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RSS2010 Vol. 22, No. 12
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2010,
22.
Abstract:
Potassium dihydrogen phosphate (KDP) and its deuterated analog are the crystals primarily selected for Pockel’s cells or frequency conversion plates in inertial confinement fusion systems. Crystals rapidly grown from point seed by temperature reduction method are presented. The growth of large size crystals including the designation of big vessel, crystal holder and seed-planting under over-heating systems are introduced. Crystals with size up to 50 cm×50 cm×41 cm were obtained successfully. It is shown that crystals grown at rapid growth rate,15 mm/day the average, possess the optimal transmission properties as those grown by conventional method. The content of impurity ions, such as Fe3+, Cr3+, Al3+ that affect the prismatic faces of KDP are determined
Potassium dihydrogen phosphate (KDP) and its deuterated analog are the crystals primarily selected for Pockel’s cells or frequency conversion plates in inertial confinement fusion systems. Crystals rapidly grown from point seed by temperature reduction method are presented. The growth of large size crystals including the designation of big vessel, crystal holder and seed-planting under over-heating systems are introduced. Crystals with size up to 50 cm×50 cm×41 cm were obtained successfully. It is shown that crystals grown at rapid growth rate,15 mm/day the average, possess the optimal transmission properties as those grown by conventional method. The content of impurity ions, such as Fe3+, Cr3+, Al3+ that affect the prismatic faces of KDP are determined
2010,
22.
Abstract:
In order to study the damage mechanism of high reflectors in high power laser systems, laser damage experiments are carried out on fundamental frequency high reflectors which are widely used in high power laser systems, and then the typical morphologies are compared and analyzed by means of step profiler, scanning electron microscope and surface profiler. The results show that the laser resistance is enhanced because of the SiO2 overlayer; typical damage morphology of the sample without silica overlayer is delamination, which is related to the thermal characteristics of materials, and delamination grows quickly during the subsequent laser irradiation; typical damage morphology of the sample with silica overlayer is plasma ablation with a pit in its center, which is related to the thermal
In order to study the damage mechanism of high reflectors in high power laser systems, laser damage experiments are carried out on fundamental frequency high reflectors which are widely used in high power laser systems, and then the typical morphologies are compared and analyzed by means of step profiler, scanning electron microscope and surface profiler. The results show that the laser resistance is enhanced because of the SiO2 overlayer; typical damage morphology of the sample without silica overlayer is delamination, which is related to the thermal characteristics of materials, and delamination grows quickly during the subsequent laser irradiation; typical damage morphology of the sample with silica overlayer is plasma ablation with a pit in its center, which is related to the thermal
2010,
22.
Abstract:
The mechanism of radiative striations in spin-coated sol-gel silica antireflective films was analyzed. Several kinds of fluoroalkanol modified sols were prepared using the Stber method in order to improve the surface properties of the spin-coated films, especially the surface roughness. Surface morphologies of the films were observed using the Nomarski optical microscope and AFM, and quantitatively evaluated by surface roughness measurement. Results show that the striation defects are eliminated, and the surface roughness (RMS) of the coatings reduces from 4.55 nm to 1.00 nm after modification, while the antireflective properties show no apparent change. The films’ peak transmittance ranges from 99.60% to 99.89% with the laser damage threshold of 21.0 to 25.3 J/cm2.
The mechanism of radiative striations in spin-coated sol-gel silica antireflective films was analyzed. Several kinds of fluoroalkanol modified sols were prepared using the Stber method in order to improve the surface properties of the spin-coated films, especially the surface roughness. Surface morphologies of the films were observed using the Nomarski optical microscope and AFM, and quantitatively evaluated by surface roughness measurement. Results show that the striation defects are eliminated, and the surface roughness (RMS) of the coatings reduces from 4.55 nm to 1.00 nm after modification, while the antireflective properties show no apparent change. The films’ peak transmittance ranges from 99.60% to 99.89% with the laser damage threshold of 21.0 to 25.3 J/cm2.
2010,
22.
Abstract:
The pinhole closure phenomena in spatial filter of high power solidstate laser system might limit the output energy and affect the safe operation of the laser system. The distribution of plasma created by intense laser radiation is studied. The numerical simulation of one dimensional plasma distribution of three typical materials (Al, Au, C) is illustrated. The simulation demonstrates that the diffusion velocity of plasma is about 107 cm/s. The possibility of pinhole closure in the boost amplifier of SG Ⅲ plototype is analyzed, which indicates that the pinhole closure under long pulse laser irradiation is not negligible．
The pinhole closure phenomena in spatial filter of high power solidstate laser system might limit the output energy and affect the safe operation of the laser system. The distribution of plasma created by intense laser radiation is studied. The numerical simulation of one dimensional plasma distribution of three typical materials (Al, Au, C) is illustrated. The simulation demonstrates that the diffusion velocity of plasma is about 107 cm/s. The possibility of pinhole closure in the boost amplifier of SG Ⅲ plototype is analyzed, which indicates that the pinhole closure under long pulse laser irradiation is not negligible．
2010,
22.
Abstract:
Theoretical analysis of ICF shell X-ray radiography mechanism and the derived digital image’s profile edge forming is carried out. In order to determine the center and radius of the microsphere accurately, the least square fitting expressions with some characteristic points on the shell edge is deduced. For shell image edges of different types (step-shaped or roof-like), the average second-order derivative algorithm or the least square Lorentz fitting peak-finding algorithm of radial absorption intensity is used to obtain the ICF shells’ circumferential edge data with a sub-pixel accuracy. The power spectra curve as a function of the mode number of outer or inner profiles are also calculated by the application of fast Fourier transform to the circumferential profile data.
Theoretical analysis of ICF shell X-ray radiography mechanism and the derived digital image’s profile edge forming is carried out. In order to determine the center and radius of the microsphere accurately, the least square fitting expressions with some characteristic points on the shell edge is deduced. For shell image edges of different types (step-shaped or roof-like), the average second-order derivative algorithm or the least square Lorentz fitting peak-finding algorithm of radial absorption intensity is used to obtain the ICF shells’ circumferential edge data with a sub-pixel accuracy. The power spectra curve as a function of the mode number of outer or inner profiles are also calculated by the application of fast Fourier transform to the circumferential profile data.
2010,
22.
Abstract:
Experiments have been performed using ultra-short (30 fs) ultra-intense laser pulse (up to 1018 W/cm2) focused into under-dense plasmas. A probe pulse was used for the shadowgraphy and the investigation on the propagation of laser under various conditions was presented. The results demonstrate that relativistic effect is the main self-focusing regime and the ratio of laser power to critical power is the key condition for self-focusing of the ultra-short ultra-intense laser in under-dense plasmas.
Experiments have been performed using ultra-short (30 fs) ultra-intense laser pulse (up to 1018 W/cm2) focused into under-dense plasmas. A probe pulse was used for the shadowgraphy and the investigation on the propagation of laser under various conditions was presented. The results demonstrate that relativistic effect is the main self-focusing regime and the ratio of laser power to critical power is the key condition for self-focusing of the ultra-short ultra-intense laser in under-dense plasmas.
2010,
22.
Abstract:
Large diameter (0.6～2.0 mm) microshells of poly (imine imine ketone)s (PIIKs) were prepared by microliquid technique and doublelayer latex technique. A double T-channel droplet generator was designed and developed for the fabrication of PIIKs microshells of controlled size continuously. Manipulative conditions of the diameter and thickness of shells were studied, and the effect of density mismatch on shell quality was discussed. Phase separation during the preparation process affects the morphology of shells. Spinodal phase separation tends to occur at the outer surface of the shells，while binodal phase separation at the inner surface. The diameters of PIIKs shells were measured, 88% of which vary in ±5% of the average diameter. The sphericity is better than 99%．
Large diameter (0.6～2.0 mm) microshells of poly (imine imine ketone)s (PIIKs) were prepared by microliquid technique and doublelayer latex technique. A double T-channel droplet generator was designed and developed for the fabrication of PIIKs microshells of controlled size continuously. Manipulative conditions of the diameter and thickness of shells were studied, and the effect of density mismatch on shell quality was discussed. Phase separation during the preparation process affects the morphology of shells. Spinodal phase separation tends to occur at the outer surface of the shells，while binodal phase separation at the inner surface. The diameters of PIIKs shells were measured, 88% of which vary in ±5% of the average diameter. The sphericity is better than 99%．
2010,
22.
