Self-induced transparency at bound excitons in CdS

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 intens ity over as much as two orders of magnitude a threshold is observed around a pulse area Theta = pi at which the evolution of a 0 pi-pulse for Theta mu ch less than pi turns into solitary 2 pi-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 w ell 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. (C) 1999 Elsevier Science B.V. All rights reserved.