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RSS2007 Vol. 19, No. 08
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2007,
19.
Abstract:
Stabilization and spectrum narrowing of the emission wavelength of high-power diode laser array is demonstrated by a volume Bragg grating (VBG) resonator. The spectral full width half maximum of the output emission was suppressed by VBG cavity from 1.7 nm to 0.4 nm, and the emission wavelength of VBG-locked diode laser array varied slightly with variation of output power and heat sink temperature. Output power of 15.12 W is achieved from VBG-locked diode laser array with a loss of approximately 2% when the injection current is 35 A.
Stabilization and spectrum narrowing of the emission wavelength of high-power diode laser array is demonstrated by a volume Bragg grating (VBG) resonator. The spectral full width half maximum of the output emission was suppressed by VBG cavity from 1.7 nm to 0.4 nm, and the emission wavelength of VBG-locked diode laser array varied slightly with variation of output power and heat sink temperature. Output power of 15.12 W is achieved from VBG-locked diode laser array with a loss of approximately 2% when the injection current is 35 A.
2007,
19.
Abstract:
Coherent combination of multiple fiber laser is an effective method to get high power laser with excellent beam quality. However, recently developed high power fiber lasers have relatively long linewidths, which means degradation of coherence and disaduentage of coherent combination. The far-field energy distribution of coherent combining high power fiber laser beam array was calculated using pseudo-partially coherent beam(PPCB) model. The results show that when the linewidths of single fiber laser beam get larger, the far-field pattern hardly changes, but the peak power and Strehl value of far-field spot reduce, which means the degradation of the combined beam. The linewidth of single fiber laser should be no more than 5 nm to keep the Strehl ratio larger than 0.8.
Coherent combination of multiple fiber laser is an effective method to get high power laser with excellent beam quality. However, recently developed high power fiber lasers have relatively long linewidths, which means degradation of coherence and disaduentage of coherent combination. The far-field energy distribution of coherent combining high power fiber laser beam array was calculated using pseudo-partially coherent beam(PPCB) model. The results show that when the linewidths of single fiber laser beam get larger, the far-field pattern hardly changes, but the peak power and Strehl value of far-field spot reduce, which means the degradation of the combined beam. The linewidth of single fiber laser should be no more than 5 nm to keep the Strehl ratio larger than 0.8.
2007,
19.
Abstract:
An experiment of laser beam propagation was carried out on 3.5 km urbanised path. The irradiance scintillation and angle of arrival were synchronously measured. The statistical characteristic of irradiance fluctuation and atmospheric refractive-index structure constant are analyzed. Estimates of scintillation fade margin for different scintillation variance and probability of fade for different fade threshold in free space optical communications are made. The atmospheric refractive-index are mostly above 10-14 m-2/3, and the scintillation index mainly range from 0.01 to 0.79, in the urbanised environment. The results can provide experimental basis for the design of free space optical communication system.
An experiment of laser beam propagation was carried out on 3.5 km urbanised path. The irradiance scintillation and angle of arrival were synchronously measured. The statistical characteristic of irradiance fluctuation and atmospheric refractive-index structure constant are analyzed. Estimates of scintillation fade margin for different scintillation variance and probability of fade for different fade threshold in free space optical communications are made. The atmospheric refractive-index are mostly above 10-14 m-2/3, and the scintillation index mainly range from 0.01 to 0.79, in the urbanised environment. The results can provide experimental basis for the design of free space optical communication system.
2007,
19.
Abstract:
Fused silica is used as the material of the phase conjugated mirror. In the LD pumped laser MOPA system, phase conjugation through the stimulated Brillouin scattering is realized at the repetition frequency of 100 Hz and 400 Hz. At the repetition frequency of 100 Hz, the beam quality factor reached 1.74 in x direction and 1.66 in y direction after double-pass amplification. The highest reflectivity is 24.33% with the input energy of 60.1 mJ, the pulse duration is compressed from 60 ns to 31.34 ns. At the repetition frequency of 400 Hz, the beam quality factor reached 2.10 in x direction and 2.12 in y direction after double-pass amplification. The pulse duration is compressed from 56.69 ns to 28.84 ns.
Fused silica is used as the material of the phase conjugated mirror. In the LD pumped laser MOPA system, phase conjugation through the stimulated Brillouin scattering is realized at the repetition frequency of 100 Hz and 400 Hz. At the repetition frequency of 100 Hz, the beam quality factor reached 1.74 in x direction and 1.66 in y direction after double-pass amplification. The highest reflectivity is 24.33% with the input energy of 60.1 mJ, the pulse duration is compressed from 60 ns to 31.34 ns. At the repetition frequency of 400 Hz, the beam quality factor reached 2.10 in x direction and 2.12 in y direction after double-pass amplification. The pulse duration is compressed from 56.69 ns to 28.84 ns.
2007,
19.
Abstract:
Using the average parameters at the outlet of a mixing nozzle calculated based on experimental data of a chemical oxygen-iodine laser(COIL) apparatus without primary buffer gas as input conditions, the flow fields from the inlet of optical cavity to the outlet of diffuser for six different diffuser configurations were numerically simulated. Contours of different flow field parameters such as Mach number, static pressure, and total pressure etc. were obtained. The flow field characteristics and the total pressure recovery performance for different diffuser configurations were analyzed. The effect of back pressure at the diffuser outlet on flow field parameters was also studied. The results indicate that the diffuser with constant cross section has better pressure recovery performance for CO
Using the average parameters at the outlet of a mixing nozzle calculated based on experimental data of a chemical oxygen-iodine laser(COIL) apparatus without primary buffer gas as input conditions, the flow fields from the inlet of optical cavity to the outlet of diffuser for six different diffuser configurations were numerically simulated. Contours of different flow field parameters such as Mach number, static pressure, and total pressure etc. were obtained. The flow field characteristics and the total pressure recovery performance for different diffuser configurations were analyzed. The effect of back pressure at the diffuser outlet on flow field parameters was also studied. The results indicate that the diffuser with constant cross section has better pressure recovery performance for CO
2007,
19.
