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RSS2014 Vol. 26, No. 01
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2014,
26: 010101.
doi: 10.3788/HPLPB201426.010101
Abstract:
A stable pulsed thulium-doped fiber laser at 2 m is obtained based on gain-switched techniques, with the central wavelength of 1 979.4 nm. The pulse width and repetition rate of the seed laser can be tuned in the range of 60~200 ns and 1~100 kHz, respectively. After two-stage thulium-doped fiber amplifiers, the average output power of 2 m seed pulses is scaled up to 17.2 W at 20 kHz, and no obvious amplified spontaneous emission noise is observed. The measured output pulse width is 82 ns and the calculated maximum output pulse energy reaches as high as 0.86 mJ, which corresponds to a peak power exceeding 10 kW.
A stable pulsed thulium-doped fiber laser at 2 m is obtained based on gain-switched techniques, with the central wavelength of 1 979.4 nm. The pulse width and repetition rate of the seed laser can be tuned in the range of 60~200 ns and 1~100 kHz, respectively. After two-stage thulium-doped fiber amplifiers, the average output power of 2 m seed pulses is scaled up to 17.2 W at 20 kHz, and no obvious amplified spontaneous emission noise is observed. The measured output pulse width is 82 ns and the calculated maximum output pulse energy reaches as high as 0.86 mJ, which corresponds to a peak power exceeding 10 kW.
2014,
26: 010102.
doi: 10.3788/HPLPB201426.010102
Abstract:
Pumped by a laser diode array with an external cavity of Littrow, whose linewidth is 0.26 nm, a cesium vapor laser is obtained using the cesium cell filled with methane of 80 kPa. At 120 ℃ of the cesium vapor cell, laser with output power of 394 mW and wavelength of 894.6 nm is realized. The lasers optical efficiency is 7.4% while the slope efficiency is 11.2% and the threshold is 1.72 W.
Pumped by a laser diode array with an external cavity of Littrow, whose linewidth is 0.26 nm, a cesium vapor laser is obtained using the cesium cell filled with methane of 80 kPa. At 120 ℃ of the cesium vapor cell, laser with output power of 394 mW and wavelength of 894.6 nm is realized. The lasers optical efficiency is 7.4% while the slope efficiency is 11.2% and the threshold is 1.72 W.
2014,
26: 010201.
doi: 10.3788/HPLPB201426.010201
Abstract:
Pulsed power driven flash X-ray generators are essential testing equipments in areas like hydrokinetics. Smaller spot size and higher radiation dose are expected according to physical requirements. Current status and key problems of several X-ray diodes are narrated, a pulse power supply driving X-ray diode from hundreds of MW to tens of GW is recited. Application prospects of rod pinch and magnetically immersed diode are analyzed. Moreover, advances of rod pinch diode and pulsed power supply, as well as key techniques realizing multi-frame flash radiography are discussed.
Pulsed power driven flash X-ray generators are essential testing equipments in areas like hydrokinetics. Smaller spot size and higher radiation dose are expected according to physical requirements. Current status and key problems of several X-ray diodes are narrated, a pulse power supply driving X-ray diode from hundreds of MW to tens of GW is recited. Application prospects of rod pinch and magnetically immersed diode are analyzed. Moreover, advances of rod pinch diode and pulsed power supply, as well as key techniques realizing multi-frame flash radiography are discussed.
2014,
26: 011001.
doi: 10.3788/HPLPB201426.011001
Abstract:
We analyze the stray light caused by surface scattering of the sum-frequency crystal in third-order correlation measurement and its influence on the contrast of the sum-frequency light. Besides, the expression of the stray light caused by surface scattering is given. When the surface roughness is 1% of the laser wavelength, the intensity of stray light reaches about 10-8. And the rougher the surface is, the more stray light it causes.
We analyze the stray light caused by surface scattering of the sum-frequency crystal in third-order correlation measurement and its influence on the contrast of the sum-frequency light. Besides, the expression of the stray light caused by surface scattering is given. When the surface roughness is 1% of the laser wavelength, the intensity of stray light reaches about 10-8. And the rougher the surface is, the more stray light it causes.
2014,
26: 011002.
doi: 10.3788/HPLPB201426.011002
Abstract:
An all-fiber multichannel laser configuration of coherent beam combining with an optical feed-back ring cavity is reported. The passive coherent combining of multichannel Yb-doped fiber amplifiers is achieved with the ring cavity. The traditional problem of energy dissipation to side lode for lower aperture filling is solved via the all-fiber laser configuration, and good beam quality is maintained. The coherent beam combination of four Yb-doped fiber amplifiers is experimentally demonstrated. Stable combination shapes with temporal and spatial characteristic are achieved. The efficiency of coherent combination is up to 96.1%, and it is an excellent result for fiber laser coherent beam combining.
An all-fiber multichannel laser configuration of coherent beam combining with an optical feed-back ring cavity is reported. The passive coherent combining of multichannel Yb-doped fiber amplifiers is achieved with the ring cavity. The traditional problem of energy dissipation to side lode for lower aperture filling is solved via the all-fiber laser configuration, and good beam quality is maintained. The coherent beam combination of four Yb-doped fiber amplifiers is experimentally demonstrated. Stable combination shapes with temporal and spatial characteristic are achieved. The efficiency of coherent combination is up to 96.1%, and it is an excellent result for fiber laser coherent beam combining.
2014,
26: 011003.
doi: 10.3788/HPLPB201426.011003
Abstract:
In order to analyze the effect of jet cooling technology on thin disk laser, starting from the turbulent heat transfer theory, we define two parameters ha and the average maximum temperature difference for evaluation of jet cooling heat transfer capacity and cooling uniformity. Using the ANSYS CFX fluid dynamics simulation software, a physical model of jet cooling was built, and the multiple jet plate structure was calculated. Furthermore, the entire jet cooling experimental device was designed, and heat source jet cooling was simulated. The results show that jet cooling heat transfer capacity and cooling uniformity are mainly affected by the structural parameters of jet plate, and ANSYS CFX calculation results can be used to guide the optimization design of the structure parameters of jet plate.
In order to analyze the effect of jet cooling technology on thin disk laser, starting from the turbulent heat transfer theory, we define two parameters ha and the average maximum temperature difference for evaluation of jet cooling heat transfer capacity and cooling uniformity. Using the ANSYS CFX fluid dynamics simulation software, a physical model of jet cooling was built, and the multiple jet plate structure was calculated. Furthermore, the entire jet cooling experimental device was designed, and heat source jet cooling was simulated. The results show that jet cooling heat transfer capacity and cooling uniformity are mainly affected by the structural parameters of jet plate, and ANSYS CFX calculation results can be used to guide the optimization design of the structure parameters of jet plate.
2014,
26: 011004.
doi: 10.3788/HPLPB201426.011004
Abstract:
We propose a compact photonic crystal Mach-Zehnder interferometer index sensor with a two-dimensional rotated square lattice, based on the photonic crystal self-collimation effect. Using the same background index, the different index of the circular rods has different effective index. The line defected and the air slab waveguide are respectively used as the beam splitter and mirror of the interferometer, and a sensing area is setting on one arm of the interferometer. The index of the circular rods changes with the concentration of the solution filled into the sensing region, thereby affecting the center wavelength of the transmission spectrum, and establishing a mathematical relationship between the solution concentration and the transmission wavelength. Then we carry out a numerical simulation of the concentration measurement of the alcohol solution, the results show that the sensor sensitivity is 250 nm/RIU in the refractive index variation within the scope of 1.33-1.37.
We propose a compact photonic crystal Mach-Zehnder interferometer index sensor with a two-dimensional rotated square lattice, based on the photonic crystal self-collimation effect. Using the same background index, the different index of the circular rods has different effective index. The line defected and the air slab waveguide are respectively used as the beam splitter and mirror of the interferometer, and a sensing area is setting on one arm of the interferometer. The index of the circular rods changes with the concentration of the solution filled into the sensing region, thereby affecting the center wavelength of the transmission spectrum, and establishing a mathematical relationship between the solution concentration and the transmission wavelength. Then we carry out a numerical simulation of the concentration measurement of the alcohol solution, the results show that the sensor sensitivity is 250 nm/RIU in the refractive index variation within the scope of 1.33-1.37.
2014,
26: 011005.
doi: 10.3788/HPLPB201426.011005
Abstract:
The calibration of energy calorimeter is one of the important aspects in the measurement of the energy of high power laser facility. Using the method of linearity fitting is suggested in the calibration of energy calorimeter. The standard deviation of slope is used as the main criterion for deciding which linearity fitting is adopted, and the correlation, the intercept, and the standard deviation of intercept are taken into account. If the slope standard error of zero crossing linear fitting is less than that of un-zero crossing linear fitting, then the intercept is considered as a random error. The calorimeter coefficient is solved according to the method of weighted average of un-equal precision. Otherwise, a great system error exists, the calorimeter coefficient is obtained by un-zero crossing linear fitting, and the value of intercept is a system error. According to the value of regression error, we can determine whether the gross error exists and how to eliminate it. In this way, the appropriate calorimeter coefficient is obtained. The analyzed results are of reference value for the exact measurement of laser energy.
The calibration of energy calorimeter is one of the important aspects in the measurement of the energy of high power laser facility. Using the method of linearity fitting is suggested in the calibration of energy calorimeter. The standard deviation of slope is used as the main criterion for deciding which linearity fitting is adopted, and the correlation, the intercept, and the standard deviation of intercept are taken into account. If the slope standard error of zero crossing linear fitting is less than that of un-zero crossing linear fitting, then the intercept is considered as a random error. The calorimeter coefficient is solved according to the method of weighted average of un-equal precision. Otherwise, a great system error exists, the calorimeter coefficient is obtained by un-zero crossing linear fitting, and the value of intercept is a system error. According to the value of regression error, we can determine whether the gross error exists and how to eliminate it. In this way, the appropriate calorimeter coefficient is obtained. The analyzed results are of reference value for the exact measurement of laser energy.
