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RSS2013 Vol. 25, No. 12
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2013,
25: 3077-3081.
doi: 3077
Abstract:
Although National Ignition Campaign (NIC) has not achieved the milestone goal of ignition, National Ignition Facility (NIF) has established unprecedented ability of experimental physics on ignition, high energy density physics and basic science by integrating laser performance, target diagnostics and target fabrication. With extraordinary capabilities, NIF researchers have designed delicate experiments to clarify physical understanding and specified several issues which are crucial to the ignition physics. While in Research Center of Laser Fusion, hohlraum energetics and implosion hydrodynamics have been studied extensively on Shenguang-Ⅱ and Shenguang-Ⅲ prototype laser facilities in recent years. Physical experiments employ several high precision diagnostics in resolving different photon range and multiple viewing areas. These detailed and accurate data have improved our understanding of target physics, and help to validate our radiation-hydrodynamic code.
Although National Ignition Campaign (NIC) has not achieved the milestone goal of ignition, National Ignition Facility (NIF) has established unprecedented ability of experimental physics on ignition, high energy density physics and basic science by integrating laser performance, target diagnostics and target fabrication. With extraordinary capabilities, NIF researchers have designed delicate experiments to clarify physical understanding and specified several issues which are crucial to the ignition physics. While in Research Center of Laser Fusion, hohlraum energetics and implosion hydrodynamics have been studied extensively on Shenguang-Ⅱ and Shenguang-Ⅲ prototype laser facilities in recent years. Physical experiments employ several high precision diagnostics in resolving different photon range and multiple viewing areas. These detailed and accurate data have improved our understanding of target physics, and help to validate our radiation-hydrodynamic code.
2013,
25: 3082-3090.
doi: 3082
Abstract:
This paper reviews the progress in the construction of SG-Ⅲ laser facility, integrated Testbed and XG-Ⅲ laser facility and that in the upgrade of the prototype of SG-Ⅲ, and the development in assembling and installing technology, and the achievements in maintaining cleanliness project and metrology in Laser Fusion Research Center, China Academy of Engineering Physics in China in 2012.
This paper reviews the progress in the construction of SG-Ⅲ laser facility, integrated Testbed and XG-Ⅲ laser facility and that in the upgrade of the prototype of SG-Ⅲ, and the development in assembling and installing technology, and the achievements in maintaining cleanliness project and metrology in Laser Fusion Research Center, China Academy of Engineering Physics in China in 2012.
2013,
25: 3091-3097.
doi: 3091
Abstract:
Targets are physical base of the laser inertial confinement fusion (ICF) researches. The quality of the targets has extremely important influences on the reliabilities and degree of precision of the ICF experimental results. The characteristics of the ICF targets, such as complexity and microscale, high precision, determine that the target fabrication process must be a system engineering. This paper presents progresses on the fabrication technologies of ICF targets. The existing problem and the future needs of ICF target fabrication technologies are also discussed.
Targets are physical base of the laser inertial confinement fusion (ICF) researches. The quality of the targets has extremely important influences on the reliabilities and degree of precision of the ICF experimental results. The characteristics of the ICF targets, such as complexity and microscale, high precision, determine that the target fabrication process must be a system engineering. This paper presents progresses on the fabrication technologies of ICF targets. The existing problem and the future needs of ICF target fabrication technologies are also discussed.
2013,
25: 3098-3105.
doi: 3098
Abstract:
The paper summarizes the recent progress of advanced manufacturing technology for the high power laser system in China. The ultra-precision manufacturing technologies, such as ultra-precision grinding, single point diamond fly-cutting and rapid polishing, have been developed for aspheric lens and KDP crystal flats. The preliminary results show the advantages in achieving high accuracy and the ability of yield. Several deterministic finishing technologies have been studied to meet the critical wavefront specifications. A novel removing-mitigating process has been applied to polishing fused silica components to reduce the subsurface defects.
The paper summarizes the recent progress of advanced manufacturing technology for the high power laser system in China. The ultra-precision manufacturing technologies, such as ultra-precision grinding, single point diamond fly-cutting and rapid polishing, have been developed for aspheric lens and KDP crystal flats. The preliminary results show the advantages in achieving high accuracy and the ability of yield. Several deterministic finishing technologies have been studied to meet the critical wavefront specifications. A novel removing-mitigating process has been applied to polishing fused silica components to reduce the subsurface defects.
2013,
25: 3106-3110.
doi: 3106
Abstract:
The high spatial resolution and multi-energy point diagnostic technology explores the core zone for ICF implosion on SG-Ⅲ prototype device. With the reflective properties of double-periodic multi-layer KB, bremsstrahlung radiation characteristics of implosion can be divided into three energy points. Three energy points images are recorded separately by multi-level recording medium, including a three-layer film and CCD. The experimental results show that 2.5 keV, and 3.5 keV clear images can be obtained using the films, and a 8 keV clear image can be obtained using the CCD. The results can be used for core analysis and processing of asymmetry, electron temperature and density distribution, The multi-level recording technology and the experimental technique based on multi-layer KB provide new diagnostic technique for ICF precision physics experiments.
The high spatial resolution and multi-energy point diagnostic technology explores the core zone for ICF implosion on SG-Ⅲ prototype device. With the reflective properties of double-periodic multi-layer KB, bremsstrahlung radiation characteristics of implosion can be divided into three energy points. Three energy points images are recorded separately by multi-level recording medium, including a three-layer film and CCD. The experimental results show that 2.5 keV, and 3.5 keV clear images can be obtained using the films, and a 8 keV clear image can be obtained using the CCD. The results can be used for core analysis and processing of asymmetry, electron temperature and density distribution, The multi-level recording technology and the experimental technique based on multi-layer KB provide new diagnostic technique for ICF precision physics experiments.
2013,
25: 3111-3114.
doi: 3111
Abstract:
On the Silex-1 laser facility, the time response characteristics of XRD detector were studied. A laser with a pulse of 32 fs and a wavelength of 800 nm was used to irradiate a plane Au target. X-ray calibrated method of time of exposure X-ray framing camera and time resolution of X-ray streak camera was explored. The time response characteristics of XRD detector and time process of X-ray emission were obtained from experiment. We obtained X-ray calibration method of time of exposure X-ray framing camera and time resolution of X-ray streak camera.
On the Silex-1 laser facility, the time response characteristics of XRD detector were studied. A laser with a pulse of 32 fs and a wavelength of 800 nm was used to irradiate a plane Au target. X-ray calibrated method of time of exposure X-ray framing camera and time resolution of X-ray streak camera was explored. The time response characteristics of XRD detector and time process of X-ray emission were obtained from experiment. We obtained X-ray calibration method of time of exposure X-ray framing camera and time resolution of X-ray streak camera.
2013,
25: 3115-3118.
doi: 3115
Abstract:
Hohlraums/halfraums are used as an intensive X-ray radiation sources in indirect drive inertial confinement fusion and high energy density physics experiments to study material properties and physical problems like radiation transport. The equivalent radiation temperatures of the hohlraums are different from those with experimental targets attached on the wall. Experiments are carried out to study influence of different types of foam-filled cylinders attached to the halfraum bottom and 3-8 eV increase of the halfraum radiation source temperature is found. The statistics show that the radiation temperatures are higher with longer and denser-foam-filled cylinders.
Hohlraums/halfraums are used as an intensive X-ray radiation sources in indirect drive inertial confinement fusion and high energy density physics experiments to study material properties and physical problems like radiation transport. The equivalent radiation temperatures of the hohlraums are different from those with experimental targets attached on the wall. Experiments are carried out to study influence of different types of foam-filled cylinders attached to the halfraum bottom and 3-8 eV increase of the halfraum radiation source temperature is found. The statistics show that the radiation temperatures are higher with longer and denser-foam-filled cylinders.
2013,
25: 3119-3122.
doi: 3119
Abstract:
A study of the high resolution monochromatic X-ray imaging techniques based on the spherically curved crystals is reported. The relationships between the key performance parameters and the design parameters of the system were analyzed. A spherically curved quartz crystal with H-like Mg resonance line and a spherically curved mica crystal with the continuous spectrums of Mo at 3.14 keV were used on SGII laser facility. The backlighted images of the capsules were obtained and the spatial resolution of the X-ray optical system was better than 5 m over a larger area. This technique can make numerous critical contributions to the current state of knowledge in inertial confinement fusion research, such as the trajectory of an imploding shell and the hydrodynamic stability.
A study of the high resolution monochromatic X-ray imaging techniques based on the spherically curved crystals is reported. The relationships between the key performance parameters and the design parameters of the system were analyzed. A spherically curved quartz crystal with H-like Mg resonance line and a spherically curved mica crystal with the continuous spectrums of Mo at 3.14 keV were used on SGII laser facility. The backlighted images of the capsules were obtained and the spatial resolution of the X-ray optical system was better than 5 m over a larger area. This technique can make numerous critical contributions to the current state of knowledge in inertial confinement fusion research, such as the trajectory of an imploding shell and the hydrodynamic stability.
2013,
25: 3123-3126.
doi: 3123
Abstract:
The magnetic lens used in high energy proton radiography system can alleviate the degradation of resolution which is induced by multi scattering of protons. A magnetic lens used for 3.6 MeV protons produced from DD fusion reactions in the implosion region is designed based on the scaling law of beamline design. A similar object-image relationship as in geometrical optical is deduced. 3D particle tracing simulation is also carried out to demonstrate the object-image relationship of the magnetic lens.
