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RSS2008 Vol. 20, No. 09
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2008,
20.
Abstract:
A long-pulse TE CO2 laser with ultraviolet-preionization using pulser/sustainer discharge technique is presented. The laser can discharge stably with 14 nF pulser capacitance and 200 nF sustainer capacitance by optimizing the parameters of pulse forming network and amending the Chang’s profile. For an active volume of 2.48 L, a gas mixture ratio of CO2, N2, He is 1∶2.5∶13 and the gas pressure of 40 kPa, the maximum output laser energy of 18.51 J with a pulse width of 32 μs is obtained at an efficiency of 14.3%.
A long-pulse TE CO2 laser with ultraviolet-preionization using pulser/sustainer discharge technique is presented. The laser can discharge stably with 14 nF pulser capacitance and 200 nF sustainer capacitance by optimizing the parameters of pulse forming network and amending the Chang’s profile. For an active volume of 2.48 L, a gas mixture ratio of CO2, N2, He is 1∶2.5∶13 and the gas pressure of 40 kPa, the maximum output laser energy of 18.51 J with a pulse width of 32 μs is obtained at an efficiency of 14.3%.
2008,
20.
Abstract:
The liquid crystal spatial light modulator(LCSLM) was used to shape the super-Gaussian seed pulse. The simulation results of the shaping, amplification and compression processes, indicate that the spectrum shaped by liquial crystal spatial light modu letar eliminates the nonlinear effect of Nd: glass chirped pulse amplification system, the spectral width of the amplified pulse is as the same as that of the initial one. But the structural parameters of the device show great impact on the signal noise ratio of the compressed pulse. We analyzed the relationship between structural parameters and signal noise ratio and the results are useful for application and optimum design of such device.
The liquid crystal spatial light modulator(LCSLM) was used to shape the super-Gaussian seed pulse. The simulation results of the shaping, amplification and compression processes, indicate that the spectrum shaped by liquial crystal spatial light modu letar eliminates the nonlinear effect of Nd: glass chirped pulse amplification system, the spectral width of the amplified pulse is as the same as that of the initial one. But the structural parameters of the device show great impact on the signal noise ratio of the compressed pulse. We analyzed the relationship between structural parameters and signal noise ratio and the results are useful for application and optimum design of such device.
2008,
20.
Abstract:
The laser pulses with several femtosecond duration close to its natural limit of the wave cycle in the visible spectral range are able to trace chemical processes of molecules. However, probing ultrafast transition process of electrons much faster than the wave cycle needs attosecond scale pulses. The experiments of attosecond XUV and X-ray pulses formed by high-harmonic generation have made much progress. The attosecond pulse train which are consecutive pulses with same carrier envelope phase can push optical frequency combs in the visible and near infrared wavelength to extreme ultraviolet regions. Temporal resolation of attosecond level is realized through measuring lateral distribution of the electron wave packet perturbed by laser ellipticity within attosecond temporal gate of electro
The laser pulses with several femtosecond duration close to its natural limit of the wave cycle in the visible spectral range are able to trace chemical processes of molecules. However, probing ultrafast transition process of electrons much faster than the wave cycle needs attosecond scale pulses. The experiments of attosecond XUV and X-ray pulses formed by high-harmonic generation have made much progress. The attosecond pulse train which are consecutive pulses with same carrier envelope phase can push optical frequency combs in the visible and near infrared wavelength to extreme ultraviolet regions. Temporal resolation of attosecond level is realized through measuring lateral distribution of the electron wave packet perturbed by laser ellipticity within attosecond temporal gate of electro
2008,
20.
Abstract:
A scheme is designed to measure the pulsed laser far field energy density based on CCD imaging, and the measurement model mapping the CCD gray value to the pulsed laser energy density on the reflective board is deduced based on radiometry and camera calibration, in which the influence of abaxial angle together with the nonuniformity of board’s diffuse reflection ratio and CCD sensor’s responsivity is considered and corrected. Uncertainty analysis shows that the uncertainty propagation coefficient of CCD’s gray value, lens’ transmittance, board’s diffuse reflection ratio and CCD sensor’s responsivity are all 1; that of lens’ iris diaphragm number is 2; that of lens’ focal length increases with the abaxial angle; and that of image center’s pixel coordinates reach the maximum at the
A scheme is designed to measure the pulsed laser far field energy density based on CCD imaging, and the measurement model mapping the CCD gray value to the pulsed laser energy density on the reflective board is deduced based on radiometry and camera calibration, in which the influence of abaxial angle together with the nonuniformity of board’s diffuse reflection ratio and CCD sensor’s responsivity is considered and corrected. Uncertainty analysis shows that the uncertainty propagation coefficient of CCD’s gray value, lens’ transmittance, board’s diffuse reflection ratio and CCD sensor’s responsivity are all 1; that of lens’ iris diaphragm number is 2; that of lens’ focal length increases with the abaxial angle; and that of image center’s pixel coordinates reach the maximum at the
2008,
20.
Abstract:
In high power solid-state laser driver, the calibration of reference wavefront is a key technique in the use of adaptive optics system. Based on the optical character of certain laser prototype system, two calibration methods are researched contrastively. Main factors affecting the accuracy of calibration are obtained. Based on the reference wavefront of the more accurate calibration result, the validity of the result is proved by far-field changing before and after AO correction. The result has been successfully used in AO system wavefront correction experiment of this prototype system.
In high power solid-state laser driver, the calibration of reference wavefront is a key technique in the use of adaptive optics system. Based on the optical character of certain laser prototype system, two calibration methods are researched contrastively. Main factors affecting the accuracy of calibration are obtained. Based on the reference wavefront of the more accurate calibration result, the validity of the result is proved by far-field changing before and after AO correction. The result has been successfully used in AO system wavefront correction experiment of this prototype system.
2008,
20.
