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RSS2017 Vol. 41, No. 6
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2017, 41(6): 775-778.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.001
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Abstract:
In order to obtain high-precision 3-D range images of target regions, a non-scanning active imaging lidar was developed by using avalanche photodiode (APD) array detector assembly with readout circuit developed by ourselves. Pulse laser at wavelength of 1.064μm was used to irradiate target areas and an APD array detector module was used to receive target diffuse reflection laser echo signal. After information processing, the target area 3-D range images were obtained. The experiment study was carried out on typical targets 3-D imaging. The results show that, the developed non-scanning active imaging lidar can obtain good target area 3-D range images with imaging distance of 1.2km, range resolution of 0.45m and imaging frame rate of 20Hz. The technology of non-scanning active imaging lidar based on APD array detector has made a breakthrough.
In order to obtain high-precision 3-D range images of target regions, a non-scanning active imaging lidar was developed by using avalanche photodiode (APD) array detector assembly with readout circuit developed by ourselves. Pulse laser at wavelength of 1.064μm was used to irradiate target areas and an APD array detector module was used to receive target diffuse reflection laser echo signal. After information processing, the target area 3-D range images were obtained. The experiment study was carried out on typical targets 3-D imaging. The results show that, the developed non-scanning active imaging lidar can obtain good target area 3-D range images with imaging distance of 1.2km, range resolution of 0.45m and imaging frame rate of 20Hz. The technology of non-scanning active imaging lidar based on APD array detector has made a breakthrough.
2017, 41(6): 779-783.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.002
Abstract:
In order to improve the longitudinal resolution of a terahertz coherence tomographic imaging system, the dispersion compensation method was used to solve the dispersion problem caused by the broadband light source. The iterative compensation algorithm based on the evaluation function was used to compensate the dispersion of the original signal after noise reduction, and clear 3-D reconstructed images were obtained. The results show that 3-D high precision reconstruction images can be obtained without predicting the thickness information and dispersion characteristics of the sample. The longitudinal resolution is up to 100μm. This research has great research value and wide application prospect in the field of high precision nondestructive detection.
In order to improve the longitudinal resolution of a terahertz coherence tomographic imaging system, the dispersion compensation method was used to solve the dispersion problem caused by the broadband light source. The iterative compensation algorithm based on the evaluation function was used to compensate the dispersion of the original signal after noise reduction, and clear 3-D reconstructed images were obtained. The results show that 3-D high precision reconstruction images can be obtained without predicting the thickness information and dispersion characteristics of the sample. The longitudinal resolution is up to 100μm. This research has great research value and wide application prospect in the field of high precision nondestructive detection.
2017, 41(6): 784-787.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.003
Abstract:
In order to analyze the output characteristics in single-pulse mode-locked fiber lasers with different net cavity dispersion, a numerical model based on the nonlinear Schr dinger equation is conducted to analyze the pulse evolution in the cavity by using the split-step Fourier method. According to the numerical simulation, the relationship between some parameters in fiber lasers and the net cavity dispersion is proven theoretically, and in the case that the net cavity dispersion is positive, the output pulse is compressed outside the cavity numerically and the compression ratio reaches up to ten times. Then the values of the required dispersion and the pulse width after compression are calculated. The results show that the maximum small-signal gain coefficient is proportional to the net cavity dispersion in general. And when the small-signal gain coefficient reaches the maximum value, the pulse width and the time-bandwidth product(TBP) increase gradually, and the 3dB bandwidth increases first and then decreases with the increase of the net cavity dispersion. The conclusion can provide reference for optimizing passively mode-locked fiber lasers.
In order to analyze the output characteristics in single-pulse mode-locked fiber lasers with different net cavity dispersion, a numerical model based on the nonlinear Schr dinger equation is conducted to analyze the pulse evolution in the cavity by using the split-step Fourier method. According to the numerical simulation, the relationship between some parameters in fiber lasers and the net cavity dispersion is proven theoretically, and in the case that the net cavity dispersion is positive, the output pulse is compressed outside the cavity numerically and the compression ratio reaches up to ten times. Then the values of the required dispersion and the pulse width after compression are calculated. The results show that the maximum small-signal gain coefficient is proportional to the net cavity dispersion in general. And when the small-signal gain coefficient reaches the maximum value, the pulse width and the time-bandwidth product(TBP) increase gradually, and the 3dB bandwidth increases first and then decreases with the increase of the net cavity dispersion. The conclusion can provide reference for optimizing passively mode-locked fiber lasers.
2017, 41(6): 788-792.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.004
Abstract:
In order to identify gap and edge defects in laser welding process, plasma visible light signal and infrared signal of molten pool during the process of stainless steel welding was monitored by a self-made optical fiber laser welding on-line monitoring system. And the signal processing methods of filtering and short time Fourier transform were used to analyze the optical signals with different defects and the variation law of time domain and frequency domain with welding defects was obtained. When a gap defect occurred, the time domain amplitude of the visible signal decreased from 1.5V to 0.2V without any components in the range of 1000Hz~4000Hz. The time domain amplitude of infrared signal decreased from 3.5V to 1.0V without any components in the range of 2000Hz~7000Hz. When an edge defect occurred, the time domain amplitude of the visible signal decreased from 2.0V to 0.5V and the time domain amplitude of infrared signal decreased from 4.0V to 0.5V without any components in the range of 0Hz~1000Hz for both signals. The results show that there is a certain correlation between the visible signal, the infrared signal and the laser welding state. The defects in the laser welding process can be effectively identified by the change of amplitude and frequency of the optical signal. The study has certain application value for actual production.
In order to identify gap and edge defects in laser welding process, plasma visible light signal and infrared signal of molten pool during the process of stainless steel welding was monitored by a self-made optical fiber laser welding on-line monitoring system. And the signal processing methods of filtering and short time Fourier transform were used to analyze the optical signals with different defects and the variation law of time domain and frequency domain with welding defects was obtained. When a gap defect occurred, the time domain amplitude of the visible signal decreased from 1.5V to 0.2V without any components in the range of 1000Hz~4000Hz. The time domain amplitude of infrared signal decreased from 3.5V to 1.0V without any components in the range of 2000Hz~7000Hz. When an edge defect occurred, the time domain amplitude of the visible signal decreased from 2.0V to 0.5V and the time domain amplitude of infrared signal decreased from 4.0V to 0.5V without any components in the range of 0Hz~1000Hz for both signals. The results show that there is a certain correlation between the visible signal, the infrared signal and the laser welding state. The defects in the laser welding process can be effectively identified by the change of amplitude and frequency of the optical signal. The study has certain application value for actual production.
