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RSS2012 Vol. 24, No. 11
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2012,
24: 2521-2522.
doi: 10.3788/HPLPB20122411.2521
Abstract:
Gain-switched by 1550 nm pulsed laser, a simultaneously gain-switched and mode-locked Tm/Ho-codoped fiber laser with a central wavelength of 1958 nm is obtained. The pulse train contains many mode-locked sub-pulses within one gain-switched pulse envelope. Using this pulsed laser as a seed source, a flat supercontinuum (SC) is generated in a Tm-doped fiber amplifier where Tm-doped fiber is both the non-linear and gain medium. For the average output power of 2. 17 W, the observed spectrum covers the spectral range of 1953 to 2593 nm with a 10 dB bandwidth of 640 nm and the long wavelength edge of SC spectrum is extended to 2750 nm.
Gain-switched by 1550 nm pulsed laser, a simultaneously gain-switched and mode-locked Tm/Ho-codoped fiber laser with a central wavelength of 1958 nm is obtained. The pulse train contains many mode-locked sub-pulses within one gain-switched pulse envelope. Using this pulsed laser as a seed source, a flat supercontinuum (SC) is generated in a Tm-doped fiber amplifier where Tm-doped fiber is both the non-linear and gain medium. For the average output power of 2. 17 W, the observed spectrum covers the spectral range of 1953 to 2593 nm with a 10 dB bandwidth of 640 nm and the long wavelength edge of SC spectrum is extended to 2750 nm.
2012,
24: 2523-2526.
doi: 10.3788/HPLPB20122411.2523
Abstract:
The effective absorption coefficient with time of strong absorbing aerosol made of carbon dusts and water of internal mixture is analyzed, and the influence of different wavelengths and radius ratios on it is discussed. The shorter the wavelength is, the larger the effective absorption coefficient is, and more quickly it increases during 1-100 s. The increase of the effective absorption coefficient during 1-100 s is larger than that during 100-1000 s, and the largest increase is 132.65% during 1-100 s. Different ratios between inner and outer radius have large influence on the effective absorption coefficient. The larger the ratio is, the larger the effective absorption coefficient is, and more quickly it increases during 1-100 s. The increase of the effective absorption coefficient during 1-100 s is larger than that during 100-1000 s, and the largest increase is 138.66% during 1-100 s.
The effective absorption coefficient with time of strong absorbing aerosol made of carbon dusts and water of internal mixture is analyzed, and the influence of different wavelengths and radius ratios on it is discussed. The shorter the wavelength is, the larger the effective absorption coefficient is, and more quickly it increases during 1-100 s. The increase of the effective absorption coefficient during 1-100 s is larger than that during 100-1000 s, and the largest increase is 132.65% during 1-100 s. Different ratios between inner and outer radius have large influence on the effective absorption coefficient. The larger the ratio is, the larger the effective absorption coefficient is, and more quickly it increases during 1-100 s. The increase of the effective absorption coefficient during 1-100 s is larger than that during 100-1000 s, and the largest increase is 138.66% during 1-100 s.
2012,
24: 2527-2530.
doi: 10.3788/HPLPB20122411.2527
Abstract:
thin dis A district cooling approach based on the thermoelectric devices array for high-power large-aperture Nd:YAG disk-type solid state laser media is presented. The cooling efficiency distribution of the thermoelectric devices is controlled by their working voltage, consequently, district temperature control of disk media is realized and a uniform lateral temperature distribution is obtained. And this method reduces the thermal effects and offeres a new idea of thermal management in disk lasers. The experiments demonstrate that the heating and cooling can be controlled to obtain a desired temperature distribution in thin gain media.
thin dis A district cooling approach based on the thermoelectric devices array for high-power large-aperture Nd:YAG disk-type solid state laser media is presented. The cooling efficiency distribution of the thermoelectric devices is controlled by their working voltage, consequently, district temperature control of disk media is realized and a uniform lateral temperature distribution is obtained. And this method reduces the thermal effects and offeres a new idea of thermal management in disk lasers. The experiments demonstrate that the heating and cooling can be controlled to obtain a desired temperature distribution in thin gain media.
2012,
24: 2531-2536.
doi: 10.3788/HPLPB20122411.2531
Abstract:
The acceleration characteristics of flyers are critical parameters for laser-driven flyer study. In this paper, a laser-driven flyer experiment was designed. The PVDF piezoelectric film sensor was employed to measure the flight time of flyers traveling different distances, also flyer velocity and acceleration were calculated. The effects of laser energy on flyer acceleration performances were analyzed. Based on the Gurney energy theory, a calculation model of laser-driven flyer velocity was established. According to experimental results, laser energy loss and effective absorption coefficient were determined, and the effects of laser energy and metal film thickness on flyer velocity were obtained. The results show that the acceleration characteristics of flyers driven by different laser energies are similar. Moreover, laser energy has little influence on acceleration time. At high laser energy, the influences of metal film thickness on flyer maximum velocity and coupling coefficient are obvious. When the metal film is thicker than a certain value, the coupling coefficient could not increase again.
The acceleration characteristics of flyers are critical parameters for laser-driven flyer study. In this paper, a laser-driven flyer experiment was designed. The PVDF piezoelectric film sensor was employed to measure the flight time of flyers traveling different distances, also flyer velocity and acceleration were calculated. The effects of laser energy on flyer acceleration performances were analyzed. Based on the Gurney energy theory, a calculation model of laser-driven flyer velocity was established. According to experimental results, laser energy loss and effective absorption coefficient were determined, and the effects of laser energy and metal film thickness on flyer velocity were obtained. The results show that the acceleration characteristics of flyers driven by different laser energies are similar. Moreover, laser energy has little influence on acceleration time. At high laser energy, the influences of metal film thickness on flyer maximum velocity and coupling coefficient are obvious. When the metal film is thicker than a certain value, the coupling coefficient could not increase again.
2012,
24: 2537-2542.
doi: 10.3788/HPLPB20122411.2537
Abstract:
The time-depended rate equation model of four-level excimer pumped alkali laser (XPAL) is established, and the population of each level and laser intensity in cavities varying with time are calculated. The result is compared with experiments, and it indicates that the threshold pump intensity of XPALs is too high. Matching the spectral width of pump to the width of absorption could not improve the absorption efficiency, neither could law down the pump threshold. When the pump intensity keeps the same, the absorption efficiency could be improved by either increasing the length of gain medium or the temperature, but the pump rate in unit volume decreases. The key to success ofXPALs is to achieve effective pump absorption.
The time-depended rate equation model of four-level excimer pumped alkali laser (XPAL) is established, and the population of each level and laser intensity in cavities varying with time are calculated. The result is compared with experiments, and it indicates that the threshold pump intensity of XPALs is too high. Matching the spectral width of pump to the width of absorption could not improve the absorption efficiency, neither could law down the pump threshold. When the pump intensity keeps the same, the absorption efficiency could be improved by either increasing the length of gain medium or the temperature, but the pump rate in unit volume decreases. The key to success ofXPALs is to achieve effective pump absorption.
2012,
24: 2543-2548.
doi: 10.3788/HPLPB20122411.2543
Abstract:
A method for focal spot reconstruction and far-field focal spot measurement based on the orthogonal wedges is proposed. In order to verify the validity of the method in extracting focal spot side lobe data, expanding measurement dynamic range of CCD and improving measurement precision of laser beam quality, the beam quality factor is taken as a useful evaluating measure here, the theoretical model of intensity profiles of the defocus spot is build and the laboratory scheme accordingly is implemented. The results show that, compared with the traditional measurement method, this method makes the dynamic range of CCD expand about 9 times, plenty of intensity information of the focal spot side lobe emerges from random noise of CCD, and the measurement precision of the beam quality factor is improved about 16%.
A method for focal spot reconstruction and far-field focal spot measurement based on the orthogonal wedges is proposed. In order to verify the validity of the method in extracting focal spot side lobe data, expanding measurement dynamic range of CCD and improving measurement precision of laser beam quality, the beam quality factor is taken as a useful evaluating measure here, the theoretical model of intensity profiles of the defocus spot is build and the laboratory scheme accordingly is implemented. The results show that, compared with the traditional measurement method, this method makes the dynamic range of CCD expand about 9 times, plenty of intensity information of the focal spot side lobe emerges from random noise of CCD, and the measurement precision of the beam quality factor is improved about 16%.
2012,
24: 2549-2554.
doi: 10.3788/HPLPB20122411.2549
Abstract:
Key words: laser techn Using optical heterodyne detection, an all-fiber laser Doppler vibrometer (LDV) was set up to investigate the air coupled vibration of scattering objects so as to recover the vibrating information of the source. Influence of the scattering object properties, such as materials, holdings, relative positions to the source, etc. , on the response to the source vibration through air coupling was investigated by the LDV and the vibration frequency response curves ranging from 200 Hz to 2700 Hz for six scattering materials were obtained. Results show that in the case of air coupled vibration of scattering objects, the response vibration amplitude is generally bigger at higher frequency; and the vibration response curve is more affected by the material of the scattering object than by the holdings or relative positions of the scattering object. ique; laser Doppler vibrometer; vibration response; optical heterodyne detection
Key words: laser techn Using optical heterodyne detection, an all-fiber laser Doppler vibrometer (LDV) was set up to investigate the air coupled vibration of scattering objects so as to recover the vibrating information of the source. Influence of the scattering object properties, such as materials, holdings, relative positions to the source, etc. , on the response to the source vibration through air coupling was investigated by the LDV and the vibration frequency response curves ranging from 200 Hz to 2700 Hz for six scattering materials were obtained. Results show that in the case of air coupled vibration of scattering objects, the response vibration amplitude is generally bigger at higher frequency; and the vibration response curve is more affected by the material of the scattering object than by the holdings or relative positions of the scattering object. ique; laser Doppler vibrometer; vibration response; optical heterodyne detection
2012,
24: 2555-2559.
doi: 10.3788/HPLPB20122411.2555
Abstract:
The paper introduces a method for testing large hyperboloidal convex mirrors with the theory of Hindle-sphere testing that involves the idea of sub-aperture stitching. In order to get the parameters of the Hindle sphere based on sub-aperture stitching, the system of Hindle-sphere testing based on sub-aperture stitching was studied through the geometric optics. The parameters of the Hindle sphere of the new method and the classic method was calculated and compared in the test of a hyperboloidal mirror. The results show that the Hindle-sphere method based on sub-aperture stitching can make the Hindle-spheres parameters more reasonable.
