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RSS2007 Vol. 19, No. 03
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2007,
19.
Abstract:
The influence of the channel parameters of the water-cooled Si mirror on temperature and thermal deformation was simulated using ANSYS finite element analysis. The results show that the channel parameters have significant effects on the thermal deformation. For a given flow rate of water, the temperature rise and thermal deformation decrease with the decreasing of channel width. With a constant flow rate and channel width, the thermal deformation decreases with the channel depth. However, the effect of channel depth on temperature rise is not obvious. For the water-cooled mirror, it would be better to make the channel small. For high power laser, the channel size of the water-cooled mirror is several hundred mm to 1 mm.
The influence of the channel parameters of the water-cooled Si mirror on temperature and thermal deformation was simulated using ANSYS finite element analysis. The results show that the channel parameters have significant effects on the thermal deformation. For a given flow rate of water, the temperature rise and thermal deformation decrease with the decreasing of channel width. With a constant flow rate and channel width, the thermal deformation decreases with the channel depth. However, the effect of channel depth on temperature rise is not obvious. For the water-cooled mirror, it would be better to make the channel small. For high power laser, the channel size of the water-cooled mirror is several hundred mm to 1 mm.
2007,
19.
Abstract:
The sub-surface damage(SSD) in optied components formed in the process of whetting and polishing is analyzed. Utilizing the mechanism of wet etching and the Marangoni interface effect, CNC chemical etching technique is used to achieve high precision matching of optics surface and elimilate the SSD at the same time. The charactersitics and positions of SSD are analyzed experimently. SSD elimination method SSD is also presented.
The sub-surface damage(SSD) in optied components formed in the process of whetting and polishing is analyzed. Utilizing the mechanism of wet etching and the Marangoni interface effect, CNC chemical etching technique is used to achieve high precision matching of optics surface and elimilate the SSD at the same time. The charactersitics and positions of SSD are analyzed experimently. SSD elimination method SSD is also presented.
2007,
19.
Abstract:
Theoretical and experimental study is presented on grating period-tuned single-resonated quasi-phase-matched optical parametric oscillator in multi-grating periodically poled MgO-doped lithium niobate(PPMgLN) pumped by 1 064 nm laser. Theoretical analyses include grating period tuning, pump threshold and converting efficiency of PPMgLN SRO. The pump source is a acousto-optically Q-switched CW- diode- side- pumped Nd:YAG laser. The pump beam polarization matches the e→e+e interaction in PPMgLN, thus the maximum nonlinear coefficient (27.4 pm/V) is effective. When pump power is 8 W, an average output power of more than 1.6 W at 3.7 mm is obtained with a corresponding slope efficiency of more than 20%, and a tunable mid-infrared wavelength output from 2.7 to 4.8 mm is also obtained by gratin
Theoretical and experimental study is presented on grating period-tuned single-resonated quasi-phase-matched optical parametric oscillator in multi-grating periodically poled MgO-doped lithium niobate(PPMgLN) pumped by 1 064 nm laser. Theoretical analyses include grating period tuning, pump threshold and converting efficiency of PPMgLN SRO. The pump source is a acousto-optically Q-switched CW- diode- side- pumped Nd:YAG laser. The pump beam polarization matches the e→e+e interaction in PPMgLN, thus the maximum nonlinear coefficient (27.4 pm/V) is effective. When pump power is 8 W, an average output power of more than 1.6 W at 3.7 mm is obtained with a corresponding slope efficiency of more than 20%, and a tunable mid-infrared wavelength output from 2.7 to 4.8 mm is also obtained by gratin
2007,
19.
Abstract:
A new kind of angle of arrival fluctuation measurement by differential image motion method(DIMM) is introduced. Fried parameter of two orthogonal base line directions can be obtained by angle of arrival fluctuation variance. The experiment results of horizontal propagation in the real atmosphere show that there are apparent differences between the four coherent length values, and the atmospheric turbulence is anisotropic. This characterization should be taken into account in applications. At least one of the measurement values of four directions is necessary for the analysis and study of determining the atmospheric coherence length.
A new kind of angle of arrival fluctuation measurement by differential image motion method(DIMM) is introduced. Fried parameter of two orthogonal base line directions can be obtained by angle of arrival fluctuation variance. The experiment results of horizontal propagation in the real atmosphere show that there are apparent differences between the four coherent length values, and the atmospheric turbulence is anisotropic. This characterization should be taken into account in applications. At least one of the measurement values of four directions is necessary for the analysis and study of determining the atmospheric coherence length.
2007,
19.
Abstract:
Through the energy attenuation method of combining two cuneiform prisms and a neutral attenuator, the polarization of COIL whose power density is 20 W/mm2 was measured. The corner cubes were used as the retroreflectors of stable cavity, thus the uniformity of laser power was improved. The laser beam irradiated the two prisms with 45° incident angle and were reflected by the cuneiform prisms. Then the beam passed normally through a neutral attenuator, and was received by a polarimeter at last. Experimental results indicate: At zero electromagnetic field the light of transverse flow of two modules of COIL without any polarizing elements is partially polarized if the resonator configuration is a foldaway stable cavity, moreover, the degree of polarization decreases gradually in the course of
Through the energy attenuation method of combining two cuneiform prisms and a neutral attenuator, the polarization of COIL whose power density is 20 W/mm2 was measured. The corner cubes were used as the retroreflectors of stable cavity, thus the uniformity of laser power was improved. The laser beam irradiated the two prisms with 45° incident angle and were reflected by the cuneiform prisms. Then the beam passed normally through a neutral attenuator, and was received by a polarimeter at last. Experimental results indicate: At zero electromagnetic field the light of transverse flow of two modules of COIL without any polarizing elements is partially polarized if the resonator configuration is a foldaway stable cavity, moreover, the degree of polarization decreases gradually in the course of
2007,
19.
