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RSS2007 Vol. 19, No. 12
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2007,
19.
Abstract:
By using Fourier optics analyzing method, the expression to the far field of combined beams is deduced and the expressions for the coherently combined beams emitted from sources positioned on the circle have been given. For the cases where the sources are uniformly distributed, the dark lines in the far field are studied for beam numbers of 2, 3 and 4, respectively. It is found that when the sources number is 2, there are only dark lines (instead of rings) on the far field pattern and when the sources numbers are 3 and 4, the dark rings are far from being the circles. Since Fourier optics method is easy to implement and can be applied to non-Gaussian beams (such as those from the fiber lasers, semiconductor lasers, etc.), so it possessed unique advantages and is of practical significance
By using Fourier optics analyzing method, the expression to the far field of combined beams is deduced and the expressions for the coherently combined beams emitted from sources positioned on the circle have been given. For the cases where the sources are uniformly distributed, the dark lines in the far field are studied for beam numbers of 2, 3 and 4, respectively. It is found that when the sources number is 2, there are only dark lines (instead of rings) on the far field pattern and when the sources numbers are 3 and 4, the dark rings are far from being the circles. Since Fourier optics method is easy to implement and can be applied to non-Gaussian beams (such as those from the fiber lasers, semiconductor lasers, etc.), so it possessed unique advantages and is of practical significance
2007,
19.
Abstract:
This paper reported that the peak intensity values of spectra are in direct ratio with corresponding species’ concentration values. Major plasma-kinetic processes and concentration varieties of major species with varied flow conditions and discharge forms were researched. Slab RF discharges with gas flow are possible in two greatly different forms that are α discharge and γ discharge. A discharge gives higher O2(1Δ)production for fewer quenching particles. Lower specific field intensity values which are helpful for the O2(1Δ)production can be achieved by adding helium. The peak O2(1Δ)concentration with oxygen and helium mixture gas flow is more than 2 times as high as pure oxygen discharge. O2(1Δ)loss in afterglow region is lower than 5% in 0.03 s, while stable O2(1Δ)concentration
This paper reported that the peak intensity values of spectra are in direct ratio with corresponding species’ concentration values. Major plasma-kinetic processes and concentration varieties of major species with varied flow conditions and discharge forms were researched. Slab RF discharges with gas flow are possible in two greatly different forms that are α discharge and γ discharge. A discharge gives higher O2(1Δ)production for fewer quenching particles. Lower specific field intensity values which are helpful for the O2(1Δ)production can be achieved by adding helium. The peak O2(1Δ)concentration with oxygen and helium mixture gas flow is more than 2 times as high as pure oxygen discharge. O2(1Δ)loss in afterglow region is lower than 5% in 0.03 s, while stable O2(1Δ)concentration
2007,
19.
Abstract:
Based on the interferential theory and diffraction integral theory, the propagation characteristic of Bessel beam generated by an axicon was studied. The applicability and advantages of the theories were discussed as well. The 3-D beam intensity distribution was simulated numerically. The relative parameters were also measured experimentally. The numerical simulation and the experimental results show that, within the maximum diffraction-free distance, the on-axis intensity distribution of the Bessel beam can be described well by the diffractive theory, while the intensity distribution of the Bessel beam approach or beyond the maximum diffraction-free distance can be properly described by the interferential theory. The experimental results are consistent with the theoretical ones.
Based on the interferential theory and diffraction integral theory, the propagation characteristic of Bessel beam generated by an axicon was studied. The applicability and advantages of the theories were discussed as well. The 3-D beam intensity distribution was simulated numerically. The relative parameters were also measured experimentally. The numerical simulation and the experimental results show that, within the maximum diffraction-free distance, the on-axis intensity distribution of the Bessel beam can be described well by the diffractive theory, while the intensity distribution of the Bessel beam approach or beyond the maximum diffraction-free distance can be properly described by the interferential theory. The experimental results are consistent with the theoretical ones.
2007,
19.
Abstract:
A theoretical analysis on Z-scan using Gaussian-Schell model beam is reported. The influences of aperture radius and degree of spatial coherence on the Z-scan curves are studied. It is found that the effect of aperture radius on the Z-scan curves is similar to the case of the fully coherent beams. It is also shown that the difference between peak and valley transmittance is getting larger with the increasing degree of spatial coherence till it stabilizes when the degree of spatial coherence is larger than a certain value. The results show that the Z-scan experiment with partially coherent beams may provide a feasible method for measuring the degree of spatial coherence.
A theoretical analysis on Z-scan using Gaussian-Schell model beam is reported. The influences of aperture radius and degree of spatial coherence on the Z-scan curves are studied. It is found that the effect of aperture radius on the Z-scan curves is similar to the case of the fully coherent beams. It is also shown that the difference between peak and valley transmittance is getting larger with the increasing degree of spatial coherence till it stabilizes when the degree of spatial coherence is larger than a certain value. The results show that the Z-scan experiment with partially coherent beams may provide a feasible method for measuring the degree of spatial coherence.
2007,
19.
Abstract:
Based on the technology of wavelength beam combining, this paper applies the diffraction of the grating and the feedback of the external cavity to demonstrate all elements of the diode laser array(LDA) locked in different wavelength, the neighboring emitters having little difference in output wavelength. The output beam from the external cavity coupler mirror is nearly parallel, the combined beam has the same beam quality as the beam of single element of the LDA, but the brightness of the combined beam grows with the number of the LDA element. The 1 cm linear array was used in the experiment, consisting of 49 wide-aperture diodes with a diode width of 100 μm and a fill factor of 0.5. The combined beam power is 2.39 W, the wavelength spread is about 27 nm, the diameter of a circle spot is
Based on the technology of wavelength beam combining, this paper applies the diffraction of the grating and the feedback of the external cavity to demonstrate all elements of the diode laser array(LDA) locked in different wavelength, the neighboring emitters having little difference in output wavelength. The output beam from the external cavity coupler mirror is nearly parallel, the combined beam has the same beam quality as the beam of single element of the LDA, but the brightness of the combined beam grows with the number of the LDA element. The 1 cm linear array was used in the experiment, consisting of 49 wide-aperture diodes with a diode width of 100 μm and a fill factor of 0.5. The combined beam power is 2.39 W, the wavelength spread is about 27 nm, the diameter of a circle spot is
2007,
19.
