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RSS2005 Vol. 17, No. 04
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2005,
17.
Abstract:
In order to perform the near-to-far-field extrapolation for one-dimensional periodic structure, the Floquet-mode method is first discussed. The complex amplitudes of each Floquet’s mode are determined based on the Fourier series expansion for the near fields on the output boundary. The far fields are then computed by the superposition of each Floquet's mode. On the other hand, an approach using the periodic Green’s function is also considered. The equivalent electromagnetic currents on the output boundary in near field region are obtained from FDTD computation. The far fields are then extrapolated using the periodic Green's function. This approach is similar to the way commonly applied for near-to-far field extrapolation. Only near fields in a single cell of the periodic structure are us
In order to perform the near-to-far-field extrapolation for one-dimensional periodic structure, the Floquet-mode method is first discussed. The complex amplitudes of each Floquet’s mode are determined based on the Fourier series expansion for the near fields on the output boundary. The far fields are then computed by the superposition of each Floquet's mode. On the other hand, an approach using the periodic Green’s function is also considered. The equivalent electromagnetic currents on the output boundary in near field region are obtained from FDTD computation. The far fields are then extrapolated using the periodic Green's function. This approach is similar to the way commonly applied for near-to-far field extrapolation. Only near fields in a single cell of the periodic structure are us
2005,
17.
Abstract:
A novel phase shifter for high power microwave is described and analyzed. The coaxial TEM mode is converted to TE11 fan-shaped waveguide mode by inserting fins into the coaxial waveguide.The phase shift changes with varying the length of the fins. A phase shifter for 4 GHz based on this principle is designed and optimized. The calculated results show that the maximum phase shift is 360° when the length of the phase shifter is 50 cm, the inner radius 2.0 cm and outer radius 4.5 cm, and the loss is below 0.1 dB in the range of 3.9~4.1 GHz. The input and output of phase shifter are co-aligned on the same axis.
A novel phase shifter for high power microwave is described and analyzed. The coaxial TEM mode is converted to TE11 fan-shaped waveguide mode by inserting fins into the coaxial waveguide.The phase shift changes with varying the length of the fins. A phase shifter for 4 GHz based on this principle is designed and optimized. The calculated results show that the maximum phase shift is 360° when the length of the phase shifter is 50 cm, the inner radius 2.0 cm and outer radius 4.5 cm, and the loss is below 0.1 dB in the range of 3.9~4.1 GHz. The input and output of phase shifter are co-aligned on the same axis.
2005,
17.
Abstract:
There exist two transmission line coupling models, Agrawal model and Taylor model, which can be used for the calculation of the aboveground cable effects excited by incident HEMP plane wave. In views of the lossy ground, we summarized and then discussed the differences between these two models in the representation of coupling formulations, exciting source terms and boundary condition. The contributions to the induced current and voltage by various electromagnetic field components, such as the vertical electrical field, the horizontal electrical field and the horizontal magnetic field, are compared in this paper in terms of integral of Green function and superposition theorem. The results validate the conclusion that the contribution of the same electromagnetic field component is not the s
There exist two transmission line coupling models, Agrawal model and Taylor model, which can be used for the calculation of the aboveground cable effects excited by incident HEMP plane wave. In views of the lossy ground, we summarized and then discussed the differences between these two models in the representation of coupling formulations, exciting source terms and boundary condition. The contributions to the induced current and voltage by various electromagnetic field components, such as the vertical electrical field, the horizontal electrical field and the horizontal magnetic field, are compared in this paper in terms of integral of Green function and superposition theorem. The results validate the conclusion that the contribution of the same electromagnetic field component is not the s
2005,
17.
Abstract:
The coaxial impedance convertor plays a very important role in the field of high power microwave. The impedance of a coaxial line can be converted by gradually changing the diameter of the inner conductor of the coaxial line, and some functions such as the polynomial, the cosine, the exponent and etc，can be applied to describe the curve of the diameter variation. In this paper, the finite-difference time-domain method (FDTD) was used to calculate the reflection coefficient in the coaxial line, and Genetic Algorithm (GA) was adopted to optimize the curve in order to design a convertor with a shortest length of the diameter-changing inner conductor and a minimal reflection coefficient. The optimization calculation of the GA was parallelized in the master-slave model and run in a Beowulf sys
The coaxial impedance convertor plays a very important role in the field of high power microwave. The impedance of a coaxial line can be converted by gradually changing the diameter of the inner conductor of the coaxial line, and some functions such as the polynomial, the cosine, the exponent and etc，can be applied to describe the curve of the diameter variation. In this paper, the finite-difference time-domain method (FDTD) was used to calculate the reflection coefficient in the coaxial line, and Genetic Algorithm (GA) was adopted to optimize the curve in order to design a convertor with a shortest length of the diameter-changing inner conductor and a minimal reflection coefficient. The optimization calculation of the GA was parallelized in the master-slave model and run in a Beowulf sys
2005,
17.
