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RSS2010 Vol. 22, No. 08
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2010,
22.
Abstract:
A driving circuit was designed for the electro-optical phase modulator, according to its structural characteristics. The circuit consists of OP37 and PA84. It is simple, but stable. The peak-to-peak value of the circuit’s output voltage is up to 200 V within the frequency range of 0 to 280 kHz. Phase compensation was designed for the output signals, and then an optical phase modulation experiment was conducted. The shift of interference fringes caused by the change of driving voltage imposed on the electro-optical modulator was observed by a photodetector.
A driving circuit was designed for the electro-optical phase modulator, according to its structural characteristics. The circuit consists of OP37 and PA84. It is simple, but stable. The peak-to-peak value of the circuit’s output voltage is up to 200 V within the frequency range of 0 to 280 kHz. Phase compensation was designed for the output signals, and then an optical phase modulation experiment was conducted. The shift of interference fringes caused by the change of driving voltage imposed on the electro-optical modulator was observed by a photodetector.
2010,
22.
Abstract:
A femtosecond pulsed laser(800 nm, 120 fs, 3 W, 1 000 Hz) was used to deposit diamond-like carbon(DLC) films on Si substrate. Effects of bias, substrate temperature and oxygen ambient on DLC films were studied. Experiments show that the best DLC film was deposited under the conditions of room temperature, no bias and low oxygen pressure(2 Pa). The hydrogenfree DLC film was deposited on one side of Si substrate, and on the other side, the common anti-reflective film was pre-deposited. The average transmittance at 3~5 μm waveband was larger than 90%, and the nano-hardness was up to 40 GPa. There were no nicks on the film after being rubbed for 105 times by a 9.8 N rubber. Furthermore, the films have passed the high temperature, low temperature and salt-fog tests in military standards. T
A femtosecond pulsed laser(800 nm, 120 fs, 3 W, 1 000 Hz) was used to deposit diamond-like carbon(DLC) films on Si substrate. Effects of bias, substrate temperature and oxygen ambient on DLC films were studied. Experiments show that the best DLC film was deposited under the conditions of room temperature, no bias and low oxygen pressure(2 Pa). The hydrogenfree DLC film was deposited on one side of Si substrate, and on the other side, the common anti-reflective film was pre-deposited. The average transmittance at 3~5 μm waveband was larger than 90%, and the nano-hardness was up to 40 GPa. There were no nicks on the film after being rubbed for 105 times by a 9.8 N rubber. Furthermore, the films have passed the high temperature, low temperature and salt-fog tests in military standards. T
2010,
22.
Abstract:
The growth of interference fringes caused by nonlinear propagation instabilities has been experimentally investigated using a femtosecond pulsed laser. This paper reports the measurements of growth rate for fringes in a glass cuvette filled with CS2 as a function of fringe spacing and intensity. The ripples grow rapidly when the modulated beam propagates in the nonlinear media, and there exists a modulation frequency where the intensity modulation grows fastest and filamentation happens. Numerical results show good agreement with the experimental results．
The growth of interference fringes caused by nonlinear propagation instabilities has been experimentally investigated using a femtosecond pulsed laser. This paper reports the measurements of growth rate for fringes in a glass cuvette filled with CS2 as a function of fringe spacing and intensity. The ripples grow rapidly when the modulated beam propagates in the nonlinear media, and there exists a modulation frequency where the intensity modulation grows fastest and filamentation happens. Numerical results show good agreement with the experimental results．
2010,
22.
Abstract:
A novel interferometer is designed based on the dispersive property of slow light media. The numerical simulation on its physical process proves that the spectral sensitivity of interferometer can be enhanced effectively using the slow light medium. And the sensitivity is proportional to the group refractive index of the slow light medium. A further investigation gives the general method of designing slow light interferometers taking into account the dispersive property of GaAs. It is theoretically demonstrated that the spectral sensitivity of an interferometer can be greatly enhanced by dispersive property of semiconductor GaAs in nearinfrared region.
A novel interferometer is designed based on the dispersive property of slow light media. The numerical simulation on its physical process proves that the spectral sensitivity of interferometer can be enhanced effectively using the slow light medium. And the sensitivity is proportional to the group refractive index of the slow light medium. A further investigation gives the general method of designing slow light interferometers taking into account the dispersive property of GaAs. It is theoretically demonstrated that the spectral sensitivity of an interferometer can be greatly enhanced by dispersive property of semiconductor GaAs in nearinfrared region.
2010,
22.
Abstract:
GaSb-based InGaAsSb/AlGaAsSb multi-quantum-wells structure are designed and grown by molecular beam epitaxy(MBE). Characterization of the layers by X-ray diffraction and photoluminescence has been performed. The results showed that the epilayer has high uniformity and quality. AlSb buffer layer can reduce free energy between substrate and epilayer, thus it works as filter to restrain the dislocations. At room temperature, the emission spectra are centered at about 2.3 μm．
GaSb-based InGaAsSb/AlGaAsSb multi-quantum-wells structure are designed and grown by molecular beam epitaxy(MBE). Characterization of the layers by X-ray diffraction and photoluminescence has been performed. The results showed that the epilayer has high uniformity and quality. AlSb buffer layer can reduce free energy between substrate and epilayer, thus it works as filter to restrain the dislocations. At room temperature, the emission spectra are centered at about 2.3 μm．
2010,
22.
Abstract:
The mechanism of gray-tracking and the influence of color center on gray-tracking are studied for KTP crystal, with a Q-switched laser whose wavelength and pulse width are 1 064 nm/532 nm and 6 ns respectively. The transmittance of crystal represents color center density. According to the relation between the transmittance and color center and the decisive role of color center density on gray-tracking, the critical gray-tracking density is defined, above which safe operation can be ensured. The experimental results show that gray-tracking absorbs not only the energy of ultraviolet and visible lights, but also that of near infrared light, giving a method for monitoring gray-tracking on line.
The mechanism of gray-tracking and the influence of color center on gray-tracking are studied for KTP crystal, with a Q-switched laser whose wavelength and pulse width are 1 064 nm/532 nm and 6 ns respectively. The transmittance of crystal represents color center density. According to the relation between the transmittance and color center and the decisive role of color center density on gray-tracking, the critical gray-tracking density is defined, above which safe operation can be ensured. The experimental results show that gray-tracking absorbs not only the energy of ultraviolet and visible lights, but also that of near infrared light, giving a method for monitoring gray-tracking on line.
2010,
22.
Abstract:
Polarization properties of defect modes of one-dimensional photonic crystals with negative-index materials are investigated by optical transfer matrix method. It is found that the defect modes in the zero-average-index gap have a strong dependence on the incident angles and polarization. Through tuning the optimized parameters of the defect layer, a series of polarization-independent and non-omnidirectional defect modes is obtained with the increase of incident angle, which is not available in conventional one-dimensional photonic crystals. Based on these defect modes, we have designed low-, high- and band pass spatial filters which have a polarization-independent feature comparing with spatial filters of conventional photonic crystals.
Polarization properties of defect modes of one-dimensional photonic crystals with negative-index materials are investigated by optical transfer matrix method. It is found that the defect modes in the zero-average-index gap have a strong dependence on the incident angles and polarization. Through tuning the optimized parameters of the defect layer, a series of polarization-independent and non-omnidirectional defect modes is obtained with the increase of incident angle, which is not available in conventional one-dimensional photonic crystals. Based on these defect modes, we have designed low-, high- and band pass spatial filters which have a polarization-independent feature comparing with spatial filters of conventional photonic crystals.
2010,
22.
Abstract:
This paper proposes theoretically a novel terahertz source based on polarization-maintaining optical fibers. Utilizing the dual-wavelength laser as the pump source and four-wave-mixing effect in the optical fibers, a compact wide-tunable narrowband terahertz source can be constructed. The surface-emitting scheme is used to decrease the absorption loss of terahertz waves in the optical fibers. The four-wave mixing process and the phase-matching conditions are discussed through the coupled-wave theory, and the analytical expression of terahertz output power is obtained. It is shown that when the pump peak power is about 1 kW, the terahertz peak power is about 350 mW at 6 THz, and the power conversion efficiency is about 0.01%. This scheme provides a possibility to realize a high-power, comp
This paper proposes theoretically a novel terahertz source based on polarization-maintaining optical fibers. Utilizing the dual-wavelength laser as the pump source and four-wave-mixing effect in the optical fibers, a compact wide-tunable narrowband terahertz source can be constructed. The surface-emitting scheme is used to decrease the absorption loss of terahertz waves in the optical fibers. The four-wave mixing process and the phase-matching conditions are discussed through the coupled-wave theory, and the analytical expression of terahertz output power is obtained. It is shown that when the pump peak power is about 1 kW, the terahertz peak power is about 350 mW at 6 THz, and the power conversion efficiency is about 0.01%. This scheme provides a possibility to realize a high-power, comp
2010,
22.