Abstract:
Taking single period injection as an example, the influence of frequency and fluctuation amplitude of the injection field on the dynamics and synchronization of semiconductor lasers are studied numerically. The single period injection is obtained through direct modulation and external modulation, and a modified correlation coefficient called similarity index is used to evaluate the synchronization performance. The results show that injection locking synchronization is realized when injection rate is large enough. In the injection locking regime, similarity index is larger for external modulation than that for direct modulation. If injection rate keeps unchanged, synchronization is little affected by modulation index, but it is affected by modulation frequency. Since outputs of the master l
Taking single period injection as an example, the influence of frequency and fluctuation amplitude of the injection field on the dynamics and synchronization of semiconductor lasers are studied numerically. The single period injection is obtained through direct modulation and external modulation, and a modified correlation coefficient called similarity index is used to evaluate the synchronization performance. The results show that injection locking synchronization is realized when injection rate is large enough. In the injection locking regime, similarity index is larger for external modulation than that for direct modulation. If injection rate keeps unchanged, synchronization is little affected by modulation index, but it is affected by modulation frequency. Since outputs of the master l
2007,
19.
Abstract:
According to the statistical model of the random phase screen, which is employed in the high power laser system, the phase noise and the first and second statistical characteristics of RMS gradient have been studied. The properties of the coherent and partially coherent lights after propagating through the random phase screen are discussed. Using the statistical model, the numerical simulation of the far-field distribution of the beams has worked out. The results show that the far-field distribution of the coherent light that propagates through the phase screen becomes unsymmetrical until the phase distribution satisfies the mathematical expectation. The partially coherent light will hold its Gussian-Schell-model charecter while propagating through the random screen. The character of the S
According to the statistical model of the random phase screen, which is employed in the high power laser system, the phase noise and the first and second statistical characteristics of RMS gradient have been studied. The properties of the coherent and partially coherent lights after propagating through the random phase screen are discussed. Using the statistical model, the numerical simulation of the far-field distribution of the beams has worked out. The results show that the far-field distribution of the coherent light that propagates through the phase screen becomes unsymmetrical until the phase distribution satisfies the mathematical expectation. The partially coherent light will hold its Gussian-Schell-model charecter while propagating through the random screen. The character of the S
2007,
19.
Abstract:
The rate equations including loss coefficients describing threshold pumped fiber lasers doped with quasi two-energy-level rare-earth ions have been analytically and fully solved. An analytical expression of the threshold pump power has been deduced, a closed-form expression for the variation of the pump power along the fiber has also been obtained, together with analytical solutions to the laser power in terms of the pump power and the position dependent atom population density. A comparison has been made between the analytical result and the previously reported ones. It indicates that various approximations have underestimated the threshold pump powers after neglecting the loss coefficients of both the laser and pump waves, while our theoretical predication is the closest to the experimen
The rate equations including loss coefficients describing threshold pumped fiber lasers doped with quasi two-energy-level rare-earth ions have been analytically and fully solved. An analytical expression of the threshold pump power has been deduced, a closed-form expression for the variation of the pump power along the fiber has also been obtained, together with analytical solutions to the laser power in terms of the pump power and the position dependent atom population density. A comparison has been made between the analytical result and the previously reported ones. It indicates that various approximations have underestimated the threshold pump powers after neglecting the loss coefficients of both the laser and pump waves, while our theoretical predication is the closest to the experimen
2007,
19.
Abstract:
In gasdynamics and chemical lasers, the supersonic diffuser plays an important role in the pressure recovery system. This paper introduces some experimental and numerical results of an experimental supersonic diffuser under the normal temperature condition. Several factors affecting the diffusing performance are comparatively analyzed, including different divergent angles, with and without endwall energizers, horizontal vanes and vertical vanes. Preliminary study shows that the supersonic diffuser efficiency can be greatly improved by means of setting small divergent angle utilized into cavity of the laser and diffuser of the pressure recovery system, using vertical vanes with proper thickness set along the direction of inner width of the diffuser and endwall energizers on the left and rig
In gasdynamics and chemical lasers, the supersonic diffuser plays an important role in the pressure recovery system. This paper introduces some experimental and numerical results of an experimental supersonic diffuser under the normal temperature condition. Several factors affecting the diffusing performance are comparatively analyzed, including different divergent angles, with and without endwall energizers, horizontal vanes and vertical vanes. Preliminary study shows that the supersonic diffuser efficiency can be greatly improved by means of setting small divergent angle utilized into cavity of the laser and diffuser of the pressure recovery system, using vertical vanes with proper thickness set along the direction of inner width of the diffuser and endwall energizers on the left and rig
2007,
19.
Abstract:
Using 1D MED101 code, the competition mechanism between nonequilibrium electrostatic field ablation and thermal equilibrium ablation was analyzed when the pulsed laser with wavelength 1 064 nm, pulse duration 1~20 ps, ablated copper in vacuum. Numerical simulation results revealed that when the pulse duration was short(1~5 ps), the nonequilibrium electrostatic field ablation occupies the ablation process, and that when the pulse duration become longer(10~20 ps), the thermal equilibrium ablation is the main process in the whole ablation. It also demonstrates that the maximum temperature of electrons versus time will have multi-peaks as the pulse duration and peak power density increase. Especially, the ablation depths of the nonequilibrium electrostatic field are 110 nm and 101 nm for pulse
Using 1D MED101 code, the competition mechanism between nonequilibrium electrostatic field ablation and thermal equilibrium ablation was analyzed when the pulsed laser with wavelength 1 064 nm, pulse duration 1~20 ps, ablated copper in vacuum. Numerical simulation results revealed that when the pulse duration was short(1~5 ps), the nonequilibrium electrostatic field ablation occupies the ablation process, and that when the pulse duration become longer(10~20 ps), the thermal equilibrium ablation is the main process in the whole ablation. It also demonstrates that the maximum temperature of electrons versus time will have multi-peaks as the pulse duration and peak power density increase. Especially, the ablation depths of the nonequilibrium electrostatic field are 110 nm and 101 nm for pulse
2007,
19.
