Email alert
RSS2011 Vol. 23, No. 03
Recommend Articles
Display Method:
2011,
23.
Abstract:
A Schwarzschild microscope at 18.2 nm for ultra-fast laser produced plasma diagnosis is developed. According to the requirements of plasma diagnosis, the microscope is designed for numerical aperture of 0.1 and magnification of 10. It is found that spatial resolution of the designed objective achieves 1 250 lp/mm within the field of ±1 mm with respect to the calculation of modular transfer function. Based on the working wavelength and incidence angle of light, the Mo/Si multilayer film with period of 9.509 nm and layer number of 30 is designed and the coatings are deposited with magnetron sputtering. The reflectivity of the developed optical elements at 18.2 nm is about 30%. In order to demonstrate the resolution of microscope, a 24 lp/mm copper grid backlit by laser produced plasma is im
A Schwarzschild microscope at 18.2 nm for ultra-fast laser produced plasma diagnosis is developed. According to the requirements of plasma diagnosis, the microscope is designed for numerical aperture of 0.1 and magnification of 10. It is found that spatial resolution of the designed objective achieves 1 250 lp/mm within the field of ±1 mm with respect to the calculation of modular transfer function. Based on the working wavelength and incidence angle of light, the Mo/Si multilayer film with period of 9.509 nm and layer number of 30 is designed and the coatings are deposited with magnetron sputtering. The reflectivity of the developed optical elements at 18.2 nm is about 30%. In order to demonstrate the resolution of microscope, a 24 lp/mm copper grid backlit by laser produced plasma is im
2011,
23.
Abstract:
Tunable transversely excited atmospheric-pressure (TEA) CO2 laser has potential applications in laser radar, laser chemistry and laser propulsion. A new type of preionizer used in tunable TEA CO2 laser was investigated. With the means of grating line selection, tunable laser output was realized by grating resonator. On the condition that the output coupling efficiency is 50% and the pressure is 40 kPa, the maximal electro-optical efficiency of 10P(20),10R(20),9P(20) and 9R(20) lines is 9.5%, 9.7%, 9.8% and 9.8%, respectively. When the gas pressure is 30 kPa and the output coupling efficiency is 50%, the repetition rate is 190 Hz of the highest value. At the same time, the average power of 10P(20),10R(20),9P(20) and 9R(20) lines is 332, 321, 340 and 338 W, respectively
Tunable transversely excited atmospheric-pressure (TEA) CO2 laser has potential applications in laser radar, laser chemistry and laser propulsion. A new type of preionizer used in tunable TEA CO2 laser was investigated. With the means of grating line selection, tunable laser output was realized by grating resonator. On the condition that the output coupling efficiency is 50% and the pressure is 40 kPa, the maximal electro-optical efficiency of 10P(20),10R(20),9P(20) and 9R(20) lines is 9.5%, 9.7%, 9.8% and 9.8%, respectively. When the gas pressure is 30 kPa and the output coupling efficiency is 50%, the repetition rate is 190 Hz of the highest value. At the same time, the average power of 10P(20),10R(20),9P(20) and 9R(20) lines is 332, 321, 340 and 338 W, respectively
2011,
23.
Abstract:
A new type of X-ray diode (XRD-Ⅱ) with ultrafast response time was developed. XRD-Ⅱ detector was improved on the basis of old XRD (XRD-Ⅰ), and its performances were studied on the 8ps laser facility. The results show that XRD-Ⅱ has excellent high-voltage tolerance (to 6 kV) and super-fast response time ( rise time is about 40 ps, and full width at half maximum (FWHM) is about 80 ps when bias voltage is 5 kV). The detector calibration was carried out on Beijing synchrotron radiation facility, which shows that the detector’s sensitivity has not deteriorated.
A new type of X-ray diode (XRD-Ⅱ) with ultrafast response time was developed. XRD-Ⅱ detector was improved on the basis of old XRD (XRD-Ⅰ), and its performances were studied on the 8ps laser facility. The results show that XRD-Ⅱ has excellent high-voltage tolerance (to 6 kV) and super-fast response time ( rise time is about 40 ps, and full width at half maximum (FWHM) is about 80 ps when bias voltage is 5 kV). The detector calibration was carried out on Beijing synchrotron radiation facility, which shows that the detector’s sensitivity has not deteriorated.
2011,
23.
Abstract:
The multilayer graded density carbon aerogel target was fabricated, which is considered to be an excellent unique target for ICF experiments and shock wave research. By polymerization reaction of resorcinol and formaldehyde and via a self-made flexible mould, a series of carbon aerogel unit sheets were obtained. Their thickness ranges from 100 to 580 μm and density ranges from 50 to 400 mg·cm-3. With low density (10 mg·cm-3) SiO2 aerogel as the bonding agent, a 5-layer graded density carbon aerogel target was fabricated. This work was focused on the microstructure of C/SiO2 aerogel interface. Scanning electron microscopy, X-ray phase contrast imaging method were used to observe the monolithic structure of the multilayer target and characterize the surfac
The multilayer graded density carbon aerogel target was fabricated, which is considered to be an excellent unique target for ICF experiments and shock wave research. By polymerization reaction of resorcinol and formaldehyde and via a self-made flexible mould, a series of carbon aerogel unit sheets were obtained. Their thickness ranges from 100 to 580 μm and density ranges from 50 to 400 mg·cm-3. With low density (10 mg·cm-3) SiO2 aerogel as the bonding agent, a 5-layer graded density carbon aerogel target was fabricated. This work was focused on the microstructure of C/SiO2 aerogel interface. Scanning electron microscopy, X-ray phase contrast imaging method were used to observe the monolithic structure of the multilayer target and characterize the surfac
2011,
23.
Abstract:
An imaging-velocity interferometer system for any reflector (VISAR) has been implemented at the “Heaven-I” excimer laser system, which is applied to laser-driven shock experiments as a method for equation of state (EOS) measurement. It contains three parts: input system, imagingrelay system and interferometer system, and a single longitudinal mode laser with 532 nm wavelength is used as the probe light. The imaging VISAR performs at spatial resolutions better than 10 μm. In the experiment with a single-step aluminium target, the shock velocity and the free surface velocity could be measured simultaneously．
An imaging-velocity interferometer system for any reflector (VISAR) has been implemented at the “Heaven-I” excimer laser system, which is applied to laser-driven shock experiments as a method for equation of state (EOS) measurement. It contains three parts: input system, imagingrelay system and interferometer system, and a single longitudinal mode laser with 532 nm wavelength is used as the probe light. The imaging VISAR performs at spatial resolutions better than 10 μm. In the experiment with a single-step aluminium target, the shock velocity and the free surface velocity could be measured simultaneously．
2011,
23.
Abstract:
Carbon aerogel(CA) was prepared by the polycondensation of resorcinol (R) and formaldehyde(F) and then activated by CO2 flow. XRD analysis indicates that in the process of activation, CO2 infiltrates into the network of CA and weakens the (002) and (100) peaks. SEM analysis shows that the CO2 activation does not destroy the framework of CA but adds a great number of nano miropores, and accordingly the specific surface area and micropore proportion of CA are greatly improved. Electrochemical characterization was performed using cyclic voltammetry and chronopotentiometry in 1 mol/L KOH aqueous solution electrolyte. The CA electrode with and without activation has a stable electrochemistry performance and preferable reversibility. The specific capacitance of C
Carbon aerogel(CA) was prepared by the polycondensation of resorcinol (R) and formaldehyde(F) and then activated by CO2 flow. XRD analysis indicates that in the process of activation, CO2 infiltrates into the network of CA and weakens the (002) and (100) peaks. SEM analysis shows that the CO2 activation does not destroy the framework of CA but adds a great number of nano miropores, and accordingly the specific surface area and micropore proportion of CA are greatly improved. Electrochemical characterization was performed using cyclic voltammetry and chronopotentiometry in 1 mol/L KOH aqueous solution electrolyte. The CA electrode with and without activation has a stable electrochemistry performance and preferable reversibility. The specific capacitance of C
2011,
23.
Abstract:
The effect of different substrates and different fluorides are studied to develop low loss, high-performance 193 nm fluoride antireflection coatings. Different fluoride antireflection coatings are deposited by a molybdenum boat evaporation process on JGS1 substrates, and the thickness of the coatings is controlled by a 1/3 baffle with pre-coating technology. Experimental results and analyses show that all of these coatings have a low residual reflectivity and small optical loss, and the optical loss at 193 nm is mainly determined by the high refractive index film. Based on these studies, an LaF3/AlF3 193 nm antireflection coating is designed and deposited. Its residual reflectivity is less than 0.14%, single-sided transmittance is 93.85%, total loss is about 6% and RMS surface roughness is
The effect of different substrates and different fluorides are studied to develop low loss, high-performance 193 nm fluoride antireflection coatings. Different fluoride antireflection coatings are deposited by a molybdenum boat evaporation process on JGS1 substrates, and the thickness of the coatings is controlled by a 1/3 baffle with pre-coating technology. Experimental results and analyses show that all of these coatings have a low residual reflectivity and small optical loss, and the optical loss at 193 nm is mainly determined by the high refractive index film. Based on these studies, an LaF3/AlF3 193 nm antireflection coating is designed and deposited. Its residual reflectivity is less than 0.14%, single-sided transmittance is 93.85%, total loss is about 6% and RMS surface roughness is
2011,
23.