Abstract:
In inertial confinement fusion experiments, three 14-channel soft X-ray spectrometers are used to detect the soft-X-ray spectra and obtain the time history of radiation flux and equivalent temperature. Base function method is one of the unfolding methods. Different parameters of the base functions and different solution methods are compared for the capability to unfold a two-peak predefined spectrum. Based on the unfolding test, the optimized base function and solution method are used to unfold spectrum in our experiment and the results are compared with the measurement of transmission grating spectrometers. The computation and analysis show that iterative method using third-order spline as base function has a better recovery of the soft-X-ray spectrum than other base functions and solutio
In inertial confinement fusion experiments, three 14-channel soft X-ray spectrometers are used to detect the soft-X-ray spectra and obtain the time history of radiation flux and equivalent temperature. Base function method is one of the unfolding methods. Different parameters of the base functions and different solution methods are compared for the capability to unfold a two-peak predefined spectrum. Based on the unfolding test, the optimized base function and solution method are used to unfold spectrum in our experiment and the results are compared with the measurement of transmission grating spectrometers. The computation and analysis show that iterative method using third-order spline as base function has a better recovery of the soft-X-ray spectrum than other base functions and solutio
2010,
22.
Abstract:
Silica opals and multilayer heterostructures were fabricated by vertical deposition technique. Polystyrene inverse opals and gradient porous structures were obtained by colloidal templating, in order to control the pore microstructure of polymer porous materials. As shown in the scanning electron microscopy images, the polystyrene porous structures are precise replicas of inverse structures of the original templates. After being infiltrated with the polystyrene, the photonic stopband position of the opal composite is redshifted compared with the original template, and it is blueshifted after the opal template being removed. The filling ratio of polystyrene was calculated according to the Bragg formula．
Silica opals and multilayer heterostructures were fabricated by vertical deposition technique. Polystyrene inverse opals and gradient porous structures were obtained by colloidal templating, in order to control the pore microstructure of polymer porous materials. As shown in the scanning electron microscopy images, the polystyrene porous structures are precise replicas of inverse structures of the original templates. After being infiltrated with the polystyrene, the photonic stopband position of the opal composite is redshifted compared with the original template, and it is blueshifted after the opal template being removed. The filling ratio of polystyrene was calculated according to the Bragg formula．
2010,
22.
Abstract:
Low density melamine-formaldehyde(MF) aerogels were prepared by sol-gel method and CO2 supercritical drying process. Melamine and formaldehyde were used as precursors and Di methyl sulfoxide (DMOS) was used as solvent. The obtained MF aerogel had a low density of 70 kg/m3. Fourier transform infrared spectroscopy, field emission scanning electron microscopy, nitrogen adsorption and desorption analysis and thermo gravimetric analyses were employed to character the structure and thermal stability of MF aerogels. The results indicated that the MF aerogels using DMOS as solvent had poorer microstructure than those using water as solvent, but presented better thermal stability.
Low density melamine-formaldehyde(MF) aerogels were prepared by sol-gel method and CO2 supercritical drying process. Melamine and formaldehyde were used as precursors and Di methyl sulfoxide (DMOS) was used as solvent. The obtained MF aerogel had a low density of 70 kg/m3. Fourier transform infrared spectroscopy, field emission scanning electron microscopy, nitrogen adsorption and desorption analysis and thermo gravimetric analyses were employed to character the structure and thermal stability of MF aerogels. The results indicated that the MF aerogels using DMOS as solvent had poorer microstructure than those using water as solvent, but presented better thermal stability.
2010,
22.
Abstract:
Using the self-regulating new micro-sphere electrodepositing device, the techniques of electrodepositing gold on hollow PS micro-spheres were established. The experiment was carried out under the following conditions：voltage was about 0.7~0.8 V, current density was 2.0 mA·cm-2, the temperature was 45 ℃, cathode rotating rate was 250 r·min-1, flow rate of the solution was 7 mL·min-1·cm-1. Hollow goldplated micro-spheres were prepared with well spherical symmetr, uniform thickness and surface smoothness under 500 nm. The speed of the gold depositing was 6 μm·h-1.
Using the self-regulating new micro-sphere electrodepositing device, the techniques of electrodepositing gold on hollow PS micro-spheres were established. The experiment was carried out under the following conditions：voltage was about 0.7~0.8 V, current density was 2.0 mA·cm-2, the temperature was 45 ℃, cathode rotating rate was 250 r·min-1, flow rate of the solution was 7 mL·min-1·cm-1. Hollow goldplated micro-spheres were prepared with well spherical symmetr, uniform thickness and surface smoothness under 500 nm. The speed of the gold depositing was 6 μm·h-1.
2010,
22.
Abstract:
Organic aerogels were synthesized by sol-gel polycondensation of phlorogluctinol(P)with acetaldehyde(A) in a slightly alcohol solution, Na2CO3 as the base catalyst, followed by crosslink, solvent exchanging, and drying with supercritical carbon dioxide.Organic aerogels were characterized by SEM and nitrogen adsorption. The aerogel has a continuous nano-network and porous structure. Compared with traditional organic aerogels,it has increased specific surface area(1 210 m2/g)and average pore diameter (11 nm), which is expected to meet the requirement of ICF targets．
Organic aerogels were synthesized by sol-gel polycondensation of phlorogluctinol(P)with acetaldehyde(A) in a slightly alcohol solution, Na2CO3 as the base catalyst, followed by crosslink, solvent exchanging, and drying with supercritical carbon dioxide.Organic aerogels were characterized by SEM and nitrogen adsorption. The aerogel has a continuous nano-network and porous structure. Compared with traditional organic aerogels,it has increased specific surface area(1 210 m2/g)and average pore diameter (11 nm), which is expected to meet the requirement of ICF targets．
2010,
22.
Abstract:
A backlit shadowgraphy technique has been developed, which can be used for nondestructive characterization of ice layer’s inner surface quality for transparent ICF capsules. The physics of the bright band formation for single-layer shell is analyzed by optical theory. With raytrace code, Tracepro, simulated shadowgraphs of transparent single-layer shells are produced to investigate the relation between bright-band position and thickness or refractive index of shells. A setup has been established for backlit shadowgraphy，and experimental shadowgraphs of transparent single-layer shells are obtained, which have a distinct bright band. A code has been developed to analyze shadowgraphs, and the shell’s inner surface power spectrum (1-D) is obtained, then its RMS surface roughness is calculat
A backlit shadowgraphy technique has been developed, which can be used for nondestructive characterization of ice layer’s inner surface quality for transparent ICF capsules. The physics of the bright band formation for single-layer shell is analyzed by optical theory. With raytrace code, Tracepro, simulated shadowgraphs of transparent single-layer shells are produced to investigate the relation between bright-band position and thickness or refractive index of shells. A setup has been established for backlit shadowgraphy，and experimental shadowgraphs of transparent single-layer shells are obtained, which have a distinct bright band. A code has been developed to analyze shadowgraphs, and the shell’s inner surface power spectrum (1-D) is obtained, then its RMS surface roughness is calculat
2010,
22.
Abstract:
On the basis of the nonlinear equation for the wave packet of the elliptically polarized laser electric field, the Lagrange density function of the nonlinear equation is constructed by means of field theory. It is shown that the energy focus of the wave packet possesses the characteristic of quasi-particles. Moreover, the conserved quantities of plasmons, momentum, and energy are given. The collapse dynamics of the wave packet at the later stage of modulation instability is discussed. The normalized density distribution of the plasmon number is regarded as weight, and the wave packet of the laser electric field is analyzed. The result shows that the scale of the wave packet will collapse to a very small value in finite time, proving that the laser electric field possesses the collapsing be
On the basis of the nonlinear equation for the wave packet of the elliptically polarized laser electric field, the Lagrange density function of the nonlinear equation is constructed by means of field theory. It is shown that the energy focus of the wave packet possesses the characteristic of quasi-particles. Moreover, the conserved quantities of plasmons, momentum, and energy are given. The collapse dynamics of the wave packet at the later stage of modulation instability is discussed. The normalized density distribution of the plasmon number is regarded as weight, and the wave packet of the laser electric field is analyzed. The result shows that the scale of the wave packet will collapse to a very small value in finite time, proving that the laser electric field possesses the collapsing be
2010,
22.
Abstract:
For the interaction experiments between ultra-intense laser and targets, characterizing the laser focusing spot is very important. Two different methods were adopted on SILEX-Ⅰ Ti:sappire femtosecond laser system. One is directly imaging the laser spot on 16bit CCD, another is measuring the transmitting energy behind a pinhole which was exactly positioned on the laser focusing spot. Both methods can give the correct distribution of the focal spot with less than error 10%.
For the interaction experiments between ultra-intense laser and targets, characterizing the laser focusing spot is very important. Two different methods were adopted on SILEX-Ⅰ Ti:sappire femtosecond laser system. One is directly imaging the laser spot on 16bit CCD, another is measuring the transmitting energy behind a pinhole which was exactly positioned on the laser focusing spot. Both methods can give the correct distribution of the focal spot with less than error 10%.
