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RSS2007 Vol. 19, No. 07
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2007,
19.
Abstract:
The beam quality of unstable resonator of TEA CO2 coaxial output laser is deteriorated remarkably by the thermal accumulation of the output coupler. In order to improve the beam quality, a vortex tube cooling system of output coupler was adopted. The divergence angle was measured at an average pulse energy of 18.3 J under condition of different frequency with and without using the vortex tube cooling system at real time, and the timesdiffractionlimited factor was studied. The results show that the times diffractionlimited factor was changed from 3.52 to 6.94 without the vortex tube cooling system and from 350 to 3.88 with the cooling system at 3 Hz during an operating time of 300 s.
The beam quality of unstable resonator of TEA CO2 coaxial output laser is deteriorated remarkably by the thermal accumulation of the output coupler. In order to improve the beam quality, a vortex tube cooling system of output coupler was adopted. The divergence angle was measured at an average pulse energy of 18.3 J under condition of different frequency with and without using the vortex tube cooling system at real time, and the timesdiffractionlimited factor was studied. The results show that the times diffractionlimited factor was changed from 3.52 to 6.94 without the vortex tube cooling system and from 350 to 3.88 with the cooling system at 3 Hz during an operating time of 300 s.
2007,
19.
Abstract:
The theoretical model of high-power ytterbium-doped double-clad fiber amplifier was described, and the method for calculating amplified spomtaneous emission(ASE) was analyzed, with the amplifier operating in CW regime and pulse regime. The characteristics of steady-state and pulse amplifiers were respectively simulated by Runge-Kutta method and finite-difference method. The results show that the pulse gets sharper and narrower on the condition of saturation gain, and utilizing double clad large mode fiber and backward pump scheme can reduce ASE and bad nonlinear effect dramatically.
The theoretical model of high-power ytterbium-doped double-clad fiber amplifier was described, and the method for calculating amplified spomtaneous emission(ASE) was analyzed, with the amplifier operating in CW regime and pulse regime. The characteristics of steady-state and pulse amplifiers were respectively simulated by Runge-Kutta method and finite-difference method. The results show that the pulse gets sharper and narrower on the condition of saturation gain, and utilizing double clad large mode fiber and backward pump scheme can reduce ASE and bad nonlinear effect dramatically.
2007,
19.
Abstract:
Comparing several kinds of resonators with annular gain media, the new type of multipass resonator with two annular spherical mirrors which uses an entire working surface output is considered suitable for a kind of high power CO2 laser. A new method for calculating the optic field distribution at the mirror of coaxial discharge laser with annular gain media is proposed. An integral area is obtained using solid geometry based on Fresnel-Kirchoff diffractive integral equation, which is divided into finite grids. Then the optic field distribution at the mirror of annular resonator is calculated. Near-field distribution in the middle of the annular area is similar to the Gaussian distribution, and the high-order mode distribution appears along the radius. Azimuthal distribution has no discrim
Comparing several kinds of resonators with annular gain media, the new type of multipass resonator with two annular spherical mirrors which uses an entire working surface output is considered suitable for a kind of high power CO2 laser. A new method for calculating the optic field distribution at the mirror of coaxial discharge laser with annular gain media is proposed. An integral area is obtained using solid geometry based on Fresnel-Kirchoff diffractive integral equation, which is divided into finite grids. Then the optic field distribution at the mirror of annular resonator is calculated. Near-field distribution in the middle of the annular area is similar to the Gaussian distribution, and the high-order mode distribution appears along the radius. Azimuthal distribution has no discrim
2007,
19.
Abstract:
For a monodispersion of water coated carbon particles in internal mixing state, the validity of equivalent refractive index for describing the internal mixture of aerosol particles with different complex refractive indexes is analyzed by their scattering efficiency and phase function. The equivalence of extinction efficiency is good in Rayleigh scattering’s range and geometrical optics’ range at different volume ratios of the carbon particle to the mixture, but the equivalence is not good in the range of Mie scattering. When the volume ratio of the strong absorbing material, carbon particle, is greater than 0.3, the equivalences of absorption efficiency and extinction efficiency are good. However, the equivalence of phase function is poor at different mixture ratios besides the range of
For a monodispersion of water coated carbon particles in internal mixing state, the validity of equivalent refractive index for describing the internal mixture of aerosol particles with different complex refractive indexes is analyzed by their scattering efficiency and phase function. The equivalence of extinction efficiency is good in Rayleigh scattering’s range and geometrical optics’ range at different volume ratios of the carbon particle to the mixture, but the equivalence is not good in the range of Mie scattering. When the volume ratio of the strong absorbing material, carbon particle, is greater than 0.3, the equivalences of absorption efficiency and extinction efficiency are good. However, the equivalence of phase function is poor at different mixture ratios besides the range of
2007,
19.
Abstract:
Based on the application demands of high-power laser phase-conjugate systems, the potential of Brillouin-enhanced four-wave mixing(BEFWM) applying in this field is represented. Correspondingly, physical mechanism and output characteristics of BEFWM with large incident signals are studied specially. It is demonstrated that BEFWM’s performances, such as response speed, pulse-shape fidelity and stability, and energy transform efficiency will increase with increasing intensity of the signals.
Based on the application demands of high-power laser phase-conjugate systems, the potential of Brillouin-enhanced four-wave mixing(BEFWM) applying in this field is represented. Correspondingly, physical mechanism and output characteristics of BEFWM with large incident signals are studied specially. It is demonstrated that BEFWM’s performances, such as response speed, pulse-shape fidelity and stability, and energy transform efficiency will increase with increasing intensity of the signals.
