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RSS2011 Vol. 23, No. 04
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2011,
23.
Abstract:
A numerical model of the thin composite disk side-pumped by ring laserdiode array (LDA) is set up. The LDA fast axis is upright to the disk surface and is compressed. The distribution of the pump, temperature and thermal stress in the thin disk is calculated by a finite element method and the influence of pump power, heat transfer coefficient and time on the temperature and thermal stress is analyzed. Results of simulation indicate that thermal extendable destroy appears on the edge of the composite surface. The rise time and recovery time of the temperature and stress show no obvious change as the pump power increases, while they decrease along with the increase of the heat transfer coefficient. The steady temperature and thermal stress of temperature correlation considering the thermod
A numerical model of the thin composite disk side-pumped by ring laserdiode array (LDA) is set up. The LDA fast axis is upright to the disk surface and is compressed. The distribution of the pump, temperature and thermal stress in the thin disk is calculated by a finite element method and the influence of pump power, heat transfer coefficient and time on the temperature and thermal stress is analyzed. Results of simulation indicate that thermal extendable destroy appears on the edge of the composite surface. The rise time and recovery time of the temperature and stress show no obvious change as the pump power increases, while they decrease along with the increase of the heat transfer coefficient. The steady temperature and thermal stress of temperature correlation considering the thermod
2011,
23.
Abstract:
Factors which have influences on the deformation of the water jet cooled mirror were analyzed. Numerical simulations of corresponding structural parameters were then made to explore general design laws of the water jet cooled mirror and an optimized scheme was achieved. The results show that, the maximum mirror surface deformation can be reduced to 0.07 μm under the conditions of 100 W net absorption power and 25 mm spot diameter, when the water jet cooled mirror is 80 mm in diameter with silicon as mirror material.
Factors which have influences on the deformation of the water jet cooled mirror were analyzed. Numerical simulations of corresponding structural parameters were then made to explore general design laws of the water jet cooled mirror and an optimized scheme was achieved. The results show that, the maximum mirror surface deformation can be reduced to 0.07 μm under the conditions of 100 W net absorption power and 25 mm spot diameter, when the water jet cooled mirror is 80 mm in diameter with silicon as mirror material.
2011,
23.
Abstract:
The double-end pumped polarizationmaintaining fiber laser was studied by using two semiconductor lasers LD1 and LD2. The output powers of the fiber laser were tested by using LD1 and LD2 single-end pumping and double-end pumping. The output power of double-end pumping was compared with the power sum of LD1 and LD2 single-end pumping, which shows that double-end pumping can enhance the pumping efficiency and output power of the fiber laser. The output power of the double-end pumped fiber laser was 6.5 W, and the output polarization degree was 0.5.
The double-end pumped polarizationmaintaining fiber laser was studied by using two semiconductor lasers LD1 and LD2. The output powers of the fiber laser were tested by using LD1 and LD2 single-end pumping and double-end pumping. The output power of double-end pumping was compared with the power sum of LD1 and LD2 single-end pumping, which shows that double-end pumping can enhance the pumping efficiency and output power of the fiber laser. The output power of the double-end pumped fiber laser was 6.5 W, and the output polarization degree was 0.5.
2011,
23.
Abstract:
The thermal field of metal plates in flows under laser irradiation has been computed. The flow was governed by the 3-D Reynolds averaged Navier-Stokes equations and the solid was governed by the energy equation. The k-ε turbulence model was used for turbulence simulation. Thus by using dynamic mesh model to simulate the flow’s “wash out” effect, the physical process of laser ablation was described commendably with fluid-solid coupling method. The results of thermal field and flow field show that the flow just cools the metal plates when the flow velocity and laser power are low. With the flow velocity and laser power getting higher, the flow’s “wash out” effect becomes more important for the thermal field of metal plates.
The thermal field of metal plates in flows under laser irradiation has been computed. The flow was governed by the 3-D Reynolds averaged Navier-Stokes equations and the solid was governed by the energy equation. The k-ε turbulence model was used for turbulence simulation. Thus by using dynamic mesh model to simulate the flow’s “wash out” effect, the physical process of laser ablation was described commendably with fluid-solid coupling method. The results of thermal field and flow field show that the flow just cools the metal plates when the flow velocity and laser power are low. With the flow velocity and laser power getting higher, the flow’s “wash out” effect becomes more important for the thermal field of metal plates.
2011,
23.
Abstract:
Air track method and impact pendulum method are two common measurement methods of impulse coupling coefficient. Relative errors were calculated and measurement experiments were carried out with the two methods, respectively. The results show that the relative error of air track method (4.6%) is smaller than that of impact pendulum method (6.1%), and measuring errors of the displacement data and the pendulum angle contribute the most to the system error. The experimental results of the two methods are basically identical: the two groups of coupling coefficients both increase with increasing incident pulse energy, and the difference between them remains no more than 6%. The impulse coupling coefficient can reach 260 N·MW-1 for incident pulse energy of 3 to 14 J.
Air track method and impact pendulum method are two common measurement methods of impulse coupling coefficient. Relative errors were calculated and measurement experiments were carried out with the two methods, respectively. The results show that the relative error of air track method (4.6%) is smaller than that of impact pendulum method (6.1%), and measuring errors of the displacement data and the pendulum angle contribute the most to the system error. The experimental results of the two methods are basically identical: the two groups of coupling coefficients both increase with increasing incident pulse energy, and the difference between them remains no more than 6%. The impulse coupling coefficient can reach 260 N·MW-1 for incident pulse energy of 3 to 14 J.
2011,
23.
Abstract:
Coherent combination of multiple segmented beams is one of the critical technical issues of high-power solid state lasers. Coherent beam combination by four group tilt/tip-piston mirrors is simulated by the stochastic parallel gradient descent (SPGD) algorithm. Locking phases is performed by running the SPGD algorithm on a coherent beam combination model. The results show that the far-field intensity ratio of four coherent beam combination within the 20-μm-diameter spot is nearly four times higher than that of incoherent beam combination in finite iterations. Simulation results validate that coherent beam combination could be realized with high-frequency response actuators and corresponding high-speed control algorithm.
Coherent combination of multiple segmented beams is one of the critical technical issues of high-power solid state lasers. Coherent beam combination by four group tilt/tip-piston mirrors is simulated by the stochastic parallel gradient descent (SPGD) algorithm. Locking phases is performed by running the SPGD algorithm on a coherent beam combination model. The results show that the far-field intensity ratio of four coherent beam combination within the 20-μm-diameter spot is nearly four times higher than that of incoherent beam combination in finite iterations. Simulation results validate that coherent beam combination could be realized with high-frequency response actuators and corresponding high-speed control algorithm.
2011,
23.
Abstract:
To improve the combining efficiency, stability and expandability of passive selfadjusting coherent combining arrays of fiber lasers, a novel coherent beam combining scheme of fiber lasers is proposed based on a common ring coupled cavity and single mode fiber filtering. Multiple 2×2 fiber couplers are inserted into the resonators of component fiber lasers, respectively, and the remaining ports of the fiber couplers are connected with each other to form the common ring coupled cavity. All the fiber lasers can realize efficient mutual injection coupling through the common ring cavity, and therefore phase locking output can be achieved. The stability of phase locking among the emitting laser beams is improved by the single mode fiber filtering technique. Passive phase locking of three fibe
To improve the combining efficiency, stability and expandability of passive selfadjusting coherent combining arrays of fiber lasers, a novel coherent beam combining scheme of fiber lasers is proposed based on a common ring coupled cavity and single mode fiber filtering. Multiple 2×2 fiber couplers are inserted into the resonators of component fiber lasers, respectively, and the remaining ports of the fiber couplers are connected with each other to form the common ring coupled cavity. All the fiber lasers can realize efficient mutual injection coupling through the common ring cavity, and therefore phase locking output can be achieved. The stability of phase locking among the emitting laser beams is improved by the single mode fiber filtering technique. Passive phase locking of three fibe
2011,
23.
Abstract:
The interaction of amplified spontaneous emission (ASE) flux and coherent laser flux as well as the effect of ASE in cuboid DF amplifiers are studied, by using a finite difference method and an iterative algorithm. The influence of input laser intensity and saturation light intensity on output power and energy extraction efficiency is discussed. The simulation of the amplifier whose gain zone is cuboid and gain coefficient is distributed as parabola indicate that the ASE intensity will decrease with the increase of input laser and the presence of input laser will make the maximum of ASE flux in the amplifier shift from the center to the entrance of the amplifier. The output power and the energy extraction efficiency will increase with the increase of input laser power when the saturation l
The interaction of amplified spontaneous emission (ASE) flux and coherent laser flux as well as the effect of ASE in cuboid DF amplifiers are studied, by using a finite difference method and an iterative algorithm. The influence of input laser intensity and saturation light intensity on output power and energy extraction efficiency is discussed. The simulation of the amplifier whose gain zone is cuboid and gain coefficient is distributed as parabola indicate that the ASE intensity will decrease with the increase of input laser and the presence of input laser will make the maximum of ASE flux in the amplifier shift from the center to the entrance of the amplifier. The output power and the energy extraction efficiency will increase with the increase of input laser power when the saturation l
2011,
23.
