Email alert
RSS2007 Vol. 19, No. 04
Recommend Articles
column
Display Method:
2007,
19.
Abstract:
980 nm GaAs/AlGaAs separate confinement hetero-structure single quantum well laser bars were grown by metal organic chemical vapor deposition. The relationships between the etching depth and the bars’ parameters have been studied. When the bar is not etched deep to the active layer, the output power and the slope efficiency are in direct proportion to the etching depth, while the threshold current are in inverse proportion to the etching depth. When the bar is etched deeper than the active layer, the output power and the slope efficiency become lower and the threshold current become higher. The best etching depth is 1.993 mm in the experiment, which is less than the depth of the active layer.
980 nm GaAs/AlGaAs separate confinement hetero-structure single quantum well laser bars were grown by metal organic chemical vapor deposition. The relationships between the etching depth and the bars’ parameters have been studied. When the bar is not etched deep to the active layer, the output power and the slope efficiency are in direct proportion to the etching depth, while the threshold current are in inverse proportion to the etching depth. When the bar is etched deeper than the active layer, the output power and the slope efficiency become lower and the threshold current become higher. The best etching depth is 1.993 mm in the experiment, which is less than the depth of the active layer.
2007,
19.
Abstract:
The 3-dimensional numerical simulation of nozzle and diffuser for COIL system is performed. Several nozzle and diffuser designs are compared and analzed. The gasdynamic process from cavity inlet till diffuser outlet is computated. The sufficient mixing of primary and secondary flows in cavity can be reached by means of aiding tab, which is 0.77 cm×0.254 cm. The computational model of diffuser is the 1/4 construction, of which the input cross-section is 30 mm×60 mm. After keeping the same cross-section size till the length is 500 mm, the diffuser is continued with the same width and 4° divergent angle in height till the length is 700 mm. The final output area size of diffuser is 79 mm×60 mm. The input (output of cavity) gas condition of diffuser is air with Mach number of 3.2, static pr
The 3-dimensional numerical simulation of nozzle and diffuser for COIL system is performed. Several nozzle and diffuser designs are compared and analzed. The gasdynamic process from cavity inlet till diffuser outlet is computated. The sufficient mixing of primary and secondary flows in cavity can be reached by means of aiding tab, which is 0.77 cm×0.254 cm. The computational model of diffuser is the 1/4 construction, of which the input cross-section is 30 mm×60 mm. After keeping the same cross-section size till the length is 500 mm, the diffuser is continued with the same width and 4° divergent angle in height till the length is 700 mm. The final output area size of diffuser is 79 mm×60 mm. The input (output of cavity) gas condition of diffuser is air with Mach number of 3.2, static pr
2007,
19.
Abstract:
Scintillation effect of divergent laser beam and beam wander effect of a focused laser beam were experimentally used to deduce the refractive index structure constant in atmospheric boundary layer over 1 km path above sea level. Different measurement results of two methods are observed. Theoretical analyses reveal that the reasons for the difference between these two methods as follows: (1)Scintillation is most sensitive to small scale eddies in the centre of the path, however, for beam wander the most sensitive eddies are large scaled and near the transmitter; (2)With the increase of the inner scale from 0 to 20 mm, values of the refractive index structure constant deduced from beam wander effect are larger than that from scintillation. The biggest difference is 3 times when the inner sca
Scintillation effect of divergent laser beam and beam wander effect of a focused laser beam were experimentally used to deduce the refractive index structure constant in atmospheric boundary layer over 1 km path above sea level. Different measurement results of two methods are observed. Theoretical analyses reveal that the reasons for the difference between these two methods as follows: (1)Scintillation is most sensitive to small scale eddies in the centre of the path, however, for beam wander the most sensitive eddies are large scaled and near the transmitter; (2)With the increase of the inner scale from 0 to 20 mm, values of the refractive index structure constant deduced from beam wander effect are larger than that from scintillation. The biggest difference is 3 times when the inner sca
2007,
19.
Abstract:
A multi-coupler side-pumped rare-earth-doped double-clad fiber laser with a novel dielectric-metal-dielectric(DMD) sandwich structure based on the theory of sub-wavelength diffraction grating is presented. A rigorous electromagnetic theory which considers the vectorial character of the light has been used to investigate and compute its pump light leakage at adjacent coupler for every coupled structure and it is found that pump light leakage is only 15.52% with a angle perpendicular to side of fiber. So this DMD sandwich structure can be applied to multi-point side-pump double-clad fiber laser effectively and the maximum coupling efficiency is greater than 80% after the second diffraction.
A multi-coupler side-pumped rare-earth-doped double-clad fiber laser with a novel dielectric-metal-dielectric(DMD) sandwich structure based on the theory of sub-wavelength diffraction grating is presented. A rigorous electromagnetic theory which considers the vectorial character of the light has been used to investigate and compute its pump light leakage at adjacent coupler for every coupled structure and it is found that pump light leakage is only 15.52% with a angle perpendicular to side of fiber. So this DMD sandwich structure can be applied to multi-point side-pump double-clad fiber laser effectively and the maximum coupling efficiency is greater than 80% after the second diffraction.
2007,
19.