Abstract:
The optics window of photoelectric equipment has strong reflecting characteristics for the incident laser beam, which is known as cat eye effect. In order to study the suitability of cat eye effect for active laser detection and analyse the effect of the incidence angle on reflected characteristics of cat eye effect, a perfect reflecting model of cat eye effect in the gradient circs was founded, then analysis and simulation of the back-reflected laser characteristics of cat eye effect were done with various incidence angle of the detecting laser at the target optical system. Moreover, the far field energy distribute characteristics of the return laser beam which could be received by the detecting system were gotten. The results show that cat eye effect only exist when the incidence angle o
The optics window of photoelectric equipment has strong reflecting characteristics for the incident laser beam, which is known as cat eye effect. In order to study the suitability of cat eye effect for active laser detection and analyse the effect of the incidence angle on reflected characteristics of cat eye effect, a perfect reflecting model of cat eye effect in the gradient circs was founded, then analysis and simulation of the back-reflected laser characteristics of cat eye effect were done with various incidence angle of the detecting laser at the target optical system. Moreover, the far field energy distribute characteristics of the return laser beam which could be received by the detecting system were gotten. The results show that cat eye effect only exist when the incidence angle o
2007,
19.
Abstract:
In the experiments, it was found that the momentum coupling coefficient of multi-pulse propulsion was lower than that of the single pulse case for the air-breathing mode. To learn the mechanism of this phenomenon, the multi-pulse simulation of the parabolic flyer taken as a moving object was carried out using the dynamic mesh method of the commercial code FLUENT, the error that made by neglecting the after-effect of the flow field was taken into account. The results show that the average momentum coupling coefficient decreases with the number of the laser pulses, but the trend of slewdown is obvious. The simulation results agree well with the experimental results, and the after-effect of the flow field induced by the laser pulse can not be neglected.
In the experiments, it was found that the momentum coupling coefficient of multi-pulse propulsion was lower than that of the single pulse case for the air-breathing mode. To learn the mechanism of this phenomenon, the multi-pulse simulation of the parabolic flyer taken as a moving object was carried out using the dynamic mesh method of the commercial code FLUENT, the error that made by neglecting the after-effect of the flow field was taken into account. The results show that the average momentum coupling coefficient decreases with the number of the laser pulses, but the trend of slewdown is obvious. The simulation results agree well with the experimental results, and the after-effect of the flow field induced by the laser pulse can not be neglected.
2007,
19.
Abstract:
The spectrum of the signal pulses with big chirped coefficient distrusts linearly around the central wavelength in the temporal domain, which characters has been used in the numerical simulation methods, namely the fourth order Runge-algorithm, to study the OPCPA system operating in saturated amplification case. We take the LBO crystal as the nonlinear gain medium in the numerical simulation. The results showed as follows. The nonlinear phase shifting of the signal pulses occurred during the optical parameters process distrusted linearly around the central wavelength fraction. There exists a quasi-periodic structure in the power conversion efficiency, which originated from the phase mismatch among the pump pulse, signal and ideal pulse. And the maximal conversion efficiency occurs at the f
The spectrum of the signal pulses with big chirped coefficient distrusts linearly around the central wavelength in the temporal domain, which characters has been used in the numerical simulation methods, namely the fourth order Runge-algorithm, to study the OPCPA system operating in saturated amplification case. We take the LBO crystal as the nonlinear gain medium in the numerical simulation. The results showed as follows. The nonlinear phase shifting of the signal pulses occurred during the optical parameters process distrusted linearly around the central wavelength fraction. There exists a quasi-periodic structure in the power conversion efficiency, which originated from the phase mismatch among the pump pulse, signal and ideal pulse. And the maximal conversion efficiency occurs at the f
2007,
19.
Abstract:
Numerical simulation of chemical oxygen-iodine laser(COIL) flows with nitrogen diluent based on RADICL setup was carried out. A finite-volume code was used to solve 3D compressible N-S equations with 10 components, 13 non-equilibrium chemical reactions. The condition for the secondary flow to match the primary flow was obtained, and the proper penetration-depth of the secondary flow was found. As a result, the rate between the secondary and the primary dynamic pressures was about 13.0. Simulation showed that gases flow slower and stay longer in the region of the nozzle and the iodine molecules dissociate faster with nitrogen diluent than that with helium diluent. It was found that the gain has a big peak near the throat of the nozzle, and decreases rapidly downstream. It showed that moving
Numerical simulation of chemical oxygen-iodine laser(COIL) flows with nitrogen diluent based on RADICL setup was carried out. A finite-volume code was used to solve 3D compressible N-S equations with 10 components, 13 non-equilibrium chemical reactions. The condition for the secondary flow to match the primary flow was obtained, and the proper penetration-depth of the secondary flow was found. As a result, the rate between the secondary and the primary dynamic pressures was about 13.0. Simulation showed that gases flow slower and stay longer in the region of the nozzle and the iodine molecules dissociate faster with nitrogen diluent than that with helium diluent. It was found that the gain has a big peak near the throat of the nozzle, and decreases rapidly downstream. It showed that moving
2007,
19.
Abstract:
The inner flow field’s influence on beam was simulated to study how to design the tube’s inner structure when blowing non-absorbing gas in them to depress thermal-effect of air. The beam-gas-effect model was adopted as well as a Z-like tube and a U-like tube were used in comparison. The results showed different inner structure of tube will produce different influence on beam. The U-like tube could hold the flow field smoother and had little influence on beam than the Z-like tube under the same blowing condition. This was because its flow velocity changed little in direction than the other one. However, the Z-like tube was a little better than the U-like tube when without blowing.
The inner flow field’s influence on beam was simulated to study how to design the tube’s inner structure when blowing non-absorbing gas in them to depress thermal-effect of air. The beam-gas-effect model was adopted as well as a Z-like tube and a U-like tube were used in comparison. The results showed different inner structure of tube will produce different influence on beam. The U-like tube could hold the flow field smoother and had little influence on beam than the Z-like tube under the same blowing condition. This was because its flow velocity changed little in direction than the other one. However, the Z-like tube was a little better than the U-like tube when without blowing.
2007,
19.
