Intracavity resonance fluorescence in the strong-coupling limit

Abstract

The standard theory of resonance fluorescence is a weak-coupling theory.1 If n ¯ is the mean photon number for the driving field, g is the atom field coupling constant, and γ is the Einstein A coefficient, formally the standard theory of resonance fluorescence assumes the limit n ¯ → ∞ , g/ γ → 0, with the ratio of Rabi frequency to atomic linewidth 2 n ¯ n g / γ finite. The limit g/γ → 0 allows the variation of the Rabi frequency 2 n g across the photon number distribution of the driving field to be neglected. By placing the atom inside an optical cavity the ratio g/γ can be changed. In this paper we calculate spectra for intracavity resonance fluorescence in the strong-coupling limit g/γ ≫ 1, g/κ ≫ 1, where κ is the cavity linewidth. We consider a single two-level atom interacting on resonance with a single cavity mode driven by a resonant coherent field. The cavity subtends a small solid angle at the atom, so that the spontaneous emission into free-space modes is not negligible. We calculate the spectrum of the light transmitted by the cavity (the transmitted spectrum) and the spectrum of the light radiated by the atom into free space (the fluorescent spectrum). The transmitted and fluorescent spectra show fundamental differences from the (weak-coupling) spectrum of free-space resonance fluorescence.