2007,
19.
Abstract:
Methods for cloud scene simulation are analyzed and studied based on the properties of real cloud edge and distribution of sky radiance. A model is used to simulate cloud scene by means of fractal geometry algorithm after effects on the sky radiance of cloud are analyzed. Firstly, spectral radiances of cloud free sky and cloudy sky are respectively calculated according to the radiative transfer theory. A simulation method for cloud edge is developed based on the improved random generator after studying the properties of real cloud edge and self similar character of the fractal principle. Finally, a kind of algorithm implemented to create cloud texture is designed by making full use of radiance distribution of cloud sky, quadric random method and Diamond-Square interpolation. Consequently,
Methods for cloud scene simulation are analyzed and studied based on the properties of real cloud edge and distribution of sky radiance. A model is used to simulate cloud scene by means of fractal geometry algorithm after effects on the sky radiance of cloud are analyzed. Firstly, spectral radiances of cloud free sky and cloudy sky are respectively calculated according to the radiative transfer theory. A simulation method for cloud edge is developed based on the improved random generator after studying the properties of real cloud edge and self similar character of the fractal principle. Finally, a kind of algorithm implemented to create cloud texture is designed by making full use of radiance distribution of cloud sky, quadric random method and Diamond-Square interpolation. Consequently,
2007,
19.
Abstract:
A homemade large-mode-area(LMA) multimode fiber before and after coiling was studied contrastively in the experiment. Single-transverse-mode output was achieved when the fiber laser was coiled around a mandrel of 65 mm radius. After coiling, beam quality factor of the laser droped from 1.24 to 1.06 and slope efficiency droped from 64.7% to 54.3%. When the launched pump power was 149 W, the corresponding output power was 94.7 W and 79.4 W, respectively. However, the brightness of the coiled fiber laser was 1.15 times that of the uncoiled. Coiled modal losses of different modes were also calculated for the fiber employed in the experiment. The measured results agree well with the calculated ones.
A homemade large-mode-area(LMA) multimode fiber before and after coiling was studied contrastively in the experiment. Single-transverse-mode output was achieved when the fiber laser was coiled around a mandrel of 65 mm radius. After coiling, beam quality factor of the laser droped from 1.24 to 1.06 and slope efficiency droped from 64.7% to 54.3%. When the launched pump power was 149 W, the corresponding output power was 94.7 W and 79.4 W, respectively. However, the brightness of the coiled fiber laser was 1.15 times that of the uncoiled. Coiled modal losses of different modes were also calculated for the fiber employed in the experiment. The measured results agree well with the calculated ones.
2007,
19.
Abstract:
For the main light amplification of high-power solid laser devices, an on-line damage-detecting system is designed. With its invariable magnification specialty, a telescope is used to on-line detect any damage information on different optical components at equivalent precision and resolution. With the theory of depth of field, by accurately adjusting the size of exit aperture of the damage-detected system, we can obtain all kinds of damage on the same inclined optical component at the same time, and minimize the negative interaction between adjacent components. The brightness field imaging method is adopted to identify the damaged components, while the darkness field imaging method is applied to measure the distribution and sizes of damage spots on the same component. Experiments have pr
For the main light amplification of high-power solid laser devices, an on-line damage-detecting system is designed. With its invariable magnification specialty, a telescope is used to on-line detect any damage information on different optical components at equivalent precision and resolution. With the theory of depth of field, by accurately adjusting the size of exit aperture of the damage-detected system, we can obtain all kinds of damage on the same inclined optical component at the same time, and minimize the negative interaction between adjacent components. The brightness field imaging method is adopted to identify the damaged components, while the darkness field imaging method is applied to measure the distribution and sizes of damage spots on the same component. Experiments have pr
2007,
19.
Abstract:
Started from the nonlocal nonlinear Schrdinger equation, the split-step method was used to numerically discuss propogation properies of (1+2) dimension spatial optical sotions with definite degrees of nonlocality, and a set of parameters of soliton were obtained. Assuming the response function for nonlocal Kerr medium is a Gaussian function, the numerical solutions of solitons were analyzed and the soliton’s stability was proved numerically with definite degrees of nonlocality. Results show that (1+2) dimension solitons depend strongly on the degrees of nonlocality. The optical beam can propagate stably with definite degrees of nonlocality. The soliton profile is Gaussian-shaped for strongly nonlocal cases, but not Gaussian-shaped for any other cases. When the degrees of nonlocality are
Started from the nonlocal nonlinear Schrdinger equation, the split-step method was used to numerically discuss propogation properies of (1+2) dimension spatial optical sotions with definite degrees of nonlocality, and a set of parameters of soliton were obtained. Assuming the response function for nonlocal Kerr medium is a Gaussian function, the numerical solutions of solitons were analyzed and the soliton’s stability was proved numerically with definite degrees of nonlocality. Results show that (1+2) dimension solitons depend strongly on the degrees of nonlocality. The optical beam can propagate stably with definite degrees of nonlocality. The soliton profile is Gaussian-shaped for strongly nonlocal cases, but not Gaussian-shaped for any other cases. When the degrees of nonlocality are
2007,
19.
Abstract:
Theories and methods of online measurement of high energy laser were introduced, and some uncertainty sources were analyzed. The elimination of abnormal data as well as means to deal with standard uncertainty and combined standard uncertainty is illuminated with some experimental data. Since two variables in the measurement modal are interrelated and dynamic, a sort of special means is established. Some project approximate methods are also used, which make the problem become easy.
