SPECTRAL LINEWIDTH NARROWING BY A NARROW BANDWIDTH SQUEEZED VACUUM INA CAVITY

The fluorescence spectrum of a strongly driven two-level atom located inside an optical cavity damped by a narrow-bandwidth squeezed vacuum is studied. We use a dressed atom model approach, first applied to squ eezed vacuum problems by Yeoman and Barnett, to derive the master equa tion of the system and discuss the role of the cavity and the squeezed vacuum in the narrowing of the spectral lines and the population trap ping effect. We find that in the presence of a single-mode cavity the effect of squeezing on the fluorescence spectrum is more evident in th e linewidths of the Rabi sidebands rather than in the linewidth of the central component. Even in the absence of squeezing, the cavity can r educe the linewidth of the central component almost to zero, whereas t he Rabi sidebands can be narrowed only to some finite value. In the pr esence of a two-mode cavity and a two-mode squeezed vacuum the signatu re of squeezing is evident in the linewidths of all spectral lines. We also establish that the narrowing of the spectral lines is very sensi tive to the detuning of the driving field from the atomic resonance. M oreover, we find that the population trapping effect, predicted for th e broadband squeezed vacuum case, may appear in a narrow-bandwidth cas e only if the input squeezed modes are perfectly matched to the cavity modes and if there is non-zero squeezing at the Rabi sidebands.