Coherent transient in dressed-state and transient spectra of Autler-Townes doublet

In this paper we present a theoretical study of the time-dependent probe response in the presence of a strong pump field in a three-level pump-probe configuration. Two situations are investigated: a cw pump with a pulsed probe field and a pulsed pump with a cw probe field. The results are explained as dressed-state nutation and nutation by dynamic Stark switching. Dressed-state quantum beats are also an important feature for both situations. Furthermore, when a 90 deg. phase shift after a {pi}/2 period is introduced in the pulsed probe field, there is a spin locking in the dressed-state transition. Our results give a satisfactory theoretical account of a previous experimental observation [Wei et al., Phys. Rev. Lett. 74, 1083 (1995)].