Evolution of ultrashort light pulses in a two-level medium visualized withthe finite-difference time domain technique

The finite-difference time-domain technique is employed to examine the evol ution of the amplitude, duration, waveform, and phase of ultrashort light p ulses propagating in a medium of two-level atoms or molecules. The results of these numerical simulations agree reasonably well with predictions of th e McCall-Hahn analysis for the evolution of the amplitude and the phase of short pulses in a two-level medium until the pulse duration becomes less th an the duration of a single optical cycle. Noticeable deviations from the M cCall-Hahn scenario were observed for pulses with durations shorter than th e duration of a single field cycle. (C) 2001 Optical Society of America.