The paper introduces a method for testing large hyperboloidal convex mirrors with the theory of Hindle-sphere testing that involves the idea of sub-aperture stitching. In order to get the parameters of the Hindle sphere based on sub-aperture stitching, the system of Hindle-sphere testing based on sub-aperture stitching was studied through the geometric optics. The parameters of the Hindle sphere of the new method and the classic method was calculated and compared in the test of a hyperboloidal mirror. The results show that the Hindle-sphere method based on sub-aperture stitching can make the Hindle-spheres parameters more reasonable.
2012,
24: 2560-2564.
doi: 10.3788/HPLPB20122411.2560
Abstract:
Beam drift exists in underwater laser propagation. Influence of the beam drift on the images correlation recognition and the irrelevance between the random noise of inter-frame images were analyzed. The distortion-invariant matched filter design was studied, a phase-matching extraction of common features between distorted images was proposed, and the common features were used as the training samples of the synthetic discriminant function, based on which anti-distortion matching filter was designed and verified by a simulation. The Matlab simulation results show that the design of anti-distortion synthetic discriminant matching filter, combined with the pre-filtering of the image to be recognized, can effectively improve the PCE value (peak- the correlation energy ratio) of the correlation peak output and the disk values (peak identification rate).
Beam drift exists in underwater laser propagation. Influence of the beam drift on the images correlation recognition and the irrelevance between the random noise of inter-frame images were analyzed. The distortion-invariant matched filter design was studied, a phase-matching extraction of common features between distorted images was proposed, and the common features were used as the training samples of the synthetic discriminant function, based on which anti-distortion matching filter was designed and verified by a simulation. The Matlab simulation results show that the design of anti-distortion synthetic discriminant matching filter, combined with the pre-filtering of the image to be recognized, can effectively improve the PCE value (peak- the correlation energy ratio) of the correlation peak output and the disk values (peak identification rate).
2012,
24: 2565-2570.
doi: 10.3788/HPLPB20122411.2565
Abstract:
In order to solve the defects of CARSFT program found in parameter estimation of coherent anti-Stokes Raman scattering (CARS) spectra, Levenberg-Marquarat (L-M) algorithm was used. Due to the complexity of CARS spectrum theoretical formulas. The Jacobian matrix was obtained by numerical differentiation. On the basis of analyzing the effects of lateral deviation, longitudinal deviation, and temperature on the fitting residual error, the initial value of the longitudinal deviation is considered to be more important on the rate of convergence. L-M algorithm was applied to fit a standard CARS spectrum in 2000 K. The more deviant the initial values of parameters are, the better result is obtained. After running 167 iterations, the temperature is stabilized to 2 005.6 K, and its residual error is 0.027 463. Another example with low signal-to-noise ratio data was followed, and the result converges. The results show that Levenberg-Marquarat algorithm has little dependence on initial values, and could be applied to temperature estimation of CARS spectra in harsh environments.
In order to solve the defects of CARSFT program found in parameter estimation of coherent anti-Stokes Raman scattering (CARS) spectra, Levenberg-Marquarat (L-M) algorithm was used. Due to the complexity of CARS spectrum theoretical formulas. The Jacobian matrix was obtained by numerical differentiation. On the basis of analyzing the effects of lateral deviation, longitudinal deviation, and temperature on the fitting residual error, the initial value of the longitudinal deviation is considered to be more important on the rate of convergence. L-M algorithm was applied to fit a standard CARS spectrum in 2000 K. The more deviant the initial values of parameters are, the better result is obtained. After running 167 iterations, the temperature is stabilized to 2 005.6 K, and its residual error is 0.027 463. Another example with low signal-to-noise ratio data was followed, and the result converges. The results show that Levenberg-Marquarat algorithm has little dependence on initial values, and could be applied to temperature estimation of CARS spectra in harsh environments.
2012,
24: 2571-2575.
doi: 10.3788/HPLPB20122411.2571
Abstract:
In order to suppress the amplified spontaneous emission (ASE) in the low-repetition rate high-energy fiber master-oscillator-power-amplifier (MOPA) system and achieve the best amplification results, it is necessary to optimize the pump pulse width. Based on solving a set of time-dependent rate and power transfer equations, the transient response of the upper level population distribution, stored energy and ASE of the Yb-doped fiber amplifier under pulsed pump are numerically studied. And the numerical optimum pump pulse width is 793 s under specific parameters given in the paper, including the pump power, fiber length, core area, Yb-doped concentration, etc. In the experiment the ASE built-up time is measured, and the optimum value is 800 s which is found by tuning the width of the pump pulse and measuring the amplification results of the fiber amplifier. The experiment shows the validity of the numerical simulation.
In order to suppress the amplified spontaneous emission (ASE) in the low-repetition rate high-energy fiber master-oscillator-power-amplifier (MOPA) system and achieve the best amplification results, it is necessary to optimize the pump pulse width. Based on solving a set of time-dependent rate and power transfer equations, the transient response of the upper level population distribution, stored energy and ASE of the Yb-doped fiber amplifier under pulsed pump are numerically studied. And the numerical optimum pump pulse width is 793 s under specific parameters given in the paper, including the pump power, fiber length, core area, Yb-doped concentration, etc. In the experiment the ASE built-up time is measured, and the optimum value is 800 s which is found by tuning the width of the pump pulse and measuring the amplification results of the fiber amplifier. The experiment shows the validity of the numerical simulation.
2012,
24: 2576-2580.
doi: 10.3788/HPLPB20122411.2576
Abstract:
In the designed experimental system of laser-generated bubble near a rigid boundary in water,The effect of air content on cavitation erosion was studied by changing the air content and using high speed camera system. The experimental results indicate that the maximumsize of the first cavitation bubble collapse increases with improving the air content in water. Improving the air content may increase the period of the cavitation bubble collapse, weaken the strength of the cavitation bubble collapse, reduce the micro liquid jet velocity, decrease the shock wave pressure to the rigid boundary, and reduce the cavitation damage on the surface of the rigid boundaries.
In the designed experimental system of laser-generated bubble near a rigid boundary in water,The effect of air content on cavitation erosion was studied by changing the air content and using high speed camera system. The experimental results indicate that the maximumsize of the first cavitation bubble collapse increases with improving the air content in water. Improving the air content may increase the period of the cavitation bubble collapse, weaken the strength of the cavitation bubble collapse, reduce the micro liquid jet velocity, decrease the shock wave pressure to the rigid boundary, and reduce the cavitation damage on the surface of the rigid boundaries.
2012,
24: 2581-2584.
doi: 10.3788/HPLPB20122411.2581
Abstract:
The fiber coupled system based on mini-bars is an effective way of avoiding complex beam shaping to reduce costs and improve brightness. Forty mini-bars mounted on copper microchannel heatsink are arranged in two stacks to collimate the output beam of the stacks with the aspherical cylindrical lens and cylindrical lens array in fast and slow axis directions in this paper. For increasing the fill factor of the beams of the stacks, the beams are combined spatially in the fast axis direction. The combined beam could be coupled into the fiber of 800 m core diameter and 0.22 numerical aperture. The opto-optical efficiency of the fiber coupled module is about 58% and the maximum output power is 1360 W with the power density of 1.73105 W/cm2 at fiber output facet.
The fiber coupled system based on mini-bars is an effective way of avoiding complex beam shaping to reduce costs and improve brightness. Forty mini-bars mounted on copper microchannel heatsink are arranged in two stacks to collimate the output beam of the stacks with the aspherical cylindrical lens and cylindrical lens array in fast and slow axis directions in this paper. For increasing the fill factor of the beams of the stacks, the beams are combined spatially in the fast axis direction. The combined beam could be coupled into the fiber of 800 m core diameter and 0.22 numerical aperture. The opto-optical efficiency of the fiber coupled module is about 58% and the maximum output power is 1360 W with the power density of 1.73105 W/cm2 at fiber output facet.
2012,
24: 2585-2590.
doi: 10.3788/HPLPB20122411.2585
Abstract:
This paper studies the modulation of the amplitude modulating nonlinear medium defects on a Gaussian beam. Based on the Fresnel diffraction integral and Taylor series expansion, the model of the beam propagating through the nonlinear medium with defects is built, and the analytical expressions for the intensity distribution at different distance of a Gaussian beam getting through the defective nonlinear medium are derived. The impact of the defect size and the additional phase shift in the medium on the intensity distribution of the beam propagating through the medium is studied. It is shown that larger defects and more additional phase shift lead to deeper beam modulation. Under the modulation of the defects and the nonlinear effect in the medium, there would be a maximum intensity near the rear surface of the nonlinear medium before the beam convergence or diffusion, when the medium has positive or negative nonlinear index of refraction, and the larger the phase shift of the beam isin the medium, the stronger the maximum intensity becomes.