The magnetic lens used in high energy proton radiography system can alleviate the degradation of resolution which is induced by multi scattering of protons. A magnetic lens used for 3.6 MeV protons produced from DD fusion reactions in the implosion region is designed based on the scaling law of beamline design. A similar object-image relationship as in geometrical optical is deduced. 3D particle tracing simulation is also carried out to demonstrate the object-image relationship of the magnetic lens.
2013,
25: 3127-3130.
doi: 3127
Abstract:
The state of hot-core in stagnation phase is very important and valuable in inertial confinement fusion. High energy X-ray (70 keV) backlight imaging is the most important method to acquire stagnation phase image. The high energy X-ray is produced by high power petawatt laser facility interaction with high Z metal target. This article was based on Shenguang-Ⅲ laser facility with 483 kJ. Our work analyzed X-ray source flux and implosion noise and proposed a whole design in high-energy X-ray backlight image system. The result indicates that high energy X-ray backlight image is able to obtain stagnation phase image in Shenguang-Ⅲ laser facility.
The state of hot-core in stagnation phase is very important and valuable in inertial confinement fusion. High energy X-ray (70 keV) backlight imaging is the most important method to acquire stagnation phase image. The high energy X-ray is produced by high power petawatt laser facility interaction with high Z metal target. This article was based on Shenguang-Ⅲ laser facility with 483 kJ. Our work analyzed X-ray source flux and implosion noise and proposed a whole design in high-energy X-ray backlight image system. The result indicates that high energy X-ray backlight image is able to obtain stagnation phase image in Shenguang-Ⅲ laser facility.
2013,
25: 3131-3134.
doi: 3131
Abstract:
In the field of laser fusion, the ablation rate of target material is mainly measured by the diagnostic of thermal wave burn-through images. The planarity of such images could make great influences on the uncertainty of ablation rate. The improvement of the image planarity has been made based on the theoretical and experimental study of the influence of diagnostical spatial resolution. After optimizing the spatial resolution to 29 m on the 420 eV channel of the diagnostic, we proved with SG-II experiment that the planarity area of thermal wave burn-through image has been increased largely and the fluctuation of thermal wave front is only 4.7 ps which is much less than the temporal measurement uncertainty (about 20 ps) of X-ray streak camera.
In the field of laser fusion, the ablation rate of target material is mainly measured by the diagnostic of thermal wave burn-through images. The planarity of such images could make great influences on the uncertainty of ablation rate. The improvement of the image planarity has been made based on the theoretical and experimental study of the influence of diagnostical spatial resolution. After optimizing the spatial resolution to 29 m on the 420 eV channel of the diagnostic, we proved with SG-II experiment that the planarity area of thermal wave burn-through image has been increased largely and the fluctuation of thermal wave front is only 4.7 ps which is much less than the temporal measurement uncertainty (about 20 ps) of X-ray streak camera.
2013,
25: 3135-3138.
doi: 3135
Abstract:
Fast ignition of laser inertial confinement fusion separates the compression and ignition, thus relaxes the requirements on compression symmetry and energy. In the experiments of pre-compression of cone-in-shell target for fast ignition on Shenguang Ⅱ laser facility, the framed X-ray backlight images show that the existence of cone and guiding wire does not affect the implosion process, which has been demonstrated by the agreement of experimental results and one-dimensional radiation hydrodynamic simulation results. Adjusting the position of cone and fuel capsule, the cone can be kept robust until the stagnation, which is crucial for the transport and deposit of hot electrons.
Fast ignition of laser inertial confinement fusion separates the compression and ignition, thus relaxes the requirements on compression symmetry and energy. In the experiments of pre-compression of cone-in-shell target for fast ignition on Shenguang Ⅱ laser facility, the framed X-ray backlight images show that the existence of cone and guiding wire does not affect the implosion process, which has been demonstrated by the agreement of experimental results and one-dimensional radiation hydrodynamic simulation results. Adjusting the position of cone and fuel capsule, the cone can be kept robust until the stagnation, which is crucial for the transport and deposit of hot electrons.
2013,
25: 3139-3144.
doi: 3139
Abstract:
Soft X-ray energy spectrometer (SXS) is an important instrument for radiation temperature measurement. According to Shenguang Ⅱ-up experimental requirements, the 15-channel soft X-ray energy spectrometer has been developed and its performances have been studied. The spectrometers structure has been improved. Circularity convex has been used to image the target for precise collimation, and angle-changeless setup has been adopted to avoid mirrors angle error. Filters, mirrors and X-ray diodes (XRDs) have been calibrated on synchrotron radiation facility. Then the results show that SXS spectrum range is 0.05-4.97 keV. And the temporal performances have been studied on the short-pulse laser facility. The temporal resolution achieves to 99.22 ps.
Soft X-ray energy spectrometer (SXS) is an important instrument for radiation temperature measurement. According to Shenguang Ⅱ-up experimental requirements, the 15-channel soft X-ray energy spectrometer has been developed and its performances have been studied. The spectrometers structure has been improved. Circularity convex has been used to image the target for precise collimation, and angle-changeless setup has been adopted to avoid mirrors angle error. Filters, mirrors and X-ray diodes (XRDs) have been calibrated on synchrotron radiation facility. Then the results show that SXS spectrum range is 0.05-4.97 keV. And the temporal performances have been studied on the short-pulse laser facility. The temporal resolution achieves to 99.22 ps.
2013,
25: 3145-3147.
doi: 3145
Abstract:
This paper reports the laser transfer in plasma produced by CH on Shengguang Ⅱ. The laser transmission rate was decided by the plasma density. When the laser incidence was 0.5 m CH on Shengguang Ⅱ, the plasma density would be under critical value after 200 ps, the laser would pass the plasma. When the plasma density was 1% critical density after 700 ps, the laser could pass the plasma completely.
This paper reports the laser transfer in plasma produced by CH on Shengguang Ⅱ. The laser transmission rate was decided by the plasma density. When the laser incidence was 0.5 m CH on Shengguang Ⅱ, the plasma density would be under critical value after 200 ps, the laser would pass the plasma. When the plasma density was 1% critical density after 700 ps, the laser could pass the plasma completely.
2013,
25: 3148-3152.
doi: 3148
Abstract:
The ultraviolet (UV) photodecomposition of solid HNS (2, 2, 4, 4, 6, 6-hexanitrostillbene) under irradiation of UV light has been studied by different experimental means, including UV-Vis spectra, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectra (EPR) and mass spectra (MS). Two new peaks locating around 310 nm and 350 nm appear in the UV-Vis spectra of HNS/acetonitrile solution after UV light irradiation. Similarly, after laser irradiation, two new peaks appear at the binding energy of 401 eV and 528 eV for N 1s and O 1s XPS narrow scan spectra, respectively. Furthermore, the mass spectrum shows two new characteristic ion peaks corresponding to mass-charge ratio of 403 and 329. Experimental results indicate that CNO2 broken and nitro-nitrite isomerization with subsequent release of NO are the main photolysis pathways during the photodecomposition of HNS.
The ultraviolet (UV) photodecomposition of solid HNS (2, 2, 4, 4, 6, 6-hexanitrostillbene) under irradiation of UV light has been studied by different experimental means, including UV-Vis spectra, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectra (EPR) and mass spectra (MS). Two new peaks locating around 310 nm and 350 nm appear in the UV-Vis spectra of HNS/acetonitrile solution after UV light irradiation. Similarly, after laser irradiation, two new peaks appear at the binding energy of 401 eV and 528 eV for N 1s and O 1s XPS narrow scan spectra, respectively. Furthermore, the mass spectrum shows two new characteristic ion peaks corresponding to mass-charge ratio of 403 and 329. Experimental results indicate that CNO2 broken and nitro-nitrite isomerization with subsequent release of NO are the main photolysis pathways during the photodecomposition of HNS.
2013,
25: 3153-3157.
doi: 3153
Abstract:
Ion temperature of implosion hotspot is a very important parameter for inertial confinement fusion. It reflects the energy level of the hotspot, and it is very sensitive to implosion symmetry and implosion speed. ICF implosion hotspot ion temperature diagnostic techniques based on neutron time-of-flight method were described. A neutron TOF spectrometer was developed using a ultrafast plastic scintillator as the neutron detector. Time response of the spectrometer has 1.1 ns FWHM and 0.5 ns rising time. TOF spectrum resolving method based on deconvolution and low pass filter was illuminated. Implosion hotspot ion temperature in low neutron yield and low ion temperature condition at Shenguang-Ⅲ facility was acquired using the diagnostic techniques.
Ion temperature of implosion hotspot is a very important parameter for inertial confinement fusion. It reflects the energy level of the hotspot, and it is very sensitive to implosion symmetry and implosion speed. ICF implosion hotspot ion temperature diagnostic techniques based on neutron time-of-flight method were described. A neutron TOF spectrometer was developed using a ultrafast plastic scintillator as the neutron detector. Time response of the spectrometer has 1.1 ns FWHM and 0.5 ns rising time. TOF spectrum resolving method based on deconvolution and low pass filter was illuminated. Implosion hotspot ion temperature in low neutron yield and low ion temperature condition at Shenguang-Ⅲ facility was acquired using the diagnostic techniques.