Abstract:
A method is put forward to stabilize the second harmonic generation using phase mismatching. BBO type Ⅰ phase matching SHG course and KTP type Ⅱ phase matching course were simulated. Simulation results show that both type Ⅰ and type Ⅱ phase matching can get 2ω stable output by letting laser deviate from phase matching angle. With the increasement of the deviating angle, the length of the nonlinear crystal required to get stable 2ω output reduces, the fluctuation and the conversion efficiency of second harmonic generation output when the stable 2ω output is obtained become smaller. Compared with KTP type Ⅱ phase matching, BBO type Ⅰ phase matching is more sensitive to deviating angle and the conversion efficiency is smaller.
A method is put forward to stabilize the second harmonic generation using phase mismatching. BBO type Ⅰ phase matching SHG course and KTP type Ⅱ phase matching course were simulated. Simulation results show that both type Ⅰ and type Ⅱ phase matching can get 2ω stable output by letting laser deviate from phase matching angle. With the increasement of the deviating angle, the length of the nonlinear crystal required to get stable 2ω output reduces, the fluctuation and the conversion efficiency of second harmonic generation output when the stable 2ω output is obtained become smaller. Compared with KTP type Ⅱ phase matching, BBO type Ⅰ phase matching is more sensitive to deviating angle and the conversion efficiency is smaller.
2007,
19.
Abstract:
The infrared small target de-noising in complicated background is studied. According to de-correlation and energy compaction of wavelet transforms, a new de-noising method is proposed. The method is put forward with the consideration of the practicality of the method, especially while the image involves complex background and a lot of noise. Firstly, the image is decomposed twice using wavelet transforms. Secondly, each wavelet detail coefficient is recalculated according to the new method in order to avoid the shortcomings of the hard or soft wavelet shrinkage. Lastly, the de-noised image is obtained by reconstruction from the processed coefficients. Simulation results show the de-noising method can preserve the shape character of small target, attenuate the background, and work efficient
The infrared small target de-noising in complicated background is studied. According to de-correlation and energy compaction of wavelet transforms, a new de-noising method is proposed. The method is put forward with the consideration of the practicality of the method, especially while the image involves complex background and a lot of noise. Firstly, the image is decomposed twice using wavelet transforms. Secondly, each wavelet detail coefficient is recalculated according to the new method in order to avoid the shortcomings of the hard or soft wavelet shrinkage. Lastly, the de-noised image is obtained by reconstruction from the processed coefficients. Simulation results show the de-noising method can preserve the shape character of small target, attenuate the background, and work efficient
2007,
19.
Abstract:
HfO2 thin films were prepared with chemical method. The influences of heat treatment, UV irradiation and addition of inorganic Al2O3 on laser-induced damage thresholds (LIDT) of HfO2 thin films were studied. HfO2 thin films were characterized by FTIR and X-ray diffraction. And 1-on-1 laser-induced damage threshold tests on HfO2 thin films and HfO2-Al2O3 composite films were carried out with a Q-switched Nd:YAG high power laser at 1 064 nm with a pulse width of 10 ns. The research results showed that the LIDT of the HfO2 thin films could be improved by heating the thin films at 150 ℃.The LIDT of the thin films heated at 150 ℃ was 42.32 J/cm2, which was 82% higher than that of the as-prepared samples. The addition of inorganic Al2O3 to the HfO2 thin films could also enhance the LIDT of thi
HfO2 thin films were prepared with chemical method. The influences of heat treatment, UV irradiation and addition of inorganic Al2O3 on laser-induced damage thresholds (LIDT) of HfO2 thin films were studied. HfO2 thin films were characterized by FTIR and X-ray diffraction. And 1-on-1 laser-induced damage threshold tests on HfO2 thin films and HfO2-Al2O3 composite films were carried out with a Q-switched Nd:YAG high power laser at 1 064 nm with a pulse width of 10 ns. The research results showed that the LIDT of the HfO2 thin films could be improved by heating the thin films at 150 ℃.The LIDT of the thin films heated at 150 ℃ was 42.32 J/cm2, which was 82% higher than that of the as-prepared samples. The addition of inorganic Al2O3 to the HfO2 thin films could also enhance the LIDT of thi
2007,
19.
Abstract:
Alpha iron nanoparticles with about 20~100 nm size were obtained in the W/O microemulsion system. The iron nanoparticles/PS composites were synthesized through a bulkpolymerization method using the dispersed mixed liquid including styrene and Fe nanoparticles modified with organic surface agent in advance. XRD, TEM, FTIR, SEM and TG-DSC were used respectively to measure the properties of iron nanoparticles, the microstructure of as-prepared composite samples, the distribution of iron nanoparticles in PS and the thermodynamic parameters of as-prepared composites. These studies reveal that the degradation and the enthalpy change of composites would increase with the doping dose of alpha iron nanoparticles increasing, but the temperature of composites degradation would reduce．
Alpha iron nanoparticles with about 20~100 nm size were obtained in the W/O microemulsion system. The iron nanoparticles/PS composites were synthesized through a bulkpolymerization method using the dispersed mixed liquid including styrene and Fe nanoparticles modified with organic surface agent in advance. XRD, TEM, FTIR, SEM and TG-DSC were used respectively to measure the properties of iron nanoparticles, the microstructure of as-prepared composite samples, the distribution of iron nanoparticles in PS and the thermodynamic parameters of as-prepared composites. These studies reveal that the degradation and the enthalpy change of composites would increase with the doping dose of alpha iron nanoparticles increasing, but the temperature of composites degradation would reduce．
2007,
19.
Abstract:
Using the model of transient stimulated rotational Raman scattering (SRRS) and considering many factors, such as the molecular density of nonlinear medium, the gain coefficient, the depletion of pump laser, the nonlinear amplification of the Stokes field, and the initial random Stokes scattered field, etc, the effect of vacuum degree on the SRRS of high-power ultraviolet laser beams in long air path has been studied. The Stokes conversion efficiency decreases and the propagation distance of the threshold increases with the increase of vacuum degree. In practice, in order to decrease the effect of SRRS on the energy and beam quality of high power ultraviolet laser beam, the atmospheric envionment of laser propogation with high vacuum degree can be used to suppress the SRRS effect.