Abstract:
Diagnosing conditions of compressed fuel is a critical aspect of ICF capsule implosion experiments. A common diagnostic technique is to add a small concentration of high- or mid-Z dopant to the fuel, and measure the emission from the dopant either spectroscopically or by imaging. With radiative hydrodynamic simulations and post-processing of X-ray imaging for implosions, the designs of the fuel capsule are optimized, and the effects of tracer in fuel on X-ray diagnostics of implosion are analyzed. The results show that for the capsule of D2 fuel doped with argon at about 1% atomic fraction, although the implosion yield reduces by about 15%, the X-ray intensity of fuel increases by 50 times and the size of X-ray imaging is enlarged by about 30%, which is beneficial to the diagnosis of the
Diagnosing conditions of compressed fuel is a critical aspect of ICF capsule implosion experiments. A common diagnostic technique is to add a small concentration of high- or mid-Z dopant to the fuel, and measure the emission from the dopant either spectroscopically or by imaging. With radiative hydrodynamic simulations and post-processing of X-ray imaging for implosions, the designs of the fuel capsule are optimized, and the effects of tracer in fuel on X-ray diagnostics of implosion are analyzed. The results show that for the capsule of D2 fuel doped with argon at about 1% atomic fraction, although the implosion yield reduces by about 15%, the X-ray intensity of fuel increases by 50 times and the size of X-ray imaging is enlarged by about 30%, which is beneficial to the diagnosis of the
2011,
23.
Abstract:
Cu nanowire array targets have been fabricated with anodic aluminum oxide(AAO) template by pulsed electrodeposition, and characterized by scanning electron microscopy(SEM), energy-dispersive X-ray spectroscopy(EDS) and X-ray diffraction(XRD). It is found that the mean diameter of Cu nanowires is larger than the mean pore size of AAO template by 32%, and the length is shortened by 5% after the removal of the template. The specimen after a deposition time of 2 000 s was characterized for length distribution of Cu nanowires. The length of Cu nanowires increases as the distance to the center of the template increases. The production of Cu Kα photons from the interaction of ultrashort pulse laser with the targets was measured. It becomes larger with the mean length of Cu nanowires increasing f
Cu nanowire array targets have been fabricated with anodic aluminum oxide(AAO) template by pulsed electrodeposition, and characterized by scanning electron microscopy(SEM), energy-dispersive X-ray spectroscopy(EDS) and X-ray diffraction(XRD). It is found that the mean diameter of Cu nanowires is larger than the mean pore size of AAO template by 32%, and the length is shortened by 5% after the removal of the template. The specimen after a deposition time of 2 000 s was characterized for length distribution of Cu nanowires. The length of Cu nanowires increases as the distance to the center of the template increases. The production of Cu Kα photons from the interaction of ultrashort pulse laser with the targets was measured. It becomes larger with the mean length of Cu nanowires increasing f
2011,
23.
Abstract:
Dual layer Polystyrene(PS)-poly-4-methyl-1-pentene(PMP) foam with thickness of 1.5 mm, used in Rayleigh-Taylor hydrodynamic instability experiments, was accurately cut employing femtosecond laser irradiation with 800 nm central wavelength, 120 fs duration, 1 kHz repetition rate focused by microscopic objective(5×, NA=0.14). During the cutting, the manner of uniform step descending of laser focus and processing parameters with average incident power of 30 mW, cutting speed of 300 μm/s were adopted. Compared with the case of nanosecond laser cutting, detrimental distortion and delamination of the dual heterogeneous layer around the femtosecond laser irradiated zone were effectively avoided. Uniform cutting edge and smooth facet were also obtained, with maximal cutting thickness exceeding
Dual layer Polystyrene(PS)-poly-4-methyl-1-pentene(PMP) foam with thickness of 1.5 mm, used in Rayleigh-Taylor hydrodynamic instability experiments, was accurately cut employing femtosecond laser irradiation with 800 nm central wavelength, 120 fs duration, 1 kHz repetition rate focused by microscopic objective(5×, NA=0.14). During the cutting, the manner of uniform step descending of laser focus and processing parameters with average incident power of 30 mW, cutting speed of 300 μm/s were adopted. Compared with the case of nanosecond laser cutting, detrimental distortion and delamination of the dual heterogeneous layer around the femtosecond laser irradiated zone were effectively avoided. Uniform cutting edge and smooth facet were also obtained, with maximal cutting thickness exceeding
2011,
23.
Abstract:
The Kα X-ray emission from femtosecond laser-material interactions has been measured with a dispersionless Kα X-ray spectrometer in front of and behind the Cu foil targets. The conversion efficiency from laser energy to Kα photons was obtained. Laser pulse width was typically 33 fs and intensity was kept within the range of 1017 W/cm2 to 1019 W/cm2 by changing laser energy from 50 mJ to 5 J. The experimental results show that the intensity of the Kα X-ray increases with the laser energy， and the X-ray background behind the target is better than that in front of the target. With a 100 μm-thick foil, the conversion efficiency is 2.2×10-5.
The Kα X-ray emission from femtosecond laser-material interactions has been measured with a dispersionless Kα X-ray spectrometer in front of and behind the Cu foil targets. The conversion efficiency from laser energy to Kα photons was obtained. Laser pulse width was typically 33 fs and intensity was kept within the range of 1017 W/cm2 to 1019 W/cm2 by changing laser energy from 50 mJ to 5 J. The experimental results show that the intensity of the Kα X-ray increases with the laser energy， and the X-ray background behind the target is better than that in front of the target. With a 100 μm-thick foil, the conversion efficiency is 2.2×10-5.
2011,
23.
Abstract:
Based on the estimated parameters of fast ignition, the requirements for laser-beam power intensity and energy are used to analyze the possibility of realizing fast ignition by coherent combination and noncoherent combination. The practical distorted wavefront is considered to analyze the farfield focal spot. Non-coherent combination needs more beams for energy requirement and to limit angle drifting in ±2 μrad through improving laser driver’s stability. Coherent combination is beneficial for achieving smaller focal spot and higher power intensity, simultaneously reducing the requirement of energy, but single beam wavefront correction can not improve the power intensity in this method, which leads to combined wavefront correction of the total clear aperture with complex monitoring a
Based on the estimated parameters of fast ignition, the requirements for laser-beam power intensity and energy are used to analyze the possibility of realizing fast ignition by coherent combination and noncoherent combination. The practical distorted wavefront is considered to analyze the farfield focal spot. Non-coherent combination needs more beams for energy requirement and to limit angle drifting in ±2 μrad through improving laser driver’s stability. Coherent combination is beneficial for achieving smaller focal spot and higher power intensity, simultaneously reducing the requirement of energy, but single beam wavefront correction can not improve the power intensity in this method, which leads to combined wavefront correction of the total clear aperture with complex monitoring a
2011,
23.
Abstract:
The theoretical model of signal-to-noise ratio(SNR) in the interferometric imaging system with rotating diffuser is proposed by means of statistical optics. According to the theoretical model, the relations between parameters of rotating diffuser, coherent time and SNR of the imaging system are analyzed numerically and demonstrated experimentally. It is shown that the rotating diffuser reduces coherent time, increases the number of unrelated speckle noises in gathering time, and thus reduces the speckle noise. An increasing in roughness or rotating frequency of diffuser or a decreasing in coherent length leads to a decreasing in coherent time. To obtain high SNR, the rotating diffuser should be well controlled so that the rotating period is approximately equal to the exposure time of CCD,
The theoretical model of signal-to-noise ratio(SNR) in the interferometric imaging system with rotating diffuser is proposed by means of statistical optics. According to the theoretical model, the relations between parameters of rotating diffuser, coherent time and SNR of the imaging system are analyzed numerically and demonstrated experimentally. It is shown that the rotating diffuser reduces coherent time, increases the number of unrelated speckle noises in gathering time, and thus reduces the speckle noise. An increasing in roughness or rotating frequency of diffuser or a decreasing in coherent length leads to a decreasing in coherent time. To obtain high SNR, the rotating diffuser should be well controlled so that the rotating period is approximately equal to the exposure time of CCD,
2011,
23.
Abstract:
Because of the electron emission, an electron sheath will appear near the cathode surface of the magnetically insulated transmission line (MITL). When the MITL comes to be stable, the sheath will reach pressure equilibrium. Based on the collisions in the electron sheath, the pressure equilibrium model is rescaled to match particle-in-cell(PIC) simulation results, providing a more accurate function of voltage, anode and cathode currents. And the peak error between theoretical and simulation results decreases from 9% to 3% in the saturated flow state. The parameter α is fitted as a function of the working voltage, which is in effect when the working voltage ranges from 2 to 7 MV with the idealized MITL.