Theories and methods of online measurement of high energy laser were introduced, and some uncertainty sources were analyzed. The elimination of abnormal data as well as means to deal with standard uncertainty and combined standard uncertainty is illuminated with some experimental data. Since two variables in the measurement modal are interrelated and dynamic, a sort of special means is established. Some project approximate methods are also used, which make the problem become easy.
2007,
19.
Abstract:
The characteristics of a new kind of linear phase retrieval(LPR) wavefront measuring method were analyzed. The process of calibration was discussed and the basic construct of the LPR was described. The influences of the system aberration, the characteristic of reconstruction matrix, and the coefficient of mode calibration on the performance of the LPR method were tested by numerical simulation. According to the calculation of the condition number of reconstruction matrix, the relationship between the target size and performance of LPR was discussed. The simulative results show that this method is feasible.
The characteristics of a new kind of linear phase retrieval(LPR) wavefront measuring method were analyzed. The process of calibration was discussed and the basic construct of the LPR was described. The influences of the system aberration, the characteristic of reconstruction matrix, and the coefficient of mode calibration on the performance of the LPR method were tested by numerical simulation. According to the calculation of the condition number of reconstruction matrix, the relationship between the target size and performance of LPR was discussed. The simulative results show that this method is feasible.
2007,
19.
Abstract:
A model of atmospheric boundary layer, which has adopted Bulk method, is used to estimate the refractive index structure parameter in southeast seashore and Hefei. A high resolution three dimensional sonic anemometers was used instead of micro-thermal probes to compute the refractive index structure parameter. This avoids sea salt contaminating metal wire. The main input parameters are air temperature, surface temperature, humidity, wind speed and the measurement height of these variables. Analysis shows that applying Bulk method model to estimate the refractive index structure parameter is feasible. Meanwhile, applying Frederickson’s formula or Thiermann’s formula for empirically determining Monin-Obukhov similarity functions have little difference. It is difficult to get the refractive
A model of atmospheric boundary layer, which has adopted Bulk method, is used to estimate the refractive index structure parameter in southeast seashore and Hefei. A high resolution three dimensional sonic anemometers was used instead of micro-thermal probes to compute the refractive index structure parameter. This avoids sea salt contaminating metal wire. The main input parameters are air temperature, surface temperature, humidity, wind speed and the measurement height of these variables. Analysis shows that applying Bulk method model to estimate the refractive index structure parameter is feasible. Meanwhile, applying Frederickson’s formula or Thiermann’s formula for empirically determining Monin-Obukhov similarity functions have little difference. It is difficult to get the refractive
2007,
19.
Abstract:
Introducing the tip-tilt and piston error as the parameter and defining the aperture function of the tiled-grating, far-field property was analyzed with Gaussian beam incidence using the theory of Fourier angular spectrum. The results showed that the output beam was Gaussian while the center of the envelope shifted, the shift magnitude was determined by angle errors and beam size. The phase difference caused by piston error translated with the tiled-grating compressor, the focal spot was affected by both non-integral number of grating space and out-of-plane piston error. Numerical simulation showed the effect on the spatial characteristic of the tiled-grating compressor due to alignment errors.
Introducing the tip-tilt and piston error as the parameter and defining the aperture function of the tiled-grating, far-field property was analyzed with Gaussian beam incidence using the theory of Fourier angular spectrum. The results showed that the output beam was Gaussian while the center of the envelope shifted, the shift magnitude was determined by angle errors and beam size. The phase difference caused by piston error translated with the tiled-grating compressor, the focal spot was affected by both non-integral number of grating space and out-of-plane piston error. Numerical simulation showed the effect on the spatial characteristic of the tiled-grating compressor due to alignment errors.
2007,
19.
Abstract:
The misalignment of 4f-configure femtosecond pulse shaping system with space-time conversion can cause aberrations of the output pulse. With theoretical analysis, the effect of the mismatched spacing between the components of 4f Fourier processing system for equally-spaced and unequally-spaced Dammann filters is calculated in this paper. It is concluded that the uniformity and the intensity of the output pulse are relevant to the spacing misalignment. As the intensity of center pulse lowers, the output pulses have more side wings. For the laser facility with 12 cm focus length, when the mismatch is less than 1 cm, the output pulse will not be affected seriously.
The misalignment of 4f-configure femtosecond pulse shaping system with space-time conversion can cause aberrations of the output pulse. With theoretical analysis, the effect of the mismatched spacing between the components of 4f Fourier processing system for equally-spaced and unequally-spaced Dammann filters is calculated in this paper. It is concluded that the uniformity and the intensity of the output pulse are relevant to the spacing misalignment. As the intensity of center pulse lowers, the output pulses have more side wings. For the laser facility with 12 cm focus length, when the mismatch is less than 1 cm, the output pulse will not be affected seriously.
2007,
19.
Abstract:
Keeping the single pulse energy of CO2 laser constant, the impulse coupling coefficients in air-breathing laser propulsion are measured at different air pressure with a high precision impact pendulum system and the altitude characteristics are analyzed. The results indicate that the impulse coupling coefficient is about 3.5×10-4 N·s·J-1 with a fluctuation lower than 5%, when the air pressure ranges from 2.8×104 Pa to 1×105 Pa and the altitude from 0 to 10 km. When the air pressure is lower than 2.8×104 Pa and the altitude higher than 10 km, the impulse coupling coefficients drop apparently in terms of conic. At the pressure of 1×103 Pa and altitude of 31 km, the impulse coupling coefficient is only 9.7×10-5 N·s·J-1.
