Resonance-Enhanced Transient Reflectivity via Exciton Polaritons

The reflection of a light pulse from a spatially dispersive medium is investigated theoretically. For laser frequency at exciton resonance, spatial dispersion enhances the reflected transients associated with the light pulse. For the case of CdS and GaAs crystals, the transient intensities are about 10% of the incident intensity at a time 0.1 ps after the trailing edge of the reflected signal. The theory predicts a crossover from exponential to slow power-law decay rate of transient reflectivity; this occurs at a characteristic time ${\zeta }_c\sim 1$ ps after the trailing edge of the pulse for CdS and GaAs.