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RSS2009 Vol. 21, No. 08
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2009,
21.
Abstract:
Theoretical analyses have been done on the cross correlation between pulses of the femtosecond laser sequence. Experimental results are also derived using a cross-correlation setup, which can be switched between intensity cross-correlation mode and interferometric cross-correlation mode. The results show that the pattern of adjacent pulses cross-correlation is similar to that of auto-correlation. In the future, the method can be used in advanced light sources based electron accelerators to stabilize signals and to locate the cavity mirror precisely.
Theoretical analyses have been done on the cross correlation between pulses of the femtosecond laser sequence. Experimental results are also derived using a cross-correlation setup, which can be switched between intensity cross-correlation mode and interferometric cross-correlation mode. The results show that the pattern of adjacent pulses cross-correlation is similar to that of auto-correlation. In the future, the method can be used in advanced light sources based electron accelerators to stabilize signals and to locate the cavity mirror precisely.
2009,
21.
Abstract:
By using the Compton scattering theory, the generation of picosecond pulses of terahertz radiation has been studied, including the photon yield and radiant power. The results show that picosecond pulses of terahertz radiation are expected to be produced by Compton scattering of microwave photons interacting with electron bunches. The photon yield of a single electron is in direct proportion to the microwave power and wavelength, and in inverse proportion to the sectional area of microwave beam. The radiant power of a single electron is in direct proportion to the microwave power and the square of electron’s Lorentz factor, and in inverse proportion to the sectional area of microwave beam. The photon yield of electron bunch is in direct proportion to the squares of microwave power and wave
By using the Compton scattering theory, the generation of picosecond pulses of terahertz radiation has been studied, including the photon yield and radiant power. The results show that picosecond pulses of terahertz radiation are expected to be produced by Compton scattering of microwave photons interacting with electron bunches. The photon yield of a single electron is in direct proportion to the microwave power and wavelength, and in inverse proportion to the sectional area of microwave beam. The radiant power of a single electron is in direct proportion to the microwave power and the square of electron’s Lorentz factor, and in inverse proportion to the sectional area of microwave beam. The photon yield of electron bunch is in direct proportion to the squares of microwave power and wave
2009,
21.
Abstract:
An optical limiter has been designed based on the step ring grating. The intensity distribution of a beam transmitting through the limiter was derived theoretically and simulated, and the changes rules of intensity distribution with grating indexes were analyzed in numerical methods. The simulation results show that this grating is a kind of blazed grating, and the incident energy would mainly distribute on one or two wide light rings apart from the aperture center for the limiter with suitable indexes. The light ring position is determined by grating depth step and period. It changes in period when the depth step increases, and the lightest ring position is independent of incident wavelengths if suitable indexes are selected, which is useful for designing effective multiband limiters.
An optical limiter has been designed based on the step ring grating. The intensity distribution of a beam transmitting through the limiter was derived theoretically and simulated, and the changes rules of intensity distribution with grating indexes were analyzed in numerical methods. The simulation results show that this grating is a kind of blazed grating, and the incident energy would mainly distribute on one or two wide light rings apart from the aperture center for the limiter with suitable indexes. The light ring position is determined by grating depth step and period. It changes in period when the depth step increases, and the lightest ring position is independent of incident wavelengths if suitable indexes are selected, which is useful for designing effective multiband limiters.
2009,
21.
Abstract:
The influence of the position of acoustic-optic Q-switch on the output pulse stability is analyzed by calculating the misalignment sensitivity of cavity mirrors. The theoretical results show placing the acoustic-optic Q-switch crystal near the output mirror can improve the stability of pulse train. The peak power of several tens of kilo-watt is achieved in fundamental mode. Using BBO crystal for fourth harmonic generation, a laser power of 1.9 W in ultraviolet is experimentally realized.
The influence of the position of acoustic-optic Q-switch on the output pulse stability is analyzed by calculating the misalignment sensitivity of cavity mirrors. The theoretical results show placing the acoustic-optic Q-switch crystal near the output mirror can improve the stability of pulse train. The peak power of several tens of kilo-watt is achieved in fundamental mode. Using BBO crystal for fourth harmonic generation, a laser power of 1.9 W in ultraviolet is experimentally realized.
2009,
21.
Abstract:
Wind lidar based on Fizeau interferometer is developed, two wind inversion algorithms are presented as well. The two wind inversion algorithms are analyzed respectively, the results show: when the wind is slow, the two algorithms have the same precision, but Gaussian fitting method has faster convergence and less effect from signal noise ratio of the fringe than maximum likelihood method; when the wind is fast, the Gaussian fitting method will cause large wind error because part of the fringe doesn’t illuminate the detector, the maximum likelihood method is preferred in this case. Hence the two algorithms are used to invert the wind speed respectively according to the estimated wind speed. Using the lidar system and the wind inversion algorithms, wind speed profile at altitudes below 1.5
Wind lidar based on Fizeau interferometer is developed, two wind inversion algorithms are presented as well. The two wind inversion algorithms are analyzed respectively, the results show: when the wind is slow, the two algorithms have the same precision, but Gaussian fitting method has faster convergence and less effect from signal noise ratio of the fringe than maximum likelihood method; when the wind is fast, the Gaussian fitting method will cause large wind error because part of the fringe doesn’t illuminate the detector, the maximum likelihood method is preferred in this case. Hence the two algorithms are used to invert the wind speed respectively according to the estimated wind speed. Using the lidar system and the wind inversion algorithms, wind speed profile at altitudes below 1.5
2009,
21.
