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I.IntroductionTbegenerationofu1trasoundbytheirradiationofpulsedlaseratso1idsurfacehasbeenwidelystlldied,boththeorctica1lyandexpcrimentallyI1-8].Intheprocessoflaserthermoelasticg6nerationofu1trasound,temperatureriseinduccdbytheabsorptionoflaserenergyproducestherma1expansion,andthcnanultrasonicsourceiscreated.Sofar,thestudyof1asergenera-honofultrasoundinso1idsconcentratesmain1yonmeta1s,anduntilrecent1y,1ittleattentionhasbenpaidtonon-mctals.Inametal,1aserenergyisabsorbedonlyatthesurfaceofthesamp… 相似文献
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I. V. Amirkhanov A. Yu. Didyk D. Z. Muzafarov I. V. Puzynin T. P. Puzynina N. R. Sarkar I. Sarkhadov Z. A. Sharipov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(4):655-661
In our previous papers, the processes of formation and evolution of thermoelastic waves produced in metals under the action
of powerful pulsed beams of small-energy ions were studied using the system of thermoelasticity equations. In this paper,
the detailed numerical study of thermoelasticity processes taking into account temperature effects in the electronic and lattice
subsystems is carried out using a temperature model of the thermal peak and the system of thermoelasticity equations in the
case of propagation of a heavy ion through a condensed medium. New data and dependences are obtained. An analysis involving
the comparison between the obtained results and the results of previous papers is presented. 相似文献
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针对空气耦合超声信号微弱、难以直接测量的问题,进行了空气耦合超声声场测量的实验研究。使用激光多普勒测振仪测量由声波引起的激光路径上的介质折射率变化,进而得到空气和固体材料内部的时域瞬态声压。通过直接测量空耦换能器的辐射声功率,给出对单个空耦换能器灵敏度的直接评价方法。用空耦换能器激励K9玻璃板的漏兰姆波,观测到空气中的直达波和反射波、固体板内和空气中的漏兰姆波,实现了空气和固体中微弱声波的非侵入式实验测量,为空耦换能器的特性评估和空耦检测系统的声场测量提供了实验方法。 相似文献
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本文对应用激光超声方法检测金属基碳纤维增强复合材料,纳米陶瓷复合材料的声学和力学性质的进展,作了简要的介绍和讨论。 相似文献
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《Ultrasonics》2013,53(1):141-149
Laser-generation of ultrasound is investigated in the coupled dynamical thermoelasticity in the presented paper. The coupled heat conduction and wave equations are solved using finite differences. It is shown that the application of staggered grids in combination with explicit integration of the wave equation facilitates the decoupling of the solution and enables the application of a combination of implicit and explicit numerical integration techniques. The presented solution is applied to model the generation of ultrasound by a laser source in isotropic and transversely isotropic materials. The influence of the coupling of the generalized thermoelasticity is investigated and it will be shown, that for ultra high frequency waves (i.e. 100 GHz) generated by laser pulses with duration in the picosecond range, the thermal feedback becomes considerable leading to a strong attenuation of the longitudinal bulk wave. Moreover, the coupling leads to dispersion influencing the wave velocities at low frequencies. The numerical simulations are compared to theoretical results available in the literature. Wave fields generated by a line focused laser source are presented by the numerical model for isotropic and for transversely isotropic materials. 相似文献
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When a laser beam is absorbed in a semi-transparent material, a volume acoustic source is created owing to penetration of the laser beam inside the material and to thermoelastic transduction. Many experimental and theoretical studies have been conducted to better understand this ultrasound generation process with normal laser light incidence on the material surface. The purpose of this paper is to analyze the effects of the asymmetry caused by oblique incidence of a laser line source on the generation of acoustic waves in semi-transparent isotropic materials. Experiments on a glass plate demonstrate that such an obliquely incident laser light strongly affects bulk acoustic waves generation. Compressional and shear waves are enhanced and the loss of symmetry of the acoustic source causes asymmetrical behavior of the acoustic waves. Surprisingly, compressional-wave amplitude decreases whereas shear-wave amplitude increases in the region where the electromagnetic energy is refracted. This feature is explained by semi-analytical calculations. 相似文献
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It is proposed to use ultrasonic signals excited by a laser pulse to investigate the elastic properties (impedances, speeds
