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RSS2014 Vol. 38, No. 2
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2014, 38(2): 145-148.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.001
[Abstract]
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Abstract:
In order to improve the accuracy of thermocouple dynamic calibration, based on a new thermocouple dynamic calibration system composed of a semiconductor laser, infrared detector and calibration thermocouples, the static calibration of the infrared detector was analyzed in the dynamic calibration system. According to the principle of back propagation(BP) neural network, the structure and the parameters of neural network were determined. The dynamic calibration experiment with ordinary K type armor-loaded thermocouple was performed and the static calibration data of infrared detector was acquired. Nonlinear curve fitting was performed using the least square method and BP neural network. The fitting results of the both the methods were analyzed and the fitting curves were obtained. The results show that, the fitting effect of BP neural network is better than the traditional least square method when there is less and uneven distributed data. The error caused by data fitting is reduced, dynamic characteristics of the thermocouple are acquired more accurately and thermocouple dynamic compensation is realized. The study has an important reference to the research of thermocouple dynamic characteristics.
In order to improve the accuracy of thermocouple dynamic calibration, based on a new thermocouple dynamic calibration system composed of a semiconductor laser, infrared detector and calibration thermocouples, the static calibration of the infrared detector was analyzed in the dynamic calibration system. According to the principle of back propagation(BP) neural network, the structure and the parameters of neural network were determined. The dynamic calibration experiment with ordinary K type armor-loaded thermocouple was performed and the static calibration data of infrared detector was acquired. Nonlinear curve fitting was performed using the least square method and BP neural network. The fitting results of the both the methods were analyzed and the fitting curves were obtained. The results show that, the fitting effect of BP neural network is better than the traditional least square method when there is less and uneven distributed data. The error caused by data fitting is reduced, dynamic characteristics of the thermocouple are acquired more accurately and thermocouple dynamic compensation is realized. The study has an important reference to the research of thermocouple dynamic characteristics.
2014, 38(2): 149-154.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.002
Abstract:
In order to study the electro-optical effect of LiNbO3 crystal under condition of non-paraxial when electric field was constant, the cyclic coordinate transformation equation of ellipsoid tensor of refractive index was adopted to deduce the expression of refractive index distribution in the optical axis orthogonal region. The dependence of refractive index, phase delay and transmittance upon the direction of incident laser was discussed. The experimental data of the transmittance changing with α, the angle between light beam and optical axis, were obtained. The results show that when the electric field is applied along y axis, a slight deflection of the incident light will lead to a significant change of the x-direction refractive index and beam transmittance whereas the y-direction refractive index has no change. The angle α between light beam and optical axis affects the electro-optical effect of LiNbO3 crystal far greater than the angle β between light vector in the x-y plane and the positive of x axis. The induced refractive index remains similar when adding electric field both in x axis and y axis but the former phase delay is smaller. The transmittance of the former also has a slower change than that of the latter between 0° and 0.4399°, Moreover, after the angle of 0.45°, the transmittance changes alternately at the positions of 0.5°,0.680°and so on, the transmittances in x axis and y axis are just the same. The result has a certain significance to improve the electro-optical properties of LiNbO3 crystal by means of angle adjustment.
In order to study the electro-optical effect of LiNbO3 crystal under condition of non-paraxial when electric field was constant, the cyclic coordinate transformation equation of ellipsoid tensor of refractive index was adopted to deduce the expression of refractive index distribution in the optical axis orthogonal region. The dependence of refractive index, phase delay and transmittance upon the direction of incident laser was discussed. The experimental data of the transmittance changing with α, the angle between light beam and optical axis, were obtained. The results show that when the electric field is applied along y axis, a slight deflection of the incident light will lead to a significant change of the x-direction refractive index and beam transmittance whereas the y-direction refractive index has no change. The angle α between light beam and optical axis affects the electro-optical effect of LiNbO3 crystal far greater than the angle β between light vector in the x-y plane and the positive of x axis. The induced refractive index remains similar when adding electric field both in x axis and y axis but the former phase delay is smaller. The transmittance of the former also has a slower change than that of the latter between 0° and 0.4399°, Moreover, after the angle of 0.45°, the transmittance changes alternately at the positions of 0.5°,0.680°and so on, the transmittances in x axis and y axis are just the same. The result has a certain significance to improve the electro-optical properties of LiNbO3 crystal by means of angle adjustment.
2014, 38(2): 155-160.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.003
Abstract:
Because of different gain, the image content displayed by the electron multiplying charge coupled device (EMCCD) was different and the image had low contrast and narrow dynamic range. Meanwhile, the overall image was dark, fuzzy and whitish. An image fusion algorithm based on wavelet transform was put forward to apply into low-light-level images with different gain levels. Firstly, two groups of low-light-level images were acquired in the same scene with different gain level. Secondly, proper fusion rules were chosen based on low-light-level image's characteristics after wavelet transform. Finally, the images were fused by wavelet transform, high quality fusion image and the performance data of fusion image, such as entropy, standard deviation, average gradient were obtained. Results show that the fusion algorithm based on wavelet transform can make the fusion image with both low and high brightness scenery and enlarge the image's dynamic range and contrast. The image quality is effectively improved.
