same. It is feasible to use arc plasma for the annealing of FBG with the advantages of short cycle and no damage of the coating layer.
In order to realize rapid annealing of fiber Bragg gratings, high temperature arc plasma heat treatment method was adopted. The related experiments were designed for verification. A fiber Bragg grating (FBG) with transmission spectrum depth of 23dB, central wavelength of 1552.09nm and 3dB bandwidth of 0.2784nm was scanned by arc plasma discharging. The results show that the transmission spectrum depth is reduced, the 3dB bandwidth is narrowed and the central wavelength shows blue shift. The variation trend of each parameter is slowed down with the increasing of the repetitive scanning times. Finally, the transmission spectrum depth is reduced by 13dB, the central wavelength is shifted blue by 0.84nm and the 3dB bandwidth is narrowed by 0.1013nm. After fiber grating is annealed in a high temperature furnace for 24h, the transmission spectrum depth, central wavelength and 3dB bandwidth remain the same. It is feasible to use arc plasma for the annealing of FBG with the advantages of short cycle and no damage of the coating layer.
2017, 41(5): 654-658.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.007
Abstract:
In order to optimize the quantum well laser at 1.31μm wavelength in long distance optical fiber communication systems, strain compensated quantum well in active region of AlGaInAs/InP material was studied. Based on strain compensation method and Kronig-Panna model theory, the band structure of quantum well was calculated. The active region was consisted of 1.12% compressive strain AlGaInAs well layer and 0.4% tensile strain AlGaInAs barrier layer. ALDS software was used to simulate the design of the device and analyze the threshold and the steady state. The results show that the laser has a low threshold current of 9mA and a high slope efficiency of 0.4W/A at 25℃room temperature. In the potential barrier layer, the appropriate strain opposite to the strain of the potential well layer can reduce the average strain in the growth process, ensure the well growth of active zone, improve the band structure of quantum well effectively, enhance the limit ability of carriers, reduce threshold current, increase saturation power and improve device performance.
In order to optimize the quantum well laser at 1.31μm wavelength in long distance optical fiber communication systems, strain compensated quantum well in active region of AlGaInAs/InP material was studied. Based on strain compensation method and Kronig-Panna model theory, the band structure of quantum well was calculated. The active region was consisted of 1.12% compressive strain AlGaInAs well layer and 0.4% tensile strain AlGaInAs barrier layer. ALDS software was used to simulate the design of the device and analyze the threshold and the steady state. The results show that the laser has a low threshold current of 9mA and a high slope efficiency of 0.4W/A at 25℃room temperature. In the potential barrier layer, the appropriate strain opposite to the strain of the potential well layer can reduce the average strain in the growth process, ensure the well growth of active zone, improve the band structure of quantum well effectively, enhance the limit ability of carriers, reduce threshold current, increase saturation power and improve device performance.
2017, 41(5): 659-663.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.008
Abstract:
In order to solve the problem that the traditional tools and methods can not meet the requirement of clearing foreign object debris economically, efficiently and safely, the method of clearing foreign object debris on overhead power lines with land-based directed energy laser remotely was proposed. Theoretical analysis, finite element simulation and experimental verification were carried out. Based on the above research, the apparatus for removing foreign bodies from overhead lines by laser was developed, tested and applied in engineering practice. The result shows that the appropriate minimum power density is 20W/cm2, and the laser irradiation of 20W/cm2 is unable to damage the wire. The laser removal apparatus can remove foreign bodies on overhead lines under live working conditions efficiently and safely at long distance.
In order to solve the problem that the traditional tools and methods can not meet the requirement of clearing foreign object debris economically, efficiently and safely, the method of clearing foreign object debris on overhead power lines with land-based directed energy laser remotely was proposed. Theoretical analysis, finite element simulation and experimental verification were carried out. Based on the above research, the apparatus for removing foreign bodies from overhead lines by laser was developed, tested and applied in engineering practice. The result shows that the appropriate minimum power density is 20W/cm2, and the laser irradiation of 20W/cm2 is unable to damage the wire. The laser removal apparatus can remove foreign bodies on overhead lines under live working conditions efficiently and safely at long distance.
2017, 41(5): 664-668.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.009
Abstract:
In order to study whether the cavity-enhanced absorption spectroscopy can be used for the detection of NH3 gas concentration, a cavity-enhanced absorption spectroscopy system was built up. In the system, a tunable distributed feedback diode laser was used as the light source, and a plano-concave optical cavity, consisting of two mirrors with high reflectivity (reflectivity about 99.9% and radius of curvature about 1m), was used as the absorption cavity. Weak absorption spectra of NH3 gas molecules near 1.5μm were measured in the 34cm absorption cell by using cavity length scanning method. The pressure in the cavity was changed by increasing the concentration of NH3 gas. The absorption spectra were measured and stored after charging NH3 each time. By data processing, the relationship between spectral line width and gas concentration was analyzed. And the change of absorbance with the increase of cavity pressure was studied. The results show a good linear relationship. The minimum detection sensitivity of 3.3×10-8cm-1 is obtained by the statistical analysis of the residual noise. The experimental results show that NH3 concentration detection with good detection precision can be realized by using high sensitivity absorption spectroscopy technology.