Abstract:
In the experiment, visible light array CCD imaging system was irradiated by continuous wave infrared laser. Crosstalk saturation and full-screen saturation were observed, and cross saturation threshold was less than 2.0×102 W/cm2, full-screen saturation was 1.2×104 W/cm2. An effective jamming area assessment method basing on the analysis of CCD’s output voltage and video signal was presented. The relationship between jamming area and laser power density, the relationship between jamming area and irradiation times was studied respectively. It is concluded that radiation power density has a more important influence on jamming effect compare to radiation times when it’s between 0.5 s to 2.0 s.
In the experiment, visible light array CCD imaging system was irradiated by continuous wave infrared laser. Crosstalk saturation and full-screen saturation were observed, and cross saturation threshold was less than 2.0×102 W/cm2, full-screen saturation was 1.2×104 W/cm2. An effective jamming area assessment method basing on the analysis of CCD’s output voltage and video signal was presented. The relationship between jamming area and laser power density, the relationship between jamming area and irradiation times was studied respectively. It is concluded that radiation power density has a more important influence on jamming effect compare to radiation times when it’s between 0.5 s to 2.0 s.
2010,
22.
Abstract:
This paper proposes theoretically a novel terahertz source based on polarization-maintaining optical fibers. Utilizing the dual-wavelength laser as the pump source and four-wave-mixing effect in the optical fibers, a compact wide-tunable narrowband terahertz source can be constructed. The surface-emitting scheme is used to decrease the absorption loss of terahertz waves in the optical fibers. The four-wave mixing process and the phase-matching conditions are discussed through the coupled-wave theory, and the analytical expression of terahertz output power is obtained. It is shown that when the pump peak power is about 1 kW, the terahertz peak power is about 350 mW at 6 THz, and the power conversion efficiency is about 0.01%. This scheme provides a possibility to realize a high-power, comp
This paper proposes theoretically a novel terahertz source based on polarization-maintaining optical fibers. Utilizing the dual-wavelength laser as the pump source and four-wave-mixing effect in the optical fibers, a compact wide-tunable narrowband terahertz source can be constructed. The surface-emitting scheme is used to decrease the absorption loss of terahertz waves in the optical fibers. The four-wave mixing process and the phase-matching conditions are discussed through the coupled-wave theory, and the analytical expression of terahertz output power is obtained. It is shown that when the pump peak power is about 1 kW, the terahertz peak power is about 350 mW at 6 THz, and the power conversion efficiency is about 0.01%. This scheme provides a possibility to realize a high-power, comp
2010,
22.
Abstract:
The key technology of fluorescence lifetime imaging microscopy is introduced. Time-correlated single photon counting in time-domain method is adopted to record fluorescence lifetime. The counting efficiency and the amount of information in the data can be increased by recording the fluorescence in several wavelength channels simultaneously. Multi-wavelength imaging is used to separate different chromophores in stead-state images. Thus the image is build up with four dimension. On the other hand, multi-photon exciting technology is used in the system. Two or more photons emitted by long-wave light source can excite a short-wave one. Several photons must reach the excited point simultaneously to produce enough energy to excite fluorescence. The long wavelength emitting light in multi-photon
The key technology of fluorescence lifetime imaging microscopy is introduced. Time-correlated single photon counting in time-domain method is adopted to record fluorescence lifetime. The counting efficiency and the amount of information in the data can be increased by recording the fluorescence in several wavelength channels simultaneously. Multi-wavelength imaging is used to separate different chromophores in stead-state images. Thus the image is build up with four dimension. On the other hand, multi-photon exciting technology is used in the system. Two or more photons emitted by long-wave light source can excite a short-wave one. Several photons must reach the excited point simultaneously to produce enough energy to excite fluorescence. The long wavelength emitting light in multi-photon
2010,
22.
Abstract:
An anisotropic metamaterial with linear dispersion relation was investigated according to Maxwell equations. Based on the linear dispersion, the relation between the elements of dielectric tensor and permeability tensor was obtained. According to the law of conservation of energy and boundary conditions of electromagnetic field, the propagation direction of wave vector and energy flow between the incident and refractive wave was researched. Light collimation, takes place when TE or TM wave propagates in this anisotropic metamaterial, and the propagation ways of TE and TM are opposite to each other.
An anisotropic metamaterial with linear dispersion relation was investigated according to Maxwell equations. Based on the linear dispersion, the relation between the elements of dielectric tensor and permeability tensor was obtained. According to the law of conservation of energy and boundary conditions of electromagnetic field, the propagation direction of wave vector and energy flow between the incident and refractive wave was researched. Light collimation, takes place when TE or TM wave propagates in this anisotropic metamaterial, and the propagation ways of TE and TM are opposite to each other.
2010,
22.
Abstract:
Based on the Drude mode, beam focusing in metamaterials with both electric and magnetic nonlinearities are investigated, both analytically and numerically. The results show that beam focusing occurs not only in self-focusing nonlinear materials (positive-index region), but also in self-defocusing nonlinear material (negative-index region). In addition, the self-focusing effect is stronger when the plasma frequency of the material shifts closer to the central frequency of the beam. In particular, when the signs for electric and magnetic susceptibilities are different, the sign of nonlinearity for metamaterials can be engineered by varying the relative magnitude between electric and the magnetic plasma frequencies. This provides us an alternative approach to manipulate beam propagation at wi
Based on the Drude mode, beam focusing in metamaterials with both electric and magnetic nonlinearities are investigated, both analytically and numerically. The results show that beam focusing occurs not only in self-focusing nonlinear materials (positive-index region), but also in self-defocusing nonlinear material (negative-index region). In addition, the self-focusing effect is stronger when the plasma frequency of the material shifts closer to the central frequency of the beam. In particular, when the signs for electric and magnetic susceptibilities are different, the sign of nonlinearity for metamaterials can be engineered by varying the relative magnitude between electric and the magnetic plasma frequencies. This provides us an alternative approach to manipulate beam propagation at wi
2010,
22.
Abstract:
In pulsed laser ranging system, the time interval measurement to improve the accuracy of the interpolation method for time interval measurement. This article analyzes the traditional digital counting method based on the principle and error, focusing on the interpolation. The objects of measurement are the conventional digital counting pulse under test and the next rising edge of a quantitative clock time interval between pulse rising edge. By capacitive discharge technology, the time interval is loaded to a time extension module (usually a high-precision capacitance) to achieve time amplification. Measurement of the enlarged time can improve the precision of time measurement. Using this method, the time interval measurement accuracy is up to 100 ps, corresponding to 1.5 cm range accuracy.
In pulsed laser ranging system, the time interval measurement to improve the accuracy of the interpolation method for time interval measurement. This article analyzes the traditional digital counting method based on the principle and error, focusing on the interpolation. The objects of measurement are the conventional digital counting pulse under test and the next rising edge of a quantitative clock time interval between pulse rising edge. By capacitive discharge technology, the time interval is loaded to a time extension module (usually a high-precision capacitance) to achieve time amplification. Measurement of the enlarged time can improve the precision of time measurement. Using this method, the time interval measurement accuracy is up to 100 ps, corresponding to 1.5 cm range accuracy.
2010,
22.
Abstract:
A 3-D numerical model of the temperature field for the laser transformation hardening was created based on finite element software ProCAST. The temperature field of the laser transformation hardening of ductile cast iron QT600-3 was calculated. According to the temperature field, the depths and widths of the hardened band were predicted. When the laser power ranged from 800 W to 1 000 W, the scan velocity ranged from 2.000 mm/s to 2.667 mm/s, and the diameter of laser beam ranged from 4 mm to 5 mm, The depths of the hardened distribute between 0.20 mm and 0.64 mm as well as the widths distribute between 2.0 mm and 3.7 mm. The depths and widths of the hardened band rises with increase in laser power or decrease in laser scanning velocity. It was found that the numerical simulated results wa
A 3-D numerical model of the temperature field for the laser transformation hardening was created based on finite element software ProCAST. The temperature field of the laser transformation hardening of ductile cast iron QT600-3 was calculated. According to the temperature field, the depths and widths of the hardened band were predicted. When the laser power ranged from 800 W to 1 000 W, the scan velocity ranged from 2.000 mm/s to 2.667 mm/s, and the diameter of laser beam ranged from 4 mm to 5 mm, The depths of the hardened distribute between 0.20 mm and 0.64 mm as well as the widths distribute between 2.0 mm and 3.7 mm. The depths and widths of the hardened band rises with increase in laser power or decrease in laser scanning velocity. It was found that the numerical simulated results wa
2010,
22.
