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RSS2008 Vol. 20, No. 01
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2008,
20.
Abstract:
A simple concept is applied to the construction of a Bessel-Gauss resonator based on an axicon with a plane output mirror. Fox-Li algorithm and numerical integral are applied respectively to describe the radical amplitude at output mirror and the three-dimensional field distribution of output beam. Analysis reveals that the dominant mode of the resonator has similar features as zero-order Bessel-Gauss beams do. Effect of varying the cavity length on the output transverse profile of the dominant mode of the cavity is discussed. Simulation results show that the features of the dominant mode of the resonator remain unchanged when the cavity length change is small. The resonator scheme based on Nd: YAG laser was implemented in an experiment to confirm the possibility of generating zero-order B
A simple concept is applied to the construction of a Bessel-Gauss resonator based on an axicon with a plane output mirror. Fox-Li algorithm and numerical integral are applied respectively to describe the radical amplitude at output mirror and the three-dimensional field distribution of output beam. Analysis reveals that the dominant mode of the resonator has similar features as zero-order Bessel-Gauss beams do. Effect of varying the cavity length on the output transverse profile of the dominant mode of the cavity is discussed. Simulation results show that the features of the dominant mode of the resonator remain unchanged when the cavity length change is small. The resonator scheme based on Nd: YAG laser was implemented in an experiment to confirm the possibility of generating zero-order B
2008,
20.
Abstract:
The algorithm of retrieving cloud height was studied. The intensity and the pulse width of the cloud backscatter is different from the atmospheric aerosol and the random noise. The cloud height could be determined by analyzing lidar returns. A selected window gliding from the ground and the integral of signals in the window is calculated. The random noise could be eliminated and the cloud information could be distinguished from aerosol by window integral. Referred to previous cloud information, the current cloud height is retrieved according to the window integral. Compared with Vaisala ceilometer, the memorable glide window integral algorithm could be used to retrieve the information of cloud exactly and reliably.
The algorithm of retrieving cloud height was studied. The intensity and the pulse width of the cloud backscatter is different from the atmospheric aerosol and the random noise. The cloud height could be determined by analyzing lidar returns. A selected window gliding from the ground and the integral of signals in the window is calculated. The random noise could be eliminated and the cloud information could be distinguished from aerosol by window integral. Referred to previous cloud information, the current cloud height is retrieved according to the window integral. Compared with Vaisala ceilometer, the memorable glide window integral algorithm could be used to retrieve the information of cloud exactly and reliably.
2008,
20.
Abstract:
In this paper, the damage modes of the carbon fiber and the glass fiber reinforced epoxy or bakelite resin matrix composites irradiated by CW laser under different power densities were analyzed, and the changes of the microstructure and the tensile strength of the composites were also researched. When the resin matrix composites were radiated at a power density more than 0.1 kW/cm2, the matrix would be decomposed and the tensile properties of the radiated samples were lost over 30% while the carbon fiber hardly damaged and the glass fiber melted. When the power density of the laser was raised to 1 kW/cm2, the matrix burned violently and the carbon fiber cloth began to split with some carbon fiber being fractured, therefore, the fracture strength of the radiated sample lost over 80%. The hi
In this paper, the damage modes of the carbon fiber and the glass fiber reinforced epoxy or bakelite resin matrix composites irradiated by CW laser under different power densities were analyzed, and the changes of the microstructure and the tensile strength of the composites were also researched. When the resin matrix composites were radiated at a power density more than 0.1 kW/cm2, the matrix would be decomposed and the tensile properties of the radiated samples were lost over 30% while the carbon fiber hardly damaged and the glass fiber melted. When the power density of the laser was raised to 1 kW/cm2, the matrix burned violently and the carbon fiber cloth began to split with some carbon fiber being fractured, therefore, the fracture strength of the radiated sample lost over 80%. The hi
Comparison of several stochastic parallel optimization control algorithms for adaptive optics system
2008,
20.
Abstract:
Optimizing the system performance metric directly is an important method for correcting wave-front distortions in adaptive optics(AO) systems. Appropriate stochastic parallel optimization control algorithm is the key to correcting distorted wave front successfully. Based on several stochastic parallel optimization control algorithms, an adaptive optics system with a 32-element deformable mirror was simulated. Genetic algorithm(GA), the unilateral perturbation stochastic parallel gradient descent (SPGD), the bilateral perturbation SPGD and simulated annealing(SA) were compared in convergence speed, correction capability and local maximum. The results show that because of the unaceptable convergence speed, GA is not suitable for the control of real-time AO system; the bilateral perturbation
Optimizing the system performance metric directly is an important method for correcting wave-front distortions in adaptive optics(AO) systems. Appropriate stochastic parallel optimization control algorithm is the key to correcting distorted wave front successfully. Based on several stochastic parallel optimization control algorithms, an adaptive optics system with a 32-element deformable mirror was simulated. Genetic algorithm(GA), the unilateral perturbation stochastic parallel gradient descent (SPGD), the bilateral perturbation SPGD and simulated annealing(SA) were compared in convergence speed, correction capability and local maximum. The results show that because of the unaceptable convergence speed, GA is not suitable for the control of real-time AO system; the bilateral perturbation
2008,
20.
Abstract:
Pyrotechnic explosion pumping method is one of the solutions to make miniature and portable laser. A chemical reagent used to pump Nd glass laser was prepared. The main ingredients of the reagent were metal powders and alkali metals’ oxysalts. The experimental apparatus of pyrotechnically pumped Nd glass laser was designed. The laser consisted of a f8 mm×100 mm Nd glass rod tightly encircled with pump sources by the side. The resonator contained a high reflection plane mirror and a concave mirror of 98% reflectivity. Output experiment used two reagents A and B with different near-infrared radiation intensity, reagent A output 29 mJ laser beam with wavelength 1 053 nm, and B didn’t output laser. Pumping radiation intensity thresholds of the two pump sources were computed. Reagent A gives
Pyrotechnic explosion pumping method is one of the solutions to make miniature and portable laser. A chemical reagent used to pump Nd glass laser was prepared. The main ingredients of the reagent were metal powders and alkali metals’ oxysalts. The experimental apparatus of pyrotechnically pumped Nd glass laser was designed. The laser consisted of a f8 mm×100 mm Nd glass rod tightly encircled with pump sources by the side. The resonator contained a high reflection plane mirror and a concave mirror of 98% reflectivity. Output experiment used two reagents A and B with different near-infrared radiation intensity, reagent A output 29 mJ laser beam with wavelength 1 053 nm, and B didn’t output laser. Pumping radiation intensity thresholds of the two pump sources were computed. Reagent A gives
2008,
20.