In order to study whether the cavity-enhanced absorption spectroscopy can be used for the detection of NH3 gas concentration, a cavity-enhanced absorption spectroscopy system was built up. In the system, a tunable distributed feedback diode laser was used as the light source, and a plano-concave optical cavity, consisting of two mirrors with high reflectivity (reflectivity about 99.9% and radius of curvature about 1m), was used as the absorption cavity. Weak absorption spectra of NH3 gas molecules near 1.5μm were measured in the 34cm absorption cell by using cavity length scanning method. The pressure in the cavity was changed by increasing the concentration of NH3 gas. The absorption spectra were measured and stored after charging NH3 each time. By data processing, the relationship between spectral line width and gas concentration was analyzed. And the change of absorbance with the increase of cavity pressure was studied. The results show a good linear relationship. The minimum detection sensitivity of 3.3×10-8cm-1 is obtained by the statistical analysis of the residual noise. The experimental results show that NH3 concentration detection with good detection precision can be realized by using high sensitivity absorption spectroscopy technology.
2017, 41(5): 669-674.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.010
Abstract:
In order to achieve high-speed acquisition and real-time high-quality image reconstruction of photoacoustic tomography signals for small animal, a 128 element arc-shaped focused ultrasound transducer with 270° coverage angle, four 32 channel NI data acquisition modules, a tunable pulsed laser and model-based photoacoustic tomography reconstruction algorithm with regularized optimization were used. The spatial resolution of the system can be up to 180μm. The in vitro and in vivo imaging experiments show that the system can complete photoacoustic tomography data acquisition within 1ms, and obtain high quality reconstructed images within 40s. The system can be used to carry out in vivo multi-spectral photoacoustic tomography of small animals.
In order to achieve high-speed acquisition and real-time high-quality image reconstruction of photoacoustic tomography signals for small animal, a 128 element arc-shaped focused ultrasound transducer with 270° coverage angle, four 32 channel NI data acquisition modules, a tunable pulsed laser and model-based photoacoustic tomography reconstruction algorithm with regularized optimization were used. The spatial resolution of the system can be up to 180μm. The in vitro and in vivo imaging experiments show that the system can complete photoacoustic tomography data acquisition within 1ms, and obtain high quality reconstructed images within 40s. The system can be used to carry out in vivo multi-spectral photoacoustic tomography of small animals.
2017, 41(5): 675-679.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.011
Abstract:
In order to extract the damage boundary of parts quickly and accurately, observe the process and results of parts damage and realize the shape reduction, and repair complex damaged parts by laser cladding remanufacturing, the defect types of the damaged parts were divided according to process characteristics of laser cladding, the damage boundary extraction and shape reduction methods of different types of defects were studied. The method of extracting boundary features of surface spots based on the curvature threshold and the normal vector threshold and the method of extracting boundary features of local deep damage based on 3-D comparison were proposed. The methods of shape reduction were presented, for the local deep damage parts by the traditional surface and for the superficial damage parts by the NURBS surface. And then, the experiments of laser cladding remanufacturing and restoration were carried out to verify the feasibility of the proposed method by path planning. The results show that the precision and efficiency of the extraction and restoration of the damaged area are improved and the cladding morphology waviness is smaller. The study provides the theoretical basis for the application of extraction and shape reduction of the damaged parts in laser cladding remanufacturing.
In order to extract the damage boundary of parts quickly and accurately, observe the process and results of parts damage and realize the shape reduction, and repair complex damaged parts by laser cladding remanufacturing, the defect types of the damaged parts were divided according to process characteristics of laser cladding, the damage boundary extraction and shape reduction methods of different types of defects were studied. The method of extracting boundary features of surface spots based on the curvature threshold and the normal vector threshold and the method of extracting boundary features of local deep damage based on 3-D comparison were proposed. The methods of shape reduction were presented, for the local deep damage parts by the traditional surface and for the superficial damage parts by the NURBS surface. And then, the experiments of laser cladding remanufacturing and restoration were carried out to verify the feasibility of the proposed method by path planning. The results show that the precision and efficiency of the extraction and restoration of the damaged area are improved and the cladding morphology waviness is smaller. The study provides the theoretical basis for the application of extraction and shape reduction of the damaged parts in laser cladding remanufacturing.