2017, 41(6): 793-797.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.005
Abstract:
In order to study luminescent properties of rare earth ions Yb3+ and Er3+ with different co-doped molar fractions and ZnF2 as matrix material, by using high temperature solid state method, samples of rare earth doped by ZnF2 at 820℃ were prepared and the up-conversion emission spectra was measured. Yb3+ and Er3+ photon absorption processes were determined by fitting the excitation power and up-conversion power. The results show that under the excitation of 980nm laser diodes, the samples have 3 up-conversion emission peaks of 533nm, 555nm and 655nm in the visible region. The intensity of red light is greater than that of green light.The number of the absorbed photons is 1.73, 1.75, and 1.88. 3 emission peaks are correspond to two-photon absorption.The materials of rare earth ion doped by ZnF2 have important application prospects in up-conversion red phosphors.
In order to study luminescent properties of rare earth ions Yb3+ and Er3+ with different co-doped molar fractions and ZnF2 as matrix material, by using high temperature solid state method, samples of rare earth doped by ZnF2 at 820℃ were prepared and the up-conversion emission spectra was measured. Yb3+ and Er3+ photon absorption processes were determined by fitting the excitation power and up-conversion power. The results show that under the excitation of 980nm laser diodes, the samples have 3 up-conversion emission peaks of 533nm, 555nm and 655nm in the visible region. The intensity of red light is greater than that of green light.The number of the absorbed photons is 1.73, 1.75, and 1.88. 3 emission peaks are correspond to two-photon absorption.The materials of rare earth ion doped by ZnF2 have important application prospects in up-conversion red phosphors.
2017, 41(6): 798-802.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.006
Abstract:
In order to improve the beam quality and spectral characteristics of a high power double clad fiber laser and improve the stability of the optical fiber system, a novel high power cladding light stripper was designed to strip the residualoptical power in the fiber cladding. High power cladding light stripper was analyzed through theoretical calculation and simulation analysis. Based on the Monte Carlo algorithm and light trajectory tracking method, the performance of the cladding light stripper was calculated. With the aid of computational fluid dynamics software ANSYS, the temperature field distribution of the cladding light stripper was analyzed. After optimizing the cascade model structure, strip efficiency of the stripper can reach up to 16.7dB, the hot-spot temperature of the cladding light stripper was reduced, and uniform strip was realized, hot-spot temperature was decreased 20.8℃ under the input power of 600W. The results show that the cladding light stripper can work stably at 70℃ when the power reaches the kilowatt level, it can meet the requirements of high power fiber laser systems.
In order to improve the beam quality and spectral characteristics of a high power double clad fiber laser and improve the stability of the optical fiber system, a novel high power cladding light stripper was designed to strip the residualoptical power in the fiber cladding. High power cladding light stripper was analyzed through theoretical calculation and simulation analysis. Based on the Monte Carlo algorithm and light trajectory tracking method, the performance of the cladding light stripper was calculated. With the aid of computational fluid dynamics software ANSYS, the temperature field distribution of the cladding light stripper was analyzed. After optimizing the cascade model structure, strip efficiency of the stripper can reach up to 16.7dB, the hot-spot temperature of the cladding light stripper was reduced, and uniform strip was realized, hot-spot temperature was decreased 20.8℃ under the input power of 600W. The results show that the cladding light stripper can work stably at 70℃ when the power reaches the kilowatt level, it can meet the requirements of high power fiber laser systems.
2017, 41(6): 803-806.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.007
Abstract:
In order to realize the adjustment of pulse width and peak power of a high power 905nm InGaAs pulse laser diode, field-programmable gate array (FPGA) was adopted to generate trigger pulse, the integrated module EL7104C was used as the driver of metal oxide semiconductor field effect transistor (MOSFET) and the switching device with MOSFET as the core was used to control the charging and discharging between the high voltage module and energy storage capacitor. The pulsed laser diode driver circuit was designed. The driving current characteristics were theoretically analyzed and experimentally verified. Pulse width and peak data were obtained under different capacitance and high voltage conditions. The specific change relationship was analyzed. The spectrum and power-current characteristics were tested. The results show that, the key factors affecting the driving current pulse width and peak current were the capacitor size and charging voltage. The pulse laser diode can be controlled with peak drive current from 0A to 40A and pulse width from 20ns to 100ns. The maximum peak power output of pulsed laser diode is up to 40W. The controllable modulation of output power and pulse width of a pulsed semiconductor laser is realized. The design and analysis have practical reference significance for the controllable driving design of near infrared high power pulsed lasers.
In order to realize the adjustment of pulse width and peak power of a high power 905nm InGaAs pulse laser diode, field-programmable gate array (FPGA) was adopted to generate trigger pulse, the integrated module EL7104C was used as the driver of metal oxide semiconductor field effect transistor (MOSFET) and the switching device with MOSFET as the core was used to control the charging and discharging between the high voltage module and energy storage capacitor. The pulsed laser diode driver circuit was designed. The driving current characteristics were theoretically analyzed and experimentally verified. Pulse width and peak data were obtained under different capacitance and high voltage conditions. The specific change relationship was analyzed. The spectrum and power-current characteristics were tested. The results show that, the key factors affecting the driving current pulse width and peak current were the capacitor size and charging voltage. The pulse laser diode can be controlled with peak drive current from 0A to 40A and pulse width from 20ns to 100ns. The maximum peak power output of pulsed laser diode is up to 40W. The controllable modulation of output power and pulse width of a pulsed semiconductor laser is realized. The design and analysis have practical reference significance for the controllable driving design of near infrared high power pulsed lasers.