Using the model of transient stimulated rotational Raman scattering (SRRS) and considering many factors, such as the molecular density of nonlinear medium, the gain coefficient, the depletion of pump laser, the nonlinear amplification of the Stokes field, and the initial random Stokes scattered field, etc, the effect of vacuum degree on the SRRS of high-power ultraviolet laser beams in long air path has been studied. The Stokes conversion efficiency decreases and the propagation distance of the threshold increases with the increase of vacuum degree. In practice, in order to decrease the effect of SRRS on the energy and beam quality of high power ultraviolet laser beam, the atmospheric envionment of laser propogation with high vacuum degree can be used to suppress the SRRS effect.
2007,
19.
Abstract:
Experiments about interaction of 527 nm laser with disk targets were conducted on “Xingguang-Ⅱ” facility. The scattering mechanism of stimulated Brillouin scattering (SBS) were studied. The energy angular distribution of scattered lights was obtained. When the laser was smoothed, the experimental results showed that the scattered light was about one order weaker than that when the laser was not smoothed (except for back scattering). The restrain effect of beam-smoothing on scattered lights was very evident. Given the laser being smoothed, the SBS energy to the back-scattering direction became bigger. The angular distribution of scattered lights almost kept the same in all azimuth direction. When 527 nm laser interacted with Al targets, the dispersion of angular distribution of scattered
Experiments about interaction of 527 nm laser with disk targets were conducted on “Xingguang-Ⅱ” facility. The scattering mechanism of stimulated Brillouin scattering (SBS) were studied. The energy angular distribution of scattered lights was obtained. When the laser was smoothed, the experimental results showed that the scattered light was about one order weaker than that when the laser was not smoothed (except for back scattering). The restrain effect of beam-smoothing on scattered lights was very evident. Given the laser being smoothed, the SBS energy to the back-scattering direction became bigger. The angular distribution of scattered lights almost kept the same in all azimuth direction. When 527 nm laser interacted with Al targets, the dispersion of angular distribution of scattered
2007,
19.
Abstract:
Resorcinol-formaldehyde(RF) gel films were synthesized by a series of processes such as sol-gel, supercritical drying and carbonization using resorcinol and formaldehyde. The main factors that affect the properties of aerogels such as HAC content and the reaction temperature were investigated to indicate the mechanism of self-assemble RF films. The micro-morphology and structures of the gel films were characterized by FT-IR and SEM. It was found the thickness of RF aerogel films is about 50 μm , the size of particles about 10 μm and there are no obvious holes. The results show that RF gel self-films form when the mass fraction of resorcinol and formaldehyde in the solution are 67% and the sol is acid. The process and mechanism of RF gel self-films are similar to the process of RF gel and
Resorcinol-formaldehyde(RF) gel films were synthesized by a series of processes such as sol-gel, supercritical drying and carbonization using resorcinol and formaldehyde. The main factors that affect the properties of aerogels such as HAC content and the reaction temperature were investigated to indicate the mechanism of self-assemble RF films. The micro-morphology and structures of the gel films were characterized by FT-IR and SEM. It was found the thickness of RF aerogel films is about 50 μm , the size of particles about 10 μm and there are no obvious holes. The results show that RF gel self-films form when the mass fraction of resorcinol and formaldehyde in the solution are 67% and the sol is acid. The process and mechanism of RF gel self-films are similar to the process of RF gel and
2007,
19.
Abstract:
Sodium stearate film of 0.28~0.40 μm thick was made by vacuum thermal evaporation. Sodium stearate film was investigated by Fourier transform IR spectroscopy. Results indicate that sodium stearate film and sodium stearate have similar properties.Research results also indicate that sodium stearate film was not easy to deliquesce in atmospherical condition, but it deliquesce easily in a solution without water. Self -standing Al filters made by PVD were tested by optical microscopy. Their surfaces have no obvious pinholes. The elements in Al filters were analyzed using Auger Electron Spectroscopy. Results indicate that there is no residua of remover in Al filters．
Sodium stearate film of 0.28~0.40 μm thick was made by vacuum thermal evaporation. Sodium stearate film was investigated by Fourier transform IR spectroscopy. Results indicate that sodium stearate film and sodium stearate have similar properties.Research results also indicate that sodium stearate film was not easy to deliquesce in atmospherical condition, but it deliquesce easily in a solution without water. Self -standing Al filters made by PVD were tested by optical microscopy. Their surfaces have no obvious pinholes. The elements in Al filters were analyzed using Auger Electron Spectroscopy. Results indicate that there is no residua of remover in Al filters．
2007,
19.
Abstract:
Base on the model of gratingpair compressor, the formula of angular dispersion caused by alignment errors was derived. The compensative relations between the tilt angular errors and groovewidth difference were obtained and the compensative methods were discussed. The results show that the relative rotation about the position normal to groove can compensate the error caused by the relative rotation about the position normal to the plan of gratings, the relative rotation about the position parallel to groove can compensate the error caused by groovewidth difference and the relative rotation about the position normal to groove or about the position normal to the plan of gratings can compensate the error caused by groove-width difference. The compensation effects of the first two metho
Base on the model of gratingpair compressor, the formula of angular dispersion caused by alignment errors was derived. The compensative relations between the tilt angular errors and groovewidth difference were obtained and the compensative methods were discussed. The results show that the relative rotation about the position normal to groove can compensate the error caused by the relative rotation about the position normal to the plan of gratings, the relative rotation about the position parallel to groove can compensate the error caused by groovewidth difference and the relative rotation about the position normal to groove or about the position normal to the plan of gratings can compensate the error caused by groove-width difference. The compensation effects of the first two metho
2007,
19.