Abstract:
Based on the theories of phase matching and acceptable composition ratio, the influence of composition ratio on the frequency conversions of CdGe(As1-xPx)2 was investigated. In consideration of Sellmeier equations, phase matching diagrams of second harmonic generation and optical parametric oscillations pumped by the popular Ho3+:YLF and Cr:Er:YSGG lasers were calculated, as well as acceptable composition ratios with various compositions. It is shown that the second harmonic generation of noncritical phase matching can be realized in 2~9 μm and parametric light in 2~18 μm can be generated by optical parametric oscillations. Acceptable composition ratios decrease approximately linearly with composition ratio, and show different tendencies with changing wavelengths.
Based on the theories of phase matching and acceptable composition ratio, the influence of composition ratio on the frequency conversions of CdGe(As1-xPx)2 was investigated. In consideration of Sellmeier equations, phase matching diagrams of second harmonic generation and optical parametric oscillations pumped by the popular Ho3+:YLF and Cr:Er:YSGG lasers were calculated, as well as acceptable composition ratios with various compositions. It is shown that the second harmonic generation of noncritical phase matching can be realized in 2~9 μm and parametric light in 2~18 μm can be generated by optical parametric oscillations. Acceptable composition ratios decrease approximately linearly with composition ratio, and show different tendencies with changing wavelengths.
2007,
19.
Abstract:
Establishing the rate equation model and thermal stress model of Yb-doped double-clad fiber lasers(DCFL), the key parameters impacting the stimulated Raman scattering(SRS) and thermal stress (such as the radius of core, the fiber length, the pump wavelength, and the pump fashion) are numerically simulated. The results indicate that the Stokes power is larger and grow rapidly for the smaller core radius, increasing the core radius will weaken the effect of SRS. Reducing the fiber length can increase the threshold of SRS, but the thermal stress of core will increase too; hence without fiber fracture induced by thermal stress, reducing fiber length can improve the output power. Adopting the pump source of 976 nm can improve the output power and reduce the thermal stress. The two end symmetric
Establishing the rate equation model and thermal stress model of Yb-doped double-clad fiber lasers(DCFL), the key parameters impacting the stimulated Raman scattering(SRS) and thermal stress (such as the radius of core, the fiber length, the pump wavelength, and the pump fashion) are numerically simulated. The results indicate that the Stokes power is larger and grow rapidly for the smaller core radius, increasing the core radius will weaken the effect of SRS. Reducing the fiber length can increase the threshold of SRS, but the thermal stress of core will increase too; hence without fiber fracture induced by thermal stress, reducing fiber length can improve the output power. Adopting the pump source of 976 nm can improve the output power and reduce the thermal stress. The two end symmetric
2007,
19.
Abstract:
The scaling laws about DF high energy laser propagation in real atmosphere are numerically analyzed by the four-dimension code of high energy laser in atmosphere combined with the square root of the sum of squares hypothesis. The scaling relations of the 63.2% encircled energy beam radius spreading and the average energy intensity in different encircled energy radius are obtained in the focal plane. The scaling relations are applicable for DF high energy laser propagation in the condition of different Fresnel numbers and different propagation effects. Based on the relations, the atmospheric propagation effects of high energy laser can be predicted and estimated effectively.
The scaling laws about DF high energy laser propagation in real atmosphere are numerically analyzed by the four-dimension code of high energy laser in atmosphere combined with the square root of the sum of squares hypothesis. The scaling relations of the 63.2% encircled energy beam radius spreading and the average energy intensity in different encircled energy radius are obtained in the focal plane. The scaling relations are applicable for DF high energy laser propagation in the condition of different Fresnel numbers and different propagation effects. Based on the relations, the atmospheric propagation effects of high energy laser can be predicted and estimated effectively.
2007,
19.
Abstract:
A method based on fractional Talbot effect is studied for single-shot measurement of laser-induced damage threshold. Using hexagonal phase grating, a laser beam is transformed into an ensemble of Gaussian-like spots with different energy densities at the test sample. Therefore, a statistical determination of the damage threshold of thin-film coatings can be performed by comparison of the intensity distribution with the damage pattern. Basic theories about the spectrum transmission and the fractional Talbot self-imaging are applied to calculating the Fresnel image of the hexagonal phase grating, and the results are testified by experiment. The laser-induced damage thresholds of HfO2/ SiO2 coating sample measured by this method and the traditional 1 on 1 method are 7.9 J/cm2 and 8.0 J/cm2, r
A method based on fractional Talbot effect is studied for single-shot measurement of laser-induced damage threshold. Using hexagonal phase grating, a laser beam is transformed into an ensemble of Gaussian-like spots with different energy densities at the test sample. Therefore, a statistical determination of the damage threshold of thin-film coatings can be performed by comparison of the intensity distribution with the damage pattern. Basic theories about the spectrum transmission and the fractional Talbot self-imaging are applied to calculating the Fresnel image of the hexagonal phase grating, and the results are testified by experiment. The laser-induced damage thresholds of HfO2/ SiO2 coating sample measured by this method and the traditional 1 on 1 method are 7.9 J/cm2 and 8.0 J/cm2, r
2007,
19.