Abstract:
This paper discusses the combined-oscillator (CO) antenna which is composed of an electric monopole and a magnetic oscillator. The finite-difference time-domain method is applied to simulate the radiation properties of the CO antenna. The efficiency of feeding from the coaxial line to the antenna is calculated. The feeding efficiencies are 65% and 81% for the mono polar and bipolar pulse excitations. The numerical results of the voltage standing-wave ratio, radiated near- and far-fields, and energy patterns are presented. The numerical simulation results demonstrate that the H-plane pattern is symmetrical about the axis with the cardiac type, and the E-plane pattern is not symmetrical about the axis with an up-shift of 15°.This kind of antenna has the broad band property and high feeding
This paper discusses the combined-oscillator (CO) antenna which is composed of an electric monopole and a magnetic oscillator. The finite-difference time-domain method is applied to simulate the radiation properties of the CO antenna. The efficiency of feeding from the coaxial line to the antenna is calculated. The feeding efficiencies are 65% and 81% for the mono polar and bipolar pulse excitations. The numerical results of the voltage standing-wave ratio, radiated near- and far-fields, and energy patterns are presented. The numerical simulation results demonstrate that the H-plane pattern is symmetrical about the axis with the cardiac type, and the E-plane pattern is not symmetrical about the axis with an up-shift of 15°.This kind of antenna has the broad band property and high feeding
2005,
17.
Abstract:
The bent TM01-TE11 mode converter is analyzed by theoretical calculation and numerical simulation, keeping the axes of the output port and that of the input in parallel. The mode converter is minimized by decreasing the inner radius of waveguide. The optimized results are shown as follows: the inner diameter of waveguide is 7.0 cm, the distance between the axes of the two ports of the mode converter is 8.03 cm, and the axial length is 15.11 cm. The overall power conversion efficiency exceeds 90% in the frequency range from 3.41 to 3.74 GHz and the efficiency reaches up to 95.6% at 3.60 GHz．
The bent TM01-TE11 mode converter is analyzed by theoretical calculation and numerical simulation, keeping the axes of the output port and that of the input in parallel. The mode converter is minimized by decreasing the inner radius of waveguide. The optimized results are shown as follows: the inner diameter of waveguide is 7.0 cm, the distance between the axes of the two ports of the mode converter is 8.03 cm, and the axial length is 15.11 cm. The overall power conversion efficiency exceeds 90% in the frequency range from 3.41 to 3.74 GHz and the efficiency reaches up to 95.6% at 3.60 GHz．
2005,
17.
Abstract:
The paper presents the instantaneous response of stored energy, reflected power in the input coupler and output power in the output coupler due to the interactions of the power source and the “switch” under generating high power microwave pulse compression by SES (stored energy switch) method. Meanwhile, the whole process has been simulated by MATLAB code. The program developed can simulate situations of different intrinsic quality factors, input coupling coefficients, output coupling coefficients, power sources and switch times of the “switch” and so on, and display images of the process. It is helpful for understanding the instantaneous response and further research on the technique of HPM pulse compression．
The paper presents the instantaneous response of stored energy, reflected power in the input coupler and output power in the output coupler due to the interactions of the power source and the “switch” under generating high power microwave pulse compression by SES (stored energy switch) method. Meanwhile, the whole process has been simulated by MATLAB code. The program developed can simulate situations of different intrinsic quality factors, input coupling coefficients, output coupling coefficients, power sources and switch times of the “switch” and so on, and display images of the process. It is helpful for understanding the instantaneous response and further research on the technique of HPM pulse compression．
2005,
17.
Abstract:
A travelling wave resonant-ring was constructed for RF window high power test of NSRL 200 MeV Linac. The principle of the resonant-ring was described. A power gain of 4.5 and a peak power of 60 MW were achieved in the ring. The power test method and procedure were given out, and the electron multiple effect was discussed. The RF window passed test under the conditions of a peak power of 30 MW, an average power of 3.7 kW and a pulse length of 2.5μs．
A travelling wave resonant-ring was constructed for RF window high power test of NSRL 200 MeV Linac. The principle of the resonant-ring was described. A power gain of 4.5 and a peak power of 60 MW were achieved in the ring. The power test method and procedure were given out, and the electron multiple effect was discussed. The RF window passed test under the conditions of a peak power of 30 MW, an average power of 3.7 kW and a pulse length of 2.5μs．
2005,
17.
Abstract:
One of the important building blocks on Qiangguang- I accelerator is the short-pulse high dose rate gamma-ray source, which is mainly used to generate short pulse intense bremsstrahlung. In this paper, the process of generating high dose rate gamma-ray with about 20 ns pulse duration on Qiangguang- I accelerator was introduced. The insulating characteristics of insulator and MITL of short-pulse high-impedance intense electron beam diode were analyzed in detail. The characterization of plasma opening switch(POS) was presented. The design approach for diode operating parameters including the diode impedance, cathode and anode was described. The experimental results show that the pulse duration of bremsstrahlung is about 20 ns, and the dose rates at areas of 2,30 and 100 cm2 are 1011, 0.7×10
One of the important building blocks on Qiangguang- I accelerator is the short-pulse high dose rate gamma-ray source, which is mainly used to generate short pulse intense bremsstrahlung. In this paper, the process of generating high dose rate gamma-ray with about 20 ns pulse duration on Qiangguang- I accelerator was introduced. The insulating characteristics of insulator and MITL of short-pulse high-impedance intense electron beam diode were analyzed in detail. The characterization of plasma opening switch(POS) was presented. The design approach for diode operating parameters including the diode impedance, cathode and anode was described. The experimental results show that the pulse duration of bremsstrahlung is about 20 ns, and the dose rates at areas of 2,30 and 100 cm2 are 1011, 0.7×10
2005,
17.
