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RSS2011 Vol. 23, No. 05
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2011,
23.
Abstract:
To identify the potential risks of spatial modulation of broad-band laser beams stacked by chirped pulses on the safety of optics, this paper numerically investigated the effect of temporal modulation on the generation and growth of spatial modulation during its nonlinear propagation. When there is no additional spatial modulation and the B integral is limited in the practical working range (usually less than 2.0 rad), no spatial modulation will be generated for both normal dispersion and anomalous dispersion; while with the B integral further increasing, spatial modulation will emerge with a rapid growth. When there is additional spatial modulation for anomalous dispersion, the spatial modulation with additional temporal modulation will grow more quickly than that without additional tempo
To identify the potential risks of spatial modulation of broad-band laser beams stacked by chirped pulses on the safety of optics, this paper numerically investigated the effect of temporal modulation on the generation and growth of spatial modulation during its nonlinear propagation. When there is no additional spatial modulation and the B integral is limited in the practical working range (usually less than 2.0 rad), no spatial modulation will be generated for both normal dispersion and anomalous dispersion; while with the B integral further increasing, spatial modulation will emerge with a rapid growth. When there is additional spatial modulation for anomalous dispersion, the spatial modulation with additional temporal modulation will grow more quickly than that without additional tempo
2011,
23.
Abstract:
The energy spectra and angle-distribution of the X-ray photons produced through 180°Thomson scattering were studied by Monte Carlo numerical simulation code CAIN. The laser intensity and electron parameters required for high quality X-ray source were also explored. Results show that to get higher photon production and suppress the nonlinear scattering, the laser intensity should not be too high. To get a monochromatic and highly luminous X-ray source, the electrons should have quasi-monoenergetic energy distributions, high energy, small divergence and short pulse length.
The energy spectra and angle-distribution of the X-ray photons produced through 180°Thomson scattering were studied by Monte Carlo numerical simulation code CAIN. The laser intensity and electron parameters required for high quality X-ray source were also explored. Results show that to get higher photon production and suppress the nonlinear scattering, the laser intensity should not be too high. To get a monochromatic and highly luminous X-ray source, the electrons should have quasi-monoenergetic energy distributions, high energy, small divergence and short pulse length.
2011,
23.
Abstract:
Two physical models of single-ring feedback phase-shift controlling chaos are discussed based on the method of chaos controlled by couplingfeedback phase-shift and its physical model. The coupler feeds the output back and the phase-shift controller controls the phase of feedback. Suitable feedback coefficient and apt feedback phase-shift can control the laser output into chaos state, stable state or periodic state effectively. Moreover, the paper analyzes the method of double-ring feedback phase-shift controlling chaos in detail, and the impact of feedback coefficient and feedback phase-shift on the model of double-ring is studied．
Two physical models of single-ring feedback phase-shift controlling chaos are discussed based on the method of chaos controlled by couplingfeedback phase-shift and its physical model. The coupler feeds the output back and the phase-shift controller controls the phase of feedback. Suitable feedback coefficient and apt feedback phase-shift can control the laser output into chaos state, stable state or periodic state effectively. Moreover, the paper analyzes the method of double-ring feedback phase-shift controlling chaos in detail, and the impact of feedback coefficient and feedback phase-shift on the model of double-ring is studied．
2011,
23.
Abstract:
The paper analyzes the damages of shock and vibration to precise mobile vehicle-mounted optical systems during transportation process and working condition, points out that structural deformation and vibration are the main factors influencing optical system stability and vehicle installation implementation, and notes that it is the key technique to achieve the optical system stability by improving the overall vehicle stiffness, stability and vibration isolation performance of the mobile vehicle-mounted optical platform. The structure and composition of the vehicle-mounted optical platform as well as high stiffness and double-layer isolation design solutions are discussed. The modal analysis of the designed double-layer optical platform isolation system is carried out with ANSYS finite elem
The paper analyzes the damages of shock and vibration to precise mobile vehicle-mounted optical systems during transportation process and working condition, points out that structural deformation and vibration are the main factors influencing optical system stability and vehicle installation implementation, and notes that it is the key technique to achieve the optical system stability by improving the overall vehicle stiffness, stability and vibration isolation performance of the mobile vehicle-mounted optical platform. The structure and composition of the vehicle-mounted optical platform as well as high stiffness and double-layer isolation design solutions are discussed. The modal analysis of the designed double-layer optical platform isolation system is carried out with ANSYS finite elem
2011,
23.
Abstract:
Based on the existing Venturi nozzle fluid supply system, an axisymmetric two-dimension computation model was presented. Flow field characteristics of Venturi nozzle under different back pressures were calculated using computational fluid dynamic methods. The numerical simulations demonstrate that, shock waves in the pipeline go through three states owing to back pressure’s increasing: oblique shock wave in straight circular pipeline, pseudo-normal shock wave in endocone adapter connector, and normal shock wave in Venturi nozzle. During the design of Venturi nozzle flowmeter, normal shock waves must be restricted beside the throat of Venturi nozzle or within a short distance downstream from the throat, which offers the advantages of low total pressure loss and stable flow field. Wall-dril
Based on the existing Venturi nozzle fluid supply system, an axisymmetric two-dimension computation model was presented. Flow field characteristics of Venturi nozzle under different back pressures were calculated using computational fluid dynamic methods. The numerical simulations demonstrate that, shock waves in the pipeline go through three states owing to back pressure’s increasing: oblique shock wave in straight circular pipeline, pseudo-normal shock wave in endocone adapter connector, and normal shock wave in Venturi nozzle. During the design of Venturi nozzle flowmeter, normal shock waves must be restricted beside the throat of Venturi nozzle or within a short distance downstream from the throat, which offers the advantages of low total pressure loss and stable flow field. Wall-dril
2011,
23.
Abstract:
The design of a 16 pass pump system for Yb:YAG thin-disk laser has been presented. The model of the system was built and simulated. Experiments based on the system using one disk cooled with water through micro channel were done. The disk was homemade, with the diameter of 10 mm, thickness of 250 μm and doping atom fraction of 10%. For the pump power of 69.5 W, when a reflector with the radius of curvature of －800 mm is used, 24.4 W 1 030 nm continuous output is achieved, with optical to optical conversion efficiency of 38.8%; when a reflector with the radius of curvature of －2 000 mm is used, 18.65 W 1 030 nm continuous output is achieved, with the beam quality factor no more than 1.1 and optical to optical conversion efficiency of 26.8%．
The design of a 16 pass pump system for Yb:YAG thin-disk laser has been presented. The model of the system was built and simulated. Experiments based on the system using one disk cooled with water through micro channel were done. The disk was homemade, with the diameter of 10 mm, thickness of 250 μm and doping atom fraction of 10%. For the pump power of 69.5 W, when a reflector with the radius of curvature of －800 mm is used, 24.4 W 1 030 nm continuous output is achieved, with optical to optical conversion efficiency of 38.8%; when a reflector with the radius of curvature of －2 000 mm is used, 18.65 W 1 030 nm continuous output is achieved, with the beam quality factor no more than 1.1 and optical to optical conversion efficiency of 26.8%．
2011,
23.
Abstract:
To provide references for the design of injectors in the combustion-driven continuous wave DF/HF chemical laser, five injectors of different structure were calibrated on flow rate by original criterion (mass-time method). Moreover, the results were explained reasonably by boundary-layer theory. The results show that the flow coefficient increases with the increase of the inlet pressure, and varies from 0.677 to 0.772. At the same condition of inlet pressure, the flow coefficient increases with the diameter and decreases with the length of the orifice. The flow coefficient of the slanting orifice is slightly smaller than the normal one with the same dimension.
To provide references for the design of injectors in the combustion-driven continuous wave DF/HF chemical laser, five injectors of different structure were calibrated on flow rate by original criterion (mass-time method). Moreover, the results were explained reasonably by boundary-layer theory. The results show that the flow coefficient increases with the increase of the inlet pressure, and varies from 0.677 to 0.772. At the same condition of inlet pressure, the flow coefficient increases with the diameter and decreases with the length of the orifice. The flow coefficient of the slanting orifice is slightly smaller than the normal one with the same dimension.
2011,
23.
Abstract:
In chemical lasers, the supersonic diffuser plays an important role in pressure system. This paper introduces some experimental results of line-divergence subsection diffuser for COIL. Preliminary study shows supersonic diffuser with right divergent angel can achieve good ability of pressure recovery and isolated optical cavity fluid field. Diffuser efficiency can be greatly improved by means of setting proper thickness vertical vans along the direction of inner width of diffuser. In addition, optimized shape of labium mouth and manpower roughness in the internal cavity of diffuser entrance can improve wall pressure distribution and diffuser efficiency．
In chemical lasers, the supersonic diffuser plays an important role in pressure system. This paper introduces some experimental results of line-divergence subsection diffuser for COIL. Preliminary study shows supersonic diffuser with right divergent angel can achieve good ability of pressure recovery and isolated optical cavity fluid field. Diffuser efficiency can be greatly improved by means of setting proper thickness vertical vans along the direction of inner width of diffuser. In addition, optimized shape of labium mouth and manpower roughness in the internal cavity of diffuser entrance can improve wall pressure distribution and diffuser efficiency．
2011,
23.