Abstract:
Thermally induced birefringence and optical distortion in electro-optic slab switches were analyzed, and the influence of distribution of intensity on thermal effects was discussed. The distribution of temperature increment, thermal stress, optical distortion and depolarization were calculated in the case of different intensity profiles (Gaussian and uniform) with KDP crystal as an example. The results indicate that the influence of nonuniformity of a light beam is significant on optical distortion and depolarization. For Gaussian light beams the depolarization is considerably lower because they mitigate the temperature gradients on the edge of the light beam, while the optical distortion is considerably larger against the spatially uniform light beam because Gaussian light beams have larg
Thermally induced birefringence and optical distortion in electro-optic slab switches were analyzed, and the influence of distribution of intensity on thermal effects was discussed. The distribution of temperature increment, thermal stress, optical distortion and depolarization were calculated in the case of different intensity profiles (Gaussian and uniform) with KDP crystal as an example. The results indicate that the influence of nonuniformity of a light beam is significant on optical distortion and depolarization. For Gaussian light beams the depolarization is considerably lower because they mitigate the temperature gradients on the edge of the light beam, while the optical distortion is considerably larger against the spatially uniform light beam because Gaussian light beams have larg
2007,
19.
Abstract:
A resonator for 1.444 mm Nd:YAG laser was designed, and 1.444 mm laser was obtained, the maximum static-state output energy was 310 mJ, electric-optics conversion efficiency was 0.56% and slope efficiency was 0.81% when the pump energy was 55 J. The 1.444 mm Q-switched laser was obtained, whose energy was 18 mJ and pulse width was 150 ns when the pump energy was 24 J. The CCD image showed that the energy distribution of the obtained laser was uniform and the divergence angle was 0.8 mrad.
A resonator for 1.444 mm Nd:YAG laser was designed, and 1.444 mm laser was obtained, the maximum static-state output energy was 310 mJ, electric-optics conversion efficiency was 0.56% and slope efficiency was 0.81% when the pump energy was 55 J. The 1.444 mm Q-switched laser was obtained, whose energy was 18 mJ and pulse width was 150 ns when the pump energy was 24 J. The CCD image showed that the energy distribution of the obtained laser was uniform and the divergence angle was 0.8 mrad.
2007,
19.
Abstract:
The paper presents a system to measure pulse instantaneous thrust using PVDF, which can respond to high frequency signal, as the sensitive element. System calibration is completed using separate Hopkinson pressure bars(SHPB) whose diameter is 37 mm. Result of calibration shows that piezoelectric characteristic of PVDF (5 mm×5 mm) is linear if the pressure is lower than 150 MPa. Piezoelectric coefficient of PVDF is about 20 pC/N after the calibrated data fitting. Thrust loading curve of parabolic laser thruster impacted by single pulse is acquired and the peak values of thrust are analyzed. Experimental results indicate that this test system can capture the characteristics of thrust loading and it is valuable for investigating laser thrusters and pulse detonation engines.
The paper presents a system to measure pulse instantaneous thrust using PVDF, which can respond to high frequency signal, as the sensitive element. System calibration is completed using separate Hopkinson pressure bars(SHPB) whose diameter is 37 mm. Result of calibration shows that piezoelectric characteristic of PVDF (5 mm×5 mm) is linear if the pressure is lower than 150 MPa. Piezoelectric coefficient of PVDF is about 20 pC/N after the calibrated data fitting. Thrust loading curve of parabolic laser thruster impacted by single pulse is acquired and the peak values of thrust are analyzed. Experimental results indicate that this test system can capture the characteristics of thrust loading and it is valuable for investigating laser thrusters and pulse detonation engines.
2007,
19.
Abstract:
Based on orthogonal subspace projection algorithm, the algorithm was used to satellite optimum channels selection for underlying surface classification. The weight functions were obtained by analyzing target spectra distribution and background radiance, transmittance computed by MODTRAN. Satellite optimum bands for underlying surface classification were selected by using weight function spectra distribution, optimum index function and the usages channels of MODIS. Channels composing result shows that the algorithm is effective for underlying surface classification.
Based on orthogonal subspace projection algorithm, the algorithm was used to satellite optimum channels selection for underlying surface classification. The weight functions were obtained by analyzing target spectra distribution and background radiance, transmittance computed by MODTRAN. Satellite optimum bands for underlying surface classification were selected by using weight function spectra distribution, optimum index function and the usages channels of MODIS. Channels composing result shows that the algorithm is effective for underlying surface classification.
2007,
19.
Abstract:
Chan-Vese(C-V) model is an excellent model of simplified Mumford-Shah models. As Chan-Vese model is based on two homogenous regions, it causes failure in edge detection of infrared images. A level set method for edge detection of infrared image based on improved Mumford-Shah model is proposed. The schemes of preserving object edges, establishing the stopping criterion and speeding up the algorithm are discussed. The experiments show that this model can overcome the failure of C-V model and detect edge of infrared images efficiently.
Chan-Vese(C-V) model is an excellent model of simplified Mumford-Shah models. As Chan-Vese model is based on two homogenous regions, it causes failure in edge detection of infrared images. A level set method for edge detection of infrared image based on improved Mumford-Shah model is proposed. The schemes of preserving object edges, establishing the stopping criterion and speeding up the algorithm are discussed. The experiments show that this model can overcome the failure of C-V model and detect edge of infrared images efficiently.
2007,
19.
Abstract:
The fourth order Runge-algorithm was used in the numerical simulation methods to study the influences of the profiles and durations of pump pulse on the compressed pulses. The LBO crystal was used for the nonlinear gain medium in the numerical simulation. When the narrower duration pump pulses were used, a higher contrast ratio of femtosecond was obtained by adopting the more smooth profiles of the pumps (namely the lower order parameters of pump pulses). The contrast ratio of the femtosecond can be improved by longer duration pump pulse. But the contrast ratio can not be further improved by improving the duration pump pulses further, while much lower conversion coefficient in OPCPA system occurs.