2017, 41(5): 680-683.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.012
Abstract:
In order to obtain high pulsed energy output from an excimer laser, the Chang's electrode theory was used to design a compact electrode for producing large area uniform electric field. Through numerical simulation of ANSYS software, the electric field distribution on the electrode surface was obtained and compared with the theoretical results of the compact Chang electrode. The effect of ultraviolet pre ionization structure on electrode discharging was analyzed. The potential and electric field distribution were simulated. The results show that the presence of preionization plate directly affects the potential and electric field distribution between electrodes. The simulation results of electric field can be used to explain the formation of discharging between the top of preionization plate and anode. The study provides deeper theoretical support for the design of large area glow discharge electrodes.
In order to obtain high pulsed energy output from an excimer laser, the Chang's electrode theory was used to design a compact electrode for producing large area uniform electric field. Through numerical simulation of ANSYS software, the electric field distribution on the electrode surface was obtained and compared with the theoretical results of the compact Chang electrode. The effect of ultraviolet pre ionization structure on electrode discharging was analyzed. The potential and electric field distribution were simulated. The results show that the presence of preionization plate directly affects the potential and electric field distribution between electrodes. The simulation results of electric field can be used to explain the formation of discharging between the top of preionization plate and anode. The study provides deeper theoretical support for the design of large area glow discharge electrodes.
2017, 41(5): 684-687.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.013
Abstract:
To improve environmental adaptability of an optical system, an athermalization refractive antenna with coaxial transceiver was designed by the passive athermalization method combined with the optics and machinery. By using ZEMAX software, the image quality of the designed antenna was simulated and analyzed when the working distance ranged from 50m to 3000m and the environment temperature ranged from -45℃ to 65℃. After building experimental platform and measuring the actual image quality, the simulation results were verified. The results show that the optical path difference is less than 0.25λ and the optical quality of the designed antenna is close to the diffraction limit within the detection range. Moreover, within the scope of environmental temperature, the energy of the 90% of the spots is concentrated in the maximum coherence length. And the spot energy distribution of each field is uniform. The research can provide the theoretical basis for the design of the optical parameters and structure parameters of the antenna.
To improve environmental adaptability of an optical system, an athermalization refractive antenna with coaxial transceiver was designed by the passive athermalization method combined with the optics and machinery. By using ZEMAX software, the image quality of the designed antenna was simulated and analyzed when the working distance ranged from 50m to 3000m and the environment temperature ranged from -45℃ to 65℃. After building experimental platform and measuring the actual image quality, the simulation results were verified. The results show that the optical path difference is less than 0.25λ and the optical quality of the designed antenna is close to the diffraction limit within the detection range. Moreover, within the scope of environmental temperature, the energy of the 90% of the spots is concentrated in the maximum coherence length. And the spot energy distribution of each field is uniform. The research can provide the theoretical basis for the design of the optical parameters and structure parameters of the antenna.
2017, 41(5): 688-692.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.014
Abstract:
In order to suppress effect of optical fringes on detection accuracy, based on the characteristics of optical fringes, a method was proposed to compensate the optical fringes produced by parallel surfaces. Theory analysis and experimental verification were performed in a carbon dioxide detection system. The process and compensation results were shown. The results show that even in the case of optical fringe drift, the method can effectively compensate the optical fringes. The fitting correlation between the measured gas absorption signal and the standard gas absorption signal is increased from 0.8298 to 0.9934. The standard deviation of the measurement value of volume fraction was reduced from 1260×10-6 to 48.5×10-6. The method is very suitable for compensating the optical fringes caused by detector windows, gas pool windows, and other optical elements integrated into the system. It has great application value in the field of tunable diode laser absorption spectroscopy.
In order to suppress effect of optical fringes on detection accuracy, based on the characteristics of optical fringes, a method was proposed to compensate the optical fringes produced by parallel surfaces. Theory analysis and experimental verification were performed in a carbon dioxide detection system. The process and compensation results were shown. The results show that even in the case of optical fringe drift, the method can effectively compensate the optical fringes. The fitting correlation between the measured gas absorption signal and the standard gas absorption signal is increased from 0.8298 to 0.9934. The standard deviation of the measurement value of volume fraction was reduced from 1260×10-6 to 48.5×10-6. The method is very suitable for compensating the optical fringes caused by detector windows, gas pool windows, and other optical elements integrated into the system. It has great application value in the field of tunable diode laser absorption spectroscopy.
2017, 41(5): 693-696.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.015
Abstract:
In order to get high sensitivity detection of volume fraction of carbon dioxide gas, a carbon dioxide gas sensor based on the principle of infrared spectrum absorption was designed by using 9m hollow-core photonic crystal fiber as sensing unit. The absorption spectra of carbon dioxide gas with different volume fractions were measured under the same absorption wavelength. The analysis results show that the linear relationship between gas absorption intensity and volume fraction of gas is presented, in accordance with Beer-Lambert law. The detective sensitivity of the system is estimated to be 4.389×10-5W. It can make the system get higher sensitivity by lengthening the photonic crystal fiber and increasing the effective distance of gas absorption.