2017, 41(6): 807-811.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.008
Abstract:
In order to generate vectorial focal field with special properties, according to the similarity between the slot antenna and linear polarizer, a metasurface with multiple subwavelength slot antenna arrays with different directions is investigated. It is used as a discrete pupil filter with complex amplitude. The incident radial polarized light passes through this filter and is focused by a high numerical aperture lens. Then the diffraction-limited ultra-long 3-D optical tube can be obtained in the focal region. Since the slot antenna can manipulate the amplitude and phase locally, every ring has its own transmittance and binary phase shift (0/π) so that it can be used to generate special vectorial focal field. This type of metasurface can guide us to find a new way for generation and manipulation of vectorial fileds.
In order to generate vectorial focal field with special properties, according to the similarity between the slot antenna and linear polarizer, a metasurface with multiple subwavelength slot antenna arrays with different directions is investigated. It is used as a discrete pupil filter with complex amplitude. The incident radial polarized light passes through this filter and is focused by a high numerical aperture lens. Then the diffraction-limited ultra-long 3-D optical tube can be obtained in the focal region. Since the slot antenna can manipulate the amplitude and phase locally, every ring has its own transmittance and binary phase shift (0/π) so that it can be used to generate special vectorial focal field. This type of metasurface can guide us to find a new way for generation and manipulation of vectorial fileds.
2017, 41(6): 812-815.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.009
Abstract:
In order to obtain 9.3μm laser output, the small signal gain coefficients of 5 kinds of CO2 isotopes were compared. After theoretical analysis and experimental verification, isotope gas 12C18O2 was chosen as the working medium and laser output of 9.3μm was obtained. After the optimization of the working pressure of the laser, the maximum 96W power output was obtained under 10.00kPa working pressure. The results show that high power laser output can be obtained when the central wavelength of 12C18O2 is near 9.3μm. The study is helpful to localize 9.3μm CO2 laser and improve the localization rate of core components.
In order to obtain 9.3μm laser output, the small signal gain coefficients of 5 kinds of CO2 isotopes were compared. After theoretical analysis and experimental verification, isotope gas 12C18O2 was chosen as the working medium and laser output of 9.3μm was obtained. After the optimization of the working pressure of the laser, the maximum 96W power output was obtained under 10.00kPa working pressure. The results show that high power laser output can be obtained when the central wavelength of 12C18O2 is near 9.3μm. The study is helpful to localize 9.3μm CO2 laser and improve the localization rate of core components.
2017, 41(6): 816-820.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.010
Abstract:
In order to explore the welding particularity of titanium alloy and stainless steel dissimilar metal and improve their welding performance, a new welding method of filling layer brass between titanium alloy and stainless steel was adopted. ANSYS finite element analysis software was applied. After theoretical analysis and experimental verification, it was concluded that the reasonable thickness of filling layer brass should be about 0.5mm~0.7mm. And based on simulation results, titanium steel dissimilar metal welding with the filling brass layer of thickness 0.5mm~0.7mm was used in welding experiment. Hardness, tensile test and scanning electron microscope (SEM) observation were carried out on the welded specimens. The results show that, when the thickness of the filler layer brass is 0.6mm, laser welding samples of Ti alloy and stainless steel has good weld morphology and mechanical properties.
In order to explore the welding particularity of titanium alloy and stainless steel dissimilar metal and improve their welding performance, a new welding method of filling layer brass between titanium alloy and stainless steel was adopted. ANSYS finite element analysis software was applied. After theoretical analysis and experimental verification, it was concluded that the reasonable thickness of filling layer brass should be about 0.5mm~0.7mm. And based on simulation results, titanium steel dissimilar metal welding with the filling brass layer of thickness 0.5mm~0.7mm was used in welding experiment. Hardness, tensile test and scanning electron microscope (SEM) observation were carried out on the welded specimens. The results show that, when the thickness of the filler layer brass is 0.6mm, laser welding samples of Ti alloy and stainless steel has good weld morphology and mechanical properties.
2017, 41(6): 821-825.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.011
Abstract:
In order to study the process of cutting carbon fiber reinforced plastics (CFRP) with 100W picosecond laser, theoretical analysis and experimental verivication were carried out by vaying a single affeting factor. Effect of average power, pulse repetition rate, scanning speed and number of repeat on the heat affected zone and scanning depth were studied. A piece of 1.5mm thick CFRP was cut in experiments. The results show that the cutting line and circular hole with almost no heat affected zone were obtained under the conditions of average power 60W, repetition rate 0.4MHz, scanning speed 10m/s, number of repeat 20 and upper surface width of the kerf 350μm. The study provides some reference for further academic research and industrial application of picosecond laser cutting CFRP.
In order to study the process of cutting carbon fiber reinforced plastics (CFRP) with 100W picosecond laser, theoretical analysis and experimental verivication were carried out by vaying a single affeting factor. Effect of average power, pulse repetition rate, scanning speed and number of repeat on the heat affected zone and scanning depth were studied. A piece of 1.5mm thick CFRP was cut in experiments. The results show that the cutting line and circular hole with almost no heat affected zone were obtained under the conditions of average power 60W, repetition rate 0.4MHz, scanning speed 10m/s, number of repeat 20 and upper surface width of the kerf 350μm. The study provides some reference for further academic research and industrial application of picosecond laser cutting CFRP.
2017, 41(6): 826-830.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.012
Abstract:
In order to obtain a wider plasma induced transparency (PIT) window, a dual layer tunable terahertz metamaterial structure was proposed. The transmission spectrum, electric field diagram and current diagram of the structure were simulated and analyzed. The formation mechanism of transmission window was analyzed by a mathematical model. The results show that the structure makes the move space of light-mode resonator wider and a wider transmission window can be obtained. The structure can change the width of PIT window by moving the position of I-shaped metal bar. The simulation results are well fitted with the theoretical results.
In order to obtain a wider plasma induced transparency (PIT) window, a dual layer tunable terahertz metamaterial structure was proposed. The transmission spectrum, electric field diagram and current diagram of the structure were simulated and analyzed. The formation mechanism of transmission window was analyzed by a mathematical model. The results show that the structure makes the move space of light-mode resonator wider and a wider transmission window can be obtained. The structure can change the width of PIT window by moving the position of I-shaped metal bar. The simulation results are well fitted with the theoretical results.