Abstract:
According to dynamic working characteristics of solid state heat capacity laser, the three dimensional(3D) temperature and thermal stress distribution of cylinder disk heat capacity laser varying with working time is simulated and analyzed using finite difference method. Dynamic variation of thermal distortions and depolarization losses of heat capacity laser is also analyzed. The simulation results are compared with those of continued water-cooled rod laser. Deformation is found to be the main factor of phase distortion for cylinder disk heat capacity laser. Moreover, the depolarization loss increases nonlinearly with the pumping time and pump power.
According to dynamic working characteristics of solid state heat capacity laser, the three dimensional(3D) temperature and thermal stress distribution of cylinder disk heat capacity laser varying with working time is simulated and analyzed using finite difference method. Dynamic variation of thermal distortions and depolarization losses of heat capacity laser is also analyzed. The simulation results are compared with those of continued water-cooled rod laser. Deformation is found to be the main factor of phase distortion for cylinder disk heat capacity laser. Moreover, the depolarization loss increases nonlinearly with the pumping time and pump power.
2011,
23.
Abstract:
A thresholding wavelet multiresolution wavefront reconstruction algorithm is proposed in view of low calculating efficiency and large stable state error of conventional wavefront reconstructors. The wavefront phase distortion is projected to wavelet basis, which makes the pseudo-inverse matrix become sparse matrix and reduces the calculation. Meanwhile, threshold is chosen to remove the high resolution wavelet-based coefficients which have little effect on calculation precision, improving operation efficiency. The algorithm is compared with least square, Zernike modal and iterative methods, and the simulation results show that this algorithm is superior in computing speed and convergence precision.
A thresholding wavelet multiresolution wavefront reconstruction algorithm is proposed in view of low calculating efficiency and large stable state error of conventional wavefront reconstructors. The wavefront phase distortion is projected to wavelet basis, which makes the pseudo-inverse matrix become sparse matrix and reduces the calculation. Meanwhile, threshold is chosen to remove the high resolution wavelet-based coefficients which have little effect on calculation precision, improving operation efficiency. The algorithm is compared with least square, Zernike modal and iterative methods, and the simulation results show that this algorithm is superior in computing speed and convergence precision.
2011,
23.
Abstract:
An orthogonal family of super Lorentz-Gauss(SLG) beam has been introduced to describe the highly divergent higher-order modes, e.g. the far-field distributions of the highly divergent higher-order mode generated by diode lasers. The fractional Fourier transform(FRFT) is applied to treat the propagation of SLG11 mode. By means of the convolution theorem of Fourier transform, an analytical expression for the field of SLG11 mode passing through an FRFT system has been derived. According to the derived analytical formula, the properties of SLG11 mode in the FRFT plane are graphically illustrated with numerical examples. The influences of the fractional order and three beam parameters on the normalized intensity of SLG11 mode in the FRFT plane are sys
An orthogonal family of super Lorentz-Gauss(SLG) beam has been introduced to describe the highly divergent higher-order modes, e.g. the far-field distributions of the highly divergent higher-order mode generated by diode lasers. The fractional Fourier transform(FRFT) is applied to treat the propagation of SLG11 mode. By means of the convolution theorem of Fourier transform, an analytical expression for the field of SLG11 mode passing through an FRFT system has been derived. According to the derived analytical formula, the properties of SLG11 mode in the FRFT plane are graphically illustrated with numerical examples. The influences of the fractional order and three beam parameters on the normalized intensity of SLG11 mode in the FRFT plane are sys
2011,
23.
Abstract:
The paper investigates the output characteristics of a chemical oxygen iodine laser(COIL) affected by nonideal resonator mirrors. Various parameters in long-time thermal deformation of silicon mirrors, such as absorption factor, supporting radius, and thermal load, are considered. The simulation results show that the absorption of mirrors plays a key role in beam quality control. If the decrease in laser output power is required to be less than 20% within the working time of 10 s, the absorption factor must be no more than 3.0×10-4. Furthermore, the beam size affects the supporting radius of four-point supporting. The additional phase aberration induced by mirror supporting deformation can be avoided as the supporting radius is greater than 1.4 times of the beam radius.
The paper investigates the output characteristics of a chemical oxygen iodine laser(COIL) affected by nonideal resonator mirrors. Various parameters in long-time thermal deformation of silicon mirrors, such as absorption factor, supporting radius, and thermal load, are considered. The simulation results show that the absorption of mirrors plays a key role in beam quality control. If the decrease in laser output power is required to be less than 20% within the working time of 10 s, the absorption factor must be no more than 3.0×10-4. Furthermore, the beam size affects the supporting radius of four-point supporting. The additional phase aberration induced by mirror supporting deformation can be avoided as the supporting radius is greater than 1.4 times of the beam radius.
2011,
23.
Abstract:
This paper proposes a model of non-Gaussian deformation in inter-satellite laser communication system, and then studies the effect of non-Gaussian deformation on pointing error based on the model in comparison with Gaussian model. Theoretical analyses and numerical simulations show that, pointing error will increase with increasing the scale of deformation, and as the distance from deformation to the center of the optical antenna increases, the pointing error will first increase and then decrease for both Gaussian and non-Gaussian models. If and only if the deformation can be well approximated by its root mean square value, the pointing error can change periodically with the variation in the depth of the deformation and the envelope of the peak value of the fluctuation depends on the origi
This paper proposes a model of non-Gaussian deformation in inter-satellite laser communication system, and then studies the effect of non-Gaussian deformation on pointing error based on the model in comparison with Gaussian model. Theoretical analyses and numerical simulations show that, pointing error will increase with increasing the scale of deformation, and as the distance from deformation to the center of the optical antenna increases, the pointing error will first increase and then decrease for both Gaussian and non-Gaussian models. If and only if the deformation can be well approximated by its root mean square value, the pointing error can change periodically with the variation in the depth of the deformation and the envelope of the peak value of the fluctuation depends on the origi
2011,
23.
Abstract:
This paper investigates the damage in optical components induced by an 880 nm high-power semiconductor CW laser. The optical components irradiated are high-reflectivity or anti-reflectivity components based on K9 glass, oxygen free copper and ZnSe crystal. The power density of irradiation on component surface is adjusted by changing laser average power and spot size there, and each component is continuously irradiated for 30 s. The laser-induced damage morphology observed by microscope shows that, for K9 glass coated with high-reflectivity film, large-area ablation appears on the surface at the power density of 600 W/cm2 and burst at 1 000 W/cm2. However, no apparent damage is observed on the gilded oxygen free copper and the ZnSe crystal coated with anti-reflectivity film at th
This paper investigates the damage in optical components induced by an 880 nm high-power semiconductor CW laser. The optical components irradiated are high-reflectivity or anti-reflectivity components based on K9 glass, oxygen free copper and ZnSe crystal. The power density of irradiation on component surface is adjusted by changing laser average power and spot size there, and each component is continuously irradiated for 30 s. The laser-induced damage morphology observed by microscope shows that, for K9 glass coated with high-reflectivity film, large-area ablation appears on the surface at the power density of 600 W/cm2 and burst at 1 000 W/cm2. However, no apparent damage is observed on the gilded oxygen free copper and the ZnSe crystal coated with anti-reflectivity film at th
2011,
23.
Abstract:
Based on the formation mechanism of targets infrared characteristic, this paper discusses a method to modulate ground targets’s infrared characteristic through artificial illuminator. The theoretical model of ground targets irradiated artificial illuminator is established, then the targets surface temperature is calculated and measured, and the targets’ infrared radiation is calculated and analyzed. The results show that the infrared characteristic of ground targets can be modulated through artificial illuminator, and the effect of modulation is determined by illumination power, time, distance, and incident angle. In general conditions, the effect of modulation is obvious at night, but not in the daytime.
Based on the formation mechanism of targets infrared characteristic, this paper discusses a method to modulate ground targets’s infrared characteristic through artificial illuminator. The theoretical model of ground targets irradiated artificial illuminator is established, then the targets surface temperature is calculated and measured, and the targets’ infrared radiation is calculated and analyzed. The results show that the infrared characteristic of ground targets can be modulated through artificial illuminator, and the effect of modulation is determined by illumination power, time, distance, and incident angle. In general conditions, the effect of modulation is obvious at night, but not in the daytime.
2011,
23.
Abstract:
The characteristics of spatial distribution of emission from electron oscillation are analyzed with a single electron model under femtosecond laser pulses of different intensity and polarizations. It shows that with the increase of laser intensity, for circularly polarized laser pulses, the angular distribution is tipped forward more and more and increase in magnitudes; for linearly polarized laser pulses, the radiation pattern is changed from the fourfold rotational symmetry bifoliate pattern same as that from a dipole antenna to twofold rotational symmetry trefoil pattern.
The characteristics of spatial distribution of emission from electron oscillation are analyzed with a single electron model under femtosecond laser pulses of different intensity and polarizations. It shows that with the increase of laser intensity, for circularly polarized laser pulses, the angular distribution is tipped forward more and more and increase in magnitudes; for linearly polarized laser pulses, the radiation pattern is changed from the fourfold rotational symmetry bifoliate pattern same as that from a dipole antenna to twofold rotational symmetry trefoil pattern.
