Broadband Terahertz Wave Generation from Monolayer Graphene Driven by Few-Cycle Laser Pulse

We theoretically investigate the characteristics of terahertz(THz) radiation from monolayer graphene exposed to normal incident few-cycle laser pulses, by numerically solving the extended semiconductor Bloch equations. Our simulations show that the THz spectra in low frequency regions are highly dependent on the carrier envelope phase(CEP) of driving laser pulses. Using an optimal CEP of few-cycle laser pulses, we can obtain broadband strong THz waves, due to the symmetry breaking of the laser-graphene system. Our results also show that the strength of the THz spectra depend on both the intensity and central wavelength of the laser pulses. The intensity dependence of the THz wave can be described by the excitation rate of graphene, while wavelength dependence can be traced back to the band velocity and the population of graphene. We find that a near single-cycle THz pulse can be obtained from graphene driven by a mid-infrared laser pulse.

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.

Generation of Nonlinear Force Driven Blocks from Skin Layer Interaction of Petawatt-Picosecond Laser Pulses for ICF

The discovery of the essential difference of maximum ion energy for TW-pslaser plasma interaction compared with, the 100 ns laser pulses led to the theory of a skin layermodel where the control of prepulses suppressed the usual relativistic self-focusing. The subsequentgeneration of two nonlinear force driven blocks has been demonstrated experimentally and inextensive numerical studies where one block moves against the laser light and the other block intothe irradiated target. These blocks of nearly solid state density DT plasma correspond to ion beamcurrent densities exceeding 10^(10) A/cm^2 where the ion velocity can be chosen up to highlyrelativistic values. Using the results of the expected ignition of DT fuel by light ion beams, aself-sustained fusion reaction front may be generated even into uncompressed solid DT fuel similarto the Nuckolls-Wood scheme where 10 kJ laser pulses produce 100 MJ fusion energy. This new andsimplified scheme of laser-ICF needs and optimisation of the involved parameters.

基于数据驱动的激光切割工艺参数优化方法研究综述

近年来,数据驱动的激光切割工艺参数优化方法受到广泛关注和研究。因此,对该领域的主要研究进展进行梳理。对比基于数据驱动和基于机理模型的激光切割工艺参数优化方法,并明确数据驱动方法的研究对象。从工艺参数和工艺质量两个方面归纳当前数据驱动激光切割工艺参数优化的研究思想及进展,并总结已有研究中采用的数据驱动方法。概述数据驱动激光切割工艺参数优化的具体实现手段。总结比较各种数据驱动参数优化方法的优劣,并展望该领域未来值得进一步研究的方向,包括完善数据获取和数据增强方法,加强模型和算法的评估,并探索更高效智能的实现手段。

Effect of laser spot size on fusion neutron yield in laser-deuterium cluster interactions

The effect of the laser spot size on the neutron yield of table-top nuclear fusion from explosions of a femtosecond intense laser pulse heated deuterium clusters is investigated by using a simplified model, in which the cluster size distribution and the energy attenuation of the laser as it propagates through the cluster jet are taken into account. It has been found that there exists a proper laser spot size for the maximum fusion neutron yield for a given laser pulse and a specific deuterium gas cluster jet. The proper spot size, which is dependent on the laser parameters and the cluster jet parameters, has been calculated and compared with the available experimental data. A reasonable agreement between the calculated results and the published experimental results is found.

Research Progress in Laser Active Debris Removal of CAST

Based on the introduction to theresearch status and trend of international space-based laser debris re-moval technology, the existing problems of space-based laser debris removal technology are systematically analyzed.In view of the existing problems, the work and research progress of the Beijing Institute of Spacecraft EnvironmentEngineering in this field are introduced from several aspects, such as dynamic behavior of laser-driven debris, orbittransfer model, ground simulation system, space-based removal system scheme and target selection strategy. The mainresearch methods include laser-driven micro-impulse measurement experiment, surface triangulation three-dimension-al reconstruction calculation method based on laser-material interaction theory, simulation calculation based on orbitaldynamics, etc. It also looks forward to the future research direction in the field of this technology.

Ultrahigh Acceleration of Plasma Blocks by Nonlinear Forces for Side-On Laser Ignition of Solid Density Fusion Fuel

A fundamental difference of very high intensity laser interaction with plasmas from solid targets appears with lasing at picosecond （ps） pulse durations in contrast to pulses of nanosec-onds （ns）. This can be seen from the more than 10,000 times higher acceleration with ps pulse du-rations than with thermal pressure determined interaction. A ps pulse duration produces instantly acting high-efficiency nonlinear （ponderomotive） electrodynamic force dominated acceleration in contrast to heating with longer pulses. The ps pulses accelerate high-density plasma blocks. This can be used by a new scheme of side-on driven laser fusion with generating a flame ignition in uncompressed fusion fuel of solid density resulting in a reaction velocity of more than 2000 km/s for DT.