2017, 41(6): 831-835.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.013
Abstract:
In order to study characteristics of discharge channels of air plasma induced by high-energy pulsed CO2 laser, a charging and discharging experimental setup of high voltage capacitor was established, in which the pulsed laser beam was focused by a parabolic reflector to trigger the plasma channel in the adjustable gap between a disk-like electrode and a needle-like electrode. Based on the measurements of electric parameters and emission spectra, the characteristics on start-up, impedance and plasma density of the discharge channel were analyzed. It is found that the start-up time become much shorter benefited from the high pulsed-energy and coaxial structure of laser beam and discharge direction, for a plasma channel with length of 50mm, the start-up time of the discharge was only about 2μs; the discharge channel has rather low impedance of 1Ω~2Ω, and this impedance has a decreasing tendency with the increasing of discharge voltage, which has no significant correlation with the length of plasma channel; the electron density after the laser-induced breakdown and before the electric discharge is on the level of 1019 cm-3 calculated from the Stark broadening of the emission lines, though the emission become much stronger after the startup of electric discharge, the plasma density keeps decreasing. These results will be helpful for the application of laser-induced plasma channel.
In order to study characteristics of discharge channels of air plasma induced by high-energy pulsed CO2 laser, a charging and discharging experimental setup of high voltage capacitor was established, in which the pulsed laser beam was focused by a parabolic reflector to trigger the plasma channel in the adjustable gap between a disk-like electrode and a needle-like electrode. Based on the measurements of electric parameters and emission spectra, the characteristics on start-up, impedance and plasma density of the discharge channel were analyzed. It is found that the start-up time become much shorter benefited from the high pulsed-energy and coaxial structure of laser beam and discharge direction, for a plasma channel with length of 50mm, the start-up time of the discharge was only about 2μs; the discharge channel has rather low impedance of 1Ω~2Ω, and this impedance has a decreasing tendency with the increasing of discharge voltage, which has no significant correlation with the length of plasma channel; the electron density after the laser-induced breakdown and before the electric discharge is on the level of 1019 cm-3 calculated from the Stark broadening of the emission lines, though the emission become much stronger after the startup of electric discharge, the plasma density keeps decreasing. These results will be helpful for the application of laser-induced plasma channel.
2017, 41(6): 836-840.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.014
Abstract:
In order to understand the luminescence mechanism and modulation characteristics of distributed feedback laser(DFB), the corresponding relationship and fitting equation between modulation current and output central wavelength of FITEL laser and JDS Uniphase laser were obtained through theoretical analysis and experiment. It was proved that two DFB lasers had non-linear relationship in practical application. The results show that the relationship between 3dB bandwidth and the driving current amplitude of FITELFRL15DCWD-A82 laser is 3.715pm/mA. The available coherence length of the laser is optimized by modulation result. It is proved that the frequency change of the driving signal does not affect 3dB spectral width. The research results can provide experimental basis for drive circuit design of a coherent detection system.
In order to understand the luminescence mechanism and modulation characteristics of distributed feedback laser(DFB), the corresponding relationship and fitting equation between modulation current and output central wavelength of FITEL laser and JDS Uniphase laser were obtained through theoretical analysis and experiment. It was proved that two DFB lasers had non-linear relationship in practical application. The results show that the relationship between 3dB bandwidth and the driving current amplitude of FITELFRL15DCWD-A82 laser is 3.715pm/mA. The available coherence length of the laser is optimized by modulation result. It is proved that the frequency change of the driving signal does not affect 3dB spectral width. The research results can provide experimental basis for drive circuit design of a coherent detection system.
2017, 41(6): 841-845.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.015
Abstract:
In order to solve the problems of difficult maintenance and emissivity determination of the traditional stove dome temperature measurement system, a method of dual band log ratio amplification temperature measurement was adopted. After theoretical deduction and experimental verification, the results show that, under the premise of setting the temperature unchanged, the measurement results of this method are almost consistent with the temperature with the change of time. The relationship between the setting temperature and measurement temperature is also verified. The absolute error of temperature measurement is less than 6℃, with high measurement accuracy. It is also verified that the output voltage of LOG112 is linearly related to the reciprocal of the actual temperature and it is consistent with the theoretical deduction. The study combines radiation thermometry with logarithmic amplification, and it is of great significance to solve the existing problems and improve the temperature measurement accuracy of vault.
In order to solve the problems of difficult maintenance and emissivity determination of the traditional stove dome temperature measurement system, a method of dual band log ratio amplification temperature measurement was adopted. After theoretical deduction and experimental verification, the results show that, under the premise of setting the temperature unchanged, the measurement results of this method are almost consistent with the temperature with the change of time. The relationship between the setting temperature and measurement temperature is also verified. The absolute error of temperature measurement is less than 6℃, with high measurement accuracy. It is also verified that the output voltage of LOG112 is linearly related to the reciprocal of the actual temperature and it is consistent with the theoretical deduction. The study combines radiation thermometry with logarithmic amplification, and it is of great significance to solve the existing problems and improve the temperature measurement accuracy of vault.
2017, 41(6): 846-851.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.016
Abstract:
In order to increase the output laser power of radically polarized light, a W-axicon was improved by changing the internal cone angle. For a W-axicon with the external cone angle of 90°, the position and direction of the reflected light will not change for different internal cone angles through analysis according to geometrical optics. In order to study the thermal distortion characteristics of the axis cone mirror, temperature deformation simulation was conducted. The result shows that the overall temperature becomes smaller and the distribution is more uniform when the inner cone angle increases. As the inner cone angle becomes larger, the decrease in the optical path of the beam center increases with respect to the decrease in the optical path edge. The Fox-Li numerical iteration was used to simulate the laser mode of the resonator. It is found that the effect of temperature deformation on the laser mode is least when the inner cone angle is 100°. The study of W-axicon temperature deformation can provide reference for W-axicon design.
In order to increase the output laser power of radically polarized light, a W-axicon was improved by changing the internal cone angle. For a W-axicon with the external cone angle of 90°, the position and direction of the reflected light will not change for different internal cone angles through analysis according to geometrical optics. In order to study the thermal distortion characteristics of the axis cone mirror, temperature deformation simulation was conducted. The result shows that the overall temperature becomes smaller and the distribution is more uniform when the inner cone angle increases. As the inner cone angle becomes larger, the decrease in the optical path of the beam center increases with respect to the decrease in the optical path edge. The Fox-Li numerical iteration was used to simulate the laser mode of the resonator. It is found that the effect of temperature deformation on the laser mode is least when the inner cone angle is 100°. The study of W-axicon temperature deformation can provide reference for W-axicon design.
