Temperature-related performance of Yb^3＋：YAG disc lasers and optimum design for diamond cooling

In this paper the temperature-related performances of the Yb^3＋：YAG disc laser has been investigated based on quasi-three level rate equation model. A compact diamond window cooling scheme also has been demonstrated. In this cooling scheme, laser disc is placed between two thin discs of single crystal synthetic diamond, the heat transfer from Yb^3＋：YAG to the diamond, in the direction of the optical axis, and then rapidly conducted radically outward through the diamond to the cooling water at the circumference of the diamond/Yb^3＋ ：YAG assembly. Simulation results show that increasing the thickness of the diamond and the overlap-length （between diamond and water） decreases the disc temperature. Therefore a 0.3-0.5 mm thick diamond window with the overlap-length of 1.5 2.0 mm will provide acceptable cost effective cooling, e.g., with a pump intensity of 15 kW/cm^2 and repetitive rate of 10 Hz, to keep the maximum temperature of the lasing disc below a reasonable value （310K）, the heat exchange coefficient of water should be about 3000 W/m^2K.

Field Emission Properties of Nano-DLC Films Prepared on Cu Substrates by Pulsed Laser Deposition

Nano-diamond like carbon（DLC） thin films were prepared on fused silica and Cu substrates by the pulsed-laser deposition technique with different laser intensities. Step-measurement, atomic force microscope（AFM）, UV-VIS-NIR transmittance spectroscopy and Raman spectroscopy were used to characterize the films. It was shown that the deposition rate increases with the laser intensity, and the films prepared under different laser intensities show different transparency. Raman measurement showed that the content of sp^3 of the Nano-DLC thin films decreases with the laser intensity. The field emission properties of the Nano-DLC thin films on Cu substrates were studied by the conventional diode method, which showed that the turn-on field increases and the current density decreases with sp^3 content in the films. A lower turn-on field of 6 V/um and a higher current density of 1 uA/cm^2 were obtained for Nano-DLC thin films on Cu substrate.

Quantum splitting of electron peaks in ultra-strong fields

Effects of multiple nonlinear Compton scattering on electrons in ultra-strong fields are described using analytic formulas similar to those in the theory of multiple bremsstrahlung.Based on these analytic formulas,a new pure quantum effect of multiple nonlinear Compton scattering called quantum peak splitting is identified:the electron peak splits into two when the average number of nonlinear Compton scatterings per electron passes a threshold of 5.1 and is below 9.Quantum peak splitting stems from the discreteness of quantum radiation reaction,with one of the split peaks being formed by electrons emitting zero to three times and the other by electrons emitting four or more times.This effect provides a new mechanism for the formation of electron peaks,imposes a new beamstrahlung limit on future colliders,and corrects the picture of quantum radiation reaction.Experiments can be performed on lasers with intensities≳10^(21)W/cm^(2),which are reachable on PW-scale facilities.

Phase and Rietveld Refinement of Pyrochlore Gd_2Zr_2O_7 Used for Immobilization of Pu(Ⅳ)

The phase of pyrochlore Gd_2Zr_2O_7 used for immobilization of Pu （Ⅳ） was investigated, tetravalent cerium was used as the simulacrum for plutonium with tetravalence, and the compounds in the system Gd_2Zr_2-_xCe_xO_7 （0.0≤x≤2.0） were synthesized via a high temperature solid reaction method with Gd_2O_3 and ZrO_2 powders being used as the starting materials. Based on the collected XRD data of the gained samples, the phase and microstructural change of compounds were calculated by means of rietveld structural refinement method. The experimental results indicated that the phases of compounds were changed from pyrochlore to fluorite-type phase with the increasing x. The linear relation between a and x was discovered in the range of fluorite-type phase, which accorded with a = 0.52748 ＋ 0.00825 x （0.2≤x≤2.0）, while V= 0.14668 ＋ 0.00711 x （0.2≤x≤2.0） was also achieved.

Morphology Structure and Electrical Properties of NiCr Thin Film Grown on the Substrate of Silicon Prepared by Magnetron Sputtering

NiCr micron-resistor was designed and prepared by magnetron sputtering and lithography on the substrate of silicon with different powers. It is found that there exists a big gap in the TCR between the annealed group and the un-annealed group. A series of tests were made to figure out the reasons lying behind the gap in the TCR between the annealed group and the un-annealed group. UV reflection results show that there is no increase in the concentration of free electrons after annealing. However, the data obtained from XRD reveal that the annealing does not have an obvious influence on the strain of thin films, but really increases the grain size of thin films. Therefore, the grain boundary scattering plays a dominant role in explaining the obvious difference in the TCR. Finally through appropriate methods, a micron-resistor for heating-up with a low TCR value was obtained.

