Self-induced transparency at bound excitons in CdS

Abstract

We study the propagation of coherent picosecond laser pulses tuned to the I 2 donor-bound exciton resonance in CdS. With variation of the input intensity over as much as two orders of magnitude a threshold is observed around a pulse area Θ= π at which the evolution of a 0 π-pulse for Θ⪡ π turns into solitary 2 π-pulse formation demonstrating the occurrence of self-induced transparency. Treating the bound excitons as two-level systems, the measured time behaviour and spectra of the pulses are well described by the combined Maxwell–optical Bloch equations with times T 1=500 ps and T 2=80 ps accounting for energy and phase relaxation.