Abstract:
The evolution of the hot-images caused by multi-scatterers in a plane perpendicular to the axis in high-power laser systems is numerically simulated by taking five parallel equispaced nonlinear medium plates (with gain and loss) as an example. The influences among the scattered beams with different parameters are analyzed, respectively. The analytical results show that the hot-images induced by coplanar multi-scatterers are also coplanar whether they exist simultaneously or severally. However, the peak intensity of the hot-images is weaker when they exist simultaneously than that when they exist severally. In addition, when the scattered beams with different parameters gain energy from the original beam and form the hot-image, the unequal competitions of energy may result in the fact that
The evolution of the hot-images caused by multi-scatterers in a plane perpendicular to the axis in high-power laser systems is numerically simulated by taking five parallel equispaced nonlinear medium plates (with gain and loss) as an example. The influences among the scattered beams with different parameters are analyzed, respectively. The analytical results show that the hot-images induced by coplanar multi-scatterers are also coplanar whether they exist simultaneously or severally. However, the peak intensity of the hot-images is weaker when they exist simultaneously than that when they exist severally. In addition, when the scattered beams with different parameters gain energy from the original beam and form the hot-image, the unequal competitions of energy may result in the fact that
2008,
20.
Abstract:
The heat dispersion of a cooler which we made was theoretically simulated and the thermal conductivity of the packaging material was analyzed. It was proved the diode laser could operate in high power density and high duty cycle. The key technique for high density packaging was improved. The thickness of the gilded heat sink was 3~5 mm, and that of the solder was 4~7 mm. The thermal resistance of the packaged LD bar was 0.115 ℃/W. The output power of the diode laser arrays was 986 W when the current was 100 A and the duty cycle 15%. The slope efficiency of each bar was 1.25 W/A and the current threshold was about 20 A. The peak power density could be as high as 1.5 kW/cm2 when the duty-cycle was 15%.
The heat dispersion of a cooler which we made was theoretically simulated and the thermal conductivity of the packaging material was analyzed. It was proved the diode laser could operate in high power density and high duty cycle. The key technique for high density packaging was improved. The thickness of the gilded heat sink was 3~5 mm, and that of the solder was 4~7 mm. The thermal resistance of the packaged LD bar was 0.115 ℃/W. The output power of the diode laser arrays was 986 W when the current was 100 A and the duty cycle 15%. The slope efficiency of each bar was 1.25 W/A and the current threshold was about 20 A. The peak power density could be as high as 1.5 kW/cm2 when the duty-cycle was 15%.
2008,
20.
Abstract:
The diffraction and near-field-intensity smoothing characteristics of periodic chirp pulse after spectral dispersion in the laser driver of inertial confinement fusion are analyzed theoretically and simulated numerically, and the effect of color cycles on the both is calculated. The calculation results indicate that the far field increases and intensity modulation is enhanced with the increase of color cycle; the near-field-intensity smoothing effect becomes better but the spatial shape distortion is enhanced along with the increasing of the color cycles and propagation distance. And through smoothing effect comparison, periodic chirp pulse is found to be better than the sinusoidal phase modulated laser beam on the smoothing of near-field-intensity.
The diffraction and near-field-intensity smoothing characteristics of periodic chirp pulse after spectral dispersion in the laser driver of inertial confinement fusion are analyzed theoretically and simulated numerically, and the effect of color cycles on the both is calculated. The calculation results indicate that the far field increases and intensity modulation is enhanced with the increase of color cycle; the near-field-intensity smoothing effect becomes better but the spatial shape distortion is enhanced along with the increasing of the color cycles and propagation distance. And through smoothing effect comparison, periodic chirp pulse is found to be better than the sinusoidal phase modulated laser beam on the smoothing of near-field-intensity.
2008,
20.
Abstract:
By using approximate expression of the hard-edge narrow slot aperture function and generalized diffraction formula, an approximate analytical expression of the output field distribution for a Gaussian beam passing through an optical system with a misaligned narrow slot aperture has been derived. Smulation results show that the output field distribution is related with Gaussian beam parameters, aperture size, ABCD matrix elements and misaligned parameters. The effect of misaligned parameters on output field distribution are also illustrated quantitatively for given optical system and Gaussian beam, and results show that the transverse displacements of the aperture and the transverse displcement and the angle displacement of the optical system bring forth non-axisymmetric distribution of int
By using approximate expression of the hard-edge narrow slot aperture function and generalized diffraction formula, an approximate analytical expression of the output field distribution for a Gaussian beam passing through an optical system with a misaligned narrow slot aperture has been derived. Smulation results show that the output field distribution is related with Gaussian beam parameters, aperture size, ABCD matrix elements and misaligned parameters. The effect of misaligned parameters on output field distribution are also illustrated quantitatively for given optical system and Gaussian beam, and results show that the transverse displacements of the aperture and the transverse displcement and the angle displacement of the optical system bring forth non-axisymmetric distribution of int
2008,
20.
Abstract:
An X-ray streak camera system with high dynamic range and a long slit photocathode of 30 mm length has been developed for plasma diagnosis in ICF experimental research. In order to enlarge dynamic range and ensure time resolution at the same time, a series of measures are adopted. The measures include reducing electron transit time inside the streak image tube greatly, enhancing the anode's voltage to 16.5 kV, abandoning micro-channel plate electron amplifier, and using fibre plate coupling and air-cooling CCD. An experimental evaluation has been carried out by means of Nd:YAG pico-second laser. The results show that the spatial resolution is 15 lp/mm, the time resolution less than 31 ps and dynamic range more than 922 can be achieved.
An X-ray streak camera system with high dynamic range and a long slit photocathode of 30 mm length has been developed for plasma diagnosis in ICF experimental research. In order to enlarge dynamic range and ensure time resolution at the same time, a series of measures are adopted. The measures include reducing electron transit time inside the streak image tube greatly, enhancing the anode's voltage to 16.5 kV, abandoning micro-channel plate electron amplifier, and using fibre plate coupling and air-cooling CCD. An experimental evaluation has been carried out by means of Nd:YAG pico-second laser. The results show that the spatial resolution is 15 lp/mm, the time resolution less than 31 ps and dynamic range more than 922 can be achieved.