The fourth order Runge-algorithm was used in the numerical simulation methods to study the influences of the profiles and durations of pump pulse on the compressed pulses. The LBO crystal was used for the nonlinear gain medium in the numerical simulation. When the narrower duration pump pulses were used, a higher contrast ratio of femtosecond was obtained by adopting the more smooth profiles of the pumps (namely the lower order parameters of pump pulses). The contrast ratio of the femtosecond can be improved by longer duration pump pulse. But the contrast ratio can not be further improved by improving the duration pump pulses further, while much lower conversion coefficient in OPCPA system occurs.
2007,
19.
Abstract:
Temperature distribution in high power fiber laser was approximately analyzed by thermal conductive equation and boundary condition.The rationality of numerical solution was validated by ANSYS simulation.The fiber laser coating’s critical temperature was set 80 ℃ and the maximum output power using the thermal conductive equation was computed when the fiber laser is cooled by fan or water, such as Ybdoped double clad fiber laser. Results indicate that when the fiber is cooled in air (the heat transfer coefficient is 10 W·m－２·K－１), fiber lasers maximum output power is 105 W. When the fiber is cooled by fan (the heat transfer coefficient is 80 W·m－２·K－１), the maximum output power is 820 W. If the output power is demanded above 1 kW, the fiber laser must be cooled by water．
Temperature distribution in high power fiber laser was approximately analyzed by thermal conductive equation and boundary condition.The rationality of numerical solution was validated by ANSYS simulation.The fiber laser coating’s critical temperature was set 80 ℃ and the maximum output power using the thermal conductive equation was computed when the fiber laser is cooled by fan or water, such as Ybdoped double clad fiber laser. Results indicate that when the fiber is cooled in air (the heat transfer coefficient is 10 W·m－２·K－１), fiber lasers maximum output power is 105 W. When the fiber is cooled by fan (the heat transfer coefficient is 80 W·m－２·K－１), the maximum output power is 820 W. If the output power is demanded above 1 kW, the fiber laser must be cooled by water．
2007,
19.
Abstract:
A middle heat exchanger with microchannels- microgrooves(MC- MG) is used to cool solid- state laser medium. Flow and heat transfer characteristics of MC- MG heat exchanger have been studied experimentally. The experimental results indicate that the Nusselt number increases as the Reynolds number increases, and the general thermal resistance decreases as the distilled water flow in microchannels increases. The total heat transfer quantity increases with the increase of distilled water flux in microchannels. The average heat transfer coefficient of the MC- MG heat exchanger can reach 1.5×104 W/ (m2·K) and its general thermal resistance is smaller than 0.3 K/W. The solution of cooling high power laser with MC- MG heat exchanger is preferable.
A middle heat exchanger with microchannels- microgrooves(MC- MG) is used to cool solid- state laser medium. Flow and heat transfer characteristics of MC- MG heat exchanger have been studied experimentally. The experimental results indicate that the Nusselt number increases as the Reynolds number increases, and the general thermal resistance decreases as the distilled water flow in microchannels increases. The total heat transfer quantity increases with the increase of distilled water flux in microchannels. The average heat transfer coefficient of the MC- MG heat exchanger can reach 1.5×104 W/ (m2·K) and its general thermal resistance is smaller than 0.3 K/W. The solution of cooling high power laser with MC- MG heat exchanger is preferable.
2007,
19.
Abstract:
The relationship between the impulse coupling coefficient and the distance of the target from focus at different incident laser energy, and the relationship between impulse coupling coefficient and laser spot diameter at different incident laser intensity were studied by applying Nd:YAG laser pulse on the Al(Cu) target. The experiments show that the target position corresponding to the peak impulse coupling coefficient moves towards to the lens with the increase of the laser energy, and the increase of the optimum intensity is small. These prove that the plasma shielding induces decreases impulse coupling coefficient to decrease after the peak value. On the other hand impulse coupling coefficient increases with the increase of the laser spot diameter in a linear way at the same incident la
The relationship between the impulse coupling coefficient and the distance of the target from focus at different incident laser energy, and the relationship between impulse coupling coefficient and laser spot diameter at different incident laser intensity were studied by applying Nd:YAG laser pulse on the Al(Cu) target. The experiments show that the target position corresponding to the peak impulse coupling coefficient moves towards to the lens with the increase of the laser energy, and the increase of the optimum intensity is small. These prove that the plasma shielding induces decreases impulse coupling coefficient to decrease after the peak value. On the other hand impulse coupling coefficient increases with the increase of the laser spot diameter in a linear way at the same incident la
2007,
19.
Abstract:
In this paper, contour plots comparing measured and calculated temperature profiles are presented. The results suggest numerical calculations accord with the measurements for dynamic temperature profiles in heat-capacity laser rods. During lasing process, the cooling condition almost doesn’t influence the dynamic temperature profiles in the active medium. The dynamic temperature profiles in the active medium are dependent on the pump absorption. However, the dynamic temperature profiles in the active medium with different cooling conditions are distinct during the cooling process.
In this paper, contour plots comparing measured and calculated temperature profiles are presented. The results suggest numerical calculations accord with the measurements for dynamic temperature profiles in heat-capacity laser rods. During lasing process, the cooling condition almost doesn’t influence the dynamic temperature profiles in the active medium. The dynamic temperature profiles in the active medium are dependent on the pump absorption. However, the dynamic temperature profiles in the active medium with different cooling conditions are distinct during the cooling process.
2007,
19.
