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RSS2009 Vol. 21, No. 11
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2009,
21.
Abstract:
Laser-induced damage of optical thin film/silica system was studied. The thin film was sol-gel derived silica antireflective coating, which was plated on silica substrate, and the laser with 355 nm wavelength and 6.3 ns pulse width was used in measurement. The results show that the laser induced damage threshold of the system equals to that of the silica substrate and increases with the latter’s increase. The threshold of the system is 4.9 J/cm2 when the threshold of the substrate is 4.8 J/cm2. When the threshold of the substrate is increased to 7.2 J/cm2 by laser pretreatment, the system threshold increases to 7.3 J/cm2. According to dynamic comparison, the substrate is the fragile part in the film/silica system, which is damaged first under la
Laser-induced damage of optical thin film/silica system was studied. The thin film was sol-gel derived silica antireflective coating, which was plated on silica substrate, and the laser with 355 nm wavelength and 6.3 ns pulse width was used in measurement. The results show that the laser induced damage threshold of the system equals to that of the silica substrate and increases with the latter’s increase. The threshold of the system is 4.9 J/cm2 when the threshold of the substrate is 4.8 J/cm2. When the threshold of the substrate is increased to 7.2 J/cm2 by laser pretreatment, the system threshold increases to 7.3 J/cm2. According to dynamic comparison, the substrate is the fragile part in the film/silica system, which is damaged first under la
2009,
21.
Abstract:
A high-efficiency, all-solid-state, 7.13 W macro-micro pulse 1 319 nm laser has been developed. The laser used thermal stabilized Z-shaped folded cavity. The gain module developed by ourselves adopted quasi continuous wave 15 diode bars ring-pumped Nd:YAG module. An active acousto-optics mode locker was used as the mode locked device. A second harmonic generation KTP crystal was inserted into the resonator for spike suppression. To get stable mode locked state, the length of the laser was exactly designed and adjusted. When the cavity length was matched to the drive frequency of the acousto-optics mode locker, the macro-micro pulse 1 319 nm laser was successfully obtained. The repetition rate of macro pulses was 400 Hz and the pulse width was about 190 μs. The repetition rate of micro pul
A high-efficiency, all-solid-state, 7.13 W macro-micro pulse 1 319 nm laser has been developed. The laser used thermal stabilized Z-shaped folded cavity. The gain module developed by ourselves adopted quasi continuous wave 15 diode bars ring-pumped Nd:YAG module. An active acousto-optics mode locker was used as the mode locked device. A second harmonic generation KTP crystal was inserted into the resonator for spike suppression. To get stable mode locked state, the length of the laser was exactly designed and adjusted. When the cavity length was matched to the drive frequency of the acousto-optics mode locker, the macro-micro pulse 1 319 nm laser was successfully obtained. The repetition rate of macro pulses was 400 Hz and the pulse width was about 190 μs. The repetition rate of micro pul
2009,
21.
Abstract:
The phase noise in a strong pumped fiber amplifier is measured using multi-dithering method. Its fluctuation property is qualitatively characterized by the power spectral density and integral spectral density, and it is concluded that the ratio of high frequency phase noise increases with the increase of pump power. The bandwidth requirement of the active phase control system is quantificationally estimated through evaluating the structure function of the measured phase noise. The experimental measurement and analysis show that the minimum bandwidths of the system are 830 Hz, 3.1 kHz and 10 kHz under the pump powers of 71 W, 181 W, and 230 W, respectively.
The phase noise in a strong pumped fiber amplifier is measured using multi-dithering method. Its fluctuation property is qualitatively characterized by the power spectral density and integral spectral density, and it is concluded that the ratio of high frequency phase noise increases with the increase of pump power. The bandwidth requirement of the active phase control system is quantificationally estimated through evaluating the structure function of the measured phase noise. The experimental measurement and analysis show that the minimum bandwidths of the system are 830 Hz, 3.1 kHz and 10 kHz under the pump powers of 71 W, 181 W, and 230 W, respectively.
2009,
21.
Abstract:
The performance of nonuniformity correction(NUC) would be deteriorated by time shift in the response of detectors in infrared focal plane arrays(IRFPAs). Therefore, a scene-based NUC algorithm is presented. In this algorithm, an adaptive filter bank is applied to estimate NUC parameters for every detector in IRFPAs. And the parameters are renewed by utilizing current imaging information to reduce the influence imposed by response drift on NUC. For an image with a nonuniformity of 26.12%, nonuniformities after 1 h correction are 3.122% for two-point NUC algorithm, 1.893% for Kalman-filter NUC algorithm and around 1.856% for the presented algorithm, which means the presented algorithm can achieve the best NUC effect steadily.