2017, 41(6): 852-857.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.017
Abstract:
Effect of process parameters on size precision of melting copper powder forming parts by means of selective laser melting forming was studied based on orthogonal experiments. The influence of technological parameters on absolute error of forming dimension and the effect of various factors on dimensional accuracy were analyzed when the thickness of feeding powder was 0.05mm. The order of the influence of each process parameter on the absolute error of size is the scanning interval, scanning speed, laser power and scanning path. The optimum parameter combination is laser power of 360W, scanning speed of 1050mm/s, scanning interval of 0.08mm and scanning mode of spiral. The results show that, the absolute error of dimension increases with the increase of laser power and decreases with the increase of scanning speed and scanning interval. The influence of different scanning paths on the absolute error of size is small. The absolute error of size increases with the increase of bulk energy density within the range of factor. The research provides the basis for the selection of parameters in laser sintering of pure copper powder.
Effect of process parameters on size precision of melting copper powder forming parts by means of selective laser melting forming was studied based on orthogonal experiments. The influence of technological parameters on absolute error of forming dimension and the effect of various factors on dimensional accuracy were analyzed when the thickness of feeding powder was 0.05mm. The order of the influence of each process parameter on the absolute error of size is the scanning interval, scanning speed, laser power and scanning path. The optimum parameter combination is laser power of 360W, scanning speed of 1050mm/s, scanning interval of 0.08mm and scanning mode of spiral. The results show that, the absolute error of dimension increases with the increase of laser power and decreases with the increase of scanning speed and scanning interval. The influence of different scanning paths on the absolute error of size is small. The absolute error of size increases with the increase of bulk energy density within the range of factor. The research provides the basis for the selection of parameters in laser sintering of pure copper powder.
2017, 41(6): 858-861.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.018
Abstract:
In order to study the laser welding process of magnesium/aluminum dissimilar metals, the experiment was conducted on AZ31B magnesium alloy and 5083 aluminum alloy with Zn interlayer by using 4kW fiber laser. The influence mechanism of Zn interlayer on Mg/Al dissimilar metal laser welding joint was obtained. The results show that the microstructure of the weld is uniform, and the heat affected zone is not obvious. The magnesium side and the center are mainly composed of α-Mg and α-Mg+Mg17Al12 eutectic structure, and the bottom of weld is the mixture of Al, Mg/Al and Mg/Zn compounds. With the thickness of Zn increased, at the bottom of the weld, the formation of Mg/Zn compounds increase, the Mg/Al compounds reduce and the distribution of microstructure is improved. The shear fracture mode transforms from cleavage to mixed manner. When Zn interlayer is 0.1mm, the shear strength reaches the maximum 25.47MPa. The study is helpful in improving the strength of the Mg/Al dissimilar metal welded joints.
In order to study the laser welding process of magnesium/aluminum dissimilar metals, the experiment was conducted on AZ31B magnesium alloy and 5083 aluminum alloy with Zn interlayer by using 4kW fiber laser. The influence mechanism of Zn interlayer on Mg/Al dissimilar metal laser welding joint was obtained. The results show that the microstructure of the weld is uniform, and the heat affected zone is not obvious. The magnesium side and the center are mainly composed of α-Mg and α-Mg+Mg17Al12 eutectic structure, and the bottom of weld is the mixture of Al, Mg/Al and Mg/Zn compounds. With the thickness of Zn increased, at the bottom of the weld, the formation of Mg/Zn compounds increase, the Mg/Al compounds reduce and the distribution of microstructure is improved. The shear fracture mode transforms from cleavage to mixed manner. When Zn interlayer is 0.1mm, the shear strength reaches the maximum 25.47MPa. The study is helpful in improving the strength of the Mg/Al dissimilar metal welded joints.
Study on corrosion acoustic emission sensor based on orthogonally polarized dual-frequency DBR laser
2017, 41(6): 862-866.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.019
Abstract:
In order to realize on-line monitoring of metal corrosion based on optical fiber sensors, a distributed Bragg reflection(DBR) fiber laser was used as the corrosion acoustic emission sensor, aiming at on-line monitoring of metal Q235 corrosion acoustic emission. The working mechanism and model of polarized orthogonal DBR fiber laser were studied, and the influence of resonator parameters of polarized orthogonal dual-frequency DBR laser as corrosion acoustic emission sensor on the performance was analyzed. The acoustic emission detection experiment based on polarized orthogonal dual-frequency DBR laser was carried out. The optimum design of polarized orthogonal DBR fiber laser was experimentally studied, and the characteristics of the corrosion stage of Q235 carbon steel were presented. The results show that polarized orthogonal DBR fiber laser can not only detect metal corrosion acoustic signal, but also characterize three major corrosion phases of metal corrosion by the variation of the average beat frequency values with the detection frequency range of 0MHz~1MHz. The research project provides the theoretical and technical basis for the optimization design and fabrication of polarized orthogonal DBR corrosion acoustic emission sensors and networks. It is of great significance on on-line corrosion monitoring of metal corrosion, especially nuclear grade key materials.
In order to realize on-line monitoring of metal corrosion based on optical fiber sensors, a distributed Bragg reflection(DBR) fiber laser was used as the corrosion acoustic emission sensor, aiming at on-line monitoring of metal Q235 corrosion acoustic emission. The working mechanism and model of polarized orthogonal DBR fiber laser were studied, and the influence of resonator parameters of polarized orthogonal dual-frequency DBR laser as corrosion acoustic emission sensor on the performance was analyzed. The acoustic emission detection experiment based on polarized orthogonal dual-frequency DBR laser was carried out. The optimum design of polarized orthogonal DBR fiber laser was experimentally studied, and the characteristics of the corrosion stage of Q235 carbon steel were presented. The results show that polarized orthogonal DBR fiber laser can not only detect metal corrosion acoustic signal, but also characterize three major corrosion phases of metal corrosion by the variation of the average beat frequency values with the detection frequency range of 0MHz~1MHz. The research project provides the theoretical and technical basis for the optimization design and fabrication of polarized orthogonal DBR corrosion acoustic emission sensors and networks. It is of great significance on on-line corrosion monitoring of metal corrosion, especially nuclear grade key materials.
