Coherent pulse propagation in GaSe

Coherent optical pulse transmitted through GaSe is investigated in both energy and time domains by using the frequency-resolved optical gating technique. The free induction decay signal due to the coherent emission from excitons is observed. The temporal evolution of the intensity of optical pulse passing through the sample exhibits a coherent dip as a result of a destructive interference between the coherent emission and the input optical field. Furthermore, the dispersion of the refractive index at the excitonic resonance is obtained.