Abstract:
A Hartmann wavefront sensor is applied to measuring the aero-optical aberrated wavefronts when the collimated light beam passes through a low speed heated turbulent jet. Proper orthogonal decomposition(POD) technique is applied to the aberraed wavefront time series then the eigenfunctions and the time coefficients are obtained. Interpolations of the eigenfunctions are made on those positions where no detectors are set. The predicted wavefronts can be represented as a product of the interpolated eigenfunction and a time coefficient. Comparisons are made in time domain and frequency domain between the predicted wavefronts and the measured wavefronts, which indicate using the interpolation method to predict the wavefront is effective. It is proved that this method has less amount of computat
A Hartmann wavefront sensor is applied to measuring the aero-optical aberrated wavefronts when the collimated light beam passes through a low speed heated turbulent jet. Proper orthogonal decomposition(POD) technique is applied to the aberraed wavefront time series then the eigenfunctions and the time coefficients are obtained. Interpolations of the eigenfunctions are made on those positions where no detectors are set. The predicted wavefronts can be represented as a product of the interpolated eigenfunction and a time coefficient. Comparisons are made in time domain and frequency domain between the predicted wavefronts and the measured wavefronts, which indicate using the interpolation method to predict the wavefront is effective. It is proved that this method has less amount of computat
2007,
19.
Abstract:
New form of Mie series which is suitable for particle scattering in an absorbing medium is demonstrated. Both single-bubble-scattering properties and phase function of bubbles in the absorbing sea water are researched based on Mie theory. At the same time, the influences of the imaginary part of the refractive index of sea water on light scattering properties of the bubble are analyzed. The results show that enhancement of bubble backscattering at 180° is an inherent optical property of the bubble and has nothing to do with the surrounding medium, and thus can be used to detect the bubble in the absorbing and non-absorbing sea water.
New form of Mie series which is suitable for particle scattering in an absorbing medium is demonstrated. Both single-bubble-scattering properties and phase function of bubbles in the absorbing sea water are researched based on Mie theory. At the same time, the influences of the imaginary part of the refractive index of sea water on light scattering properties of the bubble are analyzed. The results show that enhancement of bubble backscattering at 180° is an inherent optical property of the bubble and has nothing to do with the surrounding medium, and thus can be used to detect the bubble in the absorbing and non-absorbing sea water.
2007,
19.
Abstract:
Experiments have been performed to measure the temperature rise of Ta2O5/SiO2 multilayer coatings with substrate sapphire, fused silica and K9 at repetition rate 10 kHz, 1 064 nm pulse laser. Results calculated by ANSYS agree well with the experiment data.The maximal temperature of films irradiated by the same power density or power but different facula was calculated. The results indicate that, when irradiated by the same power laser, the size of laser facula can affect the temperature rise of films only; the temperature rise of substrate only depends on the laser power. The laser power increases, the temperature rise of substrate increases. However, when films are irradiated by the same power density laser, with the size of laser facula increases, the maximal temperature of films and sub
Experiments have been performed to measure the temperature rise of Ta2O5/SiO2 multilayer coatings with substrate sapphire, fused silica and K9 at repetition rate 10 kHz, 1 064 nm pulse laser. Results calculated by ANSYS agree well with the experiment data.The maximal temperature of films irradiated by the same power density or power but different facula was calculated. The results indicate that, when irradiated by the same power laser, the size of laser facula can affect the temperature rise of films only; the temperature rise of substrate only depends on the laser power. The laser power increases, the temperature rise of substrate increases. However, when films are irradiated by the same power density laser, with the size of laser facula increases, the maximal temperature of films and sub
2007,
19.
Abstract:
By theoretical analysis and simulation,laser -induced damage mechanisms of fiber’s end face, entry segment and fiber inside are studied. The admixtures and defects on the fiber end face induce the damage; the first reflections along the fiber core/cladding interface induce the damage of entry segment. The unexpected stress and beam self-focus in optical fibers induce the internal damage. In this case a portion of the fiber cross section experiences significant tensile stresses which aggravate defects within the fused silica, including microcracks at the fiber boundaries which were initially produced during the fiber drawing process. Damage at these locations is always catastrophic, usually resulting in a complete break across the fiber cross section, The methods of increasing fiber damage
By theoretical analysis and simulation,laser -induced damage mechanisms of fiber’s end face, entry segment and fiber inside are studied. The admixtures and defects on the fiber end face induce the damage; the first reflections along the fiber core/cladding interface induce the damage of entry segment. The unexpected stress and beam self-focus in optical fibers induce the internal damage. In this case a portion of the fiber cross section experiences significant tensile stresses which aggravate defects within the fused silica, including microcracks at the fiber boundaries which were initially produced during the fiber drawing process. Damage at these locations is always catastrophic, usually resulting in a complete break across the fiber cross section, The methods of increasing fiber damage
2007,
19.
Abstract:
On the basis of active imaging model of CW laser and range-gated, it is proved that range-gated technique is an effective method for restraining the influence of back-scattering in terms of single CCD cell SNR(single noise ratio) and image MSE(mean square error). Range-gated technique can enlarge the imaging distance and improve the image quality. Based on the model, some principles to select key parameters of range-gated are figured out. These principles are: (1) the laser pulse width is as short as possible for both increasing the single CCD cell SNR and improving the image quality, (2) the laser duty cycle is as big as possible in a certain power of laser for longer imaging distance, (3) the laser pulse frequeney is as high as possible in some cases.
On the basis of active imaging model of CW laser and range-gated, it is proved that range-gated technique is an effective method for restraining the influence of back-scattering in terms of single CCD cell SNR(single noise ratio) and image MSE(mean square error). Range-gated technique can enlarge the imaging distance and improve the image quality. Based on the model, some principles to select key parameters of range-gated are figured out. These principles are: (1) the laser pulse width is as short as possible for both increasing the single CCD cell SNR and improving the image quality, (2) the laser duty cycle is as big as possible in a certain power of laser for longer imaging distance, (3) the laser pulse frequeney is as high as possible in some cases.
2007,
19.
