HOLE-BURNING AND DISPERSIVE PROFILES AT LINE CENTER OF THE PROBE ABSORPTION-SPECTRUM OF A 2-LEVEL ATOM IN A SQUEEZED VACUUM

We study the absorption spectra of a weak probe beam that interacts wi th a driven two-level atom in the presence of a squeezed vacuum. In pa rticular, we focus on the behavior of the central resonance of the pro be absorption spectra in the region of intermediate driving intensitie s and in the large squeezed photon number limit. Squeezing-induced pim ples, hole-burning, and dispersive profiles at line center are display ed. These unusual spectral features are highly sensitive to the squeez ing phase and to the Rabi frequency of the driving field. We present a nalytical conditions for the occurrence of these effects and find that they all take place in the vicinity of the critical point dividing th e different dynamical regimes, probe absorption and amplification, of the atomic radiation. We also investigate analytically and numerically the two-time correlation functions of the atomic polarization and fin d that the cross correlations of the two dipole quadratures contribute symmetric (absorptionlike) spectral features to the absorption spectr a, whereas the self-correlations contribute asymmetric (dispersionlike ) spectral profiles, which disappear for the particular phase values P hi = 0, pi. The physical origin of the unusual spectral profiles at li ne center is also discussed in terms of the coherent population oscill ations. (C) 1996 Optical Society of America