Abstract:
An all-fiber supercontinuum generation system has been demonstrated. In the system, a short matching fiber was used to reduce the loss in the connection of the gain fibers and the photonic crystal fiber, and real-time measurement was carried out in the splicing stage to minimize the loss. Such techniques ensure a whole system conversion efficiency of 76% and a good beam quality. The broadening process was analyzed experimentally and interpreted as follows. More broadened spectrum lies in the long wavelength region rather than in the short wavelength one, which indicates that Raman effect and self-phase-modulation dominate the initial broadening process. Meanwhile, Raman-Stocks peaks were obvious. As the broadening developing, the phase matched parametric four-wave mixing begins to occur, a
An all-fiber supercontinuum generation system has been demonstrated. In the system, a short matching fiber was used to reduce the loss in the connection of the gain fibers and the photonic crystal fiber, and real-time measurement was carried out in the splicing stage to minimize the loss. Such techniques ensure a whole system conversion efficiency of 76% and a good beam quality. The broadening process was analyzed experimentally and interpreted as follows. More broadened spectrum lies in the long wavelength region rather than in the short wavelength one, which indicates that Raman effect and self-phase-modulation dominate the initial broadening process. Meanwhile, Raman-Stocks peaks were obvious. As the broadening developing, the phase matched parametric four-wave mixing begins to occur, a
2009,
21.
Abstract:
Based on the numerical modeling including stimulated Brillouin scattering and stimulated Raman scattering, the propagation-rate equations of ytterbium-doped double-clad fiber amplifiers are solved. The output characteristics of the high-power backward-pumped ytterbium-doped double-clad fiber amplifiers are studied at different signal linewidths, fiber lengths and fiber-core diameters. The methods of suppressing the stimulated Brillouin scattering and stimulated Raman scattering are also investigated. Calculated results show that the two-scatterings can be suppressed simultaneously by using an ytterbium-doped fiber with the length shorter than 0.68 m and the fiber-core diameter larger than 26 μm, or broadening the signal linewidth to more than 0.04 nm.
Based on the numerical modeling including stimulated Brillouin scattering and stimulated Raman scattering, the propagation-rate equations of ytterbium-doped double-clad fiber amplifiers are solved. The output characteristics of the high-power backward-pumped ytterbium-doped double-clad fiber amplifiers are studied at different signal linewidths, fiber lengths and fiber-core diameters. The methods of suppressing the stimulated Brillouin scattering and stimulated Raman scattering are also investigated. Calculated results show that the two-scatterings can be suppressed simultaneously by using an ytterbium-doped fiber with the length shorter than 0.68 m and the fiber-core diameter larger than 26 μm, or broadening the signal linewidth to more than 0.04 nm.
2009,
21.
Abstract:
Airborne molecular contaminations inside a high power laser facility are studied. Air samples of suspected locations are collected by special air-sampling facilities before and after laser launch. Extraction and concentration measurement of the main airborne molecules, including halogens, sulphur compounds, ammonia and soluble amines and hydrocarbons (C6～C16) are made during the sampling progress. The trace analysis suggests that the concentrations of most species except sulphur compounds, especially ammonia, soluble amines and hydrocarbons，exceed the suggested upper control limit of US NIF reference. The concentrations of halogens, sulphur compounds, ammonia and soluble amines after laser launch are lower than that before launch while the concentrations of hydrocar
Airborne molecular contaminations inside a high power laser facility are studied. Air samples of suspected locations are collected by special air-sampling facilities before and after laser launch. Extraction and concentration measurement of the main airborne molecules, including halogens, sulphur compounds, ammonia and soluble amines and hydrocarbons (C6～C16) are made during the sampling progress. The trace analysis suggests that the concentrations of most species except sulphur compounds, especially ammonia, soluble amines and hydrocarbons，exceed the suggested upper control limit of US NIF reference. The concentrations of halogens, sulphur compounds, ammonia and soluble amines after laser launch are lower than that before launch while the concentrations of hydrocar
2009,
21.