Abstract:
Based on the vectorial Debye theory, the tight focusing of double-ring-shaped radially polarized vortex beams (DRS-RPVBs) through a dielectric interface is investigated. The investigation illustrates that when the interception ratio of the aperture radius to the incident beam waist radius is proper, a tiny bottle beam can be obtained in the focal region. The size of the bottle beam is dependent on the numerical aperture of the objective and the refractive index of the medium in the focal region. In addition, the influence of the numerical aperture, interception ratio and probe depth on the focal shift is investigated. And the calculation for the real focus location indicates that, for a proper interception ratio, there exists a jump in the location.
Based on the vectorial Debye theory, the tight focusing of double-ring-shaped radially polarized vortex beams (DRS-RPVBs) through a dielectric interface is investigated. The investigation illustrates that when the interception ratio of the aperture radius to the incident beam waist radius is proper, a tiny bottle beam can be obtained in the focal region. The size of the bottle beam is dependent on the numerical aperture of the objective and the refractive index of the medium in the focal region. In addition, the influence of the numerical aperture, interception ratio and probe depth on the focal shift is investigated. And the calculation for the real focus location indicates that, for a proper interception ratio, there exists a jump in the location.
2010,
22.
Abstract:
The electron beam evaporation deposition method was employed to prepare scandium oxide(Sc2O3) films with substrate temperatures varying from 50 to 350 ℃. A spectrophotometer, a glancing incidence X-ray diffraction spectrometer and a WYKO optical profilograph were employed to investigate the optical, microstructure properties and surface roughness of the Sc2O3 films. The refractive index and the extinction coefficient were calculated from the transmittance and reflectance spectra with the help of the Essential Macleod. The laser induced damage threshold(LIDT) of the Sc2O3 films was characterized by a pulsed Nd:YAG laser system at 355 nm with a pulse duration of 8 ns. A maximum value of 2.6 J/cm2 was derived, and t
The electron beam evaporation deposition method was employed to prepare scandium oxide(Sc2O3) films with substrate temperatures varying from 50 to 350 ℃. A spectrophotometer, a glancing incidence X-ray diffraction spectrometer and a WYKO optical profilograph were employed to investigate the optical, microstructure properties and surface roughness of the Sc2O3 films. The refractive index and the extinction coefficient were calculated from the transmittance and reflectance spectra with the help of the Essential Macleod. The laser induced damage threshold(LIDT) of the Sc2O3 films was characterized by a pulsed Nd:YAG laser system at 355 nm with a pulse duration of 8 ns. A maximum value of 2.6 J/cm2 was derived, and t
2010,
22.
Abstract:
Analytic expressions of spectrum transmissivity for the parallel grating-pair is deduced, with which the influence of the stretcher and compressor on the temporal properties of the output pulse laser can be analyzed. The analysis results show that, the spectrum transmissivity depends not only on the size and groove density of the gratings, but also on the size of the incident beam, the incident angle and the distance between the gratings. In a short pulse laser system, the stretcher has a much smaller cut-off bandpass than the compressor, which will limit the enhancement of the temporal contrast of the output pulse.
Analytic expressions of spectrum transmissivity for the parallel grating-pair is deduced, with which the influence of the stretcher and compressor on the temporal properties of the output pulse laser can be analyzed. The analysis results show that, the spectrum transmissivity depends not only on the size and groove density of the gratings, but also on the size of the incident beam, the incident angle and the distance between the gratings. In a short pulse laser system, the stretcher has a much smaller cut-off bandpass than the compressor, which will limit the enhancement of the temporal contrast of the output pulse.
2010,
22.
Abstract:
When radial shear interferometer is used in high-power laser wavefront detection, due to the influence of the nonlinearity of CCD, there exist not only the first order frequency with wave-front information but also the second and the third order frequency. They may lead to overlapping spectrum, which makes it difficult to extract useful information and reduces the detection accuracy of wavefront. A theoretical analysis on mechanisms of high-order spectral component and spectrum aliasing caused by the nonlinearity of CCD is established, and the condition to avoid spectrum aliasing is pointed out. Finally, a method by increasing the spatial carrier frequency to reduce or eliminate the spectrum aliasing is proposed. Computer simulation and experimental results have verified the feasibility of
When radial shear interferometer is used in high-power laser wavefront detection, due to the influence of the nonlinearity of CCD, there exist not only the first order frequency with wave-front information but also the second and the third order frequency. They may lead to overlapping spectrum, which makes it difficult to extract useful information and reduces the detection accuracy of wavefront. A theoretical analysis on mechanisms of high-order spectral component and spectrum aliasing caused by the nonlinearity of CCD is established, and the condition to avoid spectrum aliasing is pointed out. Finally, a method by increasing the spatial carrier frequency to reduce or eliminate the spectrum aliasing is proposed. Computer simulation and experimental results have verified the feasibility of
2010,
22.
Abstract:
In order to study the effects of laser shock peening on the fatigue life of LY2 aluminum alloy, water and aluminum foil were used for confining medium and ablation medium, respectively. LY2 specimens were processed with YAG laser. The laser peening parameters were: wavelength of 532 nm, pulse duration of 10 ns, and output energy of 5 J. The laser was focused on a spot of diameter 3 mm. The experimental results show that laser shock peening can increase aluminum fatigue life by 110%. Fracture analysis results show that laser shock peening strengthens the metal surface and suppresses the crack’s initiation and expansion, improving the aluminum fatigue performance．
In order to study the effects of laser shock peening on the fatigue life of LY2 aluminum alloy, water and aluminum foil were used for confining medium and ablation medium, respectively. LY2 specimens were processed with YAG laser. The laser peening parameters were: wavelength of 532 nm, pulse duration of 10 ns, and output energy of 5 J. The laser was focused on a spot of diameter 3 mm. The experimental results show that laser shock peening can increase aluminum fatigue life by 110%. Fracture analysis results show that laser shock peening strengthens the metal surface and suppresses the crack’s initiation and expansion, improving the aluminum fatigue performance．
2010,
22.
Abstract:
The optical losses of asymmetric and symmetric waveguide structures were calculated theoretically for high power 980 nm diode lasers, by means of the continuity equation under strong injection and the Helmholtz equation of complex refractive index model. The epitaxial materials of the both waveguide structures were prepared by the metallorganic chemical vapor deposition growth technique, and corresponding laser devices were fabricated. The electro-optical performances of both devices were measured and analyzed by comparison. The theoretical calculations and experimental results indicates that, the asymmetric waveguide structure material does not reduce the optical loss, but decreases the series resistance of the diode, therefore, it reduces the joule heating, and enhances the conversion ef
The optical losses of asymmetric and symmetric waveguide structures were calculated theoretically for high power 980 nm diode lasers, by means of the continuity equation under strong injection and the Helmholtz equation of complex refractive index model. The epitaxial materials of the both waveguide structures were prepared by the metallorganic chemical vapor deposition growth technique, and corresponding laser devices were fabricated. The electro-optical performances of both devices were measured and analyzed by comparison. The theoretical calculations and experimental results indicates that, the asymmetric waveguide structure material does not reduce the optical loss, but decreases the series resistance of the diode, therefore, it reduces the joule heating, and enhances the conversion ef
2010,
22.
Abstract:
According to angular spectrum representation, formalisms describing paraxial Hermite-Gaussian and Laguerre-Gaussian beams propagating through an isotropic negative refractive index material (NIM) slab are presented. Focusing and phase compensation of paraxial Hermite-Gaussian and Laguerre-Gaussian beams by the slab are investigated. The phase difference of beams caused by Gouy phase shift in air can be compensated by the inverse Gouy phase shift in NIM, thus the phase difference between the object plane and the image equals to zero in certain matching conditions. If conditions of focusing and phase compensation are satisfied simultaneously, intensity and phase distribution at object plane can be reconstructed at the image plane.