2008,
20.
Abstract:
Neutron digital imaging is a low light level imaging technique. It is difficult to extract the quantitative information of samples due to the image degradation caused by scattering neutrons in the imaging process. In this situation, the principle of so-called scattering degradation of the low light level neutron imaging system is analyzed, and the degradation process in this system is characterized by point spread function(PSF) superposition. Using Monte Carlo method, the PSF is simulated and modeled as an analytical function of two parameters, the thickness of sample and the distance from sample to detector, and then the calculation method of PSF is presented. The result shows that constructing the PSF of this system and applying it to scattering correction for neutron images is an effect
Neutron digital imaging is a low light level imaging technique. It is difficult to extract the quantitative information of samples due to the image degradation caused by scattering neutrons in the imaging process. In this situation, the principle of so-called scattering degradation of the low light level neutron imaging system is analyzed, and the degradation process in this system is characterized by point spread function(PSF) superposition. Using Monte Carlo method, the PSF is simulated and modeled as an analytical function of two parameters, the thickness of sample and the distance from sample to detector, and then the calculation method of PSF is presented. The result shows that constructing the PSF of this system and applying it to scattering correction for neutron images is an effect
2008,
20.
Abstract:
To restrain the space charge effects causing severe broadening of an ultra-short electron pulse with high charge density, a novel method is proposed based on a compensating element. The element is an axisymmetric cylindrical cavity, of which the side wall and a fine mesh end face through which the electron pulse can get out are both grounded. The permittivity distribution of the other end face in which there is an entrance pinhole is so developed that the specific potential distribution can be formed when positive potential is applied to the conducting layer inside the pinhole. The correspondingly formed inner electric field can exert different electric force on electrons of different position, which is opposite to that of space charge effects, and eventually restrain the unwelcome electro
To restrain the space charge effects causing severe broadening of an ultra-short electron pulse with high charge density, a novel method is proposed based on a compensating element. The element is an axisymmetric cylindrical cavity, of which the side wall and a fine mesh end face through which the electron pulse can get out are both grounded. The permittivity distribution of the other end face in which there is an entrance pinhole is so developed that the specific potential distribution can be formed when positive potential is applied to the conducting layer inside the pinhole. The correspondingly formed inner electric field can exert different electric force on electrons of different position, which is opposite to that of space charge effects, and eventually restrain the unwelcome electro
2008,
20.
Abstract:
Self-organized nanostructures were observed on the surface of ZnSe crystal after irradiation by a focused beam of a femtosecond Ti: sapphire laser with a repetition rate of 250 kHz. For a linearly polarized femtosecond laser, a periodic nanograting structure on the ablation crater surface was promoted. The period of these self-organization structures is about 160 nm. The grating orientation can be adjusted by changing the laser polarization direction. A long range Bragg-like grating formed by moving the sample at the speed of 10 μm/s in the horizontal plane. For a circularly polarized laser beam, uniform spherical nanoparticles formed.
Self-organized nanostructures were observed on the surface of ZnSe crystal after irradiation by a focused beam of a femtosecond Ti: sapphire laser with a repetition rate of 250 kHz. For a linearly polarized femtosecond laser, a periodic nanograting structure on the ablation crater surface was promoted. The period of these self-organization structures is about 160 nm. The grating orientation can be adjusted by changing the laser polarization direction. A long range Bragg-like grating formed by moving the sample at the speed of 10 μm/s in the horizontal plane. For a circularly polarized laser beam, uniform spherical nanoparticles formed.
2008,
20.
Abstract:
Interfacial effect on effective optical properties of a granular composite has been investigated, in which spherical particles with graded interfaces are randomly embedded in a host matrix. Under the dilute limit, the effective dielectric coefficient of the composite is derived by means of the first-principle approach method applied to power-law dielectric gradation profile in interfaces. The effective optical responses of graded and sharp interfaces are discussed, respectively. It is found that the graded interface in graded spherical particles yields a broader optical absorption spectrum with blue-shift and the fluctuation of corresponding effective dielectric response is smaller.
Interfacial effect on effective optical properties of a granular composite has been investigated, in which spherical particles with graded interfaces are randomly embedded in a host matrix. Under the dilute limit, the effective dielectric coefficient of the composite is derived by means of the first-principle approach method applied to power-law dielectric gradation profile in interfaces. The effective optical responses of graded and sharp interfaces are discussed, respectively. It is found that the graded interface in graded spherical particles yields a broader optical absorption spectrum with blue-shift and the fluctuation of corresponding effective dielectric response is smaller.
2008,
20.
Abstract:
According to sub-nanosecond laser pulses, an electronic fast-pulse sampling method is put forward based on picosecond pulse transmission line and high speed electronic circuits. The design of strobe pulse generation and high speed sample-holding circuit are given as well as an interleaved sampling method for increasing the real-time sample rate, which is a plurality of sampling gates array configured in parallel. This electronic sampling can be used in the exact parameter measurement of multi-beam laser pulses.
According to sub-nanosecond laser pulses, an electronic fast-pulse sampling method is put forward based on picosecond pulse transmission line and high speed electronic circuits. The design of strobe pulse generation and high speed sample-holding circuit are given as well as an interleaved sampling method for increasing the real-time sample rate, which is a plurality of sampling gates array configured in parallel. This electronic sampling can be used in the exact parameter measurement of multi-beam laser pulses.
2008,
20.