Because of the electron emission, an electron sheath will appear near the cathode surface of the magnetically insulated transmission line (MITL). When the MITL comes to be stable, the sheath will reach pressure equilibrium. Based on the collisions in the electron sheath, the pressure equilibrium model is rescaled to match particle-in-cell(PIC) simulation results, providing a more accurate function of voltage, anode and cathode currents. And the peak error between theoretical and simulation results decreases from 9% to 3% in the saturated flow state. The parameter α is fitted as a function of the working voltage, which is in effect when the working voltage ranges from 2 to 7 MV with the idealized MITL.
2011,
23.
Abstract:
The main objective of this work is to study the computation of coupling on wires enclosed in the cavity with apertures by exciting sources. The analytical approach is rigorous and slow implementations. The numerical technique is too approximate to be useful. This paper presents a semi-analytical and semi-numerical approach based on method of moments-Green’s function (MoM-GF) technique and BLT equation. The MoM-GF technique is sufficiently accurate to simulate the equivalent magnetic flux to give the electromagnetic field in the cavity. And the formulas to compute the induced voltage and induced current of the two wire lines, terminations are derived employing the BLT equation based on Taylor model. The simulation on electric field shielding effectiveness of the cavity with apertures is co
The main objective of this work is to study the computation of coupling on wires enclosed in the cavity with apertures by exciting sources. The analytical approach is rigorous and slow implementations. The numerical technique is too approximate to be useful. This paper presents a semi-analytical and semi-numerical approach based on method of moments-Green’s function (MoM-GF) technique and BLT equation. The MoM-GF technique is sufficiently accurate to simulate the equivalent magnetic flux to give the electromagnetic field in the cavity. And the formulas to compute the induced voltage and induced current of the two wire lines, terminations are derived employing the BLT equation based on Taylor model. The simulation on electric field shielding effectiveness of the cavity with apertures is co
2011,
23.
Abstract:
A high power accelerator which can simultaneously produce three electron beams was developed. It is made up of primary energy storage system, spiral-strip transformer, pulse forming line using deionized water as insulation and diode with three cathodes. The three cathodes are stretched into three separate drift tubes, which can isolate the electromagnetic force between the produced electron beams. When a single cathode is connected to the diode, the accelerator can produce over 50 GW electric power; when three cathodes are connected to the diode, three electron beams each with over 10 GW electric power are produced. When the accelerator is used to drive three microwave tubes, three microwaves of 1.0 GW (L-band MILO), 1.0 GW(S-band MILO) and 300 MW(C-band VCO) can be obtained.
A high power accelerator which can simultaneously produce three electron beams was developed. It is made up of primary energy storage system, spiral-strip transformer, pulse forming line using deionized water as insulation and diode with three cathodes. The three cathodes are stretched into three separate drift tubes, which can isolate the electromagnetic force between the produced electron beams. When a single cathode is connected to the diode, the accelerator can produce over 50 GW electric power; when three cathodes are connected to the diode, three electron beams each with over 10 GW electric power are produced. When the accelerator is used to drive three microwave tubes, three microwaves of 1.0 GW (L-band MILO), 1.0 GW(S-band MILO) and 300 MW(C-band VCO) can be obtained.
2011,
23.
Abstract:
The basic theory and some key technologies of the air-cored transformer in design are introduced, and a helical line air-cored transformer with high turn ratio is designed. The primary winding is a 3-turn copper sheet, and the secondary winding is a conical winding with 1 800 turns. The output voltage of the transformer is simulated by Pspice, and then the experiment is done. The results of testing show that, the output voltage of the air-cored transformer is up to 900 kV, when the charge voltage of the primary capacitor is 2 400 V.
The basic theory and some key technologies of the air-cored transformer in design are introduced, and a helical line air-cored transformer with high turn ratio is designed. The primary winding is a 3-turn copper sheet, and the secondary winding is a conical winding with 1 800 turns. The output voltage of the transformer is simulated by Pspice, and then the experiment is done. The results of testing show that, the output voltage of the air-cored transformer is up to 900 kV, when the charge voltage of the primary capacitor is 2 400 V.
2011,
23.
Abstract:
Side focusing fields generated by offset-pole periodic cusped magnets for the propagation of sheet electron beams have been investigated theoretically and numerically. Increasing the offset length, decreasing the width of beam channel, or increasing the axial length of magnet poles will increase the strength of the side focusing fields, without changing their transverse gradient. Increasing the height of beam channel or the thickness of magnet poles will make the side focusing fields weaker, but of a better linearity. It is recommended that gradient match between the focusing force and the defocusing force acting on the sheet electron beam be made before the amplitude match between them for simplicity. The height of beam channel and the axial length of magnet poles should be chosen careful
Side focusing fields generated by offset-pole periodic cusped magnets for the propagation of sheet electron beams have been investigated theoretically and numerically. Increasing the offset length, decreasing the width of beam channel, or increasing the axial length of magnet poles will increase the strength of the side focusing fields, without changing their transverse gradient. Increasing the height of beam channel or the thickness of magnet poles will make the side focusing fields weaker, but of a better linearity. It is recommended that gradient match between the focusing force and the defocusing force acting on the sheet electron beam be made before the amplitude match between them for simplicity. The height of beam channel and the axial length of magnet poles should be chosen careful
2011,
23.
Abstract:
The dynamics behaviors of high power long pulse foilless diode were analyzed on the basis of diode design theory. The result indicated that the back flowing electrons must be cut off, and can not bombard the dielectric surface and the wall of the foil-less diode tube. In the experiment on the diode used on a long pulse linear transformer driver, through shielding design for the diode’s cathode structure, a long pulse high power annular electron beam with power up to 5 GW was obtained with repetition frequency of 25 Hz and energy transmission efficiency over 95%.
The dynamics behaviors of high power long pulse foilless diode were analyzed on the basis of diode design theory. The result indicated that the back flowing electrons must be cut off, and can not bombard the dielectric surface and the wall of the foil-less diode tube. In the experiment on the diode used on a long pulse linear transformer driver, through shielding design for the diode’s cathode structure, a long pulse high power annular electron beam with power up to 5 GW was obtained with repetition frequency of 25 Hz and energy transmission efficiency over 95%.
2011,
23.
Abstract:
The multi-active zone tunnel regeneration semiconductor laser can fully use the transmission capability of multi-mode optical fiber, but its steady-state thermal property is unclear and limits its applications in high power area. The steady-state thermal property of the laser is studied with ANSYS and Fourier’s theorem, and temperature profiles of the active zones are obtained. An estimation method of active zone’s temperature and the way to reduce the laser’s thermal resistance are presented. Calculation results show that the multi-active zone tunnel regeneration semiconductor laser can reach higher power than the single-active zone semiconductor laser in CW mode．
The multi-active zone tunnel regeneration semiconductor laser can fully use the transmission capability of multi-mode optical fiber, but its steady-state thermal property is unclear and limits its applications in high power area. The steady-state thermal property of the laser is studied with ANSYS and Fourier’s theorem, and temperature profiles of the active zones are obtained. An estimation method of active zone’s temperature and the way to reduce the laser’s thermal resistance are presented. Calculation results show that the multi-active zone tunnel regeneration semiconductor laser can reach higher power than the single-active zone semiconductor laser in CW mode．
2011,
23.
Abstract:
When light is so weak that a single photon is emitted, the single photon can be detected only in photon counting mode. The avalanche photodiode (APD) based on impact ionization effect is used as detector to construct an experimental system of photon counting imaging in low light level environment. The hardware of the system is composed of a single photon counter based on APD, a computer, a low light level illuminometer, two two-dimensional guides, a controller, an obscure box, and so on. The software of the controller is programmed in Altera’s Quartus environment. It controls the movement of the guides. Human machine interface is developed by VC++ software, with the functions of data acquisition and processing, system functions control, and photon counting image display. The photon counti
When light is so weak that a single photon is emitted, the single photon can be detected only in photon counting mode. The avalanche photodiode (APD) based on impact ionization effect is used as detector to construct an experimental system of photon counting imaging in low light level environment. The hardware of the system is composed of a single photon counter based on APD, a computer, a low light level illuminometer, two two-dimensional guides, a controller, an obscure box, and so on. The software of the controller is programmed in Altera’s Quartus environment. It controls the movement of the guides. Human machine interface is developed by VC++ software, with the functions of data acquisition and processing, system functions control, and photon counting image display. The photon counti
2011,
23.
Abstract:
The probe is usually corroded by chemical solutions in permittivity measurements. An apparatus which realizes wide-band online non-contact measurement is proposed to resolve this problem. S-parameters are obtained by full-wave simulations with the proposed coaxial apparatus to reconstruct the permittivities of several solutions. Moreover, the effective permittivities are achieved by means of genetic algorithm (GA) under prearranged measurement errors of 2%. The reconstructed results of the effective permittivies of chemical solutions agree well with previously published data with relative errors of less than 5%, showing the coaxial apparatus’ obvious advantages over conventional apparatuses.