Abstract:
Using the method of generalized Huygens-Fresnel diffraction integral, this paper deduces the analytical expression of cosine-Gaussian beams propagating in a gradient-index medium, and analyzes the corresponding propagation properties of cosine-Gaussian beams. The influence of the medium’s gradient-index parameter and the modulation parameter on the propagation properties is also discussed. The results show that the intensity of cosine-Gaussian beams propagating in a gradient-index medium varies periodically on axis. The transverse intensity distribution is largely influenced by the modulation parameter. The transmission of cosine-Gaussian beams is unstable, but the cosine-Gaussian beams can be reshaped through appropriately adjusting the modulation parameter at some spatial position.
Using the method of generalized Huygens-Fresnel diffraction integral, this paper deduces the analytical expression of cosine-Gaussian beams propagating in a gradient-index medium, and analyzes the corresponding propagation properties of cosine-Gaussian beams. The influence of the medium’s gradient-index parameter and the modulation parameter on the propagation properties is also discussed. The results show that the intensity of cosine-Gaussian beams propagating in a gradient-index medium varies periodically on axis. The transverse intensity distribution is largely influenced by the modulation parameter. The transmission of cosine-Gaussian beams is unstable, but the cosine-Gaussian beams can be reshaped through appropriately adjusting the modulation parameter at some spatial position.
2011,
23.
Abstract:
In order to predict and estimate the effects of atmospheric turbulence, vibration of terminals and misalignment on space laser communication, the amplitude of detected signals changing with lateral offset (between the center of the focused beam and the center of the photodetector in the detecting plane and defocus (between the detecting plane and the focal plane, are calculated in simulation and measured in experiment, and the fit error rate (BER), signal-to-noise ratio and jitter of the detected signals changing with lateral offset and defocus are also measured. The results show that the performance of space laser communication systems would deteriorate significantly as the lateral offset and defocus increase, and the lateral offset has more effect. The maximum defocus and lateral offset
In order to predict and estimate the effects of atmospheric turbulence, vibration of terminals and misalignment on space laser communication, the amplitude of detected signals changing with lateral offset (between the center of the focused beam and the center of the photodetector in the detecting plane and defocus (between the detecting plane and the focal plane, are calculated in simulation and measured in experiment, and the fit error rate (BER), signal-to-noise ratio and jitter of the detected signals changing with lateral offset and defocus are also measured. The results show that the performance of space laser communication systems would deteriorate significantly as the lateral offset and defocus increase, and the lateral offset has more effect. The maximum defocus and lateral offset
2011,
23.
Abstract:
The differences of laser mean intensity on target that are induced by parameter errors are analyzed, and the effects of atmospheric parameter errors on the calculation precisions are obtained. The errors of wind velocity and aerosol absorption affect the calculation results by thermal blooming. The thermal blooming is stronger, the effects are severer. In strong thermal blooming, ±(5～8)% wind velocity errors will induce about ±10% calculation errors, and ±(10～20)% errors of aerosol absorption proportion will also induce about ±10% calculation error. In weak thermal blooming and strong turbulence, ±(5～7)% errors of turbulence coherent length will induce about ±10% calculation error.
The differences of laser mean intensity on target that are induced by parameter errors are analyzed, and the effects of atmospheric parameter errors on the calculation precisions are obtained. The errors of wind velocity and aerosol absorption affect the calculation results by thermal blooming. The thermal blooming is stronger, the effects are severer. In strong thermal blooming, ±(5～8)% wind velocity errors will induce about ±10% calculation errors, and ±(10～20)% errors of aerosol absorption proportion will also induce about ±10% calculation error. In weak thermal blooming and strong turbulence, ±(5～7)% errors of turbulence coherent length will induce about ±10% calculation error.
2011,
23.
Abstract:
A method of dim infrared target detection in complex background based on adaptive lateral inhibition network is presented, in order to improve the efficiency of long-range dim infrared target detection. The lateral inhibition network math model is established, and anisotropic Gaussian filtering is used to determine the coefficient of the lateral inhibition network. The scale of the filter’s u-axes is determined by contrast-dependent-spread filter model, while the scale of the filter’s v-axes is determined by intensity-dependent-spread filter model. Compared with traditional test methods, the method can effectively suppress the background, while enhancing the target.
A method of dim infrared target detection in complex background based on adaptive lateral inhibition network is presented, in order to improve the efficiency of long-range dim infrared target detection. The lateral inhibition network math model is established, and anisotropic Gaussian filtering is used to determine the coefficient of the lateral inhibition network. The scale of the filter’s u-axes is determined by contrast-dependent-spread filter model, while the scale of the filter’s v-axes is determined by intensity-dependent-spread filter model. Compared with traditional test methods, the method can effectively suppress the background, while enhancing the target.
2011,
23.
Abstract:
In order to increase the energy efficiency and output energy of solid lasers, the output characteristics of Nd:Ce:YAG crystal was studied, compared with simple Nd:YAG crystal. The impact on initial inverted population caused by the absorption spectrum of Nd3+ and Ce3+ was analyzed. It is found that the energy efficiency of laser crystal can be increased by doping both Nd3+ and Ce3+ in YAG crystal, which increases the output energy and lowers the threshold pump energy of lasers. With the same input voltage of 750 V, the output energy of the Nd:Ce:YAG laser and Nd: YAG laser is 651.5 mJ and 390.4 mJ, respectively, the energy efficiency is 2.31% and 1.38%, and the threshold pump energy is 10.56 mJ and 15.21 mJ. The laser slope efficiency for Nd:Ce:YAG crystal is 0.49% ,
In order to increase the energy efficiency and output energy of solid lasers, the output characteristics of Nd:Ce:YAG crystal was studied, compared with simple Nd:YAG crystal. The impact on initial inverted population caused by the absorption spectrum of Nd3+ and Ce3+ was analyzed. It is found that the energy efficiency of laser crystal can be increased by doping both Nd3+ and Ce3+ in YAG crystal, which increases the output energy and lowers the threshold pump energy of lasers. With the same input voltage of 750 V, the output energy of the Nd:Ce:YAG laser and Nd: YAG laser is 651.5 mJ and 390.4 mJ, respectively, the energy efficiency is 2.31% and 1.38%, and the threshold pump energy is 10.56 mJ and 15.21 mJ. The laser slope efficiency for Nd:Ce:YAG crystal is 0.49% ,
2011,
23.
Abstract:
The propagation of the linearly chirped few-cycle pulse Gaussian beam in the free space is studied by q parameters methods. The distribution of carrier-envelope phase drift in the temporal and spatial domain is analyzed by a zero-order amplitude and first-order phase approximation independent on the chirp coefficient. The carrier-envelope phase drift undergoes a π shift from minus infinity to infinity and evolution to －π/2 on and off the axis, and the position of carrier-envelope phase drift is zero around a certain point originated from the modulation of the chirped on the relation between the phase front and the pulse front in the spatially domain．
The propagation of the linearly chirped few-cycle pulse Gaussian beam in the free space is studied by q parameters methods. The distribution of carrier-envelope phase drift in the temporal and spatial domain is analyzed by a zero-order amplitude and first-order phase approximation independent on the chirp coefficient. The carrier-envelope phase drift undergoes a π shift from minus infinity to infinity and evolution to －π/2 on and off the axis, and the position of carrier-envelope phase drift is zero around a certain point originated from the modulation of the chirped on the relation between the phase front and the pulse front in the spatially domain．
2011,
23.
Abstract:
The scintillation index of laser beams propagating through turbulent atmosphere was theoretically investigated. Then a remote detection system for the analysis of turbulent atmosphere was built with a data processing module based on the ARM7 embedded system and mathematical model of the scintillation index, which can transit data to PC by internet and display curves on PC user interface. With a rotating plate to simulate the turbulent atmosphere, the system was used to measure the scintillation index of laser beams propagating in turbulent atmosphere. The experimental results show that the scintillation index of Gaussian beams propagating through turbulent atmosphere increases with the propagating distance, consistent with the theoretical ones quite well. The system can work stably and mea
The scintillation index of laser beams propagating through turbulent atmosphere was theoretically investigated. Then a remote detection system for the analysis of turbulent atmosphere was built with a data processing module based on the ARM7 embedded system and mathematical model of the scintillation index, which can transit data to PC by internet and display curves on PC user interface. With a rotating plate to simulate the turbulent atmosphere, the system was used to measure the scintillation index of laser beams propagating in turbulent atmosphere. The experimental results show that the scintillation index of Gaussian beams propagating through turbulent atmosphere increases with the propagating distance, consistent with the theoretical ones quite well. The system can work stably and mea
2011,
23.