2014,
26: 011006.
doi: 10.3788/HPLPB201426.011006
Abstract:
In order to improve the reflectance of the GaSb-based laser cavity mask, the laser cavity film was designed in accordance with the relevant film design theory and by film-design software. The reflectance of the high anti-reflection film was higher than 95% in the band of 2-3.5 m; the transmittance of the antireflective film was higher than 99% at the wavelength of 2.5 m. The theoretical and experimental reflectance curves of high reflector and the single layer antireflection coating were compared through repeated experiments. Though the experimental results did not reach the theoretical value, they could meet the requirements of the application. The selection of the film materials was discussed by comparison of various material properties.
In order to improve the reflectance of the GaSb-based laser cavity mask, the laser cavity film was designed in accordance with the relevant film design theory and by film-design software. The reflectance of the high anti-reflection film was higher than 95% in the band of 2-3.5 m; the transmittance of the antireflective film was higher than 99% at the wavelength of 2.5 m. The theoretical and experimental reflectance curves of high reflector and the single layer antireflection coating were compared through repeated experiments. Though the experimental results did not reach the theoretical value, they could meet the requirements of the application. The selection of the film materials was discussed by comparison of various material properties.
2014,
26: 011007.
doi: 10.3788/HPLPB201426.011007
Abstract:
Laser diode pumped Nd:YVO4 laser is used as light source. Green beam whose wavelength is 532 nm is generated by frequency doubling through KTP. The quasi-non-diffracting Bessel green beam is obtained by axicon. The distribution of the green beam light field is deduced. The intensity distribution along the propagation distance and the cross-section intensity distribution of the quasi-non-diffracting Bessel green beam are simulated. In experiment, the cross-section light field distribution of Bessel green beam at different distance from axicon are recorded and the propagation distance of non-diffracting beam and the diameter of center light spot are measured. The experimental data agree well with the theoretical simulation. The experimental results demonstrate the quasi-non-diffracting Bessel green beam has good quality and is appropriate for applying.
Laser diode pumped Nd:YVO4 laser is used as light source. Green beam whose wavelength is 532 nm is generated by frequency doubling through KTP. The quasi-non-diffracting Bessel green beam is obtained by axicon. The distribution of the green beam light field is deduced. The intensity distribution along the propagation distance and the cross-section intensity distribution of the quasi-non-diffracting Bessel green beam are simulated. In experiment, the cross-section light field distribution of Bessel green beam at different distance from axicon are recorded and the propagation distance of non-diffracting beam and the diameter of center light spot are measured. The experimental data agree well with the theoretical simulation. The experimental results demonstrate the quasi-non-diffracting Bessel green beam has good quality and is appropriate for applying.
2014,
26: 011008.
doi: 10.3788/HPLPB201426.011008
Abstract:
Radially polarized light has been a focus in recent years with wide application in particle manipulation, metal cutting and improvement of microscope resolution. It can be generated by an intro-cavity grating mirror in the resonator of a laser. In this article, the influence of gratings properties on the parameters was analyzed by a program which was written by ourselves in the top-etching grating model. And a suitable grating mirror composite structure was designed with considering of the gratings process feasibility.
Radially polarized light has been a focus in recent years with wide application in particle manipulation, metal cutting and improvement of microscope resolution. It can be generated by an intro-cavity grating mirror in the resonator of a laser. In this article, the influence of gratings properties on the parameters was analyzed by a program which was written by ourselves in the top-etching grating model. And a suitable grating mirror composite structure was designed with considering of the gratings process feasibility.
2014,
26: 011009.
doi: 10.3788/HPLPB201426.011009
Abstract:
The regular circular fringes could be observed when the visible array CCD was irradiated by 532 nm pulsed laser from a distance of 31.5 m. Their generating conditions and mechanism have been investigated by changing the incident angle, the attenuation factor, repetition frequency and distance. The experimental results show that in the premise that the incident angle of laser is smaller or a little larger than the half angle of view 6.8, the regular circular fringes can be observed as long as the power density can reach 10-3 W/cm2 at the pupil of optical system. It was proved that the regular circular fringes were caused by the diffraction effect of the pupil of optical system, based on the simulation of energy distribution on the detectors surface.
The regular circular fringes could be observed when the visible array CCD was irradiated by 532 nm pulsed laser from a distance of 31.5 m. Their generating conditions and mechanism have been investigated by changing the incident angle, the attenuation factor, repetition frequency and distance. The experimental results show that in the premise that the incident angle of laser is smaller or a little larger than the half angle of view 6.8, the regular circular fringes can be observed as long as the power density can reach 10-3 W/cm2 at the pupil of optical system. It was proved that the regular circular fringes were caused by the diffraction effect of the pupil of optical system, based on the simulation of energy distribution on the detectors surface.
2014,
26: 011010.
doi: 10.3788/HPLPB201426.011010
Abstract:
In the process of Shack-Hartmann wave-front measure, meshing of Shack-Hartmann image is widely used for calculating wave-front slope. The conventional meshing method, which manually adjusts the mesh by observing the Shack-Hartmann image, is time-consuming. It is difficult to achieve real-time wave-front measure. In order to realize auto-meshing, in this paper, auto-meshing method based on image correlation is presented. In this algorithm, auto-correlation of Shack-Hartmann image is used for calculating grid interval and grid number. Then, simulative light-spot image according with the grid is obtained. At last, correlation operation between the simulative light-spot image and the Shack-Hartmann image is done to acquire optimal coordinate of the grid. This algorithm which is efficient and has no need for human intervention can achieve real-time auto-meshing.
In the process of Shack-Hartmann wave-front measure, meshing of Shack-Hartmann image is widely used for calculating wave-front slope. The conventional meshing method, which manually adjusts the mesh by observing the Shack-Hartmann image, is time-consuming. It is difficult to achieve real-time wave-front measure. In order to realize auto-meshing, in this paper, auto-meshing method based on image correlation is presented. In this algorithm, auto-correlation of Shack-Hartmann image is used for calculating grid interval and grid number. Then, simulative light-spot image according with the grid is obtained. At last, correlation operation between the simulative light-spot image and the Shack-Hartmann image is done to acquire optimal coordinate of the grid. This algorithm which is efficient and has no need for human intervention can achieve real-time auto-meshing.
2014,
26: 011011.
doi: 10.3788/HPLPB201426.011011
Abstract:
Fast steering mirror (FSM) driven by piezoelectric actuator has been widely used in multifarious precision instruments for stabilization and tracking systems, whose tracking accuracy is decided by the control accuracy of FSM. However, there is a seriously nonlinear interference of hysteresis in the driving of piezoelectric actuator. In response to this defect, an adaptive radial bass function (RBF) neural network was used to approximate the nonlinear interference of hysteresis, and based on which, the sliding mode control and backstepping algorithm were combined to design adaptive backstepping sliding mode (ABSM) controller. The simulation results show that, compared with the control accuracy of the sliding mode controller, the maximum tracking error and mean-root-square error of ABSM controller declines by 57.26% and 52.53% respectively, which improves the control accuracy of FSM evidently.
Fast steering mirror (FSM) driven by piezoelectric actuator has been widely used in multifarious precision instruments for stabilization and tracking systems, whose tracking accuracy is decided by the control accuracy of FSM. However, there is a seriously nonlinear interference of hysteresis in the driving of piezoelectric actuator. In response to this defect, an adaptive radial bass function (RBF) neural network was used to approximate the nonlinear interference of hysteresis, and based on which, the sliding mode control and backstepping algorithm were combined to design adaptive backstepping sliding mode (ABSM) controller. The simulation results show that, compared with the control accuracy of the sliding mode controller, the maximum tracking error and mean-root-square error of ABSM controller declines by 57.26% and 52.53% respectively, which improves the control accuracy of FSM evidently.
2014,
26: 011012.
doi: 10.3788/HPLPB201426.011012
Abstract:
The beam combination is an effective method to improve laser power and beam quality, the parameters of chirped pulsed Gaussian beam will affect the result. Based on the Fraunhofer diffraction integral formula, the formulas for the far-field relative intensity of two chirped pulsed Gaussian beams combination are derived. It is shown that the far-field relative intensity distribution of the combined beams depends on the chirp parameter, pulse duration, and spectral bandwidth. The numerical simulation result of the intensity indicates that, the far-field relative intensity distribution of combined beams increases and is more concentrated in the vicinity of transmission shaft with the increment of chirp parameter or with the decrement of pulse duration difference or the increment of spectral bandwidth difference.
The beam combination is an effective method to improve laser power and beam quality, the parameters of chirped pulsed Gaussian beam will affect the result. Based on the Fraunhofer diffraction integral formula, the formulas for the far-field relative intensity of two chirped pulsed Gaussian beams combination are derived. It is shown that the far-field relative intensity distribution of the combined beams depends on the chirp parameter, pulse duration, and spectral bandwidth. The numerical simulation result of the intensity indicates that, the far-field relative intensity distribution of combined beams increases and is more concentrated in the vicinity of transmission shaft with the increment of chirp parameter or with the decrement of pulse duration difference or the increment of spectral bandwidth difference.
2014,
26: 011013.
doi: 10.3788/HPLPB201426.011013
Abstract:
In detecting process, the detecting ability is not only affected by the detecting signal-to-noise ratio(SNR), also by the quality of the detecting image, and the detecting ability evaluating method in existence is only based on the SNR. To offset the deficiency of the evaluating method in existence, a new evaluation on detecting ability of the electro-optics system is put forward, which combines the detecting SNR and system modulation transfer function(MTF), and it can also give the quantitative analysis of the effect of the atmosphere, the aberration and the motion. The new evaluating method was used to simulate an electro-optical system under different conditions. The simulation indicates that the atmosphere, the aberration and the motion can affect the detecting ability seriously, and the motion reduces the detecting ability nearly 1 magnitude. The detecting ability can quantitatively studied with our method, which provides a scientific basis for optimization design of electro-optical systems.