The performance of nonuniformity correction(NUC) would be deteriorated by time shift in the response of detectors in infrared focal plane arrays(IRFPAs). Therefore, a scene-based NUC algorithm is presented. In this algorithm, an adaptive filter bank is applied to estimate NUC parameters for every detector in IRFPAs. And the parameters are renewed by utilizing current imaging information to reduce the influence imposed by response drift on NUC. For an image with a nonuniformity of 26.12%, nonuniformities after 1 h correction are 3.122% for two-point NUC algorithm, 1.893% for Kalman-filter NUC algorithm and around 1.856% for the presented algorithm, which means the presented algorithm can achieve the best NUC effect steadily.
2009,
21.
Abstract:
808 nm high duty-cycle high power semiconductor laser array was studied. Gradient refraction index separate confinement hetero-structure single quantum well broad waveguide structure(GRIN-SCH-SQW-BW) was adopted to reduce the non-radiation compound, the active layer carrier leakage, and the scattering and absorption loss. Meanwhile, it enables high doping of the P side and optimization of N side alloy conditions,which reduce the laser diode series resistance, thereby reduce the joule heat and raise the output power of the laser diode. GaInAsP/InGaP/AlGaAs GRIN-SCH-SQW-BW epilayers were grown by low pressure metal organic chemical vapor deposition(MOCVD) on N-type GaAs substrate. laser diode array was fabricated using the material. The output power of laser diode array is up to 189.64 W at
808 nm high duty-cycle high power semiconductor laser array was studied. Gradient refraction index separate confinement hetero-structure single quantum well broad waveguide structure(GRIN-SCH-SQW-BW) was adopted to reduce the non-radiation compound, the active layer carrier leakage, and the scattering and absorption loss. Meanwhile, it enables high doping of the P side and optimization of N side alloy conditions,which reduce the laser diode series resistance, thereby reduce the joule heat and raise the output power of the laser diode. GaInAsP/InGaP/AlGaAs GRIN-SCH-SQW-BW epilayers were grown by low pressure metal organic chemical vapor deposition(MOCVD) on N-type GaAs substrate. laser diode array was fabricated using the material. The output power of laser diode array is up to 189.64 W at
2009,
21.
Abstract:
An experimental system for Venturi’s critical background-pressure ratio(CPR) was set up, and a series of experiments was conducted with different mediums and Venturis. The function of the first Venturi in the experimental system and the effect of temperature on CPR were discussed. The results indicate that, the CPR of venturis with reasonable design and suitable technics is obviously higher than critical pressure ratio. Moreover, smaller specific heat ratio, better surface roughness and larger throat diameter would result in higher CPR.
An experimental system for Venturi’s critical background-pressure ratio(CPR) was set up, and a series of experiments was conducted with different mediums and Venturis. The function of the first Venturi in the experimental system and the effect of temperature on CPR were discussed. The results indicate that, the CPR of venturis with reasonable design and suitable technics is obviously higher than critical pressure ratio. Moreover, smaller specific heat ratio, better surface roughness and larger throat diameter would result in higher CPR.
2009,
21.
Abstract:
Using a modified damage function model with the percolation-relaxation function, the spallation in nanocrystalline copper by laser irradiation loading was investigated numerically. Laser-driven loadings were simulated by a Gaussian temporal pressure profile, applied at the front surface of the Ni alloy substrate. Simulation results indicated that the damage evolution had serious influence on the wave propagation in nanocrystalline copper sample. Good agreement was obtained between experimental and predicted free surface velocity profiles, which confirmed the capability of the damage model for describing the spallation process in nanocrystalline copper.
Using a modified damage function model with the percolation-relaxation function, the spallation in nanocrystalline copper by laser irradiation loading was investigated numerically. Laser-driven loadings were simulated by a Gaussian temporal pressure profile, applied at the front surface of the Ni alloy substrate. Simulation results indicated that the damage evolution had serious influence on the wave propagation in nanocrystalline copper sample. Good agreement was obtained between experimental and predicted free surface velocity profiles, which confirmed the capability of the damage model for describing the spallation process in nanocrystalline copper.
2009,
21.
Abstract:
In order to increase the wear resistance of 40Cr steel, Fe-based alloy coating was obtained on the surface of 40Cr steel substrate with preset laser cladding technique. The microhardness of both clad coating and substrate were measured by microhardness tester, and the micrographs of clad coating were scanned by SEM. Moreover, wear tests were carried out by wear tester to determine the rule of friction coefficient varying with temperature under lubrication condition. As the tests show, good metallurgical bonding was obtained between Fe-based alloy coating and 40Cr substrate. The microstructure of cross section of the clad coating presents a vertical distribution of planar crystal，dendrite crystal and cellular crystal. The microhardness value of the clad coating fluctuated between 617.5 and
In order to increase the wear resistance of 40Cr steel, Fe-based alloy coating was obtained on the surface of 40Cr steel substrate with preset laser cladding technique. The microhardness of both clad coating and substrate were measured by microhardness tester, and the micrographs of clad coating were scanned by SEM. Moreover, wear tests were carried out by wear tester to determine the rule of friction coefficient varying with temperature under lubrication condition. As the tests show, good metallurgical bonding was obtained between Fe-based alloy coating and 40Cr substrate. The microstructure of cross section of the clad coating presents a vertical distribution of planar crystal，dendrite crystal and cellular crystal. The microhardness value of the clad coating fluctuated between 617.5 and
2009,
21.