Keeping the single pulse energy of CO2 laser constant, the impulse coupling coefficients in air-breathing laser propulsion are measured at different air pressure with a high precision impact pendulum system and the altitude characteristics are analyzed. The results indicate that the impulse coupling coefficient is about 3.5×10-4 N·s·J-1 with a fluctuation lower than 5%, when the air pressure ranges from 2.8×104 Pa to 1×105 Pa and the altitude from 0 to 10 km. When the air pressure is lower than 2.8×104 Pa and the altitude higher than 10 km, the impulse coupling coefficients drop apparently in terms of conic. At the pressure of 1×103 Pa and altitude of 31 km, the impulse coupling coefficient is only 9.7×10-5 N·s·J-1.
2007,
19.
Abstract:
Based on the facility experimental records and the flashlamp fault data, ten phenomena of faults are found and they are classified into three categories, trigger failures, electrical insulation failures, and flashlamp explosions. Two distinct kinds of faults are found by further analysis, one leading to the flashlamp failures and the other leading to no flashlamp failures. A flashlamps fault tree is obtained for the shot reliability by analyzing logic relationships among the three categories of faults, disk amplifier subsystems, and the shot reliability, which illustrates the importance of the flashlamp reliability to the shot reliability. Finally, a causeeffect diagram for the faults and techniques indicating diverse causes of the flashlamp fault is presented by analyzing the flashlamp
Based on the facility experimental records and the flashlamp fault data, ten phenomena of faults are found and they are classified into three categories, trigger failures, electrical insulation failures, and flashlamp explosions. Two distinct kinds of faults are found by further analysis, one leading to the flashlamp failures and the other leading to no flashlamp failures. A flashlamps fault tree is obtained for the shot reliability by analyzing logic relationships among the three categories of faults, disk amplifier subsystems, and the shot reliability, which illustrates the importance of the flashlamp reliability to the shot reliability. Finally, a causeeffect diagram for the faults and techniques indicating diverse causes of the flashlamp fault is presented by analyzing the flashlamp
2007,
19.
Abstract:
A one-dimensional model was constructed to calculate the gas density profile within a few millimeters of the conical nozzle. The result from the model is in agreement with experiments. A program was developed to deal with data taken by the M-Z interferometry, which measures the two-dimensional spatial distribution of the gas density profile in front of the conical nozzle. In the interaction experiment, we can choose a proper backing pressure to achieve expectant density, according to the scaling of density with backing pressure. And the scaling of density with relative delay time was expected to provide instructions in establishing the relative timing between firing the jet and the arrival of the laser pulse in interaction experiments.
A one-dimensional model was constructed to calculate the gas density profile within a few millimeters of the conical nozzle. The result from the model is in agreement with experiments. A program was developed to deal with data taken by the M-Z interferometry, which measures the two-dimensional spatial distribution of the gas density profile in front of the conical nozzle. In the interaction experiment, we can choose a proper backing pressure to achieve expectant density, according to the scaling of density with backing pressure. And the scaling of density with relative delay time was expected to provide instructions in establishing the relative timing between firing the jet and the arrival of the laser pulse in interaction experiments.
2007,
19.
Abstract:
Shenguang-Ⅲ prototype is a multi-pass laser amplification system which includes a particular configuration of 4-pass amplifier. The beam rotates 90° and expands when it passes the 4-pass amplifier. A new scheme of adaptive optics for system aberration correction sets deformable mirror as cavity mirror of the 4-pass amplifier. This paper demonstrates this scheme and develops the mathematical relationship between deformable mirror and system aberration. Simulation and mathematic analysis indicate that the correcting capacity has relations with the beam expansion factor and the type of system aberration.
Shenguang-Ⅲ prototype is a multi-pass laser amplification system which includes a particular configuration of 4-pass amplifier. The beam rotates 90° and expands when it passes the 4-pass amplifier. A new scheme of adaptive optics for system aberration correction sets deformable mirror as cavity mirror of the 4-pass amplifier. This paper demonstrates this scheme and develops the mathematical relationship between deformable mirror and system aberration. Simulation and mathematic analysis indicate that the correcting capacity has relations with the beam expansion factor and the type of system aberration.
2007,
19.
Abstract:
Based on multi-segment apertures and gain media of Nd:YAG slabs, a new design of solid-state laser oscillator and its preliminary experimental results are presented.The output characteristics of the laser are researched. 2×1 multi-segment apertures and gain media of Nd:YAG slabs module are applied to the laser which is supplied by a 60 kW battery-based power supply, which adopts a pattern of constant current discharge with high current, and outputs a programmable control wave profile. The single pulse with output of 32 J was obtained, and the small signal gain was 0.047 5 cm-1. The output results show that it is a linear relation of the output energy and the pumping pulse duration during a single shot. And the output energy of 5 ms pulse nearly falls off 30% than that of the 1 ms pulse in
Based on multi-segment apertures and gain media of Nd:YAG slabs, a new design of solid-state laser oscillator and its preliminary experimental results are presented.The output characteristics of the laser are researched. 2×1 multi-segment apertures and gain media of Nd:YAG slabs module are applied to the laser which is supplied by a 60 kW battery-based power supply, which adopts a pattern of constant current discharge with high current, and outputs a programmable control wave profile. The single pulse with output of 32 J was obtained, and the small signal gain was 0.047 5 cm-1. The output results show that it is a linear relation of the output energy and the pumping pulse duration during a single shot. And the output energy of 5 ms pulse nearly falls off 30% than that of the 1 ms pulse in
2007,
19.