Abstract:
A new double-gap vircator for high power microwave generation is proposed and studied by simulation in this paper. In the vircator, the interaction cavity is a cylindrical cavity separated into two resonators by a metal foil with a hole in the center. The vircator makes use of the side-extraction and coaxial output method. The quality factors of the cavity Ⅰ and Ⅱ are 6 960 and 71.8 respectively, the resonant frequency is 2.3 GHz. For an annular electron beam of 515 kV and 10 kA, by optimizing and using partial foil structures, the rms efficiency can reach 11% at an average output power of 570 MW at 2.4 GHz. Simulations show that the optimal impedance of the beam is about 51.5 W and the output efficiency increases with the increasing of beam current and keeps larger than 10% with the bea
A new double-gap vircator for high power microwave generation is proposed and studied by simulation in this paper. In the vircator, the interaction cavity is a cylindrical cavity separated into two resonators by a metal foil with a hole in the center. The vircator makes use of the side-extraction and coaxial output method. The quality factors of the cavity Ⅰ and Ⅱ are 6 960 and 71.8 respectively, the resonant frequency is 2.3 GHz. For an annular electron beam of 515 kV and 10 kA, by optimizing and using partial foil structures, the rms efficiency can reach 11% at an average output power of 570 MW at 2.4 GHz. Simulations show that the optimal impedance of the beam is about 51.5 W and the output efficiency increases with the increasing of beam current and keeps larger than 10% with the bea
2007,
19.
Abstract:
The sheet beam klystron is a new kind of microwave vacuum device, which uses a high aspect ratio, thin rectangular beam to reduce space charge effects, increase power capability and beam-wave interaction efficiency. In this paper, an X-band SBK cavity was designed. The fundamental mode had an almost ideally flat field. 3D simulation platforms of beam-wave interaction system with plane symmetry were established to suppress the modes propagating in the drift spaces, and choke cavities and slotting the drift tube was also discussed. The results indicate that the barbell-shaped cavity could meet the need of sheet beam klystron. The cavity sizes, the height of waveguide, the width and the height of coupling cavity are sensitive to the field flatness and the drift tube noses significantly improv
The sheet beam klystron is a new kind of microwave vacuum device, which uses a high aspect ratio, thin rectangular beam to reduce space charge effects, increase power capability and beam-wave interaction efficiency. In this paper, an X-band SBK cavity was designed. The fundamental mode had an almost ideally flat field. 3D simulation platforms of beam-wave interaction system with plane symmetry were established to suppress the modes propagating in the drift spaces, and choke cavities and slotting the drift tube was also discussed. The results indicate that the barbell-shaped cavity could meet the need of sheet beam klystron. The cavity sizes, the height of waveguide, the width and the height of coupling cavity are sensitive to the field flatness and the drift tube noses significantly improv
2007,
19.
Abstract:
The response of electromagnetic pulse penetrating building walls is analyzed using FDTD and Fourier analysis method. The pulse responses within a wide frequency band are calculated based on periodic boundary condition and Gaussian pulse. Through the discussion of the calculated results, the influences of different walls are obtained, which will improve the electromagnetic shielding design to protect electronic equipments. The simulation results show that the rebar array works pretty well for shielding in low frequency, but the shielding effectiveness will become poor as the frequency increases. The periodicity of the frequency domain waveform in concrete walls indicates that there exists a lot of resonance frequency points and the transmission coefficients become comparatively higher on th
The response of electromagnetic pulse penetrating building walls is analyzed using FDTD and Fourier analysis method. The pulse responses within a wide frequency band are calculated based on periodic boundary condition and Gaussian pulse. Through the discussion of the calculated results, the influences of different walls are obtained, which will improve the electromagnetic shielding design to protect electronic equipments. The simulation results show that the rebar array works pretty well for shielding in low frequency, but the shielding effectiveness will become poor as the frequency increases. The periodicity of the frequency domain waveform in concrete walls indicates that there exists a lot of resonance frequency points and the transmission coefficients become comparatively higher on th
2007,
19.
Abstract:
Heat stress reaction was induced by irradiation of high-power 8 millimeter wave on both mice and rats. Four periods of their stress reaction——quiet period, guarding period, deadlock period, prostrating period were observed. The pain threshold temperature of a mouse is (43.1±1.8) ℃, which is not related with its weight, initial temperature of the skin and irradiated power density. The temperature increase of the skin was (8.4±1.0) ℃ by the irradiation at the power density of 3.5 W/cm2 for 3 s and it was (21.1±3.0) ℃ at the power density of 7.0 W/cm2 for 3 s. The duration of guarding period was measured. The relations between the guarding duration and the surficial area of the mouse, the effective irradiating area and irradiating power intensity have been built. The experimental resu
Heat stress reaction was induced by irradiation of high-power 8 millimeter wave on both mice and rats. Four periods of their stress reaction——quiet period, guarding period, deadlock period, prostrating period were observed. The pain threshold temperature of a mouse is (43.1±1.8) ℃, which is not related with its weight, initial temperature of the skin and irradiated power density. The temperature increase of the skin was (8.4±1.0) ℃ by the irradiation at the power density of 3.5 W/cm2 for 3 s and it was (21.1±3.0) ℃ at the power density of 7.0 W/cm2 for 3 s. The duration of guarding period was measured. The relations between the guarding duration and the surficial area of the mouse, the effective irradiating area and irradiating power intensity have been built. The experimental resu
2007,
19.
Abstract:
Bipolar junction transistors may be burned out by injected electromagnetic pulse. The effects of electromagnetic pulse injected from base on bipolar junction transistor were studied with 2-dimensional simulation. Results show that the hot spot locates on the edge of base electrode due to the distribution of current density and electric field. The energy needed for burnout is the smallest when pulses are injected from base among the three electrodes for the heat generation is centralized at that point. If the pulse width is short, the energy needed for burnout nearly remains constant while the pulse power needed is approximately in inverse proportion to the pulse width.
Bipolar junction transistors may be burned out by injected electromagnetic pulse. The effects of electromagnetic pulse injected from base on bipolar junction transistor were studied with 2-dimensional simulation. Results show that the hot spot locates on the edge of base electrode due to the distribution of current density and electric field. The energy needed for burnout is the smallest when pulses are injected from base among the three electrodes for the heat generation is centralized at that point. If the pulse width is short, the energy needed for burnout nearly remains constant while the pulse power needed is approximately in inverse proportion to the pulse width.
2007,
19.