Abstract:
In order to investigate the tribological performance of laser clad coating about die steel, laser cladding techniques were adopted with Fe alloy powders. Tests were carried out using laser clad layers as upper samples and GCr15 steel as lower samples with HT500 abrasion tester. The results were compared with 40Cr's.The morphologies of wear scars were observed with optical microscopy. The tests show that the friction coefficient of 40Cr is bigger than the clad coating's with the load less than 250 g .The friction coefficient reduces with load increasing when the load is less than 300 g. The 40Cr's friction coefficient is (0.563～0.589) and increases with time when the load is 300 g. The friction coefficient of laser is (0.431～0.457) and clad layer decreases under the same condition. The
In order to investigate the tribological performance of laser clad coating about die steel, laser cladding techniques were adopted with Fe alloy powders. Tests were carried out using laser clad layers as upper samples and GCr15 steel as lower samples with HT500 abrasion tester. The results were compared with 40Cr's.The morphologies of wear scars were observed with optical microscopy. The tests show that the friction coefficient of 40Cr is bigger than the clad coating's with the load less than 250 g .The friction coefficient reduces with load increasing when the load is less than 300 g. The 40Cr's friction coefficient is (0.563～0.589) and increases with time when the load is 300 g. The friction coefficient of laser is (0.431～0.457) and clad layer decreases under the same condition. The
2008,
20.
Abstract:
Using the local moment invariants based on edge region as the recognition feature and building multiple neural networks, a novel method for partially occluded extended target recognition is presented. First, the local moment invariants are calculated on partial edge region of a target and their invariance in digital condition is discussed. Then, multiple BP neural networks are built on one or several local areas of the occluded extended target, and the moment invariants based on edge region of these local areas are calculated as inputs of neural networks. Through the integrated result of multiple neural networks, the correct recognition ratio can be improved. The experimental results indicated that the moment invariants based on edge region are simple and valid, and the proposed method can
Using the local moment invariants based on edge region as the recognition feature and building multiple neural networks, a novel method for partially occluded extended target recognition is presented. First, the local moment invariants are calculated on partial edge region of a target and their invariance in digital condition is discussed. Then, multiple BP neural networks are built on one or several local areas of the occluded extended target, and the moment invariants based on edge region of these local areas are calculated as inputs of neural networks. Through the integrated result of multiple neural networks, the correct recognition ratio can be improved. The experimental results indicated that the moment invariants based on edge region are simple and valid, and the proposed method can
2008,
20.
Abstract:
The thermal ablation rate and mass ablation rate of cured E-51 epoxy under long pulse laser irradiation were studied. The effects of irradiation time, maximum power density, frequency and pulse width were discussed. The thermal ablation rate gradually increased along with the irradiation time, and then reached a certain value. The effects of frequency and pulse width were little. With the maximum power density increasing, the thermal ablation rate rose first obviously and then the thermal ablation rate approached to a definite value. With a fixed maximum power density, the thermal ablation rate was certain and the mass ablation rate was directly proportional to laser frequency and pulse width. The results were verified according to the optical property, surface morphology and surface temp
The thermal ablation rate and mass ablation rate of cured E-51 epoxy under long pulse laser irradiation were studied. The effects of irradiation time, maximum power density, frequency and pulse width were discussed. The thermal ablation rate gradually increased along with the irradiation time, and then reached a certain value. The effects of frequency and pulse width were little. With the maximum power density increasing, the thermal ablation rate rose first obviously and then the thermal ablation rate approached to a definite value. With a fixed maximum power density, the thermal ablation rate was certain and the mass ablation rate was directly proportional to laser frequency and pulse width. The results were verified according to the optical property, surface morphology and surface temp
2008,
20.
Abstract:
A broadband (white-light) interferometric detection method based on the Michelson interferometer principle was put forward to detect the phasing error between the segmented mirrors, and subsequently correct the misaligned segments correspondingly to achieve mirror coplanarity. The phase error between the segments was extracted from the interferograms mismatching. Double-center-wavelength combinations of broadband light sources were applied to raise the center-fringe visibility. Theoretical simulation was carried out to compare different center-fringe visibility for different wavelength combinations. The result shows that the application of the double-central-wavelength combination is effective in raising the ability of signal distinguishing of the white-light center-fringe, improving the m
A broadband (white-light) interferometric detection method based on the Michelson interferometer principle was put forward to detect the phasing error between the segmented mirrors, and subsequently correct the misaligned segments correspondingly to achieve mirror coplanarity. The phase error between the segments was extracted from the interferograms mismatching. Double-center-wavelength combinations of broadband light sources were applied to raise the center-fringe visibility. Theoretical simulation was carried out to compare different center-fringe visibility for different wavelength combinations. The result shows that the application of the double-central-wavelength combination is effective in raising the ability of signal distinguishing of the white-light center-fringe, improving the m
2008,
20.
Abstract:
On the basis of the calculation result of the simultaneous dual wavelength threshold condition, the reflectivities of reflection mirror were more than 99.73% at 1 318.8 nm and 1 338 nm wavelengths,but about 7% at 1 064 nm; the output mirror was coated with the transmissions of 34.7% and 32.5% at 1 319 nm and 1 338 nm, respectively, the transmittance of the output mirror was 95 % for 1 064 nm laser in the experiment. The strongest 1 064 nm line was effectively suppressed and a 1 319 nm and 1 338 nm dual wavelength Nd:YAG pulsed laser was successfully developed. The output energy of 0.89 J was obtained at the pump energy of 125 J with the total efficiency of 0.71% and the slope efficiency of 0.89%. The central wavelengths of the output laser are 1 318.8 nm and 1 338.2 nm with the FWHM of 0.3
On the basis of the calculation result of the simultaneous dual wavelength threshold condition, the reflectivities of reflection mirror were more than 99.73% at 1 318.8 nm and 1 338 nm wavelengths,but about 7% at 1 064 nm; the output mirror was coated with the transmissions of 34.7% and 32.5% at 1 319 nm and 1 338 nm, respectively, the transmittance of the output mirror was 95 % for 1 064 nm laser in the experiment. The strongest 1 064 nm line was effectively suppressed and a 1 319 nm and 1 338 nm dual wavelength Nd:YAG pulsed laser was successfully developed. The output energy of 0.89 J was obtained at the pump energy of 125 J with the total efficiency of 0.71% and the slope efficiency of 0.89%. The central wavelengths of the output laser are 1 318.8 nm and 1 338.2 nm with the FWHM of 0.3
2008,
20.