Because of different gain, the image content displayed by the electron multiplying charge coupled device (EMCCD) was different and the image had low contrast and narrow dynamic range. Meanwhile, the overall image was dark, fuzzy and whitish. An image fusion algorithm based on wavelet transform was put forward to apply into low-light-level images with different gain levels. Firstly, two groups of low-light-level images were acquired in the same scene with different gain level. Secondly, proper fusion rules were chosen based on low-light-level image's characteristics after wavelet transform. Finally, the images were fused by wavelet transform, high quality fusion image and the performance data of fusion image, such as entropy, standard deviation, average gradient were obtained. Results show that the fusion algorithm based on wavelet transform can make the fusion image with both low and high brightness scenery and enlarge the image's dynamic range and contrast. The image quality is effectively improved.
2014, 38(2): 161-164.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.004
Abstract:
In order to find the relationship between the refractive index and the volume fraction of acetic acid solution and alcohol solution, the principle of optical total internal reflection was chosen to measure the refractive indexes of glacial acetic acid and alcohol with different volume fractions and to obtain their relative curves. The experiments showed that the relationship between the refractive index and the volume fraction of acetic acid solution and alcohol solution was similar to the parabola. It was not the simple linear relationships. The refractive index became larger at the beginning as the solution volume fraction increased, and there was a maximum of the refractive index at a certain volume fraction. Acetic acid solution near the volume fraction of 0.90 and alcohol solution near volume fraction of 0.80 had the maximum refractive indexes respectively. The results are helpful to the comprehensive cognition of the relationship between the refractive index and the solution volume fraction.
In order to find the relationship between the refractive index and the volume fraction of acetic acid solution and alcohol solution, the principle of optical total internal reflection was chosen to measure the refractive indexes of glacial acetic acid and alcohol with different volume fractions and to obtain their relative curves. The experiments showed that the relationship between the refractive index and the volume fraction of acetic acid solution and alcohol solution was similar to the parabola. It was not the simple linear relationships. The refractive index became larger at the beginning as the solution volume fraction increased, and there was a maximum of the refractive index at a certain volume fraction. Acetic acid solution near the volume fraction of 0.90 and alcohol solution near volume fraction of 0.80 had the maximum refractive indexes respectively. The results are helpful to the comprehensive cognition of the relationship between the refractive index and the solution volume fraction.
2014, 38(2): 165-171.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.005
Abstract:
In order to improve the classification results and solve the universality in color sensing image classification using unique feature, a new support vector machine (SVM) color remote sensing image classification algorithm based on color feature and texture feature combination was proposed. The method used the combination of the color information and the texture information of color remote sensing image as the eigenvectors of SVM algorithm. The results show that the method can achieve higher precision compared with the traditional method using unique feature or texture feature. The method is effective to classify the remote sensing image.
In order to improve the classification results and solve the universality in color sensing image classification using unique feature, a new support vector machine (SVM) color remote sensing image classification algorithm based on color feature and texture feature combination was proposed. The method used the combination of the color information and the texture information of color remote sensing image as the eigenvectors of SVM algorithm. The results show that the method can achieve higher precision compared with the traditional method using unique feature or texture feature. The method is effective to classify the remote sensing image.
2014, 38(2): 172-176.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.006
Abstract:
Besides the aberration, the overlapping with 0th and ±1st images observed in the phase distribution is difficult to deal with, which is different from the phase compensation methods adopted in off-axis setup. A method was proposed to get the phase information from a single in-line Fresnel digital holography. By subtracting recoded hologram by a numerical hologram, effect of the phase curve, the 0th image and the diffraction of the rectangular aperture was eliminated. The phase can be retrieved. The theoretical analysis and the experimental results were presented. It is found that better phase result can be obtained than former digital phase mask method.
Besides the aberration, the overlapping with 0th and ±1st images observed in the phase distribution is difficult to deal with, which is different from the phase compensation methods adopted in off-axis setup. A method was proposed to get the phase information from a single in-line Fresnel digital holography. By subtracting recoded hologram by a numerical hologram, effect of the phase curve, the 0th image and the diffraction of the rectangular aperture was eliminated. The phase can be retrieved. The theoretical analysis and the experimental results were presented. It is found that better phase result can be obtained than former digital phase mask method.
2014, 38(2): 177-180.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.007
Abstract:
The image gray can be changed by severely the speckle noise, so the image resolution can be reduced and the image quality was decreased. In order to control the speckle noise, using a laser at 405nm wavelength as light source of the microscopic imaging system and a voice coil motor vibrating the optical fiber, images was obtained by the polished lens and captured with a CCD image acquisition card, the speckle noise contrasts were studied. The results show that when the fiber vibration amplitude is stable and the vibration frequency is increased from 4Hz to 55Hz, the image speckle contrasts change in the range of 0.0326~0.1197 and the overall trend gradually becomes smaller. The image speckle contrast levels off when the frequency is more than 51Hz. When the speckle contrast reaches the minimum at 0.0326, the image is clear and the laser imaging speckle can be controlled satisfactorily.