Abstract:
Considering the stability requirement of the spatial filter system in ShenguangⅡ facility, a modal test was carried out to analysis the spatial filter system to check its working performance. The key parameters which control the stability system are indicated according to the theory of vibration. Numerical analysis results show that the natural frequency of SF4 system is 83 Hz, and it satisfies the whole facility stability working performance. The adding carriage in system can increase the rigidity and change the modal. For the support table, the tabletop should be separated and the height should be low to more easily control the distortion of the optical elements on top of the table. As a kind of elastic connection, the bellow in the system can absorb the vibration energy to control the
Considering the stability requirement of the spatial filter system in ShenguangⅡ facility, a modal test was carried out to analysis the spatial filter system to check its working performance. The key parameters which control the stability system are indicated according to the theory of vibration. Numerical analysis results show that the natural frequency of SF4 system is 83 Hz, and it satisfies the whole facility stability working performance. The adding carriage in system can increase the rigidity and change the modal. For the support table, the tabletop should be separated and the height should be low to more easily control the distortion of the optical elements on top of the table. As a kind of elastic connection, the bellow in the system can absorb the vibration energy to control the
2007,
19.
Abstract:
In order to test large aperture and high steep aspheric surfaces accurately during the grinding and polishing process, a new method combining the subaperture stitching and null compensation was proposed. The principle of the technique was introduced, and a reasonable splicing mathematical model was established. A steep, high order and off-axis aspheric mirror with a aperture of 400 mm×300 mm was tested with the method. The translation and misalignment errors were eliminated by the least-squares fitting and the phase data of the full aperture were obtained, and the surface map after stitching was consistent to the integrated surface map derived by null corrector. Moreover, the errors and accuracy of the experiment were analyzed.
In order to test large aperture and high steep aspheric surfaces accurately during the grinding and polishing process, a new method combining the subaperture stitching and null compensation was proposed. The principle of the technique was introduced, and a reasonable splicing mathematical model was established. A steep, high order and off-axis aspheric mirror with a aperture of 400 mm×300 mm was tested with the method. The translation and misalignment errors were eliminated by the least-squares fitting and the phase data of the full aperture were obtained, and the surface map after stitching was consistent to the integrated surface map derived by null corrector. Moreover, the errors and accuracy of the experiment were analyzed.
2007,
19.
Abstract:
By the model of damage induced by inclusions in dielectric thin-films, with the experiment done by S.Papernov et al who deposited HfO2 thin-films containing gold nanoparticles on a cleaved fused-silica by e-beam evaporation, the absorption cross-section of gold was obtained. Furthermore, the laser-induced damage thresholds of HfO2 film induced by Au inclusions with varies radius and varies repetition frequency were calculated. The results indicate that the minimum energy density causing damage decreases first, then increases, finally decreases again with the increasing impurity radius. The relationship between the damage threshold and the damage shot number both change near-linearly with the repetition rate increase, while the former is descending, and the latter is ascending.
By the model of damage induced by inclusions in dielectric thin-films, with the experiment done by S.Papernov et al who deposited HfO2 thin-films containing gold nanoparticles on a cleaved fused-silica by e-beam evaporation, the absorption cross-section of gold was obtained. Furthermore, the laser-induced damage thresholds of HfO2 film induced by Au inclusions with varies radius and varies repetition frequency were calculated. The results indicate that the minimum energy density causing damage decreases first, then increases, finally decreases again with the increasing impurity radius. The relationship between the damage threshold and the damage shot number both change near-linearly with the repetition rate increase, while the former is descending, and the latter is ascending.
2007,
19.
Abstract:
The actual distribution of film thickness of a 2.2 meter coating plant has been studied. The uniformity of film thickness has been adjusted by correction mask in experiments. Utilizing correction mask, preferable uniformity values of optical components using planet jigs and revolution jigs have been acquired respectively by experiment and the results for large aperture optical components are satisfactory. Uniformity value has been controlled within 0.7% for concave mirrors within 700 millimeter aperture. For plane surface mirror with the same aperture, the value was within 1%. And for the aperture beyond one meter, the uniformity value of optical components has been controlled within 1%. By this means, the reflecting mirrors and antireflection mirrors have been coated for astronomical obse
The actual distribution of film thickness of a 2.2 meter coating plant has been studied. The uniformity of film thickness has been adjusted by correction mask in experiments. Utilizing correction mask, preferable uniformity values of optical components using planet jigs and revolution jigs have been acquired respectively by experiment and the results for large aperture optical components are satisfactory. Uniformity value has been controlled within 0.7% for concave mirrors within 700 millimeter aperture. For plane surface mirror with the same aperture, the value was within 1%. And for the aperture beyond one meter, the uniformity value of optical components has been controlled within 1%. By this means, the reflecting mirrors and antireflection mirrors have been coated for astronomical obse
2007,
19.