Abstract:
High frequencies beyond the cut-off frequency could pass through imaging systems after spectrum shifting, which is one of high resolution imaging technologies. The effect of this technology is obvious but difficult to achieve. To verify its feasibility and provide references for practical application, an experimental scheme has been put forward. In this scheme, the stripe field of laser interference is replaced by a cosine grating, and the imaging system is constituted by a CCD camera and a one-dimensional low-pass filter implemented by software. For the stripe field has to be moved several times equidistantly in one cycle, in this scheme, the motion of the stripe field is replaced by the translation of the cosine grating. During the experiment, the cosine grating was translated four times
High frequencies beyond the cut-off frequency could pass through imaging systems after spectrum shifting, which is one of high resolution imaging technologies. The effect of this technology is obvious but difficult to achieve. To verify its feasibility and provide references for practical application, an experimental scheme has been put forward. In this scheme, the stripe field of laser interference is replaced by a cosine grating, and the imaging system is constituted by a CCD camera and a one-dimensional low-pass filter implemented by software. For the stripe field has to be moved several times equidistantly in one cycle, in this scheme, the motion of the stripe field is replaced by the translation of the cosine grating. During the experiment, the cosine grating was translated four times
2009,
21.
Abstract:
Stimulated emission has been observed from porous silicon formed by irradiation and annealing when optically excited by a 514 nm laser. When the excitation intensity exceeded a threshold, very sharp peaks emerged in the emission spectra from 650～750 nm. The full width at half maximum(FWHM) of the emission park with Lorentzian shape is less than 0.5 nm. The sample has a special oxide structure which was fabricated by laser irradiation and annealing treatment on silicon. In the Fourier transform infrared spectroscopy(FTIR), some peaks emerge due to Si=O bonds and Si－O－Si bonds in the oxidation porous structure.Calculation shows that trap electronic states appear in the band gap of the smaller nanocrystal when double bonds or bridge bonds are formed between silicon and oxygen. The stimulat
Stimulated emission has been observed from porous silicon formed by irradiation and annealing when optically excited by a 514 nm laser. When the excitation intensity exceeded a threshold, very sharp peaks emerged in the emission spectra from 650～750 nm. The full width at half maximum(FWHM) of the emission park with Lorentzian shape is less than 0.5 nm. The sample has a special oxide structure which was fabricated by laser irradiation and annealing treatment on silicon. In the Fourier transform infrared spectroscopy(FTIR), some peaks emerge due to Si=O bonds and Si－O－Si bonds in the oxidation porous structure.Calculation shows that trap electronic states appear in the band gap of the smaller nanocrystal when double bonds or bridge bonds are formed between silicon and oxygen. The stimulat
2009,
21.
Abstract:
Energy exchange efficiency of clustering electron beams passing through a cylindrical coaxial TM812 mode cavity resonator is studied, as well as the extraction method of microwave energy from the cavity resonator. The feasibility of the cavity resonator being used as the output cavity of the millimeter wave multi-beam klystron is also demonstrated. The results show that the energy exchange efficiency can reach 3.29% for ideal clustering electron beams and 1.84% for general beams. It is found that microwave energy could be extracted from the cavity resonator by coupling the cavity resonator with an axial coaxial-line. When working frequency of the output cavity is 100.945 GHz and the external quality factor equals to 2 243, the maximal output power can be up to 15 kW according to
Energy exchange efficiency of clustering electron beams passing through a cylindrical coaxial TM812 mode cavity resonator is studied, as well as the extraction method of microwave energy from the cavity resonator. The feasibility of the cavity resonator being used as the output cavity of the millimeter wave multi-beam klystron is also demonstrated. The results show that the energy exchange efficiency can reach 3.29% for ideal clustering electron beams and 1.84% for general beams. It is found that microwave energy could be extracted from the cavity resonator by coupling the cavity resonator with an axial coaxial-line. When working frequency of the output cavity is 100.945 GHz and the external quality factor equals to 2 243, the maximal output power can be up to 15 kW according to
2009,
21.
Abstract:
This article has put forward a numerical method which could compute dispersion curves in an arbitrary coaxial periodic slow-wave structure, based on field-matching method and Fourier series theory. This numerical method has strong universality and expansibility in designing slow-wave structures. Using this numerical method, the dispersion curves of the coaxial sinusoidal ripple waveguide and the coaxial dual sinusoidal ripples waveguide were computed by programming Matlab codes, and their dispersion characteristics were analyzed and discussed. The dispersion curves of the coaxial disk-loaded waveguide were computed by this numerical method as an example. The numerical results were compared with the simulated results of a multidimensional full electromagnetic software, and the reliability o
This article has put forward a numerical method which could compute dispersion curves in an arbitrary coaxial periodic slow-wave structure, based on field-matching method and Fourier series theory. This numerical method has strong universality and expansibility in designing slow-wave structures. Using this numerical method, the dispersion curves of the coaxial sinusoidal ripple waveguide and the coaxial dual sinusoidal ripples waveguide were computed by programming Matlab codes, and their dispersion characteristics were analyzed and discussed. The dispersion curves of the coaxial disk-loaded waveguide were computed by this numerical method as an example. The numerical results were compared with the simulated results of a multidimensional full electromagnetic software, and the reliability o
2009,
21.
Abstract:
According to the electromagnetic theory, permeating depth of the 2 450 MHz microwave in homogeneous media is analyzed. A nonlinear heat transfer model is applied to predict the temperature variation in biotissues under the microwave irradiation. Based on the thermal images measured by an far-infrared imager, the heat penetration of multi-layered homogeneous medium simulating biomaterial is studied. The experimental results show the difference between permeating depth and heat penetration. The heat penetration is mainly related to the power of microwave antenna, distance between antenna and biomaterial, and duration of irradiation, etc. Adopting high power microwave, long irradiation duration or close distance can enhance heat penetration in the human body.