Abstract:
In the laser engineering system, a beam expander and an annular aperture were taken as the equivalent of the Cassegrain telescope system. The far-field irradiance distribution of an expanded Gaussian beam which had gone through an annular aperture was deduced in an inner optical system. The energy loss and the effects of the ratio of Gaussian beam-waist radius after expander to outer radius of the annular aperture on Strehl ratio were numerically computed. The results show that an optimal ratio exists for least energy loss and high Strehl ratio on the condition of the definite parameters of the Cassegrain telescope.
In the laser engineering system, a beam expander and an annular aperture were taken as the equivalent of the Cassegrain telescope system. The far-field irradiance distribution of an expanded Gaussian beam which had gone through an annular aperture was deduced in an inner optical system. The energy loss and the effects of the ratio of Gaussian beam-waist radius after expander to outer radius of the annular aperture on Strehl ratio were numerically computed. The results show that an optimal ratio exists for least energy loss and high Strehl ratio on the condition of the definite parameters of the Cassegrain telescope.
2008,
20.
Abstract:
Using high resolution radiosonde data from SPARC data center of America, employing the Tatarski formula, this paper compares the refractive index structure constant calculated by the outer scale method with the one by thd method of coupling turbulent energy dissipation rate with conventional meteorology parameters. It proves indirectly the reasonableness of Sterenborg’s chosing 1 m as the outer scale. Besides, it compares the refractive index structure constant with two different empirical formulas of outer scale from Coulman and Dewan. The analysis indicates that the two methods can both estimate the refractive index structure constant. As the observation of turbulent dissipate rate is very difficult, the reasonableness and the representativeness of the analytic expression need testing b
Using high resolution radiosonde data from SPARC data center of America, employing the Tatarski formula, this paper compares the refractive index structure constant calculated by the outer scale method with the one by thd method of coupling turbulent energy dissipation rate with conventional meteorology parameters. It proves indirectly the reasonableness of Sterenborg’s chosing 1 m as the outer scale. Besides, it compares the refractive index structure constant with two different empirical formulas of outer scale from Coulman and Dewan. The analysis indicates that the two methods can both estimate the refractive index structure constant. As the observation of turbulent dissipate rate is very difficult, the reasonableness and the representativeness of the analytic expression need testing b
2008,
20.
Abstract:
A kind of hole-net structure can be formed on silicon sample irradiated by pulse laser with power of 0.5 J·s-1·cm-2 and wavelength of 1 064 nm. The photoluminescence(PL) emission is enhanced by the hole-net structure. The PL peak center is about 700 nm. The oxidation-free silicon sample almost does not emit, which proves that oxidation of silicon may be most important in enhancing PL emission. The quantum confinement-luminescence center model is used to explain the increasing PL emission in the hole-net structure. The plasma wave model is used to explain the forming mechanism of hole-net structure. Under the optimum conditions in preparing process, the sample with enhanced PL emission and more stable low-dimensional structures can be obtained by 9 s irradiation.
A kind of hole-net structure can be formed on silicon sample irradiated by pulse laser with power of 0.5 J·s-1·cm-2 and wavelength of 1 064 nm. The photoluminescence(PL) emission is enhanced by the hole-net structure. The PL peak center is about 700 nm. The oxidation-free silicon sample almost does not emit, which proves that oxidation of silicon may be most important in enhancing PL emission. The quantum confinement-luminescence center model is used to explain the increasing PL emission in the hole-net structure. The plasma wave model is used to explain the forming mechanism of hole-net structure. Under the optimum conditions in preparing process, the sample with enhanced PL emission and more stable low-dimensional structures can be obtained by 9 s irradiation.
2008,
20.
Abstract:
ICF target material areal density and its distribution can be measured by counting beta particles passing through the material. It is necessary to calibrate the areal density measuring device using a series of standard materials with known areal densities and the same components with the materials to be analyzed. For the density measurement of a kind of ICF target material the calibrating method is proposed. This calibrating method uses the approximate, materials with composition of the ICF target material as the standard material. The transmissivity of beta particles possessing different energy can be simulated and computed by Monte-Carlo method when they pass different materials. The corresponding error to the measuring result is also obtained. The error is only several percent using pap
ICF target material areal density and its distribution can be measured by counting beta particles passing through the material. It is necessary to calibrate the areal density measuring device using a series of standard materials with known areal densities and the same components with the materials to be analyzed. For the density measurement of a kind of ICF target material the calibrating method is proposed. This calibrating method uses the approximate, materials with composition of the ICF target material as the standard material. The transmissivity of beta particles possessing different energy can be simulated and computed by Monte-Carlo method when they pass different materials. The corresponding error to the measuring result is also obtained. The error is only several percent using pap
2008,
20.
Abstract:
The total cross sections of electron impact single K-shell ionization of atomic targets Al, Ti, Cu and Mo, with a wide range of atomic numbers from 11 to 42, are evaluated in the energy range up to about 1 MeV employing the relativistic correction method ,Which incorporates the ionic and relativistic effects. The experimental cross sections for all targets are reproduced satisfactoryily in the considered energies. Bethe K-shell-ionization cross sections are in good agreement with the experimental data and other theoretical data at high energies. The relativistic effect is found to be significant in Mo targets.
The total cross sections of electron impact single K-shell ionization of atomic targets Al, Ti, Cu and Mo, with a wide range of atomic numbers from 11 to 42, are evaluated in the energy range up to about 1 MeV employing the relativistic correction method ,Which incorporates the ionic and relativistic effects. The experimental cross sections for all targets are reproduced satisfactoryily in the considered energies. Bethe K-shell-ionization cross sections are in good agreement with the experimental data and other theoretical data at high energies. The relativistic effect is found to be significant in Mo targets.
