Novel effects in transient optical reflectivity from bounded nonlocal media via exciton polaritons

Abstract

We report results of a theoretical investigation of time-dependent reflectivity from a semi-infinite, spatially dispersive medium subject to an incident pulse of finite duration. A damped oscillatory decay in the tail of transient reflectivity after the pulse cut-off is predicted, sensitive to the material and to the specific additional boundary conditions (ABC's). Physically the origin is in relaxation processes which dephase the emitted light on a time scale larger than the cut-off time of the pulse and shorter than the spontaneous dipole relaxation time. For laser frequency at the exciton resonance the transients are enhanced; near to resonance a double peak occurs due to dispersion of polariton group velocity.