Abstract

The emission spectrum of two-level atoms driven by a strong bichromatic field has been the subject of considerable theoretical and experimental study during the past few years.^[1-4] The spectrum, experimentally observed by Mossberg and co-workers,^[1] consists of a series of peaks with an essentially constant spacing δ, where 2δ is the frequency difference of the two driving fields. The peak separations are independent of the Rabi frequencies of the driving fields but the number of peaks in the spectrum increases as the Rabi frequencies increase. The peaks separated from the atomic transition frequency by even multiples of δ have a different linewidth than those separated from the atomic transition frequency by odd multiples of δ. In the present work we study the absorption spectrum of a two-level atom driven by a strong bichromatic field, illuminated by a weak probe beam with a frequency ω_P after the system has attained steady-state conditions. We assume that the atom has the transition frequency ω₀ and natural linewidth 2γ; the frequencies of the driving fields are ω₁ and ω₂, with ω₁- ω₂ = 2δ, and the corresponding Rabi frequencies are Ω₁ and Ω₂.

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