In detecting process, the detecting ability is not only affected by the detecting signal-to-noise ratio(SNR), also by the quality of the detecting image, and the detecting ability evaluating method in existence is only based on the SNR. To offset the deficiency of the evaluating method in existence, a new evaluation on detecting ability of the electro-optics system is put forward, which combines the detecting SNR and system modulation transfer function(MTF), and it can also give the quantitative analysis of the effect of the atmosphere, the aberration and the motion. The new evaluating method was used to simulate an electro-optical system under different conditions. The simulation indicates that the atmosphere, the aberration and the motion can affect the detecting ability seriously, and the motion reduces the detecting ability nearly 1 magnitude. The detecting ability can quantitatively studied with our method, which provides a scientific basis for optimization design of electro-optical systems.
2014,
26: 011014.
doi: 10.3788/HPLPB201426.011014
Abstract:
An investigation and analysis of two methods, the multi-angle knife-edge method and the right-angle double-knife-edge method, was demonstrated for the light distribution measurement. The basic principles of the two methods were introduced. Their ability of image reconstruction and anti-noise was analyzed by numerical simulation. The experimental result of the spot measurement with the right-angle double-knife-edge method was showed. As a conclusion, compared with the multi-angle scanning knife-edge method, the double-knife-edge method was more practical for focal spot measurement, especially for the tightly focusing spot.
An investigation and analysis of two methods, the multi-angle knife-edge method and the right-angle double-knife-edge method, was demonstrated for the light distribution measurement. The basic principles of the two methods were introduced. Their ability of image reconstruction and anti-noise was analyzed by numerical simulation. The experimental result of the spot measurement with the right-angle double-knife-edge method was showed. As a conclusion, compared with the multi-angle scanning knife-edge method, the double-knife-edge method was more practical for focal spot measurement, especially for the tightly focusing spot.
2014,
26: 011015.
doi: 10.3788/HPLPB201426.011015
Abstract:
A hundred-watt semiconductor laser packaged with 12 single strip-type chips divided into 2 groups where each group was set from high to low in ladder form was designed, and its thermal characteristics under steady-state work were analyzed by ANSYS. The temperature of active region of chip packaged with the highest and the lowest Cu heat sinks was obtained by changing the width, spacing and height difference of Cu heat sink, and thus the change rules of the temperature difference were derived. Finally, we designed a relatively ideal heat dissipation structure for hundred-watt semiconductor laser.
A hundred-watt semiconductor laser packaged with 12 single strip-type chips divided into 2 groups where each group was set from high to low in ladder form was designed, and its thermal characteristics under steady-state work were analyzed by ANSYS. The temperature of active region of chip packaged with the highest and the lowest Cu heat sinks was obtained by changing the width, spacing and height difference of Cu heat sink, and thus the change rules of the temperature difference were derived. Finally, we designed a relatively ideal heat dissipation structure for hundred-watt semiconductor laser.
2014,
26: 011016.
doi: 10.3788/HPLPB201426.011016
Abstract:
Using Huygens-Fresnel diffraction integral formula, the expression for the cross-spectral density of the Gaussian-Schell model (GSM) beam which is modulated by the defect of the nonlinear Kerr medium surface is derived. The intensity distribution of GSM beam through the thin Kerr medium is studied. Numerical simulation shows that defect leads to the emergence of extreme intensity point near the rear of the nonlinear medium, which is more far away from the medium when the size of defect is increased. The partially coherent beam can also converge or diverge after passing through the medium with positive or negative nonlinear refractive index. A longer spatial coherence length, and a greater additional phase shift in the medium or a bigger size of defect, will lead to a more serious modulation for the light intensity.
Using Huygens-Fresnel diffraction integral formula, the expression for the cross-spectral density of the Gaussian-Schell model (GSM) beam which is modulated by the defect of the nonlinear Kerr medium surface is derived. The intensity distribution of GSM beam through the thin Kerr medium is studied. Numerical simulation shows that defect leads to the emergence of extreme intensity point near the rear of the nonlinear medium, which is more far away from the medium when the size of defect is increased. The partially coherent beam can also converge or diverge after passing through the medium with positive or negative nonlinear refractive index. A longer spatial coherence length, and a greater additional phase shift in the medium or a bigger size of defect, will lead to a more serious modulation for the light intensity.
2014,
26: 011017.
doi: 10.3788/HPLPB201426.011017
Abstract:
Because of low frequency distorted wave front impacting on beam quality, a thin mirror with a diameter of 300 mm and a ratio of radius to thickness of 20 is optimized in order to compensate the distorted wave front. Meanwhile, the far field beam quality before and after compensating distorted wave front is discussed in detail. The analysis results show that the amplitude of the phase decreases obviously, the phase gradient reduces during the whole spatial period, the peak of far field intensity increases, the power focusability of focal spot is improved greatly and the power focusability can increase by as much as 50% compared with the results before compensation whether the space scale parameter of the low frequency phase is altered or the amplitude of the phase varies.
Because of low frequency distorted wave front impacting on beam quality, a thin mirror with a diameter of 300 mm and a ratio of radius to thickness of 20 is optimized in order to compensate the distorted wave front. Meanwhile, the far field beam quality before and after compensating distorted wave front is discussed in detail. The analysis results show that the amplitude of the phase decreases obviously, the phase gradient reduces during the whole spatial period, the peak of far field intensity increases, the power focusability of focal spot is improved greatly and the power focusability can increase by as much as 50% compared with the results before compensation whether the space scale parameter of the low frequency phase is altered or the amplitude of the phase varies.
2014,
26: 011018.
doi: 10.3788/HPLPB201426.011018
Abstract:
For the use of the magneto-optic crystal in a high-power optical isolator, the relationship between the isolation and the incident light power is analyzed with Jones matrix using the parameters of actual optical elements. A compensation scheme for thermal induced depolarization in magneto-optic crystal is proposed, which is based on external material. The design method of the compensation scheme for two different materials is given. The result shows that at the power of 50 W, by using CaF2 crystal and SiO2, the isolation can be increased by 15 dB and 4 dB respectively.
For the use of the magneto-optic crystal in a high-power optical isolator, the relationship between the isolation and the incident light power is analyzed with Jones matrix using the parameters of actual optical elements. A compensation scheme for thermal induced depolarization in magneto-optic crystal is proposed, which is based on external material. The design method of the compensation scheme for two different materials is given. The result shows that at the power of 50 W, by using CaF2 crystal and SiO2, the isolation can be increased by 15 dB and 4 dB respectively.
2014,
26: 012001.
doi: 10.3788/HPLPB201426.012001
Abstract:
In surface defects evaluation of large fine optics, dusts and digs are very difficult to be distinguished from each other. In this paper, a pattern-recognition-based automatic discrimination method between dusts and digs is proposed to solve the problem. Based on the existing surface defects evaluation system(SDES), the process of feature selection and feature extraction is described on the basis of factor analysis. The dusts and the digs are classified according to the principle of Bayes discrimination. With the images of the calibration board, a data set that can be used for training and identifying dusts and digs is prepared. In order to obtain the suitable classifier, several comparison experiments are performed. The classifier has also been employed to the unlabeled data to verify the theory. The result shows that the accuracy is above 95%, which greatly reduces the number of false alarm that would otherwise result in remanufacturing. This method has already been applied to classifying dusts and digs for large fine optics in the inertial confinement fusion (ICF) system.
In surface defects evaluation of large fine optics, dusts and digs are very difficult to be distinguished from each other. In this paper, a pattern-recognition-based automatic discrimination method between dusts and digs is proposed to solve the problem. Based on the existing surface defects evaluation system(SDES), the process of feature selection and feature extraction is described on the basis of factor analysis. The dusts and the digs are classified according to the principle of Bayes discrimination. With the images of the calibration board, a data set that can be used for training and identifying dusts and digs is prepared. In order to obtain the suitable classifier, several comparison experiments are performed. The classifier has also been employed to the unlabeled data to verify the theory. The result shows that the accuracy is above 95%, which greatly reduces the number of false alarm that would otherwise result in remanufacturing. This method has already been applied to classifying dusts and digs for large fine optics in the inertial confinement fusion (ICF) system.
2014,
26: 012002.
doi: 10.3788/HPLPB201426.012002
Abstract:
To improve the quality of laser-induced breakdown spectroscopy, the effects of magnetic confinement on plasma were studied, which was excited by Nd: YAG laser. The experimental results show that plasma radiation intensity increased with increasing magnetic field under the same laser energy. By calculating, we can see that the spectral line intensity of Al, Ba, Fe and Ti increased about 52.35%, 46.64%, 64.01% and 51.73% under 0.5 T magnetic field, the spectral signal-to-noise ratio increased about 45.44%, 69.64%, 40.26% and 41.33%, while the electron temperature and electron density of plasma was heightened by 1 355.01 K and 0.531016 cm-3, respectively, as compared to those with no magnetic confinement. It is clear that using magnetic confinement is an effective measure for the enhancement of spectrum quality.
To improve the quality of laser-induced breakdown spectroscopy, the effects of magnetic confinement on plasma were studied, which was excited by Nd: YAG laser. The experimental results show that plasma radiation intensity increased with increasing magnetic field under the same laser energy. By calculating, we can see that the spectral line intensity of Al, Ba, Fe and Ti increased about 52.35%, 46.64%, 64.01% and 51.73% under 0.5 T magnetic field, the spectral signal-to-noise ratio increased about 45.44%, 69.64%, 40.26% and 41.33%, while the electron temperature and electron density of plasma was heightened by 1 355.01 K and 0.531016 cm-3, respectively, as compared to those with no magnetic confinement. It is clear that using magnetic confinement is an effective measure for the enhancement of spectrum quality.
2014,
26: 012003.
doi: 10.3788/HPLPB201426.012003
Abstract:
The Cu-doped SiO2 composite aerogels with different Cu doping content were successfully prepared by sol-gel process and subsequently supercritical drying with carbon dioxide. Tetramethyl orthosilicate and copper (Ⅱ) acetate were used as Si source and Cu source, respectively. The structures and properties of the composite aerogels were characterized by FTIR, SEM, EDS, BET and DMA. With the increase of the content of copper, the density of the composite aerogels increased and the specific surface area decreased. All of the samples processed a structure of 3-D network, low density (less than 40 mg/cm3), high specific surface area (more than 390 m2/g) and fine formability.
