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RSS2009 Vol. 21, No. 02
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2009,
21.
Abstract:
This paper introduces the filter effect after the image with speckle noise is processed by different spin filters window. Comparing the images processed by spin filters, it is proved that the spin filter window should be one-fourth of the fringe width, and must be larger than the speckle size to filter off noise for images with large speckle noise. The gray scale extension has been applied for the fringe image to increase the fringe contrast, which was reduced by the spin and median filter.
This paper introduces the filter effect after the image with speckle noise is processed by different spin filters window. Comparing the images processed by spin filters, it is proved that the spin filter window should be one-fourth of the fringe width, and must be larger than the speckle size to filter off noise for images with large speckle noise. The gray scale extension has been applied for the fringe image to increase the fringe contrast, which was reduced by the spin and median filter.
2009,
21.
Abstract:
In hydrodynamic instability experiments, the X-ray intensity distribution will change after passing through the imaging system. In order to acquire the actual X-ray distribution, the MTF of the imaging system have to be measured accurately. The line spread function(LSF) of the imaging system was given by analyzing the edge image. The fourier transform of the LSF is the MTF of the imaging system. The image reconstruction was completed using Weiner filtering and constrained least square filtering. The boundary of the reconstruction image is clear.
In hydrodynamic instability experiments, the X-ray intensity distribution will change after passing through the imaging system. In order to acquire the actual X-ray distribution, the MTF of the imaging system have to be measured accurately. The line spread function(LSF) of the imaging system was given by analyzing the edge image. The fourier transform of the LSF is the MTF of the imaging system. The image reconstruction was completed using Weiner filtering and constrained least square filtering. The boundary of the reconstruction image is clear.
2009,
21.
Abstract:
Cr and Al were chosen to design the 30.4 nm self-supporting filter based on relation between mass absorption coefficient and wavelength. NaCl was chosen as parting agent, Al was deposited by thermal evaporation, Cr was deposited by electron-beam evaporation, and finally 30.4 nm Cr/Al/Cr self-supporting filters were prepared. Observed under microscope, the filter topography was clean and uniform without apparent pinholes. The Cr/Al/Cr filters were measured in th National Synchrotron Radiation Laboratory in Hefei, and the transmittances of Cr(5 nm)/Al(500 nm)/Cr (5 nm) filter and Cr(12.5 nm)/Al(500 nm)/Cr(12.5 nm) filter are 7.6% and 4.6% at the wavelength of 30.4 nm, respectively. The measured transmittance curves of the two filters in EUV region are in general accordance with the predictio
Cr and Al were chosen to design the 30.4 nm self-supporting filter based on relation between mass absorption coefficient and wavelength. NaCl was chosen as parting agent, Al was deposited by thermal evaporation, Cr was deposited by electron-beam evaporation, and finally 30.4 nm Cr/Al/Cr self-supporting filters were prepared. Observed under microscope, the filter topography was clean and uniform without apparent pinholes. The Cr/Al/Cr filters were measured in th National Synchrotron Radiation Laboratory in Hefei, and the transmittances of Cr(5 nm)/Al(500 nm)/Cr (5 nm) filter and Cr(12.5 nm)/Al(500 nm)/Cr(12.5 nm) filter are 7.6% and 4.6% at the wavelength of 30.4 nm, respectively. The measured transmittance curves of the two filters in EUV region are in general accordance with the predictio
2009,
21.
Abstract:
The preparation of SiO2 colloids by alkali-catalyze method was reported. The single film of SiO2 was prepared by dip coating method on K9 glass. After the films being treated in different ways, including heat, UV irradiation, ammonia and hexamethyl disilazane, and acid film coating treatments, the properties of the films were analyzed by spectrophotometry, Fourier transform infrared spectroscopy, scanning probe microscope, contact angle measuring apparatus and spectroscopic ellipsometer, et al. The contamination resist capabilities of the single film before and after accelerated contamination in vacuum were compared. The results indicate that the transmittance of the complex film with an acid film is still above 99%, and the water contact angle is 128°, the contamination resistant capabil
The preparation of SiO2 colloids by alkali-catalyze method was reported. The single film of SiO2 was prepared by dip coating method on K9 glass. After the films being treated in different ways, including heat, UV irradiation, ammonia and hexamethyl disilazane, and acid film coating treatments, the properties of the films were analyzed by spectrophotometry, Fourier transform infrared spectroscopy, scanning probe microscope, contact angle measuring apparatus and spectroscopic ellipsometer, et al. The contamination resist capabilities of the single film before and after accelerated contamination in vacuum were compared. The results indicate that the transmittance of the complex film with an acid film is still above 99%, and the water contact angle is 128°, the contamination resistant capabil
2009,
21.