2008,
20.
Abstract:
Aperture of gate hole is an important geometry parameter in a Spindt type field emission array(FEA) cathode. During the local oxidation of silicon(LOCOS) process, a SiO2 “bird beak” will form and lead to much smaller holes than the Si3N4 dot patterned by lithography. By means of LOCOS and wet etching of the silicon substrate, gate of FEA with 1 μm aperture was fabricated using a photo mask of 2.6 μmdot (designed) array. The etchant composed of nitric acid (65%) and hydrofluoric acid (40%) isotropicly etched the silicon material, resulting in simultaneous growth the depth and width of gate holes. However, the hole aperture gradually enlarged at a rate only 5% of that of the development of the depth. The ultimate hole aperture principally defined by the photo mask size and the thicknes
Aperture of gate hole is an important geometry parameter in a Spindt type field emission array(FEA) cathode. During the local oxidation of silicon(LOCOS) process, a SiO2 “bird beak” will form and lead to much smaller holes than the Si3N4 dot patterned by lithography. By means of LOCOS and wet etching of the silicon substrate, gate of FEA with 1 μm aperture was fabricated using a photo mask of 2.6 μmdot (designed) array. The etchant composed of nitric acid (65%) and hydrofluoric acid (40%) isotropicly etched the silicon material, resulting in simultaneous growth the depth and width of gate holes. However, the hole aperture gradually enlarged at a rate only 5% of that of the development of the depth. The ultimate hole aperture principally defined by the photo mask size and the thicknes
2008,
20.
Abstract:
The transmission characteristics of relativistic electron beams in the ion-focusing channel is given in this paper utilizing the single-particle theory, and the effects of the system parameters such as the ion-electron density ratio, the beam voltage and the beam current density on the propagation and focusing of the beam are discussed. The relativistic electron beam can be strongly focused by the ion channel，and it exhibits wave-like transmission as it passes through the ion channel. The radius of the focal point will gradually rise and the amplitude of the beam wave will reduce as the beam transmits in the channel .The results show that efficient transmission of relativistic electron beams in the ion-focusing channel can be reached by choosing appropriate ion-electron density ratio, b
The transmission characteristics of relativistic electron beams in the ion-focusing channel is given in this paper utilizing the single-particle theory, and the effects of the system parameters such as the ion-electron density ratio, the beam voltage and the beam current density on the propagation and focusing of the beam are discussed. The relativistic electron beam can be strongly focused by the ion channel，and it exhibits wave-like transmission as it passes through the ion channel. The radius of the focal point will gradually rise and the amplitude of the beam wave will reduce as the beam transmits in the channel .The results show that efficient transmission of relativistic electron beams in the ion-focusing channel can be reached by choosing appropriate ion-electron density ratio, b
2008,
20.
Abstract:
In order to prepare nitrogen-doped TiO2 film in the surface of SiO2 glass, Ti ion implantation was performed at room temperature in fused silica and then the as-implanted samples were annealed in nitrogen ambient up to 900 ℃. SRIM code and Rutherford backscattering spectrometry(RBS) showed a Gauss distribution of Ti ions in the surface of as-implanted samples. The experimental profile of Ti ions is consistent with the simulated one. X-ray photoelectron spectroscopy(XPS) indicated that metallic Ti and TiO2 coexisted in the as-implanted samples. After annealing at 900 ℃, metallic Ti was oxidized into TiO2, and a new compound of O－Ti－N formed because a small amount of oxygen atoms were substituted by nitrogen atoms in the lattice of TiO2. UV-Vis spectra indicated that the optical absorpti
In order to prepare nitrogen-doped TiO2 film in the surface of SiO2 glass, Ti ion implantation was performed at room temperature in fused silica and then the as-implanted samples were annealed in nitrogen ambient up to 900 ℃. SRIM code and Rutherford backscattering spectrometry(RBS) showed a Gauss distribution of Ti ions in the surface of as-implanted samples. The experimental profile of Ti ions is consistent with the simulated one. X-ray photoelectron spectroscopy(XPS) indicated that metallic Ti and TiO2 coexisted in the as-implanted samples. After annealing at 900 ℃, metallic Ti was oxidized into TiO2, and a new compound of O－Ti－N formed because a small amount of oxygen atoms were substituted by nitrogen atoms in the lattice of TiO2. UV-Vis spectra indicated that the optical absorpti
2008,
20.
Abstract:
Al films on quartz wafers were fabricated by DC magnetron sputtering. Surface roughness, crystal structure, stress stress,preferred orientation and reflectivity of Al films were studied by different annealing temperature. The AFM images show that the films are compact and smooth.The X-ray diffraction results indicate that the stress in the Al films was relaxed as annealing temperature increased from room temperature to 400 ℃, and the stress decreased from 1.56 GPa to 0.78 GPa. Microstructure analysis shows that the annealed Al films have the fcc structure, and the mean size of the nanoparticles has increased from 18.3 nm to 25.9 nm with increasing annealing temperature from room temperature to 400 ℃. As the annealing temperature rises, texture coefficient of (200) crystal face increases.
Al films on quartz wafers were fabricated by DC magnetron sputtering. Surface roughness, crystal structure, stress stress,preferred orientation and reflectivity of Al films were studied by different annealing temperature. The AFM images show that the films are compact and smooth.The X-ray diffraction results indicate that the stress in the Al films was relaxed as annealing temperature increased from room temperature to 400 ℃, and the stress decreased from 1.56 GPa to 0.78 GPa. Microstructure analysis shows that the annealed Al films have the fcc structure, and the mean size of the nanoparticles has increased from 18.3 nm to 25.9 nm with increasing annealing temperature from room temperature to 400 ℃. As the annealing temperature rises, texture coefficient of (200) crystal face increases.
2008,
20.