2011,
23.
Abstract:
Numerical simulations have been conducted to study wave drag reduction over a cylindrical blunt body with repetitive laser energy deposition. The influences of laser repetition frequency, inflow Mach number and ignition location on drag reduction performances were investigated. Because of the interaction between low density zone caused by laser energy deposition and bow shock wave over the cylinder, a circulation zone similar to virtual tip is formed in front of the blunt body. And the energy deposition modifies the upstream shock wave into an oblique one and results in large wave drag reduction. With the laser repetition frequency increasing the drag reduces: At the frequency of 200 kHz, the drag is reduced to as low as 17% of that without energy deposition, and the maximum energy efficie
Numerical simulations have been conducted to study wave drag reduction over a cylindrical blunt body with repetitive laser energy deposition. The influences of laser repetition frequency, inflow Mach number and ignition location on drag reduction performances were investigated. Because of the interaction between low density zone caused by laser energy deposition and bow shock wave over the cylinder, a circulation zone similar to virtual tip is formed in front of the blunt body. And the energy deposition modifies the upstream shock wave into an oblique one and results in large wave drag reduction. With the laser repetition frequency increasing the drag reduces: At the frequency of 200 kHz, the drag is reduced to as low as 17% of that without energy deposition, and the maximum energy efficie
2011,
23.
Abstract:
The degree of paraxiality for Gaussian vortex beams is studied based on the definition of the degree of paraxiality for monochromatic light beams. By using the angular spectrum representation, the analytical expression for the degree of paraxiality for Gaussian vortex beams is derived, and used to study the dependence of the degree of paraxiality on the Gaussian vortex beam parameters. It is shown that the degree of paraxiality for Gaussian vortex beams increases with increasing the waist width of background Gaussian beams or increasing the off-axis distance of optical vortices, and with decreasing the topological charge of optical vortices. The results are interpreted physically by using the relation between the degree of paraxiality and the far-field divergence angle.
The degree of paraxiality for Gaussian vortex beams is studied based on the definition of the degree of paraxiality for monochromatic light beams. By using the angular spectrum representation, the analytical expression for the degree of paraxiality for Gaussian vortex beams is derived, and used to study the dependence of the degree of paraxiality on the Gaussian vortex beam parameters. It is shown that the degree of paraxiality for Gaussian vortex beams increases with increasing the waist width of background Gaussian beams or increasing the off-axis distance of optical vortices, and with decreasing the topological charge of optical vortices. The results are interpreted physically by using the relation between the degree of paraxiality and the far-field divergence angle.
2011,
23.
Abstract:
A discharge-pumped 351 nm XeF(B-X) excimer laser has been developed. For improving output efficiency and energy and achieving stationary discharge, the laser adopted a new switching power supply, compact Chang’s electrodes and spark preionization structure, and the optimization of storage/discharge capacitances and working gas mixture was performed. The maximum laser efficiency of the laser is 0.88%. When the laser works at 30 kV with the maximum repetition rate of 80 Hz, the output energy is about 153 mJ/pulse, the average power is 12.9 W, the pulse-to-pulse energy stability is no more than 4%, and the beam dimensions are 7 mm×22 mm near the output window. The laser has been applied to the experiments of the printed circuit board(PCB) lithography system based on resist exposure.
A discharge-pumped 351 nm XeF(B-X) excimer laser has been developed. For improving output efficiency and energy and achieving stationary discharge, the laser adopted a new switching power supply, compact Chang’s electrodes and spark preionization structure, and the optimization of storage/discharge capacitances and working gas mixture was performed. The maximum laser efficiency of the laser is 0.88%. When the laser works at 30 kV with the maximum repetition rate of 80 Hz, the output energy is about 153 mJ/pulse, the average power is 12.9 W, the pulse-to-pulse energy stability is no more than 4%, and the beam dimensions are 7 mm×22 mm near the output window. The laser has been applied to the experiments of the printed circuit board(PCB) lithography system based on resist exposure.
2011,
23.
Abstract:
The traditional four-step phase shifting algorithm has some limitations (such as phase shift error, low resolution and coherent noise) for processing of phase-masked interferograms, which affects the performance of the dynamic phase-masked interferometer. In order to improve the analysis accuracy of the phase-masked interferogram, a phase demodulation method based on low-pass filtering is proposed. According to the fact that the phase introduced by phase mask has much higher spatial frequency than the measured phase, the proposed method extracts the phase from phase-masked interferograms by a low-pass filtering method. Numerical simulation shows that the proposed method has a higher accuracy than the traditional four-step phase shifting algorithm. The accuracy of the proposed method can be
The traditional four-step phase shifting algorithm has some limitations (such as phase shift error, low resolution and coherent noise) for processing of phase-masked interferograms, which affects the performance of the dynamic phase-masked interferometer. In order to improve the analysis accuracy of the phase-masked interferogram, a phase demodulation method based on low-pass filtering is proposed. According to the fact that the phase introduced by phase mask has much higher spatial frequency than the measured phase, the proposed method extracts the phase from phase-masked interferograms by a low-pass filtering method. Numerical simulation shows that the proposed method has a higher accuracy than the traditional four-step phase shifting algorithm. The accuracy of the proposed method can be
2011,
23.
Abstract:
Using a self-made software named CatchGhost the ghost points’ position and energy in a coaxial optic systems were calculated accurately in a short time without omission．The software can carry out massive calculation in a short time, and pick out the harmful ghosts in system automatically. Because all the elements which are related to beams’energy, including the pinhole’ effect, reflectivity, gain and loss, are counted, data of ghost points given by the software are exact and useful．
Using a self-made software named CatchGhost the ghost points’ position and energy in a coaxial optic systems were calculated accurately in a short time without omission．The software can carry out massive calculation in a short time, and pick out the harmful ghosts in system automatically. Because all the elements which are related to beams’energy, including the pinhole’ effect, reflectivity, gain and loss, are counted, data of ghost points given by the software are exact and useful．
2011,
23.
Abstract:
Using computational fluid dynamic methods, this paper simulated nozzle array with high energy N2 as carrier gas. The results indicate that using high mach number N2 to eject low Mach number O2, the stagnation pressure at cavity exit can be enhanced. The process of mixing hypersonic N2 with sonic O2 is very slow, installing mixing tabs at nozzle exit can enhance the mixing. Installing coarse tabs can get relatively uniform flowfield. Through chemical reaction with 10 species and 21 reactions, the paper simulated the mixing and reacting processes of multi-species in the cavity. Preliminary simulation results show that chemical reactions take place in the cavity, generating excited and basic-state iodine atoms. The cavity obtains positive gain and the total pr
Using computational fluid dynamic methods, this paper simulated nozzle array with high energy N2 as carrier gas. The results indicate that using high mach number N2 to eject low Mach number O2, the stagnation pressure at cavity exit can be enhanced. The process of mixing hypersonic N2 with sonic O2 is very slow, installing mixing tabs at nozzle exit can enhance the mixing. Installing coarse tabs can get relatively uniform flowfield. Through chemical reaction with 10 species and 21 reactions, the paper simulated the mixing and reacting processes of multi-species in the cavity. Preliminary simulation results show that chemical reactions take place in the cavity, generating excited and basic-state iodine atoms. The cavity obtains positive gain and the total pr
2011,
23.
Abstract:
Due to the displacement between armature and stator axes of helical explosive magnetic flux compression generators(HMFCGs), the continuous contact between stator and expanding armature may be altered to skipping, which is a major factor affecting output characteristics of HMFCGs because the flux pocketed in the skipped portion is lost. The condition of flux loss because of displacement between armature and stator axes of simple cylindrical and conical generators is mathematically analyzed, and a brief expression is derived which can be used to determine the exact condition of a given generator geometry. Based on the expression, identification of turn-skipping condition and calculation of turn-skipping ratio of a given generator geometry can be obtained by numerical calculation code on Matl
Due to the displacement between armature and stator axes of helical explosive magnetic flux compression generators(HMFCGs), the continuous contact between stator and expanding armature may be altered to skipping, which is a major factor affecting output characteristics of HMFCGs because the flux pocketed in the skipped portion is lost. The condition of flux loss because of displacement between armature and stator axes of simple cylindrical and conical generators is mathematically analyzed, and a brief expression is derived which can be used to determine the exact condition of a given generator geometry. Based on the expression, identification of turn-skipping condition and calculation of turn-skipping ratio of a given generator geometry can be obtained by numerical calculation code on Matl
2011,
23.