Abstract:
For the lack of precise control tools in spectral beam combining using reflecting volume Bragg grating, a simple experimental setup was designed using lenses as control elements of beam incident angle and collimation. The optimal grating parameters were derived based on the formula of diffraction efficiency, and the optimal lens parameters were derived based on the formula of aberrations. For the designed combining system, the influencing factors of combining results were analyzed, and the combining results for two laser beams with wavelengths of 1 553 nm and 1 559 nm were calculated. The results show that the combining efficiency of more than 90% can be achieved when the spectral widths of the two beams are less than 1.5 nm, and the combining efficiency of more than 88.7% can also be reac
For the lack of precise control tools in spectral beam combining using reflecting volume Bragg grating, a simple experimental setup was designed using lenses as control elements of beam incident angle and collimation. The optimal grating parameters were derived based on the formula of diffraction efficiency, and the optimal lens parameters were derived based on the formula of aberrations. For the designed combining system, the influencing factors of combining results were analyzed, and the combining results for two laser beams with wavelengths of 1 553 nm and 1 559 nm were calculated. The results show that the combining efficiency of more than 90% can be achieved when the spectral widths of the two beams are less than 1.5 nm, and the combining efficiency of more than 88.7% can also be reac
2011,
23.
Abstract:
A fiber Bragg grating(FBG) was inscribed into Corning Hi1060 fiber by focused irradiation of 800 nm femtosecond laser pulses. The FBG was 8 mm long with the period of 2.9 μm, which corresponds to an eight-order grating for 1 042 nm. As the output coupling mirror, the FBG was spliced to a 3 m long double-clad fiber to form the cavity of a fiber laser. A 975 nm laser diode fiber module was used as the end-pump light source. The double-clad fiber was provided by Nufern, with the core and cladding diameters of 10 μm and 125 μm, respectively. The laser output power was 71.1 mW in our experiment, and the center wavelength was 1 042 nm, with the bandwidth of 0.8 nm.
A fiber Bragg grating(FBG) was inscribed into Corning Hi1060 fiber by focused irradiation of 800 nm femtosecond laser pulses. The FBG was 8 mm long with the period of 2.9 μm, which corresponds to an eight-order grating for 1 042 nm. As the output coupling mirror, the FBG was spliced to a 3 m long double-clad fiber to form the cavity of a fiber laser. A 975 nm laser diode fiber module was used as the end-pump light source. The double-clad fiber was provided by Nufern, with the core and cladding diameters of 10 μm and 125 μm, respectively. The laser output power was 71.1 mW in our experiment, and the center wavelength was 1 042 nm, with the bandwidth of 0.8 nm.
2011,
23.
Abstract:
An optical switch based on direct fiber coupling for high power transfer has been investigated by simulations and experiments. The switch employs MEMS V-grooves for optical fiber fixture, a miniature cam as the actuator and a stepper motor as the drive source, and thus achieves the fiber alignment by the rotary movement of the cam. The switch model was built by using optical simulation software ZEMAX. The effects of mechanical misalignments on fiber to fiber coupling efficiency were then investigated, showing that the effect of lateral misalignment is most significant. The prototype of this switch has been designed and fabricated. Corresponding tests show that the switch has the high power handling capacity and high isolation required in laser ignition systems．
An optical switch based on direct fiber coupling for high power transfer has been investigated by simulations and experiments. The switch employs MEMS V-grooves for optical fiber fixture, a miniature cam as the actuator and a stepper motor as the drive source, and thus achieves the fiber alignment by the rotary movement of the cam. The switch model was built by using optical simulation software ZEMAX. The effects of mechanical misalignments on fiber to fiber coupling efficiency were then investigated, showing that the effect of lateral misalignment is most significant. The prototype of this switch has been designed and fabricated. Corresponding tests show that the switch has the high power handling capacity and high isolation required in laser ignition systems．
2011,
23.
Abstract:
In order to get a high power high repetition solid-state laser, we designed the optical resonator by LAS-CAD software, and analysis the thermal effect of laser crystal and laser peculiarity parameters. According to emulation design result, we carried out a concrete experiment and got the compact solid-state laser. The length of the resonance cavity is 400 mm, 21.6 W output power is obtained under the condition of 100 kHz repetition frequency and 60 W pumped power, resulting in an optical conversion efficiency of 36%,and a slope efficiency of 39.9%.
In order to get a high power high repetition solid-state laser, we designed the optical resonator by LAS-CAD software, and analysis the thermal effect of laser crystal and laser peculiarity parameters. According to emulation design result, we carried out a concrete experiment and got the compact solid-state laser. The length of the resonance cavity is 400 mm, 21.6 W output power is obtained under the condition of 100 kHz repetition frequency and 60 W pumped power, resulting in an optical conversion efficiency of 36%,and a slope efficiency of 39.9%.
2011,
23.
Abstract:
A 532 nm wind lidar system based on a tetrad Fabry-Perot(FP) etalon using steady frequency YAG laser as laser radiation source was designed. In this paper, the fundamental theory of the Doppler wind lidar is introduced, major parameters of emission system, receiver system, emission and receiver optics system and control system were presented. The parameters of the bandwidth and free spectrum range (FSR) width and the width of peak values of outboard double channels based on molecule backscattered signals are designed and analyzed, the parameters of inboard double channels based on aerosols are also designed. The velocity and signal noise ratio of the whole system is simulated. When the value of full width at half maximum is 1.75 GHz, the values of range peaks of the tetrad FPI etalon is 1.
A 532 nm wind lidar system based on a tetrad Fabry-Perot(FP) etalon using steady frequency YAG laser as laser radiation source was designed. In this paper, the fundamental theory of the Doppler wind lidar is introduced, major parameters of emission system, receiver system, emission and receiver optics system and control system were presented. The parameters of the bandwidth and free spectrum range (FSR) width and the width of peak values of outboard double channels based on molecule backscattered signals are designed and analyzed, the parameters of inboard double channels based on aerosols are also designed. The velocity and signal noise ratio of the whole system is simulated. When the value of full width at half maximum is 1.75 GHz, the values of range peaks of the tetrad FPI etalon is 1.
2011,
23.
Abstract:
The paper presents the state of researches on the electromagnetic characteristics of hypervelocity impact produced plasma abroad. Electromagnetic characteristics of plasma generated by hypervelocity impact include electron temperature, particle density and oscillation frequency of plasma, and magnetic fields. Characteristic parameters were diagnosed by using sweep Langmuir probe system, coil systems for magnetic induction intensity measurement. The electromagnetic characteristics of plasma generated by hypervelocity impact were analyzed.
The paper presents the state of researches on the electromagnetic characteristics of hypervelocity impact produced plasma abroad. Electromagnetic characteristics of plasma generated by hypervelocity impact include electron temperature, particle density and oscillation frequency of plasma, and magnetic fields. Characteristic parameters were diagnosed by using sweep Langmuir probe system, coil systems for magnetic induction intensity measurement. The electromagnetic characteristics of plasma generated by hypervelocity impact were analyzed.
2011,
23.
Abstract:
A new method of designing reflective multilayer polarizers working in extreme ultraviolet (EUV) range at a single wavelength using different merit functions has been developed. A merit function of product of s-reflection throughput and logarithm of reflection polarization ratio was chosen. Characteristics of Mo/Si multilayers calculated using the merit function at 13.0 nm have been compared with those calculated using the traditional method. The polarizers of high polarization ratio and large s-reflectivity can be designed by choosing the number of layers and optimizing the thickness of each layer to maximize the merit function.
A new method of designing reflective multilayer polarizers working in extreme ultraviolet (EUV) range at a single wavelength using different merit functions has been developed. A merit function of product of s-reflection throughput and logarithm of reflection polarization ratio was chosen. Characteristics of Mo/Si multilayers calculated using the merit function at 13.0 nm have been compared with those calculated using the traditional method. The polarizers of high polarization ratio and large s-reflectivity can be designed by choosing the number of layers and optimizing the thickness of each layer to maximize the merit function.
2011,
23.
Abstract:
Experiments have been conducted on the pumping system of the SILEX-Ⅰ ultra-short pulse laser facility to study the optical power limiting property of a two-photon absorption material and the improvement of near field uniformity using the material. The output laser beam from a flashlamp-pumped Nd:YAG laser SAGA was used to measure the optical limiting property of the material. The results show that the optical power limiting property is obvious. The transmission rate of the material is very high and it is greater than 90% when the input intensity is less than 0.60 GW/cm2. Moreover online experiments done on the pumping system show that, modulation of near field spots is reduced greatly after the beam passes through the material and thus near field uniformity is improved.
Experiments have been conducted on the pumping system of the SILEX-Ⅰ ultra-short pulse laser facility to study the optical power limiting property of a two-photon absorption material and the improvement of near field uniformity using the material. The output laser beam from a flashlamp-pumped Nd:YAG laser SAGA was used to measure the optical limiting property of the material. The results show that the optical power limiting property is obvious. The transmission rate of the material is very high and it is greater than 90% when the input intensity is less than 0.60 GW/cm2. Moreover online experiments done on the pumping system show that, modulation of near field spots is reduced greatly after the beam passes through the material and thus near field uniformity is improved.
2011,
23.