Abstract:
The electromagnetic field tensor method is used to calculate the electromagnetic fields inside a parallel-plate simulator and analytical expressions for the field distributions are derived in time domain. The solid metal plates are approximated as wire meshes according to the simulator structures, which are composed of the middle flat plates, the front and back triangular plates. The amplitudes of the electromagnetic field can be determined by the superposition of the different retarded time currents in the wire segments, and the direction can be determined by the simple unit vector operations of the wire segments and field point position. Calculated results show that the fields between the middle flat plates have the transverse electromagnetic distribution properties, and the field compon
The electromagnetic field tensor method is used to calculate the electromagnetic fields inside a parallel-plate simulator and analytical expressions for the field distributions are derived in time domain. The solid metal plates are approximated as wire meshes according to the simulator structures, which are composed of the middle flat plates, the front and back triangular plates. The amplitudes of the electromagnetic field can be determined by the superposition of the different retarded time currents in the wire segments, and the direction can be determined by the simple unit vector operations of the wire segments and field point position. Calculated results show that the fields between the middle flat plates have the transverse electromagnetic distribution properties, and the field compon
2009,
21.
Abstract:
The design methodology and numerical results for two bend circular waveguides(BCWGs) suitable for transmitting TM01 mode and TE01 mode, respectively, were reported. The optimized TM01 mode BCWG and TE01 mode BCWG both have a transmission efficiency of over 99.5% at center frequency with separate bandwidth of 20.0% and 14.4%. Moreover, the two BCWGs are also suitable for transmitting TE11 mode and TM11 mode, respectively. The transmission characteristics of horizontal polarized TE11 mode and vertical polarized TM11 mode are similar with those of TM01 mode and TE01 mode, respectively. Vertical polarized TE11 mode and horizontal polarized TM11 usually have high transmission efficiencies through BCWGs, since they are unlikely to couple with other modes.
The design methodology and numerical results for two bend circular waveguides(BCWGs) suitable for transmitting TM01 mode and TE01 mode, respectively, were reported. The optimized TM01 mode BCWG and TE01 mode BCWG both have a transmission efficiency of over 99.5% at center frequency with separate bandwidth of 20.0% and 14.4%. Moreover, the two BCWGs are also suitable for transmitting TE11 mode and TM11 mode, respectively. The transmission characteristics of horizontal polarized TE11 mode and vertical polarized TM11 mode are similar with those of TM01 mode and TE01 mode, respectively. Vertical polarized TE11 mode and horizontal polarized TM11 usually have high transmission efficiencies through BCWGs, since they are unlikely to couple with other modes.
2009,
21.
Abstract:
For the flash radiographic image with low signal-to-noise ratio(SNR), an adaptive image reconstruction algorithm was proposed. Based on the conventional algebraic reconstruction technique(ART) algorithm, two weight matrixes associated with the image were imported to the iterative reconstruction. One was used to control the high frequency of the reconstructed image so as to protect its edge; the other was used to control the low frequency so as to improve the SNR of the reconstructed image. Both matrixes were refreshed when the reconstructed image was iterated. Numerical simulation results show that in comparison with the conventional ART algorithm, the algorithm has stronger abilities of noise removal and edge preservation.
For the flash radiographic image with low signal-to-noise ratio(SNR), an adaptive image reconstruction algorithm was proposed. Based on the conventional algebraic reconstruction technique(ART) algorithm, two weight matrixes associated with the image were imported to the iterative reconstruction. One was used to control the high frequency of the reconstructed image so as to protect its edge; the other was used to control the low frequency so as to improve the SNR of the reconstructed image. Both matrixes were refreshed when the reconstructed image was iterated. Numerical simulation results show that in comparison with the conventional ART algorithm, the algorithm has stronger abilities of noise removal and edge preservation.
2009,
21.
Abstract:
This paper introduces the studies of the ultra-short Thomson scattering X-ray source at the accelerator laboratory of Tsinghua University in recent years. Properties such as the photon yield, the pulse length and time jitter of the produced photon pulse were predicted theoretically from the parameters of the electron bunch and the laser pulse, and the scattering angle. Preliminary experiments were successfully carried out with a 16 MeV backward-traveling-wave accelerator and the ns-Q switched laser provided by China Academy of Engineering Physics. This paper also introduces the 1.6-cell electron gun that was fabricated on site and the experiment with high RF power including the measurement of the electron bunche parameters. Based on these, we have designed an X-ray source, which is now und
This paper introduces the studies of the ultra-short Thomson scattering X-ray source at the accelerator laboratory of Tsinghua University in recent years. Properties such as the photon yield, the pulse length and time jitter of the produced photon pulse were predicted theoretically from the parameters of the electron bunch and the laser pulse, and the scattering angle. Preliminary experiments were successfully carried out with a 16 MeV backward-traveling-wave accelerator and the ns-Q switched laser provided by China Academy of Engineering Physics. This paper also introduces the 1.6-cell electron gun that was fabricated on site and the experiment with high RF power including the measurement of the electron bunche parameters. Based on these, we have designed an X-ray source, which is now und
2009,
21.