Abstract:
Laser-driven flying plates technique(LDFT) is an important and feasible way to load materials and simulate high-velocity motion law of space articles. The momentum coupling model for laser-driven flying plates is one of the important research fields of laser driven flyer plates techniques, whose essence is macroscopical representation of laser-material interaction law. According to lasersupporteddetonatingwave(LSDW) theory, this article builds a model on momentum calculation of laser driven flying plates under constraints. Taking into account the factors such as laser power density,pulse width, focus spot area, sparse wave, atmosphere parameters of flying plates surface and flyer plates area, the model demonstrates the action mechanism of flying plates by LSDW theory. Theoretical cal
Laser-driven flying plates technique(LDFT) is an important and feasible way to load materials and simulate high-velocity motion law of space articles. The momentum coupling model for laser-driven flying plates is one of the important research fields of laser driven flyer plates techniques, whose essence is macroscopical representation of laser-material interaction law. According to lasersupporteddetonatingwave(LSDW) theory, this article builds a model on momentum calculation of laser driven flying plates under constraints. Taking into account the factors such as laser power density,pulse width, focus spot area, sparse wave, atmosphere parameters of flying plates surface and flyer plates area, the model demonstrates the action mechanism of flying plates by LSDW theory. Theoretical cal
2007,
19.
Abstract:
This paper presents our numerical analyses on the walk-off effect in periodically poled lithium niobate(PPLN) for optical parametric chirped pulse amplification in the front-stage of PW laser system with our simulation program. Under the 527 nm, 3 ns and 300 MW/cm2 pumping condition, using 1 053 nm, 0.6 nJ stretched pulse(from 100 fs to 800 ps) as signal, our analyses show that the high-order group velocity in the parametric process has little effect on the conversion coefficiency, but it distorts both the temporal and spectral profiles of the output signal pulse, thus degrades the pulse contrast of the amplified signal through a PPLN with a poled period of 9.7 μm.
This paper presents our numerical analyses on the walk-off effect in periodically poled lithium niobate(PPLN) for optical parametric chirped pulse amplification in the front-stage of PW laser system with our simulation program. Under the 527 nm, 3 ns and 300 MW/cm2 pumping condition, using 1 053 nm, 0.6 nJ stretched pulse(from 100 fs to 800 ps) as signal, our analyses show that the high-order group velocity in the parametric process has little effect on the conversion coefficiency, but it distorts both the temporal and spectral profiles of the output signal pulse, thus degrades the pulse contrast of the amplified signal through a PPLN with a poled period of 9.7 μm.
2007,
19.
Abstract:
Using the LARED-S code and referring to the NIF direct-drive DT ignition target, the effect of laser nonuniformity on the interior interface in direct-drive spherical implosion with high convergence ratio was numerically studied. The two-dimensional results show that the implosion with high convergence ratio is sensitive to the nonuniformity of driving laser, and the growth of hydrodynamic instability on interior interface destroys the symmetric-drive and reduces the volume of central hot spot observably. Taking the limit that perturbation amplitude is equal to 1/3 radius of central hot spot, the simulation also gives that the requirements for the laser uniformity for different mode number(less than 12) on simple physical model are between 2.5%~0.25%, and the modes between 8~10 have the mo
Using the LARED-S code and referring to the NIF direct-drive DT ignition target, the effect of laser nonuniformity on the interior interface in direct-drive spherical implosion with high convergence ratio was numerically studied. The two-dimensional results show that the implosion with high convergence ratio is sensitive to the nonuniformity of driving laser, and the growth of hydrodynamic instability on interior interface destroys the symmetric-drive and reduces the volume of central hot spot observably. Taking the limit that perturbation amplitude is equal to 1/3 radius of central hot spot, the simulation also gives that the requirements for the laser uniformity for different mode number(less than 12) on simple physical model are between 2.5%~0.25%, and the modes between 8~10 have the mo
2007,
19.
Abstract:
The frequency dependences of both amplitude and phase-shift of the first harmonic of the ring-down signal are measured by a lock-in amplifier in a phase-shift cavity ring-down technique (PS-CRD). With different frequency ranges, the cavity decay time values fitted with either amplitude-frequency curve or phase-shift-frequency curve differ in a wide range, with a maximum error of roughly 8%. By defining a root-mean-square error function including both the amplitude error term and phase-shift error term, the maximum error is significantly diminished to 1.3% and the root-mean-square error is as small as 0.5%. The cavity decay time is statistically determined to be 0.791 μs with different frequency ranges. On the other hand, experimental parameters (i.e., the instrumental response time and th
The frequency dependences of both amplitude and phase-shift of the first harmonic of the ring-down signal are measured by a lock-in amplifier in a phase-shift cavity ring-down technique (PS-CRD). With different frequency ranges, the cavity decay time values fitted with either amplitude-frequency curve or phase-shift-frequency curve differ in a wide range, with a maximum error of roughly 8%. By defining a root-mean-square error function including both the amplitude error term and phase-shift error term, the maximum error is significantly diminished to 1.3% and the root-mean-square error is as small as 0.5%. The cavity decay time is statistically determined to be 0.791 μs with different frequency ranges. On the other hand, experimental parameters (i.e., the instrumental response time and th
2007,
19.
Abstract:
Triangular silver nanoplates have been prepared by seed-mediated growth with CTAB as soft template, and their morphologies, chemical components and optical absorption properties have been characterized by TEM, EDX and UV-Vis. The results indicate that the as-prepared nanoparticles are single-crystal Ag with face center cubic structure. The nanoplates have triangular shape and their average edge length increases from 20 nm to 100 nm by lowering the adding amount of Ag seed. CTAB exists as a thin film capping the Ag nanoparticles and prevents them from being oxidized. Three peaks appear in the absorption spectra of the Ag nanocolloid, and they can be ascribed to different modes of surface plasmon resonance of the nanoplates. The Ag nanoplates selfassemble into twodimensional array when
Triangular silver nanoplates have been prepared by seed-mediated growth with CTAB as soft template, and their morphologies, chemical components and optical absorption properties have been characterized by TEM, EDX and UV-Vis. The results indicate that the as-prepared nanoparticles are single-crystal Ag with face center cubic structure. The nanoplates have triangular shape and their average edge length increases from 20 nm to 100 nm by lowering the adding amount of Ag seed. CTAB exists as a thin film capping the Ag nanoparticles and prevents them from being oxidized. Three peaks appear in the absorption spectra of the Ag nanocolloid, and they can be ascribed to different modes of surface plasmon resonance of the nanoplates. The Ag nanoplates selfassemble into twodimensional array when
2007,
19.