2013,
25: 3158-3162.
doi: 3158
Abstract:
The active precision diagnosis technique for shock wave with two-sensitivity is a critical technology in inertial confined fusion (ICF). The main purpose is to diagnose the shock-timing trace generated by the shaped laser pulse. The imaging velocity interferometer system for any reflector (VISAR) is introduced in this paper. Some important techniques are provided, including the probe laser with single mode and shaped capability, imaging technique with high resolution and calibration character. The new target design can be widely used after analyzing the interaction of laser and target. The new flood algorithm with high confidence is programmed. The space resolution of the imaging VISAR is 5 m , and the time resolution is 10-30 ps. The uncertainty is less than 2%, which has reached the international level. The multi-shocks in transparent material can be continuously measured with this interferometer system.
The active precision diagnosis technique for shock wave with two-sensitivity is a critical technology in inertial confined fusion (ICF). The main purpose is to diagnose the shock-timing trace generated by the shaped laser pulse. The imaging velocity interferometer system for any reflector (VISAR) is introduced in this paper. Some important techniques are provided, including the probe laser with single mode and shaped capability, imaging technique with high resolution and calibration character. The new target design can be widely used after analyzing the interaction of laser and target. The new flood algorithm with high confidence is programmed. The space resolution of the imaging VISAR is 5 m , and the time resolution is 10-30 ps. The uncertainty is less than 2%, which has reached the international level. The multi-shocks in transparent material can be continuously measured with this interferometer system.
2013,
25: 3163-3167.
doi: 3163
Abstract:
This paper introduces energy response and detection efficiency calibration of single-photon counting CCD by X-ray source. In the calibration experiment, several standard X-ray sources are adopted to radiate forward the CCD detector and the counts occur. Energy response curve of CCD is close to linear, but the curve slope of different CCD is evidently different. The MATLAB program for studying the detection efficiency and the split pixel event is set up. The detection efficiency of CCD changes with photon energy in the range of 3.1-24.9 keV, and the detection efficiency obtained from the calibration experiment is in agreement with absorption efficiency that is offered by XOP software.
This paper introduces energy response and detection efficiency calibration of single-photon counting CCD by X-ray source. In the calibration experiment, several standard X-ray sources are adopted to radiate forward the CCD detector and the counts occur. Energy response curve of CCD is close to linear, but the curve slope of different CCD is evidently different. The MATLAB program for studying the detection efficiency and the split pixel event is set up. The detection efficiency of CCD changes with photon energy in the range of 3.1-24.9 keV, and the detection efficiency obtained from the calibration experiment is in agreement with absorption efficiency that is offered by XOP software.
2013,
25: 3168-3172.
doi: 3168
Abstract:
We studied material strength at high pressure ( more than 10 GPa) and high strain rates (106-108 s-1) in Al using the Shenguang Ⅲ prototype laser facility. The Al sample was maintained well below the melting temperature using a quasi-isentropic ramped drive based on a reservoir-gap-sample configuration. To measure the RT ripple growth, we used face-on radiography with a 4.7 keV laser driven Ti X-ray backlighter. This paper would show detailed designs and achieve the RT growth factors at different times. In the experiment, continuous phase plates (CPP) were used to improve the focus beam quality. The results show that CPP can effectively improve the uniformity of driven beam and the backlighter beam. Finally the experimental results reveal that the method to infer material strength by measuring RT instability growth is feasible at Shenguang Ⅲ prototype laser facility.
We studied material strength at high pressure ( more than 10 GPa) and high strain rates (106-108 s-1) in Al using the Shenguang Ⅲ prototype laser facility. The Al sample was maintained well below the melting temperature using a quasi-isentropic ramped drive based on a reservoir-gap-sample configuration. To measure the RT ripple growth, we used face-on radiography with a 4.7 keV laser driven Ti X-ray backlighter. This paper would show detailed designs and achieve the RT growth factors at different times. In the experiment, continuous phase plates (CPP) were used to improve the focus beam quality. The results show that CPP can effectively improve the uniformity of driven beam and the backlighter beam. Finally the experimental results reveal that the method to infer material strength by measuring RT instability growth is feasible at Shenguang Ⅲ prototype laser facility.
2013,
25: 3173-3179.
doi: 3173
Abstract:
With the self-similar solution of X-ray confinement in cavity, the time-dependent redistribution of thermal X rays inside the hohlraum is calculated. Distribution of radiation power intensity on the capsules surface is calculated via the view-factor method. After that, the time-dependent radiation drive symmetry of the capsule could be studied. The effects of motion of laser spots, laser pulses and pointing error of capsule on the radiation uniformity are analyzed. Multi parameter couples are scanned to reach the minimum of time-integrated value of the second coefficient of Legendre polynomials. The best lengths of hohlraum agree with the results of implosion symmetry tuning experiments on SG-Ⅱ and SG-Ⅲ prototype laser facilities. The best length-to-diameter ratio of hohlraum is close to the point design targets on the National Ignition Facility (NIF). The validated model may give some reference to the future experiments design and analysis of implosion symmetry.
With the self-similar solution of X-ray confinement in cavity, the time-dependent redistribution of thermal X rays inside the hohlraum is calculated. Distribution of radiation power intensity on the capsules surface is calculated via the view-factor method. After that, the time-dependent radiation drive symmetry of the capsule could be studied. The effects of motion of laser spots, laser pulses and pointing error of capsule on the radiation uniformity are analyzed. Multi parameter couples are scanned to reach the minimum of time-integrated value of the second coefficient of Legendre polynomials. The best lengths of hohlraum agree with the results of implosion symmetry tuning experiments on SG-Ⅱ and SG-Ⅲ prototype laser facilities. The best length-to-diameter ratio of hohlraum is close to the point design targets on the National Ignition Facility (NIF). The validated model may give some reference to the future experiments design and analysis of implosion symmetry.
2013,
25: 3180-3184.
doi: 3180
Abstract:
A novel laser conditioning method based on mid-size laser spot is introduced. A Nd:YAG laser with 10 J max energy output at 1064 nm is adopted to form a 5 mm, fluence-qualified beam spot. Compared with the small-size spot type, this method has significant advantage in time saving. Experimental setup is built for verification. First, laser scanning and damage testing are carried out on small samples. The results demonstrate an obvious effect of laser conditioning, and the best flowchart for large-aperture optics is also verified. Furthermore, the conditioning experiment to large-aperture optics with reflective film prepared by hafnia evaporating is done. A 2D-motorized motion stage is applied for the handling and scanning of 430 mm430 mm size optics. Experimental results indicate that a damage threshold of 27 J/cm2 can be achieved after the conditioning procedure. The effect of this technique is well demonstrated.
A novel laser conditioning method based on mid-size laser spot is introduced. A Nd:YAG laser with 10 J max energy output at 1064 nm is adopted to form a 5 mm, fluence-qualified beam spot. Compared with the small-size spot type, this method has significant advantage in time saving. Experimental setup is built for verification. First, laser scanning and damage testing are carried out on small samples. The results demonstrate an obvious effect of laser conditioning, and the best flowchart for large-aperture optics is also verified. Furthermore, the conditioning experiment to large-aperture optics with reflective film prepared by hafnia evaporating is done. A 2D-motorized motion stage is applied for the handling and scanning of 430 mm430 mm size optics. Experimental results indicate that a damage threshold of 27 J/cm2 can be achieved after the conditioning procedure. The effect of this technique is well demonstrated.
2013,
25: 3185-3188.
doi: 3185
Abstract:
This essay analyzes the docking of line-replaceable unit (LRU) for some huge laser facilities, where centering and collision issues are pointed out as the key technologies for LRU docking monitoring. The centering technology mainly transforms the three-dimensional problem into two-dimensional one, adopting the characteristic of machine version capturing to analyze the position and posture of LRU. The collision monitoring technology mainly takes advantage of the principle that power is generated in the collision during the process of assembly and calibration. Monitoring force in all directions on the point of collision occurred, which indirectly reflects the degree of the collision, returning feedback to the docking platform after measurement data is analyzed, and amending the docking trajectory of the LRU in time can achieve the light collision docking during the full process of LRU.
This essay analyzes the docking of line-replaceable unit (LRU) for some huge laser facilities, where centering and collision issues are pointed out as the key technologies for LRU docking monitoring. The centering technology mainly transforms the three-dimensional problem into two-dimensional one, adopting the characteristic of machine version capturing to analyze the position and posture of LRU. The collision monitoring technology mainly takes advantage of the principle that power is generated in the collision during the process of assembly and calibration. Monitoring force in all directions on the point of collision occurred, which indirectly reflects the degree of the collision, returning feedback to the docking platform after measurement data is analyzed, and amending the docking trajectory of the LRU in time can achieve the light collision docking during the full process of LRU.
2013,
25: 3189-3192.
doi: 3189
Abstract:
To meet the requirements of the inertial confinement fusion (ICF) experiments on laser driver efficient third harmonic capacity, wu optimized the program for offline measurement of the crystal phase matching angle. The optimization measures include improving the ability for the collimation of crystal, and reducing the instability of measurement due to the output change of small diameter laser. Through theoretical analysis and systematic analysis of the actual measurements, high accuracies of offline measurement of crystal are obtained. Namely, the expanded measurement uncertainty of the second harmonic phase-matching angle is 15.94 rad, and the uncertainty of the tripler phase-matching angle is 27.8 rad.
To meet the requirements of the inertial confinement fusion (ICF) experiments on laser driver efficient third harmonic capacity, wu optimized the program for offline measurement of the crystal phase matching angle. The optimization measures include improving the ability for the collimation of crystal, and reducing the instability of measurement due to the output change of small diameter laser. Through theoretical analysis and systematic analysis of the actual measurements, high accuracies of offline measurement of crystal are obtained. Namely, the expanded measurement uncertainty of the second harmonic phase-matching angle is 15.94 rad, and the uncertainty of the tripler phase-matching angle is 27.8 rad.