The Cu-doped SiO2 composite aerogels with different Cu doping content were successfully prepared by sol-gel process and subsequently supercritical drying with carbon dioxide. Tetramethyl orthosilicate and copper (Ⅱ) acetate were used as Si source and Cu source, respectively. The structures and properties of the composite aerogels were characterized by FTIR, SEM, EDS, BET and DMA. With the increase of the content of copper, the density of the composite aerogels increased and the specific surface area decreased. All of the samples processed a structure of 3-D network, low density (less than 40 mg/cm3), high specific surface area (more than 390 m2/g) and fine formability.
2014,
26: 012004.
doi: 10.3788/HPLPB201426.012004
Abstract:
The polystyrene (CH)/carbonized resorcinol formaldehyde (CRF), CRF/SiO2, CH/Al dual-layer perturbation targets for ICF resolved experiment were investigated. The CRF aerogel sheets with a density of 250 and 800 mg/cm3 were synthesized by sol-gel process. As the seed of the growth of hydrodynamic instability, the perturbation patterns were introduced onto the surface of CRF aerogel sheets and Al foil by laser micro-machining process. The CH films were directly coated on the patterned surface of CRF aerogel sheets(250 mg/cm3) and Al foil by spin-coating process while the SiO2 aerogel sheet was prepared on the CRF aerogel sheets(800 mg/cm3) by sol-gel process. The target parameters of CH/CRF, CRF/SiO2 and CH/Al dual-layer perturbation target were characterized by electro-balance, scanning electron microscope, tool microscope and surface profiler etc. The results indicated that the dual-layer perturbation target had good combination with clear interfaces, the perturbation patterns in the interfaces were sine, while the parameters were precisely measured.
The polystyrene (CH)/carbonized resorcinol formaldehyde (CRF), CRF/SiO2, CH/Al dual-layer perturbation targets for ICF resolved experiment were investigated. The CRF aerogel sheets with a density of 250 and 800 mg/cm3 were synthesized by sol-gel process. As the seed of the growth of hydrodynamic instability, the perturbation patterns were introduced onto the surface of CRF aerogel sheets and Al foil by laser micro-machining process. The CH films were directly coated on the patterned surface of CRF aerogel sheets(250 mg/cm3) and Al foil by spin-coating process while the SiO2 aerogel sheet was prepared on the CRF aerogel sheets(800 mg/cm3) by sol-gel process. The target parameters of CH/CRF, CRF/SiO2 and CH/Al dual-layer perturbation target were characterized by electro-balance, scanning electron microscope, tool microscope and surface profiler etc. The results indicated that the dual-layer perturbation target had good combination with clear interfaces, the perturbation patterns in the interfaces were sine, while the parameters were precisely measured.
2014,
26: 012005.
doi: 10.3788/HPLPB201426.012005
Abstract:
Based on the wave equation of ultra-intense linearly polarized laser pulse propagating in electron-positron plasmas, the filamentation instability was investigated. The nonlinear dispersion relation and the growth rate of instability were derived. The effects of temperature and laser intensity on the growth rate were analyzed. The results show that in an electron-positron plasma, the intensity of the filamentation instability is mainly determined by the competition between the nonlinearity in the interaction and the relativistic light ponderomotive driven density responses.
Based on the wave equation of ultra-intense linearly polarized laser pulse propagating in electron-positron plasmas, the filamentation instability was investigated. The nonlinear dispersion relation and the growth rate of instability were derived. The effects of temperature and laser intensity on the growth rate were analyzed. The results show that in an electron-positron plasma, the intensity of the filamentation instability is mainly determined by the competition between the nonlinearity in the interaction and the relativistic light ponderomotive driven density responses.
2014,
26: 012006.
doi: 10.3788/HPLPB201426.012006
Abstract:
Four 60% DKDP crystals were grown at different temperatures using point seed technique. The growing process was observed. The properties including optical transmittance, rocking curve and laser induced damage threshold were measured. The results show that the morphology of crystal grown at high temperature is more perfect than that grown at low temperature. The effect of growth temperature on optical transmittance for these crystals is slight. However, the structure perfection and the laser induced damage threshold decrease with the decrease of growth temperature.
Four 60% DKDP crystals were grown at different temperatures using point seed technique. The growing process was observed. The properties including optical transmittance, rocking curve and laser induced damage threshold were measured. The results show that the morphology of crystal grown at high temperature is more perfect than that grown at low temperature. The effect of growth temperature on optical transmittance for these crystals is slight. However, the structure perfection and the laser induced damage threshold decrease with the decrease of growth temperature.
2014,
26: 012007.
doi: 10.3788/HPLPB201426.012007
Abstract:
The present work investigates the fabrication process of precision Nd:YAG crystal slab which is extensively used in high-power slab lasers. Properties of the crystal and problems during fabrication were analyzed. A novel process based on the composite lap was proposed. Fabrication of a 100 mm30 mm3 mm sample revealed the validation of this process. Experiment results indicated that the composite lap was superior to conventional lap material for controlling edge collapsing in polishing process. Defect-free surface could be obtained using optimal size and size distribution of Al2O3 slurry. The surface figure of slab TIRs surface was 0.217, while that of the end surface was 0.1. The surface roughness approached 0.55 nm RMS. The precision of the intersection angle was 2.
The present work investigates the fabrication process of precision Nd:YAG crystal slab which is extensively used in high-power slab lasers. Properties of the crystal and problems during fabrication were analyzed. A novel process based on the composite lap was proposed. Fabrication of a 100 mm30 mm3 mm sample revealed the validation of this process. Experiment results indicated that the composite lap was superior to conventional lap material for controlling edge collapsing in polishing process. Defect-free surface could be obtained using optimal size and size distribution of Al2O3 slurry. The surface figure of slab TIRs surface was 0.217, while that of the end surface was 0.1. The surface roughness approached 0.55 nm RMS. The precision of the intersection angle was 2.
2014,
26: 012008.
doi: 10.3788/HPLPB201426.012008
Abstract:
The accuracy of transmission grating calibration on synchrotron radiation could be worsened by high-order harmonics. In order to correct this influence, a calibration method was proposed for the light source with weak high-order harmonics. This method corrected the fundamental wave diffraction efficiency using the high-order harmonics diffraction efficiencies which were obtained in calibration too. This verifying experiment was carried out on Beijing Synchrotron Radiation Facility. The experimental results show that the corrected ratio of first-zero order diffraction efficiency to zero-order agreed well with the calculated results between 100-800 eV where high-order harmonics existed. The ratio of second-order diffraction efficiency to first-order was more closed to the calculated results though some difference still existed. This difference came from the weak two-order diffraction.
The accuracy of transmission grating calibration on synchrotron radiation could be worsened by high-order harmonics. In order to correct this influence, a calibration method was proposed for the light source with weak high-order harmonics. This method corrected the fundamental wave diffraction efficiency using the high-order harmonics diffraction efficiencies which were obtained in calibration too. This verifying experiment was carried out on Beijing Synchrotron Radiation Facility. The experimental results show that the corrected ratio of first-zero order diffraction efficiency to zero-order agreed well with the calculated results between 100-800 eV where high-order harmonics existed. The ratio of second-order diffraction efficiency to first-order was more closed to the calculated results though some difference still existed. This difference came from the weak two-order diffraction.
2014,
26: 012009.
doi: 10.3788/HPLPB201426.012009
Abstract:
For the need of X-ray wavelength determination of laser plasma, a novel method was presented for wavelength determination by using curved spectral line measured with planar crystal spectrometer. In normal reference line method, the wavelength of more than two reference lines should be determined before wavelength determination. By using curved spectral line method, no reference line was used to determine wavelength. In this paper, curved image of He self-emission spectrum of aluminum plasma was recorded in experiment, and the uncertainty of this method using the present spectrometer was about 210-4 nm in theory.
For the need of X-ray wavelength determination of laser plasma, a novel method was presented for wavelength determination by using curved spectral line measured with planar crystal spectrometer. In normal reference line method, the wavelength of more than two reference lines should be determined before wavelength determination. By using curved spectral line method, no reference line was used to determine wavelength. In this paper, curved image of He self-emission spectrum of aluminum plasma was recorded in experiment, and the uncertainty of this method using the present spectrometer was about 210-4 nm in theory.
2014,
26: 012010.
doi: 10.3788/HPLPB201426.012010
Abstract:
Propagation characteristics of the shock waves induced by nanosecond laser in material were investigated by ultrafast time-resolved optical diagnosis and studied based on the basic theories of the reflection and refraction of spherical waves across a planar interface. The evolution processes of time-resolved optical images of shock waves propagation in material and plasmas expansion in air were obtained. Moreover, the reflection and refraction waves would be yielded when the generated shock waves arrived at the surface of the sample. Meanwhile, it was found that the intensity of the reflection and the refraction waves at the interface was determined by the incident angle of the shock wave, and the velocity of shock wave propagating in material was different for different shock waves.
Propagation characteristics of the shock waves induced by nanosecond laser in material were investigated by ultrafast time-resolved optical diagnosis and studied based on the basic theories of the reflection and refraction of spherical waves across a planar interface. The evolution processes of time-resolved optical images of shock waves propagation in material and plasmas expansion in air were obtained. Moreover, the reflection and refraction waves would be yielded when the generated shock waves arrived at the surface of the sample. Meanwhile, it was found that the intensity of the reflection and the refraction waves at the interface was determined by the incident angle of the shock wave, and the velocity of shock wave propagating in material was different for different shock waves.