This paper studies the modulation of the amplitude modulating nonlinear medium defects on a Gaussian beam. Based on the Fresnel diffraction integral and Taylor series expansion, the model of the beam propagating through the nonlinear medium with defects is built, and the analytical expressions for the intensity distribution at different distance of a Gaussian beam getting through the defective nonlinear medium are derived. The impact of the defect size and the additional phase shift in the medium on the intensity distribution of the beam propagating through the medium is studied. It is shown that larger defects and more additional phase shift lead to deeper beam modulation. Under the modulation of the defects and the nonlinear effect in the medium, there would be a maximum intensity near the rear surface of the nonlinear medium before the beam convergence or diffusion, when the medium has positive or negative nonlinear index of refraction, and the larger the phase shift of the beam isin the medium, the stronger the maximum intensity becomes.
2012,
24: 2591-2594.
doi: 10.3788/HPLPB20122411.2591
Abstract:
A multiple laser beams coding and decoding method is introduced, which is relevant to multiplexing technology in high power excimer laser systems. Based on small-angle incidence and reflection of laser beams, this method uses several separate arrays arranged with equal interval and reflecting mirrors to fulfill laser beams decoding or coding. The whole structure of the coding or decoding arrays is simple and compact, satisfying different coding/decoding width demand. The principle and characteristic of the coding/decoding method are explained by decoding of 18 laser beams with 10 ns pulse width.
A multiple laser beams coding and decoding method is introduced, which is relevant to multiplexing technology in high power excimer laser systems. Based on small-angle incidence and reflection of laser beams, this method uses several separate arrays arranged with equal interval and reflecting mirrors to fulfill laser beams decoding or coding. The whole structure of the coding or decoding arrays is simple and compact, satisfying different coding/decoding width demand. The principle and characteristic of the coding/decoding method are explained by decoding of 18 laser beams with 10 ns pulse width.
2012,
24: 2595-2598.
doi: 10.3788/HPLPB20122411.2595
Abstract:
In order to improve the level of the Shenguang-Ⅱs computer control, a centralized control system is designed and developed, by using the software development tools for control system of EPICS as the software framework. The overall structure and hardware of the control system are described in detail, and the development and application of the EPICS software in Linux are explored with the database and driver for instance. The experimental results show that the control system based on EPICS can meet the functional requirement of Shenguang-Ⅱ facility, which provides a new thought of using the EPICS in control system of high power laser facility.
In order to improve the level of the Shenguang-Ⅱs computer control, a centralized control system is designed and developed, by using the software development tools for control system of EPICS as the software framework. The overall structure and hardware of the control system are described in detail, and the development and application of the EPICS software in Linux are explored with the database and driver for instance. The experimental results show that the control system based on EPICS can meet the functional requirement of Shenguang-Ⅱ facility, which provides a new thought of using the EPICS in control system of high power laser facility.
2012,
24: 2599-2603.
doi: 10.3788/HPLPB20122411.2599
Abstract:
The evolution of silicon surface microstructures irradiated by Nd: YAG nanosecond laser pulses in the air under different laser fluences and scanning speeds was studied. The scanning electron microscope (SEM) images show that corrugated structure and porous structure are formed on the silicon surfaces after laser pulse irradiation. The photoluminescence (PL) spectra indicate a peak of luminescence at 710 nm. After corroding the SiOx on the silicon surfaces with hydrofluoric acid, the intensity of the luminescence peak greatly reduces, which proves that SiOx plays an important role in photoluminescence enhancement. The energy dispersive X-ray spectrum (EDS) shows that the amount of oxygen incorporated into the silicon surfaces depends on the laser fluence. Oxygen element in silicon surfaces has an important impact on enhancing PL emission.
The evolution of silicon surface microstructures irradiated by Nd: YAG nanosecond laser pulses in the air under different laser fluences and scanning speeds was studied. The scanning electron microscope (SEM) images show that corrugated structure and porous structure are formed on the silicon surfaces after laser pulse irradiation. The photoluminescence (PL) spectra indicate a peak of luminescence at 710 nm. After corroding the SiOx on the silicon surfaces with hydrofluoric acid, the intensity of the luminescence peak greatly reduces, which proves that SiOx plays an important role in photoluminescence enhancement. The energy dispersive X-ray spectrum (EDS) shows that the amount of oxygen incorporated into the silicon surfaces depends on the laser fluence. Oxygen element in silicon surfaces has an important impact on enhancing PL emission.
2012,
24: 2604-2606.
doi: 10.3788/HPLPB20122411.2604
Abstract:
A visible-light water-splitting photocatalyst was prepared by femtosecond laser: Fe nanocrystal. Both Fe nanocrystal suspended in distilled water and NaCl solution achieves total water splitting. The photocatalytic characteristics of Fe nanocrystal were analyzed by the gas chromatograph and scanning electron micrograph (SEM). Results show that the silk-like and bulk crystals appear on the surface of Fe nanocrystal after photocatalysis.
A visible-light water-splitting photocatalyst was prepared by femtosecond laser: Fe nanocrystal. Both Fe nanocrystal suspended in distilled water and NaCl solution achieves total water splitting. The photocatalytic characteristics of Fe nanocrystal were analyzed by the gas chromatograph and scanning electron micrograph (SEM). Results show that the silk-like and bulk crystals appear on the surface of Fe nanocrystal after photocatalysis.
2012,
24: 2607-2612.
doi: 10.3788/HPLPB20122411.2607
Abstract:
To regulate and control the quality and properties of hollow glass microspheres (HGMs) for inertial confinement fusion (ICF) targets, we investigated the effects of refining temperatures on the percentages of qualified HGMs for ICF targets in glass shell batches. The geometry, tensile strength, permeability, surface roughness and chemical durability of HGMs produced under different refining temperatures were also tested. The results show that increasing the refining temperature is not always favorable for improving the quality and properties of resulting HGMs. When the refining temperature is lower than 1 600 ℃, the percentages of qualified HGMs for ICF targets increase with the refining temperature. When the refining temperature is higher than 1 600 ℃, the yield decreases rapidly with the further increase of the refining temperature. The tensile strength，surface roughness and hydrogen permeability of the resulting HGMs can be improved notably by increasing the refining temperature. However, the chemical durability of HGMs at ambient condition can be reduced remarkably under higher refining temperatures.
To regulate and control the quality and properties of hollow glass microspheres (HGMs) for inertial confinement fusion (ICF) targets, we investigated the effects of refining temperatures on the percentages of qualified HGMs for ICF targets in glass shell batches. The geometry, tensile strength, permeability, surface roughness and chemical durability of HGMs produced under different refining temperatures were also tested. The results show that increasing the refining temperature is not always favorable for improving the quality and properties of resulting HGMs. When the refining temperature is lower than 1 600 ℃, the percentages of qualified HGMs for ICF targets increase with the refining temperature. When the refining temperature is higher than 1 600 ℃, the yield decreases rapidly with the further increase of the refining temperature. The tensile strength，surface roughness and hydrogen permeability of the resulting HGMs can be improved notably by increasing the refining temperature. However, the chemical durability of HGMs at ambient condition can be reduced remarkably under higher refining temperatures.
2012,
24: 2613-2617.
doi: 10.3788/HPLPB20122411.2613
Abstract:
With a photoresist pattern acquired by laser interference lithography as an etch mask, submicron aluminum-doped zinc oxide (AZO) gratings, which had excellent anti-reflection properties, were acquired by using wet etching and lift-off technology. The surface morphology was observed by an atomic force microscopy (AFM), and the reflectance spectrum was tested with a ultra-visible spectrophotometer. Results show that the AZO grating fabricated by wet etching is rougher than that acquired by lift-off technology, and the root mean squares of surface topographies of the two gratings are 25.4 nm and 7.6 nm, respectively. In the waveband range of 400-900 nm, two structural AZO gratings with the same period (980 nm) and height (160 nm) decrease the average total reflectance from 12.5% of the AZO thin film to 8.3% and 10.2%, respectively. The average specular reflectance are 6.2% and 6.6%, and diffuse reflectance are 2.1% and 3.6%, accordingly. It is concluded that wet etching-made AZO grating with rough surfaces decrease diffuse reflectance greatly, and are better in decreasing total reflectance than lift-off-made AZO grating with flatter surfaces.
With a photoresist pattern acquired by laser interference lithography as an etch mask, submicron aluminum-doped zinc oxide (AZO) gratings, which had excellent anti-reflection properties, were acquired by using wet etching and lift-off technology. The surface morphology was observed by an atomic force microscopy (AFM), and the reflectance spectrum was tested with a ultra-visible spectrophotometer. Results show that the AZO grating fabricated by wet etching is rougher than that acquired by lift-off technology, and the root mean squares of surface topographies of the two gratings are 25.4 nm and 7.6 nm, respectively. In the waveband range of 400-900 nm, two structural AZO gratings with the same period (980 nm) and height (160 nm) decrease the average total reflectance from 12.5% of the AZO thin film to 8.3% and 10.2%, respectively. The average specular reflectance are 6.2% and 6.6%, and diffuse reflectance are 2.1% and 3.6%, accordingly. It is concluded that wet etching-made AZO grating with rough surfaces decrease diffuse reflectance greatly, and are better in decreasing total reflectance than lift-off-made AZO grating with flatter surfaces.