Abstract:
Measurements of laser induced damage threshold (LIDT) of HfO2/SiO2 high-reflection (HR) dielectric mirrors at 1 064 nm were performed using four different testing methods, 1-on-1, S-on-1, R-on-1 and raster scan, according to the ISO 11254-1, -2 and other relevant standards. The difference between the four testing methods was compared and analyzed. The results suggest that R-on-1 test obtains the highest LIDT, then comes the raster scan and 1-on-1, and the S-on-1 gives the lowest. The laser cumulative effect under 1 000 pulses is not obvious, and the correlation between LIDT and spot size has not been observed when the difference of laser spot sizes is small. The influence of scanning interval and scanning fluence steps on laser conditioning effect was also discussed.
Measurements of laser induced damage threshold (LIDT) of HfO2/SiO2 high-reflection (HR) dielectric mirrors at 1 064 nm were performed using four different testing methods, 1-on-1, S-on-1, R-on-1 and raster scan, according to the ISO 11254-1, -2 and other relevant standards. The difference between the four testing methods was compared and analyzed. The results suggest that R-on-1 test obtains the highest LIDT, then comes the raster scan and 1-on-1, and the S-on-1 gives the lowest. The laser cumulative effect under 1 000 pulses is not obvious, and the correlation between LIDT and spot size has not been observed when the difference of laser spot sizes is small. The influence of scanning interval and scanning fluence steps on laser conditioning effect was also discussed.
2011,
23.
Abstract:
With the calibrated silicon photodiode as standard detector, the sensitivity of X-ray diodes (XRDs) with different photocathodes (Al and Au) has been absolutely measured on the Beijing Synchrontron Radiation Facility. The 2nd-order harmonic in the light source will cause the derived sensitivity to decrease. In order to eliminate this effect, a transmission grating was used to measure the share of the 2nd-order harmonic, and the result was utilized to correct the derived sensitivity of XRDs. A simple model for secondary electron emission of photocathode was presented, and the conversion efficiency of secondary electron was analyzed. The sensitivity in the energy range without experimental data was then calculated through the model. The uncertainty analysis was also carried out, and the resu
With the calibrated silicon photodiode as standard detector, the sensitivity of X-ray diodes (XRDs) with different photocathodes (Al and Au) has been absolutely measured on the Beijing Synchrontron Radiation Facility. The 2nd-order harmonic in the light source will cause the derived sensitivity to decrease. In order to eliminate this effect, a transmission grating was used to measure the share of the 2nd-order harmonic, and the result was utilized to correct the derived sensitivity of XRDs. A simple model for secondary electron emission of photocathode was presented, and the conversion efficiency of secondary electron was analyzed. The sensitivity in the energy range without experimental data was then calculated through the model. The uncertainty analysis was also carried out, and the resu
2011,
23.
Abstract:
Film samples, especially the complex sample, require thickness measurement in very high precision, which can not be achieved by weighing method due to the samples’ small mass. The beamlines of median energy(4B7A) and low energy(4B7B) in Beijing Synchronous Radiation Facility have energies of 0.1 keV to 6.0 keV and energy resolution of over 1 000. This paper presents a thickness measurement method for complex samples by measuring single-energy photon filtering from the samples with the two beamlines, and analyzes the measurement uncertainty at different energy points to improve the measurement precision. The thickness obtained for a complex sample with CH substrate has a measurement uncertainty of less than 1%.
Film samples, especially the complex sample, require thickness measurement in very high precision, which can not be achieved by weighing method due to the samples’ small mass. The beamlines of median energy(4B7A) and low energy(4B7B) in Beijing Synchronous Radiation Facility have energies of 0.1 keV to 6.0 keV and energy resolution of over 1 000. This paper presents a thickness measurement method for complex samples by measuring single-energy photon filtering from the samples with the two beamlines, and analyzes the measurement uncertainty at different energy points to improve the measurement precision. The thickness obtained for a complex sample with CH substrate has a measurement uncertainty of less than 1%.
2011,
23.
Abstract:
Electron beam evaporation method was applied to deposit three sets of 1 064 nm laser mirrors with different outmost layers: quarter-wavelength HfO2， half-wavelength SiO2 and quarterwavelength SiO2 layers, respectively. High reflectivity (more than 99.8%) has been achieved for all the stacks, and irradiated at normal incidence photothermal measurements of absorption are 3.0×10-6, 5.0×10-6 and 6.5×10－6, respectively. Corresponding laser induced damage thresholds (LIDTs) are 32.5 J/cm2, 45.2 J/cm2 and 28.4 J/cm2. The relations of electric field distribution, absorption, layer material characters and LIDT are also discussed．
Electron beam evaporation method was applied to deposit three sets of 1 064 nm laser mirrors with different outmost layers: quarter-wavelength HfO2， half-wavelength SiO2 and quarterwavelength SiO2 layers, respectively. High reflectivity (more than 99.8%) has been achieved for all the stacks, and irradiated at normal incidence photothermal measurements of absorption are 3.0×10-6, 5.0×10-6 and 6.5×10－6, respectively. Corresponding laser induced damage thresholds (LIDTs) are 32.5 J/cm2, 45.2 J/cm2 and 28.4 J/cm2. The relations of electric field distribution, absorption, layer material characters and LIDT are also discussed．
2011,
23.
Abstract:
Free-standing Zr film was prepared through direct-current magnetron sputtering. Polyimide (PI) film was prepared by a two-step process: After fully reaction between PMDA and ODA in DMAC, polyamic acid was produced; PI film was prepared when polyamic acid was thermally imidized. PI/Zr film was prepared through dip-coating PI film on Zr film. Based on the testing result from metrology beam-line station of National Synchrotron Radiation Center of University of Science and Technology of China, real transmittance fits with theoretical analysis fairly well. Although transmittance declines because of PI film, the Ni-like Ag soft X-ray transmittance of PI(200 nm)/Zr(300 nm) and PI(200 nm)/Zr(400 nm) films reaches 14.9% and 7.5% respectively at 13.9 nanometer.
Free-standing Zr film was prepared through direct-current magnetron sputtering. Polyimide (PI) film was prepared by a two-step process: After fully reaction between PMDA and ODA in DMAC, polyamic acid was produced; PI film was prepared when polyamic acid was thermally imidized. PI/Zr film was prepared through dip-coating PI film on Zr film. Based on the testing result from metrology beam-line station of National Synchrotron Radiation Center of University of Science and Technology of China, real transmittance fits with theoretical analysis fairly well. Although transmittance declines because of PI film, the Ni-like Ag soft X-ray transmittance of PI(200 nm)/Zr(300 nm) and PI(200 nm)/Zr(400 nm) films reaches 14.9% and 7.5% respectively at 13.9 nanometer.
2011,
23.
Abstract:
Multiphase plasma aerodynamic actuation is produced when the phases of the plasma electrodes are different. A system of particle image velocimetry(PIV) was established， and the experimental study on the characteristic of plasma aerodynamic actuation with dissymmetrical configuration as well as the velocity of the airflow induced by multiphase plasma aerodynamic actuation was performed by PIV technique. The result indicates that, the spatial structure of the airflow field based on plasma aerodynamic actuation could be accurately reflected with PIV technique. The direction of the injection flow induced by plasma aerodynamic actuation is parallel to the actuator surface, and the velocity of the induced flow increases or the flow field extends while the phases of the plasma electrodes are reg
Multiphase plasma aerodynamic actuation is produced when the phases of the plasma electrodes are different. A system of particle image velocimetry(PIV) was established， and the experimental study on the characteristic of plasma aerodynamic actuation with dissymmetrical configuration as well as the velocity of the airflow induced by multiphase plasma aerodynamic actuation was performed by PIV technique. The result indicates that, the spatial structure of the airflow field based on plasma aerodynamic actuation could be accurately reflected with PIV technique. The direction of the injection flow induced by plasma aerodynamic actuation is parallel to the actuator surface, and the velocity of the induced flow increases or the flow field extends while the phases of the plasma electrodes are reg
2011,
23.
Abstract:
UV-curable cationic composite adhesives containing TiO2 nanostructures were prepared by using 3,4-epoxycyclohexylmethyl 3, 4-epoxycyclohexanecarboxylate(CE) as monomer, triphenylsulfonium hexafluorophosphate salt (PI-432) as photoinitiator and titanium isopropoxide (TIP) as inorganic precursor. The morphology of the composite adhesives was characterized by atom force microscopy (AFM). The effect of TIP content on refractive index and transmittance of adhesives were studied. The results show that TiO2 nanostructures, the average diameter of which is 20 nm or so, can be uniformly dispersed in polymers of composite adhesives. The refractive index of adhesives can be adjusted from 1.501 9 to 1.544 9 with the change of TIP content. The transmittance of adhesives has a slight reduce with the in
UV-curable cationic composite adhesives containing TiO2 nanostructures were prepared by using 3,4-epoxycyclohexylmethyl 3, 4-epoxycyclohexanecarboxylate(CE) as monomer, triphenylsulfonium hexafluorophosphate salt (PI-432) as photoinitiator and titanium isopropoxide (TIP) as inorganic precursor. The morphology of the composite adhesives was characterized by atom force microscopy (AFM). The effect of TIP content on refractive index and transmittance of adhesives were studied. The results show that TiO2 nanostructures, the average diameter of which is 20 nm or so, can be uniformly dispersed in polymers of composite adhesives. The refractive index of adhesives can be adjusted from 1.501 9 to 1.544 9 with the change of TIP content. The transmittance of adhesives has a slight reduce with the in
2011,
23.