Abstract:
This paper analyzes the characteristics of the front rising electromagnetic pulse and introduces the basic theory of transmission line method used to analyze shielding effectiveness of rectangular cavity. The basic formulas are then revised to calculate the case when a piece of PCB is set in the rectangular cavity. The revised formulas are expanded to arbitrary angle of polarization. Computation and simulation results indicate that: for a frequency lower than the dominant frequency, the closer the observational site is to the enclosure, the worse the shielding effectiveness is, and the shielding of low frequency is better than that of high frequency; for the same areas, the shielding effectiveness of a single hole is worse than that of an aperture array; in the same conditions, the shield
This paper analyzes the characteristics of the front rising electromagnetic pulse and introduces the basic theory of transmission line method used to analyze shielding effectiveness of rectangular cavity. The basic formulas are then revised to calculate the case when a piece of PCB is set in the rectangular cavity. The revised formulas are expanded to arbitrary angle of polarization. Computation and simulation results indicate that: for a frequency lower than the dominant frequency, the closer the observational site is to the enclosure, the worse the shielding effectiveness is, and the shielding of low frequency is better than that of high frequency; for the same areas, the shielding effectiveness of a single hole is worse than that of an aperture array; in the same conditions, the shield
2008,
20.
Abstract:
A 10-stage wave erection Marx generator with coaxial structure is designed, which realizes the miniaturization of pulse power modulator with capacitance energy storage. Low-inductance capacitors of 3 nF are chosen as energy storage capacitors, and solid resistors are utilized as charging resistors. By means of rapid discharge of each short gas spark gap and ultraviolet coupling between stages, wave erection can be realized on the output load. Under the consideration of stray capacitance of electrodes to ground, equivalent eccentric transmission line effect and circuit inductance, equivalent circuit model is constructed for PSpice software to simulate the operation process. Under low charging voltage of 7 kV and 11 kV, preliminary experimental results are achieved. The output voltage wavefo
A 10-stage wave erection Marx generator with coaxial structure is designed, which realizes the miniaturization of pulse power modulator with capacitance energy storage. Low-inductance capacitors of 3 nF are chosen as energy storage capacitors, and solid resistors are utilized as charging resistors. By means of rapid discharge of each short gas spark gap and ultraviolet coupling between stages, wave erection can be realized on the output load. Under the consideration of stray capacitance of electrodes to ground, equivalent eccentric transmission line effect and circuit inductance, equivalent circuit model is constructed for PSpice software to simulate the operation process. Under low charging voltage of 7 kV and 11 kV, preliminary experimental results are achieved. The output voltage wavefo
2008,
20.
Abstract:
Photoconductive semiconductor switches (PCSS) have been used in pulsed power technology due to their advantages over conventional switches, such as fast rise time, negligible time jitter, and optical electrical isolation. History and developments of GaAs PCSS are summarized. SiC with wide band gap, high breakdown field, high saturation electron drift velocity and high thermal conductivity is considered as a promising semiconductor for PCSS. Status and latest progress of SiC PCSS employing intrinsic and extrinsic photoconductivity are reported. Applications of PCSS in ultra-wide band and compact pulsed power system are briefly introduced. The critical technological problems to be investigated in future are presented.
Photoconductive semiconductor switches (PCSS) have been used in pulsed power technology due to their advantages over conventional switches, such as fast rise time, negligible time jitter, and optical electrical isolation. History and developments of GaAs PCSS are summarized. SiC with wide band gap, high breakdown field, high saturation electron drift velocity and high thermal conductivity is considered as a promising semiconductor for PCSS. Status and latest progress of SiC PCSS employing intrinsic and extrinsic photoconductivity are reported. Applications of PCSS in ultra-wide band and compact pulsed power system are briefly introduced. The critical technological problems to be investigated in future are presented.
2008,
20.
Abstract:
A simple sol-gel method was applied to prepare high refractive index thin film used in antilaser optical area. The method composed of two steps employing a complete hydrolysis and a restrained polycondensation at low temperature. The morphology of the resulting sol was determined by dynamic light scattering(DLS) techniques and was characterized as anatase by high-resolution transmission electron microscopy(HRTEM). The thin optical films were deposited on K9 glass by a sol-gel spin-coating method. The film shows the presence of nanocrystalline anatase phase by X-ray diffraction(XRD) analysis. The film surface examined by atomic force microscopy(AFM) shows a mean square roughness of 7.5 nm. The transmission spectra of the film were measured using a UV-Vis-NIR spectrometer, and the refractive
A simple sol-gel method was applied to prepare high refractive index thin film used in antilaser optical area. The method composed of two steps employing a complete hydrolysis and a restrained polycondensation at low temperature. The morphology of the resulting sol was determined by dynamic light scattering(DLS) techniques and was characterized as anatase by high-resolution transmission electron microscopy(HRTEM). The thin optical films were deposited on K9 glass by a sol-gel spin-coating method. The film shows the presence of nanocrystalline anatase phase by X-ray diffraction(XRD) analysis. The film surface examined by atomic force microscopy(AFM) shows a mean square roughness of 7.5 nm. The transmission spectra of the film were measured using a UV-Vis-NIR spectrometer, and the refractive
2008,
20.
Abstract:
This paper studies the excitation of the stimulated Raman backscatter of ultrashort and ultrahigh intensity laser pulse. Through one dimentional particle-in-cell code LPIC++, it is found that in the relativitic condition, the stimulated Raman backscatter is not in the mormal mode but strongly coupled. The frequency spectra become broad with blueshift and the interval between the peaks are greater than the frequency of the plasma wave frequency. These results are consistent with the prediction of a srongly coupled Raman theory.
This paper studies the excitation of the stimulated Raman backscatter of ultrashort and ultrahigh intensity laser pulse. Through one dimentional particle-in-cell code LPIC++, it is found that in the relativitic condition, the stimulated Raman backscatter is not in the mormal mode but strongly coupled. The frequency spectra become broad with blueshift and the interval between the peaks are greater than the frequency of the plasma wave frequency. These results are consistent with the prediction of a srongly coupled Raman theory.
2008,
20.