2013,
25: 3193-3196.
doi: 3193
Abstract:
To decrease the addition wavefront of large aperture mirror caused by gravity influence on beam quality in inertial confinement fusion facility, the back support technology is researched in this paper. By support structure optimization, the addition wave front caused by gravity of large aperture decreases from 0.5 micron to 0.26 micron. In this paper, the drill and the join technology of the mirror and support structure and the mirror support structure is researched and the prototype is developed to validate the technology. The test indicates that the wavefront of the mirror caused by the drill and join technology can be ignored and the mirror support structure can satisfy the mirror requirement. The addition wavefront caused by gravity can be well controlled by mirror back support technology.
To decrease the addition wavefront of large aperture mirror caused by gravity influence on beam quality in inertial confinement fusion facility, the back support technology is researched in this paper. By support structure optimization, the addition wave front caused by gravity of large aperture decreases from 0.5 micron to 0.26 micron. In this paper, the drill and the join technology of the mirror and support structure and the mirror support structure is researched and the prototype is developed to validate the technology. The test indicates that the wavefront of the mirror caused by the drill and join technology can be ignored and the mirror support structure can satisfy the mirror requirement. The addition wavefront caused by gravity can be well controlled by mirror back support technology.
2013,
25: 3197-3200.
doi: 3197
Abstract:
Laser depolarization induced by the propagation-rotation structure would greatly affect the isolation ratio of the Shenguang-Ⅲ laser facility. We build a simulation model on the reflectance coefficient of the propagation-rotation structure based on the film system theory, and point out that the depolarization origins from the reflective film thickness error. Through comparison between the simulation result and the off-line experimental result, we obtain the reflectance coefficient of each reflective film inside the propagation-rotation structure. Furthermore, we obtain the total reflectance coefficient of the propagation-rotation structure and then the system isolation ratio limit.
Laser depolarization induced by the propagation-rotation structure would greatly affect the isolation ratio of the Shenguang-Ⅲ laser facility. We build a simulation model on the reflectance coefficient of the propagation-rotation structure based on the film system theory, and point out that the depolarization origins from the reflective film thickness error. Through comparison between the simulation result and the off-line experimental result, we obtain the reflectance coefficient of each reflective film inside the propagation-rotation structure. Furthermore, we obtain the total reflectance coefficient of the propagation-rotation structure and then the system isolation ratio limit.
2013,
25: 3201-3204.
doi: 3201
Abstract:
An experimental setup referring to the optical element configuration of National Ignition Facility was built. The energy loss from mitigation cone by CO2 laser was tested. The results showed that the loss ratio had a linear correlation with the density of mitigation cone while the density was low. The energy would lose faster with the increase of density if the mitigation cone was larger. Density of mitigation cone must be small than 2 cm-2 to ensure the loss ratio less than 3%.
An experimental setup referring to the optical element configuration of National Ignition Facility was built. The energy loss from mitigation cone by CO2 laser was tested. The results showed that the loss ratio had a linear correlation with the density of mitigation cone while the density was low. The energy would lose faster with the increase of density if the mitigation cone was larger. Density of mitigation cone must be small than 2 cm-2 to ensure the loss ratio less than 3%.
2013,
25: 3205-3209.
Abstract:
In order to obtain the size of a focus spot of continuous phase plate (CPP), an edge-abstracting method is proposed. It is possible to acquire a false edge profile if traditional edge-abstracting methods are used because CPP focus spot image has a great grayscale grads. After the operations of grads processing, threshold segmentation, spatial scanning and ellipse fitting, the focus spot edge can be obtained. The edge-abstracting results are compared separately with Laplace, Sobel, Krisch, Prewitt, Log arithmetic operators for grads processing, which shows that the results are more robust and reliable if Sobel or Prewitt arithmetic operators are used. And the abstracted results are compared with different threshold values for threshold segmentation, which shows the results are more reliable if the threshold value is 110 to 170 times of the grads mean value of the background grayscale levels.
In order to obtain the size of a focus spot of continuous phase plate (CPP), an edge-abstracting method is proposed. It is possible to acquire a false edge profile if traditional edge-abstracting methods are used because CPP focus spot image has a great grayscale grads. After the operations of grads processing, threshold segmentation, spatial scanning and ellipse fitting, the focus spot edge can be obtained. The edge-abstracting results are compared separately with Laplace, Sobel, Krisch, Prewitt, Log arithmetic operators for grads processing, which shows that the results are more robust and reliable if Sobel or Prewitt arithmetic operators are used. And the abstracted results are compared with different threshold values for threshold segmentation, which shows the results are more reliable if the threshold value is 110 to 170 times of the grads mean value of the background grayscale levels.
2013,
25: 3210-3214.
doi: 3210
Abstract:
An accuracy transfer method of the standard flats absolute surface error is proposed. When we acquire the absolute surface error of a standard flat, we can use this method to transfer its accuracy to another standard flat. According to the experimental results, we conclude that Zernike polynomials power term can fit the changing amount very well. In order to deal with the surface difference at different temperatures, we propose a method using the lines absolute surface data extracted by classical three-flat test to estimate the power amount. A well manufacturing optical part is tested by two interferometers. The use of this method can lessen the difference between the results of two-dimensional distribution.
An accuracy transfer method of the standard flats absolute surface error is proposed. When we acquire the absolute surface error of a standard flat, we can use this method to transfer its accuracy to another standard flat. According to the experimental results, we conclude that Zernike polynomials power term can fit the changing amount very well. In order to deal with the surface difference at different temperatures, we propose a method using the lines absolute surface data extracted by classical three-flat test to estimate the power amount. A well manufacturing optical part is tested by two interferometers. The use of this method can lessen the difference between the results of two-dimensional distribution.
2013,
25: 3215-3219.
doi: 3215
Abstract:
An online cleanliness control method based on the online monitoring system was developed for controlling the particle pollution and damage of upward-facing transport mirrors in the integration test bed. By building up gas knife system, the online cleanliness processing was effectively achieved for the particle pollution on the mirror surface. By using the gas screen, the cleanliness of the mirror surface was effectively online maintained. The image processing system was applied to assessing the effect of online cleanliness processing. The experimental results indicate that the particle pollution was reduced by the gas knife and the gas screen was useful to avoid the settlement of particle pollution.
An online cleanliness control method based on the online monitoring system was developed for controlling the particle pollution and damage of upward-facing transport mirrors in the integration test bed. By building up gas knife system, the online cleanliness processing was effectively achieved for the particle pollution on the mirror surface. By using the gas screen, the cleanliness of the mirror surface was effectively online maintained. The image processing system was applied to assessing the effect of online cleanliness processing. The experimental results indicate that the particle pollution was reduced by the gas knife and the gas screen was useful to avoid the settlement of particle pollution.
2013,
25: 3220-3224.
doi: 3220
Abstract:
The laser damage precursors in fused silica were systematically isolated and identified. The paper shows laser damage micrographs from different precursors which are formed during fabrication. Conventionally polished and subsequently scratched fused silica plates were treated by submerging in various HF-based etchants (HF, or NH4F and HF at various ratios and concentrations) under different process conditions. With the optimized etch process, laser damage resistance increased dramatically; the average threshold fluence for damage initiation for fused silica increased from 4.8 to 11.0 J/cm2.
The laser damage precursors in fused silica were systematically isolated and identified. The paper shows laser damage micrographs from different precursors which are formed during fabrication. Conventionally polished and subsequently scratched fused silica plates were treated by submerging in various HF-based etchants (HF, or NH4F and HF at various ratios and concentrations) under different process conditions. With the optimized etch process, laser damage resistance increased dramatically; the average threshold fluence for damage initiation for fused silica increased from 4.8 to 11.0 J/cm2.
2013,
25: 3225-3229.
doi: 3225
Abstract:
This paper aims at the accuracy control method in the machining of capsule micro holes with single point diamond turning technology. Firstly, a error model of capsule micro holes machining is established and the effect of each error component on micro holes dimension accuracy is theoretically analyzed. Secondly, according to the error analysis results, an accuracy control method is introduced, in which diamond tool step feeding method is adopted for micro holes accuracy control. Finally, GDP capsule micro holes machining experiments are carried out on ultra-precision machine. According to the results, the dimension error and roundness error of micro hole reduce 70.7% and 87.5% separately, which verifies the validity of the accuracy control method in this paper.
This paper aims at the accuracy control method in the machining of capsule micro holes with single point diamond turning technology. Firstly, a error model of capsule micro holes machining is established and the effect of each error component on micro holes dimension accuracy is theoretically analyzed. Secondly, according to the error analysis results, an accuracy control method is introduced, in which diamond tool step feeding method is adopted for micro holes accuracy control. Finally, GDP capsule micro holes machining experiments are carried out on ultra-precision machine. According to the results, the dimension error and roundness error of micro hole reduce 70.7% and 87.5% separately, which verifies the validity of the accuracy control method in this paper.
2013,
25: 3230-3234.
doi: 3230
Abstract:
Backlit shadowgraphy is an effective method for characterizing fuel ice in ICF cryotargets. Based on backlit shadowgraphy, the ice layer in situ characterization system can monitor the phase transformation and ice layering process of fuel in real-time as well as provide thickness and roughness of fuel ice before target shooting for physical experiments. In the experiments of cryotarget preparation, the thickness and inner roughness of fuel ice layer were calculated by the ray tracing simulation of backlit shadowgraphy and the position of bright ring in shadowgraph.