Abstract:
For the X-ray flash radiography in nucleus irradiation surroundings, research about the influence of the irradiation dose of research demand on photo-electrical receiving system was done to ensure the safe and effective using of the system. The outcome of theoretical analysis showed that the irradiation dose of research demand was far less than the radiation hardness of each component in photo-electrical receiving system and the influence of irradiation surroundings on the background noise of CCD camera was small. The experiment based on the theoretical analysis indicated that, by establishing and adopting suitable shielding measures, the background grey scale of irradiation surroundings to CCD camera for study was less than the inherent background noise of the scientific level CCD and the
For the X-ray flash radiography in nucleus irradiation surroundings, research about the influence of the irradiation dose of research demand on photo-electrical receiving system was done to ensure the safe and effective using of the system. The outcome of theoretical analysis showed that the irradiation dose of research demand was far less than the radiation hardness of each component in photo-electrical receiving system and the influence of irradiation surroundings on the background noise of CCD camera was small. The experiment based on the theoretical analysis indicated that, by establishing and adopting suitable shielding measures, the background grey scale of irradiation surroundings to CCD camera for study was less than the inherent background noise of the scientific level CCD and the
2009,
21.
Abstract:
A constrained conjugate gradient(CCG) restoration algorithm is proposed for badly blurred and noised high-energy radiography images. Constrained with prior knowledge, the algorithm converts the restoration problem to a constrained optimization one, which can be solved with the conjugate gradient algorithm. Since image restoration is an ill-posed problem, median filter and partial differential equation(PDE) are used to constrain the smoothness of deblurred image. Numerical experiment results show that the algorithm can properly retrieve edges and reduce noise simultaneously, and especially the signal to noise ratio(SNR) and subjective visual effect of the restored images are improved significantly.
A constrained conjugate gradient(CCG) restoration algorithm is proposed for badly blurred and noised high-energy radiography images. Constrained with prior knowledge, the algorithm converts the restoration problem to a constrained optimization one, which can be solved with the conjugate gradient algorithm. Since image restoration is an ill-posed problem, median filter and partial differential equation(PDE) are used to constrain the smoothness of deblurred image. Numerical experiment results show that the algorithm can properly retrieve edges and reduce noise simultaneously, and especially the signal to noise ratio(SNR) and subjective visual effect of the restored images are improved significantly.
2009,
21.
Abstract:
The relativistic and non-relativistic self-consistent-field methods were utilized to calculate the 3s-np, 3p-ns and 3p-nd excitation energies and oscillator strengths for Na-like ions (atomic number was 11~92). The relativistic effects for the M-shell transitions were discussed by comparing the relativistic results with the non-relativistic ones. It is found that the relativistic effects mainly affect the excitation energies for n=3 transitions and the effects on line strengths (or transitions matrix elements)are small. However, the relativistic effects influence both excitation energies and line strengths for n>3 transitions, and in most cases, the influence on line strengths is stronger. The results are important for calculating the opacities in the research on inertial confinement fusio
The relativistic and non-relativistic self-consistent-field methods were utilized to calculate the 3s-np, 3p-ns and 3p-nd excitation energies and oscillator strengths for Na-like ions (atomic number was 11~92). The relativistic effects for the M-shell transitions were discussed by comparing the relativistic results with the non-relativistic ones. It is found that the relativistic effects mainly affect the excitation energies for n=3 transitions and the effects on line strengths (or transitions matrix elements)are small. However, the relativistic effects influence both excitation energies and line strengths for n>3 transitions, and in most cases, the influence on line strengths is stronger. The results are important for calculating the opacities in the research on inertial confinement fusio
2009,
21.
Abstract:
The too strong pulse from a photomultiplier tube, produced by X-rays and gamma rays generated in the ICF experiment, leads to the saturation of the front-end electronics.It impedes normal circuit operation and measurement of the flight time of neutrons.An improved antisaturation nonlinear circuit has been put forward and tested on the basis of the frontend electronics structure and further analysis of its saturation.Simulation results indicate that the improved circuit could introduce great attenuations for large amplitude pulses and pass through small amplitude pulses.The baseline of the circuit can recover within 35 ns. The experimental test has got the same results as the simulation does. It shows that the improved solution is simple and effective, and it could ensure the normal cir
The too strong pulse from a photomultiplier tube, produced by X-rays and gamma rays generated in the ICF experiment, leads to the saturation of the front-end electronics.It impedes normal circuit operation and measurement of the flight time of neutrons.An improved antisaturation nonlinear circuit has been put forward and tested on the basis of the frontend electronics structure and further analysis of its saturation.Simulation results indicate that the improved circuit could introduce great attenuations for large amplitude pulses and pass through small amplitude pulses.The baseline of the circuit can recover within 35 ns. The experimental test has got the same results as the simulation does. It shows that the improved solution is simple and effective, and it could ensure the normal cir
2009,
21.