Abstract:
A 10-stage 200 kV mini-Marx generator based on waveerection principle has been designed in coaxial structure. The capacitors, connecting switches and metallic enclosures, lead to the establishment of a fast pulse forming line. And fast risetime is achieved through the proper design of the stray capacitance and interstage capacitance, in concern with coupling the spark gaps via ultra-violet energy. The generator was demonstrated to deliver pulses of more than 210 kV onto a 70 Ω load with 40 ns pulse width and 6 ns risetime. With a flash X-ray tube integrated directly into the generator as a load, the formed flash X-ray system could generate a dose of 7.7×10－6 C/kg at 25 cm away for flash X-radiography．
A 10-stage 200 kV mini-Marx generator based on waveerection principle has been designed in coaxial structure. The capacitors, connecting switches and metallic enclosures, lead to the establishment of a fast pulse forming line. And fast risetime is achieved through the proper design of the stray capacitance and interstage capacitance, in concern with coupling the spark gaps via ultra-violet energy. The generator was demonstrated to deliver pulses of more than 210 kV onto a 70 Ω load with 40 ns pulse width and 6 ns risetime. With a flash X-ray tube integrated directly into the generator as a load, the formed flash X-ray system could generate a dose of 7.7×10－6 C/kg at 25 cm away for flash X-radiography．
2011,
23.
Abstract:
Gas switches can be used to produce high power electromagnetic pulses with very fast risetime in UWB radiation systems. Due to its promising prospect in repetitive rate application, the experimental study on the high pressure hydrogen switch is conducted under pressure of 4 to 13 MPa and electrode gap spacing of 0.4 to 1.2 mm.The switch is pulse charged to more than 200 kV in less than 2 ns. Fast pulses with risetime less than 240 ps are obtained. The average breakdown electric field strength ranges from 3 to 7 MV/cm.The closure time of the hydrogen gaps decreases slightly with increasing the pressure or decreasing the gap space．
Gas switches can be used to produce high power electromagnetic pulses with very fast risetime in UWB radiation systems. Due to its promising prospect in repetitive rate application, the experimental study on the high pressure hydrogen switch is conducted under pressure of 4 to 13 MPa and electrode gap spacing of 0.4 to 1.2 mm.The switch is pulse charged to more than 200 kV in less than 2 ns. Fast pulses with risetime less than 240 ps are obtained. The average breakdown electric field strength ranges from 3 to 7 MV/cm.The closure time of the hydrogen gaps decreases slightly with increasing the pressure or decreasing the gap space．
2011,
23.
Abstract:
Ultrahigh pulsed power with short rise time has been needed in many applications. For single linear transformer driver(LTD) module with sixty cavities connected in series, this paper has explored the effect of the cavity-triggering sequences on the output current parameters of the LTD module and discussed the possibility to optimize the output parameters of single LTD module through adjusting the triggering time of each cavity. The results indicate that the current shapes of single LTD module could be adjusted effectively through adjusting the cavity triggering sequence. And the output current will have shorter risetime and higher peak if the switches in each cavity are closed after the arrival of the electromagnetic pulses from its neighbor immediately upstream. With the insulation level
Ultrahigh pulsed power with short rise time has been needed in many applications. For single linear transformer driver(LTD) module with sixty cavities connected in series, this paper has explored the effect of the cavity-triggering sequences on the output current parameters of the LTD module and discussed the possibility to optimize the output parameters of single LTD module through adjusting the triggering time of each cavity. The results indicate that the current shapes of single LTD module could be adjusted effectively through adjusting the cavity triggering sequence. And the output current will have shorter risetime and higher peak if the switches in each cavity are closed after the arrival of the electromagnetic pulses from its neighbor immediately upstream. With the insulation level
2011,
23.
Abstract:
A type of glow discharge triggered pseudospark switch is designed, and the relationship among the delay and jitter of the switch and the glow discharge current, gas pressure, trigger voltage and anode voltage is studied. When the glow discharge current is less than 0.30 mA, the switch can not be triggered; when the current increases from 0.35 mA to 0.6 mA, the delay and jitter decrease; when the current is about 0.60 mA, the delay and jitter are stable. When the He pressure is lower than 6 Pa, the switch can not be triggered, which is consistent with the theoretic value 6.95 Pa; when the He pressure is between 6 Pa and 12 Pa, the delay and jitter lessen as the gas pressure increases; the switch can work in a stable state when the gas pressure is more than 12 Pa and less than 30 Pa. When th
A type of glow discharge triggered pseudospark switch is designed, and the relationship among the delay and jitter of the switch and the glow discharge current, gas pressure, trigger voltage and anode voltage is studied. When the glow discharge current is less than 0.30 mA, the switch can not be triggered; when the current increases from 0.35 mA to 0.6 mA, the delay and jitter decrease; when the current is about 0.60 mA, the delay and jitter are stable. When the He pressure is lower than 6 Pa, the switch can not be triggered, which is consistent with the theoretic value 6.95 Pa; when the He pressure is between 6 Pa and 12 Pa, the delay and jitter lessen as the gas pressure increases; the switch can work in a stable state when the gas pressure is more than 12 Pa and less than 30 Pa. When th
2011,
23.
Abstract:
The dielectric barrier discharge(DBD) in atmospheric air is generated with coaxial dielectric structure driven by a microsecond oscillatory pulse power supply. The discharge characteristics of DBD are studied by measurement of the voltage-current waveform and capture of the lighting emission images, and the important discharge parameters such as transfer charge and discharge power are calculated. The influences of applied voltage amplitude and air gap distance on discharge characteristics and parameters of DBD are studied, and the experimental results are explained based on the analysis of the discharge mechanism. Results show that the DBD driven by a microsecond oscillatory pulse power supply consume more discharge power and transfer larger amount of charge, and the average discharge powe
The dielectric barrier discharge(DBD) in atmospheric air is generated with coaxial dielectric structure driven by a microsecond oscillatory pulse power supply. The discharge characteristics of DBD are studied by measurement of the voltage-current waveform and capture of the lighting emission images, and the important discharge parameters such as transfer charge and discharge power are calculated. The influences of applied voltage amplitude and air gap distance on discharge characteristics and parameters of DBD are studied, and the experimental results are explained based on the analysis of the discharge mechanism. Results show that the DBD driven by a microsecond oscillatory pulse power supply consume more discharge power and transfer larger amount of charge, and the average discharge powe
2011,
23.
Abstract:
The plane wave expansion method is applied to simulate the band gap of a tunable twodimensional photonic crystal micro cavity based on controlling the refractive index of defect medium. KTiOPO4(KTP) crystal is introduced to the planar photonic crystal as point defect, with its refractive index controlled by alternating current according to electro-optic effect. Numerical calculations and experimental results show that, with the refractive index of KTP increasing, the normalized frequencies of defect modes shift downward. The number of band gaps of the square lattice reduces, and the band gap of the triangle lattice narrows．
The plane wave expansion method is applied to simulate the band gap of a tunable twodimensional photonic crystal micro cavity based on controlling the refractive index of defect medium. KTiOPO4(KTP) crystal is introduced to the planar photonic crystal as point defect, with its refractive index controlled by alternating current according to electro-optic effect. Numerical calculations and experimental results show that, with the refractive index of KTP increasing, the normalized frequencies of defect modes shift downward. The number of band gaps of the square lattice reduces, and the band gap of the triangle lattice narrows．
2011,
23.
Abstract:
The damage mechanism of 4H-SiC NMOS under high energy electron and proton irradiations was analyzed. The device’s physical model, electron irradiation model and proton irradiation model were established to simulate the drain current and irradiation effects with software ISE-TCAD. The variation of drain current with gate voltage and drain voltage was obtained for 4H-SiC NMOS irradiated by 2.5 MeV electron beam of 5×1013 cm-2 fluence and 6.5 MeV proton beam of 2×1014 cm-2 fluence, respectively. The simulation results are in good agreement with experimental ones under the same conditions.
The damage mechanism of 4H-SiC NMOS under high energy electron and proton irradiations was analyzed. The device’s physical model, electron irradiation model and proton irradiation model were established to simulate the drain current and irradiation effects with software ISE-TCAD. The variation of drain current with gate voltage and drain voltage was obtained for 4H-SiC NMOS irradiated by 2.5 MeV electron beam of 5×1013 cm-2 fluence and 6.5 MeV proton beam of 2×1014 cm-2 fluence, respectively. The simulation results are in good agreement with experimental ones under the same conditions.
2011,
23.
Abstract:
The electronic structure and energy state density of Ba substituting for K in KDP crystals was studied by first principles calculations. The point defect narrows down the energy gap to about 6.3 eV, which corresponds to a two-photon absorption of 390 nm. This can explain the absorption of Ba-doped KDP crystals in ultraviolet(UV) region. Moreover, the defect only makes the surrounding crystal lattice and electronic structure slightly distorted, and thus little impact is placed on the overall structure of the crystal.
The electronic structure and energy state density of Ba substituting for K in KDP crystals was studied by first principles calculations. The point defect narrows down the energy gap to about 6.3 eV, which corresponds to a two-photon absorption of 390 nm. This can explain the absorption of Ba-doped KDP crystals in ultraviolet(UV) region. Moreover, the defect only makes the surrounding crystal lattice and electronic structure slightly distorted, and thus little impact is placed on the overall structure of the crystal.
2011,
23.