Abstract:
Coupled-wave equations and conversion efficient theory formulas for second harmonic plane wave of type Ⅰ phase matching in uniaxial crystals were obtained from wave equation of medium when second-harmonic wave absorption was taken into account. Based on the formulas, theoretical conversion efficiency formulas for second harmonic plane wave were gotten when second-harmonic wave walk-off effect was taken into account. Using type Ⅰ phase matching in uniaxial crystal K2Al2B2O7 (KABO) for example, conversion efficient of second harmonic plane wave was calculated according to the formulas. The result indicates that the optimum length of frequency doubling crystal was in existence when second-harmonic wave absorption was taken into account. The conversion efficient of second harmonic plane wave
Coupled-wave equations and conversion efficient theory formulas for second harmonic plane wave of type Ⅰ phase matching in uniaxial crystals were obtained from wave equation of medium when second-harmonic wave absorption was taken into account. Based on the formulas, theoretical conversion efficiency formulas for second harmonic plane wave were gotten when second-harmonic wave walk-off effect was taken into account. Using type Ⅰ phase matching in uniaxial crystal K2Al2B2O7 (KABO) for example, conversion efficient of second harmonic plane wave was calculated according to the formulas. The result indicates that the optimum length of frequency doubling crystal was in existence when second-harmonic wave absorption was taken into account. The conversion efficient of second harmonic plane wave
2008,
20.
Abstract:
Monolithic tantalic oxide aerogels were synthesized from inorganic salt precursors, tantalic pentachloride by hydrolysis and condensation in alcohol solvent. The propylene oxide and the epichlorohydrin were used as gelling agent respectively. The tantalic oxide wet gels was obtained and washed in acetone to remove water and remaining PO. Finally, the wet gels were dried in supercritical CO2 instrument. This approach is straightforward, inexpensive and versatile, it produces monolithic mesoporous materials with high specific surface areas and very low bulk density. Dried tantalic oxide aerogel is characterized by transmission electron microscopy(TEM) and nitrogen adsorption/ desorption analyses, and the specific surface area is about 800~ 900 m2/g.
Monolithic tantalic oxide aerogels were synthesized from inorganic salt precursors, tantalic pentachloride by hydrolysis and condensation in alcohol solvent. The propylene oxide and the epichlorohydrin were used as gelling agent respectively. The tantalic oxide wet gels was obtained and washed in acetone to remove water and remaining PO. Finally, the wet gels were dried in supercritical CO2 instrument. This approach is straightforward, inexpensive and versatile, it produces monolithic mesoporous materials with high specific surface areas and very low bulk density. Dried tantalic oxide aerogel is characterized by transmission electron microscopy(TEM) and nitrogen adsorption/ desorption analyses, and the specific surface area is about 800~ 900 m2/g.
2008,
20.
Abstract:
Experimental study of characteristics of laser induced damage on the K9 glass surface, irradiated by Nd:YAG laser operating at 1.064 μm wavelength and approximately 10 ns pulse duration and 1 Hz repetition rate, have been made. The change law of laser pulse output energy versus the repeat number of laser shots was investigated. Stereo microscope was employed to observe laser induced damage morphology after sigle-shot and multi-shot laser irradiation. The ripple damage on the K9 glass surface could be obviously observed, and the failure surface can be devided into three parts: ablation zone, microcrack zone and brittle fracture zone. After the first shot small damage spots appeared on the K9 glass surface; after multi-shot irradiation, microcracks and damage area increased gradually with t
Experimental study of characteristics of laser induced damage on the K9 glass surface, irradiated by Nd:YAG laser operating at 1.064 μm wavelength and approximately 10 ns pulse duration and 1 Hz repetition rate, have been made. The change law of laser pulse output energy versus the repeat number of laser shots was investigated. Stereo microscope was employed to observe laser induced damage morphology after sigle-shot and multi-shot laser irradiation. The ripple damage on the K9 glass surface could be obviously observed, and the failure surface can be devided into three parts: ablation zone, microcrack zone and brittle fracture zone. After the first shot small damage spots appeared on the K9 glass surface; after multi-shot irradiation, microcracks and damage area increased gradually with t
2008,
20.
Abstract:
Mo/B4C multilayer is a suitable material combination for high reflectivity mirrors in the soft X-ray wavelength region of 6.7~8.0 nm. The structures of the ideal Mo/B4C multilayer mirrors optimized based on the General Algorithm method (GA) are that the bilayers number is 150, the period is 3.59 nm, the ratio of Mo film thickness to period is 0.41 for the fixed incident of 10°. The reflectivity of such a Mo/B4C multilayer is 33.29％ at first order Bragg reflectivity peak. Mo/B4C multilayers were fabricated with a DC magnetron sputtering coater. All these multilayers were deposited on super-polished silicon substrates, of which the area is about 20 mm×30 mm. The surfacerms roughness of the Si substrate is less than 0.3 nm. The purity of the target materials Mo, B4C and Cr is respectively
Mo/B4C multilayer is a suitable material combination for high reflectivity mirrors in the soft X-ray wavelength region of 6.7~8.0 nm. The structures of the ideal Mo/B4C multilayer mirrors optimized based on the General Algorithm method (GA) are that the bilayers number is 150, the period is 3.59 nm, the ratio of Mo film thickness to period is 0.41 for the fixed incident of 10°. The reflectivity of such a Mo/B4C multilayer is 33.29％ at first order Bragg reflectivity peak. Mo/B4C multilayers were fabricated with a DC magnetron sputtering coater. All these multilayers were deposited on super-polished silicon substrates, of which the area is about 20 mm×30 mm. The surfacerms roughness of the Si substrate is less than 0.3 nm. The purity of the target materials Mo, B4C and Cr is respectively
2008,
20.
Abstract:
In the Sino-Russian joint Z-pinch experiments on Angara-5-1 facility, the framing camera with an exposure time of several 10 picosecond was employed. By setting different kinds of filters of various thickness values before the pinholes of camera and using the spectral sensitivity of the camera, multi-frame X-ray images of wire arrays Z-pinch implosions in different energy ranges were obtained. By analysing the relationship between the intensity profiles of corresponding frames and the spectral sensitivity of the camera, it is allowed to estimate X-ray photon energy range in local areas of images. And it is determined that the spectral sensitity of the picosencond-frame camera belongs to a range from 70 eV(without 2.3 mm formvar filter) and from 150 eV(with 2.3 mm formvar filter).