Abstract:
To furnish a greater choice of substrate materials for application in vacuum ultraviolet and deep ultraviolet region, the optical properties of several substrate materials such as JGS1, MgF2, CaF2, and LiF are studied in the wavelength region from 120 nm to 300 nm. The optical constants of these materials are determined from photometric measurements through a process of matching calculated and measured values of the reflectance and transmittance in the ultraviolet to deep ultraviolet region. A method to calculate optical properties of weak absorption substrates is introduced.
To furnish a greater choice of substrate materials for application in vacuum ultraviolet and deep ultraviolet region, the optical properties of several substrate materials such as JGS1, MgF2, CaF2, and LiF are studied in the wavelength region from 120 nm to 300 nm. The optical constants of these materials are determined from photometric measurements through a process of matching calculated and measured values of the reflectance and transmittance in the ultraviolet to deep ultraviolet region. A method to calculate optical properties of weak absorption substrates is introduced.
2009,
21.
Abstract:
To study conductivity of an expanding plasma cloud generated during hypervelocity impact, a scanning electrical probe diagnostic system suitable for transient plasma conductivity measurement is designed. Spherical projectile of LY12 aluminum is loaded by two-stage light-gas gun, the scanning electrical probe diagnostic system was used to measure plasma conductivity, which was generated by hypervelocity impact at different impact velocities or the same angles. The relationship between the plasma conductivity generated during the whole physical process at the positions of probes and the time was obtained by analyzing the equivalent circuit. Experimental results show that the conductivity depends on impact velocity and at the same impact angle and the sensor layout, the expanding plasma cloud
To study conductivity of an expanding plasma cloud generated during hypervelocity impact, a scanning electrical probe diagnostic system suitable for transient plasma conductivity measurement is designed. Spherical projectile of LY12 aluminum is loaded by two-stage light-gas gun, the scanning electrical probe diagnostic system was used to measure plasma conductivity, which was generated by hypervelocity impact at different impact velocities or the same angles. The relationship between the plasma conductivity generated during the whole physical process at the positions of probes and the time was obtained by analyzing the equivalent circuit. Experimental results show that the conductivity depends on impact velocity and at the same impact angle and the sensor layout, the expanding plasma cloud
2009,
21.
Abstract:
The structure, voltage-dividing theory and design method of the load were presented. The influence of skin effect on the load’s resistance in high frequency was analyzed. The distribution of electric-field intensity in the load and vacuum cavity was calculated. The equivalent capacitance and inductance of the load were calculated, of which the influence on the output waveforms was simulated using Pspice program. The ratio of output to input voltage amplitude is calibrated to be 7.59×-5. In order to avoid flashover, a metal sleeve was designed to reduce the electric field intensity at the cathode triple junction. The amplitudes of the operating voltage and current are 428 kV and 9.48 kA respectively. The resistance is calculated to be 45 Ω, consistent with the design value and
The structure, voltage-dividing theory and design method of the load were presented. The influence of skin effect on the load’s resistance in high frequency was analyzed. The distribution of electric-field intensity in the load and vacuum cavity was calculated. The equivalent capacitance and inductance of the load were calculated, of which the influence on the output waveforms was simulated using Pspice program. The ratio of output to input voltage amplitude is calibrated to be 7.59×-5. In order to avoid flashover, a metal sleeve was designed to reduce the electric field intensity at the cathode triple junction. The amplitudes of the operating voltage and current are 428 kV and 9.48 kA respectively. The resistance is calculated to be 45 Ω, consistent with the design value and
2009,
21.
Abstract:
In order to capture X-ray selfemission images with spectral and spatial resolution simultaneously from Z-pinch plasmas, an X-ray spectrograph with spherical bent mica crystal was set up. A geometric model was presented to describe the line broadening due to source size in the dispersion plane. The spectral resolution from this model which was consistent with that from ray tracing calculations showed that the best spectral resolution could be obtained when the detector was placed on the Rowland circle. X-ray spectrograph from aluminum wire array Zpinch implosion was recorded on “QiangGuang-I”generator, which indicated spectral resolution of better than 1 000．
In order to capture X-ray selfemission images with spectral and spatial resolution simultaneously from Z-pinch plasmas, an X-ray spectrograph with spherical bent mica crystal was set up. A geometric model was presented to describe the line broadening due to source size in the dispersion plane. The spectral resolution from this model which was consistent with that from ray tracing calculations showed that the best spectral resolution could be obtained when the detector was placed on the Rowland circle. X-ray spectrograph from aluminum wire array Zpinch implosion was recorded on “QiangGuang-I”generator, which indicated spectral resolution of better than 1 000．
2009,
21.