Analysis of electromagnetic pulses generated from ultrashort laser irradiation of solid targets at CLAPA

Electromagnetic pulses(EMPs)produced by the interaction of a TW femtosecond laser with solid targets at the Compact Laser Plasma Accelerator(CLAPA)are measured and interpreted.The statistical results confirm that the intensities of the EMPs are closely related to both target material and thickness.The signal of the titanium target is more abundant than that of the copper target with the same thickness,and the intensity of EMP is positively correlated with the target thickness for aluminium foil.With the boosted EMP radiations,the energy of accelerated protons is also simultaneously enhanced.In addition,EMPs emitted from the front of the target exceed those from the rear,which are also pertinent to the specific target position.The resonant waveforms in the target chamber are analyzed using the fast Fourier transform,and the local resonance and the attenuation lead to changes of the frequency spectra of EMPs with variation of detecting positions,which is well supported by the modeling results.The findings are beneficial to gaining insight into the mechanism of EMP propagation in a typical target chamber and providing more information for EMP shielding design.

Measurement of temperature changes during cavitation generated by an erbium, chromium: Yttrium, scandium, gallium garnet laser

Aim: The present study evaluated the magnitude of temperature changes in the tooth during cavitation produced by an Er,Cr:YSGG laser. Methods: The root canal of a single extracted maxillary canine was enlarged to a size 30/.02 file. Four thermocouples were attached to the tooth: one to the surface of the root and three inserted into the canal at 3, 9, and 15 mm from the apical foramen, respectively. The tooth was placed in a plastic container at room temperature around 25°C. The tooth was processed as follows. In the EDTA condition, the tooth was irrigated with 17% EDTA;in the NaOCl condition, the tooth was irrigated with 3% NaOCl;and to analyse the effect of different thicknesses of dentin, the tooth was irrigated with tap water. In all conditions, the irrigants were activated at 2 W for 120 seconds. Results: The mean temperature was 25.2°C to 27.1°C and the temperature ranged from 25.0°C to 29.6°C. The temperature elevation measured during cavitation generated by the laser didnot exceed 5°C. Conclusions: The magnitude of the temperature changes in the root canal and at the surface of the tooth did not exceed 5°C when laser-driven irrigation was used to produce cavitation in the root canal.

Thermal Physics and Statistical Mechanics Driven Inertial Confinement Fusion(ICF)Inducing a Controlled Thermonuclear Energy

In the 1970s,scientists began experimenting with powerful laser beams to compress and heat the hydrogen isotopes to the point of fusion,a technique called ICF(Inertial Confinement Fusion).In the“direct drive”approach to ICF,powerful beams of laser light are focused on a small spherical pellet containing micrograms of deuterium and tritium.The rapid heating caused by the laser“driver”makes the outer layer of the target explode.In keeping with Isaac Newton’s Third Law“For every action,there is an equal and opposite reaction”,the remaining portion of the target is driven inwards in a rocket-like implosion,causing compression of the fuel inside the capsule and the formation of a shock wave,which further heats the fuel in the very center and results in a self-sustaining burn.The fusion burn propagates outward through the cooler,outer regions of the capsule much more rapidly than the capsule can expand.Instead of magnetic fields,the plasma is confined by the inertia of its own mass—hence the term inertial confinement fusion.A similar process can be observed on an astrophysical scale in stars and the terrestrial uber world,that have exhausted their nuclear fuel,hence inertially or gravitationally collapsing and generating a supernova explosion,where the results can easily be converted to induction of energy in control forms for a peaceful purpose(i.e.,inertial fusion reaction)by means of thermal physics and statistical mechanics behavior of an ideal Fermi gas,utilizing Fermi-Degeneracy and Thomas-Fermi theory.The fundamental understanding of thermal physics and statistical mechanics enables us to have a better understanding of Fermi-Degeneracy as well as Thomas-Fermi theory of ideal gas,which results in laser compressing matter to a super high density for purpose of producing thermonuclear energy in way of controlled form for peaceful shape and form i.e.CTR(Controlled Thermonuclear Reaction).In this short review,we have concentrated on Fundamental of State Equations by driving them as it was evaluated in book Statistical Mechanics written by Mayer,J.and Mayer,M.in this article.