The image gray can be changed by severely the speckle noise, so the image resolution can be reduced and the image quality was decreased. In order to control the speckle noise, using a laser at 405nm wavelength as light source of the microscopic imaging system and a voice coil motor vibrating the optical fiber, images was obtained by the polished lens and captured with a CCD image acquisition card, the speckle noise contrasts were studied. The results show that when the fiber vibration amplitude is stable and the vibration frequency is increased from 4Hz to 55Hz, the image speckle contrasts change in the range of 0.0326~0.1197 and the overall trend gradually becomes smaller. The image speckle contrast levels off when the frequency is more than 51Hz. When the speckle contrast reaches the minimum at 0.0326, the image is clear and the laser imaging speckle can be controlled satisfactorily.
2014, 38(2): 181-185.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.008
Abstract:
In order to prepare actual optoelectronic devices using single-walled carbon nanotubes, single-walled carbon nanotube/polyimide (SWCNT/PI) film with the single-walled carbon nanotubes in mass fraction of 0.02 was prepared by means of a new gradient temperature-elevating thermal imidization method. The reflectance, transmittance, and absorbance of the film were measured with a spectrophotometer and the linear refractive index variation with wavelength of SWCNT/PI film was obtained. Simultaneously, the Sellmeyer parameters of the SWCNT/PI film were got by fitting the Sellmeyer formula. Then, the third order nonlinear optical property of the SWCNT/PI film was studied by means of z-scanning. The experiments showed that the nonlinear absorption coefficient and the nonlinear refractive coefficient of the film were -5.3×10-9cm/W and -4.1×10-13cm2/W, respectively. The results prove that SWCNT/PI film owns strong nonlinear optical property.
In order to prepare actual optoelectronic devices using single-walled carbon nanotubes, single-walled carbon nanotube/polyimide (SWCNT/PI) film with the single-walled carbon nanotubes in mass fraction of 0.02 was prepared by means of a new gradient temperature-elevating thermal imidization method. The reflectance, transmittance, and absorbance of the film were measured with a spectrophotometer and the linear refractive index variation with wavelength of SWCNT/PI film was obtained. Simultaneously, the Sellmeyer parameters of the SWCNT/PI film were got by fitting the Sellmeyer formula. Then, the third order nonlinear optical property of the SWCNT/PI film was studied by means of z-scanning. The experiments showed that the nonlinear absorption coefficient and the nonlinear refractive coefficient of the film were -5.3×10-9cm/W and -4.1×10-13cm2/W, respectively. The results prove that SWCNT/PI film owns strong nonlinear optical property.
2014, 38(2): 186-190.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.009
Abstract:
In order to prepare ceramic reinforced Ni-base composite coating, chromium carbide Ni-base composite coating was prepared on the surface of 45# steel by laser cladding, the microstructure, phase structure and microhardness of the coating were studied. The shapes of chromium carbide ceramic particles were quadrangular, hexagonal and irregular block. By the analysis, quadrangular chromium carbide was Cr3C2, hexagonal chromium carbide was Cr7C3,the composition of irregular blocky chromium carbide was indeterminacy, may be Cr3C2 or Cr7C3.The microhardness of the coating was 3.5 times of the substrate. The coating had high microhardness and dense microstructure. The results indicated that the coating was mainly composed of Cr-Ni-Fe-C, C, Cr7C3 and Cr3C2.The microstructure of the composite layer was proved to be homogeneous and dense. A good metallurgical combination was formed at the boundary of the coating layer and substrate. The research plays a vital role in theoretical research and practical application of the in-situ synthesized chromium carbide Ni-base composite coating.
In order to prepare ceramic reinforced Ni-base composite coating, chromium carbide Ni-base composite coating was prepared on the surface of 45# steel by laser cladding, the microstructure, phase structure and microhardness of the coating were studied. The shapes of chromium carbide ceramic particles were quadrangular, hexagonal and irregular block. By the analysis, quadrangular chromium carbide was Cr3C2, hexagonal chromium carbide was Cr7C3,the composition of irregular blocky chromium carbide was indeterminacy, may be Cr3C2 or Cr7C3.The microhardness of the coating was 3.5 times of the substrate. The coating had high microhardness and dense microstructure. The results indicated that the coating was mainly composed of Cr-Ni-Fe-C, C, Cr7C3 and Cr3C2.The microstructure of the composite layer was proved to be homogeneous and dense. A good metallurgical combination was formed at the boundary of the coating layer and substrate. The research plays a vital role in theoretical research and practical application of the in-situ synthesized chromium carbide Ni-base composite coating.
2014, 38(2): 191-195.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.010
Abstract:
In order to improve anti-jitter capability of a fiber coupling structure, a fiber array with self-focusing lens was designed, the optical fiber array was controlled by means of annealing algorithm and the optimal visual axis alignment position was found. The fiber array and simulated annealing algorithm were analyzed theoretically, and the data of coupling efficiency was achieved. Experimental results show that the simulated annealing algorithm can find the optimal visual axis alignment position. When spot center moving less than 2.5mm on the coupling surface, the power coupled in the fiber fluctuates less than 35%. It can meet the requirements of free space optical communication system.