In order to get high sensitivity detection of volume fraction of carbon dioxide gas, a carbon dioxide gas sensor based on the principle of infrared spectrum absorption was designed by using 9m hollow-core photonic crystal fiber as sensing unit. The absorption spectra of carbon dioxide gas with different volume fractions were measured under the same absorption wavelength. The analysis results show that the linear relationship between gas absorption intensity and volume fraction of gas is presented, in accordance with Beer-Lambert law. The detective sensitivity of the system is estimated to be 4.389×10-5W. It can make the system get higher sensitivity by lengthening the photonic crystal fiber and increasing the effective distance of gas absorption.
2017, 41(5): 697-702.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.016
Abstract:
In order to overcome the phase error caused by γ nonlinearity of projector-camera pair about red/blue checkerboard in the projector calibration processing, the reason and the characteristics of nonlinear phase error were studied and the mathematical model between the nonlinear phase error and the wrapped phase was established. Based on the mathematical model, the phase error compensation matrix was obtained to correct the unwrapped phase. The experimental results show that the root mean square of the unwrapped phase after compensation is decreased from 0.0836rad to 0.0218rad. The maximum pixel error of grid corner caused by γ nonlinearity of the projector-camera pair at digital micro-mirror device (DMD) image is approximately reduced from 0.3pixel to 0.1pixel after phase compensation. The proposed method is useful to decrease the periodic phase error caused by γ nonlinear of the projector-camera paird and obtain higher accuracy coordinates of the red/blue checkerboard grid corner at DMD images.
In order to overcome the phase error caused by γ nonlinearity of projector-camera pair about red/blue checkerboard in the projector calibration processing, the reason and the characteristics of nonlinear phase error were studied and the mathematical model between the nonlinear phase error and the wrapped phase was established. Based on the mathematical model, the phase error compensation matrix was obtained to correct the unwrapped phase. The experimental results show that the root mean square of the unwrapped phase after compensation is decreased from 0.0836rad to 0.0218rad. The maximum pixel error of grid corner caused by γ nonlinearity of the projector-camera pair at digital micro-mirror device (DMD) image is approximately reduced from 0.3pixel to 0.1pixel after phase compensation. The proposed method is useful to decrease the periodic phase error caused by γ nonlinear of the projector-camera paird and obtain higher accuracy coordinates of the red/blue checkerboard grid corner at DMD images.
2017, 41(5): 703-707.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.017
Abstract:
In order to accurately measure the 3-D real-time atmospheric wind field to cope with the problems of low-level wind shear during aircraft take-off and landing, a compact 3-D Doppler wind lidar was developed by using Doppler beam swinging (DBS) principle. The wind field data obtained by the lidar were compared with the anemometry data with the other standard equipments. It turned out that the effective measurement of atmospheric wind field was achieved by the lidar under both sunny and cloudy weather conditions. The root mean square errors of wind speed and wind direction were 0.42m/s and 5.33° respectively. The lidar, with high precision and good stability, plays an important role for wind shear warning, the forecast of low-level atmospheric wind field and wind field measurement of aircraft flight channel.
In order to accurately measure the 3-D real-time atmospheric wind field to cope with the problems of low-level wind shear during aircraft take-off and landing, a compact 3-D Doppler wind lidar was developed by using Doppler beam swinging (DBS) principle. The wind field data obtained by the lidar were compared with the anemometry data with the other standard equipments. It turned out that the effective measurement of atmospheric wind field was achieved by the lidar under both sunny and cloudy weather conditions. The root mean square errors of wind speed and wind direction were 0.42m/s and 5.33° respectively. The lidar, with high precision and good stability, plays an important role for wind shear warning, the forecast of low-level atmospheric wind field and wind field measurement of aircraft flight channel.
2017, 41(5): 708-711.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.018
Abstract:
In order to control the harmonic emission process, the chirp pulse control on the harmonic cutoff and the harmonic intensity was theoretically investigated by using 3-D Schr dinger equation. Laser profiles, ionization probabilities, time-frequency analyses of the harmonic spectra were shown to explain the extension and the enhancement of harmonic spectra. The results show that the intensity of the harmonic cutoff region in the presence of the down-chirp pulse is enhanced by one order of magnitude in comparison with the chirp-free pulse case. By properly adding a half-cycle controlling pulse, the harmonic cutoff is remarkably extended. By superposing a properly selected harmonics, a 46as pulse can be produced. The intensity of the generated pulse is one order of magnitude higher than that from the chirp-free case. The investigation is helpful to control the harmonic emission and to produce the attosecond pulse.
In order to control the harmonic emission process, the chirp pulse control on the harmonic cutoff and the harmonic intensity was theoretically investigated by using 3-D Schr dinger equation. Laser profiles, ionization probabilities, time-frequency analyses of the harmonic spectra were shown to explain the extension and the enhancement of harmonic spectra. The results show that the intensity of the harmonic cutoff region in the presence of the down-chirp pulse is enhanced by one order of magnitude in comparison with the chirp-free pulse case. By properly adding a half-cycle controlling pulse, the harmonic cutoff is remarkably extended. By superposing a properly selected harmonics, a 46as pulse can be produced. The intensity of the generated pulse is one order of magnitude higher than that from the chirp-free case. The investigation is helpful to control the harmonic emission and to produce the attosecond pulse.