2012,
24: 2618-2622.
doi: 10.3788/HPLPB20122411.2618
Abstract:
Numerical solution of the diffusion equation plays a key role in the study of inertial confinement fusion(ICF). In this paper, based on the global support operator method, a flux-based scheme is proposed. The scheme has local stencil with second-order accuracy both in space and time. For strongly distorted meshes, a procedure of normal direction fix is adopted with proper methods for the computation of corner volume weights, which obtains accurate discretization of the face flux. Numerical experiments show that the scheme can obtain accurate solution for linear problems on non-convex meshes. The method has second-order spatial and temporal accuracy on non-smooth meshes. The method can also preserve the symmetry well and can be extended to the three dimensional unstructured meshes.
Numerical solution of the diffusion equation plays a key role in the study of inertial confinement fusion(ICF). In this paper, based on the global support operator method, a flux-based scheme is proposed. The scheme has local stencil with second-order accuracy both in space and time. For strongly distorted meshes, a procedure of normal direction fix is adopted with proper methods for the computation of corner volume weights, which obtains accurate discretization of the face flux. Numerical experiments show that the scheme can obtain accurate solution for linear problems on non-convex meshes. The method has second-order spatial and temporal accuracy on non-smooth meshes. The method can also preserve the symmetry well and can be extended to the three dimensional unstructured meshes.
2012,
24: 2623-2626.
doi: 10.3788/HPLPB20122411.2623
Abstract:
In order to solve technical issues in the development of vaccum target chamber in Shenguang-Ⅲ laser facility, such as weak lateral stiffness and field precision fabrication and installation, the structural design and the whole manufacture process have been proposed. Combining the global stability design of the target area, the vertical pedestal, and the lateral support structure that can provide passive damping have been designed. The thickness of the chamber shell has been optimized. The alignment precision of the field fabrication of the target chamber is satisfied by using the special fixtures, i. e. the laser tracker, the six dimensional adjustment mechanism, and the custom-machined spacers, for accurately boring holes. The analysis shows that the mean root-mean-square value of displacement of 48 focusing lenses is 2.8 m. After construction, the height deviation of the target chamber center is 0.12 mm, the horizontal deviation is 0.18 mm. The centering deviations of the important flanges are from 0.35 mm to 0.4 mm.
In order to solve technical issues in the development of vaccum target chamber in Shenguang-Ⅲ laser facility, such as weak lateral stiffness and field precision fabrication and installation, the structural design and the whole manufacture process have been proposed. Combining the global stability design of the target area, the vertical pedestal, and the lateral support structure that can provide passive damping have been designed. The thickness of the chamber shell has been optimized. The alignment precision of the field fabrication of the target chamber is satisfied by using the special fixtures, i. e. the laser tracker, the six dimensional adjustment mechanism, and the custom-machined spacers, for accurately boring holes. The analysis shows that the mean root-mean-square value of displacement of 48 focusing lenses is 2.8 m. After construction, the height deviation of the target chamber center is 0.12 mm, the horizontal deviation is 0.18 mm. The centering deviations of the important flanges are from 0.35 mm to 0.4 mm.
2012,
24: 2627-2630.
doi: 10.3788/HPLPB20122411.2627
Abstract:
The feasibility of measuring the location of the plastic microsphere in the gold hohlraum target by using coaxial-of-focus X-ray phase contrast imaging was theoretically analyzed, based on which an experiment was carried out. The experimental results show that, due to the phase modulation of low Z and low-density materials to high energy X-ray, a certain image contrast could be formed. This effect is independent on X-ray energy, so in a certain range of sizes, simultaneous imaging of high Z high-density and low Z low-density materials in the high-energy X-ray is achieved, which overcomes the shortcomings of traditional absorption imaging. The precision assembly parameters measurement of implosion target is realized.
The feasibility of measuring the location of the plastic microsphere in the gold hohlraum target by using coaxial-of-focus X-ray phase contrast imaging was theoretically analyzed, based on which an experiment was carried out. The experimental results show that, due to the phase modulation of low Z and low-density materials to high energy X-ray, a certain image contrast could be formed. This effect is independent on X-ray energy, so in a certain range of sizes, simultaneous imaging of high Z high-density and low Z low-density materials in the high-energy X-ray is achieved, which overcomes the shortcomings of traditional absorption imaging. The precision assembly parameters measurement of implosion target is realized.
2012,
24: 2631-2636.
doi: 10.3788/HPLPB20122411.2631
Abstract:
Oxygen plasma and HPM solution (mixtures of hydrochloric acid, hydrogen peroxide, and deionized water) were applied to cleaning the multilayer dielectric (MLD) pulse compressor gratings. X-ray photoelectron spectroscopy was carried out to evaluate surface cleanliness of the gratings. It is found that photoresist and fluorocarbon residues can be efficiently removed with oxygen-plasma cleaning and metal contaminants can be completely removed with HPM cleaning. After cleaning processes, the typical diffraction efficiencies in -1st reflected order are maintained larger than 95.0% at an incidence of 66.4 in TE polarization, and the laser induced damage threshold (LIDT) for 10-ps laser pulse at 1053 nm is greatly improved to 1.6 J/cm2. The cleaning method using oxygen plasma and HPM solution can efficiently make the surface clean and therefore enhance the LIDT of MLD gratings.
Oxygen plasma and HPM solution (mixtures of hydrochloric acid, hydrogen peroxide, and deionized water) were applied to cleaning the multilayer dielectric (MLD) pulse compressor gratings. X-ray photoelectron spectroscopy was carried out to evaluate surface cleanliness of the gratings. It is found that photoresist and fluorocarbon residues can be efficiently removed with oxygen-plasma cleaning and metal contaminants can be completely removed with HPM cleaning. After cleaning processes, the typical diffraction efficiencies in -1st reflected order are maintained larger than 95.0% at an incidence of 66.4 in TE polarization, and the laser induced damage threshold (LIDT) for 10-ps laser pulse at 1053 nm is greatly improved to 1.6 J/cm2. The cleaning method using oxygen plasma and HPM solution can efficiently make the surface clean and therefore enhance the LIDT of MLD gratings.
2012,
24: 2637-2641.
doi: 10.3788/HPLPB20122411.2637
Abstract:
The discrete phase data should be fitted to calculate the reticle position of computer generated holograms (CGHs) for off-axis aspheric surfaces. The basis functions of uniform B-spline and non-uniform B-spline were deduced in detail, and the corresponding fitting methods were introduced. With an off-axis paraboloid as an example, its discrete phase data was got and fitted by uniform B-spline and non-uniform B-spline. The results show that all the data points are on the fitting surface and the fitting accuracy can meet the requirement. Meanwhile, the expression of the phase function is very simple (the highest order is only three). Moreover, the sample points can be optimized to control the amount of calculation.
The discrete phase data should be fitted to calculate the reticle position of computer generated holograms (CGHs) for off-axis aspheric surfaces. The basis functions of uniform B-spline and non-uniform B-spline were deduced in detail, and the corresponding fitting methods were introduced. With an off-axis paraboloid as an example, its discrete phase data was got and fitted by uniform B-spline and non-uniform B-spline. The results show that all the data points are on the fitting surface and the fitting accuracy can meet the requirement. Meanwhile, the expression of the phase function is very simple (the highest order is only three). Moreover, the sample points can be optimized to control the amount of calculation.
2012,
24: 2642-2646.
doi: 10.3788/HPLPB20122411.2642
Abstract:
Melamine-formaldehyde(MF) aerogels modified by phloroglucinol were prepared using melamine, phloroglucinol and formaldehyde by means of sol-gel and CO2 supercritical drying process. The lowest density of the modified MF aerogels is about 44 mg/cm3. The aerogel samples are transparent and unbroken. It is proved that shortening gelation time is caused by phloroglucinol through the Materials-Studio computer simulation. The samples were also characterized by SEM, FT-IR and TGA. These tests show that: the modified aerogels have the three dimensional space network structure, with uniform pore size distribution and thermostability.
Melamine-formaldehyde(MF) aerogels modified by phloroglucinol were prepared using melamine, phloroglucinol and formaldehyde by means of sol-gel and CO2 supercritical drying process. The lowest density of the modified MF aerogels is about 44 mg/cm3. The aerogel samples are transparent and unbroken. It is proved that shortening gelation time is caused by phloroglucinol through the Materials-Studio computer simulation. The samples were also characterized by SEM, FT-IR and TGA. These tests show that: the modified aerogels have the three dimensional space network structure, with uniform pore size distribution and thermostability.
2012,
24: 2647-2650.
doi: 10.3788/HPLPB20122411.2647
Abstract:
The microencapsulation technology was utilized to fabricate millimeter-sized monodisperse poly(-methystyrene) capsules by a triple-orifice droplet generator. The effects of the flow rate of each phase on the formation of the double emulsion droplets, the diameters of double emulsion droplets and their distributions were preliminarily investigated. Based on the obtained mono-sized double emulsion droplets, poly(-methystyrene) capsules with monodispersity less than 3% and diameters ranging from 800 to 1200 m were fabricated by a level-rotation-evaporation solidification technique.