2014,
26: 013001.
doi: 10.3788/HPLPB201426.013001
Abstract:
We obtained theinitial parameters for the 35 GHz double anode magnetron injection gun based on the trade-off equations, and got the parameters optimized by programming. We did a 3D numerical simulation using the calculation module of the magnetron injection gun of the particle simulation software, CHIPIC, and got the high performance electron gun with a ratio of transverse velocity to longitudinal velocity of 1.5 and a velocity spread of 5.4%. This beam could meet the requirements of the 35 GHz, 100 kW gyrotron oscillation tube.
We obtained theinitial parameters for the 35 GHz double anode magnetron injection gun based on the trade-off equations, and got the parameters optimized by programming. We did a 3D numerical simulation using the calculation module of the magnetron injection gun of the particle simulation software, CHIPIC, and got the high performance electron gun with a ratio of transverse velocity to longitudinal velocity of 1.5 and a velocity spread of 5.4%. This beam could meet the requirements of the 35 GHz, 100 kW gyrotron oscillation tube.
2014,
26: 013002.
doi: 10.3788/HPLPB201426.013002
Abstract:
The ultra-wideband TEM horn antenna fed by coaxial cable and loaded with lumped resistor for the application of imaging radar system is presented. The low-frequency characteristic of the antenna and its directional radiation ability are largely improved with the smoothly tapered structure and loading technology instead of the original design taking account of the radiation characteristics, the reflection from the feed section and the dimension limitations. Finally, a pair of antennas are fabricated and measured based on the theoretical analysis and simulation. It is concluded that the antenna has a good impedance bandwidth of about 11∶1, good radiation characteristics and moderate gain for voltage standing wave ratio (VSWR) below 2 by comparing the simulated results with the measurements, which may be suitable for the requirements of the radar system.
The ultra-wideband TEM horn antenna fed by coaxial cable and loaded with lumped resistor for the application of imaging radar system is presented. The low-frequency characteristic of the antenna and its directional radiation ability are largely improved with the smoothly tapered structure and loading technology instead of the original design taking account of the radiation characteristics, the reflection from the feed section and the dimension limitations. Finally, a pair of antennas are fabricated and measured based on the theoretical analysis and simulation. It is concluded that the antenna has a good impedance bandwidth of about 11∶1, good radiation characteristics and moderate gain for voltage standing wave ratio (VSWR) below 2 by comparing the simulated results with the measurements, which may be suitable for the requirements of the radar system.
2014,
26: 013003.
doi: 10.3788/HPLPB201426.013003
Abstract:
The design of an UWB matching feed structure was presented. The structure adopted a series-parallel hybrid feed method. In an ideal conditions, the structure could feed for a 200 UWB antenna from a 50 coax without reflection. Experiments based on TEM horns and reflector antenna with the structure were done. The results showed that the performance of the antennas was greatly improved, the radiated field of TEM horn increased up to 15% and the reflector antenna increased up to 27% correspondingly.
The design of an UWB matching feed structure was presented. The structure adopted a series-parallel hybrid feed method. In an ideal conditions, the structure could feed for a 200 UWB antenna from a 50 coax without reflection. Experiments based on TEM horns and reflector antenna with the structure were done. The results showed that the performance of the antennas was greatly improved, the radiated field of TEM horn increased up to 15% and the reflector antenna increased up to 27% correspondingly.
2014,
26: 013004.
doi: 10.3788/HPLPB201426.013004
Abstract:
This paper presents a novel type of overmoded bend coaxial waveguide with a 45 bend angle at a center frequency of 4.0 GHz. The basic principle of the overmoded bend coaxial waveguide is introduced, and the condition of realizing high efficiency turning transmission and a mode problem on the overmoded waveguide are analyzed. The simulation result indicates that, at the center frequency, the transmission efficiency of the fundamental mode is over 99% and the reflectance is about 0.04. In the range of 3.8 to 4.2 GHz, the transmission efficiency of the fundamental mode is over 95% and the reflectance is below 0.22. The overmoded bend coaxial waveguide with a turning radius about 80 mm, which has the features of simple structure, small turning radius and flexible bend angle, and also needs no media support, is suitable for turning transmission of the overmoded coaxial waveguide in high power microwave feeder system.
This paper presents a novel type of overmoded bend coaxial waveguide with a 45 bend angle at a center frequency of 4.0 GHz. The basic principle of the overmoded bend coaxial waveguide is introduced, and the condition of realizing high efficiency turning transmission and a mode problem on the overmoded waveguide are analyzed. The simulation result indicates that, at the center frequency, the transmission efficiency of the fundamental mode is over 99% and the reflectance is about 0.04. In the range of 3.8 to 4.2 GHz, the transmission efficiency of the fundamental mode is over 95% and the reflectance is below 0.22. The overmoded bend coaxial waveguide with a turning radius about 80 mm, which has the features of simple structure, small turning radius and flexible bend angle, and also needs no media support, is suitable for turning transmission of the overmoded coaxial waveguide in high power microwave feeder system.
2014,
26: 013005.
doi: 10.3788/HPLPB201426.013005
Abstract:
We provided an analytical study of ultra-wideband pulse spatial power combination in time domain, and got the conclusion that the multiplex pulses which had the same polarization direction and unified waveform got the maximum output power. And based on that, a linear-array fed parabolic cylinder antenna was proposed. A line array of 10 tacked TEM horns was arranged in the focal-line, which formed 10 coherent beams after illuminating the reflector. An UWB high power microwave beam on boresight was achieved by coherent superposition of these beams. Simulation results showed that compared with the single-fed antenna with the optimalaperture, the designed antenna increased the radiated power density up to 87 times, and decreased the combined beam width from 66to 8. Ultra-wideband high-power microwave pulse synthesis was realized effectively through spatial power combination.
We provided an analytical study of ultra-wideband pulse spatial power combination in time domain, and got the conclusion that the multiplex pulses which had the same polarization direction and unified waveform got the maximum output power. And based on that, a linear-array fed parabolic cylinder antenna was proposed. A line array of 10 tacked TEM horns was arranged in the focal-line, which formed 10 coherent beams after illuminating the reflector. An UWB high power microwave beam on boresight was achieved by coherent superposition of these beams. Simulation results showed that compared with the single-fed antenna with the optimalaperture, the designed antenna increased the radiated power density up to 87 times, and decreased the combined beam width from 66to 8. Ultra-wideband high-power microwave pulse synthesis was realized effectively through spatial power combination.
2014,
26: 013006.
doi: 10.3788/HPLPB201426.013006
Abstract:
Based on a low refractive index material medium using metal mesh and foam material, a microwave antenna with monopole radiation was made. Antenna directionality of the traditional antenna and the antenna using low refractive index medium was studied contrastively by the HFSS (electromagnetic simulation software). The comparison results indicated that antenna directionality of the antenna using low refractive index medium was better than that of the traditional antenna. An experiment was conducted to measure antenna directionality of the antenna using low refractive index medium. Good agreement was obtained between the experimental results and the theoretical predictions.
Based on a low refractive index material medium using metal mesh and foam material, a microwave antenna with monopole radiation was made. Antenna directionality of the traditional antenna and the antenna using low refractive index medium was studied contrastively by the HFSS (electromagnetic simulation software). The comparison results indicated that antenna directionality of the antenna using low refractive index medium was better than that of the traditional antenna. An experiment was conducted to measure antenna directionality of the antenna using low refractive index medium. Good agreement was obtained between the experimental results and the theoretical predictions.
2014,
26: 013007.
doi: 10.3788/HPLPB201426.013007
Abstract:
The high frequency characteristics and beam-wave interaction system with four cavities in the Ka-band sheet beam relativistic klystron amplifier were simulated with three-dimension electromagnetic codes. The simulation results show that for a 500 kV, 1 kA, 40∶1 aspect ratio sheet beam and 1.94 kW input power with 0.8 T leading magnetic field, the sheet beam klystron is capable of generating an output power higher than 142 MW at 40 GHz with a gain of 48.6 dB and a maximum efficiency of 28.4% at a frequency of 40 GHz.
The high frequency characteristics and beam-wave interaction system with four cavities in the Ka-band sheet beam relativistic klystron amplifier were simulated with three-dimension electromagnetic codes. The simulation results show that for a 500 kV, 1 kA, 40∶1 aspect ratio sheet beam and 1.94 kW input power with 0.8 T leading magnetic field, the sheet beam klystron is capable of generating an output power higher than 142 MW at 40 GHz with a gain of 48.6 dB and a maximum efficiency of 28.4% at a frequency of 40 GHz.
2014,
26: 013101.
doi: 10.3788/HPLPB201426.013101
Abstract:
The light path of digital holographic microscope in line is designed to meet the requirements of high spatial resolution and big field of view which are the key parameters of the movable quantum cascade laser-terahertz (QCL-THz) digital holography imager. The numerical aperture of the microscope objective is 0.707 or 0.8, the amplification times is 6 and the optimal working distance is 15 mm. It can be achieved that the field of view is 10 mm and the spatial resolution is 100 micron in this light path using terahertz source whose wavelength is 96.8 microns.
The light path of digital holographic microscope in line is designed to meet the requirements of high spatial resolution and big field of view which are the key parameters of the movable quantum cascade laser-terahertz (QCL-THz) digital holography imager. The numerical aperture of the microscope objective is 0.707 or 0.8, the amplification times is 6 and the optimal working distance is 15 mm. It can be achieved that the field of view is 10 mm and the spatial resolution is 100 micron in this light path using terahertz source whose wavelength is 96.8 microns.
2014,
26: 014001.
doi: 10.3788/HPLPB201426.014001
Abstract:
The self-developed 3D PIC/MCC algorithm is described, including the algorithm flow design, collision treatment mechanism and so on. The numerical simulation of the 15~20 mA H- cusp source developed by the China Institute of Atomic Energy is researched with this algorithm. The results show that H- cusp source can produce ion beams that uniformly distribute in objective space. Using the optimized virtual filtering field can effectively filter high-energy electrons and lead to the low-energy electron in the ion source downstream region to increase. The negative hydrogen ions volume generation efficiency is improved effectively.