2010,
22.
Abstract:
This paper introduces the fabrication of carbon aerogel sheets with different thicknesses and densities and corresponding superficial micro-treatments. By resorcinol and formaldehyde’s polymerization reaction and via a self-made flexible mould, a series of carbon aerogel sheets were obtained. Their thicknesses range from 80 to 350 μm and densities range from 50 to 600 mg·cm-3. The sheets were characterized by field emission scanning electron microscope, X-ray phase contrast imaging method and form Talysurf profiler. The results indicate that the carbon aerogel sheet has the same inner microstructure with the bulk. However, its surface has a dense layer which is obviously different from its inner microstructure. Several materials with different roughness were used to treat the
This paper introduces the fabrication of carbon aerogel sheets with different thicknesses and densities and corresponding superficial micro-treatments. By resorcinol and formaldehyde’s polymerization reaction and via a self-made flexible mould, a series of carbon aerogel sheets were obtained. Their thicknesses range from 80 to 350 μm and densities range from 50 to 600 mg·cm-3. The sheets were characterized by field emission scanning electron microscope, X-ray phase contrast imaging method and form Talysurf profiler. The results indicate that the carbon aerogel sheet has the same inner microstructure with the bulk. However, its surface has a dense layer which is obviously different from its inner microstructure. Several materials with different roughness were used to treat the
2010,
22.
Abstract:
In order to enhance the signal of the weak nonlinear strong-field phenomenon induced by free electron interaction with intense laser fields, a scheme to trap the high-energy electrons by two parallel-propagating laser beams has been proposed. The mechanism is based upon the electron inelastic scattering by intense laser beams, i.e., when the electron passes the first beam with greatly reduced transverse momentum, it will not have enough momentum to pass the second beam and thus be trapped between the two beams.
In order to enhance the signal of the weak nonlinear strong-field phenomenon induced by free electron interaction with intense laser fields, a scheme to trap the high-energy electrons by two parallel-propagating laser beams has been proposed. The mechanism is based upon the electron inelastic scattering by intense laser beams, i.e., when the electron passes the first beam with greatly reduced transverse momentum, it will not have enough momentum to pass the second beam and thus be trapped between the two beams.
2010,
22.
Abstract:
The dynamics and harmonics emission spectra due to electron motion in laser standing wave have been investigated considering a single electron model. The motion status of electron and harmonics radiation spectra are numerically analyzed. The electron with incident position at node and incident direction vertical to magnetic field oscillates rapidly under Lorentz force. The spectrum of radiation is redshifted for backward radiation and blueshifted for forward radiation, and thus spectral broadening is noticed. These effects are much more pronounced at higher laser intensity or initial electron energy, and even give rise to higher-order harmonics that eventually lead to a continuous spectrum. However, when the electron being incident at antinode and parallelly to electric field, it only move
The dynamics and harmonics emission spectra due to electron motion in laser standing wave have been investigated considering a single electron model. The motion status of electron and harmonics radiation spectra are numerically analyzed. The electron with incident position at node and incident direction vertical to magnetic field oscillates rapidly under Lorentz force. The spectrum of radiation is redshifted for backward radiation and blueshifted for forward radiation, and thus spectral broadening is noticed. These effects are much more pronounced at higher laser intensity or initial electron energy, and even give rise to higher-order harmonics that eventually lead to a continuous spectrum. However, when the electron being incident at antinode and parallelly to electric field, it only move
2010,
22.
Abstract:
The paper introduces the factors that influence the technologies for laser-driven flyer hypervelocity launch, and studies the effects of laser energy, spatial distribution of laser beam and deposition techniques of coatings on the velocity and integrity of flyers. The results indicate that the spatially “flat cap” laser beam can launch flyers of good integrity. Adding a Cr film between Al coating and substrate can enhance the adhesion between them, and also enhance the flyer velocity distinctly. With a laser of 1 064 nm wavelength and 10 ns pulse duration at laser energy of 835 mJ, the flyer driven out can reach a velocity of 10.4 km/s, whose thickness is 5 μm and diameter is 1 mm.
The paper introduces the factors that influence the technologies for laser-driven flyer hypervelocity launch, and studies the effects of laser energy, spatial distribution of laser beam and deposition techniques of coatings on the velocity and integrity of flyers. The results indicate that the spatially “flat cap” laser beam can launch flyers of good integrity. Adding a Cr film between Al coating and substrate can enhance the adhesion between them, and also enhance the flyer velocity distinctly. With a laser of 1 064 nm wavelength and 10 ns pulse duration at laser energy of 835 mJ, the flyer driven out can reach a velocity of 10.4 km/s, whose thickness is 5 μm and diameter is 1 mm.
2010,
22.
Abstract:
On the basis of one-dimensional fluid model, the characteristics of radio frequency discharge at atmospheric pressure in argon using bare metal electrode are numerically investigated. The primary processes of excitation and ionization in Ar are considered. The particles included in the model are electron, two ions Ar+ and Ar2+ and one metastable state Ar*. The spatial-temporal evolutions of the discharge density with electrode voltage and gap are calculated by solving the one-dimensional continuity and momentum equations for electrons and ions, coupled with the current continuity equation. The simulation results show that the densities of electron, Ar+, Ar2+, and ArAr* have an optimal value with the variation of electrode voltage and gap.
On the basis of one-dimensional fluid model, the characteristics of radio frequency discharge at atmospheric pressure in argon using bare metal electrode are numerically investigated. The primary processes of excitation and ionization in Ar are considered. The particles included in the model are electron, two ions Ar+ and Ar2+ and one metastable state Ar*. The spatial-temporal evolutions of the discharge density with electrode voltage and gap are calculated by solving the one-dimensional continuity and momentum equations for electrons and ions, coupled with the current continuity equation. The simulation results show that the densities of electron, Ar+, Ar2+, and ArAr* have an optimal value with the variation of electrode voltage and gap.
2010,
22.
Abstract:
For better understanding of the plasma physical mechanism in the discharge chamber, the discharge chamber of Kaufman ion thruster was researched numerically, the primary electrons are treated as particles and the secondary electrons and ions are described with drift-diffusion model. The numerical results are compared with the given experimental data, showing that: the computational method suits the numerical research of the plasma flow rules in the discharge chamber; the plasma flow distribution and evolvement rule are obtained in the steady state, which agree with the experimental measurements; primary electrons are restricted distinctly by the design of magnetic field, of which the probability of ionization collision with propellant gas is increased effectively; precise description of s
For better understanding of the plasma physical mechanism in the discharge chamber, the discharge chamber of Kaufman ion thruster was researched numerically, the primary electrons are treated as particles and the secondary electrons and ions are described with drift-diffusion model. The numerical results are compared with the given experimental data, showing that: the computational method suits the numerical research of the plasma flow rules in the discharge chamber; the plasma flow distribution and evolvement rule are obtained in the steady state, which agree with the experimental measurements; primary electrons are restricted distinctly by the design of magnetic field, of which the probability of ionization collision with propellant gas is increased effectively; precise description of s
2010,
22.
Abstract:
Experimental setup was designed to distinguish photoelectric effect, thermoelectric effect and Compton effect in X rays and metal interaction. Measurements of currents in metals irradiated by obliquely incident X rays produced by X pinch show that photoelectric effect will dominate the interaction process when the X ray intensity is lower than 105 W/cm2, and thermoelectric effect will dominate when the intensity is higher. Electrons irradiated by weak X rays show individual behavior, while they show weak correlated collective behavior with increasing intensity. Thus it is reasonable to predict that macroscopic charge density modulation will appear on metal surface irradiated by ultra-intense X rays, and directed electromagnetic pulses will be produced during the de-excitation of such state
Experimental setup was designed to distinguish photoelectric effect, thermoelectric effect and Compton effect in X rays and metal interaction. Measurements of currents in metals irradiated by obliquely incident X rays produced by X pinch show that photoelectric effect will dominate the interaction process when the X ray intensity is lower than 105 W/cm2, and thermoelectric effect will dominate when the intensity is higher. Electrons irradiated by weak X rays show individual behavior, while they show weak correlated collective behavior with increasing intensity. Thus it is reasonable to predict that macroscopic charge density modulation will appear on metal surface irradiated by ultra-intense X rays, and directed electromagnetic pulses will be produced during the de-excitation of such state
2010,
22.