According to angular spectrum representation, formalisms describing paraxial Hermite-Gaussian and Laguerre-Gaussian beams propagating through an isotropic negative refractive index material (NIM) slab are presented. Focusing and phase compensation of paraxial Hermite-Gaussian and Laguerre-Gaussian beams by the slab are investigated. The phase difference of beams caused by Gouy phase shift in air can be compensated by the inverse Gouy phase shift in NIM, thus the phase difference between the object plane and the image equals to zero in certain matching conditions. If conditions of focusing and phase compensation are satisfied simultaneously, intensity and phase distribution at object plane can be reconstructed at the image plane.
2010,
22.
Abstract:
Range imaging of laser radar can reflect the targets geometry structure, and different poses of the same target lead to a tremendous variety of range imaging. Thus pose estimation is especially important for automated target recognition (ATR). Ulf Grenander's pattern theory makes use of deformable template to represent observed image and model the variability of target pose via the actions of the matrix special orthogonal group. In Bayesian estimation framework, it samples from posterior to empirically generate the estimates using jump-diffusion process. Error analysis of pose estimation makes use of the Hilbert-Schmidt norm as an error metric. Our work focuses on pose estimation of ground-based targets of range imaging, using Ulf Grenander's pattern theory to estimate vehicle in differe
Range imaging of laser radar can reflect the targets geometry structure, and different poses of the same target lead to a tremendous variety of range imaging. Thus pose estimation is especially important for automated target recognition (ATR). Ulf Grenander's pattern theory makes use of deformable template to represent observed image and model the variability of target pose via the actions of the matrix special orthogonal group. In Bayesian estimation framework, it samples from posterior to empirically generate the estimates using jump-diffusion process. Error analysis of pose estimation makes use of the Hilbert-Schmidt norm as an error metric. Our work focuses on pose estimation of ground-based targets of range imaging, using Ulf Grenander's pattern theory to estimate vehicle in differe
2010,
22.
Abstract:
A theoretical model to describe the three-dimensional deformation distribution of an optical sample irradiated by a square-wave modulated laser is presented. The surface thermal lens(STL) signal is defined based on the deformation theory simultaneously. According to STL theory, the deformation of a highly reflective sample with BK7 substrate is measured experimentally. The results are in good agreement with deformation model. With our experiment configuration, a minimal 1.985 nm direct current (DC) deformation is measured, corresponding to 3.97 nm without modulation. The 10 pm detect limit for the deformation measurement is achieved in our experiment. The AC STL signal is also presented in the frequency domain.
A theoretical model to describe the three-dimensional deformation distribution of an optical sample irradiated by a square-wave modulated laser is presented. The surface thermal lens(STL) signal is defined based on the deformation theory simultaneously. According to STL theory, the deformation of a highly reflective sample with BK7 substrate is measured experimentally. The results are in good agreement with deformation model. With our experiment configuration, a minimal 1.985 nm direct current (DC) deformation is measured, corresponding to 3.97 nm without modulation. The 10 pm detect limit for the deformation measurement is achieved in our experiment. The AC STL signal is also presented in the frequency domain.
2010,
22.
Abstract:
To improve the power efficiency of the laser system, it is necessary to transform Gaussian intensity distribution to dark hollow intensity distribution. The phase-only liquid crystal spatial light modulator (LC-SLM) has been used to transform a quasi-Gaussian beam to a dark hollow one. The phase distribution of the shaping system was derived according to the energy conservation law and the constant optical length principle. The influences of input beam waist and shape on shaping effect were discussed based on numerical simulation. The generation of the dark hollow beam has been realized experimentally with the phase-only LC-SLM, and the conversion efficiency was larger than 99%．
To improve the power efficiency of the laser system, it is necessary to transform Gaussian intensity distribution to dark hollow intensity distribution. The phase-only liquid crystal spatial light modulator (LC-SLM) has been used to transform a quasi-Gaussian beam to a dark hollow one. The phase distribution of the shaping system was derived according to the energy conservation law and the constant optical length principle. The influences of input beam waist and shape on shaping effect were discussed based on numerical simulation. The generation of the dark hollow beam has been realized experimentally with the phase-only LC-SLM, and the conversion efficiency was larger than 99%．
2010,
22.
Abstract:
Based on the theory of interaction between laser and material, we analyze thermal characteristics of pulsed laser irradiated monocrystalline silicon. By setting up experiment equipment including a laser lamp-house, the laser wavelength is 1 064 nm, the pulse-width is 10 ns and the repetition frequency is 1 Hz, we get the plasma and the thermal radiation spectrum of the monocrystalline silicon. We theoretically analyze the high temperature surface damnification of monocrystalline silicon according to its optical-electrical characters. After analysing waveband of the plasma spectrum of monocrystalline silicon in 380~460 nm, we find out the corresponding relation between the export frequency density of the laser and the comparative intensity of the three spectral lines, SiⅠ 390.52 nm, SiⅡ38
Based on the theory of interaction between laser and material, we analyze thermal characteristics of pulsed laser irradiated monocrystalline silicon. By setting up experiment equipment including a laser lamp-house, the laser wavelength is 1 064 nm, the pulse-width is 10 ns and the repetition frequency is 1 Hz, we get the plasma and the thermal radiation spectrum of the monocrystalline silicon. We theoretically analyze the high temperature surface damnification of monocrystalline silicon according to its optical-electrical characters. After analysing waveband of the plasma spectrum of monocrystalline silicon in 380~460 nm, we find out the corresponding relation between the export frequency density of the laser and the comparative intensity of the three spectral lines, SiⅠ 390.52 nm, SiⅡ38
2010,
22.
Abstract:
This paper introduces the primary purpose, characteristics and coating methods of 1 572 nm narrow-band filters in the laser telemeter. The multiple-cavity filters with low loss and high reliability have been developed using the computer coating optimization software. After the discussion of the technique problems, such as spectrum, temperature excursion and uniformity of the filters, experimental results of environment and characteristics tests are presented. Presently, these narrow-band filters （12 nm pass-band width）have been used in 1 572 nm laser telemeters. The effects are 11 km effective ranging distance at the precision of ±5 m and the frequency of (1±0.1) Hz．
This paper introduces the primary purpose, characteristics and coating methods of 1 572 nm narrow-band filters in the laser telemeter. The multiple-cavity filters with low loss and high reliability have been developed using the computer coating optimization software. After the discussion of the technique problems, such as spectrum, temperature excursion and uniformity of the filters, experimental results of environment and characteristics tests are presented. Presently, these narrow-band filters （12 nm pass-band width）have been used in 1 572 nm laser telemeters. The effects are 11 km effective ranging distance at the precision of ±5 m and the frequency of (1±0.1) Hz．
2010,
22.
Abstract:
Characteristics of the temporal modulation riding on broad-band lasers stacked by chirped pulses are numerically investigated in nonlinear propagation. For the case of normal dispersion, the temporal modulations induced by interference among pulses and added artificially to simulate the noise weaken gradually with the increase of the propagation distance. For the case of anomalous dispersion, the temporal modulations induced by interference among pulses grow slowly at first, and start to grow rapidly after a long propagation distance; in contrast, the temporal modulations added artificially grow rapidly from the begin, indicating that the temporal peak of damage risk to the optics can be formed easily.
Characteristics of the temporal modulation riding on broad-band lasers stacked by chirped pulses are numerically investigated in nonlinear propagation. For the case of normal dispersion, the temporal modulations induced by interference among pulses and added artificially to simulate the noise weaken gradually with the increase of the propagation distance. For the case of anomalous dispersion, the temporal modulations induced by interference among pulses grow slowly at first, and start to grow rapidly after a long propagation distance; in contrast, the temporal modulations added artificially grow rapidly from the begin, indicating that the temporal peak of damage risk to the optics can be formed easily.
2010,
22.
Abstract:
The sodium laser guide star (LGS) technique which adopted range gating and common aperture mode was researched, and the projecting-detecting experiment was studied. The relationship between sodium resonance scattering and wavelength of beacon laser was analyzed. The development of sodium beacon laser, range gating device, the set of back-scattering detector, synchronous control device etc, was introduced. Sodium beacon images were collected successfully in the experiment. The law of back-scattering images’ varying according to wavelength of laser was analyzed, wavelength matching was proved to be important in sodium LGS．
The sodium laser guide star (LGS) technique which adopted range gating and common aperture mode was researched, and the projecting-detecting experiment was studied. The relationship between sodium resonance scattering and wavelength of beacon laser was analyzed. The development of sodium beacon laser, range gating device, the set of back-scattering detector, synchronous control device etc, was introduced. Sodium beacon images were collected successfully in the experiment. The law of back-scattering images’ varying according to wavelength of laser was analyzed, wavelength matching was proved to be important in sodium LGS．
2010,
22.