Abstract:
An incident coordinate system was set up on the basis of the incident direction and normal direction on crystal surface. Using the inverse surface equation of wave normals and the boundary condition about the continuity of electromagnetic field tangential component at the surface of crystal, expressions about wave normal direction, ray direction, wave normal refractive index and ray refractive index were obtained. Based on the ray direction and refractive index of extraordinary light, an expression of optical path difference between ordinary and extraordinary lights was derived, when a ray of light with arbitrary incident direction passed through uniaxial crystal with arbitrary crystal axis direction. The transmissivity and field of view of a Lyot filter were analyzed. The tuning of Lyot f
An incident coordinate system was set up on the basis of the incident direction and normal direction on crystal surface. Using the inverse surface equation of wave normals and the boundary condition about the continuity of electromagnetic field tangential component at the surface of crystal, expressions about wave normal direction, ray direction, wave normal refractive index and ray refractive index were obtained. Based on the ray direction and refractive index of extraordinary light, an expression of optical path difference between ordinary and extraordinary lights was derived, when a ray of light with arbitrary incident direction passed through uniaxial crystal with arbitrary crystal axis direction. The transmissivity and field of view of a Lyot filter were analyzed. The tuning of Lyot f
2007,
19.
Abstract:
Coherent combining of two self-organized fiber lasers is investigated theoretically and experimentally. It is shown that fiber lasers can be coherently combined using self-coherence by mutual injection， and the experimental combining efficiency can reach 92%. Interference fringes with high contrast ratio showing out-of -phase mode were obtained when there was little environmental interference. The experimental result is consistent with the conclusion deduced by the theoretical model. The motion of interference fringes caused by the environmental interference were also observed. The evolution of phase difference between two laser beams was calculated numerically in the case that the phase noise induced by environmental interference exists. The results show that the phase difference will c
Coherent combining of two self-organized fiber lasers is investigated theoretically and experimentally. It is shown that fiber lasers can be coherently combined using self-coherence by mutual injection， and the experimental combining efficiency can reach 92%. Interference fringes with high contrast ratio showing out-of -phase mode were obtained when there was little environmental interference. The experimental result is consistent with the conclusion deduced by the theoretical model. The motion of interference fringes caused by the environmental interference were also observed. The evolution of phase difference between two laser beams was calculated numerically in the case that the phase noise induced by environmental interference exists. The results show that the phase difference will c
2007,
19.
Abstract:
A novel method of aerial extended target detection based on pulse coupled neural network (PCNN) is presented. Some key techniques are improved and network model is simplified, which are more suitable for image processing, such as linear modulation, linear attenuation of dynamic threshold and step selection, and iteration time control. Meanwhile, maximum line contour point number and color negative are adopted to determine the optimal iteration times and the optimal segmented results for targets with low contrast and continuously varying background. The experimental results show that the proposed method can maintain perfect and distinct targets contour and detect aerial extended targets against complex background.
A novel method of aerial extended target detection based on pulse coupled neural network (PCNN) is presented. Some key techniques are improved and network model is simplified, which are more suitable for image processing, such as linear modulation, linear attenuation of dynamic threshold and step selection, and iteration time control. Meanwhile, maximum line contour point number and color negative are adopted to determine the optimal iteration times and the optimal segmented results for targets with low contrast and continuously varying background. The experimental results show that the proposed method can maintain perfect and distinct targets contour and detect aerial extended targets against complex background.
2007,
19.
Abstract:
The influence of temperature on the spectra and nonlinear optics properties of the 4(nitro) 4′aminoazobenzene compound Langmuir-Blodgett(LB)films were investigated using UV visible absorption spectra and second harmonic generation (SHG) technique. The SHG intensity of the monolayer LB films declined monotonically with the increase of temperature from room temperature to 80 ℃ and became faint when the temperature exceeded 80 ℃. The SHG intensity of the multilayer LB films decreased rapidly at first, then slowly, then kept steady, and then decreased when the temperature increased. The absorption spectra showed that the orderly arrangement of the molecule in the monolayer LB films was not easy to recovery after heating, and it could not recover when the temperature was above 80 ℃. But it
The influence of temperature on the spectra and nonlinear optics properties of the 4(nitro) 4′aminoazobenzene compound Langmuir-Blodgett(LB)films were investigated using UV visible absorption spectra and second harmonic generation (SHG) technique. The SHG intensity of the monolayer LB films declined monotonically with the increase of temperature from room temperature to 80 ℃ and became faint when the temperature exceeded 80 ℃. The SHG intensity of the multilayer LB films decreased rapidly at first, then slowly, then kept steady, and then decreased when the temperature increased. The absorption spectra showed that the orderly arrangement of the molecule in the monolayer LB films was not easy to recovery after heating, and it could not recover when the temperature was above 80 ℃. But it
2007,
19.
Abstract:
The hot uniform aluminium plasma was produced by irradiating thin aluminium dotted foil smoothly with the 9th 0.53 μm laser on Shenguang Ⅱ laser facility. The emitted spectrum was measured from the front and tangential direction of the target with two crystal spectrometers, and the quantitative spectrum from the front of the target was obtained. The state of laser-produced plasma was simulated with the radiation hydrodynamics code MULTI-1D, and the emitted spectrum was calculated with the spectrum code of Collision-Radiation model under the simulated plasma state. The experimental spectrum accords with the simulated one.
The hot uniform aluminium plasma was produced by irradiating thin aluminium dotted foil smoothly with the 9th 0.53 μm laser on Shenguang Ⅱ laser facility. The emitted spectrum was measured from the front and tangential direction of the target with two crystal spectrometers, and the quantitative spectrum from the front of the target was obtained. The state of laser-produced plasma was simulated with the radiation hydrodynamics code MULTI-1D, and the emitted spectrum was calculated with the spectrum code of Collision-Radiation model under the simulated plasma state. The experimental spectrum accords with the simulated one.
2007,
19.
