93,020 research outputs found

### Photon echoes of molecular photoassociation

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

An explicit formula is derived for the electromagnetic (EM) field scattered
by one small impedance particle $D$ of an arbitrary shape. If $a$ is the
characteristic size of the particle, $\lambda$ is the wavelength, $a<<\lambda$
and $\zeta$ is the boundary impedance of $D$, $[N,[E,N]]=\zeta [N,H]$ on $S$,
where $S$ is the surface of the particle, $N$ is the unit outer normal to $S$,
and $E$, $H$ is the EM field, then the scattered field is $E_{sc}=[\nabla
g(x,x_1), Q]$. Here $g(x,y)=\frac{e^{ik|x-y|}}{4\pi |x-y|}$, $k$ is the wave
number, $x_1\in D$ is an arbitrary point, and $Q=-\frac{\zeta |S|}{i\omega
\mu}\tau \nabla \times E_0$, where $E_0$ is the incident field, $|S|$ is the
area of $S$, $\omega$ is the frequency, $\mu$ is the magnetic permeability of
the space exterior to $D$, and $\tau$ is a tensor which is calculated
explicitly. The scattered field is $O(|\zeta| a^2)>> O(a^3)$ as $a\to 0$ when
$\lambda$ is fixed and $\zeta$ does not depend on $a$. Thus, $|E_{sc}|$ is much
larger than the classical value $O(a^3)$ 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 $a\to 0$ and the number $M=M(a)$
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

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