In order to improve anti-jitter capability of a fiber coupling structure, a fiber array with self-focusing lens was designed, the optical fiber array was controlled by means of annealing algorithm and the optimal visual axis alignment position was found. The fiber array and simulated annealing algorithm were analyzed theoretically, and the data of coupling efficiency was achieved. Experimental results show that the simulated annealing algorithm can find the optimal visual axis alignment position. When spot center moving less than 2.5mm on the coupling surface, the power coupled in the fiber fluctuates less than 35%. It can meet the requirements of free space optical communication system.
2014, 38(2): 196-200.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.011
Abstract:
Infrared thickness measurement is one of the main methods of online film thickness measurement, but traditional infrared thickness measurement method still has such defects that it is sensitive to the stability of light source and it is not applicable to high-speed film production line. In order to solve these problems, a dual-light path reference measurement method was used and a dual-light path infrared thickness measurement system was presented. In the system, the light source is divided into measurement light path and reference light path, using a single CCD connecting both the measurement light and the reference light as light intensity sensor. The imaging principle was described and the applicability of the system for Lambert law was discussed. Finally, calibration experiments for polyethylene and polytetrafluoroethylene film were conducted to demonstrate the accuracy. The experimental results show that the method has high precision and good robustness, and can effectively avoid the impact of the unstable of light source.
Infrared thickness measurement is one of the main methods of online film thickness measurement, but traditional infrared thickness measurement method still has such defects that it is sensitive to the stability of light source and it is not applicable to high-speed film production line. In order to solve these problems, a dual-light path reference measurement method was used and a dual-light path infrared thickness measurement system was presented. In the system, the light source is divided into measurement light path and reference light path, using a single CCD connecting both the measurement light and the reference light as light intensity sensor. The imaging principle was described and the applicability of the system for Lambert law was discussed. Finally, calibration experiments for polyethylene and polytetrafluoroethylene film were conducted to demonstrate the accuracy. The experimental results show that the method has high precision and good robustness, and can effectively avoid the impact of the unstable of light source.
2014, 38(2): 201-204.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.012
Abstract:
To investigate the effect of different laser peening area on the residual stress field in a hole specimen of 7075-T7451 aluminum alloy, the process of laser peening and residual stress distribution of the hole specimen were simulated by finite element analysis software ABAQUS. The results show that both the compressive stress of surface residual and the tensile stress of unshocked area increase as laser peening area becomes bigger,the tensile stress of unshocked area changes from 52MPa to 344MPa. The residual stress distribution along inner hole wall turns out to be worse with the increase of laser peening area, the value of the worst stress along the hole inner wall changes from the compressive stress 38MPa to the tensile stress 49MPa. Within a certain range of laser peening area, the increase of laser peening area enlarges surface compressive stress coverage and makes residual stress distribution of inner hole wall worse. For laser peening of a hole specimen, it is important to control laser peening area and the surface residual stress distribution along hole inner wall, in order to improve the fatigue resistance.
To investigate the effect of different laser peening area on the residual stress field in a hole specimen of 7075-T7451 aluminum alloy, the process of laser peening and residual stress distribution of the hole specimen were simulated by finite element analysis software ABAQUS. The results show that both the compressive stress of surface residual and the tensile stress of unshocked area increase as laser peening area becomes bigger,the tensile stress of unshocked area changes from 52MPa to 344MPa. The residual stress distribution along inner hole wall turns out to be worse with the increase of laser peening area, the value of the worst stress along the hole inner wall changes from the compressive stress 38MPa to the tensile stress 49MPa. Within a certain range of laser peening area, the increase of laser peening area enlarges surface compressive stress coverage and makes residual stress distribution of inner hole wall worse. For laser peening of a hole specimen, it is important to control laser peening area and the surface residual stress distribution along hole inner wall, in order to improve the fatigue resistance.
2014, 38(2): 205-209.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.013
Abstract:
In order to study effect of molecular structure on three-photon absorption(3PA) characteristics, two novel fluorene-based derivatives: 2, 7-bis(2-(4-methoxyphenyl)ethynyl)-9,9-dioctyl-9H-fluorene(A) and 2-bromo-7-(2-(4-methoxyphenyl)ethynyl)-9,9-dioctyl-9H-fluorene(B) were synthesized. The 3PA cross-sections of both the compounds were tested by using a Q-switched Nd:YAG laser at 1064nm. The 3PA cross-sections were obtained, i.e., (6.03±0.6)×10-76 cm6·s2/photon2 and (4.25±0.4)×10-76cm6·s2/photon2respectively. The geometries in the ground states and electronic structures of both the compounds were investigated by density functional theory methods and time-dependent density functional theory methods of Gaussian 03, and the impact on the three-photon absorption characteristics was analyzed.
In order to study effect of molecular structure on three-photon absorption(3PA) characteristics, two novel fluorene-based derivatives: 2, 7-bis(2-(4-methoxyphenyl)ethynyl)-9,9-dioctyl-9H-fluorene(A) and 2-bromo-7-(2-(4-methoxyphenyl)ethynyl)-9,9-dioctyl-9H-fluorene(B) were synthesized. The 3PA cross-sections of both the compounds were tested by using a Q-switched Nd:YAG laser at 1064nm. The 3PA cross-sections were obtained, i.e., (6.03±0.6)×10-76 cm6·s2/photon2 and (4.25±0.4)×10-76cm6·s2/photon2respectively. The geometries in the ground states and electronic structures of both the compounds were investigated by density functional theory methods and time-dependent density functional theory methods of Gaussian 03, and the impact on the three-photon absorption characteristics was analyzed.