The microencapsulation technology was utilized to fabricate millimeter-sized monodisperse poly(-methystyrene) capsules by a triple-orifice droplet generator. The effects of the flow rate of each phase on the formation of the double emulsion droplets, the diameters of double emulsion droplets and their distributions were preliminarily investigated. Based on the obtained mono-sized double emulsion droplets, poly(-methystyrene) capsules with monodispersity less than 3% and diameters ranging from 800 to 1200 m were fabricated by a level-rotation-evaporation solidification technique.
2012,
24: 2651-2654.
doi: 10.3788/HPLPB20122411.2651
Abstract:
Two experiments of laser-driven methane jet are performed on a petawatt laser, and the X-ray emitted is used to backlight small-size metal objects with SCCD(scintillator screen + CCD camera). Converters with different thicknesses are chosen considering the temperature of hot electrons which is evaluated both by the empirical formula and by the particle-in-cell (PIC) code. The X-ray energies of 377 keV and 130 keV are estimated by the two methods respectively. Consequently, converters with 1.3 mm and 0.8 mm thicknesses are chosen. Photon energies of 49 keV and 92 keV are obtained by grayscale curves of aluminum and copper step-wedges in the second experiment. It is demonstrated that the photon energy deduced from the PIC code agrees with the experimental result.
Two experiments of laser-driven methane jet are performed on a petawatt laser, and the X-ray emitted is used to backlight small-size metal objects with SCCD(scintillator screen + CCD camera). Converters with different thicknesses are chosen considering the temperature of hot electrons which is evaluated both by the empirical formula and by the particle-in-cell (PIC) code. The X-ray energies of 377 keV and 130 keV are estimated by the two methods respectively. Consequently, converters with 1.3 mm and 0.8 mm thicknesses are chosen. Photon energies of 49 keV and 92 keV are obtained by grayscale curves of aluminum and copper step-wedges in the second experiment. It is demonstrated that the photon energy deduced from the PIC code agrees with the experimental result.
2012,
24: 2655-2659.
doi: 10.3788/HPLPB20122411.2655
Abstract:
The generation mechanism of runaway electrons in non-quasi-stable state plasmas and the influence of massive gas injection on the confinement of plasmas are investigated in Ohmic and low hybrid current drive (LHCD) plasma density modulation experiments in HT-7 Tokamak. It is found that massive gas injection during the discharge made the plasma from quasi-stable state turn into non-quasi-stable state in which the quasi-stable state assumption condition of Dreicer mechanism and secondary mechanism (avalanche) of runaway electron generation does not exist. Therefore, it is necessary to use the normalized critical velocity to explain the runaway electron behavior in non-quasi-stable state plasmas. It is also found that the plasma confinement became poor during massive gas injection in the plasma density modulation experiments in HT-7 Tokamak.
The generation mechanism of runaway electrons in non-quasi-stable state plasmas and the influence of massive gas injection on the confinement of plasmas are investigated in Ohmic and low hybrid current drive (LHCD) plasma density modulation experiments in HT-7 Tokamak. It is found that massive gas injection during the discharge made the plasma from quasi-stable state turn into non-quasi-stable state in which the quasi-stable state assumption condition of Dreicer mechanism and secondary mechanism (avalanche) of runaway electron generation does not exist. Therefore, it is necessary to use the normalized critical velocity to explain the runaway electron behavior in non-quasi-stable state plasmas. It is also found that the plasma confinement became poor during massive gas injection in the plasma density modulation experiments in HT-7 Tokamak.
2012,
24: 2660-2664.
doi: 10.3788/HPLPB20122411.2660
Abstract:
A flexible curing agent containing a long methylene chain segment was synthesized by bis-functional epoxy resin modifying aliphatic amine. The structure of product was characterized by infrared spectroscopy. The epoxy resin E-44 cured with the flexible curing agent was researched. By analysis of the relationship between mechanical strength and temperature, the optimum curing condition was obtained preliminarily, which was 80 ℃, 6 h. The heat resistances of the cured products at different proportion were characterized by thermogravimetric analysis (TGA), and the dynamic parameters, reactivity, best curing temperature and time were studied by differential scanning calorimetry (DSC), the results verify the correctness of the previous work. At last, the tensile shear strength was studied, and the results show that the tensile shear strengths at -196 ℃ , room temperature and 60 ℃ are 16.84, 14.73 and 13.52 MPa respectively when the curing proportion is 1:0.5, which fully meets the practical requirements.
A flexible curing agent containing a long methylene chain segment was synthesized by bis-functional epoxy resin modifying aliphatic amine. The structure of product was characterized by infrared spectroscopy. The epoxy resin E-44 cured with the flexible curing agent was researched. By analysis of the relationship between mechanical strength and temperature, the optimum curing condition was obtained preliminarily, which was 80 ℃, 6 h. The heat resistances of the cured products at different proportion were characterized by thermogravimetric analysis (TGA), and the dynamic parameters, reactivity, best curing temperature and time were studied by differential scanning calorimetry (DSC), the results verify the correctness of the previous work. At last, the tensile shear strength was studied, and the results show that the tensile shear strengths at -196 ℃ , room temperature and 60 ℃ are 16.84, 14.73 and 13.52 MPa respectively when the curing proportion is 1:0.5, which fully meets the practical requirements.
2012,
24: 2665-2668.
doi: 10.3788/HPLPB20122411.2665
Abstract:
A method was proposed to measure off-axis aspherical mirrors by a coordinate measurement machine (CMM). The 3D coordinates of the actual points on the off-axis mirrors were obtained with this method, and were compared with the data by the theoretical model, through which the profile errors and root-mean-square values of the actual mirrors were obtained. All the fine grinding processes were guided according to the measurement results. Thus the problem that off-axis mirrors are difficult to measure and manufacture is resolved. As the off-axis mirror came into the polishing process successfully, the measurement of off-axis aspherical mirrors in the grinding process was successfully followed by that in the polishing process.
A method was proposed to measure off-axis aspherical mirrors by a coordinate measurement machine (CMM). The 3D coordinates of the actual points on the off-axis mirrors were obtained with this method, and were compared with the data by the theoretical model, through which the profile errors and root-mean-square values of the actual mirrors were obtained. All the fine grinding processes were guided according to the measurement results. Thus the problem that off-axis mirrors are difficult to measure and manufacture is resolved. As the off-axis mirror came into the polishing process successfully, the measurement of off-axis aspherical mirrors in the grinding process was successfully followed by that in the polishing process.
2012,
24: 2669-2672.
doi: 10.3788/HPLPB20122411.2669
Abstract:
A new method to measure the target velocity in laser plasma propulsion is proposed. By this method, the target velocity can be directly measured. The target thickness and the probe beam have no effects on measurement results. Compared with theoretical result, the error of experimental result is less than 2%. Furthermore, using this method, target momentum generation in laser-ablation water under different ambient temperatures is measured. Results show that the target momentum increases as the temperature decreases.
A new method to measure the target velocity in laser plasma propulsion is proposed. By this method, the target velocity can be directly measured. The target thickness and the probe beam have no effects on measurement results. Compared with theoretical result, the error of experimental result is less than 2%. Furthermore, using this method, target momentum generation in laser-ablation water under different ambient temperatures is measured. Results show that the target momentum increases as the temperature decreases.
2012,
24: 2673-2676.
doi: 10.3788/HPLPB20122411.2673
Abstract:
To improve the photolithography precision of Si support system, some main process parameters in soft bake, exposure, development were analyzed with orthogonal experiment. The influence degree of the parameters, including soft bake time, exposure time, development time and temperature, and their best combination were found. On this basis, a proper back propagation (BP) neural network was designed and trained and the experimental data were analyzed and optimized by the BP neural network. Verification experiments supported the correctness of the BP neural network. When the photoresist is 1.55 m thick, the optimum process parameters are: soft bake temperature 100 ℃, time 90 s; exposure time 5 s; development temperature 15 ℃, time 90 s. On this condition, the linewidth error can be less than 0.3 m.
To improve the photolithography precision of Si support system, some main process parameters in soft bake, exposure, development were analyzed with orthogonal experiment. The influence degree of the parameters, including soft bake time, exposure time, development time and temperature, and their best combination were found. On this basis, a proper back propagation (BP) neural network was designed and trained and the experimental data were analyzed and optimized by the BP neural network. Verification experiments supported the correctness of the BP neural network. When the photoresist is 1.55 m thick, the optimum process parameters are: soft bake temperature 100 ℃, time 90 s; exposure time 5 s; development temperature 15 ℃, time 90 s. On this condition, the linewidth error can be less than 0.3 m.
Investigation of non-uniform structure of sulfur doped monolayer for polystyrene hollow microspheres
2012,
24: 2677-2682.
doi: 10.3788/HPLPB20122411.2677
Abstract:
Detailed analysis is carried out to describe the non-uniform structure of sulfur doped monolayer for Polystyrene hollow microscopy. The results demonstrate that the appearance of this non-uniform structure comes from PSS (sodium polystyrene sulfonate, the doped sulfur agent). The film forming capability of PSS is also investigated with infrared image microscopy and polarizing microscope. PSS has a bad performance in film forming, and the ordering aggregates and crystal appear on the surfaces of the film. There is great differencein the thermal properties between the PSS film and the polystyrene film indicated by thermal treatment, and the PSS film is easy to have brittle crack and strip from the polystyrene film . Therefore, PSS is not appropriate for fabricating the hollow microspheres when the content of doped sulfur is high.