The probe is usually corroded by chemical solutions in permittivity measurements. An apparatus which realizes wide-band online non-contact measurement is proposed to resolve this problem. S-parameters are obtained by full-wave simulations with the proposed coaxial apparatus to reconstruct the permittivities of several solutions. Moreover, the effective permittivities are achieved by means of genetic algorithm (GA) under prearranged measurement errors of 2%. The reconstructed results of the effective permittivies of chemical solutions agree well with previously published data with relative errors of less than 5%, showing the coaxial apparatus’ obvious advantages over conventional apparatuses.
2011,
23.
Abstract:
This paper presents a mask fabrication method, which uses laser interference lithography to prepare interference patterns, and then transfers the patterns to the chromium layer by ion beam etching (IBE) to gain the mask. A series of rigorous numerical simulations have been done on the light transmission rate of the mask and two parameters that may affect the contrast of interference patterns for parameter optimization. An interference lithography system was constructed with 257 nm laser light source, and patterns with feature size of 100 nm were developed. Then masks with period of 200 nm and line width of 100 nm were obtained by IBE.
This paper presents a mask fabrication method, which uses laser interference lithography to prepare interference patterns, and then transfers the patterns to the chromium layer by ion beam etching (IBE) to gain the mask. A series of rigorous numerical simulations have been done on the light transmission rate of the mask and two parameters that may affect the contrast of interference patterns for parameter optimization. An interference lithography system was constructed with 257 nm laser light source, and patterns with feature size of 100 nm were developed. Then masks with period of 200 nm and line width of 100 nm were obtained by IBE.
2011,
23.
Abstract:
In order to evaluate single event upsets(SEUs) in SRAM-based FPGAs and to find the sensitive resource in configuration memory, a heavy ions irradiation experiment was carried out on a Xilinx FPGAs device XCV300PQ240. The experiment was conducted to gain the static SEU cross section and classify the SEUs in configurations memory according to different resource uses. The results demonstrate that the inter-memory of SRAM-based FPGAs is extremely sensitive to heavy-ion-induced SEUs. The LUT and routing resources are the main source of SEUs in the configuration memory, which covers more than 97.46% of the total upsets. The SEU sensitivity of various resources is different. The IOB control bit and LUT elements are more sensitive, and more attention should be paid to the LUT elements in radiatio
In order to evaluate single event upsets(SEUs) in SRAM-based FPGAs and to find the sensitive resource in configuration memory, a heavy ions irradiation experiment was carried out on a Xilinx FPGAs device XCV300PQ240. The experiment was conducted to gain the static SEU cross section and classify the SEUs in configurations memory according to different resource uses. The results demonstrate that the inter-memory of SRAM-based FPGAs is extremely sensitive to heavy-ion-induced SEUs. The LUT and routing resources are the main source of SEUs in the configuration memory, which covers more than 97.46% of the total upsets. The SEU sensitivity of various resources is different. The IOB control bit and LUT elements are more sensitive, and more attention should be paid to the LUT elements in radiatio
2011,
23.
Abstract:
A kind of photodetector was developed by microchannel plate (MCP) evaporated with Au photocathode. According to the resistive and capacitive characteristics of MCP, a method for measuring the energy dependent sensitivity was established. The response of the detector for incident energy from 2.1 to 6.0 keV was calibrated on the 3B3 medium energy X-ray beamline. An AXUV-100 silicon diode, which was produced by IRD Company and absolutely calibrated by NIST, was used as the secondary standard detector to calibrate two Au-coated-MCP detectors with 25 and 100 nm thick Au films, respectively. The experimental result, shows that, the elements’ absorption line and the thickness of Au film are very important to the quantum efficiency, and the sensitivity of the detector with 100 nm thick Au film is
A kind of photodetector was developed by microchannel plate (MCP) evaporated with Au photocathode. According to the resistive and capacitive characteristics of MCP, a method for measuring the energy dependent sensitivity was established. The response of the detector for incident energy from 2.1 to 6.0 keV was calibrated on the 3B3 medium energy X-ray beamline. An AXUV-100 silicon diode, which was produced by IRD Company and absolutely calibrated by NIST, was used as the secondary standard detector to calibrate two Au-coated-MCP detectors with 25 and 100 nm thick Au films, respectively. The experimental result, shows that, the elements’ absorption line and the thickness of Au film are very important to the quantum efficiency, and the sensitivity of the detector with 100 nm thick Au film is
2011,
23.
Abstract:
The proposed TRIUMF ARIEL project plans to build a 50 MeV electron linac at 10 mA to produce radioactive ion beams through photo-fission. The electron linac includes two major parts: injector section and driver linac. The injector section is required to accelerate electron beams from 100 keV to 10 MeV, and the following driver linac boosts the energy from 10 MeV to 50 MeV. The electron initial energy from the thermionic gun is 100 keV and 171 ps bunch length with a repetition rate of 650 MHz. Several variants of configurations have been proposed and studied to get an optimized solution. Simulations show that with careful design and specific input parameters after the gun, the beam at 50 MeV can be bunched into 11.75 ps (5.5° at 1.3 GHz) with the maximum beam size inside the superconducti
The proposed TRIUMF ARIEL project plans to build a 50 MeV electron linac at 10 mA to produce radioactive ion beams through photo-fission. The electron linac includes two major parts: injector section and driver linac. The injector section is required to accelerate electron beams from 100 keV to 10 MeV, and the following driver linac boosts the energy from 10 MeV to 50 MeV. The electron initial energy from the thermionic gun is 100 keV and 171 ps bunch length with a repetition rate of 650 MHz. Several variants of configurations have been proposed and studied to get an optimized solution. Simulations show that with careful design and specific input parameters after the gun, the beam at 50 MeV can be bunched into 11.75 ps (5.5° at 1.3 GHz) with the maximum beam size inside the superconducti
2011,
23.
Abstract:
Different turbid media have different optical parameters such as absorption coefficient, scattering coefficient, anisotropic factor and refractive index. Monte Carlo method was used to simulate the influence of optical parameters on the transmitted photons for light transmitted through different atmospheres. The result shows that the temporal distribution of transmitted light has two peaks corresponding to ballistic photons and diffuse photons, respectively. Every optical parameter affects both the number and time range of ballistic photons, snake photons and diffuse photons. From the angle of statistical simulation, it is explained why atmosphere imaging is difficult when the refractive index of atmosphere is large.
Different turbid media have different optical parameters such as absorption coefficient, scattering coefficient, anisotropic factor and refractive index. Monte Carlo method was used to simulate the influence of optical parameters on the transmitted photons for light transmitted through different atmospheres. The result shows that the temporal distribution of transmitted light has two peaks corresponding to ballistic photons and diffuse photons, respectively. Every optical parameter affects both the number and time range of ballistic photons, snake photons and diffuse photons. From the angle of statistical simulation, it is explained why atmosphere imaging is difficult when the refractive index of atmosphere is large.
2011,
23.
Abstract:
The cumulative ion saturation currents on a cylindrical probe are measured by using a negatively biased, water-cooled cylindrical electrostatic probe sweeping with a fixed speed perpendicularly across a laminar argon plasma jet, and the radial distribution of local ion saturation current density is then obtained by use of the Abel inversion. The radial distribution of the jet impact pressure is also measured dynamically using a water-cooled pressure probe. Based on the measured profiles of the local ion saturation current density and impact pressure and using related theoretical relations, the radial distribution of the plasma jet temperature is deduced. Additionally, the spectroscopic method based on the relativeintensity of spectral lines is employed to measure the plasma jet temperatu
The cumulative ion saturation currents on a cylindrical probe are measured by using a negatively biased, water-cooled cylindrical electrostatic probe sweeping with a fixed speed perpendicularly across a laminar argon plasma jet, and the radial distribution of local ion saturation current density is then obtained by use of the Abel inversion. The radial distribution of the jet impact pressure is also measured dynamically using a water-cooled pressure probe. Based on the measured profiles of the local ion saturation current density and impact pressure and using related theoretical relations, the radial distribution of the plasma jet temperature is deduced. Additionally, the spectroscopic method based on the relativeintensity of spectral lines is employed to measure the plasma jet temperatu
2011,
23.
Abstract:
The intense pulsed emission property of the large area carbon nanotube(CNT) cathode made by dipping method has been researched on the 2 MeV linear induction accelerator (LIA) injector. Results show that the CNT cathode has a capability of emitting an intense electron beam and achieving high emission current density under pulsed high voltage. The mechanism of electron emission in the CNT cathode is plasma-induced field emission. In the experiment, the maximal emission currents were 350 A on the sampling resistance ring at cathode and 167 A collected by the Faraday cup at anode. The highest emission current density at cathode was 19.4 A/cm2.
The intense pulsed emission property of the large area carbon nanotube(CNT) cathode made by dipping method has been researched on the 2 MeV linear induction accelerator (LIA) injector. Results show that the CNT cathode has a capability of emitting an intense electron beam and achieving high emission current density under pulsed high voltage. The mechanism of electron emission in the CNT cathode is plasma-induced field emission. In the experiment, the maximal emission currents were 350 A on the sampling resistance ring at cathode and 167 A collected by the Faraday cup at anode. The highest emission current density at cathode was 19.4 A/cm2.
2011,
23.