2014, 38(2): 210-213.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.014
Abstract:
In order to study the accumulation effect of film damage under repetitive laser pulses, experimental observations and thermodynamic analysis were carried out. The morphologies damaged by single and multiple laser pulses were observed under a 5000× microscope, then the thermodynamic process between the interaction of laser and plasma was analyzed. Finally the evolution rule of the film damage was found. Both of these two damaged morphologies can be explained by the thermodynamic interactions between laser and laser plasmas. The research results show that: the rough surface of thin film is induced by the laser pulses, which will absorb more laser energy than the beginning. The melt will be removed by the stronger ablation and will be accumulated outside of the laser working area. Since the laser energy is Gaussian distributed, the damaged of multiple laser pulses is centralized and the ablation is limited at the center of laser beam only. This result is a preference for study about film ablation under repetitive laser pulses.
In order to study the accumulation effect of film damage under repetitive laser pulses, experimental observations and thermodynamic analysis were carried out. The morphologies damaged by single and multiple laser pulses were observed under a 5000× microscope, then the thermodynamic process between the interaction of laser and plasma was analyzed. Finally the evolution rule of the film damage was found. Both of these two damaged morphologies can be explained by the thermodynamic interactions between laser and laser plasmas. The research results show that: the rough surface of thin film is induced by the laser pulses, which will absorb more laser energy than the beginning. The melt will be removed by the stronger ablation and will be accumulated outside of the laser working area. Since the laser energy is Gaussian distributed, the damaged of multiple laser pulses is centralized and the ablation is limited at the center of laser beam only. This result is a preference for study about film ablation under repetitive laser pulses.
2014, 38(2): 214-217.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.015
Abstract:
In order to measure the velocity distribution of dual-media nozzle droplet particles, an on-line measurement system was established based on continuous laser at 532nm wavelength and industrial cameras. The droplet trajectory images were obtained. The Steger method was used to process the particle trajectory images. The velocity distribution of droplet particles was extracted. The results show that the test method for measuring the speed distribution of the droplet particles based on particle trajectory images, meets the requirements of the online measurement.
In order to measure the velocity distribution of dual-media nozzle droplet particles, an on-line measurement system was established based on continuous laser at 532nm wavelength and industrial cameras. The droplet trajectory images were obtained. The Steger method was used to process the particle trajectory images. The velocity distribution of droplet particles was extracted. The results show that the test method for measuring the speed distribution of the droplet particles based on particle trajectory images, meets the requirements of the online measurement.
2014, 38(2): 218-224.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.016
Abstract:
In order to get better denoising result in laser interception, an improved wavelet threshold denoising algorithm was proposed. Through theoretical analysis and experimental verification, a series of simulation data were obtained. The results show that, compared with the traditional denoising algorithm, the speech signal-to-noise ratio after denoising is improved greatly. Denoising effect is obvious, signal waveform is smoother and distortion is less.
In order to get better denoising result in laser interception, an improved wavelet threshold denoising algorithm was proposed. Through theoretical analysis and experimental verification, a series of simulation data were obtained. The results show that, compared with the traditional denoising algorithm, the speech signal-to-noise ratio after denoising is improved greatly. Denoising effect is obvious, signal waveform is smoother and distortion is less.
2014, 38(2): 225-229.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.017
Abstract:
In order to analyze the effects of fixed and random wave aberration on the large-aperture mosaic compression gratings, by numerical simulation, the far-field characteristics for referenced gratings were studied. On the basis of the precise evaluation criterion, the tiling accuracy of the mosaic gratings was obtained. The results showed that the maximum piston error of the tiling precision was about 0.26 grating period when the wave aberration of sub-gratings was 1.0λ. After manual intervention, the maximum piston error was about 0.42 grating period and the maximum tip-tilt error was 0.71μrad approximately, which were both lower than before. The research is benefit for the improvement of high energy picosecond laser device.
In order to analyze the effects of fixed and random wave aberration on the large-aperture mosaic compression gratings, by numerical simulation, the far-field characteristics for referenced gratings were studied. On the basis of the precise evaluation criterion, the tiling accuracy of the mosaic gratings was obtained. The results showed that the maximum piston error of the tiling precision was about 0.26 grating period when the wave aberration of sub-gratings was 1.0λ. After manual intervention, the maximum piston error was about 0.42 grating period and the maximum tip-tilt error was 0.71μrad approximately, which were both lower than before. The research is benefit for the improvement of high energy picosecond laser device.
2014, 38(2): 230-235.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.018
Abstract:
In order to study the generation and propagation of laser-generated ultrasound in isotropic semi-infinite aluminum material, a laser-generated ultrasound in an arbitrary elastic semi-infinite medium model was established by using mixed stress-displacement finite element method and perfectly matched layer(PML). The transient wave snapshots and surface normal displacement waveforms in semi-infinite aluminum materials were obtained. The surface normal displacement waveforms were compared with the same geometrical finite element model. The results show that the mixed stress-displacement finite element method can effectively eliminate reflection waves from truncated boundary, and simulate the generation and propagation of ultrasound in semi-infinite solid material accurately. The simulation results provide an effective method for research of the laser-generated ultrasound waves in micro-nanostructure by picosecond or femtosecond laser irradiation.