Abstract:
A 1-D multifrequency non-linear model of the beam-wave interaction in a helix TWT is described. The field, phase and motion equations which contains the space charge field and the equations of the cut area are represented. Taking into account the voltage depression effect, this model has been implemented in a code which contains the functions of scanning beam voltage and input power, which is convenient for the simulation of the interaction of beam and wave. A TWT interaction is simulated by the code and the results from the code. The effects of the harmonic waves and the intermodulations are analyzed. The simulation is precise and rapid and it is of importance for the first and fast designs of a helix TWT.
A 1-D multifrequency non-linear model of the beam-wave interaction in a helix TWT is described. The field, phase and motion equations which contains the space charge field and the equations of the cut area are represented. Taking into account the voltage depression effect, this model has been implemented in a code which contains the functions of scanning beam voltage and input power, which is convenient for the simulation of the interaction of beam and wave. A TWT interaction is simulated by the code and the results from the code. The effects of the harmonic waves and the intermodulations are analyzed. The simulation is precise and rapid and it is of importance for the first and fast designs of a helix TWT.
2007,
19.
Abstract:
In the finite-difference time-domain(FDTD) method, the perfectly matched layer(PML) is a kind of high efficient absorbing boundary condition. By adding the terms of physical electric conductivity and magnetic conductivity in the conventional PML equations, a modified PML(MPML) method is presented. Three dimensional MPML equations in the cylindrical coordinate system are given and applied to truncate the open boundary of cylindrical waveguide in 2.5-dimensional simulation. Under the excitations of various modes with different frequencies, the relative errors obtained using the MPML method are 8~10 dB lower than those obtained by the conventional PML method.
In the finite-difference time-domain(FDTD) method, the perfectly matched layer(PML) is a kind of high efficient absorbing boundary condition. By adding the terms of physical electric conductivity and magnetic conductivity in the conventional PML equations, a modified PML(MPML) method is presented. Three dimensional MPML equations in the cylindrical coordinate system are given and applied to truncate the open boundary of cylindrical waveguide in 2.5-dimensional simulation. Under the excitations of various modes with different frequencies, the relative errors obtained using the MPML method are 8~10 dB lower than those obtained by the conventional PML method.
2007,
19.
Abstract:
As far as the convergence half angles of Pierce electron guns vary in a wide range，some corresponding logical functions for Tiwary non-iterative method have been proposed. Using the improved approach, the results agree well with that of Vaughan iterative method and the difference of the convergence half angle between them can be below 1°. Furthermore, the function of the anode aperture radius of Tiwary method is also logically modified, and its anode-cathode spacing and gun shot are as good as that of Vaughan method. In particular, the accuracy of the new method is not influenced by the magnitude of the convergence half angle any longer. Thus, this proposed method extends the application range of the non-iterative method from small convergence half angle to large convergence half angle e
As far as the convergence half angles of Pierce electron guns vary in a wide range，some corresponding logical functions for Tiwary non-iterative method have been proposed. Using the improved approach, the results agree well with that of Vaughan iterative method and the difference of the convergence half angle between them can be below 1°. Furthermore, the function of the anode aperture radius of Tiwary method is also logically modified, and its anode-cathode spacing and gun shot are as good as that of Vaughan method. In particular, the accuracy of the new method is not influenced by the magnitude of the convergence half angle any longer. Thus, this proposed method extends the application range of the non-iterative method from small convergence half angle to large convergence half angle e
2007,
19.
Abstract:
Theoretical model of a double- cusp gun for Ka- band second harmonic gyro- TWT amplifier was analyzed, and the electron beam performance parameters were calculated. Using EGUN simulation, a double- cusp gun producing large orbit gyration electron beam was designed with an anode voltage of 70 kV and a beam current of 3.35 A. The ratio of perpendicular to parallel velocity was 1.62 and its velocity spread was 4.2%. The distribution of electron beam velocity ratio and velocity spread on axis was discussed, and the effects of the anode voltage on electron beam performance was studied. The reseults show that proper anode voltage and cathode magnetic field are helpful in getting good electron beam parameters.
Theoretical model of a double- cusp gun for Ka- band second harmonic gyro- TWT amplifier was analyzed, and the electron beam performance parameters were calculated. Using EGUN simulation, a double- cusp gun producing large orbit gyration electron beam was designed with an anode voltage of 70 kV and a beam current of 3.35 A. The ratio of perpendicular to parallel velocity was 1.62 and its velocity spread was 4.2%. The distribution of electron beam velocity ratio and velocity spread on axis was discussed, and the effects of the anode voltage on electron beam performance was studied. The reseults show that proper anode voltage and cathode magnetic field are helpful in getting good electron beam parameters.
2007,
19.
Abstract:
This paper compares the temperature distribution and warm up time between assembly cathode heated up by conduction and non-assembly cathode heated by radiation using the thermal analysis module of ANSYS. The results show that both of them have a uniform cathode surface temperature distribution and the temperature difference at the sleeve of assembly cathode is in proportion to the input power of its heater and that compared with the non-assembly cathode, the temperature of assembly cathode is higher at the sleeve and the cathode surface, but markedly lower at the heater. Nevertheless, non-assembly cathode starts faster; moreover, improving the emissivities of the cathode’s undersurface and the heater enables the non-assembly cathode to have thermal performance similar to that of the assem
This paper compares the temperature distribution and warm up time between assembly cathode heated up by conduction and non-assembly cathode heated by radiation using the thermal analysis module of ANSYS. The results show that both of them have a uniform cathode surface temperature distribution and the temperature difference at the sleeve of assembly cathode is in proportion to the input power of its heater and that compared with the non-assembly cathode, the temperature of assembly cathode is higher at the sleeve and the cathode surface, but markedly lower at the heater. Nevertheless, non-assembly cathode starts faster; moreover, improving the emissivities of the cathode’s undersurface and the heater enables the non-assembly cathode to have thermal performance similar to that of the assem
2007,
19.