Abstract:
The technique of low-temperature electroless-plating nickel on the polyurethane foam in synthesizing nickel foams was investigated. The main factors affecting the deposition rate such as temperature, pH value, the concentration of nickle sulfate and reducing agent were explored. The obtained optimum process conditions are 30 g/L NiSO4, 30 g/L NaH2PO2, 10 g/L Na3C6O7H6, 30 g/L NH4Cl, 9.0～9.5 pH value at the reaction temperature of 45 ℃. In this technical condition, the process is stable with the deposition rate of 40 mg/(cm3·h). Nickel foams with a density of 0.74 g·cm-3 and a hole-rate of 91.7% was fabricated by electrodeposition, pyrogenation and deoxidization annealing after the electroless plating.
The technique of low-temperature electroless-plating nickel on the polyurethane foam in synthesizing nickel foams was investigated. The main factors affecting the deposition rate such as temperature, pH value, the concentration of nickle sulfate and reducing agent were explored. The obtained optimum process conditions are 30 g/L NiSO4, 30 g/L NaH2PO2, 10 g/L Na3C6O7H6, 30 g/L NH4Cl, 9.0～9.5 pH value at the reaction temperature of 45 ℃. In this technical condition, the process is stable with the deposition rate of 40 mg/(cm3·h). Nickel foams with a density of 0.74 g·cm-3 and a hole-rate of 91.7% was fabricated by electrodeposition, pyrogenation and deoxidization annealing after the electroless plating.
2007,
19.
Abstract:
This paper describes the elliptical crystal spectrograph(ECS) which is used to investigate X-ray spectroscopy of laser-produced plasmas. The spectrometer was calibrated for experiments on “Shenguang Ⅱ” X laser target chamber. The K-shell and M-shell emission lines of laser-produced plasma were measured by the space-resolved spectrometer. Some X-ray spectral lines were obtained through studying and classifying photographs of spectra recorded by X-ray CCD camera. The measured spectral resolution of spectrograph was given. The focusing spectrometer based on the ECS provides high spectral resolution and spatial resolution as well as high luminosity(high collection efficiency). Possible applications of the ECS are demonstrated.
This paper describes the elliptical crystal spectrograph(ECS) which is used to investigate X-ray spectroscopy of laser-produced plasmas. The spectrometer was calibrated for experiments on “Shenguang Ⅱ” X laser target chamber. The K-shell and M-shell emission lines of laser-produced plasma were measured by the space-resolved spectrometer. Some X-ray spectral lines were obtained through studying and classifying photographs of spectra recorded by X-ray CCD camera. The measured spectral resolution of spectrograph was given. The focusing spectrometer based on the ECS provides high spectral resolution and spatial resolution as well as high luminosity(high collection efficiency). Possible applications of the ECS are demonstrated.
2007,
19.
Abstract:
For reentrant and pillbox cavities widely used in klystrons, on the premise of omitting the thickness of the drift tube, we have deduced the characteristic equation for predicting the resonant frequency of these cavities accurately. Moreover, the analytical formulae for the characteristic impedance and intrinsic quality factor of cavities are found. For a concrete structure, the characteristic parameters of cavities are calculated by the formulae and the progroam SUPERFISH separately, and good agreement between the results is noticed.
For reentrant and pillbox cavities widely used in klystrons, on the premise of omitting the thickness of the drift tube, we have deduced the characteristic equation for predicting the resonant frequency of these cavities accurately. Moreover, the analytical formulae for the characteristic impedance and intrinsic quality factor of cavities are found. For a concrete structure, the characteristic parameters of cavities are calculated by the formulae and the progroam SUPERFISH separately, and good agreement between the results is noticed.
2007,
19.
Abstract:
In order to enhance bandwidth of output circuit for klystron, the theory of overlapped mode is analyzed. Possibility of overlapped three-mode is illuminated. Gap-impedance frequency distribution for three-mode overlapped two-gap coupled cavity type output circuit(TTCC) is calculated via equivalent circuit method. Taking a TTCC with 3 GHz center frequency for instance, 3D models for calculation are set up, and steps in designing this kind of output circuit are particularized. Parameters of structure are given. Relative bandwidth of 2 dB reaches 15%, and 19.3% of 1.5 dB is obtained by loading a filter through calculating gap-impedance frequency via field analysis method.
In order to enhance bandwidth of output circuit for klystron, the theory of overlapped mode is analyzed. Possibility of overlapped three-mode is illuminated. Gap-impedance frequency distribution for three-mode overlapped two-gap coupled cavity type output circuit(TTCC) is calculated via equivalent circuit method. Taking a TTCC with 3 GHz center frequency for instance, 3D models for calculation are set up, and steps in designing this kind of output circuit are particularized. Parameters of structure are given. Relative bandwidth of 2 dB reaches 15%, and 19.3% of 1.5 dB is obtained by loading a filter through calculating gap-impedance frequency via field analysis method.
2007,
19.
Abstract:
The energy-splitter is widely used in microwave engineering. Finite-difference time-domain(FDTD) method is used to analyze and verify new accurate energy-split structures with perfectly matched lossy left-handed-material(LHM) slabs or ring. From these numerical simulations, the sub-energy-sources at the outer focusing image points of each LHM slab are generated. All of the sub-energy-sources have almost the same magnitude in such symmetric structures. The energy splitting effect of these new LHM structures can be seen.
The energy-splitter is widely used in microwave engineering. Finite-difference time-domain(FDTD) method is used to analyze and verify new accurate energy-split structures with perfectly matched lossy left-handed-material(LHM) slabs or ring. From these numerical simulations, the sub-energy-sources at the outer focusing image points of each LHM slab are generated. All of the sub-energy-sources have almost the same magnitude in such symmetric structures. The energy splitting effect of these new LHM structures can be seen.