of sound, and densities) of layered media. The results of studying both a model medium with known parameters and a layered
composite are reported. The experimental data are in good agreement with the known properties of the samples investigated. 相似文献
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Hsin-Yi Tsai Ching Ching Yang Chih-Chung Yang Wen-Tse Hsiao Kuo-Cheng Huang 《Applied Physics A: Materials Science & Processing》2014,117(1):415-421
Laser ablation technology is used to isolate magnetic material to generate a local magnetic field effect. The impact of an induced magnetic field is enhanced by using the external magnetic field and can be widely employed to collect magnetic particles and position biomolecular in the bio-examination field. In addition, the magnetic field is affected and induced by the thermal stress produced after energy is exerted on the materials. Therefore, this study presents the phase of induced magnetic field (PIMF) of ferromagnetic film (Ni—1-μm thick) isolated using a 355-nm pulsed ultraviolet laser. In the experiment, three patterns comprising the following shapes and various isolated angle were designed for testing: hexagon (type I, 120°), L shape (type II, 90°), and cross shape (type III, 90°). The magnetic force microscopy image showed that when the isolating angle decreased, the PIMF increased, the value of which at the periphery of the corner of the type I and II patterns was ?3.96° and ?4.09°, respectively. In addition, by increasing the ablation time and residual thermal stress remaining in the material to increase the impact of the material’s properties when laser scanning speed was reduced from 1,000 to 500 mm/s, the PIMF value increased from ?4.09° to ?5.82°. The PIMF value of the type III pattern increased to ?9.87° because the residual thermal stress was twice that of the type II pattern. In the future, the experimental results can be used as a helpful reference for controlling magnetic particles in biomedical chips. 相似文献
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In this paper, an Eigenvector method (EM) for the calculation of optical resonator modes and beam propagation is introduced, in which the transit matrix of an optical resonator is obtained by dividing the mirror into finite grids based on the Fresnel–Kirchoff diffractive integral equation. Then, the eigenvectors, representing the multimode characteristics of the resonator, can be calculated by solving the integral matrix eigenequation. The merits of EM include that the considerably simpler procedure of solution of eigenvectors of the matrix eigenequation replaces the complicated iteration in traditional methods, and there is no dependence on the initial field distribution, and a number of modes can be derived once and the discrimination capability of the resonator can be evaluated easily. The examples using EM to simulate con-focal resonators with small or large Fresnel numbers are given, and the calculated results, well matched with Fox–Li method or Lagueree–Gaussian approximation analytical solution, prove that EM is highly feasible and reasonable. 相似文献
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Extension of high-order harmonic cutoff frequency by synthesizing the waveform of a laser field via the optimization of classical electron trajectory in the laser field 下载免费PDF全文
We theoretically investigate high-order harmonic generation by employing strong-field approximation (SFA) and present a new approach to the extension of the high-order harmonic cutoff frequency via an exploration of the dependence of high-order harmonic generation on the waveform of laser fields. The dependence is investigated via detailed analysis of the classical trajectories of the ionized electron moving in the continuum in the velocity-position plane. The classical trajectory consists of three sections (Acceleration Away, Deceleration Away, and Acceleration Back), and their relationship with the electron recollision energy is investigated. The analysis of classical trajectories indicates that, besides the final (Acceleration Back) section, the electron recollision energy also relies on the previous two sections. We simultaneously optimize the waveform in all three sections to increase the electron recollision energy, and an extension of the cutoff frequency up to Ip + 20.26Up is presented with a theoretically synthesized waveform of the laser field. 相似文献
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Excitations of thermoelastic waves in plates by a pulsed laser 总被引:4,自引:0,他引:4