Abstract:
Based on wavelength beam combining, we use grating diffraction and external cavity feedback to lock all elements of the laser diode array(LDA) in different wavelengths, and the neighboring emitters have slight difference in locked wavelength. The output beam from the external cavity coupler mirror is nearly parallel with the same beam quality as single element of the LDA, and its brightness grows with the element number of the LDA increasing. The 1 cm linear array used in the experiment consists of 19 wide-aperture diodes with diode width of 100 μm and a fill factor is 0.2. When the free operating output power is 49.8 W and the maximal injection current is 60.6 A, the combined beam power is 20.1 W, the wavelength spread is about 15 nm, and the far field divergence angle varys from 70 mrad
Based on wavelength beam combining, we use grating diffraction and external cavity feedback to lock all elements of the laser diode array(LDA) in different wavelengths, and the neighboring emitters have slight difference in locked wavelength. The output beam from the external cavity coupler mirror is nearly parallel with the same beam quality as single element of the LDA, and its brightness grows with the element number of the LDA increasing. The 1 cm linear array used in the experiment consists of 19 wide-aperture diodes with diode width of 100 μm and a fill factor is 0.2. When the free operating output power is 49.8 W and the maximal injection current is 60.6 A, the combined beam power is 20.1 W, the wavelength spread is about 15 nm, and the far field divergence angle varys from 70 mrad
2009,
21.
Abstract:
Coherent beam combining of two and three watt-level fiber amplifiers is demonstrated with multi-dithering technique used for phase control. In the experiment, the master laser is split into two or three channels and the power of each channel is amplified by a fiber amplifier. When the control loop is open, the far-field pattern is dynamic and blurred, and the fringe contrasts for combining are 0.19 for two beams and 0.12 for three beams. When the control loop is closed, the far-field pattern is stable and clear, the fringe contrasts for two- and three-beam combinings are improved to 0.93 and 0.81 respectively and the corresponding coherent combining efficiencies are 80% and 77%. In addition, the experimental results of two- and three-beam combinings are compared and the effect of each cont
Coherent beam combining of two and three watt-level fiber amplifiers is demonstrated with multi-dithering technique used for phase control. In the experiment, the master laser is split into two or three channels and the power of each channel is amplified by a fiber amplifier. When the control loop is open, the far-field pattern is dynamic and blurred, and the fringe contrasts for combining are 0.19 for two beams and 0.12 for three beams. When the control loop is closed, the far-field pattern is stable and clear, the fringe contrasts for two- and three-beam combinings are improved to 0.93 and 0.81 respectively and the corresponding coherent combining efficiencies are 80% and 77%. In addition, the experimental results of two- and three-beam combinings are compared and the effect of each cont
2009,
21.
Abstract:
Optical attenuation coefficient as low as 10-4~10-3 is needed in the application of the high energy laser beam on-line diagnostic system based on a scanning circular reflector. For the low linear saturation threshold of photoelectric detector, a new and reliable method used in diagnostic system is introduced to attenuate high energy laser power density using multilayer dielectric coating. The principle of the beam sampling and attenuation is presented, and transmission coefficient characteristics of the coating are investigated under laser incidence angle of 0°~15° and power density of 1~1 000 W/cm2. At last, the feasibility of the method is proved by experiments.
Optical attenuation coefficient as low as 10-4~10-3 is needed in the application of the high energy laser beam on-line diagnostic system based on a scanning circular reflector. For the low linear saturation threshold of photoelectric detector, a new and reliable method used in diagnostic system is introduced to attenuate high energy laser power density using multilayer dielectric coating. The principle of the beam sampling and attenuation is presented, and transmission coefficient characteristics of the coating are investigated under laser incidence angle of 0°~15° and power density of 1~1 000 W/cm2. At last, the feasibility of the method is proved by experiments.
2009,
21.
Abstract:
The correlativity between atmospheric transmissivity and laser wavelength was gained by using Mie scattering theory and dominant factors for attenuation of aerial target infrared radiation propagating in atmosphere.With a laboratory apparatus designed by ourselves and laser multipoint fault measuring techniques, we measured atmospheric transmissivity at 1 060 nm wavelength, then inversely calculated transmissivities at 532, 860 and 1 570 nm in real time using the correlativity between wavelength and atmospheric transmissivity. The results indicate that it is feasible to use the correlativity to inverse infrared atmospheric propagation and establish the infrared radiation real time atmospheric propagation correcting model and system platform of aerial target．
The correlativity between atmospheric transmissivity and laser wavelength was gained by using Mie scattering theory and dominant factors for attenuation of aerial target infrared radiation propagating in atmosphere.With a laboratory apparatus designed by ourselves and laser multipoint fault measuring techniques, we measured atmospheric transmissivity at 1 060 nm wavelength, then inversely calculated transmissivities at 532, 860 and 1 570 nm in real time using the correlativity between wavelength and atmospheric transmissivity. The results indicate that it is feasible to use the correlativity to inverse infrared atmospheric propagation and establish the infrared radiation real time atmospheric propagation correcting model and system platform of aerial target．
2009,
21.
