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利用单电子在固体靶表面准静态电磁场中运动的模型和非线性汤姆孙散射理论,研究了以大角度斜入射的强激光照射在固体靶表面产生的沿靶面方向发射的高能超热电子的运动及其产生的电磁辐射脉冲. 数值模拟表明,靶表面的电子在靶面附近的准静态电磁场和反射的激光场中作振荡. 当电子振荡频率接近激光频率时,电子被有效加速,被加速的电子主要沿靶面方向运动并产生向前的阿秒脉冲辐射. 讨论了电子在加速前的不同初始速度分布对辐射脉冲的时间和空间特性的影响,模拟了不同初始状态的多电子相干辐射脉冲的频谱特性.
关键词:
表面准静态电磁场
超热电子
阿秒脉冲
相干辐射 相似文献
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提出了一种利用脉冲光声技术测量固体介质中声速的方法,建立了由YAG激光器和超声探测器组成的实验系统,脉冲激光在固体表面产生脉冲超声波,通过测量脉冲声波在固体内多次反射后的出射信号及固体的厚度,即可算出固体介质中的声速.对黄铜及铝的测量结果表明,这是一种准确性较高的固体介质中声速测量方法.该测量方法可作为综合设计性物理实... 相似文献
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激光超声无损检测技术 总被引:1,自引:0,他引:1
传统的无损检测方法具有一定的局限性,例如:在高温高压、高湿、有毒等某些恶劣检测环境中,或被测工件具有放射性或腐蚀性,以及被测工件具有较快的运动速度时,已不能完全满足要求。因此,人们一直都在努力寻找适合于上述情况的无损检测方法。这里介绍一种激光超声检测技术,它是利用激光脉冲激发超声从而实现无损检测的一种方法,已逐渐成为材料无损检测的一种重要手段。本文详细介绍了激光超声的检测原理及应用,并指出目前尚存在的问题及解决措施。激光超声的激发原理激光超声是指用脉冲激光在介质中所产生的超声波或利用激光来产生超声这一物理过程。激光可以在固体中产生超声,也可以在气体和液体中产生超声。 相似文献
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采用时间与空间分辨光谱测量技术,研究了在Ar气为缓冲气体下,用脉冲Nd:YAG激光烧蚀A1产生等离子体遥发射光谱及其随气压的变化规律,对粒子的激发机理进行了讨论认为特征谱线是由复合辐射为主要机理,并用此结论在一定程序上解释了实验结果。 相似文献
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采用紧聚焦的超强短脉冲激光与固体通道靶相互作用是获得大电量、高准直相对论电子束的一种有效方式。实验中由于激光预脉冲烧蚀靶壁产生预等离子体会膨胀、填充到真空通道中,从而导致电子束品质发生变化。采用二维PIC粒子模拟程序研究了通道靶中填充预等离子体的电子加速过程。模拟结果显示,在功率密度为5.0×10^(20W/cm^(2))的超强短脉冲激光条件下,通道中填充一定密度的等离子体时激光场优先与低密度等离子体相互作用,激光脉冲与通道壁的相互作用减弱,电子加速机制由纵向场主导的真空电子加速转变为横向电场主导的等离子体电子加速,产生电子束具有更大的电荷量,但能量降低,发散角增大。 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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H. Ring R.T. Carter J.R. Huber 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(1):73-81
We demonstrate the application of a pulsed magnetic field for the creation and manipulation of coherences in molecular systems,
using quantum beat spectroscopy for the detection of the dynamics of the molecular superposition states. In all cases, the
experiments are performed on energy levels in electronically excited states of the (jet-cooled) CS2 molecule populated by a short laser pulse. In the basic experiment, following excitation of initially degenerate Zeeman sublevels
under zero field conditions with suitable laser polarization, quantum beats are generated at the moment the magnetic field
is switched on, even when the field is delayed by several excited state lifetimes. By quenching of the field, it is shown
that the molecule may be “frozen” in any superposition state of the participating sublevels. Using a combination of static
and pulsed fields with different orientations, the molecule can be prepared in a more general state, described by coherences
among all Zeeman substrates. This is achieved by choosing an appropriate time delay for the switched field, without any change
to the geometrical parameters of the experiment such as laser polarization or detection direction. Numerical simulations of
these dynamical coherence phenomena have been performed to support assignment and interpretation of the experimental results.