Abstract:
The multi-conductor transmission line(MTL) model used for analyzing taper winding in air-cored pulse transformer was build by multi-conductor transmission line theory. The reasoning formula of distributed parameter in its equivalent circuit were deduced, and then they were calculated by finite element method. Experiment was carried out to study the impulse voltage distribution on taper winding,such as turn-to-ground voltage and turn-to-turn voltage, the results were agreeable to that of calculation. Research indicates that distributed parameter on taper winding led to voltage oscillation during rising edge, which may create excessive voltage gradient in head of winding, the validity of MTL model is also proved.
The multi-conductor transmission line(MTL) model used for analyzing taper winding in air-cored pulse transformer was build by multi-conductor transmission line theory. The reasoning formula of distributed parameter in its equivalent circuit were deduced, and then they were calculated by finite element method. Experiment was carried out to study the impulse voltage distribution on taper winding,such as turn-to-ground voltage and turn-to-turn voltage, the results were agreeable to that of calculation. Research indicates that distributed parameter on taper winding led to voltage oscillation during rising edge, which may create excessive voltage gradient in head of winding, the validity of MTL model is also proved.
2009,
21.
Abstract:
For purpose of calculating the bare wire and shielded wire responses in Ｘ-ray environment, Holland thin wire model and (transmission line) TL model were used respectively. The effect of wire load, radius, X-ray energy and medium layer thickness on the responses were discussed based on the results of test. The numerical results indicate that the responses are not sensitive to the change of small load, but it is just the opposite for large load. The width of current pulse and the load energy increases with the increase of load, while the amplitude of the current decreases, and the load power has a peak value. The responses are in proportion to the inner conductor radius, and in inverse proportion to the X-ray energy. For different medium layer thickness, there exists peak value to the curre
For purpose of calculating the bare wire and shielded wire responses in Ｘ-ray environment, Holland thin wire model and (transmission line) TL model were used respectively. The effect of wire load, radius, X-ray energy and medium layer thickness on the responses were discussed based on the results of test. The numerical results indicate that the responses are not sensitive to the change of small load, but it is just the opposite for large load. The width of current pulse and the load energy increases with the increase of load, while the amplitude of the current decreases, and the load power has a peak value. The responses are in proportion to the inner conductor radius, and in inverse proportion to the X-ray energy. For different medium layer thickness, there exists peak value to the curre
2009,
21.
Abstract:
In order to simplify the calculation, elliptic Gaussian model for reflection-type optical antenna was proposed to describe localized deformation, based on which, taking reflection-type receiver antenna for example, the effects of localized deformation on acquisition error was researched. The results of analysis and numerical simulation show that the acquisition error depends on the following parameters: deformation radius, deformation depth, and the deformation distance between the localized deformation and the beam center. The acquisition error increases monotonously as the distortion radius, depth and the distance rise. With the increment of the distortion depth, the acquisition error fluctuates periodically like damped oscillation, and the fluctuation period and the peak positions don’
In order to simplify the calculation, elliptic Gaussian model for reflection-type optical antenna was proposed to describe localized deformation, based on which, taking reflection-type receiver antenna for example, the effects of localized deformation on acquisition error was researched. The results of analysis and numerical simulation show that the acquisition error depends on the following parameters: deformation radius, deformation depth, and the deformation distance between the localized deformation and the beam center. The acquisition error increases monotonously as the distortion radius, depth and the distance rise. With the increment of the distortion depth, the acquisition error fluctuates periodically like damped oscillation, and the fluctuation period and the peak positions don’
2009,
21.
Abstract:
The gradient force pattern adjusted by an annular phase distribution plate is numerically investigated by vector diffraction theory. The phase plate may alter the wavefront phase of incident Gaussian beam with tunable topological charge. Numerical simulations show that the proposed plate may adjust the tunable gradient force on the particles in the focal region. By adjusting the geometrical parameters or changing the topological charge of the phase-shifting plate, some novel polygon trap patterns may occur. For example, a triangle, quadrangle, pentagon and hexagon traps can be obained when the topological charge equals to 3, 4, 5 and 6, respectivily. Therefore, the phase plate may be very advantageous for constructing tunable optical traps. The method is versatile in that it allows precise
The gradient force pattern adjusted by an annular phase distribution plate is numerically investigated by vector diffraction theory. The phase plate may alter the wavefront phase of incident Gaussian beam with tunable topological charge. Numerical simulations show that the proposed plate may adjust the tunable gradient force on the particles in the focal region. By adjusting the geometrical parameters or changing the topological charge of the phase-shifting plate, some novel polygon trap patterns may occur. For example, a triangle, quadrangle, pentagon and hexagon traps can be obained when the topological charge equals to 3, 4, 5 and 6, respectivily. Therefore, the phase plate may be very advantageous for constructing tunable optical traps. The method is versatile in that it allows precise
2009,
21.