Abstract:
Soft X-ray Dante spectrometer is one of the primary instruments to diagnose the X-ray radiation emitted by Z-pinch plasma. To obtain the spectra and power of X-rays, unfolding treatment of the measuring data is a must. The structure of a recently developed eight-channel Dante spectrometer is introduced and a smooth unfolding algorithm using parabolic B-splines is presented. Numerical simulation shows that, for blackbody spectra with temperature ranging from 20 to 250 eV, both the spectra and power are accurately recovered. Experimental waveforms measured during Z-pinch experiments performed on the Yang accelerator. The 40.5 GW X-ray peaking power and 851 J X-ray energy unfolded from the measurements of the Dante spectrometer were in agreement with the corrected results of the sofe X-ray po
Soft X-ray Dante spectrometer is one of the primary instruments to diagnose the X-ray radiation emitted by Z-pinch plasma. To obtain the spectra and power of X-rays, unfolding treatment of the measuring data is a must. The structure of a recently developed eight-channel Dante spectrometer is introduced and a smooth unfolding algorithm using parabolic B-splines is presented. Numerical simulation shows that, for blackbody spectra with temperature ranging from 20 to 250 eV, both the spectra and power are accurately recovered. Experimental waveforms measured during Z-pinch experiments performed on the Yang accelerator. The 40.5 GW X-ray peaking power and 851 J X-ray energy unfolded from the measurements of the Dante spectrometer were in agreement with the corrected results of the sofe X-ray po
2009,
21.
Abstract:
Optical wave transmission through a subwavelength slit grooved with cavity in internal wall is investigated in a thick metallic plate by two-dimensional finite-difference time-domain method, and enhanced transmissions are found at some wavelengths in transmission spectra. Using Maxwell equations and waveguide resonance theory, the mechanism of the enhanced transmission is explored with amplitude distributions. It is considered that waveguide resonance modes play an important role in the transmission. The longitudinal modes forming in the subwavelength slit can lead to transmission peaks, and so can the cavity modes.
Optical wave transmission through a subwavelength slit grooved with cavity in internal wall is investigated in a thick metallic plate by two-dimensional finite-difference time-domain method, and enhanced transmissions are found at some wavelengths in transmission spectra. Using Maxwell equations and waveguide resonance theory, the mechanism of the enhanced transmission is explored with amplitude distributions. It is considered that waveguide resonance modes play an important role in the transmission. The longitudinal modes forming in the subwavelength slit can lead to transmission peaks, and so can the cavity modes.
2009,
21.
Abstract:
A new theoretical model has been developed to describe the whole ablation process, including the effect of dynamic absorptance and evaporation. Taking gold as an example, a finite difference method is employed to simulate the electron and lattice temperature evolution under the irradiation of single and multipulse femtosecond laser. The evolution of residual energy coefficient for multipulse as a function of pulse number is given. It is found that the calculated coefficients are in good agreement with the corresponding experimental data, proving the existence of residual energy during femtosecond multipulse ablation.
A new theoretical model has been developed to describe the whole ablation process, including the effect of dynamic absorptance and evaporation. Taking gold as an example, a finite difference method is employed to simulate the electron and lattice temperature evolution under the irradiation of single and multipulse femtosecond laser. The evolution of residual energy coefficient for multipulse as a function of pulse number is given. It is found that the calculated coefficients are in good agreement with the corresponding experimental data, proving the existence of residual energy during femtosecond multipulse ablation.
2009,
21.
Abstract:
The diffraction-free Bessel beams were generated using two different base angle axicons. The optical intensity distribution in a single Bessel beam and two Bessel beams interference were analyzed, and the characteristics of the generated bottle beams in a complete period were also analyzed. The transverse optical intensity distribution of the beam along the propagation distance was simulated numerically and the related experiments were given. The central spot size of a single Bessel beam and two Bessel beams interference were measured and the results were coincident with the theoretical analysis.
The diffraction-free Bessel beams were generated using two different base angle axicons. The optical intensity distribution in a single Bessel beam and two Bessel beams interference were analyzed, and the characteristics of the generated bottle beams in a complete period were also analyzed. The transverse optical intensity distribution of the beam along the propagation distance was simulated numerically and the related experiments were given. The central spot size of a single Bessel beam and two Bessel beams interference were measured and the results were coincident with the theoretical analysis.
2009,
21.