Abstract:
In the paper the fundamental and solution approach of TLCODDE, which was used to simulate transmission line, have been investigated. The interface voltage expressions for several typical loads driven by a transmission line, necessary for TLCODE, have been also deduced. The comparison of the TLCODE with a PSPICE circuit model has shown that the approach and equations given by the paper are validated．
In the paper the fundamental and solution approach of TLCODDE, which was used to simulate transmission line, have been investigated. The interface voltage expressions for several typical loads driven by a transmission line, necessary for TLCODE, have been also deduced. The comparison of the TLCODE with a PSPICE circuit model has shown that the approach and equations given by the paper are validated．
2005,
17.
Abstract:
Fast photography is used to investigate the back-ejecta of tantalum target material after interaction with high intensity current pulse electron beam. Velocity of back jecta of tantalum target material is presented. The electron beam energy deposition and the beam-target interaction dynamics is also computed numerically by EGS4 program and solving the series of Euler equations for mass, momentum and energy respectively.The experimental result shows that the axial velocity of back ejecta target material is faster than 2.9 mm/μs, while the simulation gives a velocity of 9.7 mm/μs under the ideal conditions. Both results give the necessary parameters for the shutter used to block off the target ejecta．
Fast photography is used to investigate the back-ejecta of tantalum target material after interaction with high intensity current pulse electron beam. Velocity of back jecta of tantalum target material is presented. The electron beam energy deposition and the beam-target interaction dynamics is also computed numerically by EGS4 program and solving the series of Euler equations for mass, momentum and energy respectively.The experimental result shows that the axial velocity of back ejecta target material is faster than 2.9 mm/μs, while the simulation gives a velocity of 9.7 mm/μs under the ideal conditions. Both results give the necessary parameters for the shutter used to block off the target ejecta．
2005,
17.
Abstract:
When vacuum electron diode is repetitively operated, it presents some peculiar characteristics. Because of its small screening radius and short delay time, graphite is chosen as the cathode material. In experiments, the following results were attained: (1) when the annular cathode is thinned or the repetitive rate is increased, because of thermal effect of current and quickening expanding speed of plasma, the consistency of pulses in a burst is worsened; (2) with the strength of guiding magnetic field increased, the plasma is more restricted and expand slower, and the total current, as well as the electron-emitting area is reduced and the impendence of diode is increased. At last, when the strength of guiding magnetic field is 1.5 T and the cathode is 1 mm thick, a uniform electron beam of
When vacuum electron diode is repetitively operated, it presents some peculiar characteristics. Because of its small screening radius and short delay time, graphite is chosen as the cathode material. In experiments, the following results were attained: (1) when the annular cathode is thinned or the repetitive rate is increased, because of thermal effect of current and quickening expanding speed of plasma, the consistency of pulses in a burst is worsened; (2) with the strength of guiding magnetic field increased, the plasma is more restricted and expand slower, and the total current, as well as the electron-emitting area is reduced and the impendence of diode is increased. At last, when the strength of guiding magnetic field is 1.5 T and the cathode is 1 mm thick, a uniform electron beam of
2005,
17.
Abstract:
In order to obtain experimental parameters of gas breakdown under repetitive nanosecond-pulses, this paper introduces measurement and influencing factors of incident voltage and discharge current, and describes repetitively stressing time which is peculiar to repetitively nanosecond-pulse breakdown. The response bandwidth of measurement component, intermittent electromagnetic interference, and transient high-frequency oscillation when insulating gas gap is brokendown can affect the measured results of electrical signals, especially lead to a short-duration disturbance on the measured signals. The wavelet soft-threshold denoising method can reduce the interference effectively. Based on the response measurement of current diverter, the deconvolution using Wiener filtering theory can compensa
In order to obtain experimental parameters of gas breakdown under repetitive nanosecond-pulses, this paper introduces measurement and influencing factors of incident voltage and discharge current, and describes repetitively stressing time which is peculiar to repetitively nanosecond-pulse breakdown. The response bandwidth of measurement component, intermittent electromagnetic interference, and transient high-frequency oscillation when insulating gas gap is brokendown can affect the measured results of electrical signals, especially lead to a short-duration disturbance on the measured signals. The wavelet soft-threshold denoising method can reduce the interference effectively. Based on the response measurement of current diverter, the deconvolution using Wiener filtering theory can compensa
2005,
17.