In order to study the generation and propagation of laser-generated ultrasound in isotropic semi-infinite aluminum material, a laser-generated ultrasound in an arbitrary elastic semi-infinite medium model was established by using mixed stress-displacement finite element method and perfectly matched layer(PML). The transient wave snapshots and surface normal displacement waveforms in semi-infinite aluminum materials were obtained. The surface normal displacement waveforms were compared with the same geometrical finite element model. The results show that the mixed stress-displacement finite element method can effectively eliminate reflection waves from truncated boundary, and simulate the generation and propagation of ultrasound in semi-infinite solid material accurately. The simulation results provide an effective method for research of the laser-generated ultrasound waves in micro-nanostructure by picosecond or femtosecond laser irradiation.
2014, 38(2): 236-239.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.019
Abstract:
In order to eliminate the zero-order image and the conjugate image interference problems in the traditional algorithm for reconstruction of digital hologram, a new algorithm based on the total variation of the two-step iterative shrinkage thresholding (TwIST) was proposed combining compressive sensing theory with reconstruction of the digital hologram. According to the characteristics of the reconstruction component, the TwIST algorithm based on the total variation improves the quality of the reconstruction of hologram. The simulation results show that the hologram can be reconstructed from a sparse hologram with TwIST reconstruction algorithm a high quality image was reconstructed from 35% of a hologram and the peak signal-to-noise ratio (PSNR) of the reconstructed image was 36.46dB without zero-order image and conjugate image interference. The study is helpful for implementing real-time computer-generated hologram.
In order to eliminate the zero-order image and the conjugate image interference problems in the traditional algorithm for reconstruction of digital hologram, a new algorithm based on the total variation of the two-step iterative shrinkage thresholding (TwIST) was proposed combining compressive sensing theory with reconstruction of the digital hologram. According to the characteristics of the reconstruction component, the TwIST algorithm based on the total variation improves the quality of the reconstruction of hologram. The simulation results show that the hologram can be reconstructed from a sparse hologram with TwIST reconstruction algorithm a high quality image was reconstructed from 35% of a hologram and the peak signal-to-noise ratio (PSNR) of the reconstructed image was 36.46dB without zero-order image and conjugate image interference. The study is helpful for implementing real-time computer-generated hologram.
2014, 38(2): 240-245.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.020
Abstract:
In order to improve the wear and corrosion resistance of SUS 304 stainless steel, an alloyed layer of Cr-CrB2 was fabricated on SUS 304 stainless steel using laser surface alloying. The datum about microstructure, phases and the corrosion property of the alloyed layer were obtained. Dense and homogeneous structure and fine grains were observed in the alloyed layer. A metallurgical bonding interface was formed between the alloyed layer and the substrate. The alloyed layer consists of austenite, martensite, Fe-Cr, chromium carbide and chromium boride. The alloyed layer shows higher corrosion resistance and lower corrosion rate than the substrate. The polarization curve of the alloyed layer has a long activaton-passivation segment. Intergranular corrosion and pitting in the grains and the grain boundaries are observed for substrate, and intergranular corrosion occurs mainly in the boundary. The alloyed layer shows intergranular corrosion in combination with pitting in the grains and grain boundaries. The size of the pitting in the substrate is larger than that in the alloyed layer. The results have a great help on the improvement of the wear and corrosion resistance of SUS 304 stainless steel.
In order to improve the wear and corrosion resistance of SUS 304 stainless steel, an alloyed layer of Cr-CrB2 was fabricated on SUS 304 stainless steel using laser surface alloying. The datum about microstructure, phases and the corrosion property of the alloyed layer were obtained. Dense and homogeneous structure and fine grains were observed in the alloyed layer. A metallurgical bonding interface was formed between the alloyed layer and the substrate. The alloyed layer consists of austenite, martensite, Fe-Cr, chromium carbide and chromium boride. The alloyed layer shows higher corrosion resistance and lower corrosion rate than the substrate. The polarization curve of the alloyed layer has a long activaton-passivation segment. Intergranular corrosion and pitting in the grains and the grain boundaries are observed for substrate, and intergranular corrosion occurs mainly in the boundary. The alloyed layer shows intergranular corrosion in combination with pitting in the grains and grain boundaries. The size of the pitting in the substrate is larger than that in the alloyed layer. The results have a great help on the improvement of the wear and corrosion resistance of SUS 304 stainless steel.
2014, 38(2): 246-250.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.021
Abstract:
In order to study polarization properties of Gaussian-Schell model beams, the method of cross-spectral density matrix was adopted to study polarization properties of Gaussian-Schell model beams propagating through a focal optical system. The conditions, under which complete polarized and complete non-polarized beams kept the degree of polarization invariable in the focal optical system, were provided. The condition where the degree of polarization distributed homogeneously at propagation plane was also given. The degree of polarization had a sharp fluctuation at focal position in a focal optical system. The degree of polarization at focal position equaled the stable value of the degree of polarization at far field. The study had important theoretical and practical significance in the field of laser transmission.
