Coherent radiation from thin films
Y. C. Lee, P. S. Lee · Physical review. B, Solid state · 1974
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 $\frac{{\ensuremath{\lambda}}_{0}}{d}$, are found. Here ${\ensuremath{\lambda}}_{0}$ is the characteristic radiation wavelength and $d$ is the average interparticle spacing. In the limit $\frac{{\ensuremath{\lambda}}_{0}}{d}\ensuremath{\gg}1$, 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 $n{(\frac{{\ensuremath{\lambda}}_{0}}{d})}^{2}$ compared to the single-atom decay rate ${\ensuremath{\gamma}}_{s}$.