2017, 41(5): 712-717.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.019
Abstract:
With the rapid development of photoacoustic imaging, it is increasingly used in aspects of biomedical imaging and diagnosis. The existing photoacoustic imaging products are limited to further popularization and promotion because of the excitation light sources, which lead to complex structure, large volume and high cost. The limitations and requirements of light source in photoacoustic imaging were analyzed. The present situation, advantages and disadvantages of different types of photoacoustic sources, including Nd:YAG, optical parametric oscillator, semiconductor lasers and light-emitting diode were summarized. This work should be helpful to select appropriate light source for photoacoustic imaging technology research and photoacoustic imaging product development.
With the rapid development of photoacoustic imaging, it is increasingly used in aspects of biomedical imaging and diagnosis. The existing photoacoustic imaging products are limited to further popularization and promotion because of the excitation light sources, which lead to complex structure, large volume and high cost. The limitations and requirements of light source in photoacoustic imaging were analyzed. The present situation, advantages and disadvantages of different types of photoacoustic sources, including Nd:YAG, optical parametric oscillator, semiconductor lasers and light-emitting diode were summarized. This work should be helpful to select appropriate light source for photoacoustic imaging technology research and photoacoustic imaging product development.
2017, 41(5): 718-722.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.020
Abstract:
In order to solve the path planning problem of complex surface cladding process, the cladding track algorithm was generated based on point cloud slicing method, the reverse of the parts was completed based on reverse technique and point cloud data of model was obtained. The scanning trajectory of laser beam was determined by the intersection point of tangent plane and point cloud. The processing point was determined by equal arch height error method. After path simulation, 45# steel was used as the experimental substrate, and a layer of Fe-based powder was coated on the surface to study the laser cladding path planning of the free form parts. The results show that the hardness of the cladding layer stabilizes at 390HRC and 1.6 times of that of the substrate after the measurement of microhardness tester. The cladding layer has uniform structure, compact structure, no obvious pores and cracks, and has a good metallurgical bond with the substrate. The method has good cladding results and verifies the feasibility of trajectory planning.
In order to solve the path planning problem of complex surface cladding process, the cladding track algorithm was generated based on point cloud slicing method, the reverse of the parts was completed based on reverse technique and point cloud data of model was obtained. The scanning trajectory of laser beam was determined by the intersection point of tangent plane and point cloud. The processing point was determined by equal arch height error method. After path simulation, 45# steel was used as the experimental substrate, and a layer of Fe-based powder was coated on the surface to study the laser cladding path planning of the free form parts. The results show that the hardness of the cladding layer stabilizes at 390HRC and 1.6 times of that of the substrate after the measurement of microhardness tester. The cladding layer has uniform structure, compact structure, no obvious pores and cracks, and has a good metallurgical bond with the substrate. The method has good cladding results and verifies the feasibility of trajectory planning.
2017, 41(5): 723-727.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.021
Abstract:
In order to obtain broadband high efficiency optical absorbers, the composite structure of graphene and 1-D photonic crystal was designed. The modified transfer matrix method was used to study the transmission characteristics. The results show that under certain conditions, the composite structure has a certain bandwidth and high efficiency absorption band in the terahertz band. The position and width of absorption band are consistent with the pass band of 1-D photonic crystal. In some special absorption bands, absorption peak reaches 1. For the same structure, absorption is also related to the incident direction. The combination of grapheme and 1-D photonic crystals further expands the range of applications.
In order to obtain broadband high efficiency optical absorbers, the composite structure of graphene and 1-D photonic crystal was designed. The modified transfer matrix method was used to study the transmission characteristics. The results show that under certain conditions, the composite structure has a certain bandwidth and high efficiency absorption band in the terahertz band. The position and width of absorption band are consistent with the pass band of 1-D photonic crystal. In some special absorption bands, absorption peak reaches 1. For the same structure, absorption is also related to the incident direction. The combination of grapheme and 1-D photonic crystals further expands the range of applications.
2017, 41(5): 728-733.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.022
Abstract:
In order to study the path recovery of helicopter formation flying in the two cases of link expiration or node outage, based on the analysis of the path loss in ultraviolet (UV) non-line-of-sight (NLOS) communication. Dijkstra algorithm was adopted to find the optimal path of helicopters flying in formation communications network under network connectivity. Path recovery was achieved by node moving at link expiration or node outage. After theoretical simulation and analysis, the path recovery of the optimal path in different links expiration was obtained. The results show that although the algorithm spends 2s~3s time to move the nodes, compared with the paths re-search method, the convergence time of three-hop and four-hop node can effectively reduce 0.2ms and 0.4ms. The path weight also can reduce 20dB and 45dB. The algorithm is feasible and has applicable value for studying path fast recovery of inter clusters.