Abstract:
A 1-D visible radiation diagnostic system is developed to investigate plasma convergence via visible radiation with one-dimensional space and continuous time resolution in wire-array Z-pinch experiments performed on Qiangguang-I facility. The loads used in the experiments include single tungsten array and single aluminum array. During the early stages of a wire array Z-pinch implosion, low density precursor plasma is formed and streams toward the axis by the virtue of the Lorentz force. Due to trailing mass around the array plasma, some visible radiation is observed during the run-in and run-out stagnation phase. Also, the implosion tracery can be derived from visible radiation streak images. When the drive current scales from 1.0 MA to 1.5 MA, the implosion compression ratio of the wire a
A 1-D visible radiation diagnostic system is developed to investigate plasma convergence via visible radiation with one-dimensional space and continuous time resolution in wire-array Z-pinch experiments performed on Qiangguang-I facility. The loads used in the experiments include single tungsten array and single aluminum array. During the early stages of a wire array Z-pinch implosion, low density precursor plasma is formed and streams toward the axis by the virtue of the Lorentz force. Due to trailing mass around the array plasma, some visible radiation is observed during the run-in and run-out stagnation phase. Also, the implosion tracery can be derived from visible radiation streak images. When the drive current scales from 1.0 MA to 1.5 MA, the implosion compression ratio of the wire a
2008,
20.
Abstract:
A non-uniform parameter double-transmission-line model is created to explore the voltage distribution in Tesla-transformer taper windings. With the method of differential approximation, the numerical results are shown that during the charging process of PFL, the maximal electric-field intensity moves gradually from the small-radius end to the large-radius end, whereas during the discharging process and the abnormal discharging process of PFL, the maximal electric-field intensity is on the large-radius end. What’s more, the maximal electrical field intensity of the three processes, which happens in the abnormal discharging process of PFL, is approximately 1.5 times the average electric-field intensity.
A non-uniform parameter double-transmission-line model is created to explore the voltage distribution in Tesla-transformer taper windings. With the method of differential approximation, the numerical results are shown that during the charging process of PFL, the maximal electric-field intensity moves gradually from the small-radius end to the large-radius end, whereas during the discharging process and the abnormal discharging process of PFL, the maximal electric-field intensity is on the large-radius end. What’s more, the maximal electrical field intensity of the three processes, which happens in the abnormal discharging process of PFL, is approximately 1.5 times the average electric-field intensity.
2008,
20.
Abstract:
Recurrence relations of the initial voltages across the primary capacitor between adjacent pulses are derivated based on the sequence processes of discharge and recharge of the primary capacitor in repetitive mode for a compact accelerator. The equation of the initial voltage across the primary capacitor in steady state is obtained. And the transition time or the number of the transition pulses between the unsteady state and the steady state can be calculated. The condition, under which the charge thyristor switch’s turn-on time is independent of the gas spark switch’s breakdown voltage, is theoretically discussed and experimentally obtained. Furthermore, the corresponding methods and steps are presented to guide the experiments. From the theoretical analyses and experimental investigati
Recurrence relations of the initial voltages across the primary capacitor between adjacent pulses are derivated based on the sequence processes of discharge and recharge of the primary capacitor in repetitive mode for a compact accelerator. The equation of the initial voltage across the primary capacitor in steady state is obtained. And the transition time or the number of the transition pulses between the unsteady state and the steady state can be calculated. The condition, under which the charge thyristor switch’s turn-on time is independent of the gas spark switch’s breakdown voltage, is theoretically discussed and experimentally obtained. Furthermore, the corresponding methods and steps are presented to guide the experiments. From the theoretical analyses and experimental investigati
2008,
20.
Abstract:
A novel transmission curved crystal spectrometer is described for hard Ｘ-ray measurements in the energy range of 10~60 keV. The spectrometer is based on a cylindrical curved quartz crystal. The curvature radius is 112 mm and the spacing of the crystal lattice is 0.425 6 nm. The experiment utilizes a Mo Ｘ-ray tube as the light source and the spectrometer is set perpendicular to the axis about 700 mm distance. Two characteristic spectra are symmetrically recorded by image plate clearly and the experiment is well consistent with theoretical analysis．The errror analysis shows that the aim accuracy is the main factor.
A novel transmission curved crystal spectrometer is described for hard Ｘ-ray measurements in the energy range of 10~60 keV. The spectrometer is based on a cylindrical curved quartz crystal. The curvature radius is 112 mm and the spacing of the crystal lattice is 0.425 6 nm. The experiment utilizes a Mo Ｘ-ray tube as the light source and the spectrometer is set perpendicular to the axis about 700 mm distance. Two characteristic spectra are symmetrically recorded by image plate clearly and the experiment is well consistent with theoretical analysis．The errror analysis shows that the aim accuracy is the main factor.
2008,
20.
Abstract:
Analysis of forces on microshells during ablation layer bounce-coating has been carried out based on the established bouncing and mechanical models. The phenomena, such as the conglutination and unbounce of microshells, the fluctuation of the bounce amplitudes and bounce rates, have been explained. Through the analysis of effecting factors on the bounce of microshells, such as the direction and the magnitude of the stimulating signal, the mass and size of microshells, the surface characters of microshells and bounce-pan, the humidity and dirty of environment, etc, serious solutions which can improve bounce-effect of microshells have been put forward. The solutions include the stimulating signal adjustment, the plasma treatment and the surface modification of the bounce-pan.
Analysis of forces on microshells during ablation layer bounce-coating has been carried out based on the established bouncing and mechanical models. The phenomena, such as the conglutination and unbounce of microshells, the fluctuation of the bounce amplitudes and bounce rates, have been explained. Through the analysis of effecting factors on the bounce of microshells, such as the direction and the magnitude of the stimulating signal, the mass and size of microshells, the surface characters of microshells and bounce-pan, the humidity and dirty of environment, etc, serious solutions which can improve bounce-effect of microshells have been put forward. The solutions include the stimulating signal adjustment, the plasma treatment and the surface modification of the bounce-pan.
2008,
20.
Abstract:
The monodispersed SiO2 microspheres were synthesized by reactant mixed equally. The colloid crystal templates were assemblied by vertical sedimentation method in ethanol at certain temperatures, and the effects of the heat treatment temperature on the morphology and the properties of opal colloid crystals were investigated. SEM, TG-DSC results indicate SiO2 colloid templates should be heat treated at 700~800 ℃, enhancing the conglutination and mechanistic intensity of opal templates. UV-Vis analysis result indicates that the heat treatment process can remove the photonic band gap location of the opal colloid crystals, and with the heat treatment temperature increasing gradually, blue shift occurs and the gap narrows.