Abstract:
A novel compound measuring method for sphericity error detection of ICF target is proposed. Combining the advantages of laser probe and CCD camera, this method can effectively integrate the data captured by laser probe and CCD camera into the same coordinate system by means of calibrating the position relationship of the two optical axes with a standard ball. The quasi-Newton method is employed to process the measured data with the noise data eliminated. Meanwhile, the diameter of target derived by CCD camera is used as partial initial conditions, which prevents the occurrence of local optimization due to inappropriate initial parameter selection. The experiment has been carried out on the experiment platform of a compact five-coordinate measuring machine under two kinds of measuring mode,
A novel compound measuring method for sphericity error detection of ICF target is proposed. Combining the advantages of laser probe and CCD camera, this method can effectively integrate the data captured by laser probe and CCD camera into the same coordinate system by means of calibrating the position relationship of the two optical axes with a standard ball. The quasi-Newton method is employed to process the measured data with the noise data eliminated. Meanwhile, the diameter of target derived by CCD camera is used as partial initial conditions, which prevents the occurrence of local optimization due to inappropriate initial parameter selection. The experiment has been carried out on the experiment platform of a compact five-coordinate measuring machine under two kinds of measuring mode,
2011,
23.
Abstract:
A relativistic backward wave oscillator (RBWO) with resonant reflector has been designed to produce dual-frequency microwaves. The 2.5 dimensional fully electromagnetic simulation software was adopted to simulate the cylindrical RBWO. Dual-frequency microwave output of 9.53 and 10.09 GHz is obtained for the beam voltage of 433 kV and guiding magnetic field of 2.2 T. The average output power is 340 MW and the average power efficiency is 24.1%.
A relativistic backward wave oscillator (RBWO) with resonant reflector has been designed to produce dual-frequency microwaves. The 2.5 dimensional fully electromagnetic simulation software was adopted to simulate the cylindrical RBWO. Dual-frequency microwave output of 9.53 and 10.09 GHz is obtained for the beam voltage of 433 kV and guiding magnetic field of 2.2 T. The average output power is 340 MW and the average power efficiency is 24.1%.
2011,
23.
Abstract:
The principle of Guanella-type transmission line transformer (TLT) is presented, and its characteristics of impedance transformation and balance to unbalance transition are analyzed by using the telegraph equation. To obtain the best input impedance at the low impedance terminal of the balun, the characteristic impedance of the transmission line is chosen according to the measured load impedance. Two 9∶1 baluns, which can operate at 1～30 MHz, are designed for 450 Ω to 50 Ω, 600.0 Ω to 66.7 Ω transformations, respectively. Because of the narrow interval between windings, the transmission line’s characteristic impedance of the 600.0 Ω to 66.7 Ω balun can hardly achieve the required value by simulation. However, the difference between the measured and the simulated input impedances o
The principle of Guanella-type transmission line transformer (TLT) is presented, and its characteristics of impedance transformation and balance to unbalance transition are analyzed by using the telegraph equation. To obtain the best input impedance at the low impedance terminal of the balun, the characteristic impedance of the transmission line is chosen according to the measured load impedance. Two 9∶1 baluns, which can operate at 1～30 MHz, are designed for 450 Ω to 50 Ω, 600.0 Ω to 66.7 Ω transformations, respectively. Because of the narrow interval between windings, the transmission line’s characteristic impedance of the 600.0 Ω to 66.7 Ω balun can hardly achieve the required value by simulation. However, the difference between the measured and the simulated input impedances o
2011,
23.
Abstract:
Based on the scales theory of electromagnetic waves, an anisotropic dielectric ellipsoid is reconstructed into an isotropic one in both electromagnetic and shape parameters. An analytical expression of the electric field inside the anisotropic dielectric ellipsoid is then presented by using the scales relation between electromagnetic fields of the two ellipsoids, and it agrees well with previously published results. The angle between directions of electric fields inside and outside the anisotropic ellipsoid is also derived. Simulations show that the direction of the external electric field has little effect on the internal field, while the dielectric tensor influences both the direction and amplitude of the internal field remarkably.
Based on the scales theory of electromagnetic waves, an anisotropic dielectric ellipsoid is reconstructed into an isotropic one in both electromagnetic and shape parameters. An analytical expression of the electric field inside the anisotropic dielectric ellipsoid is then presented by using the scales relation between electromagnetic fields of the two ellipsoids, and it agrees well with previously published results. The angle between directions of electric fields inside and outside the anisotropic ellipsoid is also derived. Simulations show that the direction of the external electric field has little effect on the internal field, while the dielectric tensor influences both the direction and amplitude of the internal field remarkably.
2011,
23.
Abstract:
A novel diplexer for the coupling output of GW level microwaves has been investigated, which consists of an array of periodically spaced cylindrical rods. The factors influencing the selection of spatial harmonics for the diplexer were researched, and some important rules for the design of the diplexer were obtained. A cylindricalrod diplexer for the coupling output of S/X band GW level microwaves was designed accordingly. The low power experiments revealed that, its S-band reflection and X-band transmission efficiencies were both higher than 97%. In further high power experiments, the diplexer was operated with microwaves of 1.8 GW and 80 ns, and no microwave breakdown was observed.
A novel diplexer for the coupling output of GW level microwaves has been investigated, which consists of an array of periodically spaced cylindrical rods. The factors influencing the selection of spatial harmonics for the diplexer were researched, and some important rules for the design of the diplexer were obtained. A cylindricalrod diplexer for the coupling output of S/X band GW level microwaves was designed accordingly. The low power experiments revealed that, its S-band reflection and X-band transmission efficiencies were both higher than 97%. In further high power experiments, the diplexer was operated with microwaves of 1.8 GW and 80 ns, and no microwave breakdown was observed.
2011,
23.
Abstract:
Two kinds of improved parallel algorithms for 3D PIC simulation have been designed, which can reduce one step of process synchronization in a time step. However, due to the motion path and initial position of particles related to random function, only one of them can guarantee the correctness of parallel computing. The improved parallel algorithms were implemented on CHIPIC3D, which was then used to simulate a relativistic backward wave oscillator tube. The simulation results show that just one improved parallel algorithm is correct with speedup and efficiency enhanced.
Two kinds of improved parallel algorithms for 3D PIC simulation have been designed, which can reduce one step of process synchronization in a time step. However, due to the motion path and initial position of particles related to random function, only one of them can guarantee the correctness of parallel computing. The improved parallel algorithms were implemented on CHIPIC3D, which was then used to simulate a relativistic backward wave oscillator tube. The simulation results show that just one improved parallel algorithm is correct with speedup and efficiency enhanced.
2011,
23.
Abstract:
A compact P-band relativistic backward wave oscillator is investigated using theoretical and simulation method. The coaxial slow wave structure and the coaxial extractor structure are designed to reduce the size and increase the efficiency of the P-band device. Detailed physical interaction pictures of the oscillator are presented. Typical simulation results are that, at the magnetic field of 1.5 T, a P-band microwave with average output power of 1.58 GW is obtained with efficiency about 32%, when the diode voltage and current are 700 kV and 7 kA, respectively. The optimized electromagnetic structure of the device is only f108 mm×856 mm in size.
A compact P-band relativistic backward wave oscillator is investigated using theoretical and simulation method. The coaxial slow wave structure and the coaxial extractor structure are designed to reduce the size and increase the efficiency of the P-band device. Detailed physical interaction pictures of the oscillator are presented. Typical simulation results are that, at the magnetic field of 1.5 T, a P-band microwave with average output power of 1.58 GW is obtained with efficiency about 32%, when the diode voltage and current are 700 kV and 7 kA, respectively. The optimized electromagnetic structure of the device is only f108 mm×856 mm in size.
2011,
23.
Abstract:
The dual-electron beam coaxial relativistic backward wave oscillator(RBWO) was firstly put forward to produce dual frequency microwave output. The properties of the RBWO we investigated with a 2.5-dimensional relativistic fully electromagnetic PIC software. The results show that, for annular relativistic electron beam with voltage of 625 kV, current of 24 kA and guided magnetic field of 0.772 T, the device can produce stable dual-frequency microwave output. The frequencies are 11.5 and 12.2 GHz the average power is about 1.15 GW and the average power efficiency is 7.7%. Three frequency microwave was obtained by changing the cycle number, and the results we discussed．
The dual-electron beam coaxial relativistic backward wave oscillator(RBWO) was firstly put forward to produce dual frequency microwave output. The properties of the RBWO we investigated with a 2.5-dimensional relativistic fully electromagnetic PIC software. The results show that, for annular relativistic electron beam with voltage of 625 kV, current of 24 kA and guided magnetic field of 0.772 T, the device can produce stable dual-frequency microwave output. The frequencies are 11.5 and 12.2 GHz the average power is about 1.15 GW and the average power efficiency is 7.7%. Three frequency microwave was obtained by changing the cycle number, and the results we discussed．
2011,
23.
