Time-resolved phase spectroscopy from femtosecond free-induction decay

We report a novel two-channel experimental scheme to record femtosecond amp litude and phase dynamics for dephasing studies. The measurement of free-in duction decay in one channel and pulse autocorrelation for the central wave length of the exciting pulses at the other channel as the reference allows the recording of time-resolved amplitude and phase dynamics of the free-ind uction decay throughout the dephasing process. The technique is applied to the study of coherent dynamics of the photocarriers in semiconductor GaAs. The observed phase dynamics is well simulated with optical Bloch vector com ponents analysis for the homogeneously broadened two-level model and the ex perimental and theoretical study is extended for the three-level system. Th e two-pulse-induced phase spectroscopy should be generally applicable to di fferent kinds of materials by recording the population difference for the t wo-level system with pulse-induced fluorescence.