Abstract:
With large deuterium clusters produced in a supersonic expansion of high pressure gases into vacuum through a cone nozzle, experiments have been carried out to investigate the evolvement of deuterium clusters in ultrashort ultraintense laser field based on the SILEX-Ⅰ laser system. Tens keV deuterium ions were observed. The energy spectrum of these ions agrees with the Coulomb explosion model. It is found that distribution of the energy spectrum is determined by the average size of clusters. A part of electrons escape from the clusters by above threshold ionization after laser irradiation, and then collision ionization starts to dominate with the enhanced screening effect produced by the initial ionization electrons．
With large deuterium clusters produced in a supersonic expansion of high pressure gases into vacuum through a cone nozzle, experiments have been carried out to investigate the evolvement of deuterium clusters in ultrashort ultraintense laser field based on the SILEX-Ⅰ laser system. Tens keV deuterium ions were observed. The energy spectrum of these ions agrees with the Coulomb explosion model. It is found that distribution of the energy spectrum is determined by the average size of clusters. A part of electrons escape from the clusters by above threshold ionization after laser irradiation, and then collision ionization starts to dominate with the enhanced screening effect produced by the initial ionization electrons．
2011,
23.
Abstract:
Laser wake field accelerator is hopeful to become a new minitype gamma source. This type of source has excellent performance characteristics such as high energy, high brightness, small focal spot and ultra shot pulse export. Bremsstrahlung spectra produced by high wake field accelerated electron incident on high Z target is calculated by Monte-Carlo toolkit Geant4, and relative scintillation efficiency and point spread function of several gamma detecting crystal are calculated in the range of bremsstrahlung spectra. The relations between crystal thickness, crystal materials, incident gamma energy and the calculated results are analysed. All these provide important guidance for designing gamma detector in future．
Laser wake field accelerator is hopeful to become a new minitype gamma source. This type of source has excellent performance characteristics such as high energy, high brightness, small focal spot and ultra shot pulse export. Bremsstrahlung spectra produced by high wake field accelerated electron incident on high Z target is calculated by Monte-Carlo toolkit Geant4, and relative scintillation efficiency and point spread function of several gamma detecting crystal are calculated in the range of bremsstrahlung spectra. The relations between crystal thickness, crystal materials, incident gamma energy and the calculated results are analysed. All these provide important guidance for designing gamma detector in future．
2011,
23.
Abstract:
Ion components, ion charge states and ion diffusion velocities of hydrogen-impregnated-electrode pulsed vacuum arc discharge plasmas were measured by time of flight (TOF) mass spectrometry. The results show that main components of the plasmas are H+, Ti+, and Ti2+, Ti3+, with Ti2+ predominating. The average ion charge of Ti ions is between 1.95 and 2.13 when the discharge current is between 40 A and 80 A, and it increases with the increasing of the discharge current. In addition, different ions have different diffusion velocities with a magnitude of 104 m/s.
Ion components, ion charge states and ion diffusion velocities of hydrogen-impregnated-electrode pulsed vacuum arc discharge plasmas were measured by time of flight (TOF) mass spectrometry. The results show that main components of the plasmas are H+, Ti+, and Ti2+, Ti3+, with Ti2+ predominating. The average ion charge of Ti ions is between 1.95 and 2.13 when the discharge current is between 40 A and 80 A, and it increases with the increasing of the discharge current. In addition, different ions have different diffusion velocities with a magnitude of 104 m/s.
2011,
23.
Abstract:
From the point of impedance matching between the probe and the grounding electrode plate, spectral response characteristics of plasmas generated by hypervelocity impact have been obtained through theoretical analysis of corresponding characteristic parameters diagnostic system. Then a kind of probe measurement system suitable for diagnosing plasma generated by hypervelocity impact was established, and power spectral characteristics were obtained for plasmas generated by solid sphere LY12 aluminum projectile impacting LY12 aluminum target. Theoretical and experimental results show that spectral responses of the plasma generated by hypervelocity impact are mainly in the low frequency range. when the frequency is lower than 5.8 kHz, the power spectrum is smooth with low amplitude; when the fr
From the point of impedance matching between the probe and the grounding electrode plate, spectral response characteristics of plasmas generated by hypervelocity impact have been obtained through theoretical analysis of corresponding characteristic parameters diagnostic system. Then a kind of probe measurement system suitable for diagnosing plasma generated by hypervelocity impact was established, and power spectral characteristics were obtained for plasmas generated by solid sphere LY12 aluminum projectile impacting LY12 aluminum target. Theoretical and experimental results show that spectral responses of the plasma generated by hypervelocity impact are mainly in the low frequency range. when the frequency is lower than 5.8 kHz, the power spectrum is smooth with low amplitude; when the fr
2011,
23.
Abstract:
Eddy currect effects should be considered in a accelerator with magnets ramping with a large repetition frequency. Field components like dipolar, quadrupolar and sextupolar ones and heating effects induced by eddy current effects will affect the chromaticities, tunes, resonance， etc. The field components and their effects on beam parameters in the ring are evaluated for difference ramping curves and ramping frequencies. The most important effect is found to be from sextupolar component in the frequency range of proton therapy, and other components will play more important roles when the repetition frequency increases. Accordingly, the ramping curve for operation is selected as a sinusoidal curve with ramping time of 0.7 s.
Eddy currect effects should be considered in a accelerator with magnets ramping with a large repetition frequency. Field components like dipolar, quadrupolar and sextupolar ones and heating effects induced by eddy current effects will affect the chromaticities, tunes, resonance， etc. The field components and their effects on beam parameters in the ring are evaluated for difference ramping curves and ramping frequencies. The most important effect is found to be from sextupolar component in the frequency range of proton therapy, and other components will play more important roles when the repetition frequency increases. Accordingly, the ramping curve for operation is selected as a sinusoidal curve with ramping time of 0.7 s.
2011,
23.
Abstract:
The thermal transport process of measuring probes within PET cyclotron is simulated based on finite difference time domain (FDTD) method. For both dynamic and static measurement modes, the highest surface temperature and back-end temperature for three probes of different (Cu, Ta, W) are obtained with the variation of power load time under thermal irradiation condition. The results show that there is no obvious difference among the three materials and the speed of probes should be 10 mm/s in dynamic mode. However, in static mode, copper turns out to be the best material for probe design due to its advantages such as high blackness and high thermal conductivity．
The thermal transport process of measuring probes within PET cyclotron is simulated based on finite difference time domain (FDTD) method. For both dynamic and static measurement modes, the highest surface temperature and back-end temperature for three probes of different (Cu, Ta, W) are obtained with the variation of power load time under thermal irradiation condition. The results show that there is no obvious difference among the three materials and the speed of probes should be 10 mm/s in dynamic mode. However, in static mode, copper turns out to be the best material for probe design due to its advantages such as high blackness and high thermal conductivity．
2011,
23.
Abstract:
According to the problem of deblur of flash radiographic image with low signal-to-noise ratio, a total variation (TV) regularization based image deblur-reconstruction algorithm is proposed. Considerring the blurring of the image system, the deblur-reconstruction model in new algorithm is established for three-dimensional (3D) object based on flash radiographic characteristics. Then a TV-norm is used as regularized term to construct a smoothing function for image deblur-reconstruction. Thus, the problem of image deblur-reconstruction is transformed in to a problem of a functional minimization. The fixed point iteration (FPI) scheme is introduced to solve the problem. The numerical experimental results show that to some extent, the new algorithm can eliminate the influence on reconstruction
According to the problem of deblur of flash radiographic image with low signal-to-noise ratio, a total variation (TV) regularization based image deblur-reconstruction algorithm is proposed. Considerring the blurring of the image system, the deblur-reconstruction model in new algorithm is established for three-dimensional (3D) object based on flash radiographic characteristics. Then a TV-norm is used as regularized term to construct a smoothing function for image deblur-reconstruction. Thus, the problem of image deblur-reconstruction is transformed in to a problem of a functional minimization. The fixed point iteration (FPI) scheme is introduced to solve the problem. The numerical experimental results show that to some extent, the new algorithm can eliminate the influence on reconstruction
2011,
23.
Abstract:
Novel magnetically insulated transmission line oscillator with 2D periodic slow wave structure is put forward, the symmetrical mode and dissymmetrical mode of which have the same working frequency. It can get microwave with pure frequency during mode competition. At the same time the efficiency is increased. 3D electromagnetic software indicate that the symmetrical mode and dissymmetrical mode of slow microwave structure of the new magnetically insulated transmission line oscillator(MILO) have the same π mode resonance frequency while PIC simulation indicate that high-power microwave with muti-mode and pure frequency of 1.22 GHz is generated and the average output power is increased to 2.8 GW from 2.4 GW compared with the original MILO when the beam voltage is 450 kV and current is 43 kA.
Novel magnetically insulated transmission line oscillator with 2D periodic slow wave structure is put forward, the symmetrical mode and dissymmetrical mode of which have the same working frequency. It can get microwave with pure frequency during mode competition. At the same time the efficiency is increased. 3D electromagnetic software indicate that the symmetrical mode and dissymmetrical mode of slow microwave structure of the new magnetically insulated transmission line oscillator(MILO) have the same π mode resonance frequency while PIC simulation indicate that high-power microwave with muti-mode and pure frequency of 1.22 GHz is generated and the average output power is increased to 2.8 GW from 2.4 GW compared with the original MILO when the beam voltage is 450 kV and current is 43 kA.