According to the electromagnetic theory, permeating depth of the 2 450 MHz microwave in homogeneous media is analyzed. A nonlinear heat transfer model is applied to predict the temperature variation in biotissues under the microwave irradiation. Based on the thermal images measured by an far-infrared imager, the heat penetration of multi-layered homogeneous medium simulating biomaterial is studied. The experimental results show the difference between permeating depth and heat penetration. The heat penetration is mainly related to the power of microwave antenna, distance between antenna and biomaterial, and duration of irradiation, etc. Adopting high power microwave, long irradiation duration or close distance can enhance heat penetration in the human body.
2009,
21.
Abstract:
Based on the mode coupling theory,the built in TE03-TE02-TE01 mode converter of the 3 mm band second-harmonic complex cavity gyrotron is studied. Adopting the structure of corrugated waveguide with tapered radius and different phase rematch techniques, reliable optimal geometry parameters can be obtained. The corrugated waveguide mode converter of 94 GHz gyrotron is designed with compact structure and high efficiency, and the burned patterns measured at the ends of the converter are produced by the gyrotron and indicates good expected mode TE01．
Based on the mode coupling theory,the built in TE03-TE02-TE01 mode converter of the 3 mm band second-harmonic complex cavity gyrotron is studied. Adopting the structure of corrugated waveguide with tapered radius and different phase rematch techniques, reliable optimal geometry parameters can be obtained. The corrugated waveguide mode converter of 94 GHz gyrotron is designed with compact structure and high efficiency, and the burned patterns measured at the ends of the converter are produced by the gyrotron and indicates good expected mode TE01．
2009,
21.
Abstract:
The propagation characteristic in mixture atmosphere of high power microwave is presented based on atmosphere polarization intensity superposition. By deducing dielectric constant of mixture atmosphere, the refractive index and attenuation coefficient of high power microwave propagation in mixture atmosphere are obtained. It can be found through research that the mixture atmosphere is a quick changed dispersing and lossy medium. The microwave pulse widen effect and propagation veloctiy induced by the dispersion characteristics of mixture atmosphere are researched, and the pulse shorten effect induced by the lossy characteristics of mixture atmosphere is analyzed. All the conclusions is self-consistent developed to the propagation theory of troposphere or ionosphere.
The propagation characteristic in mixture atmosphere of high power microwave is presented based on atmosphere polarization intensity superposition. By deducing dielectric constant of mixture atmosphere, the refractive index and attenuation coefficient of high power microwave propagation in mixture atmosphere are obtained. It can be found through research that the mixture atmosphere is a quick changed dispersing and lossy medium. The microwave pulse widen effect and propagation veloctiy induced by the dispersion characteristics of mixture atmosphere are researched, and the pulse shorten effect induced by the lossy characteristics of mixture atmosphere is analyzed. All the conclusions is self-consistent developed to the propagation theory of troposphere or ionosphere.
2009,
21.
Abstract:
With three-dimensional particle simulation software, a new type of 18 vane 5.8 GHz magnetron has been simulated. The differences between explosive emission and beam emission are compared. Using beam emission models, the influence to the magnetron characteristics by the cathode current destiny can be obtained. At the same time, the magnetic field distribution can be obtained using simulation software FEMM. On this basis, hot test simulation has been performed under non-uniform magnetic field condition. With the research provides a basis for developing 18 vane 5.8 GHz magnetron.
With three-dimensional particle simulation software, a new type of 18 vane 5.8 GHz magnetron has been simulated. The differences between explosive emission and beam emission are compared. Using beam emission models, the influence to the magnetron characteristics by the cathode current destiny can be obtained. At the same time, the magnetic field distribution can be obtained using simulation software FEMM. On this basis, hot test simulation has been performed under non-uniform magnetic field condition. With the research provides a basis for developing 18 vane 5.8 GHz magnetron.
2009,
21.
Abstract:
The propagation of the high power electromagnetic pulse has been numerically simulated in the whole ionosphere. Using the shortened ionosphere profile, the equations of high power electromagnetic pulse propagating in the cold plasma could describe the high power electromagnetic pulse propagating in the ionosphere. The perfect match layer(PML) boundary condition was adopted. The finite difference time domain(FDTD) method for solving this problem would waste great time and memory. Therefore, the pseudospectral time-domain(PSTD) method was used to solve the equations of cold plasma. The data of propagation of the high power electromagnetic pulse in the whole ionosphere acquired by this method accords with the result of (FD)2TD numerical modeling, which demonstrates the validity of PSTD algori
The propagation of the high power electromagnetic pulse has been numerically simulated in the whole ionosphere. Using the shortened ionosphere profile, the equations of high power electromagnetic pulse propagating in the cold plasma could describe the high power electromagnetic pulse propagating in the ionosphere. The perfect match layer(PML) boundary condition was adopted. The finite difference time domain(FDTD) method for solving this problem would waste great time and memory. Therefore, the pseudospectral time-domain(PSTD) method was used to solve the equations of cold plasma. The data of propagation of the high power electromagnetic pulse in the whole ionosphere acquired by this method accords with the result of (FD)2TD numerical modeling, which demonstrates the validity of PSTD algori
2009,
21.