The monodispersed SiO2 microspheres were synthesized by reactant mixed equally. The colloid crystal templates were assemblied by vertical sedimentation method in ethanol at certain temperatures, and the effects of the heat treatment temperature on the morphology and the properties of opal colloid crystals were investigated. SEM, TG-DSC results indicate SiO2 colloid templates should be heat treated at 700~800 ℃, enhancing the conglutination and mechanistic intensity of opal templates. UV-Vis analysis result indicates that the heat treatment process can remove the photonic band gap location of the opal colloid crystals, and with the heat treatment temperature increasing gradually, blue shift occurs and the gap narrows.
2008,
20.
Abstract:
Two-layer SiO2/ZrO2 thin films were deposited on K9 glass by Sol-Gel dip-coating method. The colloidal suspension of ZrO2 and SiO2 were prepared using Zr(OPr)4 and TEOS as precursors, respectively. For sample 1, the ZrO2 film was directly deposited on the pre-deposited SiO2 film. For sample 2, the ZrO2 film was deposited on the pre-deposited and heat-treated SiO2 film. Atomic force microscopy(AFM), ellipometry and UV-VIS spectroscopy were used to characterize the thin films. The samples were simulated with three-layer Cauchy theoretical model. The simulated ellipsometric parameters curves were perfectly consistent with the experimental ones. The results showed that the thickness of infiltrated layer of sample 2 was reduced by 23 nm by using heat treatment compared with that of sample 1. As
Two-layer SiO2/ZrO2 thin films were deposited on K9 glass by Sol-Gel dip-coating method. The colloidal suspension of ZrO2 and SiO2 were prepared using Zr(OPr)4 and TEOS as precursors, respectively. For sample 1, the ZrO2 film was directly deposited on the pre-deposited SiO2 film. For sample 2, the ZrO2 film was deposited on the pre-deposited and heat-treated SiO2 film. Atomic force microscopy(AFM), ellipometry and UV-VIS spectroscopy were used to characterize the thin films. The samples were simulated with three-layer Cauchy theoretical model. The simulated ellipsometric parameters curves were perfectly consistent with the experimental ones. The results showed that the thickness of infiltrated layer of sample 2 was reduced by 23 nm by using heat treatment compared with that of sample 1. As
2008,
20.
Abstract:
A novel bridged silsesquioxane with long bridging groups was synthesized with m-xylylene diisocyanate and 3-aminopropyltriethoxysilane. Bridged polysilsesquioxane sol was prepared by the sol-gel polycondensaion of as-synthesized bridged silsesquioxane under basic catalysis. Thin film was obtained by dip-coating the bridged polysilsesquioxane sol on the KDP crystal. 1H NMR was used to characterize the bridged silsesquioxane. 29Si MAS NMR and N2 absorption/desorption analysis were adopted to study the xerogel structure. The morphology of film was observed by AFM analysis. The moisture-resistance of film under relative humidity 60% for KDP crystals was studied. The laser-induced damage threshold(LIDT) of bridged polysilsesquioxane film at 355 nm and 1 064 nm was measured. The results show tha
A novel bridged silsesquioxane with long bridging groups was synthesized with m-xylylene diisocyanate and 3-aminopropyltriethoxysilane. Bridged polysilsesquioxane sol was prepared by the sol-gel polycondensaion of as-synthesized bridged silsesquioxane under basic catalysis. Thin film was obtained by dip-coating the bridged polysilsesquioxane sol on the KDP crystal. 1H NMR was used to characterize the bridged silsesquioxane. 29Si MAS NMR and N2 absorption/desorption analysis were adopted to study the xerogel structure. The morphology of film was observed by AFM analysis. The moisture-resistance of film under relative humidity 60% for KDP crystals was studied. The laser-induced damage threshold(LIDT) of bridged polysilsesquioxane film at 355 nm and 1 064 nm was measured. The results show tha
2008,
20.
Abstract:
The foamed copper was synthesized by electrodeposition technique on the basis of electroless copper plating using sodium hypophosphite as reductant. Micro-structure of foamed copper in different phase was characterized by scanning electron microscope and X-ray diffraction instruments. Small grain size and homogeneous copper in the foam silk were obtained by electroless plating. The electrodeposited copper was composed of 0.55 μm granules and there were some big granules in the middle of the electrodeposed copper silk. After heat treatment at 700 ℃, the granules crystal in the silk were dissolved, and the copper grains were bigger. Three-dimensional network foamed copper with compact crystal, density of 0.19 g/cm3, pore diameter ranged from 400 to 600 μm, and porosity of 97.9% was prepar
The foamed copper was synthesized by electrodeposition technique on the basis of electroless copper plating using sodium hypophosphite as reductant. Micro-structure of foamed copper in different phase was characterized by scanning electron microscope and X-ray diffraction instruments. Small grain size and homogeneous copper in the foam silk were obtained by electroless plating. The electrodeposited copper was composed of 0.55 μm granules and there were some big granules in the middle of the electrodeposed copper silk. After heat treatment at 700 ℃, the granules crystal in the silk were dissolved, and the copper grains were bigger. Three-dimensional network foamed copper with compact crystal, density of 0.19 g/cm3, pore diameter ranged from 400 to 600 μm, and porosity of 97.9% was prepar
2008,
20.
Abstract:
The damage behaviors of HfO2/SiO2 high reflective optical thin film fabricated by electron beam evaporation (EBE) illuminated using 1 064 nm laser and 532 nm laser showed some difference. It was found that the damage was usually caused by absorptive defects and absorption near the interfaces under the irradiation of 1 064 nm laser, and the damage was caused by electronic defects and absorptive ones under irradiation of 532 nm laser and the former had lower damage threshold. Therefore, the key point to enhance the laser resistance of optical thin films at 1 064 nm was to prevent the presence of the absorptive defects, and to those at 532 nm was to eliminate the electronic defects．
The damage behaviors of HfO2/SiO2 high reflective optical thin film fabricated by electron beam evaporation (EBE) illuminated using 1 064 nm laser and 532 nm laser showed some difference. It was found that the damage was usually caused by absorptive defects and absorption near the interfaces under the irradiation of 1 064 nm laser, and the damage was caused by electronic defects and absorptive ones under irradiation of 532 nm laser and the former had lower damage threshold. Therefore, the key point to enhance the laser resistance of optical thin films at 1 064 nm was to prevent the presence of the absorptive defects, and to those at 532 nm was to eliminate the electronic defects．
2008,
20.