In order to study the path recovery of helicopter formation flying in the two cases of link expiration or node outage, based on the analysis of the path loss in ultraviolet (UV) non-line-of-sight (NLOS) communication. Dijkstra algorithm was adopted to find the optimal path of helicopters flying in formation communications network under network connectivity. Path recovery was achieved by node moving at link expiration or node outage. After theoretical simulation and analysis, the path recovery of the optimal path in different links expiration was obtained. The results show that although the algorithm spends 2s~3s time to move the nodes, compared with the paths re-search method, the convergence time of three-hop and four-hop node can effectively reduce 0.2ms and 0.4ms. The path weight also can reduce 20dB and 45dB. The algorithm is feasible and has applicable value for studying path fast recovery of inter clusters.
2017, 41(5): 734-737.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.023
Abstract:
The output wavelength and power of a semiconductor laser varied with the temperature. In order to ensure the performance of laser, constant temperature must be controlled. A high precision temperature control system of bidirectional high current output was designed by using pulse width modulation power driver DRV595 to drive the semiconductor cooler. In the S domain, the system was modeled and analyzed, and the classical proportional-integral-differential controller was built. The bridge type sampling resistor was adopted to realize the pure hardware circuit. The structure was simple, and the complex software of the digital controller was omitted. After normal temperature test, the control accuracy of ±0.03℃ was achieved. Pulse width modulation and bidirectional MOSFET were integrated in DRV595. The biggest output current was ±4A. No-dead-time control was realized by using bi-directional current to drive semiconductor cooler. The results show that pulse width modulation mode drive and low output stage resistor greatly reduce power dissipation. The system has the advantages of stable operation, low power consumption, high control accuracy and practical value.
The output wavelength and power of a semiconductor laser varied with the temperature. In order to ensure the performance of laser, constant temperature must be controlled. A high precision temperature control system of bidirectional high current output was designed by using pulse width modulation power driver DRV595 to drive the semiconductor cooler. In the S domain, the system was modeled and analyzed, and the classical proportional-integral-differential controller was built. The bridge type sampling resistor was adopted to realize the pure hardware circuit. The structure was simple, and the complex software of the digital controller was omitted. After normal temperature test, the control accuracy of ±0.03℃ was achieved. Pulse width modulation and bidirectional MOSFET were integrated in DRV595. The biggest output current was ±4A. No-dead-time control was realized by using bi-directional current to drive semiconductor cooler. The results show that pulse width modulation mode drive and low output stage resistor greatly reduce power dissipation. The system has the advantages of stable operation, low power consumption, high control accuracy and practical value.
2017, 41(5): 738-742.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.024
Abstract:
In order to solve the "blind area" problem and control the polarization state of the output optical beam of the polarization controller in real-time, a new polarization control algorithm was proposed by using three cascading waveplates. The complexity of the algorithm was reduced and the speed of the polarization control was improved by combining the coarse control (the step-by-step approach algorithm) and the fine control (the proportional-differential algorithm). Through theoretical analysis and experimental test, the results show that the algorithm does well so that the polarization state of the device's output optical beam is always near the objective state. And the response time of the polarization controller is about 10ms. The polarization controller proposed in the paper has achieved the aim of real-time controlling the output polarization state fast and steadily by adding the feedback structure into the polarization control system.
In order to solve the "blind area" problem and control the polarization state of the output optical beam of the polarization controller in real-time, a new polarization control algorithm was proposed by using three cascading waveplates. The complexity of the algorithm was reduced and the speed of the polarization control was improved by combining the coarse control (the step-by-step approach algorithm) and the fine control (the proportional-differential algorithm). Through theoretical analysis and experimental test, the results show that the algorithm does well so that the polarization state of the device's output optical beam is always near the objective state. And the response time of the polarization controller is about 10ms. The polarization controller proposed in the paper has achieved the aim of real-time controlling the output polarization state fast and steadily by adding the feedback structure into the polarization control system.
2017, 41(5): 743-748.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.025
Abstract:
In order to improve the resolution of far-field diffraction microscopy, a pupil filter whose amplitude transmittance had the distribution of power function with radius was proposed. Theoretical analysis and numerical simulation were carried out. By using scalar diffraction theory, the formula of Fraunhofer diffraction distribution was derived when an amplitude pupil filter with the distribution of power function was added in optical path. Diffraction pattern was obtained through MATLAB software, and the main lobe width of diffraction distribution was compared. The results show that when the power number is 3, Strehl ratio of diffraction distribution is 0.16, the maximum sidelobe intensity ratio is 0.1, the resolution parameter is 0.76, and the enhancement factor of resolution is 1.3. With the increase of power number of amplitude transmittance, the main lobe width decreases. At the same time, the main lobe intensity decreases and the side lobe intensity increases. This study is helpful for the realization of super-resolution imaging in the far field optical microscopes.