Abstract:
Films are usually annealed to ameliorate their structure and improve mechanical properties in need of inertial confinement fusion(ICF) and equation of state(EOS) experiment and procedure of target assembly. Ni films with surface root mean square roughness less than 50 nm, 7 mm thick were fabricated after process annealing at 450~700 ℃. The metallographs of Ni films show that the stripped grains have been changed in to equiaxed grains after annealing at 500 ℃ for 1 h. The hardness of Ni film has changed from 4 GPa to 2.3 GPa after annealing. The X-ray diffraction spectra of Ni fims show that diffraction peak at high angle appears after annealing at temperature higher than 500 ℃，which means the texture has been moderated to some extent, and the suitable temperature for Ni film annealing
Films are usually annealed to ameliorate their structure and improve mechanical properties in need of inertial confinement fusion(ICF) and equation of state(EOS) experiment and procedure of target assembly. Ni films with surface root mean square roughness less than 50 nm, 7 mm thick were fabricated after process annealing at 450~700 ℃. The metallographs of Ni films show that the stripped grains have been changed in to equiaxed grains after annealing at 500 ℃ for 1 h. The hardness of Ni film has changed from 4 GPa to 2.3 GPa after annealing. The X-ray diffraction spectra of Ni fims show that diffraction peak at high angle appears after annealing at temperature higher than 500 ℃，which means the texture has been moderated to some extent, and the suitable temperature for Ni film annealing
2007,
19.
Abstract:
According to quasi-phase matching relationship between the second harmonic center wavelength and the grating period length of periodically poled crystal, a new experimental method to measure the grating period of periodically poled crystal accurately was presented by using broad band chirp pulse second harmonic generation technique. The relationships between the second harmonic center wavelength and the grating period, the spectra bandwidth and the crystal length were analyzed theoretically. The grating period of PPKTP crystal with the size of 10 mm×7 mm×1 mm was measured experimentally. The results show that the real grating period is 9 303.9 nm depending on the second harmonic central wavelength of 537.25 nm, while the theoretical one is 9 300 nm. The method advances the measurement p
According to quasi-phase matching relationship between the second harmonic center wavelength and the grating period length of periodically poled crystal, a new experimental method to measure the grating period of periodically poled crystal accurately was presented by using broad band chirp pulse second harmonic generation technique. The relationships between the second harmonic center wavelength and the grating period, the spectra bandwidth and the crystal length were analyzed theoretically. The grating period of PPKTP crystal with the size of 10 mm×7 mm×1 mm was measured experimentally. The results show that the real grating period is 9 303.9 nm depending on the second harmonic central wavelength of 537.25 nm, while the theoretical one is 9 300 nm. The method advances the measurement p
2007,
19.
Abstract:
The foamed nickel was synthesized by electrodeposition technique. The effect of current density, temperature, duty cycle and pulse frequency on crystal texture and magnetic properties of deposits were studied. The structure and micro-morphology were observed by scanning electron microscope and transmission electron microscope, respectively. Three-dimensional network foamed nickel with density of 0.25 g/cm3, porosity of 97.5 %, pore diameter ranged from 400 to 500 μm was prepared. Test results show that the big particles of deposits are was 1 μm in size and the crystallite size of deposits does not exceed 10 nm. The foamed nickel with low coercive force and high magnetic conductance is paramagnetic, and its magnetic conductivity and saturation magnetization rise with the increase of depo
The foamed nickel was synthesized by electrodeposition technique. The effect of current density, temperature, duty cycle and pulse frequency on crystal texture and magnetic properties of deposits were studied. The structure and micro-morphology were observed by scanning electron microscope and transmission electron microscope, respectively. Three-dimensional network foamed nickel with density of 0.25 g/cm3, porosity of 97.5 %, pore diameter ranged from 400 to 500 μm was prepared. Test results show that the big particles of deposits are was 1 μm in size and the crystallite size of deposits does not exceed 10 nm. The foamed nickel with low coercive force and high magnetic conductance is paramagnetic, and its magnetic conductivity and saturation magnetization rise with the increase of depo
2007,
19.
Abstract:
A mathematical model was developed to investigate the complex physical process of laser plasma interaction, adopting the PIC(particle-in-cell) approach to study the phenomena when heterogeneous ultra-short and ultra-high laser pulse propagated through over-dense plasma. Through the simulation of 3D laser pulse appearance in vacuum, it was found that a channel was formed due to the extremely large ponderomotive force associated with laser pulse. The lengthways electron velocity appeared in the position of the peak electric current intensity and the wave length became longer, which is coincident with the local oscillating electron heating mechanism basically.
A mathematical model was developed to investigate the complex physical process of laser plasma interaction, adopting the PIC(particle-in-cell) approach to study the phenomena when heterogeneous ultra-short and ultra-high laser pulse propagated through over-dense plasma. Through the simulation of 3D laser pulse appearance in vacuum, it was found that a channel was formed due to the extremely large ponderomotive force associated with laser pulse. The lengthways electron velocity appeared in the position of the peak electric current intensity and the wave length became longer, which is coincident with the local oscillating electron heating mechanism basically.
2007,
19.
Abstract:
Beijing Synchrotron Radiation Facility(BSRF)-3W1B beam line was used to calibrate the reffectivint of some multilayer mirrors. The wavelength-scanning method is adopted to get the multilayer mirrors' reflectirity-energy curves. The reflectivity calibration curves of 21°-B4C/Si, 21°-B4C/Mo, 10°-Cr/Ti, 15°- B4C/W, 10°- B4C/W and 6.86°-B4C/W multilayer mirrors are given in the region of 50~1 500 eV. The values of experiment and calculation are compared and analyzed. The calibration curves agree well with the theoretical ones, and the uncertainty of calibration is mainly caused by photon energy uncertainty and calibrating angle uncertainty.
Beijing Synchrotron Radiation Facility(BSRF)-3W1B beam line was used to calibrate the reffectivint of some multilayer mirrors. The wavelength-scanning method is adopted to get the multilayer mirrors' reflectirity-energy curves. The reflectivity calibration curves of 21°-B4C/Si, 21°-B4C/Mo, 10°-Cr/Ti, 15°- B4C/W, 10°- B4C/W and 6.86°-B4C/W multilayer mirrors are given in the region of 50~1 500 eV. The values of experiment and calculation are compared and analyzed. The calibration curves agree well with the theoretical ones, and the uncertainty of calibration is mainly caused by photon energy uncertainty and calibrating angle uncertainty.