2007,
19.
Abstract:
Considering that generation and maintain of small radius, high power beam is restricted by the compression ratio of electron gun, the effect of magnetic field on electron trajectories in transition region was analyzed. A method was presented to compress the beam by changing the magnetic field in transition region gradually. Compared with the traditional one, the method requires lower compression of electron gun while providing small radius beam for interaction, it also optimizes the beam quality. The method was used to simulate an electron optical system for Ku-band 6 kW TWT, some good results are obtained.
Considering that generation and maintain of small radius, high power beam is restricted by the compression ratio of electron gun, the effect of magnetic field on electron trajectories in transition region was analyzed. A method was presented to compress the beam by changing the magnetic field in transition region gradually. Compared with the traditional one, the method requires lower compression of electron gun while providing small radius beam for interaction, it also optimizes the beam quality. The method was used to simulate an electron optical system for Ku-band 6 kW TWT, some good results are obtained.
2007,
19.
Abstract:
In an MFCG, the magnetic field generated by the current of stator coils is compressed by the expanding armature. It is important to compute the value of the magnetic field exactly, for it is relevant to the output current of MFCG. Formulas of magnetic field with surface current density and that with point current density are presented. Numerical results prove that the former can describe the magnetic field more accurately than the latter, and the former is more efficient than the latter.
In an MFCG, the magnetic field generated by the current of stator coils is compressed by the expanding armature. It is important to compute the value of the magnetic field exactly, for it is relevant to the output current of MFCG. Formulas of magnetic field with surface current density and that with point current density are presented. Numerical results prove that the former can describe the magnetic field more accurately than the latter, and the former is more efficient than the latter.
2007,
19.
Abstract:
Bipolar junction transistors may be burned out by injected electromagnetic pulse. The circuits play important rolls because EMP is always coupled to circuit by antenna or aperture firstly and injected in BJT by circuit afterwards. The current distribution coefficient was studied, on the basis of which the influences of three kinds of typical components were studied with our 2-dimentional mixed-level circuit and device simulator. The conclusion is that a resistor at base has little influence on burnout process, a positive voltage source at collector has the effect of lowering the amplitude of EMP by the voltage of the source and a resistor at collector can significantly improve the durability of device against EMP.
Bipolar junction transistors may be burned out by injected electromagnetic pulse. The circuits play important rolls because EMP is always coupled to circuit by antenna or aperture firstly and injected in BJT by circuit afterwards. The current distribution coefficient was studied, on the basis of which the influences of three kinds of typical components were studied with our 2-dimentional mixed-level circuit and device simulator. The conclusion is that a resistor at base has little influence on burnout process, a positive voltage source at collector has the effect of lowering the amplitude of EMP by the voltage of the source and a resistor at collector can significantly improve the durability of device against EMP.
2007,
19.
Abstract:
A high-current ion beam emittance measurement unit Allison scanner was introduced. The scanner consists of two slits and a pair of electrical deflection plates driven by a ±1.2 kV bipolar power supply. When the scanner moves to a measurement position, the step-changed voltages are fed to the deflection plates. The divergence angle of the ions passing through the rear slit can be calculated from the voltages. The data of position, divergence angle and beam current are collected to the computer through an AD card. A program of measuring and data processing can handle the case of pulsed beam. In order to obtain correct emittance results, subtracting background and setting threshold value are important. The program can calculate the root-mean-square emittance, the beam size, the biggest posit
A high-current ion beam emittance measurement unit Allison scanner was introduced. The scanner consists of two slits and a pair of electrical deflection plates driven by a ±1.2 kV bipolar power supply. When the scanner moves to a measurement position, the step-changed voltages are fed to the deflection plates. The divergence angle of the ions passing through the rear slit can be calculated from the voltages. The data of position, divergence angle and beam current are collected to the computer through an AD card. A program of measuring and data processing can handle the case of pulsed beam. In order to obtain correct emittance results, subtracting background and setting threshold value are important. The program can calculate the root-mean-square emittance, the beam size, the biggest posit
2007,
19.
Abstract:
The deficiencies in traditional H-D curve measurements in high-energy flash X-ray radiography are analyzed and the relationship between the optical density and X-ray exposure is obtained using Monte Carlo simulations. A spherical symmetrical object is used to obtain an optical density profile. Various factors, which lead to asymmetrical distribution of the optical density, are analyzed using Monte Carlo simulations. It is shown that the main factor is the imperfect geometrical alignment of radiographic parts such as collimator and electron beam axial. Averaging the leftright optical density of symmetrical points is a reasonable method. And the method to obtain H-D curves is detailed, and accurate H-D curves are presented according to Silberstein theory. This measurement avoided the measu
The deficiencies in traditional H-D curve measurements in high-energy flash X-ray radiography are analyzed and the relationship between the optical density and X-ray exposure is obtained using Monte Carlo simulations. A spherical symmetrical object is used to obtain an optical density profile. Various factors, which lead to asymmetrical distribution of the optical density, are analyzed using Monte Carlo simulations. It is shown that the main factor is the imperfect geometrical alignment of radiographic parts such as collimator and electron beam axial. Averaging the leftright optical density of symmetrical points is a reasonable method. And the method to obtain H-D curves is detailed, and accurate H-D curves are presented according to Silberstein theory. This measurement avoided the measu
2007,
19.