Abstract:
A new kind of pulse electron gun controller for 200 MeV LINAC at National Synchrotron Radiation Laboratory was introduced in this paper, including the working principle of the pulse electron gun, the applications of I2C serial bus and embedded microcontroller in controlling system. The emphasis is on the hardware design of digital controlled current regulator, digital controlled switch voltage source and high voltage pulse power supply. The software design of fiber communication and PC controlling is also presented. The electron gun controller has successfully been used in NSRL. The result shows that it is quite reliable and the performance is good. This electronic digital system has completely replaced the old mechanical control system．
A new kind of pulse electron gun controller for 200 MeV LINAC at National Synchrotron Radiation Laboratory was introduced in this paper, including the working principle of the pulse electron gun, the applications of I2C serial bus and embedded microcontroller in controlling system. The emphasis is on the hardware design of digital controlled current regulator, digital controlled switch voltage source and high voltage pulse power supply. The software design of fiber communication and PC controlling is also presented. The electron gun controller has successfully been used in NSRL. The result shows that it is quite reliable and the performance is good. This electronic digital system has completely replaced the old mechanical control system．
2005,
17.
Abstract:
During the commission of electron storage ring of HLS(phase Ⅱ reconstruction), it was found that there was coupled-bunch instability both in injection and operation. The coupled-bunch instability seriously limited the injection beam intensity, and affected the stabilization of operation of Hefei light source. By using over compensated chromaticity and insertion octupole magnet in storage ring, the transverse coupled-bunch instability was almost suppressed, and the design goal of storing 300 mA was achieved.
During the commission of electron storage ring of HLS(phase Ⅱ reconstruction), it was found that there was coupled-bunch instability both in injection and operation. The coupled-bunch instability seriously limited the injection beam intensity, and affected the stabilization of operation of Hefei light source. By using over compensated chromaticity and insertion octupole magnet in storage ring, the transverse coupled-bunch instability was almost suppressed, and the design goal of storing 300 mA was achieved.
2005,
17.
Abstract:
The response matrix relates beam motion at the BPM locations to changes in corrector magnet strengths. A method for extracting the beta-function and phase of the beam position monitors and the corrector magnets from the measured response matrix based on storage ring theoretical model is presented. The accuracy of beta and phase thus calculated is limited by the accuracy of response matrix measurement and calibration of BPM and correctors. The error function represents the accuracy of the tune used for iteration. The correct tune corresponds to the minimum error function, which can be used to determine the actual tune.
The response matrix relates beam motion at the BPM locations to changes in corrector magnet strengths. A method for extracting the beta-function and phase of the beam position monitors and the corrector magnets from the measured response matrix based on storage ring theoretical model is presented. The accuracy of beta and phase thus calculated is limited by the accuracy of response matrix measurement and calibration of BPM and correctors. The error function represents the accuracy of the tune used for iteration. The correct tune corresponds to the minimum error function, which can be used to determine the actual tune.
2005,
17.
Abstract:
When trying to explain the latch-up window phenomena in CMOS devices induced by radiation, the so called “three-path” latch-up window model is provided. The “three-path” latch-up window model is simply based on the analysis of CMOS device latch-up circuit model. To verify the model, a test circuit has been designed to simulate parasitical latch-up paths in CMOS devices and relevant parameters are reported. Transient gamma irradiation experiment on “Qiangguang I” indicates that a latch-up window appears in the test circuit as predicated. The result validates that it is reasonable to explain some latch-up window phenomena according to the “three-path” latch-up window model．
When trying to explain the latch-up window phenomena in CMOS devices induced by radiation, the so called “three-path” latch-up window model is provided. The “three-path” latch-up window model is simply based on the analysis of CMOS device latch-up circuit model. To verify the model, a test circuit has been designed to simulate parasitical latch-up paths in CMOS devices and relevant parameters are reported. Transient gamma irradiation experiment on “Qiangguang I” indicates that a latch-up window appears in the test circuit as predicated. The result validates that it is reasonable to explain some latch-up window phenomena according to the “three-path” latch-up window model．
2005,
17.
Abstract:
The time domain electric field integral equation (EFIE) is an important method in describing the radiation and scattering of electromagnetic. The method can be implemented with great efficiency in numerically simulation for the reason of mesh division can be made in scattering region instead of whole computational domain. The EFIE method is used to study the distribution of skin current and the characteristic of waveform in aerial shielded cable excited by EMP in this paper. The problems are studied experimentally in the radiated EMP simulator. The numerical data agree with the experimental results very well, and is of higher precision and trustily.
The time domain electric field integral equation (EFIE) is an important method in describing the radiation and scattering of electromagnetic. The method can be implemented with great efficiency in numerically simulation for the reason of mesh division can be made in scattering region instead of whole computational domain. The EFIE method is used to study the distribution of skin current and the characteristic of waveform in aerial shielded cable excited by EMP in this paper. The problems are studied experimentally in the radiated EMP simulator. The numerical data agree with the experimental results very well, and is of higher precision and trustily.
2005,
17.