Abstract:
The polarization characeristics of the all fiber front-end for a laser facility prototype were analyzed. According to the polarization control demand of the laser facility prototype, a new method was developed to stablize the polarization of the fiber system with narrow bandwidth and short-pulse output. The amplitude modulator of the fiber system was pulse-biased and the autostabilizaion of the fiber system polarization was obtained by on-line detecting the polarization state of CW laser leakage from the amplitude modulaor. The decrease of the extinction ratio of the amplitude modulator in longtime operation was restrained and the stability of the all fiber frontend system was improved to 2.9%．
The polarization characeristics of the all fiber front-end for a laser facility prototype were analyzed. According to the polarization control demand of the laser facility prototype, a new method was developed to stablize the polarization of the fiber system with narrow bandwidth and short-pulse output. The amplitude modulator of the fiber system was pulse-biased and the autostabilizaion of the fiber system polarization was obtained by on-line detecting the polarization state of CW laser leakage from the amplitude modulaor. The decrease of the extinction ratio of the amplitude modulator in longtime operation was restrained and the stability of the all fiber frontend system was improved to 2.9%．
2008,
20.
Abstract:
In ICF experiment, the defects on micro-shells surface will affect the capsule implosion hydrodynamic instabitiy seriously. The relationship between the defects on micro-shell surface and power spectrum was analyzed theoretically and simulated. The results show that the root mean square roughness(RMS) of power spectrum increased with the increases of height and the rand noise, and decreased with the decrease of daimeter of defects. At the same time, the effect of defect’s height on power spectrum was more serious than that of defect’s diameter. And the RMS of power spectrum increased with the increase of defect’s quantity, and resulted in some periodic characteristic in power spectrum curve.
In ICF experiment, the defects on micro-shells surface will affect the capsule implosion hydrodynamic instabitiy seriously. The relationship between the defects on micro-shell surface and power spectrum was analyzed theoretically and simulated. The results show that the root mean square roughness(RMS) of power spectrum increased with the increases of height and the rand noise, and decreased with the decrease of daimeter of defects. At the same time, the effect of defect’s height on power spectrum was more serious than that of defect’s diameter. And the RMS of power spectrum increased with the increase of defect’s quantity, and resulted in some periodic characteristic in power spectrum curve.
2008,
20.
Abstract:
Fused silica were artificially contaminated to estimate the resistance of fused silica against laser damage. Uniform contamination thin films (less than 10 nm thick) were prepared by sputtering materials(Cu). The loss of transmission of the samples was first measured. They were tested at 355 nm in air with Nd:YAG laser. The damage morphologies were characterized by Nomarski optical microscopy. Both theory and experiments show that the laser damage resistance drops very uniformly across the entire surface，about 20%, the damage morphology contrary with that of the clean silica shows many pits on the surface, and the fused silica melts. A model for light absorption and the heat deposition was established to estimate damage thresholds. The damage threshold predictions are in qualitative agree
Fused silica were artificially contaminated to estimate the resistance of fused silica against laser damage. Uniform contamination thin films (less than 10 nm thick) were prepared by sputtering materials(Cu). The loss of transmission of the samples was first measured. They were tested at 355 nm in air with Nd:YAG laser. The damage morphologies were characterized by Nomarski optical microscopy. Both theory and experiments show that the laser damage resistance drops very uniformly across the entire surface，about 20%, the damage morphology contrary with that of the clean silica shows many pits on the surface, and the fused silica melts. A model for light absorption and the heat deposition was established to estimate damage thresholds. The damage threshold predictions are in qualitative agree
2008,
20.
Abstract:
PVA/SiO2 composite antireflective coatings which can be easily removed from glass substrate by hot water were prepared. PVA coatings were first deposited onto K9 glass substrate, followed by SiO2 as the second layer. UV-Vis spectrophotometer, ellipsometer optical microscope, scanning probe microscope, and contact angle measuring system were used to characterize the properties of the composite coatings and substrates. The results show that the peak transmittance of PVA/SiO2 composite coatings is 99.8%, and its position could be adjusted with the thickness change of SiO2 layer. After removal of the composite coatings in hotwater, the substrates are not damaged, and the basic properties, such as transmittance, surface morphology and water contact angle, remain the same as those of the substr
PVA/SiO2 composite antireflective coatings which can be easily removed from glass substrate by hot water were prepared. PVA coatings were first deposited onto K9 glass substrate, followed by SiO2 as the second layer. UV-Vis spectrophotometer, ellipsometer optical microscope, scanning probe microscope, and contact angle measuring system were used to characterize the properties of the composite coatings and substrates. The results show that the peak transmittance of PVA/SiO2 composite coatings is 99.8%, and its position could be adjusted with the thickness change of SiO2 layer. After removal of the composite coatings in hotwater, the substrates are not damaged, and the basic properties, such as transmittance, surface morphology and water contact angle, remain the same as those of the substr
2008,
20.
Abstract:
Deuterated polyethylene films with good transparency and uniform thickness were been prepared using improved solution-casting method. The effects of solution temperature, evaporation temperature, temperature and time of vacuum heating on the thickness uniformity and transparency of film were explored. The obtained optimum solution temperature, evaporation temperature and time of vacuum heating are 120～130 ℃， 80～100 ℃， 120 ℃，1 h ， respectively. The surface morphologies and thickness uniformity of the film were characterized by a KH-3000VD microscope and an AFM.