Abstract:
The reactor neutron irradiation on three types of optocouplers was experimentally studied. Current transfer ratio decreased and saturation voltage increased due to displacement damage in the range of neutron fluence from 3×1011 cm-2 to 5×1012cm-2. The degradation of light emitting diode(LED) optical power, phototransistor gain and photoresponsivity all contribute to the degradation of optocouplers’ performance. The optocouplers with PIN as detector have a much lower current transfer ratio but they are more resistant to displacement damage compared with optocouplers with phototransistor as detector on condition that both kinds of optocouplers use identical LEDs. The radiation tolerance of optocouplers with heterojunction LED is two orders of ma
The reactor neutron irradiation on three types of optocouplers was experimentally studied. Current transfer ratio decreased and saturation voltage increased due to displacement damage in the range of neutron fluence from 3×1011 cm-2 to 5×1012cm-2. The degradation of light emitting diode(LED) optical power, phototransistor gain and photoresponsivity all contribute to the degradation of optocouplers’ performance. The optocouplers with PIN as detector have a much lower current transfer ratio but they are more resistant to displacement damage compared with optocouplers with phototransistor as detector on condition that both kinds of optocouplers use identical LEDs. The radiation tolerance of optocouplers with heterojunction LED is two orders of ma
2011,
23.
Abstract:
The beam lifetime is an important parameter which can affect the operation of the storage ring. For Hefei Light Source(HLS), Touschek lifetime is an important factor affecting beam lifetime. To study the Touschek lifetime, the loss of electrons due to the Touschek effect should be detected. The concept of beam lifetime is introduced, and the theory of the Touschek effect is also discussed. The interaction between the lost electrons and vacuum chamber wall is simulated by the Monte Carlo software EGSnrc. The signals of the electron loss due to the Touschek effect are obtained with the plastic scintillation detector and then, sent to the discriminator and the coincidence gate, and finally the count rate is measured with a counter. The results indicate that the loss of electrons due to the To
The beam lifetime is an important parameter which can affect the operation of the storage ring. For Hefei Light Source(HLS), Touschek lifetime is an important factor affecting beam lifetime. To study the Touschek lifetime, the loss of electrons due to the Touschek effect should be detected. The concept of beam lifetime is introduced, and the theory of the Touschek effect is also discussed. The interaction between the lost electrons and vacuum chamber wall is simulated by the Monte Carlo software EGSnrc. The signals of the electron loss due to the Touschek effect are obtained with the plastic scintillation detector and then, sent to the discriminator and the coincidence gate, and finally the count rate is measured with a counter. The results indicate that the loss of electrons due to the To
2011,
23.
Abstract:
A 200 kV high voltage switch power supply has been developed, based on softswitching power supply technology and cascading voltage multiplier. Its working principle and structure are presented. The high voltage switch power supply mainly consists of power convertor, intermediate frequency transformer and high voltage multiplier. Its main indices are high voltage up to 200 kV, output current up to 10 mA, working frequency of 20 kHz, high voltage stability of 1%, voltage ripple coefficient of 2% and continuous working time up to 8 h. The performance of the high voltage switch power supply has met the design requirements．
A 200 kV high voltage switch power supply has been developed, based on softswitching power supply technology and cascading voltage multiplier. Its working principle and structure are presented. The high voltage switch power supply mainly consists of power convertor, intermediate frequency transformer and high voltage multiplier. Its main indices are high voltage up to 200 kV, output current up to 10 mA, working frequency of 20 kHz, high voltage stability of 1%, voltage ripple coefficient of 2% and continuous working time up to 8 h. The performance of the high voltage switch power supply has met the design requirements．
2011,
23.
Abstract:
The crossed undulator is an effective method for polarization control in soft X-ray free electron lasers(FELs). Influencing factors were statistically analyzed for polarization control with a crossed undulator in self amplified spontaneous (SASE) FELs. The effects of the coherence length of radiation, and the relative slippage length and power difference of the two field components were analyzed, and the principles for optimizing an polarization control scheme with a crossed undulator were proposed. These principles are that: the radiation should have good longtitudinal coherence, the relative slippage length of the field components should be short, and the power difference of the two field components should be small. This work provides a theoretical basis for optimization of polarization
The crossed undulator is an effective method for polarization control in soft X-ray free electron lasers(FELs). Influencing factors were statistically analyzed for polarization control with a crossed undulator in self amplified spontaneous (SASE) FELs. The effects of the coherence length of radiation, and the relative slippage length and power difference of the two field components were analyzed, and the principles for optimizing an polarization control scheme with a crossed undulator were proposed. These principles are that: the radiation should have good longtitudinal coherence, the relative slippage length of the field components should be short, and the power difference of the two field components should be small. This work provides a theoretical basis for optimization of polarization
2011,
23.
Abstract:
Based on the linear theory of gyrotron traveling wave amplifier (gyro-TWA) and the boundary condition, the model of the gyro-TWA with reflections at the output port is established. The influence of the reflections on the wave gain rate, the back wave starting length and the back wave starting current for a Ka band TE01 gyro-TWA at fundamental mode is analyzed. The simulating results show that, for the TE01 mode gyro-TWA, the linear growth rate decreases, the starting length and current of the gyro-backward wave oscillation decrease but the starting frequency varies little with the increase of the tapering angle, and the increased reflection may lower the amplifier’s stability to some extent.
Based on the linear theory of gyrotron traveling wave amplifier (gyro-TWA) and the boundary condition, the model of the gyro-TWA with reflections at the output port is established. The influence of the reflections on the wave gain rate, the back wave starting length and the back wave starting current for a Ka band TE01 gyro-TWA at fundamental mode is analyzed. The simulating results show that, for the TE01 mode gyro-TWA, the linear growth rate decreases, the starting length and current of the gyro-backward wave oscillation decrease but the starting frequency varies little with the increase of the tapering angle, and the increased reflection may lower the amplifier’s stability to some extent.
2011,
23.
Abstract:
A rigorous numerical method for the prediction of shielding effectiveness, which adopts the mode-matching technique and the mixed potential integral equation based on the method of moments, has been presented for rectangular metallic enclosure with aperture. Some influence factors, such as aperture thickness, aperture shape, incident polarization direction and high-order modes, are considered. By the numerical simulation of classical models, the high accuracy of this method is verified, and the efficiency of the method is remarkable compared with other numerical algorithms. Furthermore, some valuable conclusions in engineering are obtained: When the polarized direction of the incident wave is parallel to the short side of the rectangular aperture, the coupled energy will attain the maximum
A rigorous numerical method for the prediction of shielding effectiveness, which adopts the mode-matching technique and the mixed potential integral equation based on the method of moments, has been presented for rectangular metallic enclosure with aperture. Some influence factors, such as aperture thickness, aperture shape, incident polarization direction and high-order modes, are considered. By the numerical simulation of classical models, the high accuracy of this method is verified, and the efficiency of the method is remarkable compared with other numerical algorithms. Furthermore, some valuable conclusions in engineering are obtained: When the polarized direction of the incident wave is parallel to the short side of the rectangular aperture, the coupled energy will attain the maximum
2011,
23.
Abstract:
Microwave injection experiments were conducted on the analog-to-digital converter of three inverters to study its response to P-band microwaves of different parameters. The effectiveness and reliability of the experiments were achieved by using the eye figure to test the output performance and the temperature measurement circuit to check the operation stability, and analyzing the influence of different chips and printed circuit boards with statistical test. For injected pulse width above 70 ns, the threshold of the injected microwave power for noise margin of 50% of the signal amplitude is 4 to 6 dBm lower than that for sampling interval change of 10%; the power threshold for 30% sampling interval change is 2 to 3 dB higher than that for 10% change; the maximal nonlinear interference is 40
Microwave injection experiments were conducted on the analog-to-digital converter of three inverters to study its response to P-band microwaves of different parameters. The effectiveness and reliability of the experiments were achieved by using the eye figure to test the output performance and the temperature measurement circuit to check the operation stability, and analyzing the influence of different chips and printed circuit boards with statistical test. For injected pulse width above 70 ns, the threshold of the injected microwave power for noise margin of 50% of the signal amplitude is 4 to 6 dBm lower than that for sampling interval change of 10%; the power threshold for 30% sampling interval change is 2 to 3 dB higher than that for 10% change; the maximal nonlinear interference is 40
2011,
23.
Abstract:
Magnetron structure and quasi magnetron structure (no cathode) are the basic elements of magnetron with diffraction output (MDO). It is the groundwork for studying the mode conversion and transmission in MDO to analyze the dispersion relation of the two types of magnetron structures. Based on the field match method, the dispersion relation of quasimagnetron is obtained, and then the relation between the wave-numbers at π mode resonant points and the geometry parameters in six cavity and two-cavity magnetron and quasimagnetron are quantitatively analyzed by numerical computation respectively. For magnetron structure, when the distance between cathode and anode is unchanged, π mode wave numbers increase with decreasing the radius of resonant cavity; when the radius of resonant cavity i
Magnetron structure and quasi magnetron structure (no cathode) are the basic elements of magnetron with diffraction output (MDO). It is the groundwork for studying the mode conversion and transmission in MDO to analyze the dispersion relation of the two types of magnetron structures. Based on the field match method, the dispersion relation of quasimagnetron is obtained, and then the relation between the wave-numbers at π mode resonant points and the geometry parameters in six cavity and two-cavity magnetron and quasimagnetron are quantitatively analyzed by numerical computation respectively. For magnetron structure, when the distance between cathode and anode is unchanged, π mode wave numbers increase with decreasing the radius of resonant cavity; when the radius of resonant cavity i
2011,
23.