Abstract:
A method of radar cross section(RCS) reduction of microstrip printed dipole antenna with a uniplanar compact-EBG(UC-EBG) ground plane is proposed. Owing to its stop-band property, the proposed UC-EBG can be used as the ground plane of a microstrip printed dipole antenna. During the pass-band, the proposed UC-EBG make much more plane electromagnetic wave pass through. The simulated and measured results show that the proposed UC-EBG ground can effectively reduce the RCS of microstrip printed dipole antenna outside operating band, while its radiation is hardly affected by the proposed UC-EBG ground in the operating band.
A method of radar cross section(RCS) reduction of microstrip printed dipole antenna with a uniplanar compact-EBG(UC-EBG) ground plane is proposed. Owing to its stop-band property, the proposed UC-EBG can be used as the ground plane of a microstrip printed dipole antenna. During the pass-band, the proposed UC-EBG make much more plane electromagnetic wave pass through. The simulated and measured results show that the proposed UC-EBG ground can effectively reduce the RCS of microstrip printed dipole antenna outside operating band, while its radiation is hardly affected by the proposed UC-EBG ground in the operating band.
2009,
21.
Abstract:
The diffractive optical element is one of the main solutions to achieve uniform illumination, which is achieved through the pure phase element. There are sub-diffraction spots because of the discontinuity of pure phase element, which makes the beam lose 15% or more energy. Thus a diffractive-refractive method based on the traditional input-output algorithm is developed to design the diffractive optical element. This method makes part of a diffractive optical element continuous in phase, which reduces the light intensity in the discontinuous region of the element, therefore reduces the intensity of sub-diffraction spots. Through studying the influence of spherical phase factor on output light intensity, the phase parameter can be optimized to increase the diffraction efficiency of the incid
The diffractive optical element is one of the main solutions to achieve uniform illumination, which is achieved through the pure phase element. There are sub-diffraction spots because of the discontinuity of pure phase element, which makes the beam lose 15% or more energy. Thus a diffractive-refractive method based on the traditional input-output algorithm is developed to design the diffractive optical element. This method makes part of a diffractive optical element continuous in phase, which reduces the light intensity in the discontinuous region of the element, therefore reduces the intensity of sub-diffraction spots. Through studying the influence of spherical phase factor on output light intensity, the phase parameter can be optimized to increase the diffraction efficiency of the incid
2009,
21.
Abstract:
The paper presents a kind of researching PCM of gallium-based alloy material with high heat conductance, low volume variation rate in solid-to-liquid phase and low linear expansion coefficients. In the laboratory the actual conditions are simulated to test the PCM samples, which confirms that a group of PCM samples of gallium alloy material can meet the basic need. Then, the finite element method is used to simulate the performance of PCM under actual application condition. The results show that in the vacuum insulation conditions and at 298 K original temperature the developed gallium-based alloy PCM can help to control the mirror temperature below 313 K and control thermal distortion of the mirrors.
The paper presents a kind of researching PCM of gallium-based alloy material with high heat conductance, low volume variation rate in solid-to-liquid phase and low linear expansion coefficients. In the laboratory the actual conditions are simulated to test the PCM samples, which confirms that a group of PCM samples of gallium alloy material can meet the basic need. Then, the finite element method is used to simulate the performance of PCM under actual application condition. The results show that in the vacuum insulation conditions and at 298 K original temperature the developed gallium-based alloy PCM can help to control the mirror temperature below 313 K and control thermal distortion of the mirrors.
2009,
21.
Abstract:
The spatial pattern and spectrum of transition radiation have been measured at the normal direction from the rear surfaces of targets, employing an optical CCD camera and an OMA optical multichannel spectrometer on the 100 TW femtosecond laser facility.The spatial pattern presents a cirque shape, and the region of optical radiation has larger radiation angle and optical intensity distribution. The spectrum of transition radiation presents a sharp peak in the vicinity of 800 nm, which is the laser basic harmonic. That is the result of the coherent transition radiation generated by microbunches of hot electron beams produced in transport. The main acceleration of hot electrons comes from resonance absorption．
The spatial pattern and spectrum of transition radiation have been measured at the normal direction from the rear surfaces of targets, employing an optical CCD camera and an OMA optical multichannel spectrometer on the 100 TW femtosecond laser facility.The spatial pattern presents a cirque shape, and the region of optical radiation has larger radiation angle and optical intensity distribution. The spectrum of transition radiation presents a sharp peak in the vicinity of 800 nm, which is the laser basic harmonic. That is the result of the coherent transition radiation generated by microbunches of hot electron beams produced in transport. The main acceleration of hot electrons comes from resonance absorption．
2009,
21.