Abstract:
The propagation model of Laguerre-Gaussian beams in left-handed materials was established. Through the study of phase distribution, the rotation was found to be dependent on model parameters, Gouy phase, frequency, and dispersion. The azimuthal phase difference is the main reason for the intensity rotation. The inverse Gouy phase shift caused by the negative refractive index leads to a reverse rotation of intensity. In the normal dispersion regime, the phase and the intensity rotate in the same direction. In the anomalous dispersion regime, however, they rotate in opposite directions.
The propagation model of Laguerre-Gaussian beams in left-handed materials was established. Through the study of phase distribution, the rotation was found to be dependent on model parameters, Gouy phase, frequency, and dispersion. The azimuthal phase difference is the main reason for the intensity rotation. The inverse Gouy phase shift caused by the negative refractive index leads to a reverse rotation of intensity. In the normal dispersion regime, the phase and the intensity rotate in the same direction. In the anomalous dispersion regime, however, they rotate in opposite directions.
2010,
22.
Abstract:
A new method of defocus length detection based on optical modulator is presented after analyzing traditional detection methods. Using this method, the convergent beam is modulated with the piezoelectric ceramic driving deformable mirrors, and received by photoelectric detectors through a pinhole or slit. Then the defocus length can be obtained after correlation detection. The method can obtain defocus length and direction by one detector at the same time, and the defocus voltage varies linearly with defocus length. Experiments were conducted, in which the beam was modulated by a 100 Hz sine signal. Detected voltages within 4 mm before and 2 mm behind the focal plane were obtained, which are consistent with theoretical derivation. The technique can be applied to circular symmetric and non-c
A new method of defocus length detection based on optical modulator is presented after analyzing traditional detection methods. Using this method, the convergent beam is modulated with the piezoelectric ceramic driving deformable mirrors, and received by photoelectric detectors through a pinhole or slit. Then the defocus length can be obtained after correlation detection. The method can obtain defocus length and direction by one detector at the same time, and the defocus voltage varies linearly with defocus length. Experiments were conducted, in which the beam was modulated by a 100 Hz sine signal. Detected voltages within 4 mm before and 2 mm behind the focal plane were obtained, which are consistent with theoretical derivation. The technique can be applied to circular symmetric and non-c
2010,
22.
Abstract:
Numerical simulation was applied to the study of femto/ picosecond laser-target interaction by two-temperature equation with proper initial and boundary conditions. The influence of laser pulse shapes on the carrier and lattice temperatures on the surface of Si-target was investigated. The results indicate that the main factor of temperature increasing is laser pulse power density. Pulse shapes: significantly effect the temperature distribution of the carriers on the Si-target surface, the temperature peak for rectangle pulses is the largest, and the temperature peak of Guassian pulses is the smallest. The conclusions are the theoretical basis of preparing excellent thin films.
Numerical simulation was applied to the study of femto/ picosecond laser-target interaction by two-temperature equation with proper initial and boundary conditions. The influence of laser pulse shapes on the carrier and lattice temperatures on the surface of Si-target was investigated. The results indicate that the main factor of temperature increasing is laser pulse power density. Pulse shapes: significantly effect the temperature distribution of the carriers on the Si-target surface, the temperature peak for rectangle pulses is the largest, and the temperature peak of Guassian pulses is the smallest. The conclusions are the theoretical basis of preparing excellent thin films.
2010,
22.
Abstract:
The functionality of region-of interest(ROI) image edge detection is very important in applications where certain parts of the image are of higher importance than others. However, at present, most algorithms are designed for the whole image detection, which will affect the ROI edge detection performance. In this paper, an image edge detection algorithm based on ROI extraction is presented. The new algorithm first chooses the ROI partitioning threshold using the proposed histogram modification. Then, it segments the ROI from the whole image according to the new partitioning threshold. Finally, an optimal edge detection operator is selected to complete the ROI edge detection. Experimental results show that the new algorithm can better support the ROI edge extraction than those whole-image de
The functionality of region-of interest(ROI) image edge detection is very important in applications where certain parts of the image are of higher importance than others. However, at present, most algorithms are designed for the whole image detection, which will affect the ROI edge detection performance. In this paper, an image edge detection algorithm based on ROI extraction is presented. The new algorithm first chooses the ROI partitioning threshold using the proposed histogram modification. Then, it segments the ROI from the whole image according to the new partitioning threshold. Finally, an optimal edge detection operator is selected to complete the ROI edge detection. Experimental results show that the new algorithm can better support the ROI edge extraction than those whole-image de
2010,
22.
Abstract:
A noncollinear third-order autocorrelator was designed and manufactured for contrast ratio measurement of single shot picosecond pulses. Under the premise of obtaining correct cross-correlation signals during the parameters optimization, it was still important to consider the conversion efficiency of the third harmonic wave. The noncollinear phase matching value with the maximum efficient nonlinear coefficient was taken into account according to the polarization tensor of a nonlinear crystal KDP. The noncollinear phase matching and group-velocity mismatch were synchronously satisfied, and large noncollinear angles of the incident pulses were selected for the increase of the test range of time. The prepulse and main peak were separately measured, and two-image reconstructive technology was
A noncollinear third-order autocorrelator was designed and manufactured for contrast ratio measurement of single shot picosecond pulses. Under the premise of obtaining correct cross-correlation signals during the parameters optimization, it was still important to consider the conversion efficiency of the third harmonic wave. The noncollinear phase matching value with the maximum efficient nonlinear coefficient was taken into account according to the polarization tensor of a nonlinear crystal KDP. The noncollinear phase matching and group-velocity mismatch were synchronously satisfied, and large noncollinear angles of the incident pulses were selected for the increase of the test range of time. The prepulse and main peak were separately measured, and two-image reconstructive technology was
2010,
22.
Abstract:
The far-field anomalous spectral behaviors of a Gaussian pulsed beam passing through a linear circular apertures array are studied. By expanding a hard aperture function into a finite sum of complex Gaussian functions and starting from the Fresnel diffraction integral, the approximate analytical expression for the spectral intensity of a space-time-dependent Gaussian pulsed beam passing through a linear circular apertures array is derived. The red and blue shifts and the spectral intensity distribution are studied and illustrated with numerical calculations. It is shown that there exist spectral switches when the observation position is at the right points.
The far-field anomalous spectral behaviors of a Gaussian pulsed beam passing through a linear circular apertures array are studied. By expanding a hard aperture function into a finite sum of complex Gaussian functions and starting from the Fresnel diffraction integral, the approximate analytical expression for the spectral intensity of a space-time-dependent Gaussian pulsed beam passing through a linear circular apertures array is derived. The red and blue shifts and the spectral intensity distribution are studied and illustrated with numerical calculations. It is shown that there exist spectral switches when the observation position is at the right points.
2010,
22.
Abstract:
Based on the design scheme of spectral beam combining using transmitting volume Bragg grating, the experimental results for spectral beam combining of two fiber lasers are reported. The gain mediums used in this experiment were two large mode area erbium-ytterbium co-doped double-cladding fibers, pumped by semiconductor lasers. The output powers of the two fiber lasers were 0.39 W and 0.53 W respectively. With grating diffraction efficiency lower than 60%, the maximal output power of 0.64 W with absolute combining efficiency of about 69.6% was achieved. The influencing factors of the combining efficiency in the experiment are analyzed.
Based on the design scheme of spectral beam combining using transmitting volume Bragg grating, the experimental results for spectral beam combining of two fiber lasers are reported. The gain mediums used in this experiment were two large mode area erbium-ytterbium co-doped double-cladding fibers, pumped by semiconductor lasers. The output powers of the two fiber lasers were 0.39 W and 0.53 W respectively. With grating diffraction efficiency lower than 60%, the maximal output power of 0.64 W with absolute combining efficiency of about 69.6% was achieved. The influencing factors of the combining efficiency in the experiment are analyzed.
2010,
22.
Abstract:
In order to enhance the accuracy of laser Doppler velocimeter, the method to track the laser Doppler signal and correct the frequency spectrum with frequency spectrum refinement and frequency spectrum correction method was put forward. The Doppler signal was studied by signal processing system. The results showed that the background signal and part of the noise were got rid of, signal-to-noise ratio was raised, and Doppler frequency was tracked so that the result agreed with the actual value and that the distinguishability of frequency spectrum was improved by frequency spectrum refinement algorithm and the corrected frequency agreed well with the actual value by frequency spectrum correction algorithm.