2011,
23.
Abstract:
The large-signal beam-wave interaction of rectangular helix traveling-wave-tube(TWT) is performed using 3D particle-in-cell simulation code MAGIC. The linear tapered resistance couplers were used to reduce reflections, which may avoid modeling the actual complex input and output geometries and reduce the numbers of unused elements. The simulation results show that the simulation model is valid to compute the beam-wave interaction inside the rectangular helix TWT, and some key parameters to the interaction were analyzed. The X-band TWT is designed with the design parameters as follows: operating frequency from 8 GHz to 12 GHz, the highest output power of 480 W, bandwidth 4 GHz, and its electron efficiency reaches 11.8%．
The large-signal beam-wave interaction of rectangular helix traveling-wave-tube(TWT) is performed using 3D particle-in-cell simulation code MAGIC. The linear tapered resistance couplers were used to reduce reflections, which may avoid modeling the actual complex input and output geometries and reduce the numbers of unused elements. The simulation results show that the simulation model is valid to compute the beam-wave interaction inside the rectangular helix TWT, and some key parameters to the interaction were analyzed. The X-band TWT is designed with the design parameters as follows: operating frequency from 8 GHz to 12 GHz, the highest output power of 480 W, bandwidth 4 GHz, and its electron efficiency reaches 11.8%．
2011,
23.
Abstract:
The partial least-square regression (PLSR) method was introduced and implemented in the prediction of microwave effects. The results show that the PLSR method has an accuracy almost consistent with the adaptive neuro-fuzzy inference system (ANFIS) model’s, and their average relative error is less than 3%. The requirement for sample size of these two methods was analyzed. On the condition of small sample size, the PLSR model is more precise than the ANFIS model. Thus the PLSR method is more effective for data processing and prediction with small sample size of microwave effects.
The partial least-square regression (PLSR) method was introduced and implemented in the prediction of microwave effects. The results show that the PLSR method has an accuracy almost consistent with the adaptive neuro-fuzzy inference system (ANFIS) model’s, and their average relative error is less than 3%. The requirement for sample size of these two methods was analyzed. On the condition of small sample size, the PLSR model is more precise than the ANFIS model. Thus the PLSR method is more effective for data processing and prediction with small sample size of microwave effects.
2011,
23.
Abstract:
The equivalent parameter models for series and parallel feed microstrip arrays are respectively built, according to the array’ structure. Then the limitation of the microstrip feed network’s power loss on the gain of microstrip antenna array is analyzed quantificationally. With the help of the low loss hybrid feed network which is composed of microstrip lines and coaxial cables, a C-band 4×24 elements microstrip antenna array with high efficiency is designed based on the series-parallel feed architecture. The measurements of the array are better than design goals, especially that the gain of the array reaches 25.4 dB, 1.1 dB higher than that of the series array of the same element number, and the radiant efficiency is 64.5%. The measurements are in good accordance with the theoretical
The equivalent parameter models for series and parallel feed microstrip arrays are respectively built, according to the array’ structure. Then the limitation of the microstrip feed network’s power loss on the gain of microstrip antenna array is analyzed quantificationally. With the help of the low loss hybrid feed network which is composed of microstrip lines and coaxial cables, a C-band 4×24 elements microstrip antenna array with high efficiency is designed based on the series-parallel feed architecture. The measurements of the array are better than design goals, especially that the gain of the array reaches 25.4 dB, 1.1 dB higher than that of the series array of the same element number, and the radiant efficiency is 64.5%. The measurements are in good accordance with the theoretical
2011,
23.
Abstract:
A time-domain method is presented to determine the radiation centers of ultra wideband(UWB) antennas. Without considering the frequency of input pulses, the E- and H-plane radiation centers can be derived by measuring the time delay of waveforms in far field. When the maximal delay reaches the minimum, the reference point is the radiation center. The method is then applied to TEM horn, and its effectiveness and veracity are proved by simulating the model of paraboloidal reflector with TEM feeding horn.
A time-domain method is presented to determine the radiation centers of ultra wideband(UWB) antennas. Without considering the frequency of input pulses, the E- and H-plane radiation centers can be derived by measuring the time delay of waveforms in far field. When the maximal delay reaches the minimum, the reference point is the radiation center. The method is then applied to TEM horn, and its effectiveness and veracity are proved by simulating the model of paraboloidal reflector with TEM feeding horn.
2011,
23.
Abstract:
In order to study the working mode selection mechanism of gyrotrons, this paper investigates mode selective properties of three kinds of gyrotron cavities, i.e. cylindrical open cavity, coaxial cavity with smooth insert and coaxial cavity with corrugated insert, and further discusses the mode competition phenomenon in these cavities. Through the calculation of dispersive curves of coaxial waveguide, it is determined that coaxial cavities can rarefy the mode spectrum and reduce the competing action of some high-order modes, compared with the cylindrical open cavity, enabling stable single mode operation of gyrotron. Finally, the numerical calculation of dispersion characteristics of a coaxial gyrotron in the KIT(Karlsruhe Institute of Technology) is presented, and the results indicate that
In order to study the working mode selection mechanism of gyrotrons, this paper investigates mode selective properties of three kinds of gyrotron cavities, i.e. cylindrical open cavity, coaxial cavity with smooth insert and coaxial cavity with corrugated insert, and further discusses the mode competition phenomenon in these cavities. Through the calculation of dispersive curves of coaxial waveguide, it is determined that coaxial cavities can rarefy the mode spectrum and reduce the competing action of some high-order modes, compared with the cylindrical open cavity, enabling stable single mode operation of gyrotron. Finally, the numerical calculation of dispersion characteristics of a coaxial gyrotron in the KIT(Karlsruhe Institute of Technology) is presented, and the results indicate that
2011,
23.
Abstract:
The influence of load mismatch on resonant frequency, gap impedance and external Q factor of klystron output circuit has been studied by using microwave equivalent circuit and 3D electromagnetic software. And the influence of load mismatch on the efficiency of klystron was calculated by 1D large signal klystron code. The calculation results of C band klystron indicate that for single-gap output cavity, the change of resonant frequency caused by load mismatch is smaller and the changes of gap impedance and equivalent external Q factor are bigger. When the voltage standing wave ratio(VSWR) of load is 1.5, the resonant frequency changes about 35 MHz, the real part of gap impedance varies from 3 660 Ω to 7 998 Ω, the external Q factor varies from 36.9 to 93.5, and the efficiency at central f
The influence of load mismatch on resonant frequency, gap impedance and external Q factor of klystron output circuit has been studied by using microwave equivalent circuit and 3D electromagnetic software. And the influence of load mismatch on the efficiency of klystron was calculated by 1D large signal klystron code. The calculation results of C band klystron indicate that for single-gap output cavity, the change of resonant frequency caused by load mismatch is smaller and the changes of gap impedance and equivalent external Q factor are bigger. When the voltage standing wave ratio(VSWR) of load is 1.5, the resonant frequency changes about 35 MHz, the real part of gap impedance varies from 3 660 Ω to 7 998 Ω, the external Q factor varies from 36.9 to 93.5, and the efficiency at central f
2011,
23.
Abstract:
Two kinds of graphite cathode (normal graphite cathode and copper-graphite cathode) are used in the electron microscope experiment and the repetitively long-pulse experiment separately. The experimental results show that microstructures of the two graphite materials are obviously different, and the copper-graphite is little better than the normal graphite in the explosive emission performance of cathode, pulse width and stability of the repetitively long-pulse high-power microwave. Those experimental conclusions are still needed to be confirmed in the future.
Two kinds of graphite cathode (normal graphite cathode and copper-graphite cathode) are used in the electron microscope experiment and the repetitively long-pulse experiment separately. The experimental results show that microstructures of the two graphite materials are obviously different, and the copper-graphite is little better than the normal graphite in the explosive emission performance of cathode, pulse width and stability of the repetitively long-pulse high-power microwave. Those experimental conclusions are still needed to be confirmed in the future.
2011,
23.
Abstract:
An approach for fast ignition of laser fusion is to use hot electrons for heating, and the temperature is an important parameter to characterize the hot electrons. The temperature of the hot electrons is diagnosed by experimentally measuring the intensity ratio of Kα characteristic lines emitted from a two-layer fluorescent target in combination with a Monte-Carlo simulation. The temperature of the hot electrons measured with this method is compared with that directly measured by a magnetic spectrometer for the same shot, and a good agreement is obtained. The results show that, by choosing appropriate fluorescent layer materials and target thickness, the temperature of the hot electrons inside the target can be measured by the intensity ratio of the Kα characteristic lines.
An approach for fast ignition of laser fusion is to use hot electrons for heating, and the temperature is an important parameter to characterize the hot electrons. The temperature of the hot electrons is diagnosed by experimentally measuring the intensity ratio of Kα characteristic lines emitted from a two-layer fluorescent target in combination with a Monte-Carlo simulation. The temperature of the hot electrons measured with this method is compared with that directly measured by a magnetic spectrometer for the same shot, and a good agreement is obtained. The results show that, by choosing appropriate fluorescent layer materials and target thickness, the temperature of the hot electrons inside the target can be measured by the intensity ratio of the Kα characteristic lines.