Abstract:
The electron beam generated by the Dragon-Ⅰ linear induction accelerator strikes the bremsstrahlung converter target to generate X-ray and causes tantalum target damage and hydrodynamic expansion, which results in target density decreasing for successive pulses. The time varying target density was measured by applying a low energy X-ray with energy about 450 keV and spot diameter of 1 to 4 mm along with an intensified charge coupled derice(ICCD) camera. The experiment results show that the target density is basically unchanged for 1 μs after beam-target interaction, and no particle ejected from the front side of the target is found at the same time.
The electron beam generated by the Dragon-Ⅰ linear induction accelerator strikes the bremsstrahlung converter target to generate X-ray and causes tantalum target damage and hydrodynamic expansion, which results in target density decreasing for successive pulses. The time varying target density was measured by applying a low energy X-ray with energy about 450 keV and spot diameter of 1 to 4 mm along with an intensified charge coupled derice(ICCD) camera. The experiment results show that the target density is basically unchanged for 1 μs after beam-target interaction, and no particle ejected from the front side of the target is found at the same time.
2011,
23.
Abstract:
In order to meet the physical requirements, taper mechanism was applied to mechanical system design of in-vacuum undulator. This paper conducted a linear static analysis on taper mechanism, the key part of in-vacuum undulator developed by the Shanghai Synchrotron Radiation Facility, with finite element analysis software ANSYS Workbench, and obtained the distribution of deformation and stress and their effects on deformation and roll angle of the out-vacuum girder. The effects caused by taper mechanism were then minimized through compensating spring system to meet high accuracy at work. The analysis result was verified in the process of commissioning and is consistent with the actual situation.
In order to meet the physical requirements, taper mechanism was applied to mechanical system design of in-vacuum undulator. This paper conducted a linear static analysis on taper mechanism, the key part of in-vacuum undulator developed by the Shanghai Synchrotron Radiation Facility, with finite element analysis software ANSYS Workbench, and obtained the distribution of deformation and stress and their effects on deformation and roll angle of the out-vacuum girder. The effects caused by taper mechanism were then minimized through compensating spring system to meet high accuracy at work. The analysis result was verified in the process of commissioning and is consistent with the actual situation.
2011,
23.
Abstract:
In allusion to Brookhaven National Laboratory(BNL) type photocathode RF gun, we simulated and optimized the influence of drive laser oblique incidence on beam quality. Different distributions of drive laser were considered. We optimized the transverse emittance by tuning the injection phase and magnetic field intensity of compensating coil. The “elliptical spot” caused serious increase of transverse emittance, which can not be optimized well. Whereas, the increase caused by “time slew” could be optimized well for Gaussian distribution pulse in temporal direction. We also presented an optical method to calibrate the “elliptical spot” and “time slew” problem on the photocathode and partial measurement results. The simulation results show that: for drive laser with uniform transverse
In allusion to Brookhaven National Laboratory(BNL) type photocathode RF gun, we simulated and optimized the influence of drive laser oblique incidence on beam quality. Different distributions of drive laser were considered. We optimized the transverse emittance by tuning the injection phase and magnetic field intensity of compensating coil. The “elliptical spot” caused serious increase of transverse emittance, which can not be optimized well. Whereas, the increase caused by “time slew” could be optimized well for Gaussian distribution pulse in temporal direction. We also presented an optical method to calibrate the “elliptical spot” and “time slew” problem on the photocathode and partial measurement results. The simulation results show that: for drive laser with uniform transverse
2011,
23.
Abstract:
Making good use of harmonic radiation field is one of the most straight forward methods to generate radiation at short wavelength. The enhancement of undulator harmonic magnetic field could increase the radiation intensity at the harmonic wavelength. A modified Halbach undulator was analyzed, and its magnetic contents were computed. The analysis shows that the modified Halbach undulator could improve the third harmonic magnetic field to 25% of the fundamental. The effect of the enhanced harmonic magnetic field on the spontaneous radiation spectrum was analyzed using the electron beam parameters in Hefei Light Source. The analysis shows that when the third harmonic magnetic field is improved to 25% of the fundamental in the modified Halbach undulator, the photon flux at the third harmonic o
Making good use of harmonic radiation field is one of the most straight forward methods to generate radiation at short wavelength. The enhancement of undulator harmonic magnetic field could increase the radiation intensity at the harmonic wavelength. A modified Halbach undulator was analyzed, and its magnetic contents were computed. The analysis shows that the modified Halbach undulator could improve the third harmonic magnetic field to 25% of the fundamental. The effect of the enhanced harmonic magnetic field on the spontaneous radiation spectrum was analyzed using the electron beam parameters in Hefei Light Source. The analysis shows that when the third harmonic magnetic field is improved to 25% of the fundamental in the modified Halbach undulator, the photon flux at the third harmonic o
2011,
23.
Abstract:
The digital transverse feedback system is used to suppress the transverse beam instabilities at Hefei Light Source (HLS). During the commissioning of the feedback system, a turn-by-turn measurement system has been adopted to gather beam position information for the assessment of its feedback efficiency. The growth and damping of beam instability were observed by gradually changing the chromaticity through varying the sextupole magnet current. Corresponding growth time and damping time of instability oscillation were calculated to be 0.258 ms and 1.172 ms, respectively. Beam characteristic parameters, such as tune and phase spaces, were measured and calculated. Moreover, the whole process of beam moving near and across the 5/9 resonant line was analyzed.
The digital transverse feedback system is used to suppress the transverse beam instabilities at Hefei Light Source (HLS). During the commissioning of the feedback system, a turn-by-turn measurement system has been adopted to gather beam position information for the assessment of its feedback efficiency. The growth and damping of beam instability were observed by gradually changing the chromaticity through varying the sextupole magnet current. Corresponding growth time and damping time of instability oscillation were calculated to be 0.258 ms and 1.172 ms, respectively. Beam characteristic parameters, such as tune and phase spaces, were measured and calculated. Moreover, the whole process of beam moving near and across the 5/9 resonant line was analyzed.
2011,
23.
Abstract:
The clinical trials of tumor therapy using heavy ion beams, supplied by the cooler storage ring of the Heavy Ion Research Facility in Lanzhou (HIRFL-CSR) with the energy of 100 to 450 MeV/u, are now in progress at the Institute of Modern Physics in Lanzhou. A beam intensity and dose monitor system has been developed to real-time monitor the irradiation dose and beam intensity stability and to make sure the safety of the patients. It is composed of integral ionization chamber, current-frequency transfer electric board and LabVIEW data acquiring and analyzing system. The measurements of this system show that it can work well under the clinical condition.
The clinical trials of tumor therapy using heavy ion beams, supplied by the cooler storage ring of the Heavy Ion Research Facility in Lanzhou (HIRFL-CSR) with the energy of 100 to 450 MeV/u, are now in progress at the Institute of Modern Physics in Lanzhou. A beam intensity and dose monitor system has been developed to real-time monitor the irradiation dose and beam intensity stability and to make sure the safety of the patients. It is composed of integral ionization chamber, current-frequency transfer electric board and LabVIEW data acquiring and analyzing system. The measurements of this system show that it can work well under the clinical condition.
2011,
23.
Abstract:
In order to realize accurate power measurement and effective protection of the transmitter, the principle of directional coupler, and the method of parameter calibration and power measurement applied to the RF transmitter system are described. According to the measurements, the method has the advantages of simple installation, high precision, and dynamic calibration. After parameter calibration, the output power and standing wave ratio are measured online by installing a coaxial directional coupler between the RF power source and the resonant cavity. The measurements are then sent to the system of control, protection and monitoring to complete high-power measurement and protection of devices.
In order to realize accurate power measurement and effective protection of the transmitter, the principle of directional coupler, and the method of parameter calibration and power measurement applied to the RF transmitter system are described. According to the measurements, the method has the advantages of simple installation, high precision, and dynamic calibration. After parameter calibration, the output power and standing wave ratio are measured online by installing a coaxial directional coupler between the RF power source and the resonant cavity. The measurements are then sent to the system of control, protection and monitoring to complete high-power measurement and protection of devices.
2011,
23.
Abstract:
The transmission of strong beam electrons (1 to 10 μA) through a tapered SiO2 capillary was investigated. The time dependence of the total transmitted fraction and one-dimension angular distribution of transmitted electrons were experimentally studied. The result indicates that, the transmitted electrons have the Gaussian distribution and good temporal stability; the transmitted fraction decreases with the incident energy in a negative exponential manner, and this dependence is supported by the guiding effect model．
The transmission of strong beam electrons (1 to 10 μA) through a tapered SiO2 capillary was investigated. The time dependence of the total transmitted fraction and one-dimension angular distribution of transmitted electrons were experimentally studied. The result indicates that, the transmitted electrons have the Gaussian distribution and good temporal stability; the transmitted fraction decreases with the incident energy in a negative exponential manner, and this dependence is supported by the guiding effect model．
Local field effects induced by near-dipole-dipole interaction in optically dense and resonant medium
2011,
23.