Abstract:
The extended-interaction oscillator with disk-loaded waveguide is presented as a new terahertz vacuum electronic radiation source. The device consists of an input cavity resonator with disk-loaded waveguide, a drift tube and an output cavity. A two and one half dimensional electromagnetic particle-in-cell simulation code is used to investigate it and the results demonstrate that the total length of the slow wave structure, the length of the drift tube and the radius of the output cavity affect the output power and frequency remarkably. It is found that under the condition of the electron beam with voltage 24.85 kV and current 20 mA, peak output power of 1.322 5 W at 755.5 GHz can be generated.
The extended-interaction oscillator with disk-loaded waveguide is presented as a new terahertz vacuum electronic radiation source. The device consists of an input cavity resonator with disk-loaded waveguide, a drift tube and an output cavity. A two and one half dimensional electromagnetic particle-in-cell simulation code is used to investigate it and the results demonstrate that the total length of the slow wave structure, the length of the drift tube and the radius of the output cavity affect the output power and frequency remarkably. It is found that under the condition of the electron beam with voltage 24.85 kV and current 20 mA, peak output power of 1.322 5 W at 755.5 GHz can be generated.
2011,
23.
Abstract:
The influence of unmatched antenna load on resonance characters of quarter wavelength coaxial oscillator, which determines the output pulse spectrum, was analyzed. Based on cascading dual-port microwave network model, the relationship between load reflectance and the spectrum of output pulse was derived by involving the reflectance of unmatched load into thequivalence coupler reflectance. Numerical simulation of the generator, which contains oscillator, coupler and antenna, was performed, showing consistent results with theoretical predictions. As predicted by theory, the spectrum of the radiation pulse creates two secondary peaks around the major peak, which was also observed in the high power experiment performed.
The influence of unmatched antenna load on resonance characters of quarter wavelength coaxial oscillator, which determines the output pulse spectrum, was analyzed. Based on cascading dual-port microwave network model, the relationship between load reflectance and the spectrum of output pulse was derived by involving the reflectance of unmatched load into thequivalence coupler reflectance. Numerical simulation of the generator, which contains oscillator, coupler and antenna, was performed, showing consistent results with theoretical predictions. As predicted by theory, the spectrum of the radiation pulse creates two secondary peaks around the major peak, which was also observed in the high power experiment performed.
2011,
23.
Abstract:
A hexagonal focal-plane array of microstrip antennas with electromagnetic bandgap (EBG) structure is proposed. After an in-depth study of EBG structure to suppress mutual coupling between antennas, a hexagonal seven-element microstrip antenna array with EBG structure for reflector antenna is designed and measured. The results show that the EBG structure can suppress the mutual coupling between array elements, improving the matching condition and circular polarization performance of the antenna array. The hexagonal array with EBG structure is competent for the focal-plane array of reflector antenna.
A hexagonal focal-plane array of microstrip antennas with electromagnetic bandgap (EBG) structure is proposed. After an in-depth study of EBG structure to suppress mutual coupling between antennas, a hexagonal seven-element microstrip antenna array with EBG structure for reflector antenna is designed and measured. The results show that the EBG structure can suppress the mutual coupling between array elements, improving the matching condition and circular polarization performance of the antenna array. The hexagonal array with EBG structure is competent for the focal-plane array of reflector antenna.
2011,
23.
Abstract:
A novel dual-band microstrip antenna which is fed by 50 Ω microstrip line for wireless local area network (WLAN) applications is analyzed and designed. The antenna with slot loaded on the patch for miniaturization can operate on dual-band. The center operating frequencies of the antenna are 2.44 GHz and 5.20 GHz, and the operating frequency bandwidths are 200 MHz and 1.2 GHz, respectively. The proposed antenna has some advantages, such as low profile, simple structure, easy fabrication, low cost and good omnidirectional radiation patterns. The high-band and low-band of the antenna can be adjusted by simply modifying the radiation patches and gap size parameter.
A novel dual-band microstrip antenna which is fed by 50 Ω microstrip line for wireless local area network (WLAN) applications is analyzed and designed. The antenna with slot loaded on the patch for miniaturization can operate on dual-band. The center operating frequencies of the antenna are 2.44 GHz and 5.20 GHz, and the operating frequency bandwidths are 200 MHz and 1.2 GHz, respectively. The proposed antenna has some advantages, such as low profile, simple structure, easy fabrication, low cost and good omnidirectional radiation patterns. The high-band and low-band of the antenna can be adjusted by simply modifying the radiation patches and gap size parameter.
2011,
23.
Abstract:
To develop the evaluation methods of lightning protection system, the high resolution simulation of cloud-to-ground lightning leaders was done based on a 3-D dielectric breakdown model (DBM) in an analytic thunderstorm model, then an evaluation model was established near ground and the evaluation experiment was done. The space resolution is 50 m and the evaluation area resolution is 1 m in the experiment, which could satisfy modeling definition. Using successive overrelaxation method to solve the 3-D DBM, the trace of cloud-to-ground step lightning leaders and potential distribution in space could be gotten. When step lightning leaders arrive at the boundary of evaluation area, 2-D cubic spline method is used to transform the resolution between space and evaluation area. When leader tips a
To develop the evaluation methods of lightning protection system, the high resolution simulation of cloud-to-ground lightning leaders was done based on a 3-D dielectric breakdown model (DBM) in an analytic thunderstorm model, then an evaluation model was established near ground and the evaluation experiment was done. The space resolution is 50 m and the evaluation area resolution is 1 m in the experiment, which could satisfy modeling definition. Using successive overrelaxation method to solve the 3-D DBM, the trace of cloud-to-ground step lightning leaders and potential distribution in space could be gotten. When step lightning leaders arrive at the boundary of evaluation area, 2-D cubic spline method is used to transform the resolution between space and evaluation area. When leader tips a
2011,
23.
Abstract:
The paper presents a three-mirror quasi-optical cavity (TMQOC) high power radiation source, which includes a column slow-wave grating and two spherical mirror reflectors. A TMQOC system has been designed on the basis of simulation and theory calculation. With a ring beam passing over the column grating surface, the TMQOC radiation source can output a power of 1.2 MW at W-band, under the condition of guiding magnetic field of 2.2 T, diode voltage of 557 kV, beam current of 1.8 kA with duration of 70 ns.
The paper presents a three-mirror quasi-optical cavity (TMQOC) high power radiation source, which includes a column slow-wave grating and two spherical mirror reflectors. A TMQOC system has been designed on the basis of simulation and theory calculation. With a ring beam passing over the column grating surface, the TMQOC radiation source can output a power of 1.2 MW at W-band, under the condition of guiding magnetic field of 2.2 T, diode voltage of 557 kV, beam current of 1.8 kA with duration of 70 ns.
2011,
23.
Abstract:
Transient physical processes of electromagnetic field forming in reentrant resonator have been studied by theory, simulation and experiment. The results of the three methods, consistent with each other, show that the result difference between simulation and theory is less than 8%, and that between experiment and theory is less than 2.5%.The forming time of stable-state voltage is in inverse proportion to the resonant frequency and in direct proportion to the quality factor.
Transient physical processes of electromagnetic field forming in reentrant resonator have been studied by theory, simulation and experiment. The results of the three methods, consistent with each other, show that the result difference between simulation and theory is less than 8%, and that between experiment and theory is less than 2.5%.The forming time of stable-state voltage is in inverse proportion to the resonant frequency and in direct proportion to the quality factor.
2011,
23.
Abstract:
Supercontinuum has a wide and important application in many fields, it is one of the hottest research topics during the past four decade. However, the splicing and coupling loss is a little high owing to the mismatch of mode area between double-clad fiber and photonic crystal fiber and the maximum average output power of the supercontinuum is 50 W due to limited average output power available of ultrafast fiber lasers with high quality. In this paper, a 70 W supercontinuum generation is constructed which not only overcomes the problem of high splicing and coupling loss between fiber and photonic crystal fiber caused by the mismatch of mode area, but also relaxes the spectral requirement for the pumping fiber laser sources.
Supercontinuum has a wide and important application in many fields, it is one of the hottest research topics during the past four decade. However, the splicing and coupling loss is a little high owing to the mismatch of mode area between double-clad fiber and photonic crystal fiber and the maximum average output power of the supercontinuum is 50 W due to limited average output power available of ultrafast fiber lasers with high quality. In this paper, a 70 W supercontinuum generation is constructed which not only overcomes the problem of high splicing and coupling loss between fiber and photonic crystal fiber caused by the mismatch of mode area, but also relaxes the spectral requirement for the pumping fiber laser sources.
2011,
23.