Abstract:
In order to understand the effect of imaging lenses on imaging quality of proton radiograph, the research on the secondary proton-removing effect of imaging lenses has been carried out. The analytical results show that, the secondary protons’ energy is below one half of the original protons’ and the imaging lenses have the ability to remove secondary protons out of the detecting area. The simulation of the whole proton radiography system shows that the imaging lenses have decreased the relative optical path difference caused by secondary protons to less than 2%，and thus the image quality has been improved greatly. Thus the imaging lenses are important components in proton radiography.
In order to understand the effect of imaging lenses on imaging quality of proton radiograph, the research on the secondary proton-removing effect of imaging lenses has been carried out. The analytical results show that, the secondary protons’ energy is below one half of the original protons’ and the imaging lenses have the ability to remove secondary protons out of the detecting area. The simulation of the whole proton radiography system shows that the imaging lenses have decreased the relative optical path difference caused by secondary protons to less than 2%，and thus the image quality has been improved greatly. Thus the imaging lenses are important components in proton radiography.
2010,
22.
Abstract:
The explosion dynamics process of heteroclusters ((CH4)n，(CD4)n，(D2O)>)n） in ultraintense femtosecond laser fields has been studied theoretically using Bethe model. It is found that the average energy of hydrogen ions and deuterium ions after explosion has a linear relationship with the square of initial cluster radius, and the explosion mechanism is typical Coulomb explosion. Furthermore, the deuterium ions from the heteroclusters have higher energy than those from the homonuclear clusters ((D)>)n), indicating that highly ionized ions of high Z element have a strong acceleration effect on the ions of low Z element.
The explosion dynamics process of heteroclusters ((CH4)n，(CD4)n，(D2O)>)n） in ultraintense femtosecond laser fields has been studied theoretically using Bethe model. It is found that the average energy of hydrogen ions and deuterium ions after explosion has a linear relationship with the square of initial cluster radius, and the explosion mechanism is typical Coulomb explosion. Furthermore, the deuterium ions from the heteroclusters have higher energy than those from the homonuclear clusters ((D)>)n), indicating that highly ionized ions of high Z element have a strong acceleration effect on the ions of low Z element.
2010,
22.
Abstract:
In particle field holography, an optical system named 4F system is usually used for imaging particles in an appropriate position. At the real focus of the 4F system, air will be ionized when the laser pulse energy increases. In this case, intensity distribution of reconstructed images of off-line and in-line holography are opposite to those obtained under normal conditions. The reason is the spatial filtering. effect caused by the air ionization. Furthermore, high quality off-line particle holographic images can be obtained with air ionized, by adjusting the exposure pulse intensity.
In particle field holography, an optical system named 4F system is usually used for imaging particles in an appropriate position. At the real focus of the 4F system, air will be ionized when the laser pulse energy increases. In this case, intensity distribution of reconstructed images of off-line and in-line holography are opposite to those obtained under normal conditions. The reason is the spatial filtering. effect caused by the air ionization. Furthermore, high quality off-line particle holographic images can be obtained with air ionized, by adjusting the exposure pulse intensity.
2010,
22.
Abstract:
A plasma jetting system with the use of the coaxial dielectric barrier electrodes is introduced. It can create glow discharge helium plasma in the air, and be applied to sterilization without both reaction vessel and vacuum system. Some factors such as the electrode voltage, the frequency of power supply and the gas flow rate are considered to recognize the features of the plasma created. Higher voltage between electrodes will lead to larger discharge current, and the peak discharge current moves forward in each voltage half cycle. But over-loaded voltage will cause filamentary discharge, which is not expected in the experiment. Increasing the frequency of supply power will give rise to the peak value of discharge current and the ejection distance of the plasma. In addition, faster gas flo
A plasma jetting system with the use of the coaxial dielectric barrier electrodes is introduced. It can create glow discharge helium plasma in the air, and be applied to sterilization without both reaction vessel and vacuum system. Some factors such as the electrode voltage, the frequency of power supply and the gas flow rate are considered to recognize the features of the plasma created. Higher voltage between electrodes will lead to larger discharge current, and the peak discharge current moves forward in each voltage half cycle. But over-loaded voltage will cause filamentary discharge, which is not expected in the experiment. Increasing the frequency of supply power will give rise to the peak value of discharge current and the ejection distance of the plasma. In addition, faster gas flo
2010,
22.
Abstract:
Ni nano-particles were prepared by flow-levitation method. And then, bulk nanocrystalline Ni samples, 10 mm in diameter and 2 mm in height with a relative density of 96.8 % and a microhardness of 4.17 GPa, were fabricated by spark plasma sintering using the nano-particles. The phase composition, grain size, microstructure and microhardness of the bulk samples were characterized by X-ray diffractometer, scanning electron microscope, and Vickers microhardness tester, respectively. The results indicate that the relative density and grain size increase with increasing sintering temperature. The optimal relative density has been obtained at the sintering temperature of 650 ℃, at which the average grain size is 44.8 nm. The microhardness first increases and then decreases with increasing sinter
Ni nano-particles were prepared by flow-levitation method. And then, bulk nanocrystalline Ni samples, 10 mm in diameter and 2 mm in height with a relative density of 96.8 % and a microhardness of 4.17 GPa, were fabricated by spark plasma sintering using the nano-particles. The phase composition, grain size, microstructure and microhardness of the bulk samples were characterized by X-ray diffractometer, scanning electron microscope, and Vickers microhardness tester, respectively. The results indicate that the relative density and grain size increase with increasing sintering temperature. The optimal relative density has been obtained at the sintering temperature of 650 ℃, at which the average grain size is 44.8 nm. The microhardness first increases and then decreases with increasing sinter
2010,
22.
Abstract:
In dynamic light scattering particle sizing, the inverse range can be self-adapted closer to the true range by multi-scale transform. The simulative autocorrelation functions(ACFs) of unimodal size distribution particles of 200~600 nm and bimodal size distribution particles of 200~900 nm were inversed by the inverse range fixed and self-adaptive algorithms. Compared to the fixed algorithm, the selfadaptive algorithm is more precise and noise-tolerant. For unimodal distribution particles, it can reduce peak value error by 4.73% and peak width error by 185 nm at most. For bimodal distribution particles, when the noise level is 0～0.001, its peak value errors are less than by 11.33%,by 12.45%, and its peak width errors are less than 35 nm,160 nm. While, the fixed algorithm cannot get reason
In dynamic light scattering particle sizing, the inverse range can be self-adapted closer to the true range by multi-scale transform. The simulative autocorrelation functions(ACFs) of unimodal size distribution particles of 200~600 nm and bimodal size distribution particles of 200~900 nm were inversed by the inverse range fixed and self-adaptive algorithms. Compared to the fixed algorithm, the selfadaptive algorithm is more precise and noise-tolerant. For unimodal distribution particles, it can reduce peak value error by 4.73% and peak width error by 185 nm at most. For bimodal distribution particles, when the noise level is 0～0.001, its peak value errors are less than by 11.33%,by 12.45%, and its peak width errors are less than 35 nm,160 nm. While, the fixed algorithm cannot get reason
2010,
22.
Abstract:
Two-electrode spark gap switch is an important candidate for the switching element of huge high laser power supply systems. This paper presents the using condition and critical technology of graphite two-electrode spark gap switch. The electrical field strength simulation shows that the electrode shape which satisfies Borda profile could constitute the optimized spark gap. Referred to the known parameters about the ST-300 switch used in NIF, a series of electric tests have been done. The tests have proved that the graphite two-electrode spark gap switch can support 300 kA peak pulse current, with over 100 C transfer charge and over 1 000 shots of lifetime, therefore meeting the requirement of the 1.2 MJ huge laser power supply system.
Two-electrode spark gap switch is an important candidate for the switching element of huge high laser power supply systems. This paper presents the using condition and critical technology of graphite two-electrode spark gap switch. The electrical field strength simulation shows that the electrode shape which satisfies Borda profile could constitute the optimized spark gap. Referred to the known parameters about the ST-300 switch used in NIF, a series of electric tests have been done. The tests have proved that the graphite two-electrode spark gap switch can support 300 kA peak pulse current, with over 100 C transfer charge and over 1 000 shots of lifetime, therefore meeting the requirement of the 1.2 MJ huge laser power supply system.
2010,
22.
Abstract:
Three different electrode configurations of multigap switches, ellipse-ellipse, arc-ellipse and arc-arc types, are designed. And the simulation of electric field and the static experiment of the switches are conducted. The result shows that, the field distribution on the electrode surface and the static characteristics of the ellipse-ellipse type are the best with the field asymmetric coefficient of 1.03. The arc-ellipse type has the minimum field variation in the vertical direction of its surface with a deviation degree less than 1%.