Abstract:
A synthesis procedure of ZrO2 colloids derived from the acid-alkali two-step catalyzed hydrolysis was disclosed. The granularity and its distribution of the colloid particles were measured.Then a ZrO2 film was prepared by the spin-coating method on K9 glass. Physical properties of the thin film were characterized by ellipsometer, UV-Vis spectrophotometer, and Fourier transform infrared spectrometer. The refractive index of the coating with the two-step method was 1.74, and the laser damage threshold was 9.0 J/cm2 at 1 064 nm fundametal wavelength and 1 ns pulse duration.The measured and experimental results indicate that the two-step method have advantages over single step ones.
A synthesis procedure of ZrO2 colloids derived from the acid-alkali two-step catalyzed hydrolysis was disclosed. The granularity and its distribution of the colloid particles were measured.Then a ZrO2 film was prepared by the spin-coating method on K9 glass. Physical properties of the thin film were characterized by ellipsometer, UV-Vis spectrophotometer, and Fourier transform infrared spectrometer. The refractive index of the coating with the two-step method was 1.74, and the laser damage threshold was 9.0 J/cm2 at 1 064 nm fundametal wavelength and 1 ns pulse duration.The measured and experimental results indicate that the two-step method have advantages over single step ones.
2009,
21.
Abstract:
Based on small-signal gain formula and Fresnel reflection formula, the parasitic amplified cavities of two high power laser facilities are studied. The two facilities, facility A and facility B, have similar configuration of beam path and parasitic amplified cavities. The possibilities are analyzed that some part of the assembly could form optical oscillator and parasitic oscillation might occur. According to the experiment on facility A, it is concluded that parasitic oscillation will possibly occur in the 3rd parasitic amplified cavity of facility B. Inserting polarizing disk can control the parasitic oscillation in facility B.
Based on small-signal gain formula and Fresnel reflection formula, the parasitic amplified cavities of two high power laser facilities are studied. The two facilities, facility A and facility B, have similar configuration of beam path and parasitic amplified cavities. The possibilities are analyzed that some part of the assembly could form optical oscillator and parasitic oscillation might occur. According to the experiment on facility A, it is concluded that parasitic oscillation will possibly occur in the 3rd parasitic amplified cavity of facility B. Inserting polarizing disk can control the parasitic oscillation in facility B.
2009,
21.
Abstract:
Based on the collisional radiative model from the flexible atomic code, X-ray emission spectra for L-shell of Li-like oxygen plasma consisting of three kinds of oxygen ions (Li-like oxygen ion and another two neighboring ions) are simulated. Atomic processes in the model include dielectronic recombination(DR), radiative recombination(RR), collisional ionization(CI) and resonance excitation(RE) from the neighbouring ion charge states of the target ion (Li-like oxygen ion). It is found that DR, RR, CI and RE, other than direct collisional excitation, are very important processes by analyzing the contribution of different atomic processes to the X-ray spectum. In addition, the relationship between X-ray wavelengths, relatively radiative intensity and the electronic temperature can be seen fro
Based on the collisional radiative model from the flexible atomic code, X-ray emission spectra for L-shell of Li-like oxygen plasma consisting of three kinds of oxygen ions (Li-like oxygen ion and another two neighboring ions) are simulated. Atomic processes in the model include dielectronic recombination(DR), radiative recombination(RR), collisional ionization(CI) and resonance excitation(RE) from the neighbouring ion charge states of the target ion (Li-like oxygen ion). It is found that DR, RR, CI and RE, other than direct collisional excitation, are very important processes by analyzing the contribution of different atomic processes to the X-ray spectum. In addition, the relationship between X-ray wavelengths, relatively radiative intensity and the electronic temperature can be seen fro
2009,
21.
Abstract:
Molar concentration ratios of citric acid to Ca2+ affect properties of CaMnO3 powders. In this paper, CaMnO3 gel was prepared through the sol-gel method with deionized water and ethylene glycol as solvent, different ratios of citric acid as chelate, and metal nitrates as starting materials. Perovskite polycrystalline CaMnO3 powders were prepared via calcining the dry gel,and were analyzed with XRD, SEM and Marlvern granularity analyzer. The results show that the crystal size ranges from 20 to 50 nm, and the resulting perovskite CaMnO3 powders are flat-shaped granules of about 300～500 nm. The granularity and crystal size of the CaMnO3 powders increase slightly with the increase of the molar concentration ratio．
Molar concentration ratios of citric acid to Ca2+ affect properties of CaMnO3 powders. In this paper, CaMnO3 gel was prepared through the sol-gel method with deionized water and ethylene glycol as solvent, different ratios of citric acid as chelate, and metal nitrates as starting materials. Perovskite polycrystalline CaMnO3 powders were prepared via calcining the dry gel,and were analyzed with XRD, SEM and Marlvern granularity analyzer. The results show that the crystal size ranges from 20 to 50 nm, and the resulting perovskite CaMnO3 powders are flat-shaped granules of about 300～500 nm. The granularity and crystal size of the CaMnO3 powders increase slightly with the increase of the molar concentration ratio．
2009,
21.