Abstract:
This paper concerns solving deconvolution problem by constrain the noise in the degraded images in order to regularize the ill-posed characteristics. Adding constraint on degraded images during the deconvolution process, images of indoor point sources with aberration are restored. The results show that the method can constrain the noise in the high frequencies effectively and the restored images can reach the resolution of diffraction limit. Compared with the images restored by Wiener inverse filter, the images restored by noise constrained regularization have better vision quality,higher Strehl ratio and signal noise ratio.
This paper concerns solving deconvolution problem by constrain the noise in the degraded images in order to regularize the ill-posed characteristics. Adding constraint on degraded images during the deconvolution process, images of indoor point sources with aberration are restored. The results show that the method can constrain the noise in the high frequencies effectively and the restored images can reach the resolution of diffraction limit. Compared with the images restored by Wiener inverse filter, the images restored by noise constrained regularization have better vision quality,higher Strehl ratio and signal noise ratio.
2007,
19.
Abstract:
The energy distributions of fast electrons in fs laserplasma interactions have been measured using the magnetic spectrometers with various magnetic fields, fitted with the LiF thermoluminescent dosimeters (TLDs). The results show that the consistency and the important characters of energy distribution of fast electrons, which are similar to those of the experiment and simulation made by others. There is a concavity at 40 keV, which is due to the return current of cold electrons; and a local plateau of electrons with energies 100~350 keV, which is produced by several acceleration mechanisms in energy distribution. The effective temperature of fast electrons is consistent with the temperature scaling of the resonance absorption, which is due to Landau damping or wave breaking．
The energy distributions of fast electrons in fs laserplasma interactions have been measured using the magnetic spectrometers with various magnetic fields, fitted with the LiF thermoluminescent dosimeters (TLDs). The results show that the consistency and the important characters of energy distribution of fast electrons, which are similar to those of the experiment and simulation made by others. There is a concavity at 40 keV, which is due to the return current of cold electrons; and a local plateau of electrons with energies 100~350 keV, which is produced by several acceleration mechanisms in energy distribution. The effective temperature of fast electrons is consistent with the temperature scaling of the resonance absorption, which is due to Landau damping or wave breaking．
2007,
19.
Abstract:
Two different kinds of second harmonic antireflection(AR) coatings, with and without SiO2 barrier layer were prepared with ion assisted deposition on LiB3O5 crystal. Laser induced damage threshold(LIDT) by multiple-shot irradiation at 1 064 nm was studied and two typical damage morphologies were observed by SEM. The AR coatings with SiO2 barrier layer have an excellent LIDT, which is about 40% higher than that of coatings without barrier layer. The mechanism of LIDT enhancement by adding SiO2 barrier layer is also discussed.
Two different kinds of second harmonic antireflection(AR) coatings, with and without SiO2 barrier layer were prepared with ion assisted deposition on LiB3O5 crystal. Laser induced damage threshold(LIDT) by multiple-shot irradiation at 1 064 nm was studied and two typical damage morphologies were observed by SEM. The AR coatings with SiO2 barrier layer have an excellent LIDT, which is about 40% higher than that of coatings without barrier layer. The mechanism of LIDT enhancement by adding SiO2 barrier layer is also discussed.
2007,
19.
Abstract:
The Rayleigh scattering and Mach-Zehnder interferometry are employed to investigate the properties of argon and krypton clusters respectively. By comparing the size and density of the two kinds of clusters in detail, the factors of cluster formation are discussed. Varying the delay time between probe laser and nozzle valve, the temporal evolution of size and density is obtained, the density spatial distribution along nozzle axis with the background pressure from 1.2 MPa to 6.0 MPa is measured. Both size and density of the argon and krypton clusters reach max and the system is stable from 3 ms to 25 ms. In addition, the density increases linearly with background pressure, and decreases with the distance away from the nozzle throat.
The Rayleigh scattering and Mach-Zehnder interferometry are employed to investigate the properties of argon and krypton clusters respectively. By comparing the size and density of the two kinds of clusters in detail, the factors of cluster formation are discussed. Varying the delay time between probe laser and nozzle valve, the temporal evolution of size and density is obtained, the density spatial distribution along nozzle axis with the background pressure from 1.2 MPa to 6.0 MPa is measured. Both size and density of the argon and krypton clusters reach max and the system is stable from 3 ms to 25 ms. In addition, the density increases linearly with background pressure, and decreases with the distance away from the nozzle throat.
2007,
19.
Abstract:
The principal construction of wave-front sensor developed from the linear phase retrieval algorithm is described in this paper. In the laboratory, an experiment device was set up to study the characteristic of the new wave-front measuring method using this kind of sensor. The real time intensity in focus was measured，and then the incident wave-front phase was easily recovered using the approximately linear relationship between the little change of focus intensity and the little change of phase. The sensor can do comparatively precise measurement on the aberration of defocus，astigmatism and so on, with error rates less than 1. It doesn't influence the veracity of recovered results much even if there exists a small unsymmetrical aberration in the aberration of the symmetrical system.
The principal construction of wave-front sensor developed from the linear phase retrieval algorithm is described in this paper. In the laboratory, an experiment device was set up to study the characteristic of the new wave-front measuring method using this kind of sensor. The real time intensity in focus was measured，and then the incident wave-front phase was easily recovered using the approximately linear relationship between the little change of focus intensity and the little change of phase. The sensor can do comparatively precise measurement on the aberration of defocus，astigmatism and so on, with error rates less than 1. It doesn't influence the veracity of recovered results much even if there exists a small unsymmetrical aberration in the aberration of the symmetrical system.
2007,
19.