Abstract:
Li2O-B2O3 composite gels were successfully prepared from tri-n-butyl borate and lithium methoxide dissolved in methanol and tetrahydrofuran via sol-gel technique. Sol-gel process, micro-morphology, ingredient of the gel samples were characterized by viscosity analysis, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, transmittance electron microscopy and infra-red spectrum analysis. The results indicate that raw gel are dried after 4 h at 150 ℃ and crystallization is observed in the xerogels. Micro-morphology of Li2O-B2O3 composite gels will transfer from non-crystal to crystal at about 492 ℃, and the crystal liquates at about 808 ℃. The obtained dry gels are materials with porous configuration. The gel network appears to be composed of primary units l
Li2O-B2O3 composite gels were successfully prepared from tri-n-butyl borate and lithium methoxide dissolved in methanol and tetrahydrofuran via sol-gel technique. Sol-gel process, micro-morphology, ingredient of the gel samples were characterized by viscosity analysis, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, transmittance electron microscopy and infra-red spectrum analysis. The results indicate that raw gel are dried after 4 h at 150 ℃ and crystallization is observed in the xerogels. Micro-morphology of Li2O-B2O3 composite gels will transfer from non-crystal to crystal at about 492 ℃, and the crystal liquates at about 808 ℃. The obtained dry gels are materials with porous configuration. The gel network appears to be composed of primary units l
2009,
21.
Abstract:
A fast testing method on inspecting defects of large aperture optics was introduced. With uniform illumination by LED source at grazing incidence, the image of defects on the surface of and inside the large aperture optics could be enlarged due to scattering. The images of defects were got by high resolution CCD camera and microscope, and the approximate mathematical relation between viewing dimension and real dimension of defects was simulated. Thus the approximate real dimension and location of all defects could be calculated through the high resolution pictures.
A fast testing method on inspecting defects of large aperture optics was introduced. With uniform illumination by LED source at grazing incidence, the image of defects on the surface of and inside the large aperture optics could be enlarged due to scattering. The images of defects were got by high resolution CCD camera and microscope, and the approximate mathematical relation between viewing dimension and real dimension of defects was simulated. Thus the approximate real dimension and location of all defects could be calculated through the high resolution pictures.
2009,
21.
Abstract:
Relation between imaging characteristic of Kirkpatrick-Baez(KB) microscope and periodic multilayer films is analyzed. The optical structure of KB microscope is designed based on resolution and collection efficiency requirements. Imaging quality is simulated, and 8 keV X-ray imaging experiment by KB microscope with W/B4C periodic multilayer is performed, the resolution is about 2 μm in central field and better than 5 μm in ±100 μm field. The result comparison between simulation and experiment shows spherical aberration and mirror machining precision are the key factors influencing the resolution of central field, and the range of effective field of view is limited by angle bandwidth of periodic multilayer.
Relation between imaging characteristic of Kirkpatrick-Baez(KB) microscope and periodic multilayer films is analyzed. The optical structure of KB microscope is designed based on resolution and collection efficiency requirements. Imaging quality is simulated, and 8 keV X-ray imaging experiment by KB microscope with W/B4C periodic multilayer is performed, the resolution is about 2 μm in central field and better than 5 μm in ±100 μm field. The result comparison between simulation and experiment shows spherical aberration and mirror machining precision are the key factors influencing the resolution of central field, and the range of effective field of view is limited by angle bandwidth of periodic multilayer.
2009,
21.
Abstract:
Harmonic injection is an effective solution for suppressing the harmonic and cross-modulation signals inspired by nonlinear distoration of traveling wave tube(TWT). In this paper, Christine 1D nonlinear beam-wave interaction model is used to simulate the 2nd harmonic injection. The results show that harmonic injection can suppress the 3IM signals inspired by nonlinear distoration effictively and reduce the output power of 3IM of TWT. The experimentation of harmonic injection is introduced whose results agree well with those of simulation agree well.
Harmonic injection is an effective solution for suppressing the harmonic and cross-modulation signals inspired by nonlinear distoration of traveling wave tube(TWT). In this paper, Christine 1D nonlinear beam-wave interaction model is used to simulate the 2nd harmonic injection. The results show that harmonic injection can suppress the 3IM signals inspired by nonlinear distoration effictively and reduce the output power of 3IM of TWT. The experimentation of harmonic injection is introduced whose results agree well with those of simulation agree well.
2009,
21.
Abstract:
In this paper, the imaging velocity interferometer system for any reflector (VISAR) is introduced, which is used to diagnose the shock wave with temporal and spatial resolution capability. The technique is so that improved the transmission system can reserve the most of space information of the target, and the recording system has the picosecond resolution due to using the streak camera. The optical system and fundamentals of imaging velocity interferometer system for any reflector (VISAR) are introduced, and the optical design diagram and the resolution of this system are proposed. The basic parameters of laser source and imaging system are also proposed. The design diagram of three point supporting system for interferometer is drawn, and the basic parameter of recording system is propose
In this paper, the imaging velocity interferometer system for any reflector (VISAR) is introduced, which is used to diagnose the shock wave with temporal and spatial resolution capability. The technique is so that improved the transmission system can reserve the most of space information of the target, and the recording system has the picosecond resolution due to using the streak camera. The optical system and fundamentals of imaging velocity interferometer system for any reflector (VISAR) are introduced, and the optical design diagram and the resolution of this system are proposed. The basic parameters of laser source and imaging system are also proposed. The design diagram of three point supporting system for interferometer is drawn, and the basic parameter of recording system is propose
2009,
21.