Deuterated polyethylene films with good transparency and uniform thickness were been prepared using improved solution-casting method. The effects of solution temperature, evaporation temperature, temperature and time of vacuum heating on the thickness uniformity and transparency of film were explored. The obtained optimum solution temperature, evaporation temperature and time of vacuum heating are 120～130 ℃， 80～100 ℃， 120 ℃，1 h ， respectively. The surface morphologies and thickness uniformity of the film were characterized by a KH-3000VD microscope and an AFM.
2008,
20.
Abstract:
Coaxial vircator with feedback and beam modulation is designed and studied by theoretical and PIC simulation methods. In the vircator, there are a coaxial resonant cavity that beams pass through and a coupling gap connecting the coaxial resonant cavity and the drift tube, and beam can be modulated before microwave generated in the coaxial resonant cavity. Then the modulation can be strengthened by microwave from the drift tube to the coaxial resonant cavity through the coupling gap. Simulation results and theoretical analysis show that the coaxial vircator has high beam-wave transform efficiency and point frequency. Meanwhile, it is found that the frequency of the microwave that the vircator generates is locked by the coaxial resonant cavity, which can be tuned by tuning the parameters of
Coaxial vircator with feedback and beam modulation is designed and studied by theoretical and PIC simulation methods. In the vircator, there are a coaxial resonant cavity that beams pass through and a coupling gap connecting the coaxial resonant cavity and the drift tube, and beam can be modulated before microwave generated in the coaxial resonant cavity. Then the modulation can be strengthened by microwave from the drift tube to the coaxial resonant cavity through the coupling gap. Simulation results and theoretical analysis show that the coaxial vircator has high beam-wave transform efficiency and point frequency. Meanwhile, it is found that the frequency of the microwave that the vircator generates is locked by the coaxial resonant cavity, which can be tuned by tuning the parameters of
2008,
20.
Abstract:
The double taper helix slow wave structure is one of the most widely used slow wave structures in space TWT. The effects of parameters such as length and pitch of double-taper helix slow wave structure on the electron efficiency and gain of TWT are investigated using the Christine large signal code. The result shows that the gain and the electron efficiency of TWT are in direct proportion to the length of each part of the slow wave structure, and the length of the signal input section has largest influence on the gain; the electron efficiency of the TWT is most sensitive to the pitch of the section where the phase velocity increases. Furthermore, the slow wave structure is optimized preliminarily by simultaneously increasing the length of the signal input section, reducing the pitch of th
The double taper helix slow wave structure is one of the most widely used slow wave structures in space TWT. The effects of parameters such as length and pitch of double-taper helix slow wave structure on the electron efficiency and gain of TWT are investigated using the Christine large signal code. The result shows that the gain and the electron efficiency of TWT are in direct proportion to the length of each part of the slow wave structure, and the length of the signal input section has largest influence on the gain; the electron efficiency of the TWT is most sensitive to the pitch of the section where the phase velocity increases. Furthermore, the slow wave structure is optimized preliminarily by simultaneously increasing the length of the signal input section, reducing the pitch of th
2008,
20.
Abstract:
The properties of several materials as explosive emission cathode were studied experimentally on high voltage (0.6~1.0 MV), repetitive (100 Hz) electron accelerator, such as effective emission area, average current density, diode impedance and energy losses of electron beam. The results show that the effective emission area varies with the applied diode voltage just like square wave response. The effective emission area varies mildly 5 ns after the voltage pulse beginning. Among carbon fiber, velvet, graphite and stainless steel, the carbon fiber has the largest effective emission area and average current density. The diode impedance increases linearly with the increase of the cathode-anode gap distance. The diode impedance mismatch with the transmitting line is the main factor of the ener
The properties of several materials as explosive emission cathode were studied experimentally on high voltage (0.6~1.0 MV), repetitive (100 Hz) electron accelerator, such as effective emission area, average current density, diode impedance and energy losses of electron beam. The results show that the effective emission area varies with the applied diode voltage just like square wave response. The effective emission area varies mildly 5 ns after the voltage pulse beginning. Among carbon fiber, velvet, graphite and stainless steel, the carbon fiber has the largest effective emission area and average current density. The diode impedance increases linearly with the increase of the cathode-anode gap distance. The diode impedance mismatch with the transmitting line is the main factor of the ener
2008,
20.
Abstract:
A compact high power microwave(HPM) driver using a folded plate Blumlein line is introduced. The folded plate Blumlein line uses Kapton film as the transmission dielectric and pure transformer oil as the insulation medium. The whole size of this Blumlein line is 1.00 m×0.40 m×0.15 m. The HPM source used a C-band magnetically insulated oscillator(MILO) with characteristic resistance of about 12 Ω. The folded plate Blumlein line delivers energy to the cathode of the MILO to produce an intense electron beam of 550 kV, 40 kA and 90 ns, and a high power microwave with peak power of 350 MW and pulse width of 45 ns radiates from the C-band MILO.
A compact high power microwave(HPM) driver using a folded plate Blumlein line is introduced. The folded plate Blumlein line uses Kapton film as the transmission dielectric and pure transformer oil as the insulation medium. The whole size of this Blumlein line is 1.00 m×0.40 m×0.15 m. The HPM source used a C-band magnetically insulated oscillator(MILO) with characteristic resistance of about 12 Ω. The folded plate Blumlein line delivers energy to the cathode of the MILO to produce an intense electron beam of 550 kV, 40 kA and 90 ns, and a high power microwave with peak power of 350 MW and pulse width of 45 ns radiates from the C-band MILO.
2008,
20.