Abstract:
This paper discusses the deformation theory of large aperture optical element under thermal loads, and builds the finite element model by the software ANSYS. High precision sensors are used to measure the temperature around the optical elements in the target building and temperature change curve are plotted. The biggest temperature margin is 0.3 ℃ in 2 h. The biggest temperature margin is loaded on the finite element model of the optical element and the deformation of the optical element is got. The results indicate that the deformation of the optical element satisfy the stability requirement under present temperature control situation. At the same time, the deformation of the optical element under various temperature margins is calculated. The results indicate that the deformation of the
This paper discusses the deformation theory of large aperture optical element under thermal loads, and builds the finite element model by the software ANSYS. High precision sensors are used to measure the temperature around the optical elements in the target building and temperature change curve are plotted. The biggest temperature margin is 0.3 ℃ in 2 h. The biggest temperature margin is loaded on the finite element model of the optical element and the deformation of the optical element is got. The results indicate that the deformation of the optical element satisfy the stability requirement under present temperature control situation. At the same time, the deformation of the optical element under various temperature margins is calculated. The results indicate that the deformation of the
2007,
19.
Abstract:
Solvent effect and volume shrinkage ratio in melamine-formaldehyde gel aging process were discussed. Volume shrinkage ratio was analyzed from two aspects, the agingswelling balance and solvent effect. The results implied that the solution compositon (water and ethanol) would control the volume shrinkage ratio in aging process. Appropriate exchange steps for wet gel is that the mixture of the liquid in the gel and target solvent (ethand) is firstly used and the target solvent’s content gradually rises until it is pure target solvent, then the MF aerogel which has little volume shrinkage is obtained．
Solvent effect and volume shrinkage ratio in melamine-formaldehyde gel aging process were discussed. Volume shrinkage ratio was analyzed from two aspects, the agingswelling balance and solvent effect. The results implied that the solution compositon (water and ethanol) would control the volume shrinkage ratio in aging process. Appropriate exchange steps for wet gel is that the mixture of the liquid in the gel and target solvent (ethand) is firstly used and the target solvent’s content gradually rises until it is pure target solvent, then the MF aerogel which has little volume shrinkage is obtained．
2007,
19.
Abstract:
Based on the function analysis of target positioner for inertial confinement fusion, a kind of ICF target positioning robot system is designed to realize the adjustment and the alignment of a target. The robot system includes a target storage subsystem, a target exchange subsystem, a target transport subsystem and a 6-degree of freedom precision parallel robot subsystem, the structure and principle of every subsystem are dissertated. The system realizes micro scale position by parallel structure which is in the front of the system, and has the advantages of low mass, high stiffness, small cone angle, small volume and high precision. The robot system can position a target into a very small micro scale scope around the center of the target chamber whose diameter is several meters, the precis
Based on the function analysis of target positioner for inertial confinement fusion, a kind of ICF target positioning robot system is designed to realize the adjustment and the alignment of a target. The robot system includes a target storage subsystem, a target exchange subsystem, a target transport subsystem and a 6-degree of freedom precision parallel robot subsystem, the structure and principle of every subsystem are dissertated. The system realizes micro scale position by parallel structure which is in the front of the system, and has the advantages of low mass, high stiffness, small cone angle, small volume and high precision. The robot system can position a target into a very small micro scale scope around the center of the target chamber whose diameter is several meters, the precis
2007,
19.
Abstract:
The reflectivity calibration and correction of soft X-ray planar mirror is studied. Research is done on the 3W1B beamline of Beijing synchrotron radiation facility for mirrors with several materials, from 50 eV to 1 500 eV, with 40～120 mA beam current and 2 GeV storage ring electron energy. Variable-spacing planar grating on 3W1B generates higher harmonics necessarily, which reduces monochromaticity notably and brings about some errors. Though prefilter is used, limited by the grating dispersion effeciency and X-ray source internsity, there are still some higher harmonics during 300～750 eV. Therefore, the calibrated reflectivity must be corrected.
The reflectivity calibration and correction of soft X-ray planar mirror is studied. Research is done on the 3W1B beamline of Beijing synchrotron radiation facility for mirrors with several materials, from 50 eV to 1 500 eV, with 40～120 mA beam current and 2 GeV storage ring electron energy. Variable-spacing planar grating on 3W1B generates higher harmonics necessarily, which reduces monochromaticity notably and brings about some errors. Though prefilter is used, limited by the grating dispersion effeciency and X-ray source internsity, there are still some higher harmonics during 300～750 eV. Therefore, the calibrated reflectivity must be corrected.
2007,
19.
Abstract:
Using TEOS as precursor, ammonia as catalyst, silica antireflective coating was prepared by sol-gel process. To obtain hydrophobic properties, the silica coatings were surface-modified with fluoroal kylsilane(FAS) by self-assembly technique. FTIR-spectroscopy, UV-vis spectroscopy, scanning probe microscopy and contact angle measurement were used to measure the properties of the silica coatings. The results show that the peak transmittance of the hydrophobic coating is 99.7%, and the water contact angle of the hydrophobic coating is 110°. The FAS surface modification does not influence the optical properties of the coating, but improve its hydrophobicity remarkably．
Using TEOS as precursor, ammonia as catalyst, silica antireflective coating was prepared by sol-gel process. To obtain hydrophobic properties, the silica coatings were surface-modified with fluoroal kylsilane(FAS) by self-assembly technique. FTIR-spectroscopy, UV-vis spectroscopy, scanning probe microscopy and contact angle measurement were used to measure the properties of the silica coatings. The results show that the peak transmittance of the hydrophobic coating is 99.7%, and the water contact angle of the hydrophobic coating is 110°. The FAS surface modification does not influence the optical properties of the coating, but improve its hydrophobicity remarkably．
2007,
19.
Abstract:
Grazing-angle X-ray reflectivity(XRR) is described as an efficient, nondestructive means to measure the mass density of various amorphous carbon films down to the nanometer thickness range. Amorphous hydrogenated carbon films(α:CH films) are fabricated by low pressure plasma chemical vapor deposition method. The thickness of α:CH films is derived from XRR by the method of line fitting(according to the theory of modified Bragg equation) and by the period width(fringe space) of XRR. The mass density of the films is also derived from the critical angle of XRR based on the refractive theory. The results show that the thicknesses of films obtained by the two methods agree well, the average difference among them is only 5.5%. The mass density of the films’ error obtained from the critical ang
Grazing-angle X-ray reflectivity(XRR) is described as an efficient, nondestructive means to measure the mass density of various amorphous carbon films down to the nanometer thickness range. Amorphous hydrogenated carbon films(α:CH films) are fabricated by low pressure plasma chemical vapor deposition method. The thickness of α:CH films is derived from XRR by the method of line fitting(according to the theory of modified Bragg equation) and by the period width(fringe space) of XRR. The mass density of the films is also derived from the critical angle of XRR based on the refractive theory. The results show that the thicknesses of films obtained by the two methods agree well, the average difference among them is only 5.5%. The mass density of the films’ error obtained from the critical ang
2007,
19.
