共查询到19条相似文献,搜索用时 187 毫秒
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双色激光场对运动原子的辐射压力 总被引:3,自引:2,他引:1
本文研究了双色行波场对运动原子的辐射压力,通过数值计算,分别得到了在不同光强,不同频率,不同传播方向条件下,原子在双色场中的受激跃迁速率和辐射压力随速度变化的关系。结果表明:双色场对原子的辐射压力和行波场及驻波场相比,有着许多不同特点,这些特点可以在激光冷却中性原子,原子速度选择,原子动量扩散的研究中加以利用。 相似文献
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从双色激光场中运动原子的受激跃迁速率和激光场对原子的辐射压力关系出发,讨论了运动原子在驻波场中速度聚集效应产和珠原因及其与多光子过程的关系,给出了聚速效应出现的条件,预言了极值聚速速度的存在,通过简单的,变换,将驻波场原五速度聚集效应的相结论推广至双色激光场。 相似文献
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激光驻波场作用下原子束横向速度聚束 总被引:1,自引:0,他引:1
分别从理论和实验上研究了在负失谐强激光驻波场作用下,原子速度聚集在某一特定速度附近的现象,即速度聚束,产生速度聚束的原因是,当原子的速度小于某一临界速度时,激光对原子的辐射压力加热原子,而当原子速度大于这个临界速度时则冷却原子,因此原子将伙集于这个临界速度附近。 相似文献
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原子间的偶极相互作用对其在腔场中辐射谱的影响 总被引:19,自引:5,他引:14
研究了两个通过偶极-偶极力关联的两能级原子在单模腔场中的辐射谱,发现原子间偶极-偶极力的贡献;使辐射谱偏离关于中心频率的对称性.对真空场和强场情况作了细致的讨论. 相似文献
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利用激光驻波场会聚原子沉积纳米结构的技术可以用来研制纳米结构长度传递标准.当激光驻波场的频率大于原子的共振频率时,原子由于受到偶极力的作用将被会聚到驻波的波节处.采用了一种新的技术方案减小了实验对大的激光功率的要求.利用激光驻波场会聚准直性较好的Cr原子,并使其沉积在硅基片上形成纳米光栅结构.经原子力显微镜测试表明纳米光栅的周期为215 nm.
关键词:
激光偶极力
纳米计量
原子沉积
蓝失谐 相似文献
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Diversity of biomedical applications of acoustic radiation force 总被引:1,自引:0,他引:1
Armen Sarvazyan 《Ultrasonics》2010,50(2):230-234
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In this article we introduce the concept of multifrequency radiation force produced by a polychromatic acoustic beam propagating in a fluid. This force is a generalization of dynamic radiation force due to a bichromatic wave. We analyse the force exerted on a rigid sphere by a plane wave with N frequency components. Our approach is based on solving the related scattering problem, taking into account the nonlinearity of the fluid. The radiation force is calculated by integrating the excess of pressure in the quasilinear approximation over the surface of the sphere. Results reveal that the spectrum of the multifrequency radiation force is composed of up to N(N−1)/2 distinct frequency components. In addition, the radiation force generated by plane progressive waves is predominantly caused by parametric amplification. This is a phenomenon due to the nonlinear nature of wave propagation in fluids. 相似文献
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A. V. Razin 《Radiophysics and Quantum Electronics》2006,49(7):520-534
We study excitation of acoustic, leaky, and surface waves by a time-harmonic force source located in a homogeneous isotropic
elastic half-space contacting a homogeneous gas. The force acts in the normal direction to the interface between the media.
We consider the case where the sound velocity in the gas is less than the velocity of the Rayleigh wave propagating along
the surface of the solid. An expression is derived for the period-averaged radiation power of the surface Stoneley wave. The
total radiation power is calculated for the acoustic wave in the gas and for the leaky pseudo-Rayleigh wave. Variations in
the radiation powers of the surface and leaky waves are analyzed as functions of the source depth. If the velocities of compressional
and shear waves in the elastic medium significantly exceed the sound velocity in the gas, then the radiation power of the
Stoneley wave turns out to be a factor of 106–108 smaller than the radiation powers of other waves. The radiation power of the Stoneley wave decreases monotonically with increasing
source depth, and the decrease becomes more pronounced with the increase in the difference between the acoustic impedances
of the contacting media. If the shear-wave velocity in the solid is close to the sound velocity in the gas, then the radiation
power of the Stoneley wave is comparable with the radiation powers of other waves and exhibits maximum at a certain source
depth. For some parameters of the gas and the solid, and for certain source depths, the Stoneley wave carries away more than
a half of the total radiation power. It is shown that, for certain relations between the parameters of the media, the radiation
power of the Stoneley wave increases due to redistribution of the radiated power from the pseudo-Rayleigh leaky wave. The
total power of these waves remains approximatly constant and, with accuracy of the order of 10−3, is equal to the radiation power of the Rayleigh wave at the vacuum-solid interface. It is shown that the acoustic-wave power
which can be transmitted to the upper layers of the atmosphere during an earthquake does not exceed 0.01% of the total power
radiated at a given frequency.