Abstract:
The plasma frequency and the electron collision frequency can be deduced with the plasma diagnostic method which utilizes the transmission attenuation of microwaves at three frequencies in a non-magnetized plasma. Then the electron density can be obtained from the plasma frequency. The measurement system consists of a sweep oscillator, a pair of broad-band horns, and a scalar network, etc. The plasma produced by an electric discharge of helium with the pressure range 100~700 Pa in a closed cavity is diagnosed by this way at three frequencies of 6.2, 6.8 and 7.4 GHz. As a comparison, the Langmuir double probe method is used at the same time. The results indicate that the electron collision frequencies got by these two methods are coincident. The electron densities got by the attenuation of
The plasma frequency and the electron collision frequency can be deduced with the plasma diagnostic method which utilizes the transmission attenuation of microwaves at three frequencies in a non-magnetized plasma. Then the electron density can be obtained from the plasma frequency. The measurement system consists of a sweep oscillator, a pair of broad-band horns, and a scalar network, etc. The plasma produced by an electric discharge of helium with the pressure range 100~700 Pa in a closed cavity is diagnosed by this way at three frequencies of 6.2, 6.8 and 7.4 GHz. As a comparison, the Langmuir double probe method is used at the same time. The results indicate that the electron collision frequencies got by these two methods are coincident. The electron densities got by the attenuation of
2007,
19.
Abstract:
The TDE-85/MeTHPA epoxy resin modified by polyurethane was prepared with polyurethane prepolymer (PUP, formulated by PPG and TDI), chain-extended reagent(1,4-BDO) and crosslink agent (TMP). The curing reaction mechanism and kinetics characters of the modified resin were discussed by DSC and infrared spectrum analysis. The investigation on curing reaction mechanism indicates that polymer networkⅠwas obtained by the curing reaction between TDE-85 and MeTHPA, and polymer network Ⅱ was obtained by the chain-extended and crosslinking reaction of 1,4-BDO, TMP, and PUP, meanwhile, the graft chemical bond is formed between polymer networkⅠ and polymer network Ⅱ. The investigation on kinetics shows that the apparent activation energy of curing reaction decreased obviously with PU addition, and
The TDE-85/MeTHPA epoxy resin modified by polyurethane was prepared with polyurethane prepolymer (PUP, formulated by PPG and TDI), chain-extended reagent(1,4-BDO) and crosslink agent (TMP). The curing reaction mechanism and kinetics characters of the modified resin were discussed by DSC and infrared spectrum analysis. The investigation on curing reaction mechanism indicates that polymer networkⅠwas obtained by the curing reaction between TDE-85 and MeTHPA, and polymer network Ⅱ was obtained by the chain-extended and crosslinking reaction of 1,4-BDO, TMP, and PUP, meanwhile, the graft chemical bond is formed between polymer networkⅠ and polymer network Ⅱ. The investigation on kinetics shows that the apparent activation energy of curing reaction decreased obviously with PU addition, and
2007,
19.
Abstract:
Sideon radiography technology can directly demonstrate the change of perturbation amplitude on target surface. In the experiment at Shenguang Ⅱ laser facility, this technology is used to detect rear surface perturbation caused by the ablation surface perturbation. The perturbation amplitude observed in the experiment is higher than expected. According to our analysis, twodimension effect is the main reason for larger perturbation growth of the rear surface. Because X ray mainly irradiates the center of the ablation surface, the rear surface perturbation, which is caused by the ablation surface perturbation, exists in the center and gradually spreads around. Based on above discussion, an optimized target design is presented at last, which suggests the target size along the direction of
Sideon radiography technology can directly demonstrate the change of perturbation amplitude on target surface. In the experiment at Shenguang Ⅱ laser facility, this technology is used to detect rear surface perturbation caused by the ablation surface perturbation. The perturbation amplitude observed in the experiment is higher than expected. According to our analysis, twodimension effect is the main reason for larger perturbation growth of the rear surface. Because X ray mainly irradiates the center of the ablation surface, the rear surface perturbation, which is caused by the ablation surface perturbation, exists in the center and gradually spreads around. Based on above discussion, an optimized target design is presented at last, which suggests the target size along the direction of
2007,
19.
Abstract:
With the Needle thin film synthesis method and Conjugate graduate refinement method, all-dielectric three-wavelength non-polarizing parallel plate beam splitters are designed. The chosen of materials component and initial stack are based on Costich and Thelen’s theory. The results of design and analysis show that it maintains a very low polarization ratio in spectral range of (532±10), (633±10) and (1 315±10) nm. To the requirement for non-polarizing in 532, 633 and 1 315 nm, the reasonable angular field of design can be 45°±2°.
With the Needle thin film synthesis method and Conjugate graduate refinement method, all-dielectric three-wavelength non-polarizing parallel plate beam splitters are designed. The chosen of materials component and initial stack are based on Costich and Thelen’s theory. The results of design and analysis show that it maintains a very low polarization ratio in spectral range of (532±10), (633±10) and (1 315±10) nm. To the requirement for non-polarizing in 532, 633 and 1 315 nm, the reasonable angular field of design can be 45°±2°.
2007,
19.
Abstract:
NaF films with preferred orientation have been successfully deposited on Si(100) substrate by pulsed laser deposition. The testing of surface profiler indicates that the deposition rate of the film increases exponentially with the increase of the substrate temperature. At the same time, the activation energy of atom is caculated which is 48.67 kJ/mol. Atom force microscope photographes of these films show the mean square root of the film is only 0.553 nm. Scaning electron microscopy cross-section morphology analysis shows a columnar microstructure characterization of the films. X-ray diffraction analysis reveals the face centered constructure of films. The largest average crystallite size of 129.6 nm and the smallest lattice strain of 0.225% appear at 400 ℃.