2017, 41(6): 867-871.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.020
Abstract:
In order to correct high order aberration for an adaptive optics (AO) system and make it operate normally at cryogenic temperature, a 913-element discrete actuators continuous facesheet deformable mirror (DM) was developed. A Veeco interferometer in Ø300mm diameter was used to examine partial static performance of the deformable mirror:the influence function of an individual actuator, flattening test and the correction capability of the deformable mirror about Zernike aberrations fitting. The surface of DM from 20℃ to -10℃ was measured by a 4-D dynamic interferometer. The testing results show that the max correction ability of the deformable mirror actuated by an individual actuator is ±3.5μm. The distance between the neighbor actuators is 9.8μm and the coupling between the neighbor actuators is 9.3%. The surface of the deformable mirror after flattening is really smooth, of which the PV is 66.0nm and the RMS is 5.0nm. The fitting capability of the Zernike polynomials of the 913-element deformable mirror satisfies the demand of the adaptive optics. The thermally induced surface deformation didn't influence the performance of DM at low temperature. According to these tests, the 913-element deformable mirror satisfies the actual demands of the adaptive optics system.
In order to correct high order aberration for an adaptive optics (AO) system and make it operate normally at cryogenic temperature, a 913-element discrete actuators continuous facesheet deformable mirror (DM) was developed. A Veeco interferometer in Ø300mm diameter was used to examine partial static performance of the deformable mirror:the influence function of an individual actuator, flattening test and the correction capability of the deformable mirror about Zernike aberrations fitting. The surface of DM from 20℃ to -10℃ was measured by a 4-D dynamic interferometer. The testing results show that the max correction ability of the deformable mirror actuated by an individual actuator is ±3.5μm. The distance between the neighbor actuators is 9.8μm and the coupling between the neighbor actuators is 9.3%. The surface of the deformable mirror after flattening is really smooth, of which the PV is 66.0nm and the RMS is 5.0nm. The fitting capability of the Zernike polynomials of the 913-element deformable mirror satisfies the demand of the adaptive optics. The thermally induced surface deformation didn't influence the performance of DM at low temperature. According to these tests, the 913-element deformable mirror satisfies the actual demands of the adaptive optics system.
2017, 41(6): 872-875.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.021
Abstract:
In order to explore new high sensitivity schemes of photoelectric pickup, based on the optical tunneling effect, the change of sound pressure was translated into the change of the optical tunneling distance between the total reflection surface and pendulum optical surface of the total reflection prism. The reflection (transmission) loss of the beam at the whole opposite side of the prism was changed. The sound signal was recorded by measuring the power change of the reflected or transmitted light. To demonstrate this scheme, a set of simple experimental system was built with a semiconductor laser and a rectangular-prism, using triangular wave signal to drive the pendulous reed in the experimental apparatus. The results show that the power of the reflected light changes with the change of triangular wave signal. The variation of the power is up to 5.6%. The change of tunneling distance caused by sound signal can also affect the power of the transmitted light. The feasibility of the scheme is verified.
In order to explore new high sensitivity schemes of photoelectric pickup, based on the optical tunneling effect, the change of sound pressure was translated into the change of the optical tunneling distance between the total reflection surface and pendulum optical surface of the total reflection prism. The reflection (transmission) loss of the beam at the whole opposite side of the prism was changed. The sound signal was recorded by measuring the power change of the reflected or transmitted light. To demonstrate this scheme, a set of simple experimental system was built with a semiconductor laser and a rectangular-prism, using triangular wave signal to drive the pendulous reed in the experimental apparatus. The results show that the power of the reflected light changes with the change of triangular wave signal. The variation of the power is up to 5.6%. The change of tunneling distance caused by sound signal can also affect the power of the transmitted light. The feasibility of the scheme is verified.
2017, 41(6): 876-880.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.022
Abstract:
In order to solve the testing problem of muzzle vibration signal with complex frequency distribution under the abominable circumstances with the shooting of barrage weapons, the photoelectric detection method based on line laser speckle field was used. The mathematical relationship between the vibration signal and output current was studied, and the noise and amplitude frequency characteristics of photoelectric detection circuit based on avalanche photo diode were analyzed. A method of muzzle vibration measurement based on laser speckle effect of barrel surface was proposed. The detection experiment of vibration signal was carried out at distance of 25m, with amplitude of micron magnitude and frequency of 50Hz~16kHz. The results show that, the vibration amplitude of gun muzzle is μm magnitude. The measurement method has advantages of wide frequency response range, long measurement distance and high sensitivity. Vibration signal detection at long distance and wide frequency range is realized.
In order to solve the testing problem of muzzle vibration signal with complex frequency distribution under the abominable circumstances with the shooting of barrage weapons, the photoelectric detection method based on line laser speckle field was used. The mathematical relationship between the vibration signal and output current was studied, and the noise and amplitude frequency characteristics of photoelectric detection circuit based on avalanche photo diode were analyzed. A method of muzzle vibration measurement based on laser speckle effect of barrel surface was proposed. The detection experiment of vibration signal was carried out at distance of 25m, with amplitude of micron magnitude and frequency of 50Hz~16kHz. The results show that, the vibration amplitude of gun muzzle is μm magnitude. The measurement method has advantages of wide frequency response range, long measurement distance and high sensitivity. Vibration signal detection at long distance and wide frequency range is realized.
2017, 41(6): 881-885.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.023
Abstract:
In order to improve the detection sensitivity of a spaceborne lidar, high gain amplifier circuit was used to design the detection circuit. The relationships among detection probability, false alarm rate, signal-to-noise ratio and other indicators were analyzed theoretically. Bandwidth, gain, threshold and other parameters were optimized. Experimental verification was also carried out. The results show that the sensitivity of detection circuit is 9nW, the detection probability is 95%, and the false alarm probability is 10-5. Compared with the domestic similar products, the detection circuit has been significantly improved. The study is helpful for the development of spaceborne lidars.