基于数据驱动的激光雕刻机路径高精度控制方法

激光雕刻机路径受到激光冲击波和反射波影响,光源指向出现抖动,路径控制效果不佳。为了提高路径控制效果,提出了基于数据驱动的激光雕刻机路径高精度控制方法。根据激光冲击波原理计算冲击波阵面上的压力、声速和波速;使用控制器搜索最优控制参数,结合等价线性模型评估伪偏导函数;计算激光光源质心均值,通过控制抖动角度,实现激光雕刻光束指向控制;从数据驱动控制层表面弱化冲击波,控制激光雕刻机路径。实验结果证明应用方法获得的各点应力最大误差为2 MPa,且雕刻版面与实际基本一致,提高了雕刻路径控制效果。

Analytical solutions for a doubly driven two-level atom

We have deduced analytical solutions of an energy level diagram of the doubly driven/dressed atom for a two-level atom exposed to a strong near-resonant bichromatic laser field in a special case, i.e., the bichromatic field with frequencies ω1 and ω2, and Rabi frequencies ？1 and ？2, in which the first coupling field of ？1 acts on the bare atomic levels, and then the resulting singly dressed states are driven by the second coupling field of ？2, thus resulting in the doubly dressed atom.We have measured the probe absorption spectra of a doubly driven two-level atom. The system consists of 52S1/2, F= 2 and 5~2P_（3/2）, F＇= 3 states of ^（87）Rb atoms in a magneto-optical trap（MOT） as well as the cooling/trapping beams and an additional coupling field. As for the spectroscopic properties of the doubly driven two-level atom, theoretical analytical solutions are in general agreement with the experimental spectrum as a whole.

Intensity Correlation Function and Associated Relaxation Time of a Saturation Laser Model with Correlated Noises

我们与相关噪音为单个模式的激光的一个浸透模型调查紧张关联功能 C 和它的联系松驰时间 T-c。C 和 T-c 的 Theexpressions 借助于设计操作员方法被导出，并且在添加剂噪音和趋于增加的噪音之间的关联的效果被数字计算讨论。基于计算结果，在添加剂噪音之间的关联力量 A 和趋于增加的噪音能提高激光紧张的变化腐烂，这被发现。

高功率激光驱动核反应研究进展与展望

近年来,随着高功率激光技术的持续进步,目前在实验室已可获得超过1022W/cm2的激光聚焦强度,且还在不断提升,这为超高强度激光脉冲触发核过程和核应用开辟了可能性。这样的超强脉冲激光与物质发生相互作用时,会出现很多新的物理现象,并且其产生的高温高压高密度的等离子体极端环境以及诱发的核反应次级粒子束等,也为其他基础和应用研究提供了独特的平台。强激光产生的等离子体环境可用来模拟天体核反应的环境,研究电子屏蔽效应等因素带来的低能核反应截面测量中的不确定性因素,这是目前实验室条件下直接研究天体环境中核反应的唯一技术手段。同时,激光驱动等离子体中核反应的研究也与惯性约束聚变中的燃料设计息息相关。与常规环境温度和压力下的物质相比,等离子体环境中的核反应动力学要复杂得多,对于研究天体核反应和惯性约束聚变也至关重要。因此,除加速器和反应堆外,高功率激光器正成为研究核物理的新平台。激光与核物理的结合不仅有利于具有新颖思想和方法的基础科学研究,也有利于广泛的物理应用领域。激光核物理已成为国际上一门新的交叉学科,也是物理学的重要前沿之一。与传统核物理装置相比,超强激光器具有脉冲宽度短、时间分辨率高、通量大等特性,这给核反应研究带来独特机遇的同时,也给核反应产物测量带来了挑战。本文从激光与物质的相互作用开始,介绍了世界上的激光装置,评述了激光驱动核反应的研究意义、研究特点与挑战,总结了激光驱动核反应的实验研究方法以及产物探测与标定技术,同时介绍了最新的研究进展和对未来研究的展望。

基于机器视觉方法的诊断设备自动瞄准技术

激光惯性约束聚变实验需要使用数十台套诊断设备从不同方位对瞬态微尺度物理过程进行诊断表征。大部分诊断设备通常需要进入巨型靶室真空环境内,在厘米到米级的不同工作距离上,对聚变靶上面毫米到数十微米的靶标进行瞄准,大部分诊断设备的瞄准精度需要达到50μm水平。双目瞄准方法是在真空环境下实现远距离高精度瞄准的一种重要方法,但目前主要依赖人工判读图像识别靶标和手动操作诊断搭载平台运动实现对靶瞄准,特别是靶室内照明条件或诊断设备瞄准视线存在夹角等条件会严重影响靶标识别效果,对诊断设备瞄准精度造成较大影响。发展了一种基于机器视觉的诊断自动瞄准方法,采用Mask R-CNN算法并以大量模拟瞄准图进行靶标识别训练,有效解决了靶标自动判读问题,对靶标识别误差控制在8个像素点以内;同时基于实验室瞄准测试平台开展了靶标像素偏差与瞄准坐标偏离关系的离线标定,开展了算法引导下的瞄准精度测试,根据测试结果预估指向瞄准精度优于30μm、径向瞄准精度优于50μm,对实现诊断设备的高精度自动瞄准有一定的基础参考价值。