NaF films with preferred orientation have been successfully deposited on Si(100) substrate by pulsed laser deposition. The testing of surface profiler indicates that the deposition rate of the film increases exponentially with the increase of the substrate temperature. At the same time, the activation energy of atom is caculated which is 48.67 kJ/mol. Atom force microscope photographes of these films show the mean square root of the film is only 0.553 nm. Scaning electron microscopy cross-section morphology analysis shows a columnar microstructure characterization of the films. X-ray diffraction analysis reveals the face centered constructure of films. The largest average crystallite size of 129.6 nm and the smallest lattice strain of 0.225% appear at 400 ℃.
2007,
19.
Abstract:
A synthesis method for Pierce gun design is employed to develop a prototype. In order to evaluate the performance of the electron beam, an objective function is introduced, which takes perveance, beam waist and laminarity into consideration. A direct optimization method and the EGUN program are applied to optimize the objective function, the result has attained the goal of the design very well. This gun has been applied in experiment as a part of a travelling wave tube, and the rationality was approved through the good performance with the electron static transmission rate of 99.7%, the electron dynamic transmission rate of 98% and the electron efficiency over 34%.
A synthesis method for Pierce gun design is employed to develop a prototype. In order to evaluate the performance of the electron beam, an objective function is introduced, which takes perveance, beam waist and laminarity into consideration. A direct optimization method and the EGUN program are applied to optimize the objective function, the result has attained the goal of the design very well. This gun has been applied in experiment as a part of a travelling wave tube, and the rationality was approved through the good performance with the electron static transmission rate of 99.7%, the electron dynamic transmission rate of 98% and the electron efficiency over 34%.
2007,
19.
Abstract:
Latent failure study on the low-level human body model(HBM) electrostatic discharge(ESD) stresses on microelectric device was presented. The low-level ESD stresses were imposed on microwave low noise transistor 2SC3356 using the HBM from CB (collector-base) junctions and EB (emitter-base) junctions. It is shown that the CB junctions are more sensitive than the EB junctions, of the latent failure on 2SC3356 caused by low-level ESD and that high temperature (≥125 ℃) life tests bring about annealing effects and relief the latent defects caused by low-level ESD stresses.
Latent failure study on the low-level human body model(HBM) electrostatic discharge(ESD) stresses on microelectric device was presented. The low-level ESD stresses were imposed on microwave low noise transistor 2SC3356 using the HBM from CB (collector-base) junctions and EB (emitter-base) junctions. It is shown that the CB junctions are more sensitive than the EB junctions, of the latent failure on 2SC3356 caused by low-level ESD and that high temperature (≥125 ℃) life tests bring about annealing effects and relief the latent defects caused by low-level ESD stresses.
2007,
19.
Abstract:
Design methods for periodic permanent magnet focusing system are presented. Using E-GUN, SUPERFISH, MAFIA, and PIC, 2D and 3D simulation platforms of electron-optical system with plane symmetry are established, and the electron-optical system is X-band 100 MW sheet beam klystron is designed and simulated. The simulation result shows that the beam transmission is 99.6% in a 600 mm propogation distance when the period of the magnetic field is 60 mm, and the magnetic field intensity of the entrance is 0.1 T.
Design methods for periodic permanent magnet focusing system are presented. Using E-GUN, SUPERFISH, MAFIA, and PIC, 2D and 3D simulation platforms of electron-optical system with plane symmetry are established, and the electron-optical system is X-band 100 MW sheet beam klystron is designed and simulated. The simulation result shows that the beam transmission is 99.6% in a 600 mm propogation distance when the period of the magnetic field is 60 mm, and the magnetic field intensity of the entrance is 0.1 T.
2007,
19.
Abstract:
As a combination of load-limited MILO and tapered MILO, a double ladder cathode MILO is presented in this paper. This new type of MILO has six vanes, the first two work as the RF chokes, the middle three work as the slow wave structure, and the last one works as a microwave extractor. As a distinguishing feature of the device, its cathode is constructed by three different radii cylinders in the beam emission region. According to Maxwell equations and Floquet’s theorem, the dispersion function of TM modes is derived, and its dispersion characteristic is analyzed through numerical calculation. 2.5 D particle simulation tells that, the operation frequency of the device is 1.21 GHz which agrees with the theoretical calculation, and the introduction of a double ladder cathode has little influe
As a combination of load-limited MILO and tapered MILO, a double ladder cathode MILO is presented in this paper. This new type of MILO has six vanes, the first two work as the RF chokes, the middle three work as the slow wave structure, and the last one works as a microwave extractor. As a distinguishing feature of the device, its cathode is constructed by three different radii cylinders in the beam emission region. According to Maxwell equations and Floquet’s theorem, the dispersion function of TM modes is derived, and its dispersion characteristic is analyzed through numerical calculation. 2.5 D particle simulation tells that, the operation frequency of the device is 1.21 GHz which agrees with the theoretical calculation, and the introduction of a double ladder cathode has little influe
2007,
19.