Abstract:
Three-dimensional CFD technology was used to simulate the flow field of COIL mixing nozzle. Concentration-driven as well as pressure-driven diffusion terms were considered in the diffusion equations. The 10 species and 21 reactions chemical model was applied to implement the chemical kinetics. Some elementary fluid dynamic phenomena of a round transverse jet were obtained such as the horse-shoe-shaped jet trajectory and the counter-rotating vortex pairs. The results indicate that the pressure-driven diffusion term has contrary effects on species of different molar weight, the molecular of "heavier" species diffuses toward the pressure gradients and that of "lighter" species against the pressure gradients. It was also found that even complete jet penetration was not achieved, the gain field
Three-dimensional CFD technology was used to simulate the flow field of COIL mixing nozzle. Concentration-driven as well as pressure-driven diffusion terms were considered in the diffusion equations. The 10 species and 21 reactions chemical model was applied to implement the chemical kinetics. Some elementary fluid dynamic phenomena of a round transverse jet were obtained such as the horse-shoe-shaped jet trajectory and the counter-rotating vortex pairs. The results indicate that the pressure-driven diffusion term has contrary effects on species of different molar weight, the molecular of "heavier" species diffuses toward the pressure gradients and that of "lighter" species against the pressure gradients. It was also found that even complete jet penetration was not achieved, the gain field
2005,
17.
Abstract:
Random fluctuation of turbulence brings random fluctuation of refractive index and makes atmosphere become a random fluctuation medium, which destroys the coherence of light-wave. Research of atmospheric turbulence is actually investigation of atmospheric refractive index.The atmospheric structure constant of refractive index is an important parameter of denoting atmospheric turbulence. In this paper, the atmospheric structure constant of refractive index is measured both noonday and at night everyday, at all seasons, respectively,using HTP-2 micro-thermal meter. The vertical profile of refractire index in Hefei and the North（0～30 km）is investigated by analysis of experimental data．
Random fluctuation of turbulence brings random fluctuation of refractive index and makes atmosphere become a random fluctuation medium, which destroys the coherence of light-wave. Research of atmospheric turbulence is actually investigation of atmospheric refractive index.The atmospheric structure constant of refractive index is an important parameter of denoting atmospheric turbulence. In this paper, the atmospheric structure constant of refractive index is measured both noonday and at night everyday, at all seasons, respectively,using HTP-2 micro-thermal meter. The vertical profile of refractire index in Hefei and the North（0～30 km）is investigated by analysis of experimental data．
2005,
17.
Abstract:
Based on precise measurements of the surface-shape of cavity mirrors, a cavity model has been achieved by optical simulation software ZEMAX for a folded virtually-confocal unstable resonator employed in COIL. The influences of the surface-shape errors of cavity mirrors on beam quality, and the effects of misalignment of cavity mirrors on the wavefront of output beam, have been analyzed using the model. Beam quality measurements have been performed by using a He-Ne alignment laser in a bare cavity. The measurement results agree with the simulation data, and verify the feasibility of the modeling and simulation method.．
Based on precise measurements of the surface-shape of cavity mirrors, a cavity model has been achieved by optical simulation software ZEMAX for a folded virtually-confocal unstable resonator employed in COIL. The influences of the surface-shape errors of cavity mirrors on beam quality, and the effects of misalignment of cavity mirrors on the wavefront of output beam, have been analyzed using the model. Beam quality measurements have been performed by using a He-Ne alignment laser in a bare cavity. The measurement results agree with the simulation data, and verify the feasibility of the modeling and simulation method.．
2005,
17.
Abstract:
By means of combining a heat conduction equation for electron with molecular dynamics method, the dynamics of melting and ablation processes at Ni surfaces under femtosecond laser irradiation is studied. The temperature distribution of lattice and the components of ablation products are analyzed, single atoms and clusters constitute the ablation products. The location where ablation occurs and the time when ablation sets in are marked by a strong increase in temperature as well as a sharp decrease in density. Simulation results show that intense evaporation and tensile stresses generated in the target are responsible for the ejection of single atoms and big clusters. The propagation of laserinduced stress wave is also further investigated, and the velocity of stress wave is predicted to
By means of combining a heat conduction equation for electron with molecular dynamics method, the dynamics of melting and ablation processes at Ni surfaces under femtosecond laser irradiation is studied. The temperature distribution of lattice and the components of ablation products are analyzed, single atoms and clusters constitute the ablation products. The location where ablation occurs and the time when ablation sets in are marked by a strong increase in temperature as well as a sharp decrease in density. Simulation results show that intense evaporation and tensile stresses generated in the target are responsible for the ejection of single atoms and big clusters. The propagation of laserinduced stress wave is also further investigated, and the velocity of stress wave is predicted to
2005,
17.