The self-developed 3D PIC/MCC algorithm is described, including the algorithm flow design, collision treatment mechanism and so on. The numerical simulation of the 15~20 mA H- cusp source developed by the China Institute of Atomic Energy is researched with this algorithm. The results show that H- cusp source can produce ion beams that uniformly distribute in objective space. Using the optimized virtual filtering field can effectively filter high-energy electrons and lead to the low-energy electron in the ion source downstream region to increase. The negative hydrogen ions volume generation efficiency is improved effectively.
2014,
26: 014002.
doi: 10.3788/HPLPB201426.014002
Abstract:
An experimental system and a numerical model are developed, which use a continuous X-ray source to determine the X-ray direct drive response of strip line in vacuum. The experimental system includes a vacuum cavity, a vacuum group and an electrometer, and the numerical model is a 1-D strip line model which is able to describe the gaps between cables conductor and dielectric and the conductivity in the dielectric induced by X-ray. The continuous X-ray environment parameters, such as the X-ray spectrum, flux and so on, are obtained by using MCNP Monte Carlo program. Two strip line models are tested and the experimental results are compared with responses calculated using the numerical model above. It indicates that the X-ray direct drive current waveforms are similar and their amplitudes are approximate, if the gaps hypothesis is permitted which is destined to exist in a real strip line. Therefore, the numerical model used to describe cables response under continuous X-ray environment is reasonable to some extent.
An experimental system and a numerical model are developed, which use a continuous X-ray source to determine the X-ray direct drive response of strip line in vacuum. The experimental system includes a vacuum cavity, a vacuum group and an electrometer, and the numerical model is a 1-D strip line model which is able to describe the gaps between cables conductor and dielectric and the conductivity in the dielectric induced by X-ray. The continuous X-ray environment parameters, such as the X-ray spectrum, flux and so on, are obtained by using MCNP Monte Carlo program. Two strip line models are tested and the experimental results are compared with responses calculated using the numerical model above. It indicates that the X-ray direct drive current waveforms are similar and their amplitudes are approximate, if the gaps hypothesis is permitted which is destined to exist in a real strip line. Therefore, the numerical model used to describe cables response under continuous X-ray environment is reasonable to some extent.
2014,
26: 014003.
doi: 10.3788/HPLPB201426.014003
Abstract:
In order to investigate velocity and angle effects of light flash radiation produced by hypervelocity impact, experiments have been conducted under six kinds of experimental conditions by using an optical pyrometer measurement system and a two-stage light-gas gun loading system. Each experiment used anoptical fiber probe. The relationship of impact velocity and projectile incidence angle was obtained for hypervelocity impact on LY12 aluminum target, based on original data and calibration by Matlab programmable treatments under given experimental condition and optical fiber probe scheme. Experimental results show that, during hypervelocity impact, the impact light flash radiated temperature is approximately proportional with the square of product of impact velocity and sine of projectile incidence angle (angle between trajectory and target plane) before the radiated temperature reaches its peak, and then it is approximately proportional with the 0.75 power of the product of impact velocity and sine of projectile incidence angle after the peak appearing, which is basically identical with the theoretical derivation.
In order to investigate velocity and angle effects of light flash radiation produced by hypervelocity impact, experiments have been conducted under six kinds of experimental conditions by using an optical pyrometer measurement system and a two-stage light-gas gun loading system. Each experiment used anoptical fiber probe. The relationship of impact velocity and projectile incidence angle was obtained for hypervelocity impact on LY12 aluminum target, based on original data and calibration by Matlab programmable treatments under given experimental condition and optical fiber probe scheme. Experimental results show that, during hypervelocity impact, the impact light flash radiated temperature is approximately proportional with the square of product of impact velocity and sine of projectile incidence angle (angle between trajectory and target plane) before the radiated temperature reaches its peak, and then it is approximately proportional with the 0.75 power of the product of impact velocity and sine of projectile incidence angle after the peak appearing, which is basically identical with the theoretical derivation.
2014,
26: 014004.
doi: 10.3788/HPLPB201426.014004
Abstract:
Nonlinear resonances and halo-chaos behavior of an intense charged-particle beam are discussed. The influences of the focusing field strength and the beam perveance about the intense charged-particle beam are analyzed. The beam envelope oscillations and the orbits of the single-particle are simulated by using Poincar mapping technique. The simulation result clearly illustrates the nonlinear oscillations of the beam envelope and the spatial distribution of the corresponding test particle under different conditions. It shows that the beam self-field leads to the nonlinear oscillations of the beam envelope. With the increase of beam self-field and focusing field, a growing number of diffuse particles appear in the particle spatial distribution along with the emergence of the resonance island.
Nonlinear resonances and halo-chaos behavior of an intense charged-particle beam are discussed. The influences of the focusing field strength and the beam perveance about the intense charged-particle beam are analyzed. The beam envelope oscillations and the orbits of the single-particle are simulated by using Poincar mapping technique. The simulation result clearly illustrates the nonlinear oscillations of the beam envelope and the spatial distribution of the corresponding test particle under different conditions. It shows that the beam self-field leads to the nonlinear oscillations of the beam envelope. With the increase of beam self-field and focusing field, a growing number of diffuse particles appear in the particle spatial distribution along with the emergence of the resonance island.
2014,
26: 014005.
doi: 10.3788/HPLPB201426.014005
Abstract:
For optimization design of a neutron multiplicity counter and forming a guidance of the experiment, we describe a detailed method using Monte Carlo codes to generate neutron time pulse chain for stochastic simulation. A new fitting algorithm to calculate the die-away time was proposed. The applicability of calibrated parameters using 252Cf to plutonium samples was evaluated on the big cavity detection system, and the detection efficiency bias was calculated. Using the optimizing principle, the gate width in MSR algorithm was given for several plutonium samples. The curve of expected assay precision (RSD) vs 240Pu effective mass was given. The simulation results showed that the difference of detection efficiency between 252Cf and Plutonium was 3%. No difference was observed in gate fraction between using ratio method and formula method. With a measure time of 1000 s, the big cavity detection system had a RSD of about 4% for kg level plutonium metal. Those results will play an important role in determining necessary measurement time in plutonium measurement.
For optimization design of a neutron multiplicity counter and forming a guidance of the experiment, we describe a detailed method using Monte Carlo codes to generate neutron time pulse chain for stochastic simulation. A new fitting algorithm to calculate the die-away time was proposed. The applicability of calibrated parameters using 252Cf to plutonium samples was evaluated on the big cavity detection system, and the detection efficiency bias was calculated. Using the optimizing principle, the gate width in MSR algorithm was given for several plutonium samples. The curve of expected assay precision (RSD) vs 240Pu effective mass was given. The simulation results showed that the difference of detection efficiency between 252Cf and Plutonium was 3%. No difference was observed in gate fraction between using ratio method and formula method. With a measure time of 1000 s, the big cavity detection system had a RSD of about 4% for kg level plutonium metal. Those results will play an important role in determining necessary measurement time in plutonium measurement.
2014,
26: 014006.
doi: 10.3788/HPLPB201426.014006
Abstract:
Electromagnetic radiation model which could be used to calculate the full radiation in reverberation chamber was modeled in this paper using a large number of incidence waves which uniformly distributed on a unit sphere. The Agrawal scatter voltage formulation was used to calculate the payload current response. The influences of angle of incidence, polarization and the number of incidence waves on the payload current response were also investigated. The comparison was made between the simulation results with the Monte-Carlo result. The results showed that the simulation results obtained in this work agreed with the results of Monte-Carlo, and when the incidence angle was 0-, and polarization angle was 0-, the signal integrity could be fulfilled. When the number of incidence waves was no less than 100, the full radiation environment could be realized.
Electromagnetic radiation model which could be used to calculate the full radiation in reverberation chamber was modeled in this paper using a large number of incidence waves which uniformly distributed on a unit sphere. The Agrawal scatter voltage formulation was used to calculate the payload current response. The influences of angle of incidence, polarization and the number of incidence waves on the payload current response were also investigated. The comparison was made between the simulation results with the Monte-Carlo result. The results showed that the simulation results obtained in this work agreed with the results of Monte-Carlo, and when the incidence angle was 0-, and polarization angle was 0-, the signal integrity could be fulfilled. When the number of incidence waves was no less than 100, the full radiation environment could be realized.
2014,
26: 014007.
doi: 10.3788/HPLPB201426.014007
Abstract:
Response functions of different thickness combinations are calculated by using the Geant4 code. It is concluded that the FWHM and the minimum detectable limit depend upon the thickness of polythene and aluminum layer respectively, while the peak value depends on both of them. The radiation experiments using the D-D neutron source are carried out to obtain the detection efficiencies for four different thickness combinations, which agree with the calculated results well and this verifies the reliability of the Geant4 code.
Response functions of different thickness combinations are calculated by using the Geant4 code. It is concluded that the FWHM and the minimum detectable limit depend upon the thickness of polythene and aluminum layer respectively, while the peak value depends on both of them. The radiation experiments using the D-D neutron source are carried out to obtain the detection efficiencies for four different thickness combinations, which agree with the calculated results well and this verifies the reliability of the Geant4 code.
2014,
26: 014008.
doi: 10.3788/HPLPB201426.014008
Abstract:
The changes of the capacitance of ferroelectric cathode under high trigger voltage are analyzed. The change is the plasma diffusion along the surface of top electrode under high trigger voltage. The model of the equivalent capacitance of ferroelectric cathode is established. And on this basis, the equation of the lateral velocity of the plasma diffusion is derived. An antiferroelectric cathode material, lanthanum-doped lead zirconate stannate titanate is prepared by using the method of solid-state calcinations. The lateral velocity of the plasma diffusion is calculated by measuring the voltage and charge-recharge current of ferroelectric cathode under trigger voltage of La-doped Pb(Zr, Sn, Ti)O3 ferroelectric cathode. The result is about 1.89106 cm/s.