2007,
19.
Abstract:
Traditional digital filter method and Birge-Massart threshold wavelet method were used to study the denoisng of lightning transient electrical signals. The mean square error and magnitude error of simulation signals were calculated to compare the denoising effects, and double exponential-decay pulse signals and Gaussian white-noise were composed as the simulating signals. Denoising simulation and measured signals proved that the Birge-Massart threshold wavelet ways were better than the traditionally used smoothing filter and FIR digital low-pass filter ones. Comparing mean square error and magnitude error with different decomposition orders after simulating signals denoising, it is concluded that wavelet decomposition order in measuring lightning transient electrical signals should be 5 to
Traditional digital filter method and Birge-Massart threshold wavelet method were used to study the denoisng of lightning transient electrical signals. The mean square error and magnitude error of simulation signals were calculated to compare the denoising effects, and double exponential-decay pulse signals and Gaussian white-noise were composed as the simulating signals. Denoising simulation and measured signals proved that the Birge-Massart threshold wavelet ways were better than the traditionally used smoothing filter and FIR digital low-pass filter ones. Comparing mean square error and magnitude error with different decomposition orders after simulating signals denoising, it is concluded that wavelet decomposition order in measuring lightning transient electrical signals should be 5 to
2007,
19.
Abstract:
The resonant cavity reflector has been used in the backward wave oscillators for producing multi-gigawatt power and operating at low magnetic field. The reflection characteristics of the “cold ” resonant cavity reflector is analyzed by means of the mode-matching method, and the scattering matrix of the reflector is derived. The electric field distribution in the reflector is studied by means of numerical simulation under total reflection condition. The results indicate that with suitable inner and outer radius, high reflection can be obtained with short cavity length, and the cavity length does not affect the reflectivity remarkably.
The resonant cavity reflector has been used in the backward wave oscillators for producing multi-gigawatt power and operating at low magnetic field. The reflection characteristics of the “cold ” resonant cavity reflector is analyzed by means of the mode-matching method, and the scattering matrix of the reflector is derived. The electric field distribution in the reflector is studied by means of numerical simulation under total reflection condition. The results indicate that with suitable inner and outer radius, high reflection can be obtained with short cavity length, and the cavity length does not affect the reflectivity remarkably.
2007,
19.
Abstract:
The guidance conditions of a slab waveguide of uniaxially anisotropic metamaterial with partially negative components in permittivity and permeability tensors are derived. In terms of the combination of component signs, the even mode properties for guided TE waves are discussed in different cases. The Brillouin diagrams with real transverse wave numbers inside a slab waveguide are drawn. The results show that under some specific conditions there are infinite guided modes, which is different from the case in the traditional dielectric waveguide and isotropic metamaterial slab where only finite number of guided modes exists. It is also found that there are multiple solutions of the propagating mode with imaginary transverse wave number for certain component parameters, and the mode has the h
The guidance conditions of a slab waveguide of uniaxially anisotropic metamaterial with partially negative components in permittivity and permeability tensors are derived. In terms of the combination of component signs, the even mode properties for guided TE waves are discussed in different cases. The Brillouin diagrams with real transverse wave numbers inside a slab waveguide are drawn. The results show that under some specific conditions there are infinite guided modes, which is different from the case in the traditional dielectric waveguide and isotropic metamaterial slab where only finite number of guided modes exists. It is also found that there are multiple solutions of the propagating mode with imaginary transverse wave number for certain component parameters, and the mode has the h
2007,
19.
Abstract:
This paper presents a formally exact solution (mode-matching method) to the problem of scattering at the junction between a small coaxial line and a large rectangular waveguide. The eigen-mode functions for both coaxial line and rectangular waveguide are used to express the field components in both regions and the transverse field components are then matched to obtain the scattering parameters of the waveguide junction. The E-field mode-matching matrix is analytically derived in closed-form for efficient computation. Numerical results for a few waveguide problems involving the coaxial line-to-rectangular waveguide junction are presented and discussed. The mode-matching method results are in excellent agreement with those obtained by Ansoft's HFSS and the method has high computation efficie
This paper presents a formally exact solution (mode-matching method) to the problem of scattering at the junction between a small coaxial line and a large rectangular waveguide. The eigen-mode functions for both coaxial line and rectangular waveguide are used to express the field components in both regions and the transverse field components are then matched to obtain the scattering parameters of the waveguide junction. The E-field mode-matching matrix is analytically derived in closed-form for efficient computation. Numerical results for a few waveguide problems involving the coaxial line-to-rectangular waveguide junction are presented and discussed. The mode-matching method results are in excellent agreement with those obtained by Ansoft's HFSS and the method has high computation efficie
2007,
19.
Abstract:
As the beam is too narrow in the application of the ultra-wideband (UWB) antenna with single-source, a novel wide-beam UWB paraboloidal antenna with dual-source has been designed. The novel paraboloid was improved from an original paraboliod, which was separated in the middle and the two parts were comected by a metallic plate. The improved planar TEM horn antenna is adopted as the source, and it is fed by the coaxial-cable vertically. The dual-source were put on the fouses of the paraboloid. The radiation properties of the proposed antenna are studied using the finite-difference time-domain (FDTD) numerical method. The radiation properties of the proposed antenna can be improved by changing the structure of the paraboloidal antenna and adjusting the angle between the source and the boresi
As the beam is too narrow in the application of the ultra-wideband (UWB) antenna with single-source, a novel wide-beam UWB paraboloidal antenna with dual-source has been designed. The novel paraboloid was improved from an original paraboliod, which was separated in the middle and the two parts were comected by a metallic plate. The improved planar TEM horn antenna is adopted as the source, and it is fed by the coaxial-cable vertically. The dual-source were put on the fouses of the paraboloid. The radiation properties of the proposed antenna are studied using the finite-difference time-domain (FDTD) numerical method. The radiation properties of the proposed antenna can be improved by changing the structure of the paraboloidal antenna and adjusting the angle between the source and the boresi
2007,
19.
