激光与材料相互作用研究中的气体物理学

强激光辐照材料时,烧蚀蒸气吸收部分或全部激光辐射,成为部分离化等离子体.它的传播称为激光支持的吸收波(LSAW).LSAW屏蔽入射激光,同时发射易被材料表面吸收的短波长辐射.研究这些过程,可用辐射流体力学描述蒸气的运动。为了求解辐射流体力学方程,必须利用气体物理力学方法,算出蒸气的状态方程和不透明度.本文对涉及的一些气体物理力学问题,进行了概略介绍.     

核武器研制中的力学问题

 简要介绍了核武器研制中遇到的力学问题,涉及固体力学、流体力学、化学反应流体力学、辐射流体力学等学科.介绍了核武器研制中力学问题的特点, 即与各种物理问题的强耦合, 学科的交叉.     

《力学名词》已定稿付印

经过7年的工作,《力学名词》(第一批)已审定、定稿付印,将在1993年公布.这次公布的名词,共2500多条,分成5个部分:通用词(普通物理中力学部分、理论力学和材料力学),一般力学,固体力学,流体力学,以及其他(交叉,应用学科和新分支).除了委员会成员的工作外,学会一些专业会议(如“三流”专业会议)和个人(如梅凤翔)提供了不少有用的材料.定     

《力学名词》已定稿付印

<正> 经过7年的工作,《力学名词》(第一批)已审定、定稿付印,将在1993年公布.这次公布的名词,共2500多条,分成5个部分:通用词(普通物理中力学部分、理论力学和材料力学),一般力学,固体力学,流体力学,以及其他(交叉,应用学科和新分支).除了委员会成员的工作外,学会一些专业会议(如“三流”专业会议)和个人(如梅凤翔)提供了不少有用的材料.定     

国际计算力学协会(IACM)将举行第二届计算力学会议(WCCM)

由国际计算力学协会举办的第二届计算力学世界大会(World Cougress on Computational Mechanics)将于1990年8月27—31日在西德斯图加特举行.征稿内容包括固体力学、流体力学、应用物理与化学、计算机及数值方法四大部分.该大会的联系人姓名、地址为:     

国际计算力学协会(IACM)将举行第二届计算力学会议(WCCM)

<正> 由国际计算力学协会举办的第二届计算力学世界大会(World Cougress on Computational Mechanics)将于1990年8月27—31日在西德斯图加特举行.征稿内容包括固体力学、流体力学、应用物理与化学、计算机及数值方法四大部分.该大会的联系人姓名、地址为:     

爆室内强爆炸中的流固耦合计算

为评估强爆炸的毁伤效应,在已有的辐射流体力学及结构动力学响应部分工作的基础上,本文采用流固耦合方法对耦合界面进行了处理,并考虑辐射输运引起的能量沉积过程,使得强爆炸产生的辐射波、冲击波和结构动力学响应两部分可以较好地耦合计算,从而能够较完整地模拟爆室内强爆炸的辐射流体动力学过程.计算结果与定性物理分析相符,证明了算法的...     

与实验固体力学有关的几个光学问题

.前言力学与光学都是较成熟的学科,过去两个学科虽自独立地发展,但从历史角度来看光学经常是由于力学技术的发展而被促进.近年来,激光技术结合空气动力学创造出强有力的高能激光器,它为瞬间摧毁敌机或导弹提供可能手段.激光核聚变应用了流体力学、磁流体力学理论,再结合其他学科理论提出了向心压缩聚爆理论,所需加热激光能量大大减少,从而提供了一条获得聚变能的可能途径.同样,激光技     

关于流体力学方法论问题

 力学是以实验为基础的科学. 流体力学中绝大多数重要的概念和原理都源于实验. 对 于流体力学问题，数值模拟与物理实验的本质区别并未消失；数值模拟不能代替物理实验， 大规模数值模拟的结果仍需由巧妙设计的物理实验来检验其正确性.     