Abstract:
Fourier telescopy (FT), an active high-resolution imaging technique, uses linear interference fringes with different spatial frequencies sweeping across a target. The resulting reflected temporal signal is collected by a large receiver of lower optical quality. Different spatial frequencies of interference fringes, which are essential to extract the target spectrum, are produced by changing position of beams many times in the laboratory. The theory about spectrum extraction is discussed, and a novel beam moving mode is proposed and compared with other two modes respectively used by Trex Enterprises Inc and by Changchun Institute of Optics, Fine Mechanics and Physics from three aspects: the extracted matrix of the target spectrum, the requirements for laboratory instruments and the form of
Fourier telescopy (FT), an active high-resolution imaging technique, uses linear interference fringes with different spatial frequencies sweeping across a target. The resulting reflected temporal signal is collected by a large receiver of lower optical quality. Different spatial frequencies of interference fringes, which are essential to extract the target spectrum, are produced by changing position of beams many times in the laboratory. The theory about spectrum extraction is discussed, and a novel beam moving mode is proposed and compared with other two modes respectively used by Trex Enterprises Inc and by Changchun Institute of Optics, Fine Mechanics and Physics from three aspects: the extracted matrix of the target spectrum, the requirements for laboratory instruments and the form of
2011,
23.
Abstract:
Beam collimation mechanism of the fast axis collimation (FAC) microlens is described, and theoretical accuracy requirements for adjusting advice and the selection of lens are analyzed, for the output beam of diode laser vertical stack to achieve small divergence angle and high pointing accuracy. The images of diode laser bar in the near field and far field are realtime monitored through optical imaging methods to realize coarse and fine adjustments of FAC lens, respectively. The output power of the 20 bar vertical stack is 2 kW, and the far field divergence angle of fast axis collimated beams is 4.4 mrad, with the pointing accuracy among bars of less than ±1.7 mrad. The monitering precision and the collimation influencing factors are analyzed, and the key of optimization is pointed out
Beam collimation mechanism of the fast axis collimation (FAC) microlens is described, and theoretical accuracy requirements for adjusting advice and the selection of lens are analyzed, for the output beam of diode laser vertical stack to achieve small divergence angle and high pointing accuracy. The images of diode laser bar in the near field and far field are realtime monitored through optical imaging methods to realize coarse and fine adjustments of FAC lens, respectively. The output power of the 20 bar vertical stack is 2 kW, and the far field divergence angle of fast axis collimated beams is 4.4 mrad, with the pointing accuracy among bars of less than ±1.7 mrad. The monitering precision and the collimation influencing factors are analyzed, and the key of optimization is pointed out
2011,
23.
Abstract:
The main factors affecting the transmittance of laser transparent ceramics are studied. The effects of the scattering particles including inner pores and impurity particles, the difference of refractive index between the boundary and the grain in the boundary structure, as well as the boundary surface roughness on the transmittance of laser transparent ceramics are discussed. Moreover, the variation of the transmittance with pore size, porosity, relative refractive index of grain to boundary, and the surface roughness are analyzed quantitatively. The results indicate that the transmittance of the laser ceramics increases with the decreasing of porosity. The transmittance oscillates periodically with the increase of the pore size, and decreases obviously when the pore size and the wavelengt
The main factors affecting the transmittance of laser transparent ceramics are studied. The effects of the scattering particles including inner pores and impurity particles, the difference of refractive index between the boundary and the grain in the boundary structure, as well as the boundary surface roughness on the transmittance of laser transparent ceramics are discussed. Moreover, the variation of the transmittance with pore size, porosity, relative refractive index of grain to boundary, and the surface roughness are analyzed quantitatively. The results indicate that the transmittance of the laser ceramics increases with the decreasing of porosity. The transmittance oscillates periodically with the increase of the pore size, and decreases obviously when the pore size and the wavelengt
2011,
23.
Abstract:
The output characteristics of Cr4+:YAG passively Q-switched laser was studied theoretically and experimentally. The pulse energy and pulse width for different small signal transmission ratios of Q-switching crystal and different reflection indices of output mirror were simulated. The experimental results show good agreement with the theoretical predictions of energy and pulse width. The results indicate that, with a given laser crystal, the output energy and pulse width are determined by the small signal transmission ratio of the Q-switching crystal and the reflectance ratio of the output coupling mirror. The output energy reduces with the increase of the transmission ratio and there is an optimal reflectance ratio of the output coupling mirror to obtain the maximal output energy. The puls
The output characteristics of Cr4+:YAG passively Q-switched laser was studied theoretically and experimentally. The pulse energy and pulse width for different small signal transmission ratios of Q-switching crystal and different reflection indices of output mirror were simulated. The experimental results show good agreement with the theoretical predictions of energy and pulse width. The results indicate that, with a given laser crystal, the output energy and pulse width are determined by the small signal transmission ratio of the Q-switching crystal and the reflectance ratio of the output coupling mirror. The output energy reduces with the increase of the transmission ratio and there is an optimal reflectance ratio of the output coupling mirror to obtain the maximal output energy. The puls
2011,
23.
Abstract:
A power fiber amplifier module consisting of two stage fiber amplifiers, whose fiber core diameters were 15 μm and 25 μm respectively, was presented. It can output 30 kW peak power with 300 μJ output energy, when the input pulsed signal is 10 ns in duration，1 Hz in repetition frequency, 0.3 nm in spectrum width, and 80 nJ in energy. The output pulse’s temporal characteristic was investigated. It is found that the output energy of the amplifier module is confined by stimulated Brillouin scattering（SBS）effect when the input pulse is narrow banded, and adopting the broadband pulse could improve the SBS threshold of the fiber amplifier．
A power fiber amplifier module consisting of two stage fiber amplifiers, whose fiber core diameters were 15 μm and 25 μm respectively, was presented. It can output 30 kW peak power with 300 μJ output energy, when the input pulsed signal is 10 ns in duration，1 Hz in repetition frequency, 0.3 nm in spectrum width, and 80 nJ in energy. The output pulse’s temporal characteristic was investigated. It is found that the output energy of the amplifier module is confined by stimulated Brillouin scattering（SBS）effect when the input pulse is narrow banded, and adopting the broadband pulse could improve the SBS threshold of the fiber amplifier．
2011,
23.
Abstract:
Spectral beam combining technology is an effective approach to obtain high-power laser output. The side-lobe in diffraction efficiency of reflection Bragg grating is the main factor which limits the efficiency of spectral beam combining. In this paper, the theoretical model of spectral beam combining system based on the sinc-apodized Bragg grating is proposed. The diffraction characteristic of the sinc-apodized grating is analyzed by the chain-matrix approach, and the effects of spectral width and beam divergence on combining efficiency are considered. Numerical analysis show that the side-lobe in diffraction efficiency is suppressed well after using the sinc-apodized grating, the peaks of the first side-lobe and second side-lobe are reduced from 62% and 36% to 0.57% and 0.12%, respectivel
Spectral beam combining technology is an effective approach to obtain high-power laser output. The side-lobe in diffraction efficiency of reflection Bragg grating is the main factor which limits the efficiency of spectral beam combining. In this paper, the theoretical model of spectral beam combining system based on the sinc-apodized Bragg grating is proposed. The diffraction characteristic of the sinc-apodized grating is analyzed by the chain-matrix approach, and the effects of spectral width and beam divergence on combining efficiency are considered. Numerical analysis show that the side-lobe in diffraction efficiency is suppressed well after using the sinc-apodized grating, the peaks of the first side-lobe and second side-lobe are reduced from 62% and 36% to 0.57% and 0.12%, respectivel
2011,
23.
Abstract:
Phase diversity wavefront sensing (PDWFS), which has a simple configuration and a low cost, can be used to estimate wavefront for point source as well as extended source. However, there are various errors in its image collection and phase retrieval procedure. A numerical simulation of wavefront sensing errors caused by many factors is carried out in the case that the diversity function is defocus. These factors include the optical aberrations, focal plane position error, uncertainty of the defocus, image misalignment, image noise and so on. Approaches of eliminating or reducing these errors are given. The results show that these methods could reduce the errors effectively, and could improve the sensing accuracy greatly, which provide an important technical support for the practical applica
Phase diversity wavefront sensing (PDWFS), which has a simple configuration and a low cost, can be used to estimate wavefront for point source as well as extended source. However, there are various errors in its image collection and phase retrieval procedure. A numerical simulation of wavefront sensing errors caused by many factors is carried out in the case that the diversity function is defocus. These factors include the optical aberrations, focal plane position error, uncertainty of the defocus, image misalignment, image noise and so on. Approaches of eliminating or reducing these errors are given. The results show that these methods could reduce the errors effectively, and could improve the sensing accuracy greatly, which provide an important technical support for the practical applica
2011,
23.
Abstract:
To measure far field intensity distribution of high energy laser by thermal image method, we studied a laser screen made of thermoelectric cooling chips(TECC). We first built heating model of target surface by laser irradiation based on heat conduction equation, then found out the relationship between the temperature of target surface and the laser intensity. We proved the feasibility of using the TECC made of alumina ceramic as target screen and studied the improvement of measurement with cooling function. We developed a 200 mm×200 mm screen with cooling power of 4 800 W, which was combination of 16 chips with size of 50 mm×50 mm and cooling power of 300 W. And there are 8 objects for infrared image calibration around the screen.