The changes of the capacitance of ferroelectric cathode under high trigger voltage are analyzed. The change is the plasma diffusion along the surface of top electrode under high trigger voltage. The model of the equivalent capacitance of ferroelectric cathode is established. And on this basis, the equation of the lateral velocity of the plasma diffusion is derived. An antiferroelectric cathode material, lanthanum-doped lead zirconate stannate titanate is prepared by using the method of solid-state calcinations. The lateral velocity of the plasma diffusion is calculated by measuring the voltage and charge-recharge current of ferroelectric cathode under trigger voltage of La-doped Pb(Zr, Sn, Ti)O3 ferroelectric cathode. The result is about 1.89106 cm/s.
2014,
26: 015001.
doi: 10.3788/HPLPB201426.015001
Abstract:
A coaxial pulse voltage probe is designed to measure the signal through the input of TEM cell or GTEM cell in calibrating electromagnetic pulse(EMP) sensors. The output differential signal of the probe can be converted by numerical integration to obtain the measured EMP field, and the measurement sensitivity can be adjusted. The peak E-field distribution and the port characteristic impedance of the probe with different monopoles are simulated and compared. A spiry monopole is selected according to the simulation. Experiment verification is carried out. The frequency response and the sensitivity of the fabricated prototype coaxial probe are measured. The variation of sensitivity coefficient with the distance between the spiry monopole and the inner-conductor center is obtained. The simulation and the experiment indicate that the spiry monopole has very small perturbation to the inner field and the impedance of the coaxial probe. This kind of probe can be used in the measurement and calibration of EMP with rise time of nanosecond level.
A coaxial pulse voltage probe is designed to measure the signal through the input of TEM cell or GTEM cell in calibrating electromagnetic pulse(EMP) sensors. The output differential signal of the probe can be converted by numerical integration to obtain the measured EMP field, and the measurement sensitivity can be adjusted. The peak E-field distribution and the port characteristic impedance of the probe with different monopoles are simulated and compared. A spiry monopole is selected according to the simulation. Experiment verification is carried out. The frequency response and the sensitivity of the fabricated prototype coaxial probe are measured. The variation of sensitivity coefficient with the distance between the spiry monopole and the inner-conductor center is obtained. The simulation and the experiment indicate that the spiry monopole has very small perturbation to the inner field and the impedance of the coaxial probe. This kind of probe can be used in the measurement and calibration of EMP with rise time of nanosecond level.
2014,
26: 015002.
doi: 10.3788/HPLPB201426.015002
Abstract:
For the problem that TEM horn antenna used in the radiating-wave nuclear electromagnetic pulse (NEMP) simulator has limited ability of low frequency radiating, two basic types of TEM horn antennas (composed of plates and wires respectively) are analyzed. Based on TEM horn antenna composed of wires that can make simulator lighter, a new type of TEM horn antenna is designed by using the structure of helixes end and attaching the shielded plates circuit to antenna. Results show that compared with the common type of the TEM horn antenna composed of wires, this new type of antenna has improved the ability of low frequency radiating greatly. The pulse width of near field waveform is longer by almost seven nanoseconds, and the peak value of pulse is larger by almost one kilovolt per meter. Increasing the radius of helixes and decreasing the pitch of helixes can further enhance both pulse width and peak value of the field strength. Meanwhile, attaching the shielded plates circuit to antenna can further lower down the wave crest generated by reflected signals, which makes the near field waveforms much better.
For the problem that TEM horn antenna used in the radiating-wave nuclear electromagnetic pulse (NEMP) simulator has limited ability of low frequency radiating, two basic types of TEM horn antennas (composed of plates and wires respectively) are analyzed. Based on TEM horn antenna composed of wires that can make simulator lighter, a new type of TEM horn antenna is designed by using the structure of helixes end and attaching the shielded plates circuit to antenna. Results show that compared with the common type of the TEM horn antenna composed of wires, this new type of antenna has improved the ability of low frequency radiating greatly. The pulse width of near field waveform is longer by almost seven nanoseconds, and the peak value of pulse is larger by almost one kilovolt per meter. Increasing the radius of helixes and decreasing the pitch of helixes can further enhance both pulse width and peak value of the field strength. Meanwhile, attaching the shielded plates circuit to antenna can further lower down the wave crest generated by reflected signals, which makes the near field waveforms much better.
2014,
26: 015003.
doi: 10.3788/HPLPB201426.015003
Abstract:
Electrode erosion of gas spark gaps (GSGs) with Mo, WCu, and W main electrodes in current discharge was studied. Micrographs and erosion rates of GSG electrodes after erosion were investigated. Characteristic of electrode erosion was also analyzed. The main electrode erosion rates of Mo, WCu, and W GSG switches are 3.3210-2, 2.6310-2, and 1.7410-2 C-1m-2, respectively. The W GSG exhibits the minimum main electrode erosion rate. The experimental results indicate that main electrodes are heavily ablated at the center and present cracks and holes evidently. The main electrodes of Mo GSG exhibit melted state on the surface and Mo cathode presents a great quantity of cracks with 10 m in width and pores with 10 m in diameter. A few sphere W saliences with 20 m in diameter form on the surface of main electrodes of WCu and W GSG switches. Splashing particles are deposited on the inwall of sleeve of GSG. The WCu, Mo and W switches present the biggest deposited particles with 10 m in diameter, mediate particles with 2 m in diameter, and the smallest particles with diameter less than 1 m, respectively. Therefore, tungsten which presents excellent anti-erosion performance could be selected firstly as main electrode materials of GSG.
Electrode erosion of gas spark gaps (GSGs) with Mo, WCu, and W main electrodes in current discharge was studied. Micrographs and erosion rates of GSG electrodes after erosion were investigated. Characteristic of electrode erosion was also analyzed. The main electrode erosion rates of Mo, WCu, and W GSG switches are 3.3210-2, 2.6310-2, and 1.7410-2 C-1m-2, respectively. The W GSG exhibits the minimum main electrode erosion rate. The experimental results indicate that main electrodes are heavily ablated at the center and present cracks and holes evidently. The main electrodes of Mo GSG exhibit melted state on the surface and Mo cathode presents a great quantity of cracks with 10 m in width and pores with 10 m in diameter. A few sphere W saliences with 20 m in diameter form on the surface of main electrodes of WCu and W GSG switches. Splashing particles are deposited on the inwall of sleeve of GSG. The WCu, Mo and W switches present the biggest deposited particles with 10 m in diameter, mediate particles with 2 m in diameter, and the smallest particles with diameter less than 1 m, respectively. Therefore, tungsten which presents excellent anti-erosion performance could be selected firstly as main electrode materials of GSG.
2014,
26: 015101.
doi: 10.3788/HPLPB201426.015101
Abstract:
A series of magnetically driven flyer plates experiments were performed on Yang accelerator with electrode material of LY-12 alloy and stainless steel. By changing the module parameters, we can acquire the desired current waveform for launching flyer plates shocklessly on stripline and coaxial load configurations. Considering the efficiency factor of current history, we calculated the free-surface velocity and flyer velocity history, which were in good agreement with the measured results. In addition, with current calculation model which considered variable load inductance, we calculated load current and flyer velocity which were also in agreement with the measured results. In this way, we could design an optimized load configuration that minimized the axial variation of the striplines magnetic pressure. Furthermore, we can predict sample stress history and flyer velocity on more powerful pulse facility.
A series of magnetically driven flyer plates experiments were performed on Yang accelerator with electrode material of LY-12 alloy and stainless steel. By changing the module parameters, we can acquire the desired current waveform for launching flyer plates shocklessly on stripline and coaxial load configurations. Considering the efficiency factor of current history, we calculated the free-surface velocity and flyer velocity history, which were in good agreement with the measured results. In addition, with current calculation model which considered variable load inductance, we calculated load current and flyer velocity which were also in agreement with the measured results. In this way, we could design an optimized load configuration that minimized the axial variation of the striplines magnetic pressure. Furthermore, we can predict sample stress history and flyer velocity on more powerful pulse facility.
2014,
26: 015102.
doi: 10.3788/HPLPB201426.015102
Abstract:
Ultra-high vacuum (UHV) has been demonstrated as the most important condition for long lifetime GaAs photocathode. To create the UHV environment and extend the GaAs lifetime, the electron beam wall loss in DC injectors is studied in this paper. A DC injector is installed in free electron. laser THz (FEL-THz) facility in CAEP. The study is based on Gaussian distribution model. With theoretical analysis, numerical calculation, dynamic simulation, thermal simulation and prototype experiment discussion, this beam loss is proved to be a few watts, indicating that it is the main reason for vacuum and quantum efficiency loss, which will dramatically decline the beam-out time. Furthermore, the study also indicates that the tube diameter the after the anode should be at least 45 mm.
Ultra-high vacuum (UHV) has been demonstrated as the most important condition for long lifetime GaAs photocathode. To create the UHV environment and extend the GaAs lifetime, the electron beam wall loss in DC injectors is studied in this paper. A DC injector is installed in free electron. laser THz (FEL-THz) facility in CAEP. The study is based on Gaussian distribution model. With theoretical analysis, numerical calculation, dynamic simulation, thermal simulation and prototype experiment discussion, this beam loss is proved to be a few watts, indicating that it is the main reason for vacuum and quantum efficiency loss, which will dramatically decline the beam-out time. Furthermore, the study also indicates that the tube diameter the after the anode should be at least 45 mm.
2014,
26: 015103.
doi: 10.3788/HPLPB201426.015103
Abstract:
The mechanical center of beam position monitor (BPM) vacuum tune in particle accelerator can be drifted comparatively large away from the magnetic center of quadrupole under the environment of foundation vibration, temperature, thermal effects, etc. We tried to apply capacitor sensor to real-time drift monitoring. Firstly, we analyzed the capacitors measurement principle, and designed the scheme of synchronous measurement of beam orbit vibration. After that, we made a dedicated test capacitor sensor, and tested the sensors linearity, resolution and frequency response with data acquisition instruments in laboratory. Results show that it can monitor 2 m relative movement and up to 300 Hz vibration frequency. Capacitor sensors can be applied to the synchronous measurement of beam orbit and relative environment parameters.