Abstract:
A side appending three-cavity transmit time oscillator is proposed. Through 1-D single particle theory, the effects of the direct current transit angle and the volt modulating coefficient on the microwave power conversion efficiency are analysed. Numerical simulation is done to verify the theoretical analysis results. Numerical simulation indicates that the foilless oscillator can output an average power of 8 GW at 3.9 GHz when excited by a 400 keV, 60 kA radial electron beam, with an impedance of 6.7 Ω.
A side appending three-cavity transmit time oscillator is proposed. Through 1-D single particle theory, the effects of the direct current transit angle and the volt modulating coefficient on the microwave power conversion efficiency are analysed. Numerical simulation is done to verify the theoretical analysis results. Numerical simulation indicates that the foilless oscillator can output an average power of 8 GW at 3.9 GHz when excited by a 400 keV, 60 kA radial electron beam, with an impedance of 6.7 Ω.
2009,
21.
Abstract:
A novel finite-difference time-domain(FDTD) method is proposed to analyse electromagnetic wave transmission characteristics of magnetized plasma. The constitutive equation between current density vector and electric field strength vector is tranformed into s-domain by the principle of Laplace transform, and the inverse Laplace transform is adopted for the explicit equations between them in time-domain. Finally through exponential time stepping, the FDTD iteration equations are obtained, which can be easily solved in discrete-time-domain. By these techniques, the difficulty, that the two components of the current density vector can not be discreted because of their coupling in the constitutive equation, is solved. Reflection coefficient of anisotropic plasma slab is calculated using this me
A novel finite-difference time-domain(FDTD) method is proposed to analyse electromagnetic wave transmission characteristics of magnetized plasma. The constitutive equation between current density vector and electric field strength vector is tranformed into s-domain by the principle of Laplace transform, and the inverse Laplace transform is adopted for the explicit equations between them in time-domain. Finally through exponential time stepping, the FDTD iteration equations are obtained, which can be easily solved in discrete-time-domain. By these techniques, the difficulty, that the two components of the current density vector can not be discreted because of their coupling in the constitutive equation, is solved. Reflection coefficient of anisotropic plasma slab is calculated using this me
2009,
21.
Abstract:
Extensional method was presented for the origin of Gedney perfectly matched layer(PML) absorbing boundary condition could not be used in truncation of lossy media and was not effective in absorbing evanescent waves. The main idea of extensional PML was to overcome the limitation of Gedney PML by deriving complex permittivity and complex permeability from lossy media to PML. Evanescent coefficient was put forward also to accelerate evanescent wave fading down. The computational model was designed to study the reflection of PML to lossy media. The numerical results prove that the extensional method is very efficient in terminating computational domain composed of lossy media. The extensional PML was used in FDTD method to simulate the EMP effect of a ground laying shielded cable. Compared wi
Extensional method was presented for the origin of Gedney perfectly matched layer(PML) absorbing boundary condition could not be used in truncation of lossy media and was not effective in absorbing evanescent waves. The main idea of extensional PML was to overcome the limitation of Gedney PML by deriving complex permittivity and complex permeability from lossy media to PML. Evanescent coefficient was put forward also to accelerate evanescent wave fading down. The computational model was designed to study the reflection of PML to lossy media. The numerical results prove that the extensional method is very efficient in terminating computational domain composed of lossy media. The extensional PML was used in FDTD method to simulate the EMP effect of a ground laying shielded cable. Compared wi
2009,
21.
Abstract:
A lossy dielectric whose dielectric constant and loss tangent are 10 and 0.6 respectively is applied in the waveguide of calibration probe in order to simulate the influence of electric and magnetic field caused by the input and output coupling loop in the testing probe. The identical distribution of electric and magnetic field between testing probe and calibration probe is achieved. The application of lossy dielectric in the waveguide is capable of maintaining the symmetry between testing probe and calibration probe while the testing probe has moderate coupling and reduce the measurement error caused by low coupling of testing probe in the early device of image method．
A lossy dielectric whose dielectric constant and loss tangent are 10 and 0.6 respectively is applied in the waveguide of calibration probe in order to simulate the influence of electric and magnetic field caused by the input and output coupling loop in the testing probe. The identical distribution of electric and magnetic field between testing probe and calibration probe is achieved. The application of lossy dielectric in the waveguide is capable of maintaining the symmetry between testing probe and calibration probe while the testing probe has moderate coupling and reduce the measurement error caused by low coupling of testing probe in the early device of image method．
2009,
21.
Abstract:
For the measurement of flight time spectrum for 252Cf fast neutron and gamma ray, a new measuring system based on high-speed data acquisition card is put forward and constructed. The data acquisition card uses high speed A/D converting unit(1 GHz) and high speed processing unit. It can accomplish on-line time detecting of pulse sequence at 1 ns precision. The measurement of flight time spectrum is done by correlation function. Through data processing arrangement and cross correlation function calculation designed on PC, flight time spectra of 252Cf Source fission neutron and gamma ray can be obtained. The results agree with those from the classical measuring system in a degree of 99.9%, which consists of time-amplitude converter and multi-channel analyzer.