Backlit shadowgraphy is an effective method for characterizing fuel ice in ICF cryotargets. Based on backlit shadowgraphy, the ice layer in situ characterization system can monitor the phase transformation and ice layering process of fuel in real-time as well as provide thickness and roughness of fuel ice before target shooting for physical experiments. In the experiments of cryotarget preparation, the thickness and inner roughness of fuel ice layer were calculated by the ray tracing simulation of backlit shadowgraphy and the position of bright ring in shadowgraph.
2013,
25: 3235-3238.
doi: 3235
Abstract:
Carbon aerogels dried at ambient pressure are synthesized by using resorcinol-formaldehyde as carbon precursor and adding P123 to strengthen their skeletons. CO2 activation is used to improve surface areas and adjust pore size distribution. Carbon aerogels are characterized by BET surface measurement, constant-current charge/discharge and cyclic voltammetry (CV). It is found that a specific capacitance of 261 F/g is obtained in 6 mol/L KOH electrolytes. With a decreasing production cost, carbon aerogels dried at ambient pressure have an ideal electrochemical performance and potential application as electrode materials.
Carbon aerogels dried at ambient pressure are synthesized by using resorcinol-formaldehyde as carbon precursor and adding P123 to strengthen their skeletons. CO2 activation is used to improve surface areas and adjust pore size distribution. Carbon aerogels are characterized by BET surface measurement, constant-current charge/discharge and cyclic voltammetry (CV). It is found that a specific capacitance of 261 F/g is obtained in 6 mol/L KOH electrolytes. With a decreasing production cost, carbon aerogels dried at ambient pressure have an ideal electrochemical performance and potential application as electrode materials.
2013,
25: 3239-3242.
doi: 3239
Abstract:
Ge-doped polystyrenes with various molecular weights and low polydispersities were successfully synthesized by stable free radical polymerization of Ge-doped styrene at 120 ℃ in bulk using 2, 2, 6, 6-tetramethyl-1-piperidinyl-oxyl (TEMPO) and AIBN as mediator and initiator respectively. Ge-doped polystyrene foams were obtained by thermally-induced phase separation technique and freezing-dry technology. 1H nuclear magnetic resonance(1H-NMR), Fourier transform infrared spectra (FTIR) and scanning electron microscope(SEM) were applied to characterize the structure of polymers and foams. The results showed that Germanium content in polymer was 2.6 atom% and foams presented porous interconnected structures with macropores of about 1-10 m.
Ge-doped polystyrenes with various molecular weights and low polydispersities were successfully synthesized by stable free radical polymerization of Ge-doped styrene at 120 ℃ in bulk using 2, 2, 6, 6-tetramethyl-1-piperidinyl-oxyl (TEMPO) and AIBN as mediator and initiator respectively. Ge-doped polystyrene foams were obtained by thermally-induced phase separation technique and freezing-dry technology. 1H nuclear magnetic resonance(1H-NMR), Fourier transform infrared spectra (FTIR) and scanning electron microscope(SEM) were applied to characterize the structure of polymers and foams. The results showed that Germanium content in polymer was 2.6 atom% and foams presented porous interconnected structures with macropores of about 1-10 m.
2013,
25: 3243-3246.
doi: 3243
Abstract:
On the homemade planar-cryotarget shooting system, we have studied the effect of different filling rate on preparing planar cryotargets. The results show that with slower filling rate, the variation of hydrogen pressure in target is small. Furthermore, the liquefaction procedure is more observable and the corresponding duration of time is longer. Slower filling rate is helpful for the accurate measurement of saturated vapor pressure of liquid hydrogen at that temperature. A calibration method based on the saturated vapor pressure is developed to in-situ determine the temperature of liquid hydrogen isotopes in the target cell, and an optimum filling rate of 0.8 mL/min is obtained. These studies are important to provide high-quality and reliable hydrogen-isotopic planar cryotargets for ICF physical experiments.
On the homemade planar-cryotarget shooting system, we have studied the effect of different filling rate on preparing planar cryotargets. The results show that with slower filling rate, the variation of hydrogen pressure in target is small. Furthermore, the liquefaction procedure is more observable and the corresponding duration of time is longer. Slower filling rate is helpful for the accurate measurement of saturated vapor pressure of liquid hydrogen at that temperature. A calibration method based on the saturated vapor pressure is developed to in-situ determine the temperature of liquid hydrogen isotopes in the target cell, and an optimum filling rate of 0.8 mL/min is obtained. These studies are important to provide high-quality and reliable hydrogen-isotopic planar cryotargets for ICF physical experiments.
2013,
25: 3247-3250.
doi: 3247
Abstract:
Metal nanowires array is one of the important materials for the research of X-ray intense radiation source. To meet the demand of physical experiment, well-ordered, globally oriented polyethylene composite fiber embedding micro or nanowires array of polystyrene was prepared by bundling and melt drawing technology, porous polyethylene template was obtained after section cutting and dissolving processes. Optical microscope and SEM results show regular porous array structure in the template. And the pore size can be adjusted in the range from two hundred nanometers to tens of microns, the spacing of pores can be adjusted in the range from one to tens of microns. According to the designed size and the measured value, the size of the template can be designed and controlled by this method, which indicates that the size control of the nanowires array could be realized.
Metal nanowires array is one of the important materials for the research of X-ray intense radiation source. To meet the demand of physical experiment, well-ordered, globally oriented polyethylene composite fiber embedding micro or nanowires array of polystyrene was prepared by bundling and melt drawing technology, porous polyethylene template was obtained after section cutting and dissolving processes. Optical microscope and SEM results show regular porous array structure in the template. And the pore size can be adjusted in the range from two hundred nanometers to tens of microns, the spacing of pores can be adjusted in the range from one to tens of microns. According to the designed size and the measured value, the size of the template can be designed and controlled by this method, which indicates that the size control of the nanowires array could be realized.
2013,
25: 3251-3254.
doi: 3251
Abstract:
Silicon flexure microstructure has very important function for supporting and cooling roles in ICF target. In this paper, a silicon arm is fabricated using deep reactive ion etching(DRIE) method. The results of scanning electron microscopy(SEM), white light interferometer and optical microscopy measurement show that the Si microstructure has a smooth surface and vertical sidewalls, the angle of vertical sidewall is nearly 88 degrees. The displacement of silicon flexure microstructure along radial direction is more than 20 m.
Silicon flexure microstructure has very important function for supporting and cooling roles in ICF target. In this paper, a silicon arm is fabricated using deep reactive ion etching(DRIE) method. The results of scanning electron microscopy(SEM), white light interferometer and optical microscopy measurement show that the Si microstructure has a smooth surface and vertical sidewalls, the angle of vertical sidewall is nearly 88 degrees. The displacement of silicon flexure microstructure along radial direction is more than 20 m.
2013,
25: 3255-3258.
doi: 3255
Abstract:
By comparing the chemical component and machined performance of two kinds of 1100 Al rod, the higher purity one is chosen for Al mandrel. Al mandrel is prepared by diamond turning machine with a surface roughness less than 20 nm (RMS) and Al/Cu hybrid mandrel is explored by depositing a 5 m thick copper layer on Al mandrel via magnetron sputtering deposition. The surface roughness, thickness uniformity and crystallinity of Cu film are analyzed by white light interferometer, XRD. The results show that the prepared Cu film with surface roughness less than 30 nm (RMS), thickness uniformity more than 95%, and cylindricity less than 1 m appears (111) preferential orientation growth. The interfacial bonding strength between Cu film and substrate is strong enough for depositing 11 m thick hohlraum wall containing depleted uranium (DU).
By comparing the chemical component and machined performance of two kinds of 1100 Al rod, the higher purity one is chosen for Al mandrel. Al mandrel is prepared by diamond turning machine with a surface roughness less than 20 nm (RMS) and Al/Cu hybrid mandrel is explored by depositing a 5 m thick copper layer on Al mandrel via magnetron sputtering deposition. The surface roughness, thickness uniformity and crystallinity of Cu film are analyzed by white light interferometer, XRD. The results show that the prepared Cu film with surface roughness less than 30 nm (RMS), thickness uniformity more than 95%, and cylindricity less than 1 m appears (111) preferential orientation growth. The interfacial bonding strength between Cu film and substrate is strong enough for depositing 11 m thick hohlraum wall containing depleted uranium (DU).
2013,
25: 3259-3264.
doi: 3259
Abstract:
The nuclear fusion reaction is an ideal approach to solve the shortage of energy and produce sustainable clean energy. The National Ignition Facility device has been built in the United States in order to demonstrate the nuclear fusion reaction. It can provide a clear development direction for the inertial fusion energy. Fabricating target is one of the three main bodies for NIF. How to fabricate an ignition target to meet design requirements becomes tireless efforts of scientists to pursue goals. The objective of this paper is to introduce the requirement background of candidate Be target, research status, advantages of Be target, design specifications, preparation technology, as well as some key technical issues existed in fabrication process. It will provide an useful reference information for the target fabrication science in our country, and lay a foundation for the ability building of target fabrication.