Measurement of Raman scattering gain coefficient in large-aperture DKDP crystals irradiated by 351 nm pulses

Transverse stimulated Raman scattering （TSRS） gain coefficient in a large aperture 65% deu terated potassium dihydrogen phosphate （DKDP） is measured at 351 nm. The measurement involves the use of an optical fiber sensor system to detect Raman scattering light in the DKDP crystal. A Raman scattering gain coefficient of 0. 109 cm/GW is obtained and will be used to set upper limit of the DKDP crystals in our laser fa cility to avoid the TSRS induced energy loss and laser damage. The effect of bulk damage on growth behavior of TSRS is also examined and it is found that bulk damage has little impact on the TSRS growth. Thus the influ ence of bulk damage on the measurement of TSRS gain coefficient can be ignored.

Properties of nanocrystalline copper prepared by vacuum-warm-compaction method

Nanocrystalline Cu with average grain size of 22.8-25.3 nm was prepared by vacuum-warm-compaction method. Scanning electronic microscope,HMV-2 type microhardness tester,X-ray diffractometer,and 6157 type electrometer were used to determine the microstructure,microhardness and electrical resistivity of as-prepared nanocrystalline Cu,respectively. The results show that the microhardness of nanocrystalline Cu increases with larger pressure,longer duration of pressure or higher temperature. The highest microhardness of nanocrystalline Cu is 3.8 GPa,which is 7 times higher than that of coarse-grained copper. The electrical resistivity of as-prepared specimens is(1.2-1.4)×10-7 -·m at temperature 233-293 K,which is 5-6 times higher than that of the coarse-grained copper.

Laser-driven flier impact experiments at the SG-III prototype laser facility

Laser-driven flier impact experiments have been designed and performed at the SG-III prototype laser facility. The continuum phase plate（CPP） technique is used for the 3 ns quadrate laser pulse to produce a relatively uniform irradiated spot of 2 mm. The peak laser intensity is 2.7×10^13W/cm^2 and it accelerates the aluminum flier with a density gradient configuration to a high average speed of 21.3 km/s, as determined by the flight-of-time method with line VISAR. The flier decelerates on impact with a transparent silica window, providing a measure of the flatness of the flier after one hundred microns of flight. The subsequent shock wave acceleration, pursuing, and decay in the silica window are interpreted by hydrodynamic simulation. This method provides a promising method to create unique conditions for the study of a material＇s properties.

Single-pinhole diffraction of few-cycle isolated attosecond pulses with a two-color field

The spatio-temporal characterization of an isolated attosecond pulse is investigated theoretically in a two-color field. Our results show that a few-cycle isolated attosecond pulse With the center wavelength of 16 nm can be generated effectively by adding a weak controlling field. Using the split and delay units, the isolated attosecond pulse can be split to the two same ones, and then single-pinhole diffractive patterns of the two pulses with different delays can be achieved. The diffractive patterns depend severely on the periods of the attosecond pulses, which can be helpful to obtain temporal information of the coherent sources.

Effect of molecular weight on the quality of poly(alpha-methylstyrene) mandrel

Hollow poly(alpha-methylstyrene)(PAMS)shows application in inertial confinement fusion experiments as the degradable mandrels of glow plasma polymer shells.However,the molecular weight of PAMS has great influence on the quality of mandrels.In this work,this influence was systematically studied using several PAMS samples with different molecular weights.For PAMS shells with 900 mm inner diameter and different wall thickness,when the molecular weight of PAMS is in the range of 300e500 kg·mol^(-1),perfect sphericity and good wall thickness uniformity can be obtained.In contrast,when increasing molecular weight to 800 kg·mol^(-1),the sphericity and the wall thickness uniformity become worse.Moreover,compared with the wall uniformity,the sphericity of PAMS shells was much less sensitive to the molecular weight.The results also showed that the stability of W1/O compound droplets of PAMS shells were less affected by the molecular weight.It was revealed that the wall uniformity and the sphericity of the PAMS shells were associated with the diffusion rates of fluorobenzene(FB).

First-Principles Study of the Structural, Electronic and Optical Properties ofHexagonal LiIO_(3)

The structural parameters,electronic structure,chemical bonding and optical properties of hexagonal LiIO_(3) are investigated in the framework of density functional theory.The calculated lattice parameters are in agreement with the previous experimental work.The band structure,density of states,and Mulliken charge population are obtained,and indicate that hexagonal LiIO_(3) has an indirect band gap of 2.81 eV.Furthermore,the optical properties are also calculated and analyzed in detail.It is shown that hexagonal LiIO_(3) is a promising dielectric material.

Measurement of ZnO/Al_(2)O_(3) Heterojunction Band Offsets by in situ X-Ray Photoelectron Spectroscopy

ZnO films are grown on c-sapphire substrates by laser molecular beam epitaxy.The band offsets of the ZnO/Al_(2)O_(3) heterojunction are studied by in situ x-ray photoelectron spectroscopy.The valence band of Al_(2)O_(3) is found to be 3.59±0.05 eV below that of ZnO.Together with the resulting conduction band offset of 2.04±0.05 eV,this indicates that a type-I staggered band line exists at the ZnO/Al_(2)O_(3) heterojunction.