For the measurement of flight time spectrum for 252Cf fast neutron and gamma ray, a new measuring system based on high-speed data acquisition card is put forward and constructed. The data acquisition card uses high speed A/D converting unit(1 GHz) and high speed processing unit. It can accomplish on-line time detecting of pulse sequence at 1 ns precision. The measurement of flight time spectrum is done by correlation function. Through data processing arrangement and cross correlation function calculation designed on PC, flight time spectra of 252Cf Source fission neutron and gamma ray can be obtained. The results agree with those from the classical measuring system in a degree of 99.9%, which consists of time-amplitude converter and multi-channel analyzer.
2009,
21.
Abstract:
The real-time algorithm of correlation calculation and frequency spectrum analysis is presented for neutron pulse series up to 1 GHz sampling rates based on PC. The fast-moving method is proposed based on the special “0” and “1” structure of the series and spectrum analysis process is optimized. Memory management and streaming SIMD(single-instruction multiple-data) extensions are adopted in the algorithm for optimizing. Simulation demonstrates that the presented correlation algorithm consumes 0.29 μs when data block length is 1 024 points and count rate is 3×106 s-1, while the correlation algorithm of Intel Math Kernel Library consumes 129.95 μs. Practical experiment shows that the algorithm meets the demand of real-time correlation calculation and frequency spectrum analysis.
The real-time algorithm of correlation calculation and frequency spectrum analysis is presented for neutron pulse series up to 1 GHz sampling rates based on PC. The fast-moving method is proposed based on the special “0” and “1” structure of the series and spectrum analysis process is optimized. Memory management and streaming SIMD(single-instruction multiple-data) extensions are adopted in the algorithm for optimizing. Simulation demonstrates that the presented correlation algorithm consumes 0.29 μs when data block length is 1 024 points and count rate is 3×106 s-1, while the correlation algorithm of Intel Math Kernel Library consumes 129.95 μs. Practical experiment shows that the algorithm meets the demand of real-time correlation calculation and frequency spectrum analysis.
2009,
21.
Abstract:
Edge detection of flash X-ray radiography image is a principal means to extract quantitative boundary information of primary implosion material. The precision of edge detection is an important index for judging flash X-ray radiography diagnostic level .In terms of feature of high-energy flash X-ray radiography image, typical Sobel edge detection algorithm in digital image processing is analyzed in this paper. A simple algorithm for threshold alternative and localization criteria based on maximum gradient is proposed to overcome typical Sobel operater’s disadvantages of the obtained image edges being thick and causing edge point misjudgement. The simulated result shows that the obtained edges of the image are thin and the edge position extracted by the algorithm is accurate.
Edge detection of flash X-ray radiography image is a principal means to extract quantitative boundary information of primary implosion material. The precision of edge detection is an important index for judging flash X-ray radiography diagnostic level .In terms of feature of high-energy flash X-ray radiography image, typical Sobel edge detection algorithm in digital image processing is analyzed in this paper. A simple algorithm for threshold alternative and localization criteria based on maximum gradient is proposed to overcome typical Sobel operater’s disadvantages of the obtained image edges being thick and causing edge point misjudgement. The simulated result shows that the obtained edges of the image are thin and the edge position extracted by the algorithm is accurate.
2009,
21.
Abstract:
A two-stage helical explosive magnetic flux compression generator (type 08 MFCG) is described in this paper. The generator design parameters were obtained from calculation by computation code BCYSSYS for HEMG pulsed-power source based on equivalent circuit. Experimental results show that, type 08 MFCG can output pulse current up to 220 kA and energy up to 72 kJ on 3 μH inductance load within the effective pulse duration of 21 μs, and the experimental results are compared with the calculated ones, which demonstrates the feasibility of the code BCYSSYS for generator design.
A two-stage helical explosive magnetic flux compression generator (type 08 MFCG) is described in this paper. The generator design parameters were obtained from calculation by computation code BCYSSYS for HEMG pulsed-power source based on equivalent circuit. Experimental results show that, type 08 MFCG can output pulse current up to 220 kA and energy up to 72 kJ on 3 μH inductance load within the effective pulse duration of 21 μs, and the experimental results are compared with the calculated ones, which demonstrates the feasibility of the code BCYSSYS for generator design.
2009,
21.