The nuclear fusion reaction is an ideal approach to solve the shortage of energy and produce sustainable clean energy. The National Ignition Facility device has been built in the United States in order to demonstrate the nuclear fusion reaction. It can provide a clear development direction for the inertial fusion energy. Fabricating target is one of the three main bodies for NIF. How to fabricate an ignition target to meet design requirements becomes tireless efforts of scientists to pursue goals. The objective of this paper is to introduce the requirement background of candidate Be target, research status, advantages of Be target, design specifications, preparation technology, as well as some key technical issues existed in fabrication process. It will provide an useful reference information for the target fabrication science in our country, and lay a foundation for the ability building of target fabrication.
2013,
25: 3265-3268.
doi: 3265
Abstract:
A preparation method of the titanium doped hollow glass microsphere (Ti-HGM) was investigated, which uses tetrabutyl titanate (Ti(OC4H9)4) as dopant and follows the sol-gel route of titanium doped glass sol - titanium doped glass gel - dried titanium doped gass gel particle - titanium doped hollow glass microsphere, in order to uniformly dope the hollow glass microsphere for inertial confinement fusion targets. The results show that the doping effect decreased the wall-thickness uniformity and concentricity of Ti-HGMs, and had no influence on diameter and wall thickness. The Ti-HGMs of Ti, Si atomic ratio of 2.23% were almost uniformly doped, and the gas-storage half-life of nearly 70% Ti-HGMs was more than one month at room temperature.
A preparation method of the titanium doped hollow glass microsphere (Ti-HGM) was investigated, which uses tetrabutyl titanate (Ti(OC4H9)4) as dopant and follows the sol-gel route of titanium doped glass sol - titanium doped glass gel - dried titanium doped gass gel particle - titanium doped hollow glass microsphere, in order to uniformly dope the hollow glass microsphere for inertial confinement fusion targets. The results show that the doping effect decreased the wall-thickness uniformity and concentricity of Ti-HGMs, and had no influence on diameter and wall thickness. The Ti-HGMs of Ti, Si atomic ratio of 2.23% were almost uniformly doped, and the gas-storage half-life of nearly 70% Ti-HGMs was more than one month at room temperature.
2013,
25: 3269-3273.
doi: 3269
Abstract:
With the rapid progress of high power laser technology in China, the specifications on the diameters of PS-PVA double-layer hollow microspheres used in inertial confinement fusion (ICF) physical experiments have increased to 700 m～900 m. In order to improve the yield of the double-layer hollow microspheres with 700 m～900 m diameter, both the surface modification on the PS microspheres by ozonizing and the optimization on the structure of impeller for stirring paddle were used to improve the traditional emulsion microencapsulation technique. The hydrophobic surface of the PS microsphere showed hydrophilic properties after the ozonization modification, which enhanced the interaction between PS microspheres and PVA coatings. Moreover, the optimization on the structure of impeller for stirring paddle improved the uniformity of the liquid field in the container, resulting in the movement stability of the microspheres. The above modifications benefited improving the yield of the large-diameter double-layer hollow microspheres.
With the rapid progress of high power laser technology in China, the specifications on the diameters of PS-PVA double-layer hollow microspheres used in inertial confinement fusion (ICF) physical experiments have increased to 700 m～900 m. In order to improve the yield of the double-layer hollow microspheres with 700 m～900 m diameter, both the surface modification on the PS microspheres by ozonizing and the optimization on the structure of impeller for stirring paddle were used to improve the traditional emulsion microencapsulation technique. The hydrophobic surface of the PS microsphere showed hydrophilic properties after the ozonization modification, which enhanced the interaction between PS microspheres and PVA coatings. Moreover, the optimization on the structure of impeller for stirring paddle improved the uniformity of the liquid field in the container, resulting in the movement stability of the microspheres. The above modifications benefited improving the yield of the large-diameter double-layer hollow microspheres.
2013,
25: 3274-3278.
doi: 3274
Abstract:
The lithium borohydride incorporated within carbon scaffolds was prepared by its confinement to the nanoscale into a nanoporous carbon aerogel. The host within LiBH4 loading reached 80%. The structures and properties of the products were investigated by using scanning electron microscope (SEM), transmission electron microscope (TEM), infrared absorption (IR) spectra, and so on. LiBH4 filled the micropores in carbon aerogel firstly. Then LiBH4 incorporated together with the mesopores. Dehydrogenation rates at 300 ℃ were up to 5 times faster than the reported results observed in the sample of LiBH4 mixed with nonporous graphite.
The lithium borohydride incorporated within carbon scaffolds was prepared by its confinement to the nanoscale into a nanoporous carbon aerogel. The host within LiBH4 loading reached 80%. The structures and properties of the products were investigated by using scanning electron microscope (SEM), transmission electron microscope (TEM), infrared absorption (IR) spectra, and so on. LiBH4 filled the micropores in carbon aerogel firstly. Then LiBH4 incorporated together with the mesopores. Dehydrogenation rates at 300 ℃ were up to 5 times faster than the reported results observed in the sample of LiBH4 mixed with nonporous graphite.
2013,
25: 3279-3281.
doi: 3279
Abstract:
This paper presents a simple method for the preparation of brominated target materials. These materials were obtained by copolymerization of different ratio of p-bromostyrene and styrene, and the brominated composition was measured from 0.6% to 4.2%. Moreover, these copolymer materials had good thermal stability with high decomposition temperatures (385 ℃) and high molecular weight. Furthermore, the films prepared from these materials showed excellent toughness.
This paper presents a simple method for the preparation of brominated target materials. These materials were obtained by copolymerization of different ratio of p-bromostyrene and styrene, and the brominated composition was measured from 0.6% to 4.2%. Moreover, these copolymer materials had good thermal stability with high decomposition temperatures (385 ℃) and high molecular weight. Furthermore, the films prepared from these materials showed excellent toughness.
2013,
25: 3282-3286.
doi: 3282
Abstract:
Precise measurement of foam shape after assembling is necessary. Optical interferometry can obtain cross-sectional structure images of sample with 1-2 mm depth below surface, therefore the shape change is observed. In this paper, optical interferometry is applied to quality demonstration of foam in hohlraum. An optical interferometer based on low coherent light source is established and inner structure images of assembled foam are obtained with a spatial resolution better than 10 m. Superficial and inner structure changes of the foam after extraction are detected, which helps to demonstrate the quality of the assembled foam.
Precise measurement of foam shape after assembling is necessary. Optical interferometry can obtain cross-sectional structure images of sample with 1-2 mm depth below surface, therefore the shape change is observed. In this paper, optical interferometry is applied to quality demonstration of foam in hohlraum. An optical interferometer based on low coherent light source is established and inner structure images of assembled foam are obtained with a spatial resolution better than 10 m. Superficial and inner structure changes of the foam after extraction are detected, which helps to demonstrate the quality of the assembled foam.
2013,
25: 3287-3291.
doi: 3287
Abstract:
For large optics of high-power laser facility, the controlling technology of mid-spatial frequency error is developed. Firstly, the CCOS convolution residual error caused by regular path is analyzed, and the residual error model is established. And then, the optimization parameters for controlling mid-spatial frequency error are achieved by this model. Finally, according to the optimization parameters, the mid-spatial frequency error of 400 mm aperture window is remarkably improved. After several CCOS iteration, the peak-to-valley(PV) is 170.856 nm, the root-mean-square(RMS) of PSD1 is 1.67 nm and no obvious mid-spatial frequency error is found. The result shows that the mid-spatial frequency error of 400 mm aperture window is under control, and the 400 mm aperture windows can be achieved and meet the requirement of mid-spatial frequency error in high-power laser facility.
For large optics of high-power laser facility, the controlling technology of mid-spatial frequency error is developed. Firstly, the CCOS convolution residual error caused by regular path is analyzed, and the residual error model is established. And then, the optimization parameters for controlling mid-spatial frequency error are achieved by this model. Finally, according to the optimization parameters, the mid-spatial frequency error of 400 mm aperture window is remarkably improved. After several CCOS iteration, the peak-to-valley(PV) is 170.856 nm, the root-mean-square(RMS) of PSD1 is 1.67 nm and no obvious mid-spatial frequency error is found. The result shows that the mid-spatial frequency error of 400 mm aperture window is under control, and the 400 mm aperture windows can be achieved and meet the requirement of mid-spatial frequency error in high-power laser facility.
2013,
25: 3292-3296.
doi: 3292
Abstract:
For high-precision deterministic processing, the equal profile of dwell-time and an adaptive step size algorithm are presented in this paper to solve processing path feed-rate. Firstly, we analyze the issues that exist in the conventional and other step algorithms. And then, for these issues, the adaptive step size algorithm is introduced. Finally, a f600 mm plane reflector element is taken to be an instance. The result shows that after four combinations of processing, the surface accuracy of peak-valley (PV) value and the root mean square (RMS) value was reduced to 4.81 nm (/131.6) and 0.495 nm(/1278.4) from 110.22 nm (/5.7) and 13.998 nm (/45.2) (=632.8 nm) respectively in the 98% caliber of the element. By using the new algorithm in our ion beam figuring machine, we obtained a reflector optical element whose PV value was less than /70 in 100 mm caliber.
For high-precision deterministic processing, the equal profile of dwell-time and an adaptive step size algorithm are presented in this paper to solve processing path feed-rate. Firstly, we analyze the issues that exist in the conventional and other step algorithms. And then, for these issues, the adaptive step size algorithm is introduced. Finally, a f600 mm plane reflector element is taken to be an instance. The result shows that after four combinations of processing, the surface accuracy of peak-valley (PV) value and the root mean square (RMS) value was reduced to 4.81 nm (/131.6) and 0.495 nm(/1278.4) from 110.22 nm (/5.7) and 13.998 nm (/45.2) (=632.8 nm) respectively in the 98% caliber of the element. By using the new algorithm in our ion beam figuring machine, we obtained a reflector optical element whose PV value was less than /70 in 100 mm caliber.