Detailed analysis is carried out to describe the non-uniform structure of sulfur doped monolayer for Polystyrene hollow microscopy. The results demonstrate that the appearance of this non-uniform structure comes from PSS (sodium polystyrene sulfonate, the doped sulfur agent). The film forming capability of PSS is also investigated with infrared image microscopy and polarizing microscope. PSS has a bad performance in film forming, and the ordering aggregates and crystal appear on the surfaces of the film. There is great differencein the thermal properties between the PSS film and the polystyrene film indicated by thermal treatment, and the PSS film is easy to have brittle crack and strip from the polystyrene film . Therefore, PSS is not appropriate for fabricating the hollow microspheres when the content of doped sulfur is high.
2012,
24: 2683-2686.
doi: 10.3788/HPLPB20122411.2683
Abstract:
Some important issues, such as the characteristics of gyrotron resonator, suppression of spurious modes and beam-wave interaction, are studied by using linear and nonlinear theories. A 95 GHz gyrotron operating at the third cyclotron harmonic is designed. The gyrotron operates at the TE64 mode with a single standard open cavity. In this gyrotron a ideal 45 kV, 5 A electron beam with a pitch ratio of 1.5 is required. The gyrotron performance is analyzed with the nonlinear theory. It is shown that a 14 kW output power can be realized, the corresponding orbit efficiency and total efficiency are 18% and 11%, respectively.
Some important issues, such as the characteristics of gyrotron resonator, suppression of spurious modes and beam-wave interaction, are studied by using linear and nonlinear theories. A 95 GHz gyrotron operating at the third cyclotron harmonic is designed. The gyrotron operates at the TE64 mode with a single standard open cavity. In this gyrotron a ideal 45 kV, 5 A electron beam with a pitch ratio of 1.5 is required. The gyrotron performance is analyzed with the nonlinear theory. It is shown that a 14 kW output power can be realized, the corresponding orbit efficiency and total efficiency are 18% and 11%, respectively.
2012,
24: 2687-2692.
doi: 10.3788/HPLPB20122411.2687
Abstract:
Based on Maxwells equations, a weakly conditionally stable finite-difference time-domain(FDTD) method for periodic structures is proposed. The stability condition is verified theoretically. Which is looser than that of the conventional FDTD method. And the Sherman-Morrison formula has been used to solve the non-tridiagonal linear system. The new algorithm has better accuracy and efficiency than the ADI-FDTD, especially for large time step size. A numerical example is presented to demonstrate the efficiency and accuracy of the proposed algorithm. Results show the CPU time for this method can be reduced to about 33% of the ADI-FDTD method.
Based on Maxwells equations, a weakly conditionally stable finite-difference time-domain(FDTD) method for periodic structures is proposed. The stability condition is verified theoretically. Which is looser than that of the conventional FDTD method. And the Sherman-Morrison formula has been used to solve the non-tridiagonal linear system. The new algorithm has better accuracy and efficiency than the ADI-FDTD, especially for large time step size. A numerical example is presented to demonstrate the efficiency and accuracy of the proposed algorithm. Results show the CPU time for this method can be reduced to about 33% of the ADI-FDTD method.
2012,
24: 2693-2697.
doi: 10.3788/HPLPB20122411.2693
Abstract:
The transition waveguides between folded groove guide slow-wave structure and 3 mm standard rectangular waveguide are designed, which are formed by tapered double groove-loaded rectangular waveguides. The influences of structural parameters on transmission performance are discussed based on the simulation results by CST Microwave Studio. Moreover, the transmission performances and loss characteristics of three transition waveguides, i. e. linearly tapered , parabolically tapered and exponentially tapereddouble groove-loaded rectangular waveguidesare analyzed in W band. The simulation results show that the bandwidth of the exponentially tapered transition waveguide is wider than those of the other two structures, while the voltage standing wave ratio (VSWR) is less than 1.15. Furthermore, the whole length of it is much shorter than those of the other two structures when the VSWR is less than 1.25 within 90-99 GHz. However, the loss of the linearly tapered structure is smaller than that of the other structures in 90-97 GHz frequency range.
The transition waveguides between folded groove guide slow-wave structure and 3 mm standard rectangular waveguide are designed, which are formed by tapered double groove-loaded rectangular waveguides. The influences of structural parameters on transmission performance are discussed based on the simulation results by CST Microwave Studio. Moreover, the transmission performances and loss characteristics of three transition waveguides, i. e. linearly tapered , parabolically tapered and exponentially tapereddouble groove-loaded rectangular waveguidesare analyzed in W band. The simulation results show that the bandwidth of the exponentially tapered transition waveguide is wider than those of the other two structures, while the voltage standing wave ratio (VSWR) is less than 1.15. Furthermore, the whole length of it is much shorter than those of the other two structures when the VSWR is less than 1.25 within 90-99 GHz. However, the loss of the linearly tapered structure is smaller than that of the other structures in 90-97 GHz frequency range.
2012,
24: 2698-2702.
doi: 10.3788/HPLPB20122411.2698
Abstract:
The interaction circuit for the V-band high-power traveling-wave tube (TWT) was designed by employing the folded-waveguide slow-wave structure and a 3∶1 aspect-ratio sheet electron beam as the beam-wave interaction circuit. The effect of the sheet-beam channel on the high frequency properties was analyzed, and the optimized structural parameters were obtained under the consideration of dispersion and impedance. A 3-D circuit model of the sheet-beam folded-waveguide TWT was constructed and the beam-wave interaction of this circuit was simulated using the CST particle studio. From our calculations, the sheet-beam folded-waveguide TWT can produce output power of over 160 W with the gain over 34.7 dB ranging from 58 GHz to 62 GHz, when the cathode voltage and beam current are set to 17 kV and 150 mA respectively.
The interaction circuit for the V-band high-power traveling-wave tube (TWT) was designed by employing the folded-waveguide slow-wave structure and a 3∶1 aspect-ratio sheet electron beam as the beam-wave interaction circuit. The effect of the sheet-beam channel on the high frequency properties was analyzed, and the optimized structural parameters were obtained under the consideration of dispersion and impedance. A 3-D circuit model of the sheet-beam folded-waveguide TWT was constructed and the beam-wave interaction of this circuit was simulated using the CST particle studio. From our calculations, the sheet-beam folded-waveguide TWT can produce output power of over 160 W with the gain over 34.7 dB ranging from 58 GHz to 62 GHz, when the cathode voltage and beam current are set to 17 kV and 150 mA respectively.
2012,
24: 2703-2708.
doi: 10.3788/HPLPB20122411.2703
Abstract:
A hybrid method combining parallel finite-difference time-domain (PFDTD) and parallel time-domain physical optics (PTDPO) is presented for computing radiation fields of large dual reflector antennas. The radiation fields can not be simulated by singular time-domain methods and the accurate results couldnt be got by singular frequency technologies. Two process groups for parallel computing are firstly set up, one is for PFDTD computing and the other is for PTDPO computing. Then the near magnetic fields of the dual reflectors feed are got by the PFDTD method. Based on these fields, the magnetic fields near or on the sub-reflector are parallel computed with Kirchhoffs surface integral representation (KSIR). The magnetic fields on the main reflector are also obtained by KSIR. The radiation far-fields of the dual reflector are calculated by the PTDPO method at last. The radiation patterns of the Cassegrain dual reflector antenna, whose main-reflector aperture size is 40 wavelengths, show the results near the axis simulated by the PFDTD-PTDPO hybrid method agree well with those by the PFDTD method. The radiation simulation in time domain near the axes of dual reflectors with the same feed and different aperture size is given. The hybrid method has the ability of simulating any large dual reflector antennas with the aperture size of hundreds of wavelengths, even if the reflectors feed is very big or offset.
A hybrid method combining parallel finite-difference time-domain (PFDTD) and parallel time-domain physical optics (PTDPO) is presented for computing radiation fields of large dual reflector antennas. The radiation fields can not be simulated by singular time-domain methods and the accurate results couldnt be got by singular frequency technologies. Two process groups for parallel computing are firstly set up, one is for PFDTD computing and the other is for PTDPO computing. Then the near magnetic fields of the dual reflectors feed are got by the PFDTD method. Based on these fields, the magnetic fields near or on the sub-reflector are parallel computed with Kirchhoffs surface integral representation (KSIR). The magnetic fields on the main reflector are also obtained by KSIR. The radiation far-fields of the dual reflector are calculated by the PTDPO method at last. The radiation patterns of the Cassegrain dual reflector antenna, whose main-reflector aperture size is 40 wavelengths, show the results near the axis simulated by the PFDTD-PTDPO hybrid method agree well with those by the PFDTD method. The radiation simulation in time domain near the axes of dual reflectors with the same feed and different aperture size is given. The hybrid method has the ability of simulating any large dual reflector antennas with the aperture size of hundreds of wavelengths, even if the reflectors feed is very big or offset.
2012,
24: 2709-2712.
doi: 10.3788/HPLPB20122411.2709
Abstract:
The guiding magnetic field system is designed to conduct the experimental investigation of the L-band low-impedance foilless transit-radiation oscillator. The total capacitance of the system is 5.4 mF. The length of the designed solenoid is 45 cm, and its theoretical inductance and impedance are 42 mH and 0.66 respectively. Based on the design, the coil is fabricated and the corresponding platform for the experiment is established. The real inductance and impedance are 40 mH and 0.61 respectively. The target experiment testifies that the intense relativistic electron beam can be well guided by the designed magnetic field system.