工程力学要为我国经济建设服务

今天和大家座谈,我想讲下面四个问题:1.什么是工程力学?物理学家认为,力学是物理的一部分.这是指古典力学而言的.但工程力学不同于古典力学.十九世纪古典力学基本上处于停滞阶段.Love 教授关于弹性力学的书及 Lamb 教授关于流体力学的书是前一时期固体力学与流体力学的发展最高水平的总结.本世纪二十、三十年代,用已有的理论和方法已不能解决工 ...     

Water vapor cooling when radiation of wavelength λ=2.8 μm is absorbed

Investigations of the processes arising under the influence of electromagnetic radiation on resonantly absorbing gaseous media have now been widely developed. Particular interest is shown in the penetration of a pulse of laser radiation through the atmosphere. The main component absorbing the radiation of both CO₂ and HF lasers (wavelengths, respectively, 10.6 and 2.8 m) in the earth's atmosphere is water vapor [1]. Numerous experimental investigations show that the integrated coefficient of laser radiation absorption by water vapor is fairly large [1–3], while at the same time the energy absorption leads to the heating of the medium in a channel around the beam and, as a consequence, to its defocusing. However, all these investigations were carried out with continuous sources of laser radiation or with pulses of fairly great duration. It will be shown below that gas cooling in the channel around the beam is possible when a pulse of radiation with wavelength 2.8 m whose duration is less than the vibrational-translational (V-T) relaxation time of the energy absorbed by the H₂O molecules passes through a stationary medium containing water vapor.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 141–151, May–June, 1986.     

Effect of the recoil pressure induced by evaporation on motion of powder particles in the light field during laser cladding

A model is proposed, which takes into account acceleration of powder particles by a force induced by recoil of material vapors from the irradiated region of the particle surface. Results of a numerical analysis of heat and mass transfer in the case of motion of individual stainless steel powder particles in a gas flow and in a light field of laser radiation under conditions of laser cladding are presented. Acceleration of particles is found to depend on their diameter, carrier gas velocity, powder material properties, laser radiation power, and degree of attenuation of the power density in the laser beam in the direction of its action on the substrate. The calculated results are compared with experimental data on light-propulsion acceleration of individual particles (of aluminum, aluminum oxide, and graphite) under the action of pulsed laser radiation.     

Simultaneous high speed digital cinematographic and X-ray radiographic imaging of a intense multi-fluid interaction with rapid phase changes

As typical for the study of the vapor explosions, the qualitative and quantitative understanding of the phenomena requires visualization of both material and interface dynamics. A new approach to multi-fluid multiphase visualization is presented with the focus on the development of a synchronized high-speed visualization by digital cinematography and X-ray radiography. The developed system, named SHARP (simultaneous high-speed acquisition of X-ray radiography and photography), and its image processing methodology, directed to an image synchronization procedure and a separate quantification of vapor and molten material dynamics, is presented in this paper. Furthermore, we exploit an intrinsic property of the X-ray radiation, namely the differences in linear mass attenuation coefficients over the beam path through a multi-component system, to characterize the evolution of molten material distribution. Analysis of the data obtained by the SHARP system and image processing procedure developed granted new insights into the physics of the vapor explosion phenomena, as well as, quantitative information of the associated dynamic micro-interactions.     

Model of explosive pulsed vaporization of dielectric liquids by intense laser irradiation of their surfaces

The mechanism of explosive vaporization interaction of laser radiation with matter is studied theoretically. It is shown that, in dielectric liquids with a free surface, periodic explosive boiling is possible if the laser radiation intensity exceeds the rate of heat transfer from the region of laser radiation absorption. Analytical expressions are obtained to estimate the pulsating boiling period and the thickness of the surface liquid layer dispersed by fluctuation vapor bubbles during each boiling. The degree of absorption of laser radiation by the aerosol formed above the liquid surface is estimated. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 6, pp. 17–24, November–December, 2008.     