Abstract:
The output modes of sub-picosecond ultrashort pulse distributed feedback dye laser which is used as an oscillator for a high brightness KrF laser system were analyzed with coupling wave theory. The analysis shows that for a practical distributed feedback dye laser, single longitudinal mode oscillation is always obtained because of periodical gain modulation. A method based on spectrum modulation measurement to obtain a stable single pulse operation of DFDL was provided as well as numerical simulation．The measured spectrum shows that for the sub-picosecond DFDL used in the laser system, a stable single pulse, single longitudinal mode output is obtained under two times above pumping threshold．
The output modes of sub-picosecond ultrashort pulse distributed feedback dye laser which is used as an oscillator for a high brightness KrF laser system were analyzed with coupling wave theory. The analysis shows that for a practical distributed feedback dye laser, single longitudinal mode oscillation is always obtained because of periodical gain modulation. A method based on spectrum modulation measurement to obtain a stable single pulse operation of DFDL was provided as well as numerical simulation．The measured spectrum shows that for the sub-picosecond DFDL used in the laser system, a stable single pulse, single longitudinal mode output is obtained under two times above pumping threshold．
2005,
17.
Abstract:
The effects of annealing on electron-beam evaporated single Al2O3 layers were investigated. The films were annealed in air for 1.5 hours at different temperatures from 250～400 ℃. The transmittance spectra were measured in the wavelength range of 190~400 nm. Microstructures of the samples were characterized by X-ray diffraction (XRD). Profile and surface roughness measurement instrument was used to determine the rms surface roughness. It was found that the transmission spectra shifted to short wavelength gradually as the annealing temperature increased and the total optical loss decreased. The film structure remained amorphous even after annealing at 400 ℃ temperature. And the samples annealed at higher temperature had the higher rms surface roughness. The decreasing optical loss with an
The effects of annealing on electron-beam evaporated single Al2O3 layers were investigated. The films were annealed in air for 1.5 hours at different temperatures from 250～400 ℃. The transmittance spectra were measured in the wavelength range of 190~400 nm. Microstructures of the samples were characterized by X-ray diffraction (XRD). Profile and surface roughness measurement instrument was used to determine the rms surface roughness. It was found that the transmission spectra shifted to short wavelength gradually as the annealing temperature increased and the total optical loss decreased. The film structure remained amorphous even after annealing at 400 ℃ temperature. And the samples annealed at higher temperature had the higher rms surface roughness. The decreasing optical loss with an
2005,
17.
Abstract:
The failure of charge coupled devices (CCD ) irradiated by 800nm fs laser with pulse duration of 60 fs was studied.The result shows that the failure threshold of CCD irradiated by fs laser is 4.22×10－3 J/cm2. and it is 2～3 order lower than the failare threshold of CCD irradiated by ns laser. According to the micro-analysis of CCD, it is found that the damage does not take place at the light activated elements but at the grid electrode of the device．
The failure of charge coupled devices (CCD ) irradiated by 800nm fs laser with pulse duration of 60 fs was studied.The result shows that the failure threshold of CCD irradiated by fs laser is 4.22×10－3 J/cm2. and it is 2～3 order lower than the failare threshold of CCD irradiated by ns laser. According to the micro-analysis of CCD, it is found that the damage does not take place at the light activated elements but at the grid electrode of the device．
2005,
17.
Abstract:
The optical and laser properties of several laser glasses have been discussed. According to the properties of the gain and the B integral in the high power laser amplifier chain,an optimal configuration is advanced that high gain glasses and low n2 glases are used in the different amplifier stages simultaneously. In this way, the restriction of the B integral effect to the maximal output capability can be weaken and the output capability difference between short pulses and long pulses can be decreased.The simulated result shows that the optimal configuration can potentially provide a 30%~40% output energy improvement as compared with the present configuration at 1 ns．
The optical and laser properties of several laser glasses have been discussed. According to the properties of the gain and the B integral in the high power laser amplifier chain,an optimal configuration is advanced that high gain glasses and low n2 glases are used in the different amplifier stages simultaneously. In this way, the restriction of the B integral effect to the maximal output capability can be weaken and the output capability difference between short pulses and long pulses can be decreased.The simulated result shows that the optimal configuration can potentially provide a 30%~40% output energy improvement as compared with the present configuration at 1 ns．
2005,
17.
Abstract:
Based on the change of misalignment sensitivity with the length of cavity, a kind of ring-down cavity is put forward, which is stable resonator, and its cavity length is 0.73 times as that of confocal cavity. According to propagation equation of Gaussian beam and matrix of misadjust resonator, as well as principle of cavity ring-down method and data processing of fitting, a physical model of reflectivity measuring is set up for misadjustment of cavity length or angle of titled cavity mirrors. Applying this model, the influence of minute cavity misadjustment on measured reflectivity of cavity mirrors in the stable resonator is analyzed, which is compared to that in confocal resonator. Used as ring-down cavity, this stable resonator has, firstly, more influence of misalignment of cavity mirr
Based on the change of misalignment sensitivity with the length of cavity, a kind of ring-down cavity is put forward, which is stable resonator, and its cavity length is 0.73 times as that of confocal cavity. According to propagation equation of Gaussian beam and matrix of misadjust resonator, as well as principle of cavity ring-down method and data processing of fitting, a physical model of reflectivity measuring is set up for misadjustment of cavity length or angle of titled cavity mirrors. Applying this model, the influence of minute cavity misadjustment on measured reflectivity of cavity mirrors in the stable resonator is analyzed, which is compared to that in confocal resonator. Used as ring-down cavity, this stable resonator has, firstly, more influence of misalignment of cavity mirr
2005,
17.