In order to enhance the accuracy of laser Doppler velocimeter, the method to track the laser Doppler signal and correct the frequency spectrum with frequency spectrum refinement and frequency spectrum correction method was put forward. The Doppler signal was studied by signal processing system. The results showed that the background signal and part of the noise were got rid of, signal-to-noise ratio was raised, and Doppler frequency was tracked so that the result agreed with the actual value and that the distinguishability of frequency spectrum was improved by frequency spectrum refinement algorithm and the corrected frequency agreed well with the actual value by frequency spectrum correction algorithm.
2010,
22.
Abstract:
A two-cavity Fabry-Perot(F-P) structure is compared to the conventional F-P structure. The characteristics of transmission spectra for the conventional and the two-cavity F-P structures are theoretically analyzed. Based on the theoretical analysis, the transmission spectra of conventional, symmetric and asymmetric two-cavity F-P structures are simulated, and the results are discussed. The results show that, while the increase of the cavity length of a conventional F-P structure results in multiple resonant peaks on both sides of the main peak, the two-cavity F-P structures of the same total length can improve spectral range effectively and keep the main peak without degrading the performance through proper design of the mirror reflectivity and cavity lengths. The mirror reflectivity also
A two-cavity Fabry-Perot(F-P) structure is compared to the conventional F-P structure. The characteristics of transmission spectra for the conventional and the two-cavity F-P structures are theoretically analyzed. Based on the theoretical analysis, the transmission spectra of conventional, symmetric and asymmetric two-cavity F-P structures are simulated, and the results are discussed. The results show that, while the increase of the cavity length of a conventional F-P structure results in multiple resonant peaks on both sides of the main peak, the two-cavity F-P structures of the same total length can improve spectral range effectively and keep the main peak without degrading the performance through proper design of the mirror reflectivity and cavity lengths. The mirror reflectivity also
Numerical optimization of jet location in N2-chemical oxygen iodine laser without primary buffer gas
2010,
22.
Abstract:
3-D Navier-Stocks equation with multi species and chemical reaction process was applied with CFD method on the chemical oxygen iodine laser(COIL) model using nitrogen as diluents gas to investigate the detailed flow field and the coupling between physical and chemical process, especially the appropriate mixing technique. It is found that mixing by jet in the subsonic section is inapplicable to the N2-COIL without primary buffer gas; jet in supersonic is necessary and with the appropriate flow rate ratio, the small signal gain could reach 1.5% cm-1 in the position of cavity; the efficient area of gain is widened since the thickness of boundary layer is reduced as the result of mixture weight increase.
3-D Navier-Stocks equation with multi species and chemical reaction process was applied with CFD method on the chemical oxygen iodine laser(COIL) model using nitrogen as diluents gas to investigate the detailed flow field and the coupling between physical and chemical process, especially the appropriate mixing technique. It is found that mixing by jet in the subsonic section is inapplicable to the N2-COIL without primary buffer gas; jet in supersonic is necessary and with the appropriate flow rate ratio, the small signal gain could reach 1.5% cm-1 in the position of cavity; the efficient area of gain is widened since the thickness of boundary layer is reduced as the result of mixture weight increase.
2010,
22.
Abstract:
A selective laser melting (SLM) system equipped with fiber laser was designed to study the technical parameters, energy density, relative density, surface profile and characteristics of micro structures of 316L stainless steel powder. Results show that the scan speed has most significant effect on fabrication results, and the relative density increases with the energy density as an appropriate operational technical factor in SLM process. Surface profiles are determined by the ratio between laser power and scan speed. The relations among energy input, the melting and solidification way of the powder, the ratio between laser power and scan speed, relative density and surface profiles are deeply discussed. The micro-structure of SLM part’s fused line that between adjacent tracks or interlaye
A selective laser melting (SLM) system equipped with fiber laser was designed to study the technical parameters, energy density, relative density, surface profile and characteristics of micro structures of 316L stainless steel powder. Results show that the scan speed has most significant effect on fabrication results, and the relative density increases with the energy density as an appropriate operational technical factor in SLM process. Surface profiles are determined by the ratio between laser power and scan speed. The relations among energy input, the melting and solidification way of the powder, the ratio between laser power and scan speed, relative density and surface profiles are deeply discussed. The micro-structure of SLM part’s fused line that between adjacent tracks or interlaye
2010,
22.
Abstract:
The ion parameters, electronic parameters and its spatial distribution were measured respectively by ion-sensitive probe and double Langmuir probe on a non-symmetric magnetic mirror field ECR plasma apparatus. The effects of gas pressure on plasma parameters and the spatial distribution were analyzed. The etching of CVD diamond thick films was accomplished by the ECR plasma under optimized pressure conditions and the etching mechanism is studied. The results showed that the electronic temperature was 5～10 eV, the ion temperature was about 1 eV and the electron density was in the order of 1010 cm-3. With the increasing of gas pressure, the electron density increased firstly and then decreased, the temperature of the electron and ion gradually decreased. The spatial distribution of plasma d
The ion parameters, electronic parameters and its spatial distribution were measured respectively by ion-sensitive probe and double Langmuir probe on a non-symmetric magnetic mirror field ECR plasma apparatus. The effects of gas pressure on plasma parameters and the spatial distribution were analyzed. The etching of CVD diamond thick films was accomplished by the ECR plasma under optimized pressure conditions and the etching mechanism is studied. The results showed that the electronic temperature was 5～10 eV, the ion temperature was about 1 eV and the electron density was in the order of 1010 cm-3. With the increasing of gas pressure, the electron density increased firstly and then decreased, the temperature of the electron and ion gradually decreased. The spatial distribution of plasma d
2010,
22.
Abstract:
The measurement of the fraction of laser-entrance energy, which is carried out mainly through the measurement of scattering light, is very important in the measurement of coupling efficiency of the hohlraum. The angular distribution of scattering light is measured on the Shenguang-Ⅲ prototype laser facility using the PIN detector array. It is demonstrated that the nonlinear laser plasma interaction, in which the stimulated Raman scattering fraction is about 10% and the stimulated Brillouin scattering about 20%, is stronger than that on Shenguang-Ⅱ laser facility. The laser target coupling efficiency thus evaluated is taken into the formula which describes the radiation temperature scaling law. The calculated radiation temperature agrees well with the experimental Dante results, which ind
The measurement of the fraction of laser-entrance energy, which is carried out mainly through the measurement of scattering light, is very important in the measurement of coupling efficiency of the hohlraum. The angular distribution of scattering light is measured on the Shenguang-Ⅲ prototype laser facility using the PIN detector array. It is demonstrated that the nonlinear laser plasma interaction, in which the stimulated Raman scattering fraction is about 10% and the stimulated Brillouin scattering about 20%, is stronger than that on Shenguang-Ⅱ laser facility. The laser target coupling efficiency thus evaluated is taken into the formula which describes the radiation temperature scaling law. The calculated radiation temperature agrees well with the experimental Dante results, which ind
2010,
22.
Abstract:
Full-aperture backscatter station (FABS) installed on Shenguang-ⅡLaser Facility is reported. This diagnostic is a spatially averaged mix of light from all of the laser-plasma interactions in the field of view collected by the laser beam focusing lens. Lights in two different wavelength ranges (348～354 nm and 400～700 nm) corresponding to stimulated Brillouin and stimulated Raman backscattering are measured by two calorimeters. The energy, power, and spectrum of backscattered light can be given respectively. The time-resolved spectra will be determined with a goal of SRS temporal response with 10 ps resolution and dimensional response with 0.5 nm resolution. Near backscattered light outside focusing lens is diagnosed based on an array of PIN diodes.
Full-aperture backscatter station (FABS) installed on Shenguang-ⅡLaser Facility is reported. This diagnostic is a spatially averaged mix of light from all of the laser-plasma interactions in the field of view collected by the laser beam focusing lens. Lights in two different wavelength ranges (348～354 nm and 400～700 nm) corresponding to stimulated Brillouin and stimulated Raman backscattering are measured by two calorimeters. The energy, power, and spectrum of backscattered light can be given respectively. The time-resolved spectra will be determined with a goal of SRS temporal response with 10 ps resolution and dimensional response with 0.5 nm resolution. Near backscattered light outside focusing lens is diagnosed based on an array of PIN diodes.
