ANALYTICAL SOLUTION FOR THE MOLLOW AND AUTLER-TOWNES PROBE ABSORPTION-SPECTRA OF A 3-LEVEL ATOM IN A SQUEEZED VACUUM

The Mellow and Autler-Townes probe absorption spectra of a three-level atom in a cascade configuration with the lower transition coherently driven and also coupled to a narrow bandwidth squeezed-vacuum field ar e studied. Analytical studies of the modifications caused by the finit e squeezed-vacuum bandwidth to the spectra are made for the case when the Rabi frequency of the driving field is much larger than the natura l linewidth. The squeezed vacuum center frequency and the driving lase r frequency are assumed equal. We show that the spectral features depe nd on the bandwidth of a squeezed vacuum field and whether the sources of the squeezing field are degenerate (DPA) or nondegenerate (NDPA) p arametric amplifiers. In a broadband or narrow bandwidth squeezed vacu um generated by a NDPA, the central component of the Mellow spectrum c an be significantly narrower than that in the normal vacuum. When the source of the squeezed vacuum is a DPA, the central feature is insensi tive to squeezing. The Rabi sidebands, however, can be significantly n arrowed only in the squeezed vacuum produced by the DPA. The two lines of the Autler-Townes absorption spectrum can be narrowed only in a na rrow bandwidth squeezed vacuum, whereas they are independent of the ph ase and are always broadened in a broadband squeezed vacuum.