Abstract:
A new meteorologic radiosonde for turbulence was introduced, which coupled a microthermal sensor to a conventional meteorologic radiosonde. It could obtain two-way refractive index structure parameter, general meteorologic parameters (temperature, humidity and pressure), temperature spectrum etc. synchronously. Experiments of results in Hefei and Changchun indicate the system can achieve high precision and stability. The system noise detected in the dynamic circumstance of high altitude low temperature corresponds with that in static state normal temperature on the ground. The equivalent refractive index structure parameter resulted from the system noise in dynamic state is less than 2×10-18 m-2/3. This radiosonde can meet the need of atmospheric optical turbulence
A new meteorologic radiosonde for turbulence was introduced, which coupled a microthermal sensor to a conventional meteorologic radiosonde. It could obtain two-way refractive index structure parameter, general meteorologic parameters (temperature, humidity and pressure), temperature spectrum etc. synchronously. Experiments of results in Hefei and Changchun indicate the system can achieve high precision and stability. The system noise detected in the dynamic circumstance of high altitude low temperature corresponds with that in static state normal temperature on the ground. The equivalent refractive index structure parameter resulted from the system noise in dynamic state is less than 2×10-18 m-2/3. This radiosonde can meet the need of atmospheric optical turbulence
2009,
21.
Abstract:
A Gaussian beam combination model of rectangular array was established. By numerical analysis method, influences of beam separation distance, characteristics of unit beam and array structure on far field peak intensity and beam quality of incoherent combination and the same phase coherent combination were researched. Some results generated by the different phase coherent combination were described, and the features of coaxial combination, non-coaxial combination, incoherent and coherent combination were discussed. The results show that beam quality of incoherent combination and the same phase coherent combination deteriorate with the increase of the unit beam number as well as the ratio of beam separation distance to unit beam waist. For the different phase coherent combination there are s
A Gaussian beam combination model of rectangular array was established. By numerical analysis method, influences of beam separation distance, characteristics of unit beam and array structure on far field peak intensity and beam quality of incoherent combination and the same phase coherent combination were researched. Some results generated by the different phase coherent combination were described, and the features of coaxial combination, non-coaxial combination, incoherent and coherent combination were discussed. The results show that beam quality of incoherent combination and the same phase coherent combination deteriorate with the increase of the unit beam number as well as the ratio of beam separation distance to unit beam waist. For the different phase coherent combination there are s
2009,
21.
Abstract:
The analytical expressions of the field and intensity distributions of higher-order Bessel-Gaussian pulsed beams diffracted by an aperture have been derived, which enables us to study the evolution of the phase singularities of the diffracted higher-order Bessel-Gaussian pulsed beams. It is shown that there always exists an optical vortex at the center of the beams and the topological charge is conserved. The phase contours rotate anti clockwise about the z-axis with the increasing pulse frequency and duration. The size of the vortex core decreases with the increasing pulse frequency, but is almost unaffected by pulse duration. The phase contours rotate anti clockwise and clockwise about the z-axis with the increasing truncation parameter and propagation distance respectively. The size of
The analytical expressions of the field and intensity distributions of higher-order Bessel-Gaussian pulsed beams diffracted by an aperture have been derived, which enables us to study the evolution of the phase singularities of the diffracted higher-order Bessel-Gaussian pulsed beams. It is shown that there always exists an optical vortex at the center of the beams and the topological charge is conserved. The phase contours rotate anti clockwise about the z-axis with the increasing pulse frequency and duration. The size of the vortex core decreases with the increasing pulse frequency, but is almost unaffected by pulse duration. The phase contours rotate anti clockwise and clockwise about the z-axis with the increasing truncation parameter and propagation distance respectively. The size of
2009,
21.
Abstract:
An aerosol extinction calculating model for any path in space based on the measured aerosol size distribution (Junge exponent), surface visibility, relative humidity and aerosol extinction profile has been developed, The model covers spectral range from visible- to far infrared- wavelength (1~25 000 cm-1). The calculated results by this model and by the intern ationally popular software (MODTRAN) have been compared with the measured results of grading-sun-photometer (pgs100), Since the parameters of aerosol size distribution and height distribution are considered in the model, the computed result of the present model is more close to the real data than the result of MODTRAN. Analysis shows that the parameters have great effect on aerosol extinction, which illustrates that the measured para
An aerosol extinction calculating model for any path in space based on the measured aerosol size distribution (Junge exponent), surface visibility, relative humidity and aerosol extinction profile has been developed, The model covers spectral range from visible- to far infrared- wavelength (1~25 000 cm-1). The calculated results by this model and by the intern ationally popular software (MODTRAN) have been compared with the measured results of grading-sun-photometer (pgs100), Since the parameters of aerosol size distribution and height distribution are considered in the model, the computed result of the present model is more close to the real data than the result of MODTRAN. Analysis shows that the parameters have great effect on aerosol extinction, which illustrates that the measured para
2009,
21.