To measure far field intensity distribution of high energy laser by thermal image method, we studied a laser screen made of thermoelectric cooling chips(TECC). We first built heating model of target surface by laser irradiation based on heat conduction equation, then found out the relationship between the temperature of target surface and the laser intensity. We proved the feasibility of using the TECC made of alumina ceramic as target screen and studied the improvement of measurement with cooling function. We developed a 200 mm×200 mm screen with cooling power of 4 800 W, which was combination of 16 chips with size of 50 mm×50 mm and cooling power of 300 W. And there are 8 objects for infrared image calibration around the screen.
2011,
23.
Abstract:
Numerical simulations are conducted on the imaging of Fourier telescopy System with equalspaced antenna array in T shape geometries, and the imaging quality is evaluated by the Strehl distribution of different targets. The results testify that the array with the same numbered antennas in each of the three arms gains the target’s spectrum distribution that is the most symmetrical in the horizontal and vertical directions, and can obtain good imaging quality and high Strehl ratio, for antenna arrays of such structure, the images are reconstructed for multiple objects with 3 to 18 antennas in each arm. It is found that, while the single arm’s antenna number is no more than 10, increasing the number of antennas can obviously improve the reconstructed image’s quality and distinguish the ob
Numerical simulations are conducted on the imaging of Fourier telescopy System with equalspaced antenna array in T shape geometries, and the imaging quality is evaluated by the Strehl distribution of different targets. The results testify that the array with the same numbered antennas in each of the three arms gains the target’s spectrum distribution that is the most symmetrical in the horizontal and vertical directions, and can obtain good imaging quality and high Strehl ratio, for antenna arrays of such structure, the images are reconstructed for multiple objects with 3 to 18 antennas in each arm. It is found that, while the single arm’s antenna number is no more than 10, increasing the number of antennas can obviously improve the reconstructed image’s quality and distinguish the ob
2011,
23.
Abstract:
Image focus-of-attention detection is the key technology of image region-of-interest extraction based on human visual attention model. A new image focus-of-attention detection algorithm is proposed based on double-threshold visual attention model. First, the intensity, colors, orientations and the center moments of discrete moment transform are extracted to generate the conspicuity maps for each feature. Second, the conspicuity maps are combined to get a saliency map. Finally, according to the gray-scale histogram of the saliency map, the static threshold and dynamic threshold are found to confirm the positions and numbers of the image focuses of attention. The experimental results show that the new algorithm has more outstanding performance in accuracy of image focus-of-attention detectio
Image focus-of-attention detection is the key technology of image region-of-interest extraction based on human visual attention model. A new image focus-of-attention detection algorithm is proposed based on double-threshold visual attention model. First, the intensity, colors, orientations and the center moments of discrete moment transform are extracted to generate the conspicuity maps for each feature. Second, the conspicuity maps are combined to get a saliency map. Finally, according to the gray-scale histogram of the saliency map, the static threshold and dynamic threshold are found to confirm the positions and numbers of the image focuses of attention. The experimental results show that the new algorithm has more outstanding performance in accuracy of image focus-of-attention detectio
2011,
23.
Abstract:
The wall of secondary gas flow distribution pipeline in primary nozzle blade will be heated during CW chemical laser operation. Effects on flow field characteristics of distribution flow pipeline with hot wall boundary under conditions of single end or double ends gas supply were analyzed based on three-dimension computational fluid dynamics methods. The hot wall boundary makes the total temperature of general pipeline higher and higher along the direction of main gas flow movement, and the total temperature of branch pipeline inlet goes up simultaneously, which results in corresponding decrease in mass flow rates of branch pipeline outlets. The fluctuating amplitude of mass flow rates of branch pipeline outlets with hot wall boundary is bigger than that with adiabatic wall boundary, and t
The wall of secondary gas flow distribution pipeline in primary nozzle blade will be heated during CW chemical laser operation. Effects on flow field characteristics of distribution flow pipeline with hot wall boundary under conditions of single end or double ends gas supply were analyzed based on three-dimension computational fluid dynamics methods. The hot wall boundary makes the total temperature of general pipeline higher and higher along the direction of main gas flow movement, and the total temperature of branch pipeline inlet goes up simultaneously, which results in corresponding decrease in mass flow rates of branch pipeline outlets. The fluctuating amplitude of mass flow rates of branch pipeline outlets with hot wall boundary is bigger than that with adiabatic wall boundary, and t
2011,
23.
Abstract:
Experimental measurement and numerical simulation are employed to study the effects of laser irradiation on aluminum alloy tank containing water. Firstly, by analyzing the surface pictures and measuring the temperature histories, the effects of water on the ablation of aluminum alloy plate irradiated by 1 053 nm pulsed laser are investigated. The results show that heat conduction and convection play a very important role in the ablation of the aluminum alloy plate. When the tank is empty, the aluminum alloy plate is melt through after eight laser pulses irradiation. And when the tank is filled with water, the aluminum alloy plate has not been melt through after ten laser pulses irradiation. Then, a numerical model is presented to calculate the temperature distribution of the aluminum alloy
Experimental measurement and numerical simulation are employed to study the effects of laser irradiation on aluminum alloy tank containing water. Firstly, by analyzing the surface pictures and measuring the temperature histories, the effects of water on the ablation of aluminum alloy plate irradiated by 1 053 nm pulsed laser are investigated. The results show that heat conduction and convection play a very important role in the ablation of the aluminum alloy plate. When the tank is empty, the aluminum alloy plate is melt through after eight laser pulses irradiation. And when the tank is filled with water, the aluminum alloy plate has not been melt through after ten laser pulses irradiation. Then, a numerical model is presented to calculate the temperature distribution of the aluminum alloy
2011,
23.
Abstract:
A scheme using metamaterials is proposed to modulate beamwidth and obtain a line beam from a beam with finite width based on transformation optics, and the constitutive tensors of metamaterials are educed. The good performance of the proposed medium is verified through full-wave numerical simulations based on the finite element method. Such an electromagnetic wave-manipulating medium provides alternative ways either to expand or to compress the electromagnetic beamwidth. And the line beam with very high energy density at the beam center would find applications in enhancing nonlinear optical effects or other areas.
A scheme using metamaterials is proposed to modulate beamwidth and obtain a line beam from a beam with finite width based on transformation optics, and the constitutive tensors of metamaterials are educed. The good performance of the proposed medium is verified through full-wave numerical simulations based on the finite element method. Such an electromagnetic wave-manipulating medium provides alternative ways either to expand or to compress the electromagnetic beamwidth. And the line beam with very high energy density at the beam center would find applications in enhancing nonlinear optical effects or other areas.
2011,
23.
Abstract:
A half-year contradistinctive experiment for visibility detecting has been performed using CSY2 visibility lidar developed by ourselves in Xiaogan of Hubei province and Peking. The output of CSY2 visibility lidar was lower than the outputs of eyeballing and MITRAS meter due to forward scattering caused by raindrop. Based on Marshall-Palmer particle spectral distribution function, the forward scattering effect on 1 064 μm laser propagation of raindrop was analyzed, and a new modified formula for visibility, was proposed, with which measurement error of visibility can be largely reduced in moderate and heavy rain．
A half-year contradistinctive experiment for visibility detecting has been performed using CSY2 visibility lidar developed by ourselves in Xiaogan of Hubei province and Peking. The output of CSY2 visibility lidar was lower than the outputs of eyeballing and MITRAS meter due to forward scattering caused by raindrop. Based on Marshall-Palmer particle spectral distribution function, the forward scattering effect on 1 064 μm laser propagation of raindrop was analyzed, and a new modified formula for visibility, was proposed, with which measurement error of visibility can be largely reduced in moderate and heavy rain．
2011,
23.
Abstract:
Fundamental equations governing the temperature field of thermally decomposing resin composite irradiated by laser are derived from mass and energy conservation laws with the control volume method. The thermal decomposition of resin is described by a multi-step model. An assumption is proposed that the flow of pyrolysis gas is one-dimensional, which makes it possible to consider the influence of pyrolysis gas convective transport and realize the closure of the three-dimensional model without introducing mechanical quantities. In view of the anisotropy of resin composite, expressions of the thermal conductivities of partially pyrolyzed material are deduced, as well as the computing formula for the laser absorption coefficient of partially pyrolyzed material. The energy conservation equation
Fundamental equations governing the temperature field of thermally decomposing resin composite irradiated by laser are derived from mass and energy conservation laws with the control volume method. The thermal decomposition of resin is described by a multi-step model. An assumption is proposed that the flow of pyrolysis gas is one-dimensional, which makes it possible to consider the influence of pyrolysis gas convective transport and realize the closure of the three-dimensional model without introducing mechanical quantities. In view of the anisotropy of resin composite, expressions of the thermal conductivities of partially pyrolyzed material are deduced, as well as the computing formula for the laser absorption coefficient of partially pyrolyzed material. The energy conservation equation