The guiding magnetic field system is designed to conduct the experimental investigation of the L-band low-impedance foilless transit-radiation oscillator. The total capacitance of the system is 5.4 mF. The length of the designed solenoid is 45 cm, and its theoretical inductance and impedance are 42 mH and 0.66 respectively. Based on the design, the coil is fabricated and the corresponding platform for the experiment is established. The real inductance and impedance are 40 mH and 0.61 respectively. The target experiment testifies that the intense relativistic electron beam can be well guided by the designed magnetic field system.
2012,
24: 2713-2717.
doi: 10.3788/HPLPB20122411.2713
Abstract:
Attenuation characteristics of High Power Microwave (HPM) with different frequencies (L, S, C, X band) penetrating through reinforcement nets were studied by simulation tests combined with the finite-difference time-domain method in this paper. The research models reflect various kind of reinforcement nets with different diameters, different meshes, different spacings between layers, and different arrangement. The results show that shielding effectiveness of reinforcement nets against HPM exists. And shielding effectiveness is better when the mesh is smaller than half of the wave-length, or when the spacing between layers is odd number times a quarter of the wave-length, or when the reinforcement nets are arrange is stagger. The reinforcement nets with dissimilar forms can be comprehensively utilized in protective constructions for the best result.
Attenuation characteristics of High Power Microwave (HPM) with different frequencies (L, S, C, X band) penetrating through reinforcement nets were studied by simulation tests combined with the finite-difference time-domain method in this paper. The research models reflect various kind of reinforcement nets with different diameters, different meshes, different spacings between layers, and different arrangement. The results show that shielding effectiveness of reinforcement nets against HPM exists. And shielding effectiveness is better when the mesh is smaller than half of the wave-length, or when the spacing between layers is odd number times a quarter of the wave-length, or when the reinforcement nets are arrange is stagger. The reinforcement nets with dissimilar forms can be comprehensively utilized in protective constructions for the best result.
2012,
24: 2718-2722.
doi: 10.3788/HPLPB20122411.2718
Abstract:
To study space-charge forces influence on beam transport in dipole magnet field, the matrix method was applied to analyze the transport matrices in dipole magnet field of non-intense pulsed beam and intense pulsed beam theoretically, and a computer code was programmed for the pulsed beam transporting in dipole magnet field. Powell optimization techniques were used to calculate non-intense pulsed beam for attaining the given optical conditions and iteration procedures were adopted to compute intense pulsed beam for obtaining self-consistent solutions in this computer code. The calculations were made by using the code and other codes under the condition of different beam current, and the simulation results were compared and analyzed. The results show that greater beam current causes more apparent beam envelope lateral divergence and more powerful space-charge effect.
To study space-charge forces influence on beam transport in dipole magnet field, the matrix method was applied to analyze the transport matrices in dipole magnet field of non-intense pulsed beam and intense pulsed beam theoretically, and a computer code was programmed for the pulsed beam transporting in dipole magnet field. Powell optimization techniques were used to calculate non-intense pulsed beam for attaining the given optical conditions and iteration procedures were adopted to compute intense pulsed beam for obtaining self-consistent solutions in this computer code. The calculations were made by using the code and other codes under the condition of different beam current, and the simulation results were compared and analyzed. The results show that greater beam current causes more apparent beam envelope lateral divergence and more powerful space-charge effect.
2012,
24: 2723-2726.
doi: 10.3788/HPLPB20122411.2723
Abstract:
This paper discusses a method of calculating the growth rate of the secondary electron number after electron multipacting in the spoke superconductive cavity for Accelerator Driven sub-critical System(ADS) with CST Particle Studio. The result shows that there are two types of multipacting in the spoke cavity above: two-point one order multipacting on the top of the spoke pole and one-point one-order multipacting at the corner of the spoke cylinder face. The crest of the growth rate of multipacting is at the accelerator cavity voltage of 0.65 MV while there is no multipacting when the voltage is higher than 1 MV in the simulation. A comparison about the growth rate curve between two different secondary electron emission coefficients of niobium in the inner face of the cavity is also showed.
This paper discusses a method of calculating the growth rate of the secondary electron number after electron multipacting in the spoke superconductive cavity for Accelerator Driven sub-critical System(ADS) with CST Particle Studio. The result shows that there are two types of multipacting in the spoke cavity above: two-point one order multipacting on the top of the spoke pole and one-point one-order multipacting at the corner of the spoke cylinder face. The crest of the growth rate of multipacting is at the accelerator cavity voltage of 0.65 MV while there is no multipacting when the voltage is higher than 1 MV in the simulation. A comparison about the growth rate curve between two different secondary electron emission coefficients of niobium in the inner face of the cavity is also showed.
2012,
24: 2727-2730.
doi: 10.3788/HPLPB20122411.2727
Abstract:
The realization of events trigger signal pre-processing in the nuclear physics experiment data acquisition system is briefly introduced, by using the FPGA （field-programmable gate array） chips and VHDL language. The general requirements of trigger signal processing in nuclear physics experiment are listed. The 60Co gamma spectra test experiment is introduced to detail these requirements. The trigger signal pre-processing in self-programming systems is presented. According to a given timing diagram, the trigger signal processing is realized with the VHDL language and FPGA technique. Through the actual waveform simulation and the experiments, this method is proved to be feasible and flexibility. This method can be of reference value for other data acquisition system trigger signal processing.
The realization of events trigger signal pre-processing in the nuclear physics experiment data acquisition system is briefly introduced, by using the FPGA （field-programmable gate array） chips and VHDL language. The general requirements of trigger signal processing in nuclear physics experiment are listed. The 60Co gamma spectra test experiment is introduced to detail these requirements. The trigger signal pre-processing in self-programming systems is presented. According to a given timing diagram, the trigger signal processing is realized with the VHDL language and FPGA technique. Through the actual waveform simulation and the experiments, this method is proved to be feasible and flexibility. This method can be of reference value for other data acquisition system trigger signal processing.
2012,
24: 2731-2734.
doi: 10.3788/HPLPB20122411.2731
Abstract:
Three kinds of defect-particle-scattering models are put forward for nondestructive examination project. The generalized perfectly matched layer can work very well in the terminate loss media. Against the half-space problem about wafers and defect particles, the connect boundary condition is given by the three-wave method. The reciprocity theorem is applied to near-far field extrapolation. The angular distribution of many kinds of Cu and SiO2 defect particles and field distribution of the inlaid Cu sphere particles by p polarization and s polarization are given. Results show that the angular distribution and field distribution are related to the shape of particles. The shake of scattering field about ellipsoid particles is more drastic than column particles. The differential field intensity is very minor with s polarization, which makes against to inverse the characteristic of defect particles. Therefore, p polarization light is suggested to use in nondestructive examination in the project.
Three kinds of defect-particle-scattering models are put forward for nondestructive examination project. The generalized perfectly matched layer can work very well in the terminate loss media. Against the half-space problem about wafers and defect particles, the connect boundary condition is given by the three-wave method. The reciprocity theorem is applied to near-far field extrapolation. The angular distribution of many kinds of Cu and SiO2 defect particles and field distribution of the inlaid Cu sphere particles by p polarization and s polarization are given. Results show that the angular distribution and field distribution are related to the shape of particles. The shake of scattering field about ellipsoid particles is more drastic than column particles. The differential field intensity is very minor with s polarization, which makes against to inverse the characteristic of defect particles. Therefore, p polarization light is suggested to use in nondestructive examination in the project.
2012,
24: 2735-2740.
doi: 10.3788/HPLPB20122411.2735
Abstract:
The Nb(C, N) ceramic particulates reinforced Fe-based composite coatings have been successfully synthesized in situ by prior pasting laser cladding on steel 42CrMo. The phase constituents and microstructure of the composite coatings were investigated using X-ray diffraction, and scanning electron micrography. The results indicate that the coatings consist mainly of Fe-Cr fine phases with good resistance to oxidation and corrosion and a few of -Fe phases. In-situ synthesized Nb(C, N) particulates are uniformly distributed with blocky morphology in the composite coatings. The wear test shows that these reinforcement particulates improves wear resistance of the coatings significantly. The wear mass loss of the substrate with coating is about one ninth of that of the substrate without coatings. The coatings have better oxidation resistance through 750 ℃ constant temperature oxidation, and the oxide scale mainly consists of NbO1.1 and Cr2O3. The oxidation products of the substrate are Fe2O3 , and easy to spall off, resulting in a poor effect in substrate protection. The oxide scale of the coatings is one fifth as thick as that of raw substrate
The Nb(C, N) ceramic particulates reinforced Fe-based composite coatings have been successfully synthesized in situ by prior pasting laser cladding on steel 42CrMo. The phase constituents and microstructure of the composite coatings were investigated using X-ray diffraction, and scanning electron micrography. The results indicate that the coatings consist mainly of Fe-Cr fine phases with good resistance to oxidation and corrosion and a few of -Fe phases. In-situ synthesized Nb(C, N) particulates are uniformly distributed with blocky morphology in the composite coatings. The wear test shows that these reinforcement particulates improves wear resistance of the coatings significantly. The wear mass loss of the substrate with coating is about one ninth of that of the substrate without coatings. The coatings have better oxidation resistance through 750 ℃ constant temperature oxidation, and the oxide scale mainly consists of NbO1.1 and Cr2O3. The oxidation products of the substrate are Fe2O3 , and easy to spall off, resulting in a poor effect in substrate protection. The oxide scale of the coatings is one fifth as thick as that of raw substrate
2012,
24: 2741-2745.
doi: 10.3788/HPLPB20122411.2741
Abstract:
Based on two-dimensional LC network, a zero-electric and zero-magnetic material (ZEM) focuser is designed, and the equivalent node voltage distribution matrix is derived. The focuser with triangular, quadrilateral, hexagonal and octagonal contours is investigated, and the effects of shape and size on its performance are simulated. The results show that, the focusing effect is independent of the shape of the focuser when the size of the focusing area is smaller than twice the wavelength; energy at the focus point increases gradually with the focusing area; when the size of the focusing area is bigger than twice the wavelength, the main focusing area disappears and a number of sub-focusing points are generated at the same time.