2013,
25: 3297-3300.
doi: 3297
Abstract:
In inertial confinement fusion (ICF) research process, the form of focal spot is extremely crucial. Especially in the indirect driven implosion, energy circled fraction is higher than 95% in focal spot. Based on the offline test platform, the focusing spot of continuous phase plates with different application error is clearly imaged on CCD. By experimental analysis, it is found that the beam rotation error, caliber error, translational error and inclination error have a high tolerance in affecting focal plane of CPP. Energy circled fraction is higher than 95%, the range is less than 0.5%. Nevertheless, the waterfront aberration seriously affects the shaping ability of the CPP. Clearly, the main factor of reducing energy circled fraction to less than 90% is waterfront aberration.
In inertial confinement fusion (ICF) research process, the form of focal spot is extremely crucial. Especially in the indirect driven implosion, energy circled fraction is higher than 95% in focal spot. Based on the offline test platform, the focusing spot of continuous phase plates with different application error is clearly imaged on CCD. By experimental analysis, it is found that the beam rotation error, caliber error, translational error and inclination error have a high tolerance in affecting focal plane of CPP. Energy circled fraction is higher than 95%, the range is less than 0.5%. Nevertheless, the waterfront aberration seriously affects the shaping ability of the CPP. Clearly, the main factor of reducing energy circled fraction to less than 90% is waterfront aberration.
2013,
25: 3301-3306.
doi: 3301
Abstract:
The pulse width is different, the mechanism of the laser-matter interaction is different. Damage results from plasma formation and ablation for10 ps and from heat depositing and conventional melting for ＞100 ps. Two theoretical models of transparent dielectrics irradiated by multi-pulses laser are respectively developed based on the above-mentioned different mechanism. One is the dielectric breakdown model based on electron density evolution equation for femtosecond multi-pluses laser, the other is the dielectric heat-damage model based on Fouriers heat exchange equation for nanosecond multi-pluses laser. Using these models, the effects of laser parameters and material parameters on the laser-induced damage threshold of dielectrics are analyzed. The analysis results show that different parameters have different influence on the damage threshold. The effect of parameters on the multi -pulses damage threshold is not entirely the same to the single-pulse damage threshold. The multi-pulses damage mechanism of dielectrics is discussed in detail, considering the effect of different parameters. The discussion provides more information for understanding its damage process and more knowledge to improve its damage thresholds. And the relationship between damage threshold and pulse number is illustrated, it is in good agreement with experimental results. The illustration can help us to predict the multi-pulses damage threshold and the lifetime of optical components.
The pulse width is different, the mechanism of the laser-matter interaction is different. Damage results from plasma formation and ablation for10 ps and from heat depositing and conventional melting for ＞100 ps. Two theoretical models of transparent dielectrics irradiated by multi-pulses laser are respectively developed based on the above-mentioned different mechanism. One is the dielectric breakdown model based on electron density evolution equation for femtosecond multi-pluses laser, the other is the dielectric heat-damage model based on Fouriers heat exchange equation for nanosecond multi-pluses laser. Using these models, the effects of laser parameters and material parameters on the laser-induced damage threshold of dielectrics are analyzed. The analysis results show that different parameters have different influence on the damage threshold. The effect of parameters on the multi -pulses damage threshold is not entirely the same to the single-pulse damage threshold. The multi-pulses damage mechanism of dielectrics is discussed in detail, considering the effect of different parameters. The discussion provides more information for understanding its damage process and more knowledge to improve its damage thresholds. And the relationship between damage threshold and pulse number is illustrated, it is in good agreement with experimental results. The illustration can help us to predict the multi-pulses damage threshold and the lifetime of optical components.
2013,
25: 3307-3310.
doi: 3307
Abstract:
Based on theoretical model of continuous polishing, the influence of processing parameters on the polishing result was discussed. Possible causes of mid-spatial frequency error in the process were analyzed. The simulation results demonstrated that the low spatial frequency error was mainly caused by large rotating ratio. The mid-spatial frequency error would decrease as the low spatial frequency error became lower. The regular groove shape was the primary reason of the mid-spatial frequency error. When irregular and fitful grooves were adopted, the mid-spatial frequency error could be lessened. Moreover, the workpiece swing could make the polishing process more uniform and reduce the mid-spatial frequency error caused by the fix-eccentric plane polishing.
Based on theoretical model of continuous polishing, the influence of processing parameters on the polishing result was discussed. Possible causes of mid-spatial frequency error in the process were analyzed. The simulation results demonstrated that the low spatial frequency error was mainly caused by large rotating ratio. The mid-spatial frequency error would decrease as the low spatial frequency error became lower. The regular groove shape was the primary reason of the mid-spatial frequency error. When irregular and fitful grooves were adopted, the mid-spatial frequency error could be lessened. Moreover, the workpiece swing could make the polishing process more uniform and reduce the mid-spatial frequency error caused by the fix-eccentric plane polishing.
2013,
25: 3311-3314.
doi: 3311
Abstract:
A 600 mm aperture SiC flat mirror was polished up to an aperture of 35 nm (RMS) with computer-controlled optical surfacing (CCOS) in a very short period. The SiC mirror structure, the choose of the diamond powder, and other procedures in CCOS are presented in the paper. The adjustment of the removal function in the polishing process was carefully performed in order to increase the polishing efficiency of the silicon material, and the efficiency in PV and RMS convergence was obtained according to the experiment results. In addition, the efficiency in polishing SiC material needs to be further analyzed to make sure that the batch production of this kind of hard material mirror is possible.
A 600 mm aperture SiC flat mirror was polished up to an aperture of 35 nm (RMS) with computer-controlled optical surfacing (CCOS) in a very short period. The SiC mirror structure, the choose of the diamond powder, and other procedures in CCOS are presented in the paper. The adjustment of the removal function in the polishing process was carefully performed in order to increase the polishing efficiency of the silicon material, and the efficiency in PV and RMS convergence was obtained according to the experiment results. In addition, the efficiency in polishing SiC material needs to be further analyzed to make sure that the batch production of this kind of hard material mirror is possible.
2013,
25: 3315-3317.
doi: 3315
Abstract:
We studied the double-side polishing process of large-aperture ultra-thin component based on the technology of ring polishing and pendulum. The technical optimization included the speed ratio control, polishing pad shape modification and polishing particle size convergence. Computer simulation produced evidence in support of the optimization. The trouble of ultra-thin components damage in original separator was overcome by material replacement and separator thinning. We achieved the convergence of surface shape by adjusting the speed ratio on SYP152 double-side polishing machine. Through these experiments, we verified the feasibility of this processing method, the surface PV value could attain to less than 1.5(=632.8 nm) , the surface roughness could be reduced to less than 1 nm.
We studied the double-side polishing process of large-aperture ultra-thin component based on the technology of ring polishing and pendulum. The technical optimization included the speed ratio control, polishing pad shape modification and polishing particle size convergence. Computer simulation produced evidence in support of the optimization. The trouble of ultra-thin components damage in original separator was overcome by material replacement and separator thinning. We achieved the convergence of surface shape by adjusting the speed ratio on SYP152 double-side polishing machine. Through these experiments, we verified the feasibility of this processing method, the surface PV value could attain to less than 1.5(=632.8 nm) , the surface roughness could be reduced to less than 1 nm.
2013,
25: 3318-3324.
doi: 3318
Abstract:
Conditioning effect on several kinds of optical substrates and film components by quasi-CW laser was investigated. Many samples showed absorption decreasing curves (ADC) under 532 nm and 355 nm irradiation, while keeping absorption values under 1064 nm irradiation. A phenomenological model was built to understand ADC. The model was based on that ADC should be mainly related to accumulated irradiation energy density. According to the model, the head part of ADC was influenced more by mechanism of laser conditioning, and the tail part formed mainly from Gaussian Beam. Normalized ADC and normalized high-asymptote parameter were considered as two tools to make comparison among different curves and get some mechanism information by the model. The results of re-analysis experiment data supported the model, and indicated that the real curves were more like e model shape.
Conditioning effect on several kinds of optical substrates and film components by quasi-CW laser was investigated. Many samples showed absorption decreasing curves (ADC) under 532 nm and 355 nm irradiation, while keeping absorption values under 1064 nm irradiation. A phenomenological model was built to understand ADC. The model was based on that ADC should be mainly related to accumulated irradiation energy density. According to the model, the head part of ADC was influenced more by mechanism of laser conditioning, and the tail part formed mainly from Gaussian Beam. Normalized ADC and normalized high-asymptote parameter were considered as two tools to make comparison among different curves and get some mechanism information by the model. The results of re-analysis experiment data supported the model, and indicated that the real curves were more like e model shape.
2013,
25: 3325-3328.
doi: 3325
Abstract:
Mid-spatial frequency wavefront error of optics is characterized with the power spectrum density (PSD) specification, and is divided into two parts: PSD1 (wavelength 2.5-33 mm) and PSD2 (wavelength 0.12-2.5 mm). Rather than the PSD1 error which has been researched in the literature, the present work focuses on the PSD2 range. Potential factors affecting PSD2 error are firstly analyzed. Polishing experiments reveal that computer controlled small-tool polishing process does not worsen PSD2 error compared to the full-aperture process, while the lap has a decisive effect. The optics polished by pitch laps shows a fair PSD2 error of 0.7 nm (RMS), which is much lower than the specified 1.1 nm. The polyurethane pad commonly results in a much higher PSD2 error of more than 1.5 nm (RMS). For this problem, we adopt diamond conditioner to dress the pad and decrease pad surface roughness. The validation of restraining PSD2 error by diamond dressing has been confirmed.