Electronic and Optical Properties of Rocksalt CdO: A first-Principles Density-Functional Theory Study

The structural, electronic and optical properties of rocksalt CdO have been studied using the plane-wave-based pseudo-potential density functional theory within generalized gradient approximation. The calculated lattice parameters are in agreement with previous experimental work. The band structure, density of states, and Mulliken charge population are obtained, which indicates that rocksalt CdO having the properties of a halfmetal due to an indirect band gap of -0.51eV. The mechanical properties show that rocksalt CdO is mechanically stable, isotropic and malleable. Significantly, we propose a correct value for ε1(0) of about 4.75, which offers theoretical data for the design and application for rocksalt CdO in optoelectronic materials.

Growth and Characterization of Indium Doped Zinc Oxide Films Sputtered from Powder Targets

Indium doped Zn O films were grown on quartz glass substrates by radio frequency magnetron sputtering from powder targets. Indium content in the targets varied from 1at% to 9at%. In doping on the structure, optical and electrical properties of Zn O thin films were studied. X-ray diffraction shows that all the films are hexagonal wurtzite with c-axis perpendicular to the substrates. There is a positive strain in the films and it increases with indium content. All the films show a high transmittance of 86% in the visible light region. Undoped Zn O thin film exhibits a high transmittance in the near infrared region. The transmittance of indium doped Zn O thin films decreases sharply in the near infrared region, and a cut-off wavelength can be found. The lowest resistivity of 4.3×10^（-4） Ω·cm and the highest carrier concentration of 1.86×10^（21） cm^（-3） can be obtained from Zn O thin films with an indium content of 5at% in the target.

Dielectric Laser Accelerators Driven by Ultrashort, Ultraintense Long-Wave Infrared Lasers

Particle acceleration driven by intense lasers has long been a frontier of research in the field of laser engineering physics due to its extremely high acceleration gradient.Recently,dielectric laser accelerators(DLAs)have become a new research hotspot due to their ability to achieve gigavolt-per-meter acceleration gradients on compact chip-level all-optical structures.In comparison to the currently widely used solid-state laser with a 1-μm wavelength,long-wave infrared(LWIR)lasers with a length of about 10μm offer several unique advantages,including the ability to obtain a large electric charge of particle beams and lower energy divergence.These advantages have been validated in plasma-based laser accelerators as well as DLAs.Although the system is still in its early stages of development,the use of LWIR lasers for driving DLAs has special significance,including but not limited to easier processing of optical chips and larger acceleration channels.This review will provide a detailed introduction to this field from 2 aspects:DLAs and ultrashort and ultraintense LWIR lasers based on CO_(2) laser amplifiers.

高功率激光系统空间滤波小孔等离子体特性

为解决高功率固体激光系统空间滤波小孔堵孔问题,针对空间滤波小孔中的等离子体溅射现象,对等离子体扩散1维分布模型进行了分析。分别对铝、金和碳等3种典型材料1维分布情况及扩散速度进行了数值模拟,得到等离子体扩散速度大约为107cm/s。根据模拟计算结果,分析了神光Ⅲ原型装置助推放大级的堵孔风险,结果表明,在长脉冲情况下等离子体溅射造成的影响不可忽略。

超短超强激光在稀薄等离子体中的自聚焦传输

开展超短超强激光与次稠密等离子体相互作用实验,采用探针光对激光等离子体相互作用区域进行阴影成像,研究了不同激光功率与临界功率比值及不同激光脉冲长度与等离子体波波长比值下的激光在次稠密等离子体中的自聚焦传输。结果表明:相对论效应是超短脉冲在次稠密等离子体中的主要自聚焦机制,激光功率与临界功率比值是影响超短脉冲在次稠密等离子体中形成自聚焦的关键条件。

Recent progress in ICF target fabrication at RCLF

Target is one of the essential parts in inertial confinement fusion(ICF)experiments.To ensure the symmetry and hydrodynamic stability in the implosion,there are stringent specifications for the target.Driven by the need to fabricate the target required by ICF experiments,a series of target fabrication techniques,including capsule fabrication techniques and the techniques of target characterization and assembly,are developed by the Research Center of Laser Fusion(RCLF),China Academy of Engineering Physics(CAEP).The capsule fabrication techniques for preparing polymer shells,glow discharge polymer(GDP)shells and hollow glass micro-sphere(HGM)are studied,and the techniques of target characterization and assembly are also investigated in this paper.Fundamental research about the target fabrication is also done to improve the quality of the target.Based on the development of target fabrication techniques,some kinds of target have been prepared and applied in the ICF experiments.

ICF实验软X光能谱的基函数解谱法

惯性约束聚变实验中,14通道软X光能谱仪是测量软X射线能谱、等效积分温度和辐射能流时间过程的重要诊断设备。基函数法是还原能谱分布的一种常用方法。通过对双峰谱形的还原,对不同类型基函数的选择、基函数参数的设置和求解方法等影响解谱的因素进行了比较分析。根据大量算例的结果,使用优化后的基函数和求解方法对实际测量辐射谱进行了计算,并与透射光栅谱仪的测量结果进行了比较。结果显示,根据谱仪通道响应选择三次样条的节点,能够较好还原软X射线的能谱。