Abstract:
In order to use the two-bunch acceleration technology to further double the positron injection rate from BEPCII (Beijing Electron Positron Collider Upgrade Project) linac to the storage ring, a pre-injector with two SHBs (Sub-harmonic Buncher) is being constructed to replace the old BEPCII bunching system. In this paper, we propose a new scheme to use a photoinjector as the pre-injector, the performance of which is comparable with or better than the sub-harmonic bunching system: at most 25% emittance and energy spread, 100% transport efficiency, absence of satellite bunch, etc. Beam dynamics of the photoinjector based pre-injector in both low charge and high charge cases are studied and compared with both the pre-injector with SHBs and the old BEPCII pre-injector. The high charge beam prod
In order to use the two-bunch acceleration technology to further double the positron injection rate from BEPCII (Beijing Electron Positron Collider Upgrade Project) linac to the storage ring, a pre-injector with two SHBs (Sub-harmonic Buncher) is being constructed to replace the old BEPCII bunching system. In this paper, we propose a new scheme to use a photoinjector as the pre-injector, the performance of which is comparable with or better than the sub-harmonic bunching system: at most 25% emittance and energy spread, 100% transport efficiency, absence of satellite bunch, etc. Beam dynamics of the photoinjector based pre-injector in both low charge and high charge cases are studied and compared with both the pre-injector with SHBs and the old BEPCII pre-injector. The high charge beam prod
2008,
20.
Abstract:
Theoretical analysis and experiments have been done to find out the factors which decide the self-restoration ability of low remanence magnetic cores. The results show that in the right working circuit, the cores with appropriate pulse permeability can self-restore to its remanence within 1 s. Two sample cores have been proved to satisfy all the three demands to be cavity cores of a multi-pulse inductive accelerator, i.e., the cores’ self-restoration time is less than 1 μs, its pulse average permeability is greater than 300 and flux density change area is greater than 0.7 T. The magnetic cores restoration problem in MHz repeat frequency high voltage multi-pulse is likely to be solved by choosing the right material of the cavity cores of the multi-pulse inductive accelerator．
Theoretical analysis and experiments have been done to find out the factors which decide the self-restoration ability of low remanence magnetic cores. The results show that in the right working circuit, the cores with appropriate pulse permeability can self-restore to its remanence within 1 s. Two sample cores have been proved to satisfy all the three demands to be cavity cores of a multi-pulse inductive accelerator, i.e., the cores’ self-restoration time is less than 1 μs, its pulse average permeability is greater than 300 and flux density change area is greater than 0.7 T. The magnetic cores restoration problem in MHz repeat frequency high voltage multi-pulse is likely to be solved by choosing the right material of the cavity cores of the multi-pulse inductive accelerator．
2008,
20.
Abstract:
Aiming at the characteristics of high-energy X-ray industrial computerized tomography(CT), a data transmission system based on USB2.0 was developed. The system consists of a USB2.0 interface and a transmission control unit. The USB20 interface unit uses Cypress’s EZ-USB FX2-CY7C68013A chip, which is set as the slave FIFO interface model to transfer data to host computer by bulk transfer mode. The transmission control unit uses Altera’s Cyclone- EP1C6Q240C8N chip which defines buffer to receive the data from detecting part, generate logic control signals and timing sequence signals, and send the data to the endpoint buffer of USB. The data transmission system was tested well and can meet the requirements of high-energy X-ray industrial CT. Also it can expand easily and take up a few sys
Aiming at the characteristics of high-energy X-ray industrial computerized tomography(CT), a data transmission system based on USB2.0 was developed. The system consists of a USB2.0 interface and a transmission control unit. The USB20 interface unit uses Cypress’s EZ-USB FX2-CY7C68013A chip, which is set as the slave FIFO interface model to transfer data to host computer by bulk transfer mode. The transmission control unit uses Altera’s Cyclone- EP1C6Q240C8N chip which defines buffer to receive the data from detecting part, generate logic control signals and timing sequence signals, and send the data to the endpoint buffer of USB. The data transmission system was tested well and can meet the requirements of high-energy X-ray industrial CT. Also it can expand easily and take up a few sys
2008,
20.
Abstract:
The prepulse restraining inductance was confirmed to be 5 μH according to the numerical simulation based on the relation of pulse transmitting line voltage，pulse outer line voltage and diode current with inductance value. The method for calculating the large-scale sparse inductance inside a shield was put forward by experimental study. The inductance with length of 630 mm, the coil of 1 160 mm in diameter and the inductance pipe of 102 mm in diameter were confirmed according to the simulated electric field between the inductance and the inner shield of PTL and windings. By numerically simulating the equivalent circuit of spiral water PTL composed of inductance and inner shield, the transmitting time of 349 ns was obtained, which was larger than the half -peak breadth of main pulse. Duri
The prepulse restraining inductance was confirmed to be 5 μH according to the numerical simulation based on the relation of pulse transmitting line voltage，pulse outer line voltage and diode current with inductance value. The method for calculating the large-scale sparse inductance inside a shield was put forward by experimental study. The inductance with length of 630 mm, the coil of 1 160 mm in diameter and the inductance pipe of 102 mm in diameter were confirmed according to the simulated electric field between the inductance and the inner shield of PTL and windings. By numerically simulating the equivalent circuit of spiral water PTL composed of inductance and inner shield, the transmitting time of 349 ns was obtained, which was larger than the half -peak breadth of main pulse. Duri
2008,
20.
Abstract:
Beam diagnositic control system for the heavy-ion cancer therapy project at the Heavy Ion Research Facility in Lanzhou(HIRFL) has been designed and constructed in the Institute of Modern Physics, Chinese Academy of Sciences. The system was developed on the basis of the PXI bus technology and LabVIEW, including beam intensity monitoring, radiation dose monitoring, and monitoring of scanning magnets’ power supplies. System tests and clinical operations show that this control system could meet basic requirements of the heavy-ion cancer therapy, such as radiation dose control and safety protection.
Beam diagnositic control system for the heavy-ion cancer therapy project at the Heavy Ion Research Facility in Lanzhou(HIRFL) has been designed and constructed in the Institute of Modern Physics, Chinese Academy of Sciences. The system was developed on the basis of the PXI bus technology and LabVIEW, including beam intensity monitoring, radiation dose monitoring, and monitoring of scanning magnets’ power supplies. System tests and clinical operations show that this control system could meet basic requirements of the heavy-ion cancer therapy, such as radiation dose control and safety protection.