Abstract:
The basic theories, the characteristics and the woking process of the extended interaction oscillator(EIO) were introduced. A type of EIO was simulated using PIC. The effect of the cathode voltage, the radius of the electron beam, the number and the period length of the resonant cavity on the output power, frequency and conversion efficiency were analyzed. The simulation results shown that when the working voltage is 28.5～30 kV, the resonant cavity starts to oscillate. When the input cathode voltage is 29 kV, the current is 10 A, and when the radius of electronic beam is 1.4 mm and the number of period is 4, the output power is 128 kW, the frequency is 12.9 GHz, and the efficiency is up to 37.93%.
The basic theories, the characteristics and the woking process of the extended interaction oscillator(EIO) were introduced. A type of EIO was simulated using PIC. The effect of the cathode voltage, the radius of the electron beam, the number and the period length of the resonant cavity on the output power, frequency and conversion efficiency were analyzed. The simulation results shown that when the working voltage is 28.5～30 kV, the resonant cavity starts to oscillate. When the input cathode voltage is 29 kV, the current is 10 A, and when the radius of electronic beam is 1.4 mm and the number of period is 4, the output power is 128 kW, the frequency is 12.9 GHz, and the efficiency is up to 37.93%.
2007,
19.
Abstract:
Charge density distribution of the large-orbit hollow beam, which is applied to a Gyro-TWA, is obtained from time-integrated image. The image is created by a phosphor scintillator on the cross section vertical to the transmission axial. Comparison of average beam radius, beam pitch angle obtained from the images and from computer simulations and the differences were analyzed. The experimental results are consistent with the simulated ones and significant for the debugging of the Gyro-TWA using this gyral electron beam.
Charge density distribution of the large-orbit hollow beam, which is applied to a Gyro-TWA, is obtained from time-integrated image. The image is created by a phosphor scintillator on the cross section vertical to the transmission axial. Comparison of average beam radius, beam pitch angle obtained from the images and from computer simulations and the differences were analyzed. The experimental results are consistent with the simulated ones and significant for the debugging of the Gyro-TWA using this gyral electron beam.
2007,
19.
Abstract:
The current synchronization trigger mode is important for Z-pinch experiments carried out on the YANG accelerator. The technology can solve the problem of low synchronization precision. The inherent delay time between the load current waveform and the experimental phenomenon can be adopted to obtain the synchronization trigger time. The correlative time precision about ns level can be achieved in this way. The photoelectric isolator and optical fiber are used in the synchronization trigger system to eliminate the electro-magnetic interference and many accurate measurements on the YANG accelerator can be realized. The application of this trigger mode to the multi-framing gated camera synchronization trigger system has done the trick. The evolution course of Z-pinch imploding plasma has been
The current synchronization trigger mode is important for Z-pinch experiments carried out on the YANG accelerator. The technology can solve the problem of low synchronization precision. The inherent delay time between the load current waveform and the experimental phenomenon can be adopted to obtain the synchronization trigger time. The correlative time precision about ns level can be achieved in this way. The photoelectric isolator and optical fiber are used in the synchronization trigger system to eliminate the electro-magnetic interference and many accurate measurements on the YANG accelerator can be realized. The application of this trigger mode to the multi-framing gated camera synchronization trigger system has done the trick. The evolution course of Z-pinch imploding plasma has been
2007,
19.
Abstract:
The induction voltage adder is often used for voltage multiplication. During inductive adding there are wave incidence and reflection. Travel wave method has been used to analyze this process with the assistance of transformation matrix. Its stable solution is the same as that of lump parameter method when the detail of voltage variation can also be presented. The equivalent circuit model of pulsed power source and induction adder has been established to simulate a 3.5 MeV injector which is based on the principle of inductive adder. The results are similar to experiment data in general. The difference between cavity wave and Blumlein output is explained by travel wave method in this paper. The research indicates that travel wave analysis and simulation are reliable in the design of an indu
The induction voltage adder is often used for voltage multiplication. During inductive adding there are wave incidence and reflection. Travel wave method has been used to analyze this process with the assistance of transformation matrix. Its stable solution is the same as that of lump parameter method when the detail of voltage variation can also be presented. The equivalent circuit model of pulsed power source and induction adder has been established to simulate a 3.5 MeV injector which is based on the principle of inductive adder. The results are similar to experiment data in general. The difference between cavity wave and Blumlein output is explained by travel wave method in this paper. The research indicates that travel wave analysis and simulation are reliable in the design of an indu
2007,
19.
Abstract:
The ground simulation tests of proton irradiation for Kapton/Al films were conducted using the space synthesis irradiating facility, in which the energy of protons was chosen as 90 keV, and the flux was 5.0×1011 cm-2·s-1. The degradation of optical property was investigated through changes of the spectral reflectance of specimens before and after the irradiation. The damage mechanism was studied by means of ultraviolet/visible absorption spectra and Fourier transform infrared of spectra. The analysis results demonstrate that some complex reactions occurred in the surface layer of the specimens during the irradiation. The optical energy gap reduces gradually with increasing fluence. The red shift of the end absorption edge and a strong increase in absorbance in the visible region are evid
The ground simulation tests of proton irradiation for Kapton/Al films were conducted using the space synthesis irradiating facility, in which the energy of protons was chosen as 90 keV, and the flux was 5.0×1011 cm-2·s-1. The degradation of optical property was investigated through changes of the spectral reflectance of specimens before and after the irradiation. The damage mechanism was studied by means of ultraviolet/visible absorption spectra and Fourier transform infrared of spectra. The analysis results demonstrate that some complex reactions occurred in the surface layer of the specimens during the irradiation. The optical energy gap reduces gradually with increasing fluence. The red shift of the end absorption edge and a strong increase in absorbance in the visible region are evid
2007,
19.
Abstract:
A novel electron-beam lithography based on overlapped increment scanning is presented. The impact of the depth and exposure dose on the absorbed energy density, and the relationship between the solution rate and the absorbed energy density are analyzed theoretically. The result shows the more the exposure dose increases, the greater the solution rate becomes. Based on this, seven overlapped increment scanning exposure experiments are conducted on 570 nm PMMA in the SDS-3 electron beam lithography system at 20 keV and distinct three-dimensional structures of the conic of trapezoid and the conic are obtained. It means the overlapped increment scanning can be used to three-dimensional fabrication.