In order to improve the detection sensitivity of a spaceborne lidar, high gain amplifier circuit was used to design the detection circuit. The relationships among detection probability, false alarm rate, signal-to-noise ratio and other indicators were analyzed theoretically. Bandwidth, gain, threshold and other parameters were optimized. Experimental verification was also carried out. The results show that the sensitivity of detection circuit is 9nW, the detection probability is 95%, and the false alarm probability is 10-5. Compared with the domestic similar products, the detection circuit has been significantly improved. The study is helpful for the development of spaceborne lidars.
2017, 41(6): 886-890.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.024
Abstract:
In order to complete the design of cooling components within the limited envelope structure of a small laser and guarantee installation accuracy of the laser and cooling parts, the accuracy of transmitting telescope and heat dissipation of water tank, according to the given technical specifications of laser and the determined metal materials and welding methods, the detailed integration and miniaturization design of the cooling parts were carried out. Finite element analysis method and SolidWorks software were used to analyze the static state of the important parts in the cooling parts to ensure its accuracy and reliability. Finally, temperature characteristics test, shock and vibration characteristics test and impact vibration test under high and low temperatures were carried out. The results show that some quality problems, such as tearing and leakage, do not appear in the cooling parts. Beam divergence angle of 2.5mrad, output energy of 86mJ and pulse width of 12ns meet the design requirements. The design is stable and reliable, and can be used in a wide range of airborne laser range finders or indicators.
In order to complete the design of cooling components within the limited envelope structure of a small laser and guarantee installation accuracy of the laser and cooling parts, the accuracy of transmitting telescope and heat dissipation of water tank, according to the given technical specifications of laser and the determined metal materials and welding methods, the detailed integration and miniaturization design of the cooling parts were carried out. Finite element analysis method and SolidWorks software were used to analyze the static state of the important parts in the cooling parts to ensure its accuracy and reliability. Finally, temperature characteristics test, shock and vibration characteristics test and impact vibration test under high and low temperatures were carried out. The results show that some quality problems, such as tearing and leakage, do not appear in the cooling parts. Beam divergence angle of 2.5mrad, output energy of 86mJ and pulse width of 12ns meet the design requirements. The design is stable and reliable, and can be used in a wide range of airborne laser range finders or indicators.
2017, 41(6): 891-896.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.025
Abstract:
In order to realize wide range indoor environment laser ranging, a high speed laser ranging system was designed by the principle of trigonometric ranging. Environmental informations were collected with a high resolution linear CCD sensor, and the binary signal was output. The binary signal was processed by a 32-bit single chip microcomputer. The distance between laser spot and lens center of the ranging module was obtained according to the distance obtained by the piecewise fitting method. After the experimental verification, the results show that the rangefinder has the measurement frequency of 714Hz. The maximum measurement distance is 6311mm and the minimum measurement distance is 48mm. The average error is 2.8mm and the maximum measurement error is 11mm. The distance measurement system can meet the requirements of large-scale indoor environment measurement.
In order to realize wide range indoor environment laser ranging, a high speed laser ranging system was designed by the principle of trigonometric ranging. Environmental informations were collected with a high resolution linear CCD sensor, and the binary signal was output. The binary signal was processed by a 32-bit single chip microcomputer. The distance between laser spot and lens center of the ranging module was obtained according to the distance obtained by the piecewise fitting method. After the experimental verification, the results show that the rangefinder has the measurement frequency of 714Hz. The maximum measurement distance is 6311mm and the minimum measurement distance is 48mm. The average error is 2.8mm and the maximum measurement error is 11mm. The distance measurement system can meet the requirements of large-scale indoor environment measurement.
2017, 41(6): 897-903.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.026
Abstract:
In order to solve the rapid increase of the encryption time because of the increasing image size in the existing image encryption algorithm, the optimized encryption algorithm based on logistic and Arnold mapping was used to achieve the optimization of the fast image encryption algorithm. The algorithm was based on two kinds of chaotic maps to the original image, pixel scrambling and gray value substitution. Pixel scrambling was to select the H adjacent pixels according to the image size, appropriately adjust the H value and realize the encryption time optimization. Gray value substitution is to generate chaotic sequences by Arnold mapping, operate the scrambling image and get the cipher image. The results show that, for 256×256 Lena standard images, the encryption time is reduced to 0.0817s. The algorithm has advantages of large key space and fast encryption speed, and can effectively resist the attack of exhaustive, statistical, and differential means.
In order to solve the rapid increase of the encryption time because of the increasing image size in the existing image encryption algorithm, the optimized encryption algorithm based on logistic and Arnold mapping was used to achieve the optimization of the fast image encryption algorithm. The algorithm was based on two kinds of chaotic maps to the original image, pixel scrambling and gray value substitution. Pixel scrambling was to select the H adjacent pixels according to the image size, appropriately adjust the H value and realize the encryption time optimization. Gray value substitution is to generate chaotic sequences by Arnold mapping, operate the scrambling image and get the cipher image. The results show that, for 256×256 Lena standard images, the encryption time is reduced to 0.0817s. The algorithm has advantages of large key space and fast encryption speed, and can effectively resist the attack of exhaustive, statistical, and differential means.
2017, 41(6): 904-908.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.027
Abstract:
In order to study effect of rare earth element CeO2 on laser cladding coatings, cladding layers with different contents of rare earth oxides were prepared by laser cladding overlap processing, using 45# steel as substrate, Ni60 and Ni60+CeO2 powder as cladding material. Through experiments of cladding layer dye test, microstructure observation, and microhardness mensuration, effect of different contents of rare earth oxides on cladding layer surface cracks' number, microstructure, and hardness was analyzed. The results show that the optimal doping mass fraction of CeO2 is 0.004. The crack number of the cladding coating is reduced and the micro structure of the cladding layer is even and tiny with the doping of rare earth element CeO2. The microhardness of the cladding coating surface is much higher than that of the matrix. The Vivtorinox hardness is 3.6 times of that of the matrix. The hardness of the lapping zone is about 3 times of that of the matrix. The addition of rare earth element can restrain the crack, refine the grain and improve the hardness of cladding layer to some extent.