Abstract:
In order to overcome the difficulties of manufacturing, a novel contrawound helix slowwave system is presented. The 3D soft CST MWS is used to simulate and investigate the influence of dimension parameters on the system’s dispersion and interaction impedance. The results show that the radius of contrawound helix can be larger than that of helical without causing a sharp decrease of interaction impedance and the decrease of tape width helps bring down the phase velocity and improve the interaction impedance.The results also indicate that in certain range,the reduction of pitch increases the phase velocity. A novel contrawound helix system is designed for 8 mm millimeterwave TWT, the interaction impedance is over 21 Ω, and the operation voltage is about 20 kV. It has a low requirement
In order to overcome the difficulties of manufacturing, a novel contrawound helix slowwave system is presented. The 3D soft CST MWS is used to simulate and investigate the influence of dimension parameters on the system’s dispersion and interaction impedance. The results show that the radius of contrawound helix can be larger than that of helical without causing a sharp decrease of interaction impedance and the decrease of tape width helps bring down the phase velocity and improve the interaction impedance.The results also indicate that in certain range,the reduction of pitch increases the phase velocity. A novel contrawound helix system is designed for 8 mm millimeterwave TWT, the interaction impedance is over 21 Ω, and the operation voltage is about 20 kV. It has a low requirement
2007,
19.
Abstract:
In wide band klystrons with high perveance electron beam, the charged particles show obvious transverse movement, and the energy exchange between kinetic electrons and gap field is a nonlinear interaction process. Fully considering these physical phenomena, 2.5 dimensional large signal program was put forward the corresponding theoretical formulae based on ring model. The program was further developed for beam-wave interaction analysis. As an example, a practical S-band klystron was investigated with this tool, and the results approach the experimental data with higher precision than a one dimensional program does.
In wide band klystrons with high perveance electron beam, the charged particles show obvious transverse movement, and the energy exchange between kinetic electrons and gap field is a nonlinear interaction process. Fully considering these physical phenomena, 2.5 dimensional large signal program was put forward the corresponding theoretical formulae based on ring model. The program was further developed for beam-wave interaction analysis. As an example, a practical S-band klystron was investigated with this tool, and the results approach the experimental data with higher precision than a one dimensional program does.
2007,
19.
Abstract:
An S band high power microwave multiplexer with three channels is investigated through numerical computation. The realized multiplexer works in the band of 2.65~2.75, 2.80~2.90 and 2.95~3.05 GHz. In each pass band, the transmission loss is less than 0.1 dB and the reflection loss is more than 15 dB, the isolation is more than 30 dB. As a result, the energy efficiency is as high as 95%. The power handling capacity of the multiplexer with widened waveguide is demonstrated to be GW level by a full wave analysis software.
An S band high power microwave multiplexer with three channels is investigated through numerical computation. The realized multiplexer works in the band of 2.65~2.75, 2.80~2.90 and 2.95~3.05 GHz. In each pass band, the transmission loss is less than 0.1 dB and the reflection loss is more than 15 dB, the isolation is more than 30 dB. As a result, the energy efficiency is as high as 95%. The power handling capacity of the multiplexer with widened waveguide is demonstrated to be GW level by a full wave analysis software.
2007,
19.
Abstract:
The nonlinear consistent equations were put forward which could describe beam-wave interaction in an relativistic backward wave oscillator(RBWO), using the nonlinear theory of RBWO. The nonlinear consistent equations were solved by numerical computation, some basic rules of superradiation caused by a non-stationary beam-wave interaction were opened out in an RBWO. Some relations and discriminations were presented between superradiation and stimulated radiation in an RBWO.
The nonlinear consistent equations were put forward which could describe beam-wave interaction in an relativistic backward wave oscillator(RBWO), using the nonlinear theory of RBWO. The nonlinear consistent equations were solved by numerical computation, some basic rules of superradiation caused by a non-stationary beam-wave interaction were opened out in an RBWO. Some relations and discriminations were presented between superradiation and stimulated radiation in an RBWO.
2007,
19.
Abstract:
A novel method in time domain for the response of high power EMP with braided-shield multiconductor cable is proposed. The current on the shield can be used as the stimulus of the MTL equations based on the definition of the transfer impedance. The current on the shield, the core current and the core to shield voltage are obtained by the FDTD method combining the MTL equations with the field equations. A comparative study is carried out against the transfer impedance models proposed by Vance and Tyni. As an example of the application of the FDTD-MTL method, the response of high power EMP with three-conductor braided-shield cable is obtained．
A novel method in time domain for the response of high power EMP with braided-shield multiconductor cable is proposed. The current on the shield can be used as the stimulus of the MTL equations based on the definition of the transfer impedance. The current on the shield, the core current and the core to shield voltage are obtained by the FDTD method combining the MTL equations with the field equations. A comparative study is carried out against the transfer impedance models proposed by Vance and Tyni. As an example of the application of the FDTD-MTL method, the response of high power EMP with three-conductor braided-shield cable is obtained．
2007,
19.
Abstract:
The microwave frequency of the coaxial vircator oscillator were 3.4 GHz and 3.7 GHz using different filtration efficienty of the anode mesh. Based on the experimental results, the beam distribution in the coaxial virtual cathode was analyzed. The eigenmode of the coaxial virtual cathode was calculated using resonance cavity theory, and the results were compared with the experimental ones. The conclusion is that the distribution the beam in the mesh has important effect on the output microwave mode. The output microwave frequency is the result of the interaction between the resonance cavity and the cathodeanode gap. The filtrate of the anode mesh also has important effect on the frequency, the filtration efficiency increase, the microwave frequency increased correspondingly．
The microwave frequency of the coaxial vircator oscillator were 3.4 GHz and 3.7 GHz using different filtration efficienty of the anode mesh. Based on the experimental results, the beam distribution in the coaxial virtual cathode was analyzed. The eigenmode of the coaxial virtual cathode was calculated using resonance cavity theory, and the results were compared with the experimental ones. The conclusion is that the distribution the beam in the mesh has important effect on the output microwave mode. The output microwave frequency is the result of the interaction between the resonance cavity and the cathodeanode gap. The filtrate of the anode mesh also has important effect on the frequency, the filtration efficiency increase, the microwave frequency increased correspondingly．
2007,
19.