Abstract:
An improved process for fabrication of hollow microspheres used as innertial confinement fusion targets is the decomposable mandrel technique. Thermal gravity analysis and pyrolysis gas chromatorgraph/mass spectrometry were applied to obtaining the thermal pyrolysis behavior of poly-alpha-methylstyrene with weight-average relative molecular mass of 1.14×106. Experiment indicated that the pyrolysis temperature of poly-alpha-methylstyrene covered from 260 ℃ to 320 ℃, and that of glow discharge polymer covered from 350 ℃ to 420 ℃. Poly-alpha-methylstyrene degraded mostly to its monomer, alpha-methylstyrene. Tetrahydrofuran and alpha-methylstyrene dimer were found in the pyrolysis products. Tetrahydrofuran was the solvent used in preparation of poly-alpha-methylstyrene. The mass fraction
An improved process for fabrication of hollow microspheres used as innertial confinement fusion targets is the decomposable mandrel technique. Thermal gravity analysis and pyrolysis gas chromatorgraph/mass spectrometry were applied to obtaining the thermal pyrolysis behavior of poly-alpha-methylstyrene with weight-average relative molecular mass of 1.14×106. Experiment indicated that the pyrolysis temperature of poly-alpha-methylstyrene covered from 260 ℃ to 320 ℃, and that of glow discharge polymer covered from 350 ℃ to 420 ℃. Poly-alpha-methylstyrene degraded mostly to its monomer, alpha-methylstyrene. Tetrahydrofuran and alpha-methylstyrene dimer were found in the pyrolysis products. Tetrahydrofuran was the solvent used in preparation of poly-alpha-methylstyrene. The mass fraction
2007,
19.
Abstract:
Two different types of 1 064, 532 nm frequency-doubled antireflection coatings for X-LBO were deposited by electron beam evaporation. One stack is substrate /ZrO2/Y2O3/Al2O3/SiO2/air, and the other is substrate /Al2O3/ZrO2/Y2O3/Al2O3/SiO2/air. The main difference between the two was the presence of alumina interlayer, and the optical behavior and adhesion between film and LBO substrate were investigated. Both coatings showed good optical performance that the reflectance of the coatings at 1 064 nm or 532 nm is less than 0.5%, but the coating with alumina interlayer showed stronger adhesion after annealing at 473 K for 2 h by contrast with that without alumina interlayer, which indicated that the alumina interlayer helped the coating resist the strong thermal stress from the thermal expansi
Two different types of 1 064, 532 nm frequency-doubled antireflection coatings for X-LBO were deposited by electron beam evaporation. One stack is substrate /ZrO2/Y2O3/Al2O3/SiO2/air, and the other is substrate /Al2O3/ZrO2/Y2O3/Al2O3/SiO2/air. The main difference between the two was the presence of alumina interlayer, and the optical behavior and adhesion between film and LBO substrate were investigated. Both coatings showed good optical performance that the reflectance of the coatings at 1 064 nm or 532 nm is less than 0.5%, but the coating with alumina interlayer showed stronger adhesion after annealing at 473 K for 2 h by contrast with that without alumina interlayer, which indicated that the alumina interlayer helped the coating resist the strong thermal stress from the thermal expansi
2007,
19.
Abstract:
A six-port reflectometer for measuring the electrical thickness of radome and permittivity of dielectric material is introduced, which consists of a symmetrical five-port waveguide junction and a directional coupler. The key part of this system is the five-port junction, it has been simulated and designed by HFSS. The reflection coefficient of sliding shorts measured by this system has been given and the result shows that the system is stable and accurate. A measurement method of the reflection coefficient of the radome electrical thickness has been introduced. Through measuring the phase of reflection coefficients of radome wall, the relative change of electrical thickness of radome wall can be got. Short circuits waveguide method to measure the permittivity of materials has been given, t
A six-port reflectometer for measuring the electrical thickness of radome and permittivity of dielectric material is introduced, which consists of a symmetrical five-port waveguide junction and a directional coupler. The key part of this system is the five-port junction, it has been simulated and designed by HFSS. The reflection coefficient of sliding shorts measured by this system has been given and the result shows that the system is stable and accurate. A measurement method of the reflection coefficient of the radome electrical thickness has been introduced. Through measuring the phase of reflection coefficients of radome wall, the relative change of electrical thickness of radome wall can be got. Short circuits waveguide method to measure the permittivity of materials has been given, t
2007,
19.
Abstract:
A Cassegrain dual reflector antenna which consists of a TEM horn, a hyperbolical subreflector and a parabolic reflector, was developed to radiate high power UWB microwave. The Cassegrain dual reflector is formed by a 4.5 m parabolic reflector (the ratio of focal length to diameter is 0.4) and a 70 cm hyperbolical subreflector (focal length is 22.5 cm). The size and the F/D parameter of the parabolic single reflector antenna in experiment are the same as that of the dual reflector antenna. The gain of the Cassegrain dual reflector antenna and the parabolic single reflector antenna were simulated by FEKO program. The gain of the Cassegrain dual reflector is 1~2 dB higher than that of the parabolic single reflector at the frequency band between 0.2 GHz to 1.0 GHz, while the gain is 1~2 dB low
A Cassegrain dual reflector antenna which consists of a TEM horn, a hyperbolical subreflector and a parabolic reflector, was developed to radiate high power UWB microwave. The Cassegrain dual reflector is formed by a 4.5 m parabolic reflector (the ratio of focal length to diameter is 0.4) and a 70 cm hyperbolical subreflector (focal length is 22.5 cm). The size and the F/D parameter of the parabolic single reflector antenna in experiment are the same as that of the dual reflector antenna. The gain of the Cassegrain dual reflector antenna and the parabolic single reflector antenna were simulated by FEKO program. The gain of the Cassegrain dual reflector is 1~2 dB higher than that of the parabolic single reflector at the frequency band between 0.2 GHz to 1.0 GHz, while the gain is 1~2 dB low
2007,
19.
