BULK POLARITON BEATINGS AND 2-DIMENSIONAL RADIATIVE DECAY - ANALYSIS OF TIME-RESOLVED TRANSMISSION THROUGH A DISPERSIVE FILM

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