In order to study polarization properties of Gaussian-Schell model beams, the method of cross-spectral density matrix was adopted to study polarization properties of Gaussian-Schell model beams propagating through a focal optical system. The conditions, under which complete polarized and complete non-polarized beams kept the degree of polarization invariable in the focal optical system, were provided. The condition where the degree of polarization distributed homogeneously at propagation plane was also given. The degree of polarization had a sharp fluctuation at focal position in a focal optical system. The degree of polarization at focal position equaled the stable value of the degree of polarization at far field. The study had important theoretical and practical significance in the field of laser transmission.
2014, 38(2): 251-254.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.022
Abstract:
For reducing attosecond pulses energy loss in the focusing reflection process and measurement error caused by attosecond pulse focusing aberration measurement, as well as improving the operability of attosecond pulse spectroscopy monitoring, a combined focusing and spectrum-analysis system for attosecond pulse was designed through step-by-step performance optimization. The structure and characteristic parameters were given in detail. The focusing and spectrum-analyzing components are gold-coated grazing incidence toroidal mirror and grazing incidence concave focusing grating, respectively. The proposed system can find application in research platform of attosecond spectroscopy using high energy short attosecond pulse as basic probe tool.
For reducing attosecond pulses energy loss in the focusing reflection process and measurement error caused by attosecond pulse focusing aberration measurement, as well as improving the operability of attosecond pulse spectroscopy monitoring, a combined focusing and spectrum-analysis system for attosecond pulse was designed through step-by-step performance optimization. The structure and characteristic parameters were given in detail. The focusing and spectrum-analyzing components are gold-coated grazing incidence toroidal mirror and grazing incidence concave focusing grating, respectively. The proposed system can find application in research platform of attosecond spectroscopy using high energy short attosecond pulse as basic probe tool.
2014, 38(2): 255-259.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.023
Abstract:
In order to measure Stokes vectors simply and conveniently, a dual-photoelastic-modulator working at different frequencies was adopted to generate high frequency modulation component loaded with the parameters to be measured after light modulation because of the frequency superposition. Four Stokes components suitable for all polarization measurements were obtained once through a phase-locked polarization measurement. After theoretical analysis, simulation verification and error analysis, the effects of phase delay and incidence angle on the measurement results were studied. The results show that all the measured polarization components can be obtained with only one measurement and the method provides theoretical support for further engineering implementation.
In order to measure Stokes vectors simply and conveniently, a dual-photoelastic-modulator working at different frequencies was adopted to generate high frequency modulation component loaded with the parameters to be measured after light modulation because of the frequency superposition. Four Stokes components suitable for all polarization measurements were obtained once through a phase-locked polarization measurement. After theoretical analysis, simulation verification and error analysis, the effects of phase delay and incidence angle on the measurement results were studied. The results show that all the measured polarization components can be obtained with only one measurement and the method provides theoretical support for further engineering implementation.
2014, 38(2): 260-265.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.024
Abstract:
In order to explore effect of wall thickness on the generation and detection of ultrasound signal, several idealized eccentric pipe models were established based on the finite element method. Effect of different uniform wall-thickness and thickness change at the excitation source, detection point and the propagation path on ultrasonic signal was analyzed. The simulation results show that: when the wall is thinner, the Rayleigh waves cannot be detected; the wall thickness on the propagation path becomes small to some extent, the filtering effect will be so obvious that the high-frequency component is filtered out, but will resume within a certain extent in the pipes with thicker wall. This work will provide a useful guidance for the further application of laser ultrasonic in cylinder nondestructive testing field.
In order to explore effect of wall thickness on the generation and detection of ultrasound signal, several idealized eccentric pipe models were established based on the finite element method. Effect of different uniform wall-thickness and thickness change at the excitation source, detection point and the propagation path on ultrasonic signal was analyzed. The simulation results show that: when the wall is thinner, the Rayleigh waves cannot be detected; the wall thickness on the propagation path becomes small to some extent, the filtering effect will be so obvious that the high-frequency component is filtered out, but will resume within a certain extent in the pipes with thicker wall. This work will provide a useful guidance for the further application of laser ultrasonic in cylinder nondestructive testing field.
2014, 38(2): 266-269.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.025
Abstract:
To study the atmospheric transmission characteristics of laser, the laser power attenuation formula was established at a certain distance based on the general model of laser atmosphere transmission. The laser atmospheric transmittance at 1.06μm and the power onto the target were calculated with MATLAB software. Results show that the model provides the reliable theory basis for laser influencing space probe and remove of tiny pieces, and certain reference for further study about laser atmospheric attenuation characteristics.
To study the atmospheric transmission characteristics of laser, the laser power attenuation formula was established at a certain distance based on the general model of laser atmosphere transmission. The laser atmospheric transmittance at 1.06μm and the power onto the target were calculated with MATLAB software. Results show that the model provides the reliable theory basis for laser influencing space probe and remove of tiny pieces, and certain reference for further study about laser atmospheric attenuation characteristics.