Received: 8 April 1998 / Accepted: 3 June 1998 相似文献
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A method is developed to obtain the photoacoustic spectra of solids by immersing them in a liquid cell with a submersed tranducer and detecting the acoustic pulse generated due to bulk absorption of pulsed laser radiation in the solids. Proper choice of liquids enables spectra to be obtained which are independent of the optical properties of the solid surfaces of the surrounding liquid. This technique is compared to other established PAS methods. 相似文献
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Yasuhiro Maeda Masaki Yumoto Norihito Saito Takayo Ogawa Kazuo Kurokawa Akihiko Nakano Masafumi Yamashita Satoshi Wada 《Optical Review》2010,17(3):305-308
We have achieved a rapid and random wavelength tuned picosecond pulsed laser and a widely tunable UV-blue picosecond pulsed
laser by using the intracavity second harmonic generation of the laser. The tuning range was from 384 to 434 nm with picosecond
pulse oscillation. In addition, we demonstrated biological imaging using a fluorescent protein excited by the widely tunable
UV-blue picosecond pulsed laser. We found that the laser is suitable for biological imaging using the fluorescent protein
as an excitation light source without damages. 相似文献
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A plastic-clad optical fibre system has been examined as a delivery system of pulsed laser energy for the generation of ultrasound. The onset of significant optical damage caused by the laser has been investigated. By using multimode fibres of 1 m length with 600 μm core size, it was found that laser power densities from the fibre were sufficient to produce ultrasonic waveforms corresponding to both the thermoelastic and plasma generation regimes. Out-of-plane acoustic displacements of >250 pm can be achieved through 2.5 cm thick aluminium test samples, showing that fibre optical delivery systems may be considered in systems using laser-generated ultrasound for non-destructive testing applications. 相似文献
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A. A. Makarov G. N. Makarov A. A. Puretzky V. V. Tyakht 《Applied Physics A: Materials Science & Processing》1980,23(4):391-401
Basic experimental characteristics of collisionless luminescence of OsO4 molecule excited by pulsed ir laser radiation are presented. The theoretical model of the process is developed and a comparison
with experiment is carried out both for one-frequency and two-frequency ir excitation. From such comparison information is
obtained on the fraction of molecules excited by laser radiation as well as on the spectroscopic characteristics of highly
excited states. 相似文献
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Radiation from a CO2 laser-produced plasma has been used to produce laser action in CdS at 5260 Å. This technique compares favorably with optical pumping of CdS by 3371 Å radiation from a pulsed N2 laser and its potential as a new source for the optical pumping of solids at short wavelengths is strongly indicated. 相似文献
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多纵模高光谱分辨率激光雷达是一种新型的高光谱分辨率激光雷达.本文在研究典型高功率Nd:YAG脉冲激光器的多纵模模式及其在大气中传输的气溶胶米散射和瑞利散射光谱的基础上,设计紫外域多纵模高光谱分辨率激光雷达系统,采用窄带干涉滤光片滤除太阳背景光的影响,设计可调谐马赫-曾德尔干涉仪,分离提取多纵模激光回波中的气溶胶米散射和瑞利散射光谱,并利用马赫-曾德尔干涉仪双通道输出的互补性原理,精确反演气溶胶光学参量.系统仿真结果表明,所设计的紫外域多纵模高光谱分辨率激光雷达能够实现10 km高度内的气溶胶光学参量精细探测. 相似文献
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The scanning laser source (SLS) technique is a promising new laser ultrasonic tool for the detection of small surface-breaking defects. The SLS approach is based on monitoring the changes in laser generated ultrasound as a laser source is scanned over a defect. Changes in amplitude and frequency content have been observed for ultrasound generated by the laser over uniform and defective areas. In this paper, the SLS technique is simulated numerically using the mass spring lattice model. Thermoelastic laser generation of ultrasound in an elastic material is modeled using a shear dipole distribution. The spatial and temporal energy distribution profiles of typical pulsed laser sources are used to model the laser source. The amplitude and spectral variations in the laser generated ultrasound as the SLS scans over a large aluminum block containing a small surface-breaking crack are observed. The experimentally observed SLS amplitude and spectral signatures are shown to be captured very well by the model. In addition, the possibility of utilizing the SLS technique to size surface-breaking cracks that are sub-wavelength in depth is explored. 相似文献