Abstract:
In order to get extensive knowledge of radical production in a corona induced non-thermal plasma, the effect of discharge parameter, gas condition on emission intensity of OH(A2S+→X2P, 0-0) in a nozzle-to-plate corona radical shower system are experimentally investigated using emission spectroscopy considering the collisional quenching rate. The results are that: both discharge voltage and current have direct influence on OH emission, OH production increases as discharge power rises; remarkable emission spectrum of OH(A2S+→X2P, 0-0) is detected in N2 DC corona discharge, but few OH radicals exist in air discharge; humidification of electrode gas can enhance the OH emission, and the existence of Ar increases the OH emission, while O2 may reduce the OH emission, the possible reason is th
In order to get extensive knowledge of radical production in a corona induced non-thermal plasma, the effect of discharge parameter, gas condition on emission intensity of OH(A2S+→X2P, 0-0) in a nozzle-to-plate corona radical shower system are experimentally investigated using emission spectroscopy considering the collisional quenching rate. The results are that: both discharge voltage and current have direct influence on OH emission, OH production increases as discharge power rises; remarkable emission spectrum of OH(A2S+→X2P, 0-0) is detected in N2 DC corona discharge, but few OH radicals exist in air discharge; humidification of electrode gas can enhance the OH emission, and the existence of Ar increases the OH emission, while O2 may reduce the OH emission, the possible reason is th
2007,
19.
Abstract:
Electric carbon fiber is a promising material to emit cold electron under intensive electric field. Experiment was conducted to test carbon fiber’s emission at the pressures of 0.1 MPa, 10-1 Pa and 10-5 Pa. The diode gap between the fiber tip and the electron collecting anode was about 5 mm. In atmosphere, the applied voltage and the emitted current have a Fowler-Nordheim relation. According to Fowler-Nordheim theorem, the field intensified factor was 3.75×105 when the voltage was 7 kV and the current was 61.4 μA. In low vacuum (about 10-1 Pa) condition, the anode collected current only less than 10 μA under 20 kV. In high vacuum (about 10-5 Pa) condition, the anode collected larger anode current up to 300 μA without flashover, the relation between voltage and current was close to the
Electric carbon fiber is a promising material to emit cold electron under intensive electric field. Experiment was conducted to test carbon fiber’s emission at the pressures of 0.1 MPa, 10-1 Pa and 10-5 Pa. The diode gap between the fiber tip and the electron collecting anode was about 5 mm. In atmosphere, the applied voltage and the emitted current have a Fowler-Nordheim relation. According to Fowler-Nordheim theorem, the field intensified factor was 3.75×105 when the voltage was 7 kV and the current was 61.4 μA. In low vacuum (about 10-1 Pa) condition, the anode collected current only less than 10 μA under 20 kV. In high vacuum (about 10-5 Pa) condition, the anode collected larger anode current up to 300 μA without flashover, the relation between voltage and current was close to the
2007,
19.
Abstract:
Magnet design and modeling is a crucial task in the design of cyclotrons, which includes iterative processes from an initial model. The magnetic field distribution should fulfill the requirements of isochronisms and transverse focusing of the beam, as well as avoiding dangerous resonance crossing. This paper introduces an automated magnet design, modeling and shimming method under the pythonic integrated environment based on virtual prototyping, a novel technique to shorten development period and reduce costs for physical prototypes. Detailed magnet shimming processes with the support of the 3D magnetic field simulation code TOSCA and an original developed particle tracking code PTP are described. As a case study, the main magnet design of a 16 MeV H- compact isochronous cyclotron is illus
Magnet design and modeling is a crucial task in the design of cyclotrons, which includes iterative processes from an initial model. The magnetic field distribution should fulfill the requirements of isochronisms and transverse focusing of the beam, as well as avoiding dangerous resonance crossing. This paper introduces an automated magnet design, modeling and shimming method under the pythonic integrated environment based on virtual prototyping, a novel technique to shorten development period and reduce costs for physical prototypes. Detailed magnet shimming processes with the support of the 3D magnetic field simulation code TOSCA and an original developed particle tracking code PTP are described. As a case study, the main magnet design of a 16 MeV H- compact isochronous cyclotron is illus
2007,
19.
Abstract:
A linear induction accelerator (LIA) cell includes the pulse power system, the cavity and the reset system. By methods of cable delay and cable open circuit reflection, a burst double-pulse output can be generated by traditional LIA pulse power system. With the original reset system and the reconstructive power system, the experimental inductive cavity filled with ferrite cores will be worked in burst double-pulse mode. The experimental results prove that by simple reconstruction, an LIA cell can generate double accelerating pulses of interval less than 1 μs with the voltage intensity more than 200 kV, risetime less than 35 ns and flattop more than 60 ns.
A linear induction accelerator (LIA) cell includes the pulse power system, the cavity and the reset system. By methods of cable delay and cable open circuit reflection, a burst double-pulse output can be generated by traditional LIA pulse power system. With the original reset system and the reconstructive power system, the experimental inductive cavity filled with ferrite cores will be worked in burst double-pulse mode. The experimental results prove that by simple reconstruction, an LIA cell can generate double accelerating pulses of interval less than 1 μs with the voltage intensity more than 200 kV, risetime less than 35 ns and flattop more than 60 ns.