Abstract:
Based on the Collins formula, the transformation properties of incoherent one-dimensional off-axis Gaussian beams passing through the fractional Fourier transform(FRFT) system were studied. The analytical expressions for the intensity distribution of this beam were derived. By using the derived expressions, some numerical calculation examples were presented to illustrate the intensity properties on the FRFT plane. It is shown that the intensity distribution on the FRFT plane depend on FRFT order and sub-beams number. The variation of intensity distribution with FRFT order is periodic, and the period is 2. When the FRFT order is even, the number of sub-beam has a great effect on the normalized intensity distribution and the effect decreases with the order in crease; when the FRFT order incr
Based on the Collins formula, the transformation properties of incoherent one-dimensional off-axis Gaussian beams passing through the fractional Fourier transform(FRFT) system were studied. The analytical expressions for the intensity distribution of this beam were derived. By using the derived expressions, some numerical calculation examples were presented to illustrate the intensity properties on the FRFT plane. It is shown that the intensity distribution on the FRFT plane depend on FRFT order and sub-beams number. The variation of intensity distribution with FRFT order is periodic, and the period is 2. When the FRFT order is even, the number of sub-beam has a great effect on the normalized intensity distribution and the effect decreases with the order in crease; when the FRFT order incr
2009,
21.
Abstract:
Diode laser array curvature “smile” produced in the packaging process affects the lasering characteristics, life and beam quality of lasers. Using uniaxial amplification system composed of a high-resolution CCD, a fast axis collimation lens and cylindrical lenses, via laser emitters imaging and facula intensity-based centroid algorithm, the “smile” of diode laser array is measured. The experimental results show that: in the vicinity of threshold current, “smile” of the diode laser array with In solder is less than 2 μm. Influences of FAC lens and CCD resolution on the results are analyzed.
Diode laser array curvature “smile” produced in the packaging process affects the lasering characteristics, life and beam quality of lasers. Using uniaxial amplification system composed of a high-resolution CCD, a fast axis collimation lens and cylindrical lenses, via laser emitters imaging and facula intensity-based centroid algorithm, the “smile” of diode laser array is measured. The experimental results show that: in the vicinity of threshold current, “smile” of the diode laser array with In solder is less than 2 μm. Influences of FAC lens and CCD resolution on the results are analyzed.
2009,
21.
Abstract:
The ablation threshold measurement and absorption characteristic analysis in the ablation courses of polyaryl amide-fibers/epoxy and carbon-fibers/epoxy composites irradiated by 1.319 μm continuous wave laser beam were studied by the double integrating spheres-photodiode system and the camera recording method. The results show that the average ablation threshold of polyaryl amide-fibers/epoxy composite decreases with the material thickness increasing, but the thickness does’t effect the average ablation threshold of carbon-fibers/epoxy composite, which is about 70 W/cm2. The reflectivities of two composites increase slowly with the laser power intensity increasing before ablation, and change from 0.40 to 0.45 for polyaryl amide-fibers/epoxy composite and from 0.15 to 0.20 for carbon-fibe
The ablation threshold measurement and absorption characteristic analysis in the ablation courses of polyaryl amide-fibers/epoxy and carbon-fibers/epoxy composites irradiated by 1.319 μm continuous wave laser beam were studied by the double integrating spheres-photodiode system and the camera recording method. The results show that the average ablation threshold of polyaryl amide-fibers/epoxy composite decreases with the material thickness increasing, but the thickness does’t effect the average ablation threshold of carbon-fibers/epoxy composite, which is about 70 W/cm2. The reflectivities of two composites increase slowly with the laser power intensity increasing before ablation, and change from 0.40 to 0.45 for polyaryl amide-fibers/epoxy composite and from 0.15 to 0.20 for carbon-fibe
2009,
21.
Abstract:
A series of fourth harmonic generation(FHG) experiments based on a laser diode pumped acousto-optic Q-switched Nd:YVO2 laser employing KTP and BBO crystals was conducted. When the incident pump power of the green laser was 1.10 W and the beam waist radius was 12 μm, a 210 mW quasi-continuous UV laser pulse train was obtained and the power conversion efficiency was 19.1%. The results illustrate that for the same incident power, the FHG conversion efficiency varies with the waist width of the green laser beam. At last, we investigate the far field distributions of the UV laser in both o and e light vibration planes, and point that the elliptical shape distribution and the fringe pattern a caused by the different acceptance angles of the BBO crystal in the two planes.