Mid-spatial frequency wavefront error of optics is characterized with the power spectrum density (PSD) specification, and is divided into two parts: PSD1 (wavelength 2.5-33 mm) and PSD2 (wavelength 0.12-2.5 mm). Rather than the PSD1 error which has been researched in the literature, the present work focuses on the PSD2 range. Potential factors affecting PSD2 error are firstly analyzed. Polishing experiments reveal that computer controlled small-tool polishing process does not worsen PSD2 error compared to the full-aperture process, while the lap has a decisive effect. The optics polished by pitch laps shows a fair PSD2 error of 0.7 nm (RMS), which is much lower than the specified 1.1 nm. The polyurethane pad commonly results in a much higher PSD2 error of more than 1.5 nm (RMS). For this problem, we adopt diamond conditioner to dress the pad and decrease pad surface roughness. The validation of restraining PSD2 error by diamond dressing has been confirmed.
2013,
25: 3329-3332.
doi: 3329
Abstract:
By calculating the nonuniformity in overlapping area between sub-apertures, errors such as positioning error, system error and stitching model pattern that affect the stitching testing prelision of large aperture continuous phase plate(CPP) are summarized and analyzed. Some results indicate that positioning errors are the major reason affecting the stitching precision and the nonuniformity in overlapping area could be decreased as the system errors are handled effectively. Furthermore, there is no more obvious difference in the choice of stitching pattern concerning the stitching result. The statistical result shows that the root-mean-square of the residual error(ERMS) raises in the overlapping area as the increment of depth as CPP's wavefront at the testing level of pixel, which means that the stitching testing precision declines simultaneously.
By calculating the nonuniformity in overlapping area between sub-apertures, errors such as positioning error, system error and stitching model pattern that affect the stitching testing prelision of large aperture continuous phase plate(CPP) are summarized and analyzed. Some results indicate that positioning errors are the major reason affecting the stitching precision and the nonuniformity in overlapping area could be decreased as the system errors are handled effectively. Furthermore, there is no more obvious difference in the choice of stitching pattern concerning the stitching result. The statistical result shows that the root-mean-square of the residual error(ERMS) raises in the overlapping area as the increment of depth as CPP's wavefront at the testing level of pixel, which means that the stitching testing precision declines simultaneously.
2013,
25: 3333-3337.
doi: 3333
Abstract:
It has become more important for the accurate measurement of the mid-frequency wavefront of the large-aperture optics in high-power laser systems. The root mean square of mid-frequency wavefront is one of the most important specifications. According to the frequency range of mid-frequency wavefront and frequency response characteristics of the measurement devices, the mid-frequency region can be divided into two separate bands, the low-frequency band and the high-frequency band. The wavefront in different band can be measured by interferomter and optical profiler respectively. The full-aperture mid-frequency wavefront over the low-frequency band can be measured by a large-aperture interferometer. Comparing measurement results of the large-aperture interferometer and the small-aperture interferometer, one method named synthesizing averaging sub-aperture wavefronts is proposed to measure the root mean square of the full-aperture wavefront in the same frequency region. Using discrete sampling method, the mid-frequency wavefront of large-aperture optics over the high-frequency band can be measured by optical profiler. It is experimentally shown that the 33 sampling pattern is enough for the measurement of the wavefront with 410 mm410 mm size.
It has become more important for the accurate measurement of the mid-frequency wavefront of the large-aperture optics in high-power laser systems. The root mean square of mid-frequency wavefront is one of the most important specifications. According to the frequency range of mid-frequency wavefront and frequency response characteristics of the measurement devices, the mid-frequency region can be divided into two separate bands, the low-frequency band and the high-frequency band. The wavefront in different band can be measured by interferomter and optical profiler respectively. The full-aperture mid-frequency wavefront over the low-frequency band can be measured by a large-aperture interferometer. Comparing measurement results of the large-aperture interferometer and the small-aperture interferometer, one method named synthesizing averaging sub-aperture wavefronts is proposed to measure the root mean square of the full-aperture wavefront in the same frequency region. Using discrete sampling method, the mid-frequency wavefront of large-aperture optics over the high-frequency band can be measured by optical profiler. It is experimentally shown that the 33 sampling pattern is enough for the measurement of the wavefront with 410 mm410 mm size.
2013,
25: 3338-3342.
doi: 3338
Abstract:
Laser conditioning is one of the important methods to improve the laser damage threshold of film optics. Firstly, a large aperture laser was used to irradiate the HfO2/SiO2 reflectors, which were evaporated from hafnia and silica by e-beam. Secondly, a laser calorimeter was used to test the film absorption before and after laser irradiation. Focused ion beam (FIB) was few reported using on laser film, it was used to study the damage morphology and explore the cause of damage. The shooting of the partial ejection on nodule was obtained for the first time, which provided the basis for study the damage process. The results show that film absorption was decreased obviously after the laser irradiation, laser conditioning can raise the laser damage threshold by the cleaning mechanism. For the HfO2/SiO2 reflectors, laser conditioning was effective to eject the nodules on substrate. It resulted from the nodule residue not to affect the subsequent laser. In addition, laser conditioning was not effective to the nodule in the film, which might be from the material spatter in coating process. In this case, other method could be used to get rid of the nodules.
Laser conditioning is one of the important methods to improve the laser damage threshold of film optics. Firstly, a large aperture laser was used to irradiate the HfO2/SiO2 reflectors, which were evaporated from hafnia and silica by e-beam. Secondly, a laser calorimeter was used to test the film absorption before and after laser irradiation. Focused ion beam (FIB) was few reported using on laser film, it was used to study the damage morphology and explore the cause of damage. The shooting of the partial ejection on nodule was obtained for the first time, which provided the basis for study the damage process. The results show that film absorption was decreased obviously after the laser irradiation, laser conditioning can raise the laser damage threshold by the cleaning mechanism. For the HfO2/SiO2 reflectors, laser conditioning was effective to eject the nodules on substrate. It resulted from the nodule residue not to affect the subsequent laser. In addition, laser conditioning was not effective to the nodule in the film, which might be from the material spatter in coating process. In this case, other method could be used to get rid of the nodules.
2013,
25: 3343-3347.
doi: 3343
Abstract:
In order to measure and evaluate the far-field intensity caused by large-aperture continuous phase plates, off-line measurement system with 351 nm laser for the far-field intensity was built according to the physical demand parameters of the laser system in ICF equipment. The experiment for CPP with 330 mm330 mm aperture was carried out. The measurement reproducibility and accuracy were analyzed according to the calculated result with scale diffraction theory. The diameter of dispersion focus is about 2.9 times diffraction-limited diameter and the maximal size that the system can measure is f600 mm or 430 mm430 mm. The reproducibility for measuring encircled energy fraction in defocusing amount 2 mm is better than 0.2%. The shape and distribution from experiment accord with the calculated result, the measured encircled energy percentage is 0.85% less than the calculated result and the measured radius is 13 m larger than the calculated result, the difference is caused by temporal smoothing of the measurement system, so the measurement accuracy could be enhanced through shortening time of exposure of CCD and reducing the optical aberration of the measurement system.
In order to measure and evaluate the far-field intensity caused by large-aperture continuous phase plates, off-line measurement system with 351 nm laser for the far-field intensity was built according to the physical demand parameters of the laser system in ICF equipment. The experiment for CPP with 330 mm330 mm aperture was carried out. The measurement reproducibility and accuracy were analyzed according to the calculated result with scale diffraction theory. The diameter of dispersion focus is about 2.9 times diffraction-limited diameter and the maximal size that the system can measure is f600 mm or 430 mm430 mm. The reproducibility for measuring encircled energy fraction in defocusing amount 2 mm is better than 0.2%. The shape and distribution from experiment accord with the calculated result, the measured encircled energy percentage is 0.85% less than the calculated result and the measured radius is 13 m larger than the calculated result, the difference is caused by temporal smoothing of the measurement system, so the measurement accuracy could be enhanced through shortening time of exposure of CCD and reducing the optical aberration of the measurement system.
2013,
25: 3348-3352.
doi: 3348
Abstract:
The KDP crystal antireflective coatings prepared by spin coating method were discussed. The coating was modified using hexamethyl disilazane (HMDS), and had good moisture-resistant property. Some technique problems such as clamping safety during the spin process were analysed. The coating uniformity, the transmittance, moisture-resistant property and the laser induced damage threshold (LIDT) were measured. The transmittance ununiformity of the coating was about 0.3%, the transmittance at 1053 nm was over 99.8%, the water contact angle was over 152, and the LIDT was about 10 J/cm2 (355 nm, 3 ns).
The KDP crystal antireflective coatings prepared by spin coating method were discussed. The coating was modified using hexamethyl disilazane (HMDS), and had good moisture-resistant property. Some technique problems such as clamping safety during the spin process were analysed. The coating uniformity, the transmittance, moisture-resistant property and the laser induced damage threshold (LIDT) were measured. The transmittance ununiformity of the coating was about 0.3%, the transmittance at 1053 nm was over 99.8%, the water contact angle was over 152, and the LIDT was about 10 J/cm2 (355 nm, 3 ns).