Three different electrode configurations of multigap switches, ellipse-ellipse, arc-ellipse and arc-arc types, are designed. And the simulation of electric field and the static experiment of the switches are conducted. The result shows that, the field distribution on the electrode surface and the static characteristics of the ellipse-ellipse type are the best with the field asymmetric coefficient of 1.03. The arc-ellipse type has the minimum field variation in the vertical direction of its surface with a deviation degree less than 1%.
2010,
22.
Abstract:
The design proposal of spiral pulse-forming line with high voltage and μs pulse width is presented, and the spiral structure is firstly used for the generator with μs-long pulse width and high output voltage. The inner conductor of the pulse-forming line is a spiral line, and the working material is deionized water. The basic parameters of the structure are equivalent capacitance 41.25 nF, equivalent inductance 1.06 μH, characteristic impedance 12.1 Ω, pulse width 1 μs, the maximum charging voltage 1 MV, the maximum storage energy 20.6 kJ, and matched output voltage 500 kV. The design result indicates that, with the same output pulse width, the spiral pulse-forming line is about 1/4 the length of the traditional single metal line.
The design proposal of spiral pulse-forming line with high voltage and μs pulse width is presented, and the spiral structure is firstly used for the generator with μs-long pulse width and high output voltage. The inner conductor of the pulse-forming line is a spiral line, and the working material is deionized water. The basic parameters of the structure are equivalent capacitance 41.25 nF, equivalent inductance 1.06 μH, characteristic impedance 12.1 Ω, pulse width 1 μs, the maximum charging voltage 1 MV, the maximum storage energy 20.6 kJ, and matched output voltage 500 kV. The design result indicates that, with the same output pulse width, the spiral pulse-forming line is about 1/4 the length of the traditional single metal line.
2010,
22.
Abstract:
Based on the experimental device of the linear transformer driver, the effect of magnetizing inductance on the pulse waveform drop is theoretically and simulatively studied in this paper. The formulae are deduced, with which the effect of magnetizing inductance is calculated. In addition, the output pulse waveform is simulated through the Pspice software. The theoretical and simulated results agree well with each other, which show that the waveform drop is more obvious with the smaller magnetizing inductance. In order to reduce the waveform drop, we have designed an apparatus which can offer direct current of 50 A for bias magnetization， with which the LTD can steadily obtain output pulse with rise time of 35 ns, voltage of 125 kV, pulse duration of 130 ns and little waveform drop (less t
Based on the experimental device of the linear transformer driver, the effect of magnetizing inductance on the pulse waveform drop is theoretically and simulatively studied in this paper. The formulae are deduced, with which the effect of magnetizing inductance is calculated. In addition, the output pulse waveform is simulated through the Pspice software. The theoretical and simulated results agree well with each other, which show that the waveform drop is more obvious with the smaller magnetizing inductance. In order to reduce the waveform drop, we have designed an apparatus which can offer direct current of 50 A for bias magnetization， with which the LTD can steadily obtain output pulse with rise time of 35 ns, voltage of 125 kV, pulse duration of 130 ns and little waveform drop (less t
2010,
22.
Abstract:
A compact 200 kV pulse transformer with step-up ratio of 109 was developed to miniaturize high-voltage pulse transformer. Researches on coupling, high-voltage insulation and output characteristics of the transformer were carried out by electromagnetic theory, circuit simulation and experiments. Important parameters were calculated and designed. As the closed magnetic core of the transformer was made of crystal-tropism siliconsteel strip, the effective coupling coefficient reached as high as 0.95. With insulated structure of polymeric cylinder and alternate-winding method, the secondary windings of transformer could deliver a high-voltage pulse of 230 kV and full width at half maximum (FWHM) of 3 μs when initial voltage of the primary energy-storage capacitor was 2.1 kV. Results of simul
A compact 200 kV pulse transformer with step-up ratio of 109 was developed to miniaturize high-voltage pulse transformer. Researches on coupling, high-voltage insulation and output characteristics of the transformer were carried out by electromagnetic theory, circuit simulation and experiments. Important parameters were calculated and designed. As the closed magnetic core of the transformer was made of crystal-tropism siliconsteel strip, the effective coupling coefficient reached as high as 0.95. With insulated structure of polymeric cylinder and alternate-winding method, the secondary windings of transformer could deliver a high-voltage pulse of 230 kV and full width at half maximum (FWHM) of 3 μs when initial voltage of the primary energy-storage capacitor was 2.1 kV. Results of simul
2010,
22.
Abstract:
Auto-regression (AR) model, one power spectrum estimation method of stationary random signals, and artifical neutral network were adopted to recognize nuclear and lightning electromagnetic pulses. Self-correlation function and Burg algorithms were used to acquire the AR model coefficients as eigenvalues, and BP artificial neural network was introduced as the classifier with different numbers of hidden layers and hidden layer nodes. The results show that AR model is effective in those signals, feature extraction, and the Burg algorithm is more effective than the self-correlation function algorithm.
Auto-regression (AR) model, one power spectrum estimation method of stationary random signals, and artifical neutral network were adopted to recognize nuclear and lightning electromagnetic pulses. Self-correlation function and Burg algorithms were used to acquire the AR model coefficients as eigenvalues, and BP artificial neural network was introduced as the classifier with different numbers of hidden layers and hidden layer nodes. The results show that AR model is effective in those signals, feature extraction, and the Burg algorithm is more effective than the self-correlation function algorithm.
2010,
22.
Abstract:
The principle of pulsed X-ray spot size measurement with lamination method was presented. The spatial resolution and output response for uniformly distributed line source of the metal-film lamination were calculated numerically. The corresponding relation between the FWHM of the response curve and the spot size was obtained. And the calculation results indicate that the metal-film lamination is not suitable for measurement of spot size less than 2 mm. Rod-pinch diode(RPD) experiments were performed on the inductive voltage adder, and the axial extent of the RPD X-ray source was measured with lamination method. Under the hypothesis of uniformly distributed line source, the axial spot size of the X-ray source was obtained, about 5.2 mm, consistent with the measuring result of the pinhole cam
The principle of pulsed X-ray spot size measurement with lamination method was presented. The spatial resolution and output response for uniformly distributed line source of the metal-film lamination were calculated numerically. The corresponding relation between the FWHM of the response curve and the spot size was obtained. And the calculation results indicate that the metal-film lamination is not suitable for measurement of spot size less than 2 mm. Rod-pinch diode(RPD) experiments were performed on the inductive voltage adder, and the axial extent of the RPD X-ray source was measured with lamination method. Under the hypothesis of uniformly distributed line source, the axial spot size of the X-ray source was obtained, about 5.2 mm, consistent with the measuring result of the pinhole cam
2010,
22.
Abstract:
As an efficient cooling method for high power lasers, spray cooling gets more and more attentions. The progress in spray cooling technology is reviewed. Emphasis is placed on the heat transfer mechanism, the influencing factors of heat transfer capability and the temperature uniformity of heat transfer surface. The solutions to solve the existing problems are proposed, such as the integration of refrigeration system and spray system, R600a and other eco-friendly refrigerants with high latent heat, and the system of refrigeration spray cooling with air assisted atomizer and appropriate coolants for the system. Future trends of spray cooling for high power solid-state laser is also discussed.
As an efficient cooling method for high power lasers, spray cooling gets more and more attentions. The progress in spray cooling technology is reviewed. Emphasis is placed on the heat transfer mechanism, the influencing factors of heat transfer capability and the temperature uniformity of heat transfer surface. The solutions to solve the existing problems are proposed, such as the integration of refrigeration system and spray system, R600a and other eco-friendly refrigerants with high latent heat, and the system of refrigeration spray cooling with air assisted atomizer and appropriate coolants for the system. Future trends of spray cooling for high power solid-state laser is also discussed.
2010,
22.
Abstract:
The effects of diffuser inlet area ratio on pressure recovery and sealing capability of free-vortex aerodynamic window were investigated experimentally based on active diffuser. The results show that the diffuser inlet area ratio is an important factor influencing the diffuser’s pressure recovery, and the sealing pressure ratio and operation stability of aerodynamic window can be improved by optimizing the ratio. Compared with traditional diffusers, the active diffuser has smaller optimum inlet area ratio, which makes the aerodynamic window jet more closer to the ideal free-vortex jet. The optimum inlet area ratio is approximately 2.03 for active diffuser, under which the critical pressure of the blowing from diffuser’s inner wall is lowest, and the blowing from diffuser’s outer wall al
The effects of diffuser inlet area ratio on pressure recovery and sealing capability of free-vortex aerodynamic window were investigated experimentally based on active diffuser. The results show that the diffuser inlet area ratio is an important factor influencing the diffuser’s pressure recovery, and the sealing pressure ratio and operation stability of aerodynamic window can be improved by optimizing the ratio. Compared with traditional diffusers, the active diffuser has smaller optimum inlet area ratio, which makes the aerodynamic window jet more closer to the ideal free-vortex jet. The optimum inlet area ratio is approximately 2.03 for active diffuser, under which the critical pressure of the blowing from diffuser’s inner wall is lowest, and the blowing from diffuser’s outer wall al
2010,
22.
