Bulk polariton beatings and two-dimensional radiative decay: Analysis of time-resolved transmission through a dispersive film

The time-resolved transmission (TRT) through a slab described by a local dielectric function with resonance behavior is studied. For films with a thickness d > lambda(where X is the wavelength of light in the crystal) an analytic formula which describes the recently observed polariton beatings [Frohlich, D. et al., Phys. Rev. Lett. 67, 1991, 2343] is obtained. For d < lambda the TRT is expressed in terms of the normal modes of the slab: the radiative decay of the quasi-two-dimensional excitation is recovered when only the lowest modes contribute, as it happens for very narrow slabs, while the interference between different modes evolves into the polariton beatings on increasing the film thickness. (C) 1997 Elsevier Science Ltd.