Coherent radiation from thin films

Abstract

The spontaneous coherent radiation from thin crystal films of $n$ layers is studied. By treating each layer as a unit and by employing the method of multiple-time-scale expansion, exact solutions for such systems, with no restriction on the value $\frac{{\lambda }_0}{d}$, are found. Here ${\lambda }_0$ is the characteristic radiation wavelength and $d$ is the average interparticle spacing. In the limit $\frac{{\lambda }_0}{d}\gg 1$, it is seen that there exist correlated states of the film which are exact analog of Dicke's superradiant states. The decay rate for the superradiant states is roughly enhanced by a factor of $n{\left(\frac{{\lambda }_0}{d}\right)}^2$ compared to the single-atom decay rate ${\gamma }_s$.