In order to study effect of rare earth element CeO2 on laser cladding coatings, cladding layers with different contents of rare earth oxides were prepared by laser cladding overlap processing, using 45# steel as substrate, Ni60 and Ni60+CeO2 powder as cladding material. Through experiments of cladding layer dye test, microstructure observation, and microhardness mensuration, effect of different contents of rare earth oxides on cladding layer surface cracks' number, microstructure, and hardness was analyzed. The results show that the optimal doping mass fraction of CeO2 is 0.004. The crack number of the cladding coating is reduced and the micro structure of the cladding layer is even and tiny with the doping of rare earth element CeO2. The microhardness of the cladding coating surface is much higher than that of the matrix. The Vivtorinox hardness is 3.6 times of that of the matrix. The hardness of the lapping zone is about 3 times of that of the matrix. The addition of rare earth element can restrain the crack, refine the grain and improve the hardness of cladding layer to some extent.
2017, 41(6): 909-915.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.028
Abstract:
In order to fabricate specific morphology and size on a mold by means of the laser texture, and explore the mechanism of the formation of topography, a three-dimensional transient model of the laser texturing process was established based on the Fluent software. The temperature field and flow field of molten pool were calculated, and the experimental parameters were determined:laser power density 2.04×104W/mm2~3.57×104W/mm2, pulse width 100μs~1000μs. The thermal conductivity, thermal convection, thermophysical properties of materials and other factors were considered. The enthalpy method was used to deal with the boundary of solid-liquid phase transition, the laser heat source was loaded through user defined function. Based on numerical simulation, the influence of laser power density and pulse width on the morphologies and geometrical parameters of laser texturing were studied by varying a single factor with nitrogen gas as the auxiliary gas. Spherical crown, concave crown and M shape were obtained. The results have guiding significance for mold texturing.
In order to fabricate specific morphology and size on a mold by means of the laser texture, and explore the mechanism of the formation of topography, a three-dimensional transient model of the laser texturing process was established based on the Fluent software. The temperature field and flow field of molten pool were calculated, and the experimental parameters were determined:laser power density 2.04×104W/mm2~3.57×104W/mm2, pulse width 100μs~1000μs. The thermal conductivity, thermal convection, thermophysical properties of materials and other factors were considered. The enthalpy method was used to deal with the boundary of solid-liquid phase transition, the laser heat source was loaded through user defined function. Based on numerical simulation, the influence of laser power density and pulse width on the morphologies and geometrical parameters of laser texturing were studied by varying a single factor with nitrogen gas as the auxiliary gas. Spherical crown, concave crown and M shape were obtained. The results have guiding significance for mold texturing.
2017, 41(6): 916-920.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.029
Abstract:
In order to realize refractive index (RI) measurement with low cost and high precision, a multimode fiber liquid refractive index sensor based on U-shaped microstructure was fabricated by femtosecond laser micromachining. The relationship of the variation of the optical power of the sensor, the depth of the U-shaped groove and the refractive index of the liquid in the U-shaped groove were studied. The influence of the different ablation lengths on the sensitivity was also discussed. The sensing mechanism was analyzed based on the influence of the radiation theory and the model. The results show that the sensor has a good linear response in the range of 1.3331~1.3731(refractive index), and can reach 5700μW/RIU (refractive index unit) sensitivity. While in the case of 10dB loss, a good sensitivity can be obtained at 20μm ablation length. The sensor has advantages of simple structure, easy preparation, high sensitivity and low cost. It has wide application prospect in chemistry, biology, medicine and environmental monitoring.
In order to realize refractive index (RI) measurement with low cost and high precision, a multimode fiber liquid refractive index sensor based on U-shaped microstructure was fabricated by femtosecond laser micromachining. The relationship of the variation of the optical power of the sensor, the depth of the U-shaped groove and the refractive index of the liquid in the U-shaped groove were studied. The influence of the different ablation lengths on the sensitivity was also discussed. The sensing mechanism was analyzed based on the influence of the radiation theory and the model. The results show that the sensor has a good linear response in the range of 1.3331~1.3731(refractive index), and can reach 5700μW/RIU (refractive index unit) sensitivity. While in the case of 10dB loss, a good sensitivity can be obtained at 20μm ablation length. The sensor has advantages of simple structure, easy preparation, high sensitivity and low cost. It has wide application prospect in chemistry, biology, medicine and environmental monitoring.
2017, 41(6): 921-926.
doi: 10.7510/jgjs.issn.1001-3806.2017.06.030
Abstract:
In order to extract the local characteristics of hyperspectral data, a dimensionality reduction method of hyperspectral imagery manifold learning based on spectral gradient angle was proposed from the nonlinear structure of hyperspectral imagery. Locality preserving projection (LPP) of localized manifold learning algorithm was performed to reduce the dimensionality of hyperspectral remote sensing data. In order to improve the distance metric, similarity measurement of spectral gradient angle, which can better characterize local features of hyperspectral images, was applied to LPP method. The real hyperspectral images were subjected to dimensionality reduction experiments.The results were better than the original LPP method and the LPP method using the spectral angle. The results show that the proposed method is superior to LPP method and LPP method using the spectral angle in the spectral normalized eigenvalues. Meanwhile, the proposed method can also obtain a good performance in information retainment and have better local information retention. Therefore, the manifold learning method with spectral gradient angle has a better performance in dimensionality reduction of hyperspectral images.
In order to extract the local characteristics of hyperspectral data, a dimensionality reduction method of hyperspectral imagery manifold learning based on spectral gradient angle was proposed from the nonlinear structure of hyperspectral imagery. Locality preserving projection (LPP) of localized manifold learning algorithm was performed to reduce the dimensionality of hyperspectral remote sensing data. In order to improve the distance metric, similarity measurement of spectral gradient angle, which can better characterize local features of hyperspectral images, was applied to LPP method. The real hyperspectral images were subjected to dimensionality reduction experiments.The results were better than the original LPP method and the LPP method using the spectral angle. The results show that the proposed method is superior to LPP method and LPP method using the spectral angle in the spectral normalized eigenvalues. Meanwhile, the proposed method can also obtain a good performance in information retainment and have better local information retention. Therefore, the manifold learning method with spectral gradient angle has a better performance in dimensionality reduction of hyperspectral images.