Abstract:
A conformal mesh-generating technique for FDTD analysis based on the object data originated from triangle-patch modeling in commercial software is presented. The crossing-points between grid lines and triangle-patch on the surface of objects are calculated using the projection and cross-point method. These cross-points are collated according to their coordinate values. The locations of conformal meshes and the corresponding length of the edges, which are used in the conformal FDTD method, are derived by considering the coordinates and the serial number’s parity of crossing-points. The conformal FDTD method, in which the magnetic field formulas are modified while the grid is on the curved surface, is then used to deal with electromagnetic scattering by a curved perfectly electric conductin
A conformal mesh-generating technique for FDTD analysis based on the object data originated from triangle-patch modeling in commercial software is presented. The crossing-points between grid lines and triangle-patch on the surface of objects are calculated using the projection and cross-point method. These cross-points are collated according to their coordinate values. The locations of conformal meshes and the corresponding length of the edges, which are used in the conformal FDTD method, are derived by considering the coordinates and the serial number’s parity of crossing-points. The conformal FDTD method, in which the magnetic field formulas are modified while the grid is on the curved surface, is then used to deal with electromagnetic scattering by a curved perfectly electric conductin
2007,
19.
Abstract:
Using a three-dimension fully electromagnetic particle-in-cell(PIC) code, double-gap output cavity of the S-band Relativistic Klystron Amplifier is simulated numerically. It is found that the microwave extraction power and efficiency is increased by employing the double-gap output cavity to change the distance of beam-microwave interaction. The relations between output power and depth of the modulated current and that between output power and r-distance of coupler hole, as well as the relation between output power and distance that electron beams is close to drifting wall are obtained. Furthermore, the relation between output power and DC transitional angle is presented and it accords with that of the theory. An 800 MW averaged power over the oscillator period is generated by simulation, w
Using a three-dimension fully electromagnetic particle-in-cell(PIC) code, double-gap output cavity of the S-band Relativistic Klystron Amplifier is simulated numerically. It is found that the microwave extraction power and efficiency is increased by employing the double-gap output cavity to change the distance of beam-microwave interaction. The relations between output power and depth of the modulated current and that between output power and r-distance of coupler hole, as well as the relation between output power and distance that electron beams is close to drifting wall are obtained. Furthermore, the relation between output power and DC transitional angle is presented and it accords with that of the theory. An 800 MW averaged power over the oscillator period is generated by simulation, w
2007,
19.
Abstract:
A new low-impedance axial transit-time oscillator with six cavities at C-band was designed, based on three-cavity transit time oscillator(TTO). The impedance of this oscillator is about 15 Ω, the microwave is exported in coaxial wave-guide. The oscillator possesses a large area cathode without extra magnetics. The oscillator is simulated in 2D model by 2.5-dimentional PIC code, the peak values of input voltage and current are 483 kV and 32.5 kA respectively; the average peak value of output microwave is over 3.0 GW, the main frequency is 3.75 GHz. The power efficiency of microwave is above 19% and better than that of the normal low-impedance osillators.
A new low-impedance axial transit-time oscillator with six cavities at C-band was designed, based on three-cavity transit time oscillator(TTO). The impedance of this oscillator is about 15 Ω, the microwave is exported in coaxial wave-guide. The oscillator possesses a large area cathode without extra magnetics. The oscillator is simulated in 2D model by 2.5-dimentional PIC code, the peak values of input voltage and current are 483 kV and 32.5 kA respectively; the average peak value of output microwave is over 3.0 GW, the main frequency is 3.75 GHz. The power efficiency of microwave is above 19% and better than that of the normal low-impedance osillators.
2007,
19.
Abstract:
According to the requirement of hard-tube magnetically insulated line oscillator(MILO), the diode of MILO is investigated. It has an insulator made of porcelain with ring slot and its shelter is improved. The length of the diode is shortened. With the improved diode, the device of MILO is optimized. In order to condense the apparatus, the integrity of the radiation antenna and microwave mode converter is also optimized. The experimental results are given: employing an electron beam of about 450 kV and 35 kA, L-band hard-tube MILO generates over 1.5 GW high power microwave with over 20 ns pulse duration at 1.22 GHz, the power efficiency is about 10%.
According to the requirement of hard-tube magnetically insulated line oscillator(MILO), the diode of MILO is investigated. It has an insulator made of porcelain with ring slot and its shelter is improved. The length of the diode is shortened. With the improved diode, the device of MILO is optimized. In order to condense the apparatus, the integrity of the radiation antenna and microwave mode converter is also optimized. The experimental results are given: employing an electron beam of about 450 kV and 35 kA, L-band hard-tube MILO generates over 1.5 GW high power microwave with over 20 ns pulse duration at 1.22 GHz, the power efficiency is about 10%.
2007,
19.
Abstract:
The mechanical properties of the main part of PKU photo-injector (3+1/2 cavity) are introduced. By optimizing the number and position of the stiff rings of the cavity with ANSYS and SUPERFISH code, the Lorentz force detuning problem when the cavity worked at pulsed mode and the “flat” field profile problem when the cavity was tuned at low temperature were solved. Besides, a tuner with a room temperature motor and a gear box for the cavity to work at the right frequency under 2 K circumstance was designed.
The mechanical properties of the main part of PKU photo-injector (3+1/2 cavity) are introduced. By optimizing the number and position of the stiff rings of the cavity with ANSYS and SUPERFISH code, the Lorentz force detuning problem when the cavity worked at pulsed mode and the “flat” field profile problem when the cavity was tuned at low temperature were solved. Besides, a tuner with a room temperature motor and a gear box for the cavity to work at the right frequency under 2 K circumstance was designed.
2007,
19.
Abstract:
Compared with the IH structure (110-mode), the CH structure (210-mode) can operate at higher frequencies (150~700 MHz) and can accelerate ions to higher energies (up to 150 MeV). Detailed microwave studio(MWS) simulations were performed for this structure. Since a multi-gap cavity can be approximated as a quasi-periodic structure, it is possible to analyze one bl/2-cell at an energy corresponding to the cavity centre. A reduced copper conductivity of 85% was adopted in effective shunt impedance calculations. Geometry variations with respect to RF frequency and shunt impedance can be performed rapidly by that method in the first stage of optimization. Using the transit time factor calculated by the beam dynamics simulation code LORASR, effective shunt impedances from 100 MΩ/m down to 45 M?