2010,
22.
Abstract:
Poly(vincylcyclohexane) (PVCH) was prepared with polystyrene(PS) saturated using heterogeneous hydrogenation techniques. The structure of the synthesized polymers was characterized by means of FT-IR, 1H NMR spectroscopy and GPC, and the results show a good agreement with the proposed structure. The optimum condition for PVCH synthesis was obtained via many experiments. DSC and TG measurements show that PVCH possesses good thermal stability (Tg=146 ℃, TD>345 ℃) compared with PS. The solubility of PVCH is improved, i.e. it can completely dissolve in petroleum ether and cyclohexane.
Poly(vincylcyclohexane) (PVCH) was prepared with polystyrene(PS) saturated using heterogeneous hydrogenation techniques. The structure of the synthesized polymers was characterized by means of FT-IR, 1H NMR spectroscopy and GPC, and the results show a good agreement with the proposed structure. The optimum condition for PVCH synthesis was obtained via many experiments. DSC and TG measurements show that PVCH possesses good thermal stability (Tg=146 ℃, TD>345 ℃) compared with PS. The solubility of PVCH is improved, i.e. it can completely dissolve in petroleum ether and cyclohexane.
2010,
22.
Abstract:
According to the requirement of ICF, a method based on statistical theory has been proposed to measure the power spectrum density(PSD) of large aperture optical components. The method breaks the large-aperture wavefront into small regions, and obtains the PSD of the large-aperture wavefront by weighted averaging of the PSDs of the regions, where the weight factor is each region’s area. Simulation and experiment demonstrate the effectiveness of the proposed method. They also show that, the obtained PSDs of the large-aperture wavefront by statistical method and sub-aperture stitching method fit well, when the number of small regions is no less than 8×8. The statistical method is not sensitive to translation stage’s errors and environment instabilities, thus it is appropriate for PSD measu
According to the requirement of ICF, a method based on statistical theory has been proposed to measure the power spectrum density(PSD) of large aperture optical components. The method breaks the large-aperture wavefront into small regions, and obtains the PSD of the large-aperture wavefront by weighted averaging of the PSDs of the regions, where the weight factor is each region’s area. Simulation and experiment demonstrate the effectiveness of the proposed method. They also show that, the obtained PSDs of the large-aperture wavefront by statistical method and sub-aperture stitching method fit well, when the number of small regions is no less than 8×8. The statistical method is not sensitive to translation stage’s errors and environment instabilities, thus it is appropriate for PSD measu
2010,
22.
Abstract:
Nano TiO2 thin film produced by plasma-enhanced chemical vapor deposition method are deposited on the silicon substrate with the mixture of TiCl4 sources, argon and oxygen gases. Some technological parameters affecting the film performances are discussed. The results indicate that the surface of TiO2 film is even, its crystal structure is compact and the smallest crystal grain size is approximately 15 nm. The film crystal form change mainly relies on the deposition temperature. The film is amorphous for temperature lower than 300 ℃ and shows the anatase structure above the deposition temperature of 300 ℃.
Nano TiO2 thin film produced by plasma-enhanced chemical vapor deposition method are deposited on the silicon substrate with the mixture of TiCl4 sources, argon and oxygen gases. Some technological parameters affecting the film performances are discussed. The results indicate that the surface of TiO2 film is even, its crystal structure is compact and the smallest crystal grain size is approximately 15 nm. The film crystal form change mainly relies on the deposition temperature. The film is amorphous for temperature lower than 300 ℃ and shows the anatase structure above the deposition temperature of 300 ℃.
2010,
22.
Abstract:
An A-B-A insulation structure is proposed to improve the characteristics of surface flashover in vacuum by adjusting the conductivity and permittivity of layer A. According to the electric field theory of series dielectrics, the DC and pulsed field distributions of the structure are calculated and the influences of the conductivity and permittivity of layer A on the electric fields of the vacuum-insulator-cathode triple junction and the vacuum-layer A-layer B triple junction are analyzed. It is found that this structure can effectively reduce, the electric field at the former junction while keep that at the later not too intense. The impact of layer A with different surface charges on the electric field of the two junctions is also analyzed. At last, the variation tendency of surface flash
An A-B-A insulation structure is proposed to improve the characteristics of surface flashover in vacuum by adjusting the conductivity and permittivity of layer A. According to the electric field theory of series dielectrics, the DC and pulsed field distributions of the structure are calculated and the influences of the conductivity and permittivity of layer A on the electric fields of the vacuum-insulator-cathode triple junction and the vacuum-layer A-layer B triple junction are analyzed. It is found that this structure can effectively reduce, the electric field at the former junction while keep that at the later not too intense. The impact of layer A with different surface charges on the electric field of the two junctions is also analyzed. At last, the variation tendency of surface flash
2010,
22.
Abstract:
The paper reviews the recent worldwide research and application of transparent Nd:YAG laser ceramics, especially in the last two years, and focuses on the analysis of the recent research in China. It points out that the transparent Nd:YAG laser ceramic is the current focus in ceramic research. At last, it puts forward the research difficulties and points out that the research in China is still far behind the world level. In conclusion, the colleges and institutes of material and optics in China, should cooperate on theory and progressing of the transparent Nd:YAG ceramics.
The paper reviews the recent worldwide research and application of transparent Nd:YAG laser ceramics, especially in the last two years, and focuses on the analysis of the recent research in China. It points out that the transparent Nd:YAG laser ceramic is the current focus in ceramic research. At last, it puts forward the research difficulties and points out that the research in China is still far behind the world level. In conclusion, the colleges and institutes of material and optics in China, should cooperate on theory and progressing of the transparent Nd:YAG ceramics.
2010,
22.
Abstract:
To measure impact flash generated during hypervelocity impact and further investigate rules of impact flash intensity varying with time, which is generated by hypervelocity impact at close impact velocities and different incidence angles from target plane, a transient impact flash measurement pyrometer suitable for transient flash measurement is designed. LY12 aluminum spherical projectile is loaded by two stage light gas gun, using transient pyrometer measurement system designed measure impact flash phenomena, which was generated by LY12 aluminum projectile impacted the LY12 aluminum target at close impact velocity and different impact angles of 30°，45°，60° and 90°. The relationships between average impact flash intensity peaks and different impact angles are acquired. Average impac
To measure impact flash generated during hypervelocity impact and further investigate rules of impact flash intensity varying with time, which is generated by hypervelocity impact at close impact velocities and different incidence angles from target plane, a transient impact flash measurement pyrometer suitable for transient flash measurement is designed. LY12 aluminum spherical projectile is loaded by two stage light gas gun, using transient pyrometer measurement system designed measure impact flash phenomena, which was generated by LY12 aluminum projectile impacted the LY12 aluminum target at close impact velocity and different impact angles of 30°，45°，60° and 90°. The relationships between average impact flash intensity peaks and different impact angles are acquired. Average impac
2010,
22.
Abstract:
A theoretical analysis is carried out to study the evolution of a laser-induced plasma channel in air. The extended nonlinear Schr-dinger equation describing the propagation of laser pulses in air is presented and analyzed, which includes the influence of diffraction, dispersion and multiphoton ionization, Raman scattering, plasma wake fields and relativistic focusing. The electron density and the beam intensity flux along the filament are estimated by solving the Schr-dinger equation using split-step Fourier method and finite difference method. The numerical calculations confirm that the position and pattern of the filaments are dependent on the wavelength, energy, pulse duration and transverse waist of the initial laser pulse．
A theoretical analysis is carried out to study the evolution of a laser-induced plasma channel in air. The extended nonlinear Schr-dinger equation describing the propagation of laser pulses in air is presented and analyzed, which includes the influence of diffraction, dispersion and multiphoton ionization, Raman scattering, plasma wake fields and relativistic focusing. The electron density and the beam intensity flux along the filament are estimated by solving the Schr-dinger equation using split-step Fourier method and finite difference method. The numerical calculations confirm that the position and pattern of the filaments are dependent on the wavelength, energy, pulse duration and transverse waist of the initial laser pulse．
Optimization and experiment research of high power linearly polarized radial waveguide array antenna
2010,
22.