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Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 7, pp. 577–592, July 2006. 相似文献
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The onset of the wave resistance, via generation of capillary-gravity waves of a small object moving with velocity V, is investigated experimentally. Because of the existence of a minimum phase velocity V(c) for surface waves, the problem is similar to the generation of rotons in superfluid helium near their minimum. In both cases waves or rotons are produced at V>V(c) due to Cherenkov radiation. We find that the transition to the wave drag state is continuous: in the vicinity of the bifurcation the wave resistance force is proportional to sqrt[V-V(c)] for various fluids. 相似文献
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A mean force exerted on a small rigid sphere by a sound wave in a viscous fluid is calculated. The force is expressed as a sum of drag force coming from the external steady flow existing in the absence of the sphere and contributions that are cross products of velocity and velocity derivatives of the incident field. Because of the drag force and an acoustic streaming generated near the sphere, the mean force does not coincide with the acoustic radiation pressure, i.e., the mean momentum flux carried by the sound field through any surface enclosing the sphere. If the sphere radius R is considerably smaller than the viscous wave penetration depth delta, the drag force can give the leading-order contribution (in powers of delta/R) to the mean force and the latter can then be directed against the radiation pressure. In another limit, delta< or =R, the drag force and acoustic streaming play a minor role, and the mean force reduces to the radiation pressure, which can be expressed through source strengths of the scattered sound field. The effect of viscosity can then be significant only if the incident wave is locally plane traveling. 相似文献
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F. G. Mitri 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,43(3):379-386
In this study, the acoustic radiation force resulting from the interaction
of a plane progressive wave with a coated sphere was examined. The linear
acoustic scattering problem was obtained first by solving the classical
boundary conditions to obtain the required coefficients. The radiation force
was then determined by averaging the momentum flux tensor expressed in terms
of the total scattering pressure or velocity potential in an ideal fluid.
Numerical calculations of the radiation force function Yp , which is the
radiation force per unit energy density and unit cross-section, were
displayed versus the dimensionless size parameter x=k1 b (k1 is the
wave number in the exterior fluid and b the radius of the uncoated sphere)
over a large range of frequencies. Particular emphasis has been focused on
the coating thickness and the absorption of sound inside the outer covering
layer. The fluid-loading effect on the radiation force function curves was
also analysed. 相似文献
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In nonlinear acoustic regime, a body insonified by a sound field is known to experience a steady force that is called the acoustic radiation force (RF). This force is a second-order quantity of the velocity potential function of the ambient medium. Exploiting the sufficiency of linear solution representation of potential function in RF formulation, and following the classical resonance scattering theorem (RST) which suggests the scattered field as a superposition of the resonant field and a background (non-resonant) component, we will show that the radiation force is a composition of three components: background part, resonant part and their interaction. Due to the nonlinearity effects, each part contains the contribution of pure partial waves in addition to their mutual interaction. The numerical results propose the residue component (i.e., subtraction of the background component from the RF) as a good indicator of the contribution of circumferential surface waves in RF. Defining the modal series of radiation force function and its components, it will be shown that within each partial wave, the resonance contribution can be synthesized as the Breit-Wigner form for adequately none-close resonant frequencies. The proposed formulation may be helpful essentially due to its inherent value as a canonical subject in physical acoustics. Furthermore, it may make a tunnel through the circumferential resonance reducing effects on radiation forces. 相似文献
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This paper derives the force of the electromagnetic radiation on left-handed materials (LHMs) by a direct applica-tion of the Lorentz law of classical electrodynamics.The expressions of radiation force are given for TE-polarised and TM-polarised fields.The numerical results demonstrate that electromagnetic waves exert an inverse lateral radiation force on each edge of the beams,that is,the lateral pressure is expansive for TE-polarised beams and compressive for TM-polarised beams.The investigation of the radiation force will provide insights into the fundamental properties of LHMs and will provide to better understanding of the interaction of light with LHMs. 相似文献