Compared with the IH structure (110-mode), the CH structure (210-mode) can operate at higher frequencies (150~700 MHz) and can accelerate ions to higher energies (up to 150 MeV). Detailed microwave studio(MWS) simulations were performed for this structure. Since a multi-gap cavity can be approximated as a quasi-periodic structure, it is possible to analyze one bl/2-cell at an energy corresponding to the cavity centre. A reduced copper conductivity of 85% was adopted in effective shunt impedance calculations. Geometry variations with respect to RF frequency and shunt impedance can be performed rapidly by that method in the first stage of optimization. Using the transit time factor calculated by the beam dynamics simulation code LORASR, effective shunt impedances from 100 MΩ/m down to 45 M?
2007,
19.
Abstract:
A new wire photon beam position monitor with a spring system was designed and installed in the machine diagnostic beamline in Hefei Light Source(HLS). The linearity range is 4 mm, and the sensitivity is about 0.197 9 mm-1. The beam current has a little effect on the synchrotron radiation vertical size. The signal-to-noise ratio and the linearity can be improved, but the sensitivity decreases with a positive bias voltage applied to the copper block.
A new wire photon beam position monitor with a spring system was designed and installed in the machine diagnostic beamline in Hefei Light Source(HLS). The linearity range is 4 mm, and the sensitivity is about 0.197 9 mm-1. The beam current has a little effect on the synchrotron radiation vertical size. The signal-to-noise ratio and the linearity can be improved, but the sensitivity decreases with a positive bias voltage applied to the copper block.
2007,
19.
Abstract:
This paper presents the measurement principle and the design of transverse impedance measurement setup with the wire method. The transverse impedance measurement system with a single wire is composed of a device under test (DUT)/reference line (REF), an inner wire, an adjuster used to adjust the transverse position of inner wire precisely and to excite the dipole resonant mode of DUT, impedance matching section and measurement instrument. The dipole mode and the impedance of the device under test(DUT, 2 856 MHz gibbous cavity) simulated by Microwave Studio are in agreement with the data calculated by ABCI code. The results demonstrated the rationality of system design and availability of system.
This paper presents the measurement principle and the design of transverse impedance measurement setup with the wire method. The transverse impedance measurement system with a single wire is composed of a device under test (DUT)/reference line (REF), an inner wire, an adjuster used to adjust the transverse position of inner wire precisely and to excite the dipole resonant mode of DUT, impedance matching section and measurement instrument. The dipole mode and the impedance of the device under test(DUT, 2 856 MHz gibbous cavity) simulated by Microwave Studio are in agreement with the data calculated by ABCI code. The results demonstrated the rationality of system design and availability of system.
2007,
19.
Abstract:
The energy spectrum and the angular distribution of the hot electrons generated by an ultra-intense femtosecond laser interacting with a solid target are studied. The intensity of the femtosecond laser is 8.5×1018 W·cm-2 and the pulse duration is 30 fs in experiment. The temperature of the hot electrons at the normal of the target is 550 keV. Resonance absorption is the main mechanism that leads to the laser acceleration of the hot electrons at the normal of the target. And it accords with large plasma density scale length generated by pre-pulse which preceded the main pulse. The emission direction of the hot electron is normal to the rear surface for 30 μm target, and the emission peak disappears for 2 mm target.
The energy spectrum and the angular distribution of the hot electrons generated by an ultra-intense femtosecond laser interacting with a solid target are studied. The intensity of the femtosecond laser is 8.5×1018 W·cm-2 and the pulse duration is 30 fs in experiment. The temperature of the hot electrons at the normal of the target is 550 keV. Resonance absorption is the main mechanism that leads to the laser acceleration of the hot electrons at the normal of the target. And it accords with large plasma density scale length generated by pre-pulse which preceded the main pulse. The emission direction of the hot electron is normal to the rear surface for 30 μm target, and the emission peak disappears for 2 mm target.
2007,
19.
Abstract:
According to the sensitivity curves of resists, the empirical formula of contrast was adopted to determine the relationship between exposure dose and etching depth accurately. Exposure experiments were carried out with positive resist PMMA. With curve fitting of the calculated results, the depth-dose curve is obtained and keeps consistent with the experimental results basically. When the doses are in the range of 20~35 μC/cm2, the difference between the experimental results and the calculated ones is least. Using the contrast method in the etching can save experimental time and raise the etching efficiency.
According to the sensitivity curves of resists, the empirical formula of contrast was adopted to determine the relationship between exposure dose and etching depth accurately. Exposure experiments were carried out with positive resist PMMA. With curve fitting of the calculated results, the depth-dose curve is obtained and keeps consistent with the experimental results basically. When the doses are in the range of 20~35 μC/cm2, the difference between the experimental results and the calculated ones is least. Using the contrast method in the etching can save experimental time and raise the etching efficiency.
2007,
19.
Abstract:
A surface treatment setup of coating TiN film on the inner face of stainless steel pipe vacuum chamber for accelerators at low temperature is described. A series of surface treatment parameters have been achieved through many coating experiments on a stainless steel pipe which is 86 mm in diameter and 2 000 mm in length. The test results show that TiN film of the best quality could be coated on the inner face of stainless steel pipe under 80～90 Pa and 160~180 ℃, and the deposition rate achieves 0.145 nm/s. The secondary electron yield of the coated chamber decreases distinctly compared with that of the uncoated chamber.
A surface treatment setup of coating TiN film on the inner face of stainless steel pipe vacuum chamber for accelerators at low temperature is described. A series of surface treatment parameters have been achieved through many coating experiments on a stainless steel pipe which is 86 mm in diameter and 2 000 mm in length. The test results show that TiN film of the best quality could be coated on the inner face of stainless steel pipe under 80～90 Pa and 160~180 ℃, and the deposition rate achieves 0.145 nm/s. The secondary electron yield of the coated chamber decreases distinctly compared with that of the uncoated chamber.
2007,
19.