Abstract:
In this paper a full density matrix treatment is adopted to deal with the interaction between long-pulse, circularly-polarized light and the sodium atoms. The time evolution curve of each of the 24 sub-state’s population probability can be obtained by solving the Bloch equation of twenty-four hyperfine levels. It is found that during the long pulse time(more than 100 ns), the final transition is only between the sub-level 3S1/2(2,2) and 3P/3/2 and the probability of the excited sub-state has become steady. Comparison between the 2-level model and the full density matrix method proves the rationality of rate equation and the simplicity of 2-level model for the long pulse, circularly-polarized light.
In this paper a full density matrix treatment is adopted to deal with the interaction between long-pulse, circularly-polarized light and the sodium atoms. The time evolution curve of each of the 24 sub-state’s population probability can be obtained by solving the Bloch equation of twenty-four hyperfine levels. It is found that during the long pulse time(more than 100 ns), the final transition is only between the sub-level 3S1/2(2,2) and 3P/3/2 and the probability of the excited sub-state has become steady. Comparison between the 2-level model and the full density matrix method proves the rationality of rate equation and the simplicity of 2-level model for the long pulse, circularly-polarized light.
2009,
21.
Abstract:
The field-pattern of various defect modes in the coaxial photonic crystal microcavity has been simulated using the numerical calculation method. The quality factor (Q-factor) and power loss of the microcavity have been calculated and the effect of geometrical parameters on the resonance characters was analyzed. Based on the defect microcavity, a periodic slow-wave system was constructed and the dispersion relation of this system has been discussed. The results indicate that a single defect mode can be gained in the microcavity and the resonance characters are sensitively affected by the longitudinal length of the cavity and the dielectric constant of medium rings. The slow-wave system has presented a good dispersion property and a relatively smooth slow-wave ratio curve with a wide range o
The field-pattern of various defect modes in the coaxial photonic crystal microcavity has been simulated using the numerical calculation method. The quality factor (Q-factor) and power loss of the microcavity have been calculated and the effect of geometrical parameters on the resonance characters was analyzed. Based on the defect microcavity, a periodic slow-wave system was constructed and the dispersion relation of this system has been discussed. The results indicate that a single defect mode can be gained in the microcavity and the resonance characters are sensitively affected by the longitudinal length of the cavity and the dielectric constant of medium rings. The slow-wave system has presented a good dispersion property and a relatively smooth slow-wave ratio curve with a wide range o
2009,
21.
Abstract:
Solid-state modulators based on power MOSFETs are promising pulsed power sources in producing high-voltage fast pulses with the pulse width agility in megahertz repetition rate. A solid-state modulator with 9 modules, each with 6 power MOSFETs in parallel, was designed and tested. The 9 modules were stacked in an inductive-adder configuration. The output voltage with amplitude of 6.2 kV, rise time of 20 ns and pulse width of 110 ns was achieved under 720 V charging voltage and 51 Ω resistance load in 2.5 MHz repetition rate.
Solid-state modulators based on power MOSFETs are promising pulsed power sources in producing high-voltage fast pulses with the pulse width agility in megahertz repetition rate. A solid-state modulator with 9 modules, each with 6 power MOSFETs in parallel, was designed and tested. The 9 modules were stacked in an inductive-adder configuration. The output voltage with amplitude of 6.2 kV, rise time of 20 ns and pulse width of 110 ns was achieved under 720 V charging voltage and 51 Ω resistance load in 2.5 MHz repetition rate.
2009,
21.
Abstract:
A UV illuminated switch of three sections in series was designed based on UV illumination technology and capacitance-resistance coupling circuit. The switch consists of UV illumination gap and self-breakdown gaps. The distance of self-breakdown gap was calculated based on the experimental data of same switch under pulse with 240 ns risetime. The nonuniform factor of self-breakdown gap is 1.58. The step shield of outer cylinder was used to get the surface field no more than 50 kV/cm. The voltage of UV illumination gap was designed as about 1% of the voltage of self-breakdown gap. It was indicated that the voltage of UV illumination gap is higher than breakdown voltage of rod-rod electrode within 0.1～0.7 MPa.
A UV illuminated switch of three sections in series was designed based on UV illumination technology and capacitance-resistance coupling circuit. The switch consists of UV illumination gap and self-breakdown gaps. The distance of self-breakdown gap was calculated based on the experimental data of same switch under pulse with 240 ns risetime. The nonuniform factor of self-breakdown gap is 1.58. The step shield of outer cylinder was used to get the surface field no more than 50 kV/cm. The voltage of UV illumination gap was designed as about 1% of the voltage of self-breakdown gap. It was indicated that the voltage of UV illumination gap is higher than breakdown voltage of rod-rod electrode within 0.1～0.7 MPa.
2009,
21.