Abstract:
The interactions between an ultrashort intense pulse and a dense resonant medium with local-field effects induced by near-dipole-dipole interaction were investigated. According to the semi-classical theory of light-matter interaction, the modified Bloch equations were established with near-dipole-dipole interactions in an optically dense two-level medium, and an accurate and efficient fourth-order Runge-Kutta method was applied for solving the equations. The numerical results show that, during the transient coherence, the evolutions of Bloch vectors and the final state of inversion are strongly modulated by the local-field effects. Furthermore, two modulation schemes of Bloch vectors in dense two-level media were proposed.
The interactions between an ultrashort intense pulse and a dense resonant medium with local-field effects induced by near-dipole-dipole interaction were investigated. According to the semi-classical theory of light-matter interaction, the modified Bloch equations were established with near-dipole-dipole interactions in an optically dense two-level medium, and an accurate and efficient fourth-order Runge-Kutta method was applied for solving the equations. The numerical results show that, during the transient coherence, the evolutions of Bloch vectors and the final state of inversion are strongly modulated by the local-field effects. Furthermore, two modulation schemes of Bloch vectors in dense two-level media were proposed.
2011,
23.
Abstract:
In order to explore kinetic behaviors of electrolysis of tantalum, the electrolytic polishing of tantalum in sulfuric acid-methanol solution was experimentally studied. The influence of electrolyte composition, cell potential and stirring speed on the thinning speed of tantalum was investigated. And the S.A.Arrhenius activation energy was calculated via altering the reaction temperature. The results show that the polarized behavior of tantalum is consistent with general metal polarization when the volume ratio of sulfuric acid to methanol is 1∶7. For voltage from 10 to 20 V, the thinning speed is around the steady value of 11.45 μm/min when the stirring speed is more than 8 m/s. When the stirring speed is less than 8 m/s, the electrolysis process is controlled by the rate of diffusion, w
In order to explore kinetic behaviors of electrolysis of tantalum, the electrolytic polishing of tantalum in sulfuric acid-methanol solution was experimentally studied. The influence of electrolyte composition, cell potential and stirring speed on the thinning speed of tantalum was investigated. And the S.A.Arrhenius activation energy was calculated via altering the reaction temperature. The results show that the polarized behavior of tantalum is consistent with general metal polarization when the volume ratio of sulfuric acid to methanol is 1∶7. For voltage from 10 to 20 V, the thinning speed is around the steady value of 11.45 μm/min when the stirring speed is more than 8 m/s. When the stirring speed is less than 8 m/s, the electrolysis process is controlled by the rate of diffusion, w
2011,
23.
Abstract:
Number densities of active particles（N2(v6),N2(A3),O2(a1),O and O3） in non-equilibrium plasma were calculated and analyzed under the condition of air discharges with various initial temperatures, reduced electric fields and electron number densities. The results show that, the density of active particles increases with the rising of initial temperature, and the maximum number density of oxygen atom is 4.90×7 , 5.2×1010 and 5.51×1010 cm-3, when the initial temperature is 300, 400 and 500 K, respectively. The density of active particles also increases with the reduced electric field increasing, while the number density of vibrantionally excited N2 varies far less significantly. Moreover, the number
Number densities of active particles（N2(v6),N2(A3),O2(a1),O and O3） in non-equilibrium plasma were calculated and analyzed under the condition of air discharges with various initial temperatures, reduced electric fields and electron number densities. The results show that, the density of active particles increases with the rising of initial temperature, and the maximum number density of oxygen atom is 4.90×7 , 5.2×1010 and 5.51×1010 cm-3, when the initial temperature is 300, 400 and 500 K, respectively. The density of active particles also increases with the reduced electric field increasing, while the number density of vibrantionally excited N2 varies far less significantly. Moreover, the number
2011,
23.
Abstract:
In the interaction of a high-intensity laser pulse with a solid target, most of the absorbed laser energy is converted into hot electrons. These electrons transport in solid targets, and in the same time can ionize the K-shell electrons, and produce Kα radiation, which can serve as a backlit source to diagnose dense matters by radiography. To achieve high Kα yield, simulations were done with the ITS code to study the Kα radiation. The effects of hot electron temperature, target thickness, and emission angle on the Kα radiation were investigated. It is found that, for fixed laser power density or hot electron temperature, there is an optimal target thickness, at which the yield of Kα photons reaches the maximum. The simulated results explained the experimental results.
In the interaction of a high-intensity laser pulse with a solid target, most of the absorbed laser energy is converted into hot electrons. These electrons transport in solid targets, and in the same time can ionize the K-shell electrons, and produce Kα radiation, which can serve as a backlit source to diagnose dense matters by radiography. To achieve high Kα yield, simulations were done with the ITS code to study the Kα radiation. The effects of hot electron temperature, target thickness, and emission angle on the Kα radiation were investigated. It is found that, for fixed laser power density or hot electron temperature, there is an optimal target thickness, at which the yield of Kα photons reaches the maximum. The simulated results explained the experimental results.
2011,
23.
Abstract:
Calculations of dielectronic recombination(DR) rate coefficients from the ground state 3s23p63d104s24p64d of Rb-like W37+ ions through doubly excited states (3s23p63d104s24p64d))-1nln′l′(n,n′=4,5) are performed using the fully relativistic configuration interaction method. Total DR rate coefficients are obtained in the temperature range from 1 to 5×104 eV. Comparison of the DR rate coefficients from different subshell excitations shows that 4p subshell excitation dominates at low temperature, while 3d subshell excitation dominates at high temperature. The two-electron and one-photon radiative transitions are found to be important due to the stro
Calculations of dielectronic recombination(DR) rate coefficients from the ground state 3s23p63d104s24p64d of Rb-like W37+ ions through doubly excited states (3s23p63d104s24p64d))-1nln′l′(n,n′=4,5) are performed using the fully relativistic configuration interaction method. Total DR rate coefficients are obtained in the temperature range from 1 to 5×104 eV. Comparison of the DR rate coefficients from different subshell excitations shows that 4p subshell excitation dominates at low temperature, while 3d subshell excitation dominates at high temperature. The two-electron and one-photon radiative transitions are found to be important due to the stro
2011,
23.
Abstract:
To study the total reflection through effect and filtering properties of 1D photonic crystal, the transition matrix method is adopted to calculate the transmissivity of TE wave and TM wave propagating through 1D photonic crystal with incident angle greater than full reflection angle. Variation of the through effect with the medium optical thickness and cycle number of 1D photonic crystal is obtained. The frequency of total reflection peaks decreases with the increase of the medium optical thickness，and the numbers of total reflection peaks and crystal cycles are equal. The through effect has excellent polarization filtering properties, with which simple-structured and easy-to-control polarization filters can be designed.
To study the total reflection through effect and filtering properties of 1D photonic crystal, the transition matrix method is adopted to calculate the transmissivity of TE wave and TM wave propagating through 1D photonic crystal with incident angle greater than full reflection angle. Variation of the through effect with the medium optical thickness and cycle number of 1D photonic crystal is obtained. The frequency of total reflection peaks decreases with the increase of the medium optical thickness，and the numbers of total reflection peaks and crystal cycles are equal. The through effect has excellent polarization filtering properties, with which simple-structured and easy-to-control polarization filters can be designed.
2011,
23.
Abstract:
As probability theory and interval analysis have some shortages in uncertainty quantification of target voltage in the case of limited test samples of key parameters, an uncertainty quantification method based on Dempster-Shafer(D-S) theory was described. Basic belief assignments were calculated on the basis of small samples, and belief and plausibility functions were used to construct the lower and upper probability distributions of target voltage amplitude with Monte Carlo simulation. Experiments and simulations were conducted to obtain the information of target voltage amplitude, such as its approximating probabilistic distribution, confidence interval, and interval of expected values. The results show that, compared with the conventional probability method, the method avoids the proble
As probability theory and interval analysis have some shortages in uncertainty quantification of target voltage in the case of limited test samples of key parameters, an uncertainty quantification method based on Dempster-Shafer(D-S) theory was described. Basic belief assignments were calculated on the basis of small samples, and belief and plausibility functions were used to construct the lower and upper probability distributions of target voltage amplitude with Monte Carlo simulation. Experiments and simulations were conducted to obtain the information of target voltage amplitude, such as its approximating probabilistic distribution, confidence interval, and interval of expected values. The results show that, compared with the conventional probability method, the method avoids the proble
2011,
23.
Abstract:
The lanthanum hexaboride (LaB6) thin film cathode was deposited on large-area glass substrate and Ta substrate by the method of electron-beam deposition under the substrate temperature of 250 ℃ and the vacuum of 2×10-4 Pa. The deposited LaB6 thin films are predominantly (100)-oriented. The lattice displacement between LaB6 film and the LaB6 bulk target is minimal and the crystal size is relatively small at 45° deposition. Theoretically, the LaB6 film deposited at 45° has the possibility of forming low stress contact on different substrates. The work function of the LaB6 film cathode was measured to be 2.56 eV, which also proves the (100)-oriented growth of LaB6 films.