应用于多层靶准等熵压缩实验的反积分方法

针对磁驱动和激光驱动准等熵压缩实验物理中多层结构靶设计和实验数据处理的需求,在反积分处理方法的基础上,提出了多层靶的层间传递方法,实现了多层靶内加载历史的反演计算。通过正、反积分数值实验以及激光驱动实验的正、反计算,验证了多层靶中反积分数据处理方法的有效性,在绝大部分计算范围内,多层靶的反积分处理精度可以达到1%以内。利用反积分方法开展了多层靶物理实验的波形设计,并分析了不同厚度胶层的多层靶对斜波加载实验的影响。

基于深度学习的钻孔辐射压离子加速建模

超短超强激光脉冲与固体靶相互作用可通过钻孔辐射压加速机制产生百MeV量级的离子束,离子束的品质强烈依赖于激光和靶的作用参量.本文以近400组激光驱动固体靶的粒子模拟结果作为数据集,以激光强度、靶密度、靶厚和离子质量作为输入参量,基于全连接神经网络建立了一个离子峰值能量和截止能量连续映射模型.该模型用较为稀疏的参量取值获得了较大参量范围内的分析结果,大大减少了多维参量大范围扫参的计算量.基于连续映射模型的结果,得到了钻孔辐射压加速机制下离子峰值能量的修正公式和截止能量的拟合公式,可为激光离子加速的实验设计提供重要参考.

RDX驱动台阶式飞片的速度试验研究

为提高RDX驱动台阶式飞片的可靠性,基于光子多普勒测速技术(Photonic Doppler Velocimetry,PDV)搭建了激光点火RDX驱动台阶式钛合金飞片的速度测试系统,试验研究了RDX装药量、飞片剪切厚度及飞片厚度对飞片速度的影响。结果表明:当装药量从40 mg增加至85 mg,飞片峰值速度由494.46 m·s^(-1)线性增加至591.86 m·s^(-1);当飞片剪切厚度从0.2 mm增加至0.8 mm,飞片峰值速度由508.98 m·s^(-1)线性增加至557.53 m·s^(-1);当飞片厚度从1.0 mm增加至2.5 mm,飞片峰值速度由561.32 m·s^(-1)指数衰减至397.34 m·s^(-1),同时飞片动能由1.347J线性增加至1.688 J。因此,通过增加RDX装药量、飞片剪切厚度或飞片厚度可以提高RDX驱动飞片冲击起爆的可靠性。

小型激光器驱动飞片的平均速度测量研究

提出了一种小型激光器驱动飞片的平均速度测量方法 ,即利用石英晶体的压电效应可以最终得到飞片的平均速度。详细介绍了激光驱动飞片的过程 ,石英计的设计等 ,对系统的响应灵敏度和实验数据进行了分析 ,结果显示 :这一方法具有简单可靠的特点 。

激光惯性约束聚变靶靶丸制备与表征

激光惯性约束聚变的核心思想是利用球形内爆技术对聚变燃料进行增压,使热核燃料达到高温、高密度的等离子体状态,进而实现聚变点火。基于对称压缩、流体界面不稳定性和实验诊断的考虑,ICF实验对作为热核燃料容器的空心微球的品质在球形度、壁厚均匀性、表面粗糙度以及掺杂水平等方面提出了严格的要求。为满足这些要求,陆续发展了乳液微封装技术、降解芯轴技术、低压等离子体聚合/掺杂技术、干凝胶玻璃微球制备技术等用于多层塑料微球和空心玻璃微球的研制。另一方面,针对ICF靶丸量小、质轻以及表面要求高的特点,发展了相应的非破坏性靶丸参数表征技术,如X光照相技术、4π形貌表征技术、微球掺杂水平测量技术以及微球内燃料负载水平快速测试技术。基于这些制备与表征技术,初步实现了多层塑料微球、玻璃微球、聚-!-甲基苯乙烯芯轴微球、梯度掺杂CH微球的研制,满足了"神光Ⅱ"、"神光Ⅲ原型"及"神光Ⅲ主机"上开展的一系列内爆物理实验的要求,同时为未来点火物理实验用靶丸的研制提供了技术支撑。