Abstract:
A numerical model of atmospheric turbulence in surface layer over desert is presented. Through measuring meteorological parameters including temperature, humidity, pressure and wind speed, atmospheric turbulence strength in the surface layer can be obtained. The calculation results of the model show that, generally, the maximum strength appears the midday, and the minimum appears about the sunrise and the sunset, while the strength changes irregularly at night, reflecting the atmospheric turbulence variational characteristics in the surface layer perfectly. In all the meteorological parameters, the variation of temperature affects the atmospheric turbulence strength directly. The strength changes in the same direction as the change in temperature, and larger strength variation corresponds
A numerical model of atmospheric turbulence in surface layer over desert is presented. Through measuring meteorological parameters including temperature, humidity, pressure and wind speed, atmospheric turbulence strength in the surface layer can be obtained. The calculation results of the model show that, generally, the maximum strength appears the midday, and the minimum appears about the sunrise and the sunset, while the strength changes irregularly at night, reflecting the atmospheric turbulence variational characteristics in the surface layer perfectly. In all the meteorological parameters, the variation of temperature affects the atmospheric turbulence strength directly. The strength changes in the same direction as the change in temperature, and larger strength variation corresponds
2010,
22.
Abstract:
Coherent beam combining of four fiber laser beams with multi-dithering based on field programmable gate array(FPGA) control module was demonstrated. When the phase control system is in close loop, the phase errors between the beams induced by atmospheric turbulence and mechanical vibrations are compensated and the contrast of the far-field coherent combined beam profile is improved to 0.93 from 0.21 in the open loop, and the power in the given area is 3.3 times higher. Even if the fibers are dithered, the contrast of far-field beam profile is still held at 0.72.
Coherent beam combining of four fiber laser beams with multi-dithering based on field programmable gate array(FPGA) control module was demonstrated. When the phase control system is in close loop, the phase errors between the beams induced by atmospheric turbulence and mechanical vibrations are compensated and the contrast of the far-field coherent combined beam profile is improved to 0.93 from 0.21 in the open loop, and the power in the given area is 3.3 times higher. Even if the fibers are dithered, the contrast of far-field beam profile is still held at 0.72.
2010,
22.
Abstract:
An idea of using laser Doppler velocimeter(LDV) to offer the velocity in vehicle inertial navigation system was proposed. The principles of measuring its own velocity of laser Doppler and relative theory of wavelet transform were expounded. Doppler signal was processed using wavelet transform, simulation and experiment showed that: after signal decomposition, processing the wavelet at each level, acquired good de-noising effect; in common threshold principles of de-noising, rigorous SURE and minimax principles did not lose the useful information easily, but heuristic SURE and fixed threshold principles acquired better de-noising effect; results of frequency extraction with wavelet transform and fast Fourier translation (FFT) were consistent, but velocity and correspondent moment could be a
An idea of using laser Doppler velocimeter(LDV) to offer the velocity in vehicle inertial navigation system was proposed. The principles of measuring its own velocity of laser Doppler and relative theory of wavelet transform were expounded. Doppler signal was processed using wavelet transform, simulation and experiment showed that: after signal decomposition, processing the wavelet at each level, acquired good de-noising effect; in common threshold principles of de-noising, rigorous SURE and minimax principles did not lose the useful information easily, but heuristic SURE and fixed threshold principles acquired better de-noising effect; results of frequency extraction with wavelet transform and fast Fourier translation (FFT) were consistent, but velocity and correspondent moment could be a
2010,
22.
Abstract:
Starting from the Rayleigh-Sommerfeld diffraction integral, analytical expressions for the free-space propagation of radial array nonparaxial elliptical Gaussian beams in coherent and incoherent combinations are derived, and some special cases including the far-field distributions and paraxial expressions are given. It is shown that the intensity distribution of the resulting beam depends on the f-parameter, radial array radius, beam number, propagation distance and combination scheme. The far-field maximum intensity of the resulting beam with N beamlets in coherent and incoherent combinations is N2- and N-times of that of the single beamlet, respectively.
Starting from the Rayleigh-Sommerfeld diffraction integral, analytical expressions for the free-space propagation of radial array nonparaxial elliptical Gaussian beams in coherent and incoherent combinations are derived, and some special cases including the far-field distributions and paraxial expressions are given. It is shown that the intensity distribution of the resulting beam depends on the f-parameter, radial array radius, beam number, propagation distance and combination scheme. The far-field maximum intensity of the resulting beam with N beamlets in coherent and incoherent combinations is N2- and N-times of that of the single beamlet, respectively.
2010,
22.
Abstract:
This paper presents the calibration of the input-output characteristic of integrating current transformer (ICT) by digital signal generation and oscilloscope, gives the ratio of input and output of the calibrated ICT under different input pulse durations and amplitudes, the effect of input pulse duration on the ICT output pulse duration, the response of the ICT to the consecutive input pulses. The calibration reveals that the relation between input and output of ICT is linearity, and the ICT will output one signal when the interval of the successive signals is very small, and also the shape and duration of the output are independent of that of the input signal.
This paper presents the calibration of the input-output characteristic of integrating current transformer (ICT) by digital signal generation and oscilloscope, gives the ratio of input and output of the calibrated ICT under different input pulse durations and amplitudes, the effect of input pulse duration on the ICT output pulse duration, the response of the ICT to the consecutive input pulses. The calibration reveals that the relation between input and output of ICT is linearity, and the ICT will output one signal when the interval of the successive signals is very small, and also the shape and duration of the output are independent of that of the input signal.
2010,
22.
Abstract:
Analyzing the interaction mechanism of laser with target and vaporized target material, a one-dimensional bulk absorption model to simulate the solid target ablated directly by the laser beam is presented, numerical calculation of impulse acting on the target in vacuum with different laser parameters is performed with fluid dynamics theory and 1D Lagrange difference scheme. The calculated values of the impulse coupling coefficient are in good agreement with the experimental results and Phipps’s empirical value. From the calculated results, the impulse coupling coefficient decreases with the increment of laser intensity when the laser pulse generates a plasma.
Analyzing the interaction mechanism of laser with target and vaporized target material, a one-dimensional bulk absorption model to simulate the solid target ablated directly by the laser beam is presented, numerical calculation of impulse acting on the target in vacuum with different laser parameters is performed with fluid dynamics theory and 1D Lagrange difference scheme. The calculated values of the impulse coupling coefficient are in good agreement with the experimental results and Phipps’s empirical value. From the calculated results, the impulse coupling coefficient decreases with the increment of laser intensity when the laser pulse generates a plasma.
2010,
22.
Abstract:
In the process of optical parametric chirped pulse amplification, a chirp matching method for signal-and-pump synchronization has been established by studying the variation of conversion efficiency with pump pulse chirped parameters and the corresponding relationship between signal and pump wavelengths. Taking KDP crystal as the nonlinear crystal, the effects of chirp match and synchronization jitter on the pulse profile and conversion efficiency of optical parametric chirped pulse amplification have been studied. The results indicate that, in the case of time synchronization, the chirp matched pulse profile is considerably symmetrical and the conversion efficiency is high. For a given synchronization jitter, the signal gain and pulse profile after amplification are quite different for dif
In the process of optical parametric chirped pulse amplification, a chirp matching method for signal-and-pump synchronization has been established by studying the variation of conversion efficiency with pump pulse chirped parameters and the corresponding relationship between signal and pump wavelengths. Taking KDP crystal as the nonlinear crystal, the effects of chirp match and synchronization jitter on the pulse profile and conversion efficiency of optical parametric chirped pulse amplification have been studied. The results indicate that, in the case of time synchronization, the chirp matched pulse profile is considerably symmetrical and the conversion efficiency is high. For a given synchronization jitter, the signal gain and pulse profile after amplification are quite different for dif
2010,
22.
Abstract:
A 1-D energy balance model is used to describe the electrical responses of photoconductor (PC)-type HgCdTe detector under out-band 10.6 μm laser irradiation. The simulated resistance-vs-time curve agrees with the experimental curve in terms of curvilinear trend. The analyses of simulated results show that the sharp change of detector resistance results from the sharp change of carrier temperature at the very beginning and the very ending of laser irradiation, and that the slow change of the resistance results from the slow change of lattice temperature during and after laser irradiation, which is identical with the conclusions from the analyses of experimental results．
A 1-D energy balance model is used to describe the electrical responses of photoconductor (PC)-type HgCdTe detector under out-band 10.6 μm laser irradiation. The simulated resistance-vs-time curve agrees with the experimental curve in terms of curvilinear trend. The analyses of simulated results show that the sharp change of detector resistance results from the sharp change of carrier temperature at the very beginning and the very ending of laser irradiation, and that the slow change of the resistance results from the slow change of lattice temperature during and after laser irradiation, which is identical with the conclusions from the analyses of experimental results．
2010,
22.