In the Sino-Russian joint Z-pinch experiments on Angara-5-1 facility, the framing camera with an exposure time of several 10 picosecond was employed. By setting different kinds of filters of various thickness values before the pinholes of camera and using the spectral sensitivity of the camera, multi-frame X-ray images of wire arrays Z-pinch implosions in different energy ranges were obtained. By analysing the relationship between the intensity profiles of corresponding frames and the spectral sensitivity of the camera, it is allowed to estimate X-ray photon energy range in local areas of images. And it is determined that the spectral sensitity of the picosencond-frame camera belongs to a range from 70 eV(without 2.3 mm formvar filter) and from 150 eV(with 2.3 mm formvar filter).
2008,
20.
Abstract:
The design of double-gap output cavity for relativistic klystron amplifier is provided. The angle and position of support rods and gap length are described. Using a three-dimension fully electromagnetic Particle-in-Cell (PIC) code, the simulation of microwave extraction from modulated intense relativistic electron beams which pass through double-gap output cavity is investigated, and the beams and double-gap output cavity geometry parameters are optimized. An output microwave power of 1.1 GW is generated by simulation, with an electron beam voltage of 640 kV, a current of 6 kA and 80% modulation depth of the fundamental wave. The efficiency is 28%. The S-band RKA double-gap output cavity was designed according to high frequency analysis and particle simulation results. Subsequently, the ex
The design of double-gap output cavity for relativistic klystron amplifier is provided. The angle and position of support rods and gap length are described. Using a three-dimension fully electromagnetic Particle-in-Cell (PIC) code, the simulation of microwave extraction from modulated intense relativistic electron beams which pass through double-gap output cavity is investigated, and the beams and double-gap output cavity geometry parameters are optimized. An output microwave power of 1.1 GW is generated by simulation, with an electron beam voltage of 640 kV, a current of 6 kA and 80% modulation depth of the fundamental wave. The efficiency is 28%. The S-band RKA double-gap output cavity was designed according to high frequency analysis and particle simulation results. Subsequently, the ex
2008,
20.
Abstract:
A new method to measure the aberrations of entire beam path is presented. An additional CCD in far-field for detecting focal spot is located. Different deformable mirror’s surface shapes are generated which can bring additional aberrations to ICF optical system and create their corresponding focal spots. Then additional aberrations and different intensity signal of focal spots can be recorded simultaneously by Hartmann-Shack sensor and CCD respectively. An amendatory phase-retrieval method is introduced, which can reconstruct the aberrations of entire beam path from different pairs of additional aberrations and their corresponding focal spots intensity. The simulative results show that the adaptive optics system can correct the aberrations of entire beam path of ICF successfully based on
A new method to measure the aberrations of entire beam path is presented. An additional CCD in far-field for detecting focal spot is located. Different deformable mirror’s surface shapes are generated which can bring additional aberrations to ICF optical system and create their corresponding focal spots. Then additional aberrations and different intensity signal of focal spots can be recorded simultaneously by Hartmann-Shack sensor and CCD respectively. An amendatory phase-retrieval method is introduced, which can reconstruct the aberrations of entire beam path from different pairs of additional aberrations and their corresponding focal spots intensity. The simulative results show that the adaptive optics system can correct the aberrations of entire beam path of ICF successfully based on
2008,
20.
Abstract:
Based on the measured values on the axis of the magnetic system of the traveling wave tube(TWT), an axis-symmetrical equivalent model of magnetic ring, whose volume is equal to that of the practical non-axis-symmetrical magnetic ring with a gap, is presented. The magnetic field on-axis of this model including pole shoes on both sides is the same as that of the practical open ring with pole shoes. The computed values of the periodic magnetic system containing the equivalent models by the 2D FEMM are in agreement with the measured results of the real system with open magnetic rings.
Based on the measured values on the axis of the magnetic system of the traveling wave tube(TWT), an axis-symmetrical equivalent model of magnetic ring, whose volume is equal to that of the practical non-axis-symmetrical magnetic ring with a gap, is presented. The magnetic field on-axis of this model including pole shoes on both sides is the same as that of the practical open ring with pole shoes. The computed values of the periodic magnetic system containing the equivalent models by the 2D FEMM are in agreement with the measured results of the real system with open magnetic rings.
2008,
20.
Abstract:
The motion of the electron in the conversion region has been analysed. The equations of the electron motion are given and calculated. The effects of the beam radius, the initial energy ratio, the length of the conversion region and the magnetic field are taken into account in the numerical simulation. When the ratio of the beam radius to the cyclotron radius is 0.25, the ratio of the transversal energy to the longitudinal energy is 2.83, the unitary length is 3 and the nonlinearity coefficient is -0.1, and the conversion efficiency can reach 90%.
The motion of the electron in the conversion region has been analysed. The equations of the electron motion are given and calculated. The effects of the beam radius, the initial energy ratio, the length of the conversion region and the magnetic field are taken into account in the numerical simulation. When the ratio of the beam radius to the cyclotron radius is 0.25, the ratio of the transversal energy to the longitudinal energy is 2.83, the unitary length is 3 and the nonlinearity coefficient is -0.1, and the conversion efficiency can reach 90%.
2008,
20.
Abstract:
Based on the angular periodicity of the helix slow-wave structure, an improved simulation method for simulating the high frequency characteristic is proposed using the boundary condition of Master/Slave in the commercial software HFSS. The simulation model for helix slow wave structure with three rods is modified from one screw-pitch to one third. Compared with the simulation results of classical model, the computation time decreases at least 3/4 by the improved model while the results are identical. Morever, the advantage of the improved method will be more evident when the frequency is much higher.
Based on the angular periodicity of the helix slow-wave structure, an improved simulation method for simulating the high frequency characteristic is proposed using the boundary condition of Master/Slave in the commercial software HFSS. The simulation model for helix slow wave structure with three rods is modified from one screw-pitch to one third. Compared with the simulation results of classical model, the computation time decreases at least 3/4 by the improved model while the results are identical. Morever, the advantage of the improved method will be more evident when the frequency is much higher.
2008,
20.