Abstract:
A (2M, 4) scheme of the high-order finite-difference time-domain (FDTD) method based on the second order wave equation is proposed. This scheme is of the fourth order accuracy in time domain using the symplectic integrator propagator (SIP), and is of the 2Mth order accuracy in space domain using the discrete singular convolution (DSC) method. This scheme is similar to the traditional (2M, 4) scheme where SIP and DSC method is used and the distinction between them are listed as follows. Firstly, this new scheme is based on the wave equation. Secondly, computational region is discretized by uniform mesh rather than Yee mesh. Thirdly, the new scheme can save more memory and computation time because only one field component is used for calculation. Numerical examples show that when compared wi
A (2M, 4) scheme of the high-order finite-difference time-domain (FDTD) method based on the second order wave equation is proposed. This scheme is of the fourth order accuracy in time domain using the symplectic integrator propagator (SIP), and is of the 2Mth order accuracy in space domain using the discrete singular convolution (DSC) method. This scheme is similar to the traditional (2M, 4) scheme where SIP and DSC method is used and the distinction between them are listed as follows. Firstly, this new scheme is based on the wave equation. Secondly, computational region is discretized by uniform mesh rather than Yee mesh. Thirdly, the new scheme can save more memory and computation time because only one field component is used for calculation. Numerical examples show that when compared wi
2007,
19.
Abstract:
When the sheet electron beam is transmitting in solenoid magnetic fields, Diocotron mode or Diocotron instability comes into being, which could lead to collapse of beam propagation. In this paper, Diocotron mode theory is derived from Maxwell equations. Forces on electrons is analyzed in periodic cusped magnetic(PCM) focusing, and the result shows PCM can restrain Diocotron mode. Using 3D PIC program, formation of Diocotron mode is analyzed, and PCM focusing sheet electron beam and restraining Diocotron mode are simulated. The effect of Diocotron mode in sheet electron beam is also studied with changed PCM magnitude. The results show that space charge force and magnetic force need rebalance, which leads profile of beam to be thicken, when PCM magnitude is reduced.
When the sheet electron beam is transmitting in solenoid magnetic fields, Diocotron mode or Diocotron instability comes into being, which could lead to collapse of beam propagation. In this paper, Diocotron mode theory is derived from Maxwell equations. Forces on electrons is analyzed in periodic cusped magnetic(PCM) focusing, and the result shows PCM can restrain Diocotron mode. Using 3D PIC program, formation of Diocotron mode is analyzed, and PCM focusing sheet electron beam and restraining Diocotron mode are simulated. The effect of Diocotron mode in sheet electron beam is also studied with changed PCM magnitude. The results show that space charge force and magnetic force need rebalance, which leads profile of beam to be thicken, when PCM magnitude is reduced.
2007,
19.
Abstract:
For calculating the coaxial line responses in X rays environment, transmission line (TL) method and finite difference time domain (FDTD) method are presented up respectively. Using charges of the central wire, distributed charge in insulation and the result of test, the current source of TL equations and the current density of Maxwell equations are presented. As an example, the central wire currents of the load under the condition of the matching load of cable ends are calculated using the two methods for energy of 60 keV, and the central wire currents of different energies are calculated with TL method. Numerical results indicate that the responses currents of the two methods are consistent, electrostatic field exists in the insulator, and the central wire currents have a maximum value fo
For calculating the coaxial line responses in X rays environment, transmission line (TL) method and finite difference time domain (FDTD) method are presented up respectively. Using charges of the central wire, distributed charge in insulation and the result of test, the current source of TL equations and the current density of Maxwell equations are presented. As an example, the central wire currents of the load under the condition of the matching load of cable ends are calculated using the two methods for energy of 60 keV, and the central wire currents of different energies are calculated with TL method. Numerical results indicate that the responses currents of the two methods are consistent, electrostatic field exists in the insulator, and the central wire currents have a maximum value fo
2007,
19.
Abstract:
HfO2 films have been deposited by electron beam evaporation of hafnium oxide, reactive evaporation without ion beam assistance and reactive ion beam assisted deposition(RIBAD). Optical and structural properties and laser-induced damage threshold(LIDT) of the films have been studied. It is found that HfO2 film deposited with reactive deposition has less defects and good uniformity. The sample deposited by RIBAD has higher refraction index, and can reduce absorption at a certain condition, but it LIDT is under improvement. The crystal structure of the sample deposited with RIBAD is monoclinic, and when the bombardment energy rises, the preferred orientation changes from (002) to (-111).
HfO2 films have been deposited by electron beam evaporation of hafnium oxide, reactive evaporation without ion beam assistance and reactive ion beam assisted deposition(RIBAD). Optical and structural properties and laser-induced damage threshold(LIDT) of the films have been studied. It is found that HfO2 film deposited with reactive deposition has less defects and good uniformity. The sample deposited by RIBAD has higher refraction index, and can reduce absorption at a certain condition, but it LIDT is under improvement. The crystal structure of the sample deposited with RIBAD is monoclinic, and when the bombardment energy rises, the preferred orientation changes from (002) to (-111).
2007,
19.