Abstract:
An interaction potential with ch-2x form is introduced to describe the electron motion in superlattice quantum well, and in the frame of quantum mechanics, Schrodinger equation is transformed to the hypergeometric equation by this potential. The eigenvalue and the eigefunction of the system are calculated, and the distribution and the level number in quantum well are also discussed. As an example, the transition energy between two bands for material Ga1-xAlxAs-GaAs- Ga1-xAlxAs is calculated. It shows that the level number and the transition energy are related to the system parameters, such as the potential well depth, width etc. The photo-electric properties of superlattice materials can be controlled and regulated by regulating the system parameters.
An interaction potential with ch-2x form is introduced to describe the electron motion in superlattice quantum well, and in the frame of quantum mechanics, Schrodinger equation is transformed to the hypergeometric equation by this potential. The eigenvalue and the eigefunction of the system are calculated, and the distribution and the level number in quantum well are also discussed. As an example, the transition energy between two bands for material Ga1-xAlxAs-GaAs- Ga1-xAlxAs is calculated. It shows that the level number and the transition energy are related to the system parameters, such as the potential well depth, width etc. The photo-electric properties of superlattice materials can be controlled and regulated by regulating the system parameters.
2007,
19.
Abstract:
A series of ZnO thin films were deposited on silicon (100) substrate by facing target radio frequency magnetron sputtering system, and were annealed and supersonically treated. The samples were characterized by X-ray diffraction(XRD), atomic force microscopy(AFM), and photoluminescence(PL) spectrum. XRD results show that the as-deposited film has less preferential C-axis orientation, while increasing the annealing temperature gets preferential C-axis orientation better. The grain size of the sample becomes larger and the residual stress changes from compress stress to tensile stress with the increase of the annealing temperature. The PL spectrums indicate that there is no emission for the as-deposited film at room temperature. As the annealing temperature increases, both a 378 nm ultraviol
A series of ZnO thin films were deposited on silicon (100) substrate by facing target radio frequency magnetron sputtering system, and were annealed and supersonically treated. The samples were characterized by X-ray diffraction(XRD), atomic force microscopy(AFM), and photoluminescence(PL) spectrum. XRD results show that the as-deposited film has less preferential C-axis orientation, while increasing the annealing temperature gets preferential C-axis orientation better. The grain size of the sample becomes larger and the residual stress changes from compress stress to tensile stress with the increase of the annealing temperature. The PL spectrums indicate that there is no emission for the as-deposited film at room temperature. As the annealing temperature increases, both a 378 nm ultraviol
2007,
19.
Abstract:
The paper sets up an installation to produce glow discharge plasma and treat the capacitor film. Three kinds of capacitor films, including PP, PET and PPS films are treated by N2, O2 and Ar plasma. The infrared spectrums show that the change of matter on the film surface is affected by the kind of film, plasma and the treatment strength. The SEM images show apparent corrosions on the treated film surface, which can be explained as that the amorphous component is etched off, and the crystal grains are exposed. Energy spectrum analysis indicates that element of C decreases a little, while N and O increase slightly. The DC Breakdown voltages of treated and untreated films are nearly the same. However, the corrosion of the film surface due to the plasma treatment will make the immersion of fil
The paper sets up an installation to produce glow discharge plasma and treat the capacitor film. Three kinds of capacitor films, including PP, PET and PPS films are treated by N2, O2 and Ar plasma. The infrared spectrums show that the change of matter on the film surface is affected by the kind of film, plasma and the treatment strength. The SEM images show apparent corrosions on the treated film surface, which can be explained as that the amorphous component is etched off, and the crystal grains are exposed. Energy spectrum analysis indicates that element of C decreases a little, while N and O increase slightly. The DC Breakdown voltages of treated and untreated films are nearly the same. However, the corrosion of the film surface due to the plasma treatment will make the immersion of fil
2007,
19.
Abstract:
In wire-array Z-pinch experiments the images of one-dimensional temporal-spatial X-ray power were recorded by charge-coupled device(CCD). Data processing to correct the effects of non-ideal aspects, including the nonuniform optical transmission efficiency, unsatisfactory focalization and coupling between image intensifier and CCD, was performed. Both point spread function(PSF) and calibrated optical transmission coefficient were used in the process. Consistent soft X-ray power(SXR) pulse with the experimental one obtained by X-ray power meter(XRPM) was derived. Rise times between the two SXR pulses of different shots were in good accordance.
In wire-array Z-pinch experiments the images of one-dimensional temporal-spatial X-ray power were recorded by charge-coupled device(CCD). Data processing to correct the effects of non-ideal aspects, including the nonuniform optical transmission efficiency, unsatisfactory focalization and coupling between image intensifier and CCD, was performed. Both point spread function(PSF) and calibrated optical transmission coefficient were used in the process. Consistent soft X-ray power(SXR) pulse with the experimental one obtained by X-ray power meter(XRPM) was derived. Rise times between the two SXR pulses of different shots were in good accordance.
2007,
19.
Abstract:
A 4 MV coax-to-triplate multi-channel water dielectric self-breaking switch is designed for the oil and water section of a pulse power machine. The machine contains 24 modules with identical components. Eeach module contains Marx generator, intermediate store capacitor, laser triggered gas switch, water pulse forming line, water selfbreaking switch, transmission line and water resistance load. The water switch consists of three linear arrayed selfbreaking gaps, a prepulse shield(PPS) and supporting hardware. An experiment is conducted to investigate the switch with or without PPS. Each gap of the switch with PPS is made up of two hemispherical electrodes,80 mm and 50 mm for input and output elatrodes respectively，and each gap of the switch without PPS is plane to pin electrode（30 mm?
A 4 MV coax-to-triplate multi-channel water dielectric self-breaking switch is designed for the oil and water section of a pulse power machine. The machine contains 24 modules with identical components. Eeach module contains Marx generator, intermediate store capacitor, laser triggered gas switch, water pulse forming line, water selfbreaking switch, transmission line and water resistance load. The water switch consists of three linear arrayed selfbreaking gaps, a prepulse shield(PPS) and supporting hardware. An experiment is conducted to investigate the switch with or without PPS. Each gap of the switch with PPS is made up of two hemispherical electrodes,80 mm and 50 mm for input and output elatrodes respectively，and each gap of the switch without PPS is plane to pin electrode（30 mm?