Laser heating of its erosional low-temperature plasma in the process of gasdynamic motion

A study is made of the gasdynamical and optical properties of erosional laser plasma jets in the presence and absence of laser radiation. It is shown that in processes of plasma formation during the action of laser radiation of moderate intensity (q 10⁷ W/cm²) on absorbing materials, the heating of the disintegration products by the attacking laser radiation plays an important role. The temperature distribution is obtained along the plasma jet which forms during the laser attack counter to its propagation in a quartz tube confining the dispersion. The temperature maximum is found at the exit from the tube, is caused by the heating of the erosional laser plasma by the incident laser radiation in the process of its one-dimensional gasdynamical motion, and indicates the screening of the surface from the laser radiation. It is established that the screening is affected by the gasdynamical structure of the plasma jet and by the spacing of the plasma clusters corresponding to the regular pulses of laser radiation.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 13–18, January–February, 1974.The authors are grateful to M. A. El'yashevich for his interest in the work.     

Real-time determination and controlof the laser-drilled holes depth

We present an optodynamical method for the real-time determination of the depth of laser-drilled holes. The method consists of the detection of shock waves generated during the interaction of the laser beam with the irradiated material using a piezoelectric transducer (PZT), and measurement of the shock waves propagation time through the sample using the PZT signal. The experimental observations reveal that the propagation time has an almost exponential decay with the number of pulses and is strongly dependent on the laser radiation wavelength. The quantity of ablated substrate material per laser pulse is a nonlinear function of the number of consecutive laser pulses incident on the same spot at the irradiated sample surface.Received: 29 September 2003, Accepted: 30 September 2004, Published online: 27 January 2005[/PUBLISHED]Correspondence to: M. Stafe and C. Negutu     

A plasma wiggler beamline for 100 TW to 10 PW lasers

We introduce the theoretical framework of laser wakefield acceleration and plasma wiggler radiation generation in the matched regime, give scaling laws and apply the scheme to laser systems planned for the near future. We compare the anticipated electron and x-ray beam parameters for a 100 TW, 1 PW and 10 PW short pulse Ti:Sapphire laser with previous experimental results. Depending on the chosen laser configuration, x-rays from a plasma wiggler beamline (PWB) can be several orders of magnitude brighter than current betatron sources, and comparable to or better than 3rd generation synchrotron facilities. Furthermore, increasing the laser power from 0.1 to 10 PW, the spectral peak of the betatron radiation shifts into the hard x-ray and γ-ray regime. We also discuss a basic layout of a PWB and motivate 100 TW, 1 PW and 10 PW beamlines with a wide range of uses, experiments and applications. The ability to couple the PWBs with various optical laser drivers has the potential to facilitate uses across the spectrum of light source applications.     

Modeling of the Free-Surface Shape in Laser Cutting of Metals. 1. Effect of Polarization of the Gaussian Beam on the Shape of the Surface Formed

A three-dimensional problem of describing the shape of a surface formed owing to interaction of laser radiation with a substance in processes of laser cutting of metals is considered. The effect of radiation polarization (linear, elliptic, and circular) on the absorption factor is analyzed. For calculating the latter, a generalized formula is proposed, which takes into account the spatial orientation of the plane of incidence of radiation. The influence of laser-radiation parameters on the surface shape and cut depth is studied numerically. In the case of generation of a beam with the TEM₀₀ mode, it is shown that the use of elliptic polarization of radiation with a certain ratio of semi-axes, aligned with the beam direction, is preferable.     

Sound generation by a laser beam in a liquid with absorbing particles

Sound generation by a laser beam within a liquid, related to liquid boiling at absorption centers, has been studied relatively little. Acoustic effects upon liquid boiling in a laser beam were first reported in [1]. A change in the index of refraction of a liquid has been observed under the action of acoustical radiation of microbubbles formed on absorbing particles in the zone irradiated by a laser beam [2–4]. However direct measurements of acoustical radiation from a set of microbubbles uniformly distributed over the volume of laser beam-liquid interaction has yet to be performed, to the authors' knowledge. The present study is a preliminary report of results of an experimental study of this class of opticoacoustical phenomena.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 9–12, January–February, 1984.In conclusion, the authors consider it their pleasant duty to thank G. A. Askar'yan for evaluating the study and S. V. Luk'yanov for assistance in measuring the particle size distribution.