In order to improve the resolution of far-field diffraction microscopy, a pupil filter whose amplitude transmittance had the distribution of power function with radius was proposed. Theoretical analysis and numerical simulation were carried out. By using scalar diffraction theory, the formula of Fraunhofer diffraction distribution was derived when an amplitude pupil filter with the distribution of power function was added in optical path. Diffraction pattern was obtained through MATLAB software, and the main lobe width of diffraction distribution was compared. The results show that when the power number is 3, Strehl ratio of diffraction distribution is 0.16, the maximum sidelobe intensity ratio is 0.1, the resolution parameter is 0.76, and the enhancement factor of resolution is 1.3. With the increase of power number of amplitude transmittance, the main lobe width decreases. At the same time, the main lobe intensity decreases and the side lobe intensity increases. This study is helpful for the realization of super-resolution imaging in the far field optical microscopes.
2017, 41(5): 749-753.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.026
Abstract:
In order to decrease the influence of observational gross error on the fitting precision of sphere target, aiming at data characteristics of sphere target by terrestrial 3-D laser scanning and based on weighted total least squares, weight function IGG Ⅲ scheme was adopted to adaptively modify the fitting weight matrix and a new fitting method of sphere point clouds was proposed. Simulated spherical datas and scanning spherical datas were fitted separately with the new method. The results show that, based on the consideration of both observation vector error and coefficient matrix error, more accurate sphere parameters are obtained by means of reasonable definition and optimization of fitting weight matrix. The fitting evaluation index of the new method is better than the conventional method's.
In order to decrease the influence of observational gross error on the fitting precision of sphere target, aiming at data characteristics of sphere target by terrestrial 3-D laser scanning and based on weighted total least squares, weight function IGG Ⅲ scheme was adopted to adaptively modify the fitting weight matrix and a new fitting method of sphere point clouds was proposed. Simulated spherical datas and scanning spherical datas were fitted separately with the new method. The results show that, based on the consideration of both observation vector error and coefficient matrix error, more accurate sphere parameters are obtained by means of reasonable definition and optimization of fitting weight matrix. The fitting evaluation index of the new method is better than the conventional method's.
2017, 41(5): 754-758.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.027
Abstract:
In order to study the surface nanocrystallization and microstructure evolution of Ti-6Al-4V alloy, the samples of Ti-6Al-4V alloy were peened with different times by using short-pulse Nd:YAG laser, the corresponding surface microstructure and microhardness were obtained. With the increase of the number of laser impact, the grain size gradually decreased and nanocrystals were formed. After more than three impacts, the number of nanocrystals obviously increased with a more uniform size distribution and the orientation of equiaxed nanocrystals on the surface became more random. After more than 5 times of laser impacts, the nanocrystalline grain size of Ti-6Al-4V titanium alloy did not decrease significantly with the increase of the number of laser impacts, and maintained at 50nm~130nm. The depth of the nanostructure layer was not increased obviously and was about 15μm~20μm. After more than 5 times of laser impacts, the titanium alloy surface hardness tended to be stable, and the maximum hardness was about 525HV~530HV. The results show that the nanocrystallization degree of Ti-6Al-4V titanium alloy improves with the increase of the number of laser impacts. After five impacts, the nanocrystallization of the titanium alloy surface is saturated. The surface has a better nanocrystalline distribution and higher hardness. The study indicates that the surface of titanium alloy through multiple laser impacts can prompt the grain size transformation from micron to nanometer.
In order to study the surface nanocrystallization and microstructure evolution of Ti-6Al-4V alloy, the samples of Ti-6Al-4V alloy were peened with different times by using short-pulse Nd:YAG laser, the corresponding surface microstructure and microhardness were obtained. With the increase of the number of laser impact, the grain size gradually decreased and nanocrystals were formed. After more than three impacts, the number of nanocrystals obviously increased with a more uniform size distribution and the orientation of equiaxed nanocrystals on the surface became more random. After more than 5 times of laser impacts, the nanocrystalline grain size of Ti-6Al-4V titanium alloy did not decrease significantly with the increase of the number of laser impacts, and maintained at 50nm~130nm. The depth of the nanostructure layer was not increased obviously and was about 15μm~20μm. After more than 5 times of laser impacts, the titanium alloy surface hardness tended to be stable, and the maximum hardness was about 525HV~530HV. The results show that the nanocrystallization degree of Ti-6Al-4V titanium alloy improves with the increase of the number of laser impacts. After five impacts, the nanocrystallization of the titanium alloy surface is saturated. The surface has a better nanocrystalline distribution and higher hardness. The study indicates that the surface of titanium alloy through multiple laser impacts can prompt the grain size transformation from micron to nanometer.
