PROBE ABSORPTION-SPECTRA FOR DRIVEN ATOMIC SYSTEMS IN A NARROW BANDWIDTH SQUEEZED VACUUM

The behavior of a three level atom in a cascade configuration with the lower transition coherently driven and also coupled to a narrow bandw idth squeezed vacuum field is studied. A master equation treatment bas ed on dressed atom states is used and expressions for probe absorption spectra are obtained via linear response theory and the quantum regre ssion theorem. The expressions obtained also apply to the broad bandwi dth squeezed vacuum case. Numerical studies of the modifications cause d by the finite squeezed vacuum bandwidth to the Mellow and Autler-Tow nes probe absorption spectra are made for the case where the squeezed vacuum field center frequency and the driving laser frequency coincide and where upper transition relaxation terms are ignored. The squeezed vacuum source is assumed to be a degenerate parametric amplifier for the numerical calculations. Cases where the driving laser is resonant and detuned are examined. The spectral features are sensitively depend ent on the phase of the squeezed vacuum field for a given driving lase r phase. Dispersive features in the Mellow probe absorption spectrum c an become absorptive, and vice versa. It is found in the probe absorpt ion spectra that for certain choices of the squeezed vacuum phase line s narrower than for the broadband squeezed vacuum are obtained in the finite bandwidth situation. In both the Mellow and Autler-Townes spect ra features narrower than for the normal vacuum case are obtained when the laser field is detuned, and in the Autler-Townes case this occurs for resonance also.