Abstract:
The laser-induced damage threshold (LIDT) is regulated by the ISO11254 standard based on the damage frequency method, and its uncertainty information is useful for the researchers. Analysis shows that the origins of the uncertainty, which valves can be solved by statistics and linear fit theory, lie in measurements of the energy and effective area of the laser beam, calculation of the damage probability in a limited fluence range and the linear fit process in the damage frequency scheme. At last, an 1 064 nm HR thin-film sample was tested in this work. The results indicate that the last two origins are the major uncertainty of the LIDT, they are respectively about 4% and 18% while the LIDT is 7.79 J/cm2, and the total relative combined uncertainty of LIDT of the sample reaches 18.72%.
The laser-induced damage threshold (LIDT) is regulated by the ISO11254 standard based on the damage frequency method, and its uncertainty information is useful for the researchers. Analysis shows that the origins of the uncertainty, which valves can be solved by statistics and linear fit theory, lie in measurements of the energy and effective area of the laser beam, calculation of the damage probability in a limited fluence range and the linear fit process in the damage frequency scheme. At last, an 1 064 nm HR thin-film sample was tested in this work. The results indicate that the last two origins are the major uncertainty of the LIDT, they are respectively about 4% and 18% while the LIDT is 7.79 J/cm2, and the total relative combined uncertainty of LIDT of the sample reaches 18.72%.
2005,
17.
Abstract:
A new type of all-fiber velocity interferometer(AFVISAR),working at the 532 nm, has been developed which has the advantages of both the traditional velocity interferometer(VISAR) and the AFVISAR.The interferometer consists of only fibers or fiber coupled components and has no optical elements such as optic lens or reflectors. It is very compact and easy to operate. Unlike AFVISAR, the laser beam in this new VISAR system arrives at and reflects from the target surface through a multimode fiber component, goes back into and interferences with each other in a ［3*3］ single-mode fiber coupler. Its working principle was elaborated in this paper. Preliminary experiments using shock Hopkinson bar device show that the new interferometer can successfully probe the velocity profiles of a metal spec
A new type of all-fiber velocity interferometer(AFVISAR),working at the 532 nm, has been developed which has the advantages of both the traditional velocity interferometer(VISAR) and the AFVISAR.The interferometer consists of only fibers or fiber coupled components and has no optical elements such as optic lens or reflectors. It is very compact and easy to operate. Unlike AFVISAR, the laser beam in this new VISAR system arrives at and reflects from the target surface through a multimode fiber component, goes back into and interferences with each other in a ［3*3］ single-mode fiber coupler. Its working principle was elaborated in this paper. Preliminary experiments using shock Hopkinson bar device show that the new interferometer can successfully probe the velocity profiles of a metal spec
2005,
17.
Abstract:
Temperature distribution in Yb-doped double-clad high power fiber lasers (DCFL) was analyzed by the thermal conductive equations, and pump way and pump absorption coefficients which may influence cavity temperature were discussed based on this analytic solution. Results indicate that the temperature variation in radius can be neglected compared to that in axial direction; local temperature will be very high if merely adopted traditional end pump, then symmetrical two-end pump should be used in practice; temperature characteristics improves by reducing pump absorption coefficient, whereas output power decreases together. In conclusion an approach under distributed pump and with nonuniform pump absorption coefficients is proposed to get the best match of temperature distribution and output p
Temperature distribution in Yb-doped double-clad high power fiber lasers (DCFL) was analyzed by the thermal conductive equations, and pump way and pump absorption coefficients which may influence cavity temperature were discussed based on this analytic solution. Results indicate that the temperature variation in radius can be neglected compared to that in axial direction; local temperature will be very high if merely adopted traditional end pump, then symmetrical two-end pump should be used in practice; temperature characteristics improves by reducing pump absorption coefficient, whereas output power decreases together. In conclusion an approach under distributed pump and with nonuniform pump absorption coefficients is proposed to get the best match of temperature distribution and output p
2005,
17.
Abstract:
Based on the wave shape of Marx device at National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, the influence of discharge parameters upon the temporal evolvement of capillary discharge produced plasmas conditions and the gain coefficient of 3p_3s transition in Neon-like Ar was simulated. In the simulation, argon with a density of 1.07×10-6 g·cm-3 was filled into a ceramic capillary with an inner diameter of 3.1 mm, the peak of the discharge current pulse was 27.81 kA, and the width of the current pulse was 61.4 ns. The results show that the shorter the pulse rise time is, the higher the gain coefficient is. When the pulse rise time is 20~40 ns, the peak of the current pulse is 25~40 ns, and the current pulse width is 50~70 ns, the higher gain coefficient c
Based on the wave shape of Marx device at National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, the influence of discharge parameters upon the temporal evolvement of capillary discharge produced plasmas conditions and the gain coefficient of 3p_3s transition in Neon-like Ar was simulated. In the simulation, argon with a density of 1.07×10-6 g·cm-3 was filled into a ceramic capillary with an inner diameter of 3.1 mm, the peak of the discharge current pulse was 27.81 kA, and the width of the current pulse was 61.4 ns. The results show that the shorter the pulse rise time is, the higher the gain coefficient is. When the pulse rise time is 20~40 ns, the peak of the current pulse is 25~40 ns, and the current pulse width is 50~70 ns, the higher gain coefficient c
2005,
17.
