DYNAMICS OF A DRIVEN 2-LEVEL ATOM COUPLED TO A FREQUENCY-TUNABLE CAVITY

A cavity-modified master equation is derived for a coherently driven t wo-level atom coupled to a single-mode cavity in the bad cavity limit, in which the cavity frequency is tuned to either the center or one of the sidebands of the Mellow triplet. The atomic populations in both t he bare- and dressed-state representations are analyzed in terms of th e cavity-modified transition rates. In the bare-state basis, the role of the cavity may be interpreted as enhancing the stimulated absorptio n of the atom while suppressing the stimulated emission. The bare-stat e population may thus be inverted under appropriate conditions. The dr essed-state inversion, however, originates from the enhancement of the atom-cavity interaction when the cavity is resonant with the atomic d ressed-state transition. We show that two-phase quadratures of the ato mic polarization decay at different rates. The decay of the in-phase ( or out-of-phase) quadrature may be greatly inhibited as the driving in tensity increases, depending on the cavity resonant frequency. The spe ctrum of the atomic fluorescence emitted out the side of the cavity is also studied. The spectral profiles are sensitive to the cavity frequ ency. When the cavity frequency is tuned to the center of the Mellow r esonances, the fluorescence spectrum is;symmetrical with three peaks w hose linewidths and heights are intensity dependent. When the cavity f requency is tuned to one of the Mellow sidebands, however, it is asymm etric, and the central peak and the sideband on resonance with the cav ity can be significantly suppressed for strong driving fields. All thr ee spectral lines can be narrowed by increasing the Rabi frequency. Th e physics of these striking spectral features is explored in the dress ed-state basis. We also investigate the probe absorption spectrum. Whe n the cavity frequency is tuned to the center of the Mellow fluorescen ce triplet, the central component exhibits a Lorentzian line shape, wh ile the side bands show the Rayleigh-wing line shape. Probe gain may o ccur at Line center due to cavity-induced, bare-state population inver sion. When the cavity is tuned to resonance with one sideband, only tw o sidebands, with Lorentzian profiles, dominate. Gain can occur at the sideband far off resonant with the cavity. The sideband gain is a con sequence of an unbalanced dressed-state population distribution. [S105 0-2947(98)07706-3].