2011,
23.
Abstract:
A certain number of standard commercial fluorescent lamps were placed directly against one another around the inner surface of a metal cavity to produce a plasma layer there. The scattering of microwaves with a series of incident angles by the plasma covered metal cavity was studied experimentally. The strong loss of return microwave observed is as large as 5 to 25 dB in the frequency range from 0.80 to 1.75 GHz, and trends to a peak of 26.71 dB when the frequency of incident wave approaching to 1.75 GHz. The incident angles where the best attenuation appears are different with different incident wave frequencies. The effects of plasma on microwave attenuations were analyzed. It can be drawn that the plasma has potential in radar cross section reduction of cavity structures like inlets.
A certain number of standard commercial fluorescent lamps were placed directly against one another around the inner surface of a metal cavity to produce a plasma layer there. The scattering of microwaves with a series of incident angles by the plasma covered metal cavity was studied experimentally. The strong loss of return microwave observed is as large as 5 to 25 dB in the frequency range from 0.80 to 1.75 GHz, and trends to a peak of 26.71 dB when the frequency of incident wave approaching to 1.75 GHz. The incident angles where the best attenuation appears are different with different incident wave frequencies. The effects of plasma on microwave attenuations were analyzed. It can be drawn that the plasma has potential in radar cross section reduction of cavity structures like inlets.
2011,
23.
Abstract:
A dual-functional extreme ultraviolet(EUV) multilayer (ML) mirror was designed for high-reflectivity at 19.5 nm ( Fe Ⅻ line ) and low-reflectivity at 30.4 nm ( He Ⅱ line ). The design based on genetic algorithm (GA) utilized a stack composed of two periodic multilayers: a bottom multilayer for high reflectivity at 19.5 nm, and a top multilayer for low-reflectivity at 30.4 nm. The multilayer mirror was prepared by direct current magnetron sputtering, and characterized by grazing-incident X-ray diffraction(XRD) and synchrotron radiation(SR). The experiment results show that the dual-functional multilayer achieves the reflectivity of 33.3% at 19.5 nm and 9.6×10-4 at 30.4 nm at incident angle of 13°.
A dual-functional extreme ultraviolet(EUV) multilayer (ML) mirror was designed for high-reflectivity at 19.5 nm ( Fe Ⅻ line ) and low-reflectivity at 30.4 nm ( He Ⅱ line ). The design based on genetic algorithm (GA) utilized a stack composed of two periodic multilayers: a bottom multilayer for high reflectivity at 19.5 nm, and a top multilayer for low-reflectivity at 30.4 nm. The multilayer mirror was prepared by direct current magnetron sputtering, and characterized by grazing-incident X-ray diffraction(XRD) and synchrotron radiation(SR). The experiment results show that the dual-functional multilayer achieves the reflectivity of 33.3% at 19.5 nm and 9.6×10-4 at 30.4 nm at incident angle of 13°.
2011,
23.
Abstract:
Hollow polymer microspheres were prepared by alkali/cooling method at high temperature under high pressure using monodisperse styrene-methylacrylic acid copolymer particles. The effects of components of emulsifiers on the particles and of the pressure on their hollow structure were clarified. As clearly revealed by the SEM and TEM analyses, the type of emulsifiers had great effect on dispersion of copolymer particles. The monodisperion of P(St/MAA) becomes better as the content of Tween-80 increases. When the mass ratio between emulsifiers Tween-80 and Span-80 was 3∶1, hollow polymer microspheres were obtained by monodispersed P(St-MAA) particles. And hollow polymer microspheres with 50 nm average shell thickness formed at high temperature under high pressure.
Hollow polymer microspheres were prepared by alkali/cooling method at high temperature under high pressure using monodisperse styrene-methylacrylic acid copolymer particles. The effects of components of emulsifiers on the particles and of the pressure on their hollow structure were clarified. As clearly revealed by the SEM and TEM analyses, the type of emulsifiers had great effect on dispersion of copolymer particles. The monodisperion of P(St/MAA) becomes better as the content of Tween-80 increases. When the mass ratio between emulsifiers Tween-80 and Span-80 was 3∶1, hollow polymer microspheres were obtained by monodispersed P(St-MAA) particles. And hollow polymer microspheres with 50 nm average shell thickness formed at high temperature under high pressure.
2011,
23.
Abstract:
The optical spectra from the interaction between a 30 fs, 1×1019 W/cm2 laser pulse and foil targets on SILEX-Ⅰ are studied. Evident red shifts of the second and three-half harmonic emissions in the specular reflection direction are observed from a 3 μm thick copper target. The recession velocity at the reflection surface is deduced to be 2.6×108 cm/s. For the 200 nm thick CH target, a supercontinuum extending from 300 to 940 nm is observed in the direction of laser propagation. The density distribution of plasmas induced by laser prepulse is simulated using MULTI-1D hydrodynamic code. The results show that, laser prepulse has a profound effect on the pre-plasma density distribution of a foil target, which leads to the differences in the observed spectra.
The optical spectra from the interaction between a 30 fs, 1×1019 W/cm2 laser pulse and foil targets on SILEX-Ⅰ are studied. Evident red shifts of the second and three-half harmonic emissions in the specular reflection direction are observed from a 3 μm thick copper target. The recession velocity at the reflection surface is deduced to be 2.6×108 cm/s. For the 200 nm thick CH target, a supercontinuum extending from 300 to 940 nm is observed in the direction of laser propagation. The density distribution of plasmas induced by laser prepulse is simulated using MULTI-1D hydrodynamic code. The results show that, laser prepulse has a profound effect on the pre-plasma density distribution of a foil target, which leads to the differences in the observed spectra.
2011,
23.
Abstract:
Transparent BeH2 films have been prepared with vaporized beryllium atoms reacting with active hydrogen atoms. Scanning electron microscopy photographs show that the surfaces of BeH2 films have microvoids, and the infrared spectrum reveals an intense absorption band at 722 cm-1. BeH2 reticular structures based on tetrahedron structure have been calculated by density functional theory method. The frequency and intensity of three vibration modes obtained from the calculations are in reasonably good agreement with those observed in references for BeH2 powders. The calculated frequency of Be－H－Be bond bending vibrations is 747 cm-1, which is consistent with the measured IR absorption band of BeH2 films in this paper. It can be speculated that the structures of BeH2 films
Transparent BeH2 films have been prepared with vaporized beryllium atoms reacting with active hydrogen atoms. Scanning electron microscopy photographs show that the surfaces of BeH2 films have microvoids, and the infrared spectrum reveals an intense absorption band at 722 cm-1. BeH2 reticular structures based on tetrahedron structure have been calculated by density functional theory method. The frequency and intensity of three vibration modes obtained from the calculations are in reasonably good agreement with those observed in references for BeH2 powders. The calculated frequency of Be－H－Be bond bending vibrations is 747 cm-1, which is consistent with the measured IR absorption band of BeH2 films in this paper. It can be speculated that the structures of BeH2 films
2011,
23.
Abstract:
In order to manufacture reaction bonded silicon carbide(RB-SiC) mirrors of fine optical surface, 100 μm thick Si coatings were prepared by RF magnetron sputtering on RB-SiC substrates of 70 mm diameter and then polished. Tests with ZYGO surface profilometer show that the RMS surface roughness of the surface-modified RB-SiC achieves 0.496 nm. X-ray diffraction analyses reveal the polycrystalline structure of the Si coatings. Moreover, the adhesion between Si coating and RB-SiC substrate measured by direct pull-off method is more than 10.7 MPa. Therefore, the magnetron sputtered Si coating can satisfy the requirements of RB-SiC surface modification．
In order to manufacture reaction bonded silicon carbide(RB-SiC) mirrors of fine optical surface, 100 μm thick Si coatings were prepared by RF magnetron sputtering on RB-SiC substrates of 70 mm diameter and then polished. Tests with ZYGO surface profilometer show that the RMS surface roughness of the surface-modified RB-SiC achieves 0.496 nm. X-ray diffraction analyses reveal the polycrystalline structure of the Si coatings. Moreover, the adhesion between Si coating and RB-SiC substrate measured by direct pull-off method is more than 10.7 MPa. Therefore, the magnetron sputtered Si coating can satisfy the requirements of RB-SiC surface modification．
2011,
23.
Abstract:
Three kinds of anti-reflective SiO2 films, without impurities, with SiO2 particulate impurities and with CeO2 particulate impurities, were deposited on K9 glass by sol-gel dip-coating method. The influence of impurities on laser-induced damage of films was investigated before and after preconditioning with a 1 064 nm Nd:YAG pulsed laser. No obvious change in morphologies and damage threshold appears for pure films after conditioning. For the films with SiO2 impurities, 10 μm-size SiO2 particles show obvious micro-focusing effect and act as damage-initiating seeds, which can be removed by conditioning. Moreover, the samples with CeO2 impurities have intense absorbing character, and their laser-induced damage threshold is les
Three kinds of anti-reflective SiO2 films, without impurities, with SiO2 particulate impurities and with CeO2 particulate impurities, were deposited on K9 glass by sol-gel dip-coating method. The influence of impurities on laser-induced damage of films was investigated before and after preconditioning with a 1 064 nm Nd:YAG pulsed laser. No obvious change in morphologies and damage threshold appears for pure films after conditioning. For the films with SiO2 impurities, 10 μm-size SiO2 particles show obvious micro-focusing effect and act as damage-initiating seeds, which can be removed by conditioning. Moreover, the samples with CeO2 impurities have intense absorbing character, and their laser-induced damage threshold is les
2011,
23.