The lanthanum hexaboride (LaB6) thin film cathode was deposited on large-area glass substrate and Ta substrate by the method of electron-beam deposition under the substrate temperature of 250 ℃ and the vacuum of 2×10-4 Pa. The deposited LaB6 thin films are predominantly (100)-oriented. The lattice displacement between LaB6 film and the LaB6 bulk target is minimal and the crystal size is relatively small at 45° deposition. Theoretically, the LaB6 film deposited at 45° has the possibility of forming low stress contact on different substrates. The work function of the LaB6 film cathode was measured to be 2.56 eV, which also proves the (100)-oriented growth of LaB6 films.
2011,
23.
Abstract:
Based on the relation among electron range, incident energy and energy exponential, energy exponential about 1.72 in aluminum and energy exponential about 1.62 in gold for high energy incident electron were computed by ESTAR program, respectively .Based on the relation between the ranges in aluminum and gold at high incident electron energy and energy exponentials, the constants of energy exponential were computed with experimental values, respectively, and the formulas for ranges in aluminum and gold at high incident electron energy were derived. Ranges calculated with the formulas are in good agreement with existing experimental data.
Based on the relation among electron range, incident energy and energy exponential, energy exponential about 1.72 in aluminum and energy exponential about 1.62 in gold for high energy incident electron were computed by ESTAR program, respectively .Based on the relation between the ranges in aluminum and gold at high incident electron energy and energy exponentials, the constants of energy exponential were computed with experimental values, respectively, and the formulas for ranges in aluminum and gold at high incident electron energy were derived. Ranges calculated with the formulas are in good agreement with existing experimental data.
2011,
23.
Abstract:
The equivalent circuit of passive integrator has been established and simulated considering its stray parameters. The higher frequency restriction of the integrator is found to be determined by the stray inductance from integral capacitor and the stray capacitance from integral resistor, whose influence grows as the RC time constant increases, for integrators of the same structure. Coaxial structure can reduce the stray inductance from integral capacitor and thus enlarge the bandwidth of the integrator. A coaxial passive integrator with the RC time constant of 10 μs has been designed and fabricated. Frequency response tests show that, its operation band ranges from 50 kHz to 80 MHz when the error is less than 5%. The output waveform of the integrator connected with a D-dot probe is not di
The equivalent circuit of passive integrator has been established and simulated considering its stray parameters. The higher frequency restriction of the integrator is found to be determined by the stray inductance from integral capacitor and the stray capacitance from integral resistor, whose influence grows as the RC time constant increases, for integrators of the same structure. Coaxial structure can reduce the stray inductance from integral capacitor and thus enlarge the bandwidth of the integrator. A coaxial passive integrator with the RC time constant of 10 μs has been designed and fabricated. Frequency response tests show that, its operation band ranges from 50 kHz to 80 MHz when the error is less than 5%. The output waveform of the integrator connected with a D-dot probe is not di
2011,
23.
Abstract:
A current diagnostic system included a B-dot array and a Rogowski coil was designed for the Flash Ⅱ accelerator diode. Flashes on the insulator surface were monitored and their impact on the output of the diode was discussed based on the differences between the current probes. The waveforms of the B-dot near the position of flashes were distorted, and the waveforms of the other B-dots and the Rogowski coil accorded with those without flash. Compared with no flash situation, the electron beam intensity and energy of the diode, derived with measurements of the B-dot far away from the flash, did not reduce obviously. Flashes on the insulator surface were local discharges and had little impact on the output of high current diodes for the accelerators like Flash-Ⅱ accelerator．
A current diagnostic system included a B-dot array and a Rogowski coil was designed for the Flash Ⅱ accelerator diode. Flashes on the insulator surface were monitored and their impact on the output of the diode was discussed based on the differences between the current probes. The waveforms of the B-dot near the position of flashes were distorted, and the waveforms of the other B-dots and the Rogowski coil accorded with those without flash. Compared with no flash situation, the electron beam intensity and energy of the diode, derived with measurements of the B-dot far away from the flash, did not reduce obviously. Flashes on the insulator surface were local discharges and had little impact on the output of high current diodes for the accelerators like Flash-Ⅱ accelerator．
2011,
23.
Abstract:
The point-plane geometry with iron electrode system was employed in the electrical tree initiation experiment under high voltage nanosecond pulses, with both single and multiple needle electrodes. The result of the latter electrode scheme has a good correlation with that of the former, with higher efficiency at the mean time. Electrical tree initiation experiments were done by the step-up method and accumulation method at different frequencies, and the initiation characteristics of polystyrene were derived. The initiation voltage drops as the pulse frequency rises up from 50 Hz to 500 Hz, while it increases as the frequency rises in the range of 500 Hz to 800 Hz. Aging experiments for different pulsed power utilities were also designed.
The point-plane geometry with iron electrode system was employed in the electrical tree initiation experiment under high voltage nanosecond pulses, with both single and multiple needle electrodes. The result of the latter electrode scheme has a good correlation with that of the former, with higher efficiency at the mean time. Electrical tree initiation experiments were done by the step-up method and accumulation method at different frequencies, and the initiation characteristics of polystyrene were derived. The initiation voltage drops as the pulse frequency rises up from 50 Hz to 500 Hz, while it increases as the frequency rises in the range of 500 Hz to 800 Hz. Aging experiments for different pulsed power utilities were also designed.
2011,
23.
Abstract:
During the experimental study of a long-pulse intense-current foilless diode, surface flashover along its insulator was observed. The analysis of the phenomenon shows that, too short distance between the shield ring and insulator resulted in an intense electric field at the edge of the shield ring, which leaded to the emission of electrons; with effect of intense electromagnetic field, the electrons came into collision with the surface of the insulator, causing secondary electron emission avalanche, and then resulted in vacuum surface flashover. The structure of the shield ring was improved by use of electrostatic field simulation and particle simulation. The improved diode, whose voltage and current are respectively 600 kV and 10 kA, works steadily with guiding magnetic field of 1 T. Vacu
During the experimental study of a long-pulse intense-current foilless diode, surface flashover along its insulator was observed. The analysis of the phenomenon shows that, too short distance between the shield ring and insulator resulted in an intense electric field at the edge of the shield ring, which leaded to the emission of electrons; with effect of intense electromagnetic field, the electrons came into collision with the surface of the insulator, causing secondary electron emission avalanche, and then resulted in vacuum surface flashover. The structure of the shield ring was improved by use of electrostatic field simulation and particle simulation. The improved diode, whose voltage and current are respectively 600 kV and 10 kA, works steadily with guiding magnetic field of 1 T. Vacu
2011,
23.
Abstract:
A three-electrode, field-distortion-triggered rail gap switch was developed. The self-breakdown curve of the rail gap switch was obtained with different gas species for insulation, i.e. N2, SF6(15%)/Ar(85%) and dry air, which shows a linearity and a small standard deviation. The experimental results of triggering breakdown demonstrate that, the switch has with the mixed gas of SF6 and Ar wider working voltage, lower working ratio, shorter breakdown delay and smaller jitter compared with that with pure N2 gas or dry air. By using digital camera to record the integral discharging image, the influence of the insulation gas and deposited energy etc. on discharging channel formation was investigated. The results demonstrate that it is helpful to incre
A three-electrode, field-distortion-triggered rail gap switch was developed. The self-breakdown curve of the rail gap switch was obtained with different gas species for insulation, i.e. N2, SF6(15%)/Ar(85%) and dry air, which shows a linearity and a small standard deviation. The experimental results of triggering breakdown demonstrate that, the switch has with the mixed gas of SF6 and Ar wider working voltage, lower working ratio, shorter breakdown delay and smaller jitter compared with that with pure N2 gas or dry air. By using digital camera to record the integral discharging image, the influence of the insulation gas and deposited energy etc. on discharging channel formation was investigated. The results demonstrate that it is helpful to incre
2011,
23.
Abstract:
A synchronization system for laser triggered transformer-type coaxial spiral pulse modulator was designed. Using the electrical pulse to trigger the primary trigger switch and the laser pulse to trigger the main gas switch of the pulse forming line (PFL), the PFL is successfully triggered by controlling the working time of both the pulses. The delay and jitter of the electrical pulse generator, pulse transformer, pulse voltage at the load, laser flash-lamp and Q-switch signal were measured and analyzed. The charging voltage of the PFL was sampled after being filtered for avoiding the electromagnetic interference and then introduced to the comparison device to generate transistor-transistor logic pulse to trigger the Q-switch of Nd:YAG pulse laser device. When the PFL is charged at -590 kV
A synchronization system for laser triggered transformer-type coaxial spiral pulse modulator was designed. Using the electrical pulse to trigger the primary trigger switch and the laser pulse to trigger the main gas switch of the pulse forming line (PFL), the PFL is successfully triggered by controlling the working time of both the pulses. The delay and jitter of the electrical pulse generator, pulse transformer, pulse voltage at the load, laser flash-lamp and Q-switch signal were measured and analyzed. The charging voltage of the PFL was sampled after being filtered for avoiding the electromagnetic interference and then introduced to the comparison device to generate transistor-transistor logic pulse to trigger the Q-switch of Nd:YAG pulse laser device. When the PFL is charged at -590 kV
