Abstract
We study the absorption spectra of a weak probe beam that interacts with a driven two-level atom in the presence of a squeezed vacuum. In particular, we focus on the behavior of the central resonance of the probe absorption spectra in the region of intermediate driving intensities and in the large squeezed photon number limit. Squeezing-induced pimples, hole-burning, and dispersive profiles at line center are displayed. These unusual spectral features are highly sensitive to the squeezing phase and to the Rabi frequency of the driving field. We present analytical conditions for the occurrence of these effects and find that they all take place in the vicinity of the critical point dividing the 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 find that the cross correlations of the two dipole quadratures contribute symmetric (absorptionlike) spectral features to the absorption spectra, whereas the self-correlations contribute asymmetric (dispersionlike) spectral profiles, which disappear for the particular phase values Φ = 0, π. The physical origin of the unusual spectral profiles at line center is also discussed in terms of the coherent population oscillations.
© 1996 Optical Society of America
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