Abstract:
The performance affecting factors were analyzed to improve the high power linearlypolarized radial waveguide array antenna in its aperture efficiency, reflection and so on. Based on the analysis, three optimization approaches were adopted, i.e., improving the performance of cell antenna, adjusting the layout of array antenna and improving the radial waveguide and probe. Theoretical analysis, numerical simulation and experimental measurement of the array antenna were carried out. The experiment shows that at 1.57 GHz, the voltage standing wave ratio (VSWR) is 1.19, the gain is 17.65 dBi, and the axial ratio is -39.2 dB. In the range of 1.47 to 1.77 GHz, the VSWR is below 1.4.
The performance affecting factors were analyzed to improve the high power linearlypolarized radial waveguide array antenna in its aperture efficiency, reflection and so on. Based on the analysis, three optimization approaches were adopted, i.e., improving the performance of cell antenna, adjusting the layout of array antenna and improving the radial waveguide and probe. Theoretical analysis, numerical simulation and experimental measurement of the array antenna were carried out. The experiment shows that at 1.57 GHz, the voltage standing wave ratio (VSWR) is 1.19, the gain is 17.65 dBi, and the axial ratio is -39.2 dB. In the range of 1.47 to 1.77 GHz, the VSWR is below 1.4.
2010,
22.
Abstract:
Electromagnetic PIC simulation contains three key computational procedures: solving Maxwell’s equations, solving Lorentz equation and particle motion equation, updating charge density and current density. According to the characteristics of the three computational procedures, parallel algorithms based on OpenMP were designed. Then the performance of the parallel algorithms were tested and analyzed. In the light of the performance analysis, the parallel computation based on OpenMP of CHIPIC3D software was implemented. At last, the parallel version of CHIPIC3D was used to simulate a kind of extended interaction oscillator, and the results show the parallel algorithm is correct and the speedup is enhanced.
Electromagnetic PIC simulation contains three key computational procedures: solving Maxwell’s equations, solving Lorentz equation and particle motion equation, updating charge density and current density. According to the characteristics of the three computational procedures, parallel algorithms based on OpenMP were designed. Then the performance of the parallel algorithms were tested and analyzed. In the light of the performance analysis, the parallel computation based on OpenMP of CHIPIC3D software was implemented. At last, the parallel version of CHIPIC3D was used to simulate a kind of extended interaction oscillator, and the results show the parallel algorithm is correct and the speedup is enhanced.
2010,
22.
Abstract:
An improved shift operator finite-difference time-domain (SO-FDTD) method for the high order Debye, Drude, Lorentz and hybrid model dispersive media is presented. The susceptibility function of dispersive media is firstly represented as the sum of rational fractions. The computational complexity and large storage requirement in the conventional SO-FDTD method for the high order dispersive model is solved by introducing an intermediate variable and setting a temporary variable. Meanwhile, the generality of updated formulation in the improved SO-FDTD method is superior to that of the conventional recursive convolution FDTD(RC-FDTD) method, in which different formulations are required for different dispersive models. Finally, the generality and feasibility of the presented scheme are validate
An improved shift operator finite-difference time-domain (SO-FDTD) method for the high order Debye, Drude, Lorentz and hybrid model dispersive media is presented. The susceptibility function of dispersive media is firstly represented as the sum of rational fractions. The computational complexity and large storage requirement in the conventional SO-FDTD method for the high order dispersive model is solved by introducing an intermediate variable and setting a temporary variable. Meanwhile, the generality of updated formulation in the improved SO-FDTD method is superior to that of the conventional recursive convolution FDTD(RC-FDTD) method, in which different formulations are required for different dispersive models. Finally, the generality and feasibility of the presented scheme are validate
2010,
22.
Abstract:
In order to understand the response characteristics of induction voltage adder (IVA) to square pulses and find out some design philosophies of a compact, high efficient IVA system, theoretical analysis and experimental research are carried out. This paper introduces the operating principles of IVA, establishes an equivalent circuit model and analyses the response characteristics. Elementary experimental researches are carried out on an IVA module charged by a pulse forming network (PFN) which can output 1 μs pulses with an impedance of about 1.2 Ω. The rising edge and flat top of the output waveform are in good agreement with those of the input waveform. The flat top drops as expected. Theoretical analyses are well verified.
In order to understand the response characteristics of induction voltage adder (IVA) to square pulses and find out some design philosophies of a compact, high efficient IVA system, theoretical analysis and experimental research are carried out. This paper introduces the operating principles of IVA, establishes an equivalent circuit model and analyses the response characteristics. Elementary experimental researches are carried out on an IVA module charged by a pulse forming network (PFN) which can output 1 μs pulses with an impedance of about 1.2 Ω. The rising edge and flat top of the output waveform are in good agreement with those of the input waveform. The flat top drops as expected. Theoretical analyses are well verified.
2010,
22.
Abstract:
In order to decrease response time and improve accuracy of high-pulse current measurement, a new kind of ns-range Rogowski coil with closed magnetic core is developed. Important parameters are calculated and designed according to electromagnetic theories. By using 50 Ω damping resistor, the parasitic high-frequency oscillations are improved at the front edge and back edge of the output voltage pulse. Pspice circuit analysis is employed to simulate the equivalent circuit of the Rogowski coil and good simulation results are obtained which correspond to theoretical design. Calibration experiments are carried out with 50 ns and 10 ns square pulse source, and results show that response time of the coil are 2.43 ns and 1.10 ns and sensitivity is 3.34 A/V. This coil is used to detect the current
In order to decrease response time and improve accuracy of high-pulse current measurement, a new kind of ns-range Rogowski coil with closed magnetic core is developed. Important parameters are calculated and designed according to electromagnetic theories. By using 50 Ω damping resistor, the parasitic high-frequency oscillations are improved at the front edge and back edge of the output voltage pulse. Pspice circuit analysis is employed to simulate the equivalent circuit of the Rogowski coil and good simulation results are obtained which correspond to theoretical design. Calibration experiments are carried out with 50 ns and 10 ns square pulse source, and results show that response time of the coil are 2.43 ns and 1.10 ns and sensitivity is 3.34 A/V. This coil is used to detect the current
2010,
22.
Abstract:
This paper summarizes the design and test results of a four-bricks fast linear transformer driver (FLTD) stage. When the charge voltage of the stage is 160 kV, the output current is 103.4 kA, and the risetime is 78 ns(10%~90%). Discharge synchronization(Δtd) of four switches with charge voltage 120 kV has been studied with differential loop. The experimental results indicate that the peak current and output waveforms are almost free from fluctuation with Δtd＜15 ns, and the standard deviation of peak current is 3.62 kA. If Δtd=15~25 ns, the peak current has a slight loss, the standard deviation of peak current is 8.59 kA, and the output waveforms have small aberrations. If Δtd＞25 ns, the peak current lowers significantly with the standard deviation increasing obviously, and the output
This paper summarizes the design and test results of a four-bricks fast linear transformer driver (FLTD) stage. When the charge voltage of the stage is 160 kV, the output current is 103.4 kA, and the risetime is 78 ns(10%~90%). Discharge synchronization(Δtd) of four switches with charge voltage 120 kV has been studied with differential loop. The experimental results indicate that the peak current and output waveforms are almost free from fluctuation with Δtd＜15 ns, and the standard deviation of peak current is 3.62 kA. If Δtd=15~25 ns, the peak current has a slight loss, the standard deviation of peak current is 8.59 kA, and the output waveforms have small aberrations. If Δtd＞25 ns, the peak current lowers significantly with the standard deviation increasing obviously, and the output
2010,
22.
Abstract:
The analytic expression of output voltage, describing exactly the transient transmission process of the spiral Blumlein pulse forming line with a purely resistive load, has been derived by solving the telegraph equations with Laplace transform. The results are about the same as those of wave propagation method. For the spiral Blumlein line, the transmission time of the inner line is usually not equal to that of the outer line, so which has its own characteristic compared with the traditional Blumlein line. The plateau time of the main pulse is determined by the line with shorter transmission time. Following the main pulse, a small step will be formed with the duration of twice the transmission time difference of th two lines. No matter whether the termination matches or not, the transmissi
The analytic expression of output voltage, describing exactly the transient transmission process of the spiral Blumlein pulse forming line with a purely resistive load, has been derived by solving the telegraph equations with Laplace transform. The results are about the same as those of wave propagation method. For the spiral Blumlein line, the transmission time of the inner line is usually not equal to that of the outer line, so which has its own characteristic compared with the traditional Blumlein line. The plateau time of the main pulse is determined by the line with shorter transmission time. Following the main pulse, a small step will be formed with the duration of twice the transmission time difference of th two lines. No matter whether the termination matches or not, the transmissi