Abstract:
Lead zirconate titanate(PZT) ferroelectric materials were prepared by the traditional solid phase reaction method, and the passive capacitors of parallel slab were processed. At last the total dose radiation effect on the PZT ferroelectric material capacitors with the ELV-8 electron linear accelerator were tested. The ferroelectric performance parameters of capacitors before and after radiation were tested and compared. The results show that the encircling area of polarization-field hysteresis loop is gradually decreased, and that the parameters such as the saturation polarization, the remnant polarization and the coercive field exhibit a linear decrease with the increase of irradiation dose of high energy electron. When the irradiation dose is 1×108 rad（Si）, the attenuation ranges o
Lead zirconate titanate(PZT) ferroelectric materials were prepared by the traditional solid phase reaction method, and the passive capacitors of parallel slab were processed. At last the total dose radiation effect on the PZT ferroelectric material capacitors with the ELV-8 electron linear accelerator were tested. The ferroelectric performance parameters of capacitors before and after radiation were tested and compared. The results show that the encircling area of polarization-field hysteresis loop is gradually decreased, and that the parameters such as the saturation polarization, the remnant polarization and the coercive field exhibit a linear decrease with the increase of irradiation dose of high energy electron. When the irradiation dose is 1×108 rad（Si）, the attenuation ranges o
2007,
19.
Abstract:
It is a traditional method to diagnose electron-cyclotron-resonance (ECR) plasma source, using a single probe to measure the current-voltage curve of the plasma, based on which and theoretic formula the plasma density can be computed. The article adopts a Langmuir probe having a role of emission electrons to measure two different current-voltage curves with and without emission. It is ease to get the plasma potential via the inflexion of the two curves and compute directly various physical quantities by the assistant computor, such as electron temperature, electron/ion density, plasma potential etc. The deviation is about percent 1.8 between the measurement results by traditional and the new method, but the latter has higher efficiency.
It is a traditional method to diagnose electron-cyclotron-resonance (ECR) plasma source, using a single probe to measure the current-voltage curve of the plasma, based on which and theoretic formula the plasma density can be computed. The article adopts a Langmuir probe having a role of emission electrons to measure two different current-voltage curves with and without emission. It is ease to get the plasma potential via the inflexion of the two curves and compute directly various physical quantities by the assistant computor, such as electron temperature, electron/ion density, plasma potential etc. The deviation is about percent 1.8 between the measurement results by traditional and the new method, but the latter has higher efficiency.
2007,
19.
Abstract:
Construction of an undulator includes magnet block measurement, sorting, field measurement and adjustment. Optimizing SDUV-FEL undulator by simulated annealing algorithm using measurement results of the magnet blocks by Helmholtz coil before installing undulator magnets, the cost function can be reduced by three orders of magnitude. The practical parameters of one segment meet the design specifications after adjusting the magnetic field.
Construction of an undulator includes magnet block measurement, sorting, field measurement and adjustment. Optimizing SDUV-FEL undulator by simulated annealing algorithm using measurement results of the magnet blocks by Helmholtz coil before installing undulator magnets, the cost function can be reduced by three orders of magnitude. The practical parameters of one segment meet the design specifications after adjusting the magnetic field.
2007,
19.
Abstract:
Utilizing one accelerator to produce dual or multi-beam electrons has the advantages of high synchronization, high efficiency, and high power, which is the key technique for microwave power combining. The intense dual-beam was simulated with diode impedance about 10 W and input voltage of 442.6 kV. The simulation gave a total beam current of 47.6 kA, a gross power of 20 GW, and synchronization time-difference less than 6 ns. Bombarding the stainless steel witness-target and diagnosing the synchronous dual-beam were experimentally studied. The two stainless steel cathodes were 30 mm long with a radius of 20 mm and a distance of 100 mm between them, and the emitting surfaces were velvet. At diode voltage of 442.8 kV, total beam of 48.78 kA and synchronization time-difference of 4~6 ns were o
Utilizing one accelerator to produce dual or multi-beam electrons has the advantages of high synchronization, high efficiency, and high power, which is the key technique for microwave power combining. The intense dual-beam was simulated with diode impedance about 10 W and input voltage of 442.6 kV. The simulation gave a total beam current of 47.6 kA, a gross power of 20 GW, and synchronization time-difference less than 6 ns. Bombarding the stainless steel witness-target and diagnosing the synchronous dual-beam were experimentally studied. The two stainless steel cathodes were 30 mm long with a radius of 20 mm and a distance of 100 mm between them, and the emitting surfaces were velvet. At diode voltage of 442.8 kV, total beam of 48.78 kA and synchronization time-difference of 4~6 ns were o
2007,
19.
Abstract:
The opening process of long conduction time plasma opening switch has been studied by particle-in-cell simulation. The building of computing model and complex boundaries is introducedin detail. Simulation results reveal the opening gap formation process and its mechanism. It is shown that both Hall erosion and electrostatic erosion affect the gap formation process, however, the latter is introduced by the magnetic field expulsion and dominates the opening stage eventually.
The opening process of long conduction time plasma opening switch has been studied by particle-in-cell simulation. The building of computing model and complex boundaries is introducedin detail. Simulation results reveal the opening gap formation process and its mechanism. It is shown that both Hall erosion and electrostatic erosion affect the gap formation process, however, the latter is introduced by the magnetic field expulsion and dominates the opening stage eventually.
2007,
19.
Abstract:
With the indirect-feed two-step helicalexplosivemagnetic generator as the initial power source, on the basis of the equivalent circuit pattern, we establish a program named BCYSSYS. The inductance load of the type 04 explosive-magnetic generator was calculated by the BCYSSYS, and the calculated result was compared with the experimental one. Capacitive load was considered. Moreover, utilizing the data sheet of the copper resistivity against specific action during the course of wire exploding, computation was carried out for the inductive energy storage pulsedpower conditioning system with an exploding wire opening switch, in which explosive magnetic generator works as an power source．
With the indirect-feed two-step helicalexplosivemagnetic generator as the initial power source, on the basis of the equivalent circuit pattern, we establish a program named BCYSSYS. The inductance load of the type 04 explosive-magnetic generator was calculated by the BCYSSYS, and the calculated result was compared with the experimental one. Capacitive load was considered. Moreover, utilizing the data sheet of the copper resistivity against specific action during the course of wire exploding, computation was carried out for the inductive energy storage pulsedpower conditioning system with an exploding wire opening switch, in which explosive magnetic generator works as an power source．
