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