Abstract:
The accurate three dimensional helix travlingwave tube coldtest simulation model is presented using the electromagnetic code HFSS. For electric field in the perturbation rod, four prominent approximations of perturbation method are analyzed with the simulation model. Firstly, the electric field is supposed uniform in the axial coordinate, neglecting the higher axial space harmonics. Secondly, the electric field is supposed uniform in the azimuthal coordinate, neglecting the higher azimuthal space harmonics. Thirdly, the azimuthal electric field is supposed zero, neglecting the transverse electric field. Finally, the electric field is supposed equal before perturbation and after. Also, the affection of the perturbation rod’s dimension and relative permittivity on interaction impedance
The accurate three dimensional helix travlingwave tube coldtest simulation model is presented using the electromagnetic code HFSS. For electric field in the perturbation rod, four prominent approximations of perturbation method are analyzed with the simulation model. Firstly, the electric field is supposed uniform in the axial coordinate, neglecting the higher axial space harmonics. Secondly, the electric field is supposed uniform in the azimuthal coordinate, neglecting the higher azimuthal space harmonics. Thirdly, the azimuthal electric field is supposed zero, neglecting the transverse electric field. Finally, the electric field is supposed equal before perturbation and after. Also, the affection of the perturbation rod’s dimension and relative permittivity on interaction impedance
2008,
20.
Abstract:
S-band tapered magnetically insulated transmission line oscillator designs using slowly tapered vanes and sharply tapered vanes were presented and analyzed. Simulation results show that: this structure can produce microwave at mean power of 2.5 GW and frequency of 2.65 GHz under the diode voltage of 500 kV; the structure improves the efficiency of beam-microwave conversion from 12% of a traditional tapered magnetically insulated transmission line oscillator to 15% . In the following experiments, average power of 1 GW has been obtained at frequency of 2.69 GHz which was in good agreement with the simulation.
S-band tapered magnetically insulated transmission line oscillator designs using slowly tapered vanes and sharply tapered vanes were presented and analyzed. Simulation results show that: this structure can produce microwave at mean power of 2.5 GW and frequency of 2.65 GHz under the diode voltage of 500 kV; the structure improves the efficiency of beam-microwave conversion from 12% of a traditional tapered magnetically insulated transmission line oscillator to 15% . In the following experiments, average power of 1 GW has been obtained at frequency of 2.69 GHz which was in good agreement with the simulation.
2008,
20.
Abstract:
Based on the general coupled wave equations in corrugated circular waveguide with trapered radius, this paper presents the numerical optimization method Runge-Kutta to get the design parameters of 3 mm TE03-TE02 and TE02-TE01 high efficiency mode converter. The optimized structure and computational results are obtained by optimized programme. Simulation results of the structure by CST microwave studio are in excellent agreement with the numerical computed values. The center frequency of TE03-TE02 and TE02-TE01 mode converter is 94 GHz, and the mode converters designed in this way have high conversion efficiencies above 98.5% with their absolute bandwidth exceeding 3.5 GHz and 7.0 GHz respectively.
Based on the general coupled wave equations in corrugated circular waveguide with trapered radius, this paper presents the numerical optimization method Runge-Kutta to get the design parameters of 3 mm TE03-TE02 and TE02-TE01 high efficiency mode converter. The optimized structure and computational results are obtained by optimized programme. Simulation results of the structure by CST microwave studio are in excellent agreement with the numerical computed values. The center frequency of TE03-TE02 and TE02-TE01 mode converter is 94 GHz, and the mode converters designed in this way have high conversion efficiencies above 98.5% with their absolute bandwidth exceeding 3.5 GHz and 7.0 GHz respectively.
2008,
20.
Abstract:
Shanghai synchrotron radiation facility (SSRF) is a third-generation light source under construction. It requires high level of electron beam orbit stability. Mechanical stability of the magnet girder assemblies (MGAs) is essential for electron beam orbit stability. Tests on the SSRF MGA prototype show that its resonant amplification is about 50 at about 19 Hz, which is five times larger than required. Hence vibration damping research for the MGA is necessary, a kind of constrained layer damping plates using viscoelastic materials was developed for attenuating the resonant amplification. The MGA prototype with damping plates had good damping performance in tests, and the resonant amplification was reduced by 91.8%. The damping plates could be used to improve the mechanical stability of the
Shanghai synchrotron radiation facility (SSRF) is a third-generation light source under construction. It requires high level of electron beam orbit stability. Mechanical stability of the magnet girder assemblies (MGAs) is essential for electron beam orbit stability. Tests on the SSRF MGA prototype show that its resonant amplification is about 50 at about 19 Hz, which is five times larger than required. Hence vibration damping research for the MGA is necessary, a kind of constrained layer damping plates using viscoelastic materials was developed for attenuating the resonant amplification. The MGA prototype with damping plates had good damping performance in tests, and the resonant amplification was reduced by 91.8%. The damping plates could be used to improve the mechanical stability of the
2008,
20.
Abstract:
The transverse bunch-by-bunch feedback system has been constructed at Hefei light source to cure and damp the coupled bunch instability. There are two important modules in the system: the vector calculation module and the notch filter. The vector calculation module is a signal processing module used to adjust the phase of the feedback signals and the notch filter can filter the revolution frequency component in a signal, which will save the feedback power.
The transverse bunch-by-bunch feedback system has been constructed at Hefei light source to cure and damp the coupled bunch instability. There are two important modules in the system: the vector calculation module and the notch filter. The vector calculation module is a signal processing module used to adjust the phase of the feedback signals and the notch filter can filter the revolution frequency component in a signal, which will save the feedback power.
2008,
20.
Abstract:
The main part of the 100 MeV electron linac consists of a thermionic electron gun, a bunching system and 4 SLAC type accelerating tubes. The bunching system and the accelerating tubes are fed by a 45 MW S-band microwave power source. The beam dynamics of the linac is studied and optimized using several beam dynamics simulation programs. After optimization, the beam energy, energy spread and the normalized emittance is designed to be greater than 100 MeV, less than 1% and 30 mm·mrad, respectively.
The main part of the 100 MeV electron linac consists of a thermionic electron gun, a bunching system and 4 SLAC type accelerating tubes. The bunching system and the accelerating tubes are fed by a 45 MW S-band microwave power source. The beam dynamics of the linac is studied and optimized using several beam dynamics simulation programs. After optimization, the beam energy, energy spread and the normalized emittance is designed to be greater than 100 MeV, less than 1% and 30 mm·mrad, respectively.