Abstract:
A compact 40 kW/10 kV digital control constant-current capacitor charging power supply(CCPS )has been developed based on the series resonance and high frequency inverter technologies. The logical design of resonant parameters and the high frequency high voltage transformer was adopted and the power density of 0.5 MW/m3 was achieved. The protection technology of the CCPS was studied, and the performance of the CCPS was improved by using multiple protecting techniques and safeguards. A scheme of remote control and parallel operation of the power supply was introduced. Some experimental results were given with a 1 MJ/10 kV capacitive load.
A compact 40 kW/10 kV digital control constant-current capacitor charging power supply(CCPS )has been developed based on the series resonance and high frequency inverter technologies. The logical design of resonant parameters and the high frequency high voltage transformer was adopted and the power density of 0.5 MW/m3 was achieved. The protection technology of the CCPS was studied, and the performance of the CCPS was improved by using multiple protecting techniques and safeguards. A scheme of remote control and parallel operation of the power supply was introduced. Some experimental results were given with a 1 MJ/10 kV capacitive load.
2009,
21.
Abstract:
The design of the fast kicker prototype magnet for China Spallation Neutron Source(CSNS) rapid cycling synchronous(RCS) extraction has been introduced. Single-turn structure of SNS in U.S. was adopted for magnet power supply research difficulties and operation reliability. The choice for material of iron core, all the structure design and the method of collimation for the magnet were also described. Simulation results of Opera show that when the length of the core is 220 mm, the effective magnetic length is about 302 mm and the maximal magnetic density is around 0.215 T at four interior angles. Corresponding field uniformity is within 0.8% in the area of 133 mm×200 mm. Theoretical analysis and program simulation of Opera have verified the feasibility of magnet basic structure.
The design of the fast kicker prototype magnet for China Spallation Neutron Source(CSNS) rapid cycling synchronous(RCS) extraction has been introduced. Single-turn structure of SNS in U.S. was adopted for magnet power supply research difficulties and operation reliability. The choice for material of iron core, all the structure design and the method of collimation for the magnet were also described. Simulation results of Opera show that when the length of the core is 220 mm, the effective magnetic length is about 302 mm and the maximal magnetic density is around 0.215 T at four interior angles. Corresponding field uniformity is within 0.8% in the area of 133 mm×200 mm. Theoretical analysis and program simulation of Opera have verified the feasibility of magnet basic structure.
2009,
21.
Abstract:
With nanosecond voltage pulses produced by a fast Marx generator, breakdown experiments of gas switches under a number of pulse voltages have been carried out. Corresponding breakdown voltage，breakdown delay and jitter were acquired for the switches under different pressures. The characteristics as how breakdown voltage and delay vary with operating pressure were summarized. The demand of gas switch as how different application was also presented．
With nanosecond voltage pulses produced by a fast Marx generator, breakdown experiments of gas switches under a number of pulse voltages have been carried out. Corresponding breakdown voltage，breakdown delay and jitter were acquired for the switches under different pressures. The characteristics as how breakdown voltage and delay vary with operating pressure were summarized. The demand of gas switch as how different application was also presented．
2009,
21.
Abstract:
The metallized film capacitor is one of the most important components of the inertial confinement fusion(ICF) facility. The reliability of the capacitor greatly influences the reliability and operational cost of the whole facility. Based on the analysis of the failure mechanism of the capacitor, we model the degradation process with Wiener process. The time-to-failure distribution is derived. A reliability assessment method combining performance degradation data and lifetime data is proposed. A precision analysis is made for both the proposed method and degradation data based reliability assessment method, using the precision analysis approach given in this paper. Results show that the proposed method has a better precision compared with the degradation data based method.
The metallized film capacitor is one of the most important components of the inertial confinement fusion(ICF) facility. The reliability of the capacitor greatly influences the reliability and operational cost of the whole facility. Based on the analysis of the failure mechanism of the capacitor, we model the degradation process with Wiener process. The time-to-failure distribution is derived. A reliability assessment method combining performance degradation data and lifetime data is proposed. A precision analysis is made for both the proposed method and degradation data based reliability assessment method, using the precision analysis approach given in this paper. Results show that the proposed method has a better precision compared with the degradation data based method.
2009,
21.
Abstract:
The broadening of excimer laser pulses during amplification was analysed. To attain a shorter laser pulse, a compressing technique called pulse negative feedback was developed with the gain saturation switch applied to the amplification in an discharge pumping excimer laser.Combined with the echelon-free induced spatial incoherence technique, it can output shorter pulses with the beam uniformity maintained. A 100 mJ, 10 ns laser pulse was achieved in the LPX-150 excimer laser which acts as the laser source of the “heaven-Ⅰ” system. The spatial uniformity of the pulse remained within 3%.
The broadening of excimer laser pulses during amplification was analysed. To attain a shorter laser pulse, a compressing technique called pulse negative feedback was developed with the gain saturation switch applied to the amplification in an discharge pumping excimer laser.Combined with the echelon-free induced spatial incoherence technique, it can output shorter pulses with the beam uniformity maintained. A 100 mJ, 10 ns laser pulse was achieved in the LPX-150 excimer laser which acts as the laser source of the “heaven-Ⅰ” system. The spatial uniformity of the pulse remained within 3%.