The method of the eigenfunction expansion, also known as the expansion in normal modes, is employed to study numerically the axisymmetric excitation of the thermoelastic waves in plates by a pulsed laser. This method gives a systematic treatment and allows one to investigate not only the quasistatic and dynamic thermoelastic responses of pulsed photothermal deformation on the time scale of 1 s, but also the thermoelastic generation of longitudinal, transverse, and surface acoustic waves in thick materials, as well as the excitations of the Rayleigh-Lamb wave modes in thin plates. The formalism is particularly suitable for waveform analyses of the excitations of transient Lamb waves in thin plates because one needs only to calculate the contributions of several lower eigenmodes. The numerical technique provides a quantitative tool for the experimental determination of material properties, especially the mechanical and elastic properties of free-standing films and thicker sheet materials by thermoelastic detection. 相似文献
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Jijun Wang Zhonghua Shen Baiqiang Xu Xiaowu Ni Jianfei Guan Jian Lu 《Optics & Laser Technology》2007,39(4):806-813
The use of a pulsed laser for the generation of the elastic waves in non-metallic materials in the thermoelastic regime is investigated by using finite element method (FEM), taking into account not only thermal diffusion and the finite spatial and temporal shape of the laser pulse, but also optical penetration and the temperature dependence of material properties. The optimum finite element model is established based on analysis of two important parameters, meshing size and time step, and the stability of solution. Temperature distributions and temperature gradient fields in non-metallic material for different time steps are obtained, this temperature field is equivalent to a bulk force source to generate ultrasonic wave. The laser-generated ultrasound waveforms at the epicenter and surface acoustic waveforms (SAWs) are obtained and the influence of optical penetration into the material on the temperature field and the ultrasound waveforms are analyzed. The numerical results indicate that the heat penetration into non-metallic material is caused mainly by the optical penetration, and the ultrasound waveforms, especially the shape of the precursor, are strongly dependent on the optical penetration depth into non-metallic material. 相似文献
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建立了3维温度场及应力场模型,并采用有限元分析方法对Nd:YAG作为激活介质的固体热容激光器与热稳态固体激光器进行了对比研究。激光二极管阵列距离晶体3.5 mm,阵列功率2×4.2 kW,bar间隔0.4 mm,每bar发光面积为1 μm×5 mm,频率100 Hz,脉宽100 μs,Nd:YAG晶体初始温度20 ℃,冷却水温20 ℃。计算结果表明:热容模式激光介质的表面温度高于中心温度,稳态模式刚好相反, 稳态模式温差极值(19.8 ℃)是热容模式(6.4 ℃)的3.1倍,温度梯度极值(11.9 ℃/mm)是热容模式(2.46 ℃/mm)的4.8倍,热流密度极值(0.136 W/mm2)是热容模式(0.021 W/mm2))的6.4倍;稳态模式激光介质的表面出现张应力,中心出现压应力,热容模式则刚好相反,稳态模式压应力极值(18.27 MPa)是热容模式(12.1 MPa)的1.5倍,张应力极值(38.39 MPa)是热容模式(10.3 MPa)的3.9倍。由于晶体可以承受的压应力的破坏阈值远高于张应力,所以热容模式的固体激光器比稳态模式的固体激光器可以工作在更高的泵浦功率水平上。 相似文献
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Generating and detecting ultrasound is a standard method of nondestructive evaluation of materials. Pulsed lasers are used to generate ultrasound remotely in situations that prohibit the use of contact transducers. The scanning rate is limited by the repetition rates of the pulsed lasers, ranging between 10 and 100 Hz for lasers with sufficient pulse widths and energies. Alternately, a high-power continuous-wave laser can be scanned across the surface, creating an ultrasonic wavefront. Since generation is continuous, the scanning rate can be as much as 4 orders of magnitude higher than with pulsed lasers. This paper introduces the concept, comparing the theoretical scanning speed with generation by pulsed laser. 相似文献
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为探究临床常用的7 MHz高频聚焦超声在多层生物组织中的声传播以及毫秒级时间内的生物传热规律问题,基于Westervelt方程和Pennes传热方程,使用有限元方法建立高频聚焦超声辐照多层组织的非线性热黏性声传播及传热模型。首先分析了线性模型和非线性模型之间的差异,然后在非线性模型下探究换能器的参数对声场和温度场的影响。仿真结果显示:在7 MHz频率下,当换能器输出声功率超过5 W时,声波传播的非线性效应不可忽视(p <0.05);当声功率从5 W增大到15 W时,非线性模型与线性模型预测的温度偏差从20%增加到34.703%;高频聚焦超声波的非线性行为比低频更加显著,基频能量向高次谐波转移的程度增大,声功率为10 W和15 W时4次谐波与基波之比分别达到7.33%和12.12%;高频换能器参数的改变对组织中声场和温度场分布的影响较大,换能器焦距从12 mm减小到11.2 mm,焦点处最高温度增加了77%。结果表明,7 MHz聚焦超声的非线性声传播需要考虑到4次谐波的影响。该文提出的多层组织非线性仿真模型可为高频聚焦超声换能器参数优化及制定安全、有效的术前治疗方案提供理论参考。 相似文献
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利用热弹性理论分析了在光学材料中由于缺陷吸收激光能量引起的温度和热应力分布,并且针对一个简单的裂纹模型分析了热应力产生的应力强度因子,并且给出了一些主要参数对于应力强度因子的影响的规律。 相似文献
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