Abstract:
This paper studies the optical aberrations in the case when the optical beam is propagating through the flow field of two optical windows with different shapes, respectively. The flow field is governed by the the 3-D Reynolds averaged Navier-Stokes (N-S) equations. To split the viscosity flux and the convective flux of the N-S equations, the second order central scheme and the ROE scheme are adopted respectively. With the implicit Gauss-Seidel scheme, the code is advanced in time. The k-ε turbulence model is used for turbulence simulations. Aero-optic effects are analyzed with the methods of geometrical optics and physical optics by introducing the mean flow and turbulence.The numerical results show that the beam quality and drag coefficient would be significantly influenced by the shape
This paper studies the optical aberrations in the case when the optical beam is propagating through the flow field of two optical windows with different shapes, respectively. The flow field is governed by the the 3-D Reynolds averaged Navier-Stokes (N-S) equations. To split the viscosity flux and the convective flux of the N-S equations, the second order central scheme and the ROE scheme are adopted respectively. With the implicit Gauss-Seidel scheme, the code is advanced in time. The k-ε turbulence model is used for turbulence simulations. Aero-optic effects are analyzed with the methods of geometrical optics and physical optics by introducing the mean flow and turbulence.The numerical results show that the beam quality and drag coefficient would be significantly influenced by the shape
2010,
22.
Abstract:
CCD diffused transmission imaging method is used to measure laser intensity distribution and power. The measurement principle of the design is presented. The designed system’s configuration is summarized. There are particular introduction for each part of the system. The scattering properties of the diffusion screen is researched through experiment. There is highlighting information on the design of optical system, light path, reflector, focal length and aperture of camera lens, and depth of field of CCD camera are respectively introduced. The data processing software are introduced. The design implements large laser spot intensity distribution measurement and power measurement in small space at the same time, it has the advantages of high resolution(5 mm) for intensity distribution measu
CCD diffused transmission imaging method is used to measure laser intensity distribution and power. The measurement principle of the design is presented. The designed system’s configuration is summarized. There are particular introduction for each part of the system. The scattering properties of the diffusion screen is researched through experiment. There is highlighting information on the design of optical system, light path, reflector, focal length and aperture of camera lens, and depth of field of CCD camera are respectively introduced. The data processing software are introduced. The design implements large laser spot intensity distribution measurement and power measurement in small space at the same time, it has the advantages of high resolution(5 mm) for intensity distribution measu
2010,
22.
Abstract:
The Langley-Plot calibration principles and measurement apparatus of total atmospheric transmittance were introduced. The multi-objective star calibration of total atmospheric transmittance measurements with stellar irradiance is presented, and calibration experimentations of the K,A spectral type stars were carried out .The calibration values based on the K, A types of stellar spectra were obtained. Comparison experiments between multi-objective star method and Langley-Plot method were carried out, and the reasonableness and correctness of multi-objective star calibration method have been verified. When take real-time measurement with the same type stellar spectra, the corresponding calibration parameters can be used to carry out the measurements of the atmospheric transmittance.
The Langley-Plot calibration principles and measurement apparatus of total atmospheric transmittance were introduced. The multi-objective star calibration of total atmospheric transmittance measurements with stellar irradiance is presented, and calibration experimentations of the K,A spectral type stars were carried out .The calibration values based on the K, A types of stellar spectra were obtained. Comparison experiments between multi-objective star method and Langley-Plot method were carried out, and the reasonableness and correctness of multi-objective star calibration method have been verified. When take real-time measurement with the same type stellar spectra, the corresponding calibration parameters can be used to carry out the measurements of the atmospheric transmittance.
2010,
22.
Abstract:
In order to understand the influence of the tangential airflow on the thermal response of resin composite irradiated by laser, the convective heat transfer coefficient and the blanketing effect are studied by the heat transfer theory of boundary layer, and the one-dimensional thermal response model of resin composite irradiated by laser is solved with finite difference method. The simulation results indicate that the high-speed tangential airflow increases the convective heat exchange of the target surface, consequently reduces the heating efficiency of the laser obviously. The convective heat transfer coefficient and the blanketing factor base on the heat transfer theory of boundary layer are proper, and are suitable for numerical simulation of tangential airflow impacting on the thermal
In order to understand the influence of the tangential airflow on the thermal response of resin composite irradiated by laser, the convective heat transfer coefficient and the blanketing effect are studied by the heat transfer theory of boundary layer, and the one-dimensional thermal response model of resin composite irradiated by laser is solved with finite difference method. The simulation results indicate that the high-speed tangential airflow increases the convective heat exchange of the target surface, consequently reduces the heating efficiency of the laser obviously. The convective heat transfer coefficient and the blanketing factor base on the heat transfer theory of boundary layer are proper, and are suitable for numerical simulation of tangential airflow impacting on the thermal
2010,
22.
Abstract:
Beam position monitor (BPM), as the most popular component in beam instrumentation system of particle accelerator, carrying not only beam position information but also other information like beam charge, is suitable for multi parameters diagnostics. This paper introduce BPM theory and numeric simulation results of pickup, discusses the feasibility of beam current measurement using BPM. Several beam experiments have been performed in the SSRF storage ring to calibrate current factor of 140 BPMs, evaluate current measurement resolution, beam position dependency and RF frequency dependency. The performance and limitation of this method was discussed based on these experiments.
Beam position monitor (BPM), as the most popular component in beam instrumentation system of particle accelerator, carrying not only beam position information but also other information like beam charge, is suitable for multi parameters diagnostics. This paper introduce BPM theory and numeric simulation results of pickup, discusses the feasibility of beam current measurement using BPM. Several beam experiments have been performed in the SSRF storage ring to calibrate current factor of 140 BPMs, evaluate current measurement resolution, beam position dependency and RF frequency dependency. The performance and limitation of this method was discussed based on these experiments.
2010,
22.
Abstract:
In order to overcome the limitation that the two-wire monitor cannot measure the beam position in vertical and horizontal directions at the same time, a new photon beam position measurement system based on four-quadrant detector has been developed at the Hefei Light Source(HLS), and the logarithmic ratio method is used for data processing. After the calibration of the optical imaging system and the four-quadrant detector, main parameters of the photon beam position measurement system were obtained. In horizontal direction, the linear range is ±1.83 mm, and the sensitivity is 0.471 2 mm-1. In vertical direction, the linear range is ±1.32 mm, and the sensitivity is 0.635 0 mm-1. The system has a good performance price ratio.
In order to overcome the limitation that the two-wire monitor cannot measure the beam position in vertical and horizontal directions at the same time, a new photon beam position measurement system based on four-quadrant detector has been developed at the Hefei Light Source(HLS), and the logarithmic ratio method is used for data processing. After the calibration of the optical imaging system and the four-quadrant detector, main parameters of the photon beam position measurement system were obtained. In horizontal direction, the linear range is ±1.83 mm, and the sensitivity is 0.471 2 mm-1. In vertical direction, the linear range is ±1.32 mm, and the sensitivity is 0.635 0 mm-1. The system has a good performance price ratio.
2010,
22.
Abstract:
Gas switch and vacuum diode are important parts of high power pulse modulator; the measurements of their characteristic parameters are focused on voltage and current. In this paper, using the photodiode and optic fiber, the optical characteristic parameters of the gas discharge switch and vacuum diode are obtained. Factors that influence the measurement have been theoretically analyzed and simulatively studied. Experiments were done at the charging voltage of the pulse forming line of 1.7 MV, the vacuum diode voltage is 1.07 MV, and vacuum current is 18 kA. The relations between the breakdown voltage, current and the optical characteristics are obtained from experiments; the feasibility of using the optical method to measure the voltage and current of the high power pulse modulator are als
Gas switch and vacuum diode are important parts of high power pulse modulator; the measurements of their characteristic parameters are focused on voltage and current. In this paper, using the photodiode and optic fiber, the optical characteristic parameters of the gas discharge switch and vacuum diode are obtained. Factors that influence the measurement have been theoretically analyzed and simulatively studied. Experiments were done at the charging voltage of the pulse forming line of 1.7 MV, the vacuum diode voltage is 1.07 MV, and vacuum current is 18 kA. The relations between the breakdown voltage, current and the optical characteristics are obtained from experiments; the feasibility of using the optical method to measure the voltage and current of the high power pulse modulator are als
2010,
22.