Abstract:
The objective of this work is to investigate the influence of furnace atmosphere properties on the kinetic behaviors of liquid hollow glass microsphere in the fabrication of target by sol-gel technology. The effects of the composition, temperature and pressure of Ar/He gas mixture on the terminal velocity, Reynolds number and Weber number of liquid glass microsphere were studied. Furthermore, the influences of the microsphere diameter and wall thickness on the terminal velocity, Reynolds number and Weber number were also investigated. The results show that the furnace atmosphere composition, temperature and pressure have little influence on the microsphere terminal velocity, but have a great effect on the Reynolds number and Weber number. The microsphere diameter and wall thickness are two
The objective of this work is to investigate the influence of furnace atmosphere properties on the kinetic behaviors of liquid hollow glass microsphere in the fabrication of target by sol-gel technology. The effects of the composition, temperature and pressure of Ar/He gas mixture on the terminal velocity, Reynolds number and Weber number of liquid glass microsphere were studied. Furthermore, the influences of the microsphere diameter and wall thickness on the terminal velocity, Reynolds number and Weber number were also investigated. The results show that the furnace atmosphere composition, temperature and pressure have little influence on the microsphere terminal velocity, but have a great effect on the Reynolds number and Weber number. The microsphere diameter and wall thickness are two
2005,
17.
Abstract:
Using linear absorption spectra and second harmonic generation(SHG) technique, the influence of temperature on optical properties and Langmuir-Blodgett(LB) films structure of rare earth sandwich double naphthalocyanines were investigated.The absorption spectra show that the LB film structure and interaction between the molecules have been changed by heating. The bi-(tetra-tert-butyl-naphthalocyaninato)-orbium molecules formed J-aggregates in LB films, which resulted in absorption spectra red shift. A maximum of the second harmonic generation signal intensity was observed at about 65 ℃ due to a first-order phase transition. The minimum of the second harmonic generation signal intensity was obtained at about 180 ℃, which means that the molecule structure is stable.
Using linear absorption spectra and second harmonic generation(SHG) technique, the influence of temperature on optical properties and Langmuir-Blodgett(LB) films structure of rare earth sandwich double naphthalocyanines were investigated.The absorption spectra show that the LB film structure and interaction between the molecules have been changed by heating. The bi-(tetra-tert-butyl-naphthalocyaninato)-orbium molecules formed J-aggregates in LB films, which resulted in absorption spectra red shift. A maximum of the second harmonic generation signal intensity was observed at about 65 ℃ due to a first-order phase transition. The minimum of the second harmonic generation signal intensity was obtained at about 180 ℃, which means that the molecule structure is stable.
2005,
17.
Abstract:
The mechanics of the mirror was analyzed using the finite element package ANSYS to show the effect of the structural parameters and actuated voltages on the deflection of the actuator. A lumped parameter model was developed for predicting the transient motion of mirrors, taking into account electrostatic and tensile forces and viscous air damping via squeeze film theory. The results show that the elastic membrane thickness, actuator span and gap spacing have a strong effect on the deflection, the actuator undergoes the deflection increasing nonlinearly at voltages below pull-in voltage and snap through instability at voltages above pull-in voltage when subjected to a voltage ramp, the re-set time and repeatability are attractive when the actuated voltage is set to zero.
The mechanics of the mirror was analyzed using the finite element package ANSYS to show the effect of the structural parameters and actuated voltages on the deflection of the actuator. A lumped parameter model was developed for predicting the transient motion of mirrors, taking into account electrostatic and tensile forces and viscous air damping via squeeze film theory. The results show that the elastic membrane thickness, actuator span and gap spacing have a strong effect on the deflection, the actuator undergoes the deflection increasing nonlinearly at voltages below pull-in voltage and snap through instability at voltages above pull-in voltage when subjected to a voltage ramp, the re-set time and repeatability are attractive when the actuated voltage is set to zero.
2005,
17.
Abstract:
Based on the Marangoni interface effect,the theory and test of the removal function of numerically controlled chemical polishing are studied.Wet etching of optics surface is adopted in large optical components manufacture.Before the optical components test, the roughness of the optical components. measured by WKYO apparatus, is 0.72 nm; after the test, the roughness is 0.71 nm. Based on the Preston supposition, the theory and the removal function of numerically controlled chemical polishing are setup. The removal function curve of small tool polishing is Gauss-like．
Based on the Marangoni interface effect,the theory and test of the removal function of numerically controlled chemical polishing are studied.Wet etching of optics surface is adopted in large optical components manufacture.Before the optical components test, the roughness of the optical components. measured by WKYO apparatus, is 0.72 nm; after the test, the roughness is 0.71 nm. Based on the Preston supposition, the theory and the removal function of numerically controlled chemical polishing are setup. The removal function curve of small tool polishing is Gauss-like．