Abstract:
In this paper, high frequency behavior of a Rogowski coil is analyzed. Considering the model of the coil frequency response, the damping ratio based on termination resistor can be used to divide the coil frequency band into three bands: derivation band, proportion band and resonance band. Corresponding outside integrator circuits are built according to characteristics of each band. A novel compound integrator circuit consisted of self-integration, passive RC integration and active RC integration is presented. The compound integrator improves the measurement upper bandwidth limit of transducer to the coil’s natural frequency. A transducer using a printing circuit board(PCB) coil of 100 turns is constructed with designed frequency of 10 Hz~17 MHz and sensitivity of 1 mV/A. The transducer is
In this paper, high frequency behavior of a Rogowski coil is analyzed. Considering the model of the coil frequency response, the damping ratio based on termination resistor can be used to divide the coil frequency band into three bands: derivation band, proportion band and resonance band. Corresponding outside integrator circuits are built according to characteristics of each band. A novel compound integrator circuit consisted of self-integration, passive RC integration and active RC integration is presented. The compound integrator improves the measurement upper bandwidth limit of transducer to the coil’s natural frequency. A transducer using a printing circuit board(PCB) coil of 100 turns is constructed with designed frequency of 10 Hz~17 MHz and sensitivity of 1 mV/A. The transducer is
2009,
21.
Abstract:
Based on Hugoniot data, deformation Morse potential and Grüneisen model, a new method is introduced to determine the equation of state of solid material under high pressure. Physical significance of the method is specific and expression form is concise. The equation of state of Au calculated by this method agrees well with that of Sesame equation of state database. The relative error is in the 0~10% range when the density of Au is within 20~28 g/cm3.
Based on Hugoniot data, deformation Morse potential and Grüneisen model, a new method is introduced to determine the equation of state of solid material under high pressure. Physical significance of the method is specific and expression form is concise. The equation of state of Au calculated by this method agrees well with that of Sesame equation of state database. The relative error is in the 0~10% range when the density of Au is within 20~28 g/cm3.
2009,
21.
Abstract:
A compensated Monte-Carlo collision model(CMCC) was proposed, which took the average collision times computed from normal distribution as the probability of single particle collision during a time step. Hereby the ignored multi-time collisions were compensated by additive single collisions. The electron motion in discharged He gas was simulated with CMCC model on different reduced field conditions. Simulation results showed that CMCC model with long time step got the same electron velocity distribution and temperature as conventional MCC model with short time step. It was proved that the CMCC model had high efficiency especially for PIC simulation of high pressure gas discharges.
A compensated Monte-Carlo collision model(CMCC) was proposed, which took the average collision times computed from normal distribution as the probability of single particle collision during a time step. Hereby the ignored multi-time collisions were compensated by additive single collisions. The electron motion in discharged He gas was simulated with CMCC model on different reduced field conditions. Simulation results showed that CMCC model with long time step got the same electron velocity distribution and temperature as conventional MCC model with short time step. It was proved that the CMCC model had high efficiency especially for PIC simulation of high pressure gas discharges.
2009,
21.
Abstract:
In order to satisfy application demand for high performance and miniaturization of pulsed power system, two types of micro-stacked insulators were designed and fabricated. One was fabricated from interleaved layers of brass and PI (polyimide), the other was fabricated from stainless steel and FEP (fluorinated ethylene propylene). Based on the nanosecond (10 ns/30 ns) pulsed power vacuum experimental facility with Marx generator and single coaxial pulse-forming line, the vacuum surface flashover characteristics of the micro-stacked insulators were tested. To get a precise calibration of the measurement system, a magnetic pulse compression power supply with a relatively high pulse amplitude output of about 20 kV was used, and a voltage-dividing ratio of 25 133∶1 was acquired. Two types of m
In order to satisfy application demand for high performance and miniaturization of pulsed power system, two types of micro-stacked insulators were designed and fabricated. One was fabricated from interleaved layers of brass and PI (polyimide), the other was fabricated from stainless steel and FEP (fluorinated ethylene propylene). Based on the nanosecond (10 ns/30 ns) pulsed power vacuum experimental facility with Marx generator and single coaxial pulse-forming line, the vacuum surface flashover characteristics of the micro-stacked insulators were tested. To get a precise calibration of the measurement system, a magnetic pulse compression power supply with a relatively high pulse amplitude output of about 20 kV was used, and a voltage-dividing ratio of 25 133∶1 was acquired. Two types of m
2009,
21.
Abstract:
A thyristor switched three-stage magnetic pulse compressor for ArF excimer laser was studied. This all solid state pulse power module can replace the commonly used thyratron switch. The thyristor and magnetic core used were both domestic products. The rise time of a high voltage pulse was compressed from 5 μs to 150 ns. Output energy of 0.35 J to 0.68 J and voltage of 10 kV to 14 kV were obtained. The energy transfer efficiency of the three-stage magnetic pulse compressor was 35%. At last, the reason for low efficiency was discussed and several measures were provided to improve the energy transfer efficiency.
A thyristor switched three-stage magnetic pulse compressor for ArF excimer laser was studied. This all solid state pulse power module can replace the commonly used thyratron switch. The thyristor and magnetic core used were both domestic products. The rise time of a high voltage pulse was compressed from 5 μs to 150 ns. Output energy of 0.35 J to 0.68 J and voltage of 10 kV to 14 kV were obtained. The energy transfer efficiency of the three-stage magnetic pulse compressor was 35%. At last, the reason for low efficiency was discussed and several measures were provided to improve the energy transfer efficiency.
