93,020 research outputs found

    Photon echoes of molecular photoassociation

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    Revivals of optical coherence of molecular photoassociation driven by two ultrashort laser pulses are addressed in the Condon approach. Based on textbook examples and numerical simulation of KrF excimer molecules, a prediction is made about an existence of photon echo on free-bound transitions. Delayed rise and fall of nonlinear polarization in the half-collisions are to be resulted from the resonant quantum states interference whether it be in gas, liquid or solid phases.Comment: 15 pages and 5 figures presented at ICONO '98'(Moscow, 1998): Fundamental Aspects of Laser-Matter Interaction, New Nonlinear Optical Materials and Physics of Low-Dimensional Structure

    Scattering of electromagnetic waves by small impedance particles of an arbitrary shape

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    An explicit formula is derived for the electromagnetic (EM) field scattered by one small impedance particle DD of an arbitrary shape. If aa is the characteristic size of the particle, λ\lambda is the wavelength, a<<λa<<\lambda and ζ\zeta is the boundary impedance of DD, [N,[E,N]]=ζ[N,H][N,[E,N]]=\zeta [N,H] on SS, where SS is the surface of the particle, NN is the unit outer normal to SS, and EE, HH is the EM field, then the scattered field is Esc=[g(x,x1),Q]E_{sc}=[\nabla g(x,x_1), Q]. Here g(x,y)=eikxy4πxyg(x,y)=\frac{e^{ik|x-y|}}{4\pi |x-y|}, kk is the wave number, x1Dx_1\in D is an arbitrary point, and Q=ζSiωμτ×E0Q=-\frac{\zeta |S|}{i\omega \mu}\tau \nabla \times E_0, where E0E_0 is the incident field, S|S| is the area of SS, ω\omega is the frequency, μ\mu is the magnetic permeability of the space exterior to DD, and τ\tau is a tensor which is calculated explicitly. The scattered field is O(ζa2)>>O(a3)O(|\zeta| a^2)>> O(a^3) as a0a\to 0 when λ\lambda is fixed and ζ\zeta does not depend on aa. Thus, Esc|E_{sc}| is much larger than the classical value O(a3)O(a^3) for the field scattered by a small particle. It is proved that the effective field in the medium, in which many small particles are embedded, has a limit as a0a\to 0 and the number M=M(a)M=M(a) of the particles tends to \infty at a suitable rate. Thislimit solves a linear integral equation. The refraction coefficient of the limiting medium is calculated analytically. This yields a recipe for creating materials with a desired refraction coefficient