Abstract:
C. elegans were exposed to high power millimeter waves(MMWs) with different mean power densities, to investigate their behavioral response and cell morphology changes under MMW irradiation. The time-course photomicrography system was used to record the behavioral changes of C. elegans. The behavioral response and cell morphology changes were further observed by stereoscopic microscopes. The results show that freely moving C. elegans will escape from the MMW irradiation region quickly. After the exposure to MMWs with output mean power of 10 W and 12 W, the bending speed of C. elegans increases significantly at first, while the movement gradually slows down until the bodies get rigid. However, exposed to 5 W MMW, C. elegans show a distinctive tolerant reaction because of the thermal effect.
C. elegans were exposed to high power millimeter waves(MMWs) with different mean power densities, to investigate their behavioral response and cell morphology changes under MMW irradiation. The time-course photomicrography system was used to record the behavioral changes of C. elegans. The behavioral response and cell morphology changes were further observed by stereoscopic microscopes. The results show that freely moving C. elegans will escape from the MMW irradiation region quickly. After the exposure to MMWs with output mean power of 10 W and 12 W, the bending speed of C. elegans increases significantly at first, while the movement gradually slows down until the bodies get rigid. However, exposed to 5 W MMW, C. elegans show a distinctive tolerant reaction because of the thermal effect.
2010,
22.
Abstract:
To enhance the total power capability and gain of the high power mesoband electromagnetic pulse radiator, the study of a high power mesoband patch antenna array was conducted, including analysis of antenna elements, mutual coupling analysis, design of power divider and discussion on radiation characteristics of mesoband electromagnetic pulse. Using high power twolayer wideband patch antenna as array element, variations of ports reflection and mutual coupling factors with element spacing were analyzed, and 30 cm was chosen as the spacing with the analysis of gain versus element spacing. A 1∶4 coaxial power divider was designed with wide frequency band achieved using impedance tapered structure, and its reflection ratio was below 0.1 from 224 to 415 MHz. The simulation of the array with t
To enhance the total power capability and gain of the high power mesoband electromagnetic pulse radiator, the study of a high power mesoband patch antenna array was conducted, including analysis of antenna elements, mutual coupling analysis, design of power divider and discussion on radiation characteristics of mesoband electromagnetic pulse. Using high power twolayer wideband patch antenna as array element, variations of ports reflection and mutual coupling factors with element spacing were analyzed, and 30 cm was chosen as the spacing with the analysis of gain versus element spacing. A 1∶4 coaxial power divider was designed with wide frequency band achieved using impedance tapered structure, and its reflection ratio was below 0.1 from 224 to 415 MHz. The simulation of the array with t
2010,
22.
Abstract:
A jiggle particle swarm optimization (JPSO) algorithm has been adopted for multi-parameter optimization of 2D electro-optical problems. Given the target track of electron trajectory and scope of optimization, it can find rotating axisymmetric vacuum boundaries and magnetic structures whose electron trajectories are close to the target one. The algorithm consists of two phases. In the first phase, up and down test method (jiggle) is adopted with continuous reference to the best particle’s information. In the second phase, the basic particle swarm optimization (PSO) algorithm is adopted. The JPSO algorithm can find the global best solution with higher probability than the basic PSO algorithm, and shows multi-core computer’s potential in engineering design of electro-optical problems. This
A jiggle particle swarm optimization (JPSO) algorithm has been adopted for multi-parameter optimization of 2D electro-optical problems. Given the target track of electron trajectory and scope of optimization, it can find rotating axisymmetric vacuum boundaries and magnetic structures whose electron trajectories are close to the target one. The algorithm consists of two phases. In the first phase, up and down test method (jiggle) is adopted with continuous reference to the best particle’s information. In the second phase, the basic particle swarm optimization (PSO) algorithm is adopted. The JPSO algorithm can find the global best solution with higher probability than the basic PSO algorithm, and shows multi-core computer’s potential in engineering design of electro-optical problems. This
2010,
22.
Abstract:
Experimental study on the electron emission of silicon carbide nanowires cathode samples fabricated by the pyrolysis of polycarbosilane at 1 200 ℃ was carried out. The results show that the silicon carbide nanowires cathode has higher electron emission current density, which is 23.7 kA/cm2 at the condition of 115 kV stimulation voltage and 10 mm distance between the cathode and anode, compared to 14.0 kA/cm2 for the velvet cathode. Also, it emits electron beams of better quality and has longer service life.
Experimental study on the electron emission of silicon carbide nanowires cathode samples fabricated by the pyrolysis of polycarbosilane at 1 200 ℃ was carried out. The results show that the silicon carbide nanowires cathode has higher electron emission current density, which is 23.7 kA/cm2 at the condition of 115 kV stimulation voltage and 10 mm distance between the cathode and anode, compared to 14.0 kA/cm2 for the velvet cathode. Also, it emits electron beams of better quality and has longer service life.
2010,
22.
Abstract:
High frequency characteristics analysis is presented on a washer loaded wide-gap reentrant output cavity for the S-band relativistic wide-gap klystron amplifier(WKA). At resonant frequency points, the electric field modes of the wide-gap output cavity with large coupling hole are not TM011 anymore. To avoid these unwanted modes and their influences on cavity gap field distribution, a large enough distance between designed working frequency and resonant frequency is required. At the same time, an effort to reduce the output cavity external quality factor is also necessary. The output cavity power extraction effect was simulated by using a three-dimension fully electromagnetic particle-in-cell(PIC) code. At beam voltage of 600 kV, cathode current of 5 kA and current modulation dep
High frequency characteristics analysis is presented on a washer loaded wide-gap reentrant output cavity for the S-band relativistic wide-gap klystron amplifier(WKA). At resonant frequency points, the electric field modes of the wide-gap output cavity with large coupling hole are not TM011 anymore. To avoid these unwanted modes and their influences on cavity gap field distribution, a large enough distance between designed working frequency and resonant frequency is required. At the same time, an effort to reduce the output cavity external quality factor is also necessary. The output cavity power extraction effect was simulated by using a three-dimension fully electromagnetic particle-in-cell(PIC) code. At beam voltage of 600 kV, cathode current of 5 kA and current modulation dep
2010,
22.
Abstract:
Aperture coupling is a main coupling mode through which ultra wide band(UWB) electromagnetic pulse(EMP) can disturb or damage many equipments. Coupling effects of slots with different shapes in a cuboid object are studied using finite difference in time domain(FDTD) method. Selecting slots with dimension of several millimeters as research object, coupling effects by varied incident angles and varied pulse widths are analyzed. Interior resonance effect, increase effect around slots and several distributing rules of electric field in the cavity are got. The main results include: clear increase effect occurs around rectangle slot; coupling coefficients of triangle slot and array are obviously smaller than that of other slots; coupling effect of incident pulse with short pulse width is obvious
Aperture coupling is a main coupling mode through which ultra wide band(UWB) electromagnetic pulse(EMP) can disturb or damage many equipments. Coupling effects of slots with different shapes in a cuboid object are studied using finite difference in time domain(FDTD) method. Selecting slots with dimension of several millimeters as research object, coupling effects by varied incident angles and varied pulse widths are analyzed. Interior resonance effect, increase effect around slots and several distributing rules of electric field in the cavity are got. The main results include: clear increase effect occurs around rectangle slot; coupling coefficients of triangle slot and array are obviously smaller than that of other slots; coupling effect of incident pulse with short pulse width is obvious
2010,
22.
Abstract:
Sheet electron beams can transport stably in periodically cusped magnetic fields(PCMs). Two-plane focusing and edge focusing of the sheet beams with rectangular cross section of finite width are investigated using single-particle model. Theoretical and numerical analyses show that offset-pole PCM configuration is effective in edge focusing, while both PCM and offset-pole PCM configurations are incapable of two-plane edge focusing. The PCM-PQM(periodic quadrupole magnetic field) configuration has inherent advantages for independent adjustment of edge fields so that two-plane focusing and edge focusing can be accomplished in both transverse dimensions.
Sheet electron beams can transport stably in periodically cusped magnetic fields(PCMs). Two-plane focusing and edge focusing of the sheet beams with rectangular cross section of finite width are investigated using single-particle model. Theoretical and numerical analyses show that offset-pole PCM configuration is effective in edge focusing, while both PCM and offset-pole PCM configurations are incapable of two-plane edge focusing. The PCM-PQM(periodic quadrupole magnetic field) configuration has inherent advantages for independent adjustment of edge fields so that two-plane focusing and edge focusing can be accomplished in both transverse dimensions.