Abstract:
For high energy particles produced in advanced fuel D-3He fusion reactions, the calculation accuracy of their slowing down time has a direct and notable impact on energy balance and pressure of high energy particles during the initial phase of thermalization processes in the background plasma. Analysis shows prominent Coulomb logarithm quantum mechanical effects of the reciprocity between the high energy particles and the ions of background plasma. It is better to make use of the proper Coulomb logarithm quantum mechanical effect at the high energy end in studying the particles’ slowing process and take quantum truncation to process Coulomb logarithm of the reciprocity between the high energy particles and the ions of background plasma also, as energy is more than 25Z2iZ2tAt keV.
For high energy particles produced in advanced fuel D-3He fusion reactions, the calculation accuracy of their slowing down time has a direct and notable impact on energy balance and pressure of high energy particles during the initial phase of thermalization processes in the background plasma. Analysis shows prominent Coulomb logarithm quantum mechanical effects of the reciprocity between the high energy particles and the ions of background plasma. It is better to make use of the proper Coulomb logarithm quantum mechanical effect at the high energy end in studying the particles’ slowing process and take quantum truncation to process Coulomb logarithm of the reciprocity between the high energy particles and the ions of background plasma also, as energy is more than 25Z2iZ2tAt keV.
2007,
19.
Abstract:
MCNP simulation method of neutron radiography is introduced.The process that Maxwell thermal neutron penetrates the samples is simulated,and clear images are obtained.The contrast of simulation results and actual neutron radiography is also given.The simulation images are very similar to the experimental images.The analyse of the effect of scattered neutrons is included.As the distance between objects and scintillation screen increases, the scattered component decreases. For a distance of double object size, the influence of the scattered neutrons to the image can be ignored.The ability that thermal neutrons penetrates Al,Pb,Fe and Cu is discussed.The reason for the difference between simulation and experimental results is studied.The conclusion can be drawn that the MCNP simulation method
MCNP simulation method of neutron radiography is introduced.The process that Maxwell thermal neutron penetrates the samples is simulated,and clear images are obtained.The contrast of simulation results and actual neutron radiography is also given.The simulation images are very similar to the experimental images.The analyse of the effect of scattered neutrons is included.As the distance between objects and scintillation screen increases, the scattered component decreases. For a distance of double object size, the influence of the scattered neutrons to the image can be ignored.The ability that thermal neutrons penetrates Al,Pb,Fe and Cu is discussed.The reason for the difference between simulation and experimental results is studied.The conclusion can be drawn that the MCNP simulation method
2007,
19.
Abstract:
An approach to reducing the pulse duration of the compact two-stage helical explosive magnetic generators (EMGs) is to increase the conical angle of the helical coil in the second stage, but it will result in quick effective inductance decrease of the second stage inner coil. To find the optimal conical angle, three configurations were designed and tested, which have the same first stage but different half-conical angles for the second stage, i.e., 6°，8°，10°, respectively. Experimental results show that the currents on the inductive loads are 140 kA, 90 kA, 50 kA with the pulse durations 12.5 μs, 8.5 μs, 6.3 μs respectively for the three configurations.
An approach to reducing the pulse duration of the compact two-stage helical explosive magnetic generators (EMGs) is to increase the conical angle of the helical coil in the second stage, but it will result in quick effective inductance decrease of the second stage inner coil. To find the optimal conical angle, three configurations were designed and tested, which have the same first stage but different half-conical angles for the second stage, i.e., 6°，8°，10°, respectively. Experimental results show that the currents on the inductive loads are 140 kA, 90 kA, 50 kA with the pulse durations 12.5 μs, 8.5 μs, 6.3 μs respectively for the three configurations.
2007,
19.
Abstract:
A bunch charge monitor system has been designed for the photocathode RF gun of Accelerator Laboratory, Tsinghua University. Integrating current transformer is the most important part of the system, and parts of the system after integrating current transformer consist of a preamplifier, an integrator, an AD converter and a data collection module. The system does not destroy the beam, and it can monitor the bunch charge in the high-radiation environment around accelerator. The results of some off-line tests show that the system is feasible.
A bunch charge monitor system has been designed for the photocathode RF gun of Accelerator Laboratory, Tsinghua University. Integrating current transformer is the most important part of the system, and parts of the system after integrating current transformer consist of a preamplifier, an integrator, an AD converter and a data collection module. The system does not destroy the beam, and it can monitor the bunch charge in the high-radiation environment around accelerator. The results of some off-line tests show that the system is feasible.
2007,
19.
Abstract:
In an axially symmetric magnetic field, charged particles move along the axis and rotate around the axis at the same time. Accordingly, the transverse motion can be decomposed into two parts, the focusing movement and the rotation of the meridian plane, and the 4-dimensional transfer matrix can be expressed as the product of a focusing matrix and two rotation matrices. The overall transfer matrix is re-derived in this article with the rotation matrices and the focusing matrix. Then the corresponding sigma matrix is given to further estimate the beam emittance extracted from electron cyclotron resonance ion source. The second moment of the beam distribution function is discussed in detail.
In an axially symmetric magnetic field, charged particles move along the axis and rotate around the axis at the same time. Accordingly, the transverse motion can be decomposed into two parts, the focusing movement and the rotation of the meridian plane, and the 4-dimensional transfer matrix can be expressed as the product of a focusing matrix and two rotation matrices. The overall transfer matrix is re-derived in this article with the rotation matrices and the focusing matrix. Then the corresponding sigma matrix is given to further estimate the beam emittance extracted from electron cyclotron resonance ion source. The second moment of the beam distribution function is discussed in detail.