Based on two-dimensional LC network, a zero-electric and zero-magnetic material (ZEM) focuser is designed, and the equivalent node voltage distribution matrix is derived. The focuser with triangular, quadrilateral, hexagonal and octagonal contours is investigated, and the effects of shape and size on its performance are simulated. The results show that, the focusing effect is independent of the shape of the focuser when the size of the focusing area is smaller than twice the wavelength; energy at the focus point increases gradually with the focusing area; when the size of the focusing area is bigger than twice the wavelength, the main focusing area disappears and a number of sub-focusing points are generated at the same time.
2012,
24: 2746-2750.
doi: 10.3788/HPLPB20122411.2746
Abstract:
This paper presents the establishment and validation of the 3D numerical model of plasma ignition to investigate the plasma ignition process in supersonic combustion chamber. Parameters of flow field and chemical reactions in the plasma ignition combustion chamber are calculated. The effects of plasma ignition on combustion are analyzed. The calculation results show that high temperature plasma jet increases the stay time of mixed gas in combustion chamber to improve the ignition efficiency; the combustion zone is incompressible and pressure balanced; velocity vector offset is generated when plasma jet shoots at mixed gases; water is the main product of hydrogen/air combustion and the local temperature is mainly affected by the exothermic reactions.
This paper presents the establishment and validation of the 3D numerical model of plasma ignition to investigate the plasma ignition process in supersonic combustion chamber. Parameters of flow field and chemical reactions in the plasma ignition combustion chamber are calculated. The effects of plasma ignition on combustion are analyzed. The calculation results show that high temperature plasma jet increases the stay time of mixed gas in combustion chamber to improve the ignition efficiency; the combustion zone is incompressible and pressure balanced; velocity vector offset is generated when plasma jet shoots at mixed gases; water is the main product of hydrogen/air combustion and the local temperature is mainly affected by the exothermic reactions.
2012,
24: 2751-2756.
doi: 10.3788/HPLPB20122411.2751
Abstract:
In order to improve the efficiency of solar cell, we make some changes of laser ablation. This study focuses on using 355 nm laser with nanosecond pulse duration to ablate ZnO:Al (P1), -Si (P2), and back contact (P3) selectively. Isolation resistances are measured by multimeter. Scanning electron microscope and 3D laser scan microscope are used to measure ablation grooves microstructure and 3D images. Laser Raman spectroscopy is employed to detect the crystallization of -Si in the edge of ablation. The experimental results show that the effect of groove ablated by 355 nm laser whose isolation resistance reaches up to 20 M is best when a 600 mm/s, 40 kHz, 1.74 W laser works on its focal position, and the ablation with 355 nm laser can effectively decrease the influence caused by laser heating effect and the crystallization area of -Si in the edge of ablation.
In order to improve the efficiency of solar cell, we make some changes of laser ablation. This study focuses on using 355 nm laser with nanosecond pulse duration to ablate ZnO:Al (P1), -Si (P2), and back contact (P3) selectively. Isolation resistances are measured by multimeter. Scanning electron microscope and 3D laser scan microscope are used to measure ablation grooves microstructure and 3D images. Laser Raman spectroscopy is employed to detect the crystallization of -Si in the edge of ablation. The experimental results show that the effect of groove ablated by 355 nm laser whose isolation resistance reaches up to 20 M is best when a 600 mm/s, 40 kHz, 1.74 W laser works on its focal position, and the ablation with 355 nm laser can effectively decrease the influence caused by laser heating effect and the crystallization area of -Si in the edge of ablation.
2012,
24: 2757-2762.
doi: 10.3788/HPLPB20122411.2757
Abstract:
Using circuit analysis and theoretical modeling, the problem of identifying worst-case irradiation and test bias for total ionizing dose (TID) effect of CMOS circuits is studied. Small scale analog and digital circuits are introduced and analyzed, thus worst-case bias conditions are identified step by step. To digital circuits, the concept of the sensitive factor is introduced to calculate the sensitive level of circuits to TID effect under different combinations of bias during irradiation and during test. The results are validated and verified by experimental tests or circuit simulation, which proves the rationality of the identification method.
Using circuit analysis and theoretical modeling, the problem of identifying worst-case irradiation and test bias for total ionizing dose (TID) effect of CMOS circuits is studied. Small scale analog and digital circuits are introduced and analyzed, thus worst-case bias conditions are identified step by step. To digital circuits, the concept of the sensitive factor is introduced to calculate the sensitive level of circuits to TID effect under different combinations of bias during irradiation and during test. The results are validated and verified by experimental tests or circuit simulation, which proves the rationality of the identification method.
2012,
24: 2763-2767.
doi: 10.3788/HPLPB20122411.2763
Abstract:
By the waveform modulation with the pulse form network (PFN) of a small experimental pulsed power system, the saw-tooth waveform, convex-topped waveform and flat-topped waveform are gotten, and the three kinds of pulse current waveforms are used for the sliding experiment of the solid armature of the electromagnetic rail driving system (EMRDS). By measuring the ultimate muzzle velocity of the experimental armature, the effects of different pulse current waveforms on the sliding performance of the solid armature are compared. The experimental results show that under low charging and discharging energy the abruptly changed saw-tooth waveform is easy to cause contact fail, and often makes the ablation phenomenon happen, so it is unfavorable to the sliding performance of solid armatures; under the same charging and discharging energy, the measured muzzle velocity under the convex-topped waveform pulse is higher than that under the flat-topped one, which means the efficiency of the former is higher than that of the latter; the flat-topped waveform can bear higher charging and discharging energy than the convex-topped one, and its ultimate muzzle velocity is also higher; among the three kinds of waveforms, the flat-topped waveform is the most propitious to the sliding performance of solid armatures because it can provide good contact of the solid armature and rail.
By the waveform modulation with the pulse form network (PFN) of a small experimental pulsed power system, the saw-tooth waveform, convex-topped waveform and flat-topped waveform are gotten, and the three kinds of pulse current waveforms are used for the sliding experiment of the solid armature of the electromagnetic rail driving system (EMRDS). By measuring the ultimate muzzle velocity of the experimental armature, the effects of different pulse current waveforms on the sliding performance of the solid armature are compared. The experimental results show that under low charging and discharging energy the abruptly changed saw-tooth waveform is easy to cause contact fail, and often makes the ablation phenomenon happen, so it is unfavorable to the sliding performance of solid armatures; under the same charging and discharging energy, the measured muzzle velocity under the convex-topped waveform pulse is higher than that under the flat-topped one, which means the efficiency of the former is higher than that of the latter; the flat-topped waveform can bear higher charging and discharging energy than the convex-topped one, and its ultimate muzzle velocity is also higher; among the three kinds of waveforms, the flat-topped waveform is the most propitious to the sliding performance of solid armatures because it can provide good contact of the solid armature and rail.
2012,
24: 2768-2772.
doi: 10.3788/HPLPB20122411.2768
Abstract:
A high power pulse device called primary test stand (PTS) is under development, which contains 24 modules with identical components, and with the design parameters of 8 MA to 10 MA current and the frontal rise time of 90 ns. For laser triggered gas switches on PTS can be independently triggered by 12 lasers, and by shorting out the water switches, it is possible to operate PTS in three different modes, i. e. the short-pulse high current mode, long-pulse high current mode, and waveform shaping mode for isentropic compression experiments. The load currents are estimated by a full-circuit model of PTS. These predicted currents are about 10 MA for the same equivalent inductance load in three different modes. In the short-pulse mode PTS will be able to provide currents up to 10 MA with risetime of 100 ns. In the long-pulse mode PTS will be able to provide currents up to 10 MA with risetime of 200 ns. Tailored waveform output will also be possible on PTS, with risetime up to 400 ns. The waveform shaping mode is studied by the settings of triggered manners of laser triggered gas switches and operation models of water switches.
A high power pulse device called primary test stand (PTS) is under development, which contains 24 modules with identical components, and with the design parameters of 8 MA to 10 MA current and the frontal rise time of 90 ns. For laser triggered gas switches on PTS can be independently triggered by 12 lasers, and by shorting out the water switches, it is possible to operate PTS in three different modes, i. e. the short-pulse high current mode, long-pulse high current mode, and waveform shaping mode for isentropic compression experiments. The load currents are estimated by a full-circuit model of PTS. These predicted currents are about 10 MA for the same equivalent inductance load in three different modes. In the short-pulse mode PTS will be able to provide currents up to 10 MA with risetime of 100 ns. In the long-pulse mode PTS will be able to provide currents up to 10 MA with risetime of 200 ns. Tailored waveform output will also be possible on PTS, with risetime up to 400 ns. The waveform shaping mode is studied by the settings of triggered manners of laser triggered gas switches and operation models of water switches.