A novel electron-beam lithography based on overlapped increment scanning is presented. The impact of the depth and exposure dose on the absorbed energy density, and the relationship between the solution rate and the absorbed energy density are analyzed theoretically. The result shows the more the exposure dose increases, the greater the solution rate becomes. Based on this, seven overlapped increment scanning exposure experiments are conducted on 570 nm PMMA in the SDS-3 electron beam lithography system at 20 keV and distinct three-dimensional structures of the conic of trapezoid and the conic are obtained. It means the overlapped increment scanning can be used to three-dimensional fabrication.
2007,
19.
Abstract:
Using a geometrical optical method, a model for analytic calculation about ellipticity error effect in neutron penumbral imaging is established. An analytic formula of neutron absorbing length is derived from the model, and a general analytical expression for neutron penumbral imaging process is achieved. Based on this model, a numerical simulation of image aberration caused by ellipticity error is realized. The point spread functions under various ellipticity errors and their effects on a round object’s reconstruction are obtained. A semi-quantitative result shows that the effect on imaging quality can be omitted when the ellipticity error is less than 0.01. Compared with the Monte-Carlo method, the analytic model is more effective in computation and easy to apply to other similar code i
Using a geometrical optical method, a model for analytic calculation about ellipticity error effect in neutron penumbral imaging is established. An analytic formula of neutron absorbing length is derived from the model, and a general analytical expression for neutron penumbral imaging process is achieved. Based on this model, a numerical simulation of image aberration caused by ellipticity error is realized. The point spread functions under various ellipticity errors and their effects on a round object’s reconstruction are obtained. A semi-quantitative result shows that the effect on imaging quality can be omitted when the ellipticity error is less than 0.01. Compared with the Monte-Carlo method, the analytic model is more effective in computation and easy to apply to other similar code i
2007,
19.
Abstract:
This paper describes the field emission characteristics of electrochemically fabricated lanthanum hexaboride (LaB6) single tip emitters. It is found that high pressure operation will significantly enlarge the effective emission area and emission current density. This phenomenon is contributed to the bombardment of ions generated by residual gas molecules interacting with emitted electrons. High pressure operation is probably a method to activate LaB6 field emitters.
This paper describes the field emission characteristics of electrochemically fabricated lanthanum hexaboride (LaB6) single tip emitters. It is found that high pressure operation will significantly enlarge the effective emission area and emission current density. This phenomenon is contributed to the bombardment of ions generated by residual gas molecules interacting with emitted electrons. High pressure operation is probably a method to activate LaB6 field emitters.
2007,
19.
Abstract:
The state-of-the-art about surface flashover across semiconductor all over the world is reviewed. Different types of electrode configuration are employed and influence factors on flashover characteristics are discussed. The process of flashover is divided into three phases. The self-defining equivalent conductance parameter is introduced as a criterion. Through measurement and simulation of thermal process of the current filament, it is believed that the temperature of filament channel could approach the melting point of the semiconducting material, which supports the hypothesis that temperature of flashover channel is high enough to arouse desorption of gas molecules. Furthermore, the experimental results of gas desorption primarily prove that there could be a channel outside the surface
The state-of-the-art about surface flashover across semiconductor all over the world is reviewed. Different types of electrode configuration are employed and influence factors on flashover characteristics are discussed. The process of flashover is divided into three phases. The self-defining equivalent conductance parameter is introduced as a criterion. Through measurement and simulation of thermal process of the current filament, it is believed that the temperature of filament channel could approach the melting point of the semiconducting material, which supports the hypothesis that temperature of flashover channel is high enough to arouse desorption of gas molecules. Furthermore, the experimental results of gas desorption primarily prove that there could be a channel outside the surface
2007,
19.
Abstract:
According to the principle of pulse wavefront compression, the model of a shock line circuit is proposed and the computing formulas of wavefront compression are deduced. The shock line is a nearly continuous high-impedance transmission line loaded at the same small spacings by reverse-biased varactor diodes. With the propagation of the input negative-falltime pulse along the transmission line, the capacitance of varactor diodes is decreased by the increase of reverse bias voltage, and the variation in propagation delay at the nodes results in the compression of negative-going wavefronts during propagation. So the wavefront of ultrafast pulses generated by the shock line can be 1 ps.
According to the principle of pulse wavefront compression, the model of a shock line circuit is proposed and the computing formulas of wavefront compression are deduced. The shock line is a nearly continuous high-impedance transmission line loaded at the same small spacings by reverse-biased varactor diodes. With the propagation of the input negative-falltime pulse along the transmission line, the capacitance of varactor diodes is decreased by the increase of reverse bias voltage, and the variation in propagation delay at the nodes results in the compression of negative-going wavefronts during propagation. So the wavefront of ultrafast pulses generated by the shock line can be 1 ps.
2007,
19.
Abstract:
The influence of the approaching speed of two conductors on the air electrostatic discharge (ESD) was investigated by theoretical analysis and experimental measurement. The self-capacitance (mutual-capacitance) coefficient, the potential difference, the rate of change of potential difference with respect to discharge gap separation, the rate of change of potential difference with respect to time for approaching two conductors were calculated. The correlations between discharge peak currents and induced peak-peak voltages and different approaching speeds at 5 kV and 10 kV discharge voltage levels were obtained by experiment. The approaching speed determines the rate of change of potential difference with respect to time at the time of breakdown, and it also determines the air discharge trai
The influence of the approaching speed of two conductors on the air electrostatic discharge (ESD) was investigated by theoretical analysis and experimental measurement. The self-capacitance (mutual-capacitance) coefficient, the potential difference, the rate of change of potential difference with respect to discharge gap separation, the rate of change of potential difference with respect to time for approaching two conductors were calculated. The correlations between discharge peak currents and induced peak-peak voltages and different approaching speeds at 5 kV and 10 kV discharge voltage levels were obtained by experiment. The approaching speed determines the rate of change of potential difference with respect to time at the time of breakdown, and it also determines the air discharge trai