2014, 38(2): 270-273.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.026
Abstract:
To solve the problem that stability of radiation wavelength and luminous intensity of a laser diode were affected easily by temperature, a high precision laser diode temperature control system was designed. Temperature acquisition circuit was designed by means of AD620 and LTC1864 and temperature control circuit by MAX1968 and LTC1655. The whole system was controlled accurately by a TMS320F2812 controller. Adaptive fuzzy proportion-integration-differentiation control strategy was proposed and the software was achieved. At the environmental temperature around 15℃, control precision of temperature was up to ±0.05℃ when the target temperature was set to 25℃ and 20℃ respectively. Experimental results show that the temperature control system has the advantages of fast response and high stability.
To solve the problem that stability of radiation wavelength and luminous intensity of a laser diode were affected easily by temperature, a high precision laser diode temperature control system was designed. Temperature acquisition circuit was designed by means of AD620 and LTC1864 and temperature control circuit by MAX1968 and LTC1655. The whole system was controlled accurately by a TMS320F2812 controller. Adaptive fuzzy proportion-integration-differentiation control strategy was proposed and the software was achieved. At the environmental temperature around 15℃, control precision of temperature was up to ±0.05℃ when the target temperature was set to 25℃ and 20℃ respectively. Experimental results show that the temperature control system has the advantages of fast response and high stability.
2014, 38(2): 274-277.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.027
Abstract:
In order to obtain high-quality three primary colors to realize large color gamut display. Red, green and blue F-P filters were designed by means of transfer matrix method in optical thin film technology. Then these filters were put together to obtain a new filter allowing three primary colors to pass through and reflect other stray colors. The filter can satisfy the design target well. With this filter, color display function of displayer can be enhanced drastically.
In order to obtain high-quality three primary colors to realize large color gamut display. Red, green and blue F-P filters were designed by means of transfer matrix method in optical thin film technology. Then these filters were put together to obtain a new filter allowing three primary colors to pass through and reflect other stray colors. The filter can satisfy the design target well. With this filter, color display function of displayer can be enhanced drastically.
2014, 38(2): 278-282.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.028
Abstract:
Fiber lasers have grown rapidly for their unique advantages, which become very competitive in many applications such as industrial processing, defense and military, medical and other fields. The progress of continuous wave and pulse Yb-doped double-clad fiber laser at home and abroad was reported. All-fiber lasers with combiners and fiber gratings were introduced. Simultaneously, pulse fiber lasers with high beam quality, high average power and high peak power based on master oscillator fiber power amplifier technology were presented. The influencing factors of increasing power of fiber laser, including damage of the optical fiber, nonlinear effects, thermal effects, were analyzed. Finally, the development trends of the Yb-doped double-clad fiber lasers were predicated.
Fiber lasers have grown rapidly for their unique advantages, which become very competitive in many applications such as industrial processing, defense and military, medical and other fields. The progress of continuous wave and pulse Yb-doped double-clad fiber laser at home and abroad was reported. All-fiber lasers with combiners and fiber gratings were introduced. Simultaneously, pulse fiber lasers with high beam quality, high average power and high peak power based on master oscillator fiber power amplifier technology were presented. The influencing factors of increasing power of fiber laser, including damage of the optical fiber, nonlinear effects, thermal effects, were analyzed. Finally, the development trends of the Yb-doped double-clad fiber lasers were predicated.
2014, 38(2): 283-288.
doi: 10.7510/jgjs.issn.1001-3806.2014.02.029
Abstract:
The Fabry-Perot etalon was the key component of a Rayleigh Doppler wind lidar. In order to accurately determine the Doppler shift proportional to the wind velocity, the principle of Rayleigh Doppler frequency measurement was deeply analyzed, and the optimum parameters of the etalon were determined after analyzing the detection error at the maximum height designed. The calibration method and idea were introduced in detail. The factors making the full width at half maximum(FWHM) of the transmission curves broadened were analyzed, the calibration accuracy of the transmission curve affecting the velocity sensitivity and the system measuring error was also analyzed in detail. The design and calibration were verified in experiments. The result indicated that the velocity sensitivity of etalon decreased 0.118%/(m·s-1) due to the broadened FWHM of transmission curves and with the signal-to-noise ratio no less than 10, the accuracy of the line-of-sight velocity increased 2m/s at 40km altitude height.
The Fabry-Perot etalon was the key component of a Rayleigh Doppler wind lidar. In order to accurately determine the Doppler shift proportional to the wind velocity, the principle of Rayleigh Doppler frequency measurement was deeply analyzed, and the optimum parameters of the etalon were determined after analyzing the detection error at the maximum height designed. The calibration method and idea were introduced in detail. The factors making the full width at half maximum(FWHM) of the transmission curves broadened were analyzed, the calibration accuracy of the transmission curve affecting the velocity sensitivity and the system measuring error was also analyzed in detail. The design and calibration were verified in experiments. The result indicated that the velocity sensitivity of etalon decreased 0.118%/(m·s-1) due to the broadened FWHM of transmission curves and with the signal-to-noise ratio no less than 10, the accuracy of the line-of-sight velocity increased 2m/s at 40km altitude height.