Abstract:
According to the ionization mechanism of transparent material under super high pressure, the direct diagnosis method of shock wave has been analyzed. With the Drude free electron model, the reflectivity difference of shock wave front under different pressures was analyzed. The blank effect in the detector was studied, which is caused by the X-ray ionization of transparent material, after analyzing the reflectivity data in space-time scale. The experiment shows that the beginning point and duration of blank effect are consistent with the start point and duration of laser pulse, respectively. And the reflectivity of shock wave front is about 35% when the shock velocity is 32 km/s. The reason and solution for blank effect was presented. The formula to calculate the shock wave velocity in tran
According to the ionization mechanism of transparent material under super high pressure, the direct diagnosis method of shock wave has been analyzed. With the Drude free electron model, the reflectivity difference of shock wave front under different pressures was analyzed. The blank effect in the detector was studied, which is caused by the X-ray ionization of transparent material, after analyzing the reflectivity data in space-time scale. The experiment shows that the beginning point and duration of blank effect are consistent with the start point and duration of laser pulse, respectively. And the reflectivity of shock wave front is about 35% when the shock velocity is 32 km/s. The reason and solution for blank effect was presented. The formula to calculate the shock wave velocity in tran
2011,
23.
Abstract:
The method for improving the uniformity of the image using multilayer films condenser is proposed. The optical structure of the condenser is designed, which concentrates 80% energy radiated by plasma to about 0.8 mm diameter range. Based on the system’s wavelength and incidence angle of light, the Mo/Si multilayer films with period of 9.64 nm and layers of 30 is designed and the coatings are deposited with magnetron sputtering. The reflectivity of optical elements at 18.2 nm is 51.7%. The grid backlit by EUV rays focused using condenser is imaging via Schwarzschild microscope on CCD. The results show that spatial resolution of 2.5 μm can be achieved in the 1.2 mm field, and the non-uniformity of image caused by the obscuration of objective is eliminated absolutely.
The method for improving the uniformity of the image using multilayer films condenser is proposed. The optical structure of the condenser is designed, which concentrates 80% energy radiated by plasma to about 0.8 mm diameter range. Based on the system’s wavelength and incidence angle of light, the Mo/Si multilayer films with period of 9.64 nm and layers of 30 is designed and the coatings are deposited with magnetron sputtering. The reflectivity of optical elements at 18.2 nm is 51.7%. The grid backlit by EUV rays focused using condenser is imaging via Schwarzschild microscope on CCD. The results show that spatial resolution of 2.5 μm can be achieved in the 1.2 mm field, and the non-uniformity of image caused by the obscuration of objective is eliminated absolutely.
2011,
23.
Abstract:
Cyanide-free gold plating introducing Na3Au(SO3)2 as the gold compound is employed to prepare gold films by electroless plating and pulsed electroplating. The gold films are coated on an anodic aluminum oxide template, which is then dissolved in nitric acid solution. Scanning electron microscopy and X-ray diffraction analyses show that the gold films prepared by both methods present a porous structure. However, the difference in their microstructures is evident: the sample prepared by electroless plating possesses a dendritic structure, and that prepared by electroplating consists of nanowires.
Cyanide-free gold plating introducing Na3Au(SO3)2 as the gold compound is employed to prepare gold films by electroless plating and pulsed electroplating. The gold films are coated on an anodic aluminum oxide template, which is then dissolved in nitric acid solution. Scanning electron microscopy and X-ray diffraction analyses show that the gold films prepared by both methods present a porous structure. However, the difference in their microstructures is evident: the sample prepared by electroless plating possesses a dendritic structure, and that prepared by electroplating consists of nanowires.
2011,
23.
Abstract:
Nanoporous copper with bicontinuous ligament structures can be synthesized by free corrosion dealloying in dilute HCl solution with arc melted Mn-Cu alloys. The effect of initial alloy composition on micromorphology of nanoporous Cu and residual Mn atom fraction is investigated. The results indicate that, for alloys with Cu of more than 43% atom fraction, the dissolution of Mn is limited, leaving islands of retained Mn-Cu alloys. Bicontinuous ligament structures can be obtained as the initial Cu atom fraction decreases from 32% down to 23%. The ligaments of size from 20 to 100 nm and the nanopore of size from 30 to 80 nm can be tailored by controlling the initial alloy composition. However, the copper ligaments become large nanoparticles as the initial Cu atom fraction is below 20% and man
Nanoporous copper with bicontinuous ligament structures can be synthesized by free corrosion dealloying in dilute HCl solution with arc melted Mn-Cu alloys. The effect of initial alloy composition on micromorphology of nanoporous Cu and residual Mn atom fraction is investigated. The results indicate that, for alloys with Cu of more than 43% atom fraction, the dissolution of Mn is limited, leaving islands of retained Mn-Cu alloys. Bicontinuous ligament structures can be obtained as the initial Cu atom fraction decreases from 32% down to 23%. The ligaments of size from 20 to 100 nm and the nanopore of size from 30 to 80 nm can be tailored by controlling the initial alloy composition. However, the copper ligaments become large nanoparticles as the initial Cu atom fraction is below 20% and man
2011,
23.
Abstract:
The response function of square-aperture piezoelectric film deformable mirror is calculated using Fourier series method. Then the optimization of some parameters such as correlation coefficient and beam aperture is done by numerical simulation. The results show that, correlation coefficient is linear with the side-length of electrode and remains above 0.6 for beam aperture of 100 mm×100 mm with 4 to 14 electrodes of 5 to 25 mm side-length in each row, ensuring the mirror’s strong ability to correcting low-order aberrations. Beam aperture ratio is also an important parameter affecting the mirror’s aberration correction ability, and its optimal value is simulated to be 0.8 in our conditions.
The response function of square-aperture piezoelectric film deformable mirror is calculated using Fourier series method. Then the optimization of some parameters such as correlation coefficient and beam aperture is done by numerical simulation. The results show that, correlation coefficient is linear with the side-length of electrode and remains above 0.6 for beam aperture of 100 mm×100 mm with 4 to 14 electrodes of 5 to 25 mm side-length in each row, ensuring the mirror’s strong ability to correcting low-order aberrations. Beam aperture ratio is also an important parameter affecting the mirror’s aberration correction ability, and its optimal value is simulated to be 0.8 in our conditions.
2011,
23.
Abstract:
We report a high-power fiber laser in all-fiber format. The system consists of 36 pump ports, both counter and forward pump configuration are employed. In the experiment, 1 008 W fiber laser is obtained when 24 pump ports are employed with a total pump power of 1 477 W. The optical-to-optical conversion efficiency is 68%. The central wavelength of the output laser is 1 082 nm with a 3 dB bandwidth of 3 nm. Presently, the output power is limited by the pump source. It can be predicted that the laser power can be further scaled if more pump sources are employed.
We report a high-power fiber laser in all-fiber format. The system consists of 36 pump ports, both counter and forward pump configuration are employed. In the experiment, 1 008 W fiber laser is obtained when 24 pump ports are employed with a total pump power of 1 477 W. The optical-to-optical conversion efficiency is 68%. The central wavelength of the output laser is 1 082 nm with a 3 dB bandwidth of 3 nm. Presently, the output power is limited by the pump source. It can be predicted that the laser power can be further scaled if more pump sources are employed.
2011,
23.
Abstract:
Based on published fracture experiments and 3D transient finite-element analyses, and taking the first principal stress as the criterion and the Griffith crack theory to determine the critical fracture stress, a Weibull statistical model is established to predict the fracture possibility of Nd:glass with certain pump parameters. Other issues which limit the pump power are also presented. The results show that the fracture limit of laser medium depends on the optical polishing technology. For a short pulse and high energy Nd:glass laser, taking Americas polishing technology in the 1990s as reference, the pump saturation limits the pump power to 18 kW/cm2 when the repetition rate is lower than 1 Hz, while the thermal fracture limits the pump power when the repetition rate is higher than 10 Hz.
Based on published fracture experiments and 3D transient finite-element analyses, and taking the first principal stress as the criterion and the Griffith crack theory to determine the critical fracture stress, a Weibull statistical model is established to predict the fracture possibility of Nd:glass with certain pump parameters. Other issues which limit the pump power are also presented. The results show that the fracture limit of laser medium depends on the optical polishing technology. For a short pulse and high energy Nd:glass laser, taking Americas polishing technology in the 1990s as reference, the pump saturation limits the pump power to 18 kW/cm2 when the repetition rate is lower than 1 Hz, while the thermal fracture limits the pump power when the repetition rate is higher than 10 Hz.