A series of fourth harmonic generation(FHG) experiments based on a laser diode pumped acousto-optic Q-switched Nd:YVO2 laser employing KTP and BBO crystals was conducted. When the incident pump power of the green laser was 1.10 W and the beam waist radius was 12 μm, a 210 mW quasi-continuous UV laser pulse train was obtained and the power conversion efficiency was 19.1%. The results illustrate that for the same incident power, the FHG conversion efficiency varies with the waist width of the green laser beam. At last, we investigate the far field distributions of the UV laser in both o and e light vibration planes, and point that the elliptical shape distribution and the fringe pattern a caused by the different acceptance angles of the BBO crystal in the two planes.
2009,
21.
Abstract:
Focusing the laser (10 ns, 1 064 nm) through K9 glass is used to study the relation between the damage appearance of the glass and the focusing position of the high intensity ns laser pulse. When the laser pulses focus at the sample’s center, the absorbed energy increases with the pulses energy linearly and the area of damage also increases. When the laser pulses focus on the sample’s surface, the absorbed energy increases with the energy increasing at first, then decreases and tends to stabilize, which is the result of the air breakdown with large energy absorption．
Focusing the laser (10 ns, 1 064 nm) through K9 glass is used to study the relation between the damage appearance of the glass and the focusing position of the high intensity ns laser pulse. When the laser pulses focus at the sample’s center, the absorbed energy increases with the pulses energy linearly and the area of damage also increases. When the laser pulses focus on the sample’s surface, the absorbed energy increases with the energy increasing at first, then decreases and tends to stabilize, which is the result of the air breakdown with large energy absorption．
2009,
21.
Abstract:
A novel line-imaging velocity interferometer was developed and implemented, which is suited for small scale specimens shock wave experiments. Using a combination of fiber array, electron-multiplier phototube and digital oscilloscope for recording a comb fringe signal, the velocimeter was capable of 1 ns time resolution and 86 μm spatial resolution. Velocity measurement for Al flyer driven by laser was implemented to test this system. The results showed that the flyer has a 20 ns acceleration history and 14.8 mrad planarity. The experiment confirmed that the new system is valuable for temporal-spatial shock diagnositics.
A novel line-imaging velocity interferometer was developed and implemented, which is suited for small scale specimens shock wave experiments. Using a combination of fiber array, electron-multiplier phototube and digital oscilloscope for recording a comb fringe signal, the velocimeter was capable of 1 ns time resolution and 86 μm spatial resolution. Velocity measurement for Al flyer driven by laser was implemented to test this system. The results showed that the flyer has a 20 ns acceleration history and 14.8 mrad planarity. The experiment confirmed that the new system is valuable for temporal-spatial shock diagnositics.
2009,
21.
Abstract:
Combining fractal area measurement with fractal fitting error, a new algorithm of extended target detection in complex background is proposed. Through analyzing the self-similarity of fractal surface, the fractal feature named area measurement was developed. Using this fractal feature and the characteristic of extended target, potential target regions were detected. Then, the fractal fitting error of every pixel of original image was estimated, and probabilistic relaxation iteration algorithm(PRIA) was utilized to enhance these errors between the natural background and man-made target. Thus, the target was detected by comparing potential target regions and enhanced fractal feature image. Finally, the background conglutinations were eliminated through mathematical morphology operations. The
Combining fractal area measurement with fractal fitting error, a new algorithm of extended target detection in complex background is proposed. Through analyzing the self-similarity of fractal surface, the fractal feature named area measurement was developed. Using this fractal feature and the characteristic of extended target, potential target regions were detected. Then, the fractal fitting error of every pixel of original image was estimated, and probabilistic relaxation iteration algorithm(PRIA) was utilized to enhance these errors between the natural background and man-made target. Thus, the target was detected by comparing potential target regions and enhanced fractal feature image. Finally, the background conglutinations were eliminated through mathematical morphology operations. The
2009,
21.
Abstract:
The limiting magnitude of an electro-optical system can be improved through the spectral filtering technology in daytime space target observation. Considering the characteristic of spectral filtering and the inconsistent responses to different wave bands, the precision of magnitude measurement for spectral filtering technology was analyzed based on the measurement method in exist, and a correction method was given. The magnitude of a space target was measured by an electrooptical system based on the measurement way in existence and the result was simulated through the correction method. The two results were analyzed comparatively, proving that the spectral filtering can improve the detecting ability at the expense of precision deterioration (0.5 magnitude at most)．
The limiting magnitude of an electro-optical system can be improved through the spectral filtering technology in daytime space target observation. Considering the characteristic of spectral filtering and the inconsistent responses to different wave bands, the precision of magnitude measurement for spectral filtering technology was analyzed based on the measurement method in exist, and a correction method was given. The magnitude of a space target was measured by an electrooptical system based on the measurement way in existence and the result was simulated through the correction method. The two results were analyzed comparatively, proving that the spectral filtering can improve the detecting ability at the expense of precision deterioration (0.5 magnitude at most)．
