TRANSIENT OPTICAL REFLECTIVITY IN LAYERED SEMICONDUCTORS

The reflection dynamics of a subpicosecond optical pulse was investiga ted under the Brewster angle of incidence at the exciton resonance in the layered compound GaSe. The reflected pulse has a tail of a few pic osecond which follows the decay of the resonant polarization. A time o scillatory decay of the transient reflectivity was observed. This beha vior can be explained by quantum beats in the polarization decay of co herently excited singlet and triplet excitons.