2017, 41(5): 759-763.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.028
Abstract:
In order to get photonic crystal fiber with anomalous dispersion, which can be used as the gain part of a Yb3+-doped pulse fiber laser, a structure of photonic crystal fiber(PCF) with Yb3+-doped aluminosilicate glass core was designed. The cross-section of the core was oval, the cladding was the ordinary hexagonal structure with air holes in the same diameter, and there were four small air oval holes between the core and the cladding. The influences of air hole's diameter d, pitch Λ and the ratio d/Λ of the cladding on the relationship between dispersion and wavelength were studied, as well as the influence of four small air oval holes on the relationship between dispersion and birefringence. The results show that when Λ is 2.3μm and d/Λ is 0.5, the anomalous dispersion is observed, and this photonic crystal fiber can be used as the gain part of a Yb3+-doped pulse fiber laser as well. The research is helpful for the use of Yb3+-doped PCF as the gain part of a pulse fiber laser.
In order to get photonic crystal fiber with anomalous dispersion, which can be used as the gain part of a Yb3+-doped pulse fiber laser, a structure of photonic crystal fiber(PCF) with Yb3+-doped aluminosilicate glass core was designed. The cross-section of the core was oval, the cladding was the ordinary hexagonal structure with air holes in the same diameter, and there were four small air oval holes between the core and the cladding. The influences of air hole's diameter d, pitch Λ and the ratio d/Λ of the cladding on the relationship between dispersion and wavelength were studied, as well as the influence of four small air oval holes on the relationship between dispersion and birefringence. The results show that when Λ is 2.3μm and d/Λ is 0.5, the anomalous dispersion is observed, and this photonic crystal fiber can be used as the gain part of a Yb3+-doped pulse fiber laser as well. The research is helpful for the use of Yb3+-doped PCF as the gain part of a pulse fiber laser.
2017, 41(5): 764-768.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.029
Abstract:
In order to monitor high-power laser welding status in real time, the method based on multi-feature fusion was put forward to predict the weld formation. Choosing the welding of 304 austenitic stainless steel plates by high power disk laser as the experimental target, the spectral distribution of laser welding was obtained by a spectrometer. A high-speed camera in ultraviolet band and visible light band was applied to capture the metal vapor visual images. Comprehensive analysis and experimental verification were conducted on the relationship between characteristic parameters and welding status. Back propagation neural network model was set up with characteristic parameters to predict the weld formation, and the average values of relative errors of weld width and penetration are 0.18mm and 0.72mm. Experimental results show that the proposed method can reflect the state change of weld width and penetration accurately and is helpful for monitoring high-power disk laser welding process in real time.
In order to monitor high-power laser welding status in real time, the method based on multi-feature fusion was put forward to predict the weld formation. Choosing the welding of 304 austenitic stainless steel plates by high power disk laser as the experimental target, the spectral distribution of laser welding was obtained by a spectrometer. A high-speed camera in ultraviolet band and visible light band was applied to capture the metal vapor visual images. Comprehensive analysis and experimental verification were conducted on the relationship between characteristic parameters and welding status. Back propagation neural network model was set up with characteristic parameters to predict the weld formation, and the average values of relative errors of weld width and penetration are 0.18mm and 0.72mm. Experimental results show that the proposed method can reflect the state change of weld width and penetration accurately and is helpful for monitoring high-power disk laser welding process in real time.
2017, 41(5): 769-774.
doi: 10.7510/jgjs.issn.1001-3806.2017.05.030
Abstract:
In order to solve the problem of large amount of data, high complexity and long time consuming in traditional digital image processing algorithm, a method for center location of optical fiber spot was presented based on field-programmable gate array (FPGA). By using digital signal processing system and development tools (DSP builder), image preprocessing algorithm and edge detection algorithm were designed. The least square method was used to fit the boundary of light spot. The parallel capability for data processing was enhanced and the processing speed was improved by means of pipeline design. Theoretical analysis and experimental verification were carried out on Cyclone V platform. The image boundary and the central coordinate data were obtained. The results show that under the condition that the absolute error of spot center location is less than 0.1pixel, the computer speed can be improved by more than 21 times based on FPGA. The spot center can be located quickly and accurately on FPGA platform.
In order to solve the problem of large amount of data, high complexity and long time consuming in traditional digital image processing algorithm, a method for center location of optical fiber spot was presented based on field-programmable gate array (FPGA). By using digital signal processing system and development tools (DSP builder), image preprocessing algorithm and edge detection algorithm were designed. The least square method was used to fit the boundary of light spot. The parallel capability for data processing was enhanced and the processing speed was improved by means of pipeline design. Theoretical analysis and experimental verification were carried out on Cyclone V platform. The image boundary and the central coordinate data were obtained. The results show that under the condition that the absolute error of spot center location is less than 0.1pixel, the computer speed can be improved by more than 21 times based on FPGA. The spot center can be located quickly and accurately on FPGA platform.