The mechanical center of beam position monitor (BPM) vacuum tune in particle accelerator can be drifted comparatively large away from the magnetic center of quadrupole under the environment of foundation vibration, temperature, thermal effects, etc. We tried to apply capacitor sensor to real-time drift monitoring. Firstly, we analyzed the capacitors measurement principle, and designed the scheme of synchronous measurement of beam orbit vibration. After that, we made a dedicated test capacitor sensor, and tested the sensors linearity, resolution and frequency response with data acquisition instruments in laboratory. Results show that it can monitor 2 m relative movement and up to 300 Hz vibration frequency. Capacitor sensors can be applied to the synchronous measurement of beam orbit and relative environment parameters.
2014,
26: 015104.
doi: 10.3788/HPLPB201426.015104
Abstract:
The paper introduces control survey network of installation strategy in the new HIMM (Heavy Ion Medical Machine). The 3D survey network is based on laser tracker and SA (Spatial Analyzer). Nine fiducial references and two scale bars were designed to guarantee high accuracy in control survey network, and Digital Level was used for altitude. The final RMS error of the global network could reach 0.04 mm, which guarantees the transverse position of quadrupoles requirement (0.10 mm) on the synchrotron.
The paper introduces control survey network of installation strategy in the new HIMM (Heavy Ion Medical Machine). The 3D survey network is based on laser tracker and SA (Spatial Analyzer). Nine fiducial references and two scale bars were designed to guarantee high accuracy in control survey network, and Digital Level was used for altitude. The final RMS error of the global network could reach 0.04 mm, which guarantees the transverse position of quadrupoles requirement (0.10 mm) on the synchrotron.
2014,
26: 015105.
doi: 10.3788/HPLPB201426.015105
Abstract:
The active beam scanning system for heavy ion therapy has some advantages in some respects. In order to achieve spot scanning using pencil beam for heavy ion therapy, the control system needs to control scanning magnet. The therapy plan generates dose data and tumor area therapy data, and transmits them to the dose controller and spot scanning controller. At the same time, the accelerator control system transmits synchronous timing event data to the spot scanning controller, then the spot scanning controller waits for synchronous trigger from the synchronous timing system. When the dose controller sends trigger plus to the spot scanning controller, the spot scanning controller needs to change spot based on the tumor area therapy data, and curves it by interpolation algorithm. The dose controller counts dose pluses from the front-end electronics of the gas ionization chamber. When therapy dose is over, the dose controller sends a plus to control the Faraday cup to block heavy ion beam to realize safe therapy by spot scanning. Experiments show that with the current running power supply, magnet devices, and beam quality, the spot scanning control system can control pencil beam scanning spot by spot between 2 mm.
The active beam scanning system for heavy ion therapy has some advantages in some respects. In order to achieve spot scanning using pencil beam for heavy ion therapy, the control system needs to control scanning magnet. The therapy plan generates dose data and tumor area therapy data, and transmits them to the dose controller and spot scanning controller. At the same time, the accelerator control system transmits synchronous timing event data to the spot scanning controller, then the spot scanning controller waits for synchronous trigger from the synchronous timing system. When the dose controller sends trigger plus to the spot scanning controller, the spot scanning controller needs to change spot based on the tumor area therapy data, and curves it by interpolation algorithm. The dose controller counts dose pluses from the front-end electronics of the gas ionization chamber. When therapy dose is over, the dose controller sends a plus to control the Faraday cup to block heavy ion beam to realize safe therapy by spot scanning. Experiments show that with the current running power supply, magnet devices, and beam quality, the spot scanning control system can control pencil beam scanning spot by spot between 2 mm.
2014,
26: 015106.
doi: 10.3788/HPLPB201426.015106
Abstract:
Stringent tolerance budget is restricted on the linear accelerator (linac) parameters, such as the mean beam energy stability, peak current variation, electron bunch arrival time jitter, and the transverse beam position offset, in order to generate stable output pulses in modern linac driven free electron laser facility. In this paper, a corrugated pipe is used as a beam energy stabilizer. Analytical and numerical methods for designing such kind of stabilizer are described, and the simulation results show that the beam energy jitter can be reduced more than 10% after this structure is adopted for the case of Dalian Coherent Light Source (DCLS) linac.
Stringent tolerance budget is restricted on the linear accelerator (linac) parameters, such as the mean beam energy stability, peak current variation, electron bunch arrival time jitter, and the transverse beam position offset, in order to generate stable output pulses in modern linac driven free electron laser facility. In this paper, a corrugated pipe is used as a beam energy stabilizer. Analytical and numerical methods for designing such kind of stabilizer are described, and the simulation results show that the beam energy jitter can be reduced more than 10% after this structure is adopted for the case of Dalian Coherent Light Source (DCLS) linac.
2014,
26: 019001.
doi: 10.3788/HPLPB201426.019001
Abstract:
3D reconstruction method based on computer vision is widely used in various industries. Though the 3D reconstruction of opaque surfaces with Lambertian reflectance on which the current research is mainly concentrated is a well-studied issue, the non-Lambertian surfaces pose challenging problems for the 3D reconstruction. Unfortunately, most surfaces of the objects in the actual scene are non-Lambertian, therefore, a growing body of recent work has concentrated on the real-world problems, and has been concerned primarily with non-Lambertian surfaces reconstruction from images in the field of computer vision. Although this state of the art report does not cover exhaustively the generic methods of 3D reconstruction for non-Lambertian surfaces, it does contain examples of all the significantly different approaches to the steps in this field. The works discussed in the survey are categorized and reviewed in order. The main categories of classification are defined in terms of the illumination used for capturing the image and the principle based on. Due to lack of the common test bench available on the web and stereo data sets of non-Lambertian surfaces with ground truth, it is difficult to compare the computational efficiency and matching quality of the various schemes. In that case, here we are concerned with only the principle and characteristics of the existing methods, the scope of application and the latest trends in the research. We conclude the survey by discussing open problems and future perspectives and hope to provide an entry point to this existing field.
3D reconstruction method based on computer vision is widely used in various industries. Though the 3D reconstruction of opaque surfaces with Lambertian reflectance on which the current research is mainly concentrated is a well-studied issue, the non-Lambertian surfaces pose challenging problems for the 3D reconstruction. Unfortunately, most surfaces of the objects in the actual scene are non-Lambertian, therefore, a growing body of recent work has concentrated on the real-world problems, and has been concerned primarily with non-Lambertian surfaces reconstruction from images in the field of computer vision. Although this state of the art report does not cover exhaustively the generic methods of 3D reconstruction for non-Lambertian surfaces, it does contain examples of all the significantly different approaches to the steps in this field. The works discussed in the survey are categorized and reviewed in order. The main categories of classification are defined in terms of the illumination used for capturing the image and the principle based on. Due to lack of the common test bench available on the web and stereo data sets of non-Lambertian surfaces with ground truth, it is difficult to compare the computational efficiency and matching quality of the various schemes. In that case, here we are concerned with only the principle and characteristics of the existing methods, the scope of application and the latest trends in the research. We conclude the survey by discussing open problems and future perspectives and hope to provide an entry point to this existing field.
2014,
26: 019002.
doi: 10.3788/HPLPB201426.019002
Abstract:
In order to manufacture the colorful metals, the iron surface was scanned from four directions by linearly polarized and circularly polarized femtosecond lasers respectively. When the processed area which was scanned by the linearly polarized laser was observed from different directions, it appeared in different colors. However, when the iron surface was scanned by the circular polarized laser, the resulted pattern color observed from different angles changed unobviously. The experimental results were analyzed by scanning electron microscope (SEM).The results showed that the surface of the colorful metals which were scanned by the linearly polarized laser is full of laser-induced periodic surface structure covered with nanostructures (NC-LIPSS) and the periodic surface structure direction was always perpendicular to the laser polarization direction. Simultaneously, the SEM images showed that the iron periodic surface structure which was manufactured by circularly polarized femtosecond laser was not obvious, and a large number of nanoparticles were obtained.
In order to manufacture the colorful metals, the iron surface was scanned from four directions by linearly polarized and circularly polarized femtosecond lasers respectively. When the processed area which was scanned by the linearly polarized laser was observed from different directions, it appeared in different colors. However, when the iron surface was scanned by the circular polarized laser, the resulted pattern color observed from different angles changed unobviously. The experimental results were analyzed by scanning electron microscope (SEM).The results showed that the surface of the colorful metals which were scanned by the linearly polarized laser is full of laser-induced periodic surface structure covered with nanostructures (NC-LIPSS) and the periodic surface structure direction was always perpendicular to the laser polarization direction. Simultaneously, the SEM images showed that the iron periodic surface structure which was manufactured by circularly polarized femtosecond laser was not obvious, and a large number of nanoparticles were obtained.
2014,
26: 019003.
doi: 10.3788/HPLPB201426.019003
Abstract:
Long-term observation of stratospheric temperature was conducted using Rayleigh lidar, in order to understand variation regularities of the stratospheric temperature. The analysis results of the observation dataset show that, the tratospheric temperature was affected by gravity wave, the breakdown of gravity wave led to temperature increasing, and the scope of variation was about 12%; temperature increased in lower stratosphere and decreased in upper stratosphere during April and October; in the aspect of inter-monthly variation, stratospheric temperature was relatively stable except the influence of the planetary wave, and there were differences between Rayleigh result and the model. Furthermore, the information of gravity wave was retrieved from the temperature profile.
Long-term observation of stratospheric temperature was conducted using Rayleigh lidar, in order to understand variation regularities of the stratospheric temperature. The analysis results of the observation dataset show that, the tratospheric temperature was affected by gravity wave, the breakdown of gravity wave led to temperature increasing, and the scope of variation was about 12%; temperature increased in lower stratosphere and decreased in upper stratosphere during April and October; in the aspect of inter-monthly variation, stratospheric temperature was relatively stable except the influence of the planetary wave, and there were differences between Rayleigh result and the model. Furthermore, the information of gravity wave was retrieved from the temperature profile.
