Analytical solutions for light absorption spectra of two driven atoms

Authors:

• Z. Ficek,
• Ryszard Tanaś,
• S. Kielich

Abstract

The absorption spectra of a pair of two-level atoms driven on resonance by a coherent laser field are considered analytically including the dipole-dipole interaction between the atoms. Analytical formulae for the absorption spectra are derived for four regions of the dipole-dipole interaction Omega ₁₂: Omega >> gamma >> mod Omega ₁₂ mod , Omega >> mod Omega ₁₂ mod >> gamma Omega approximately= mod Omega ₁₂ mod >> gamma , mod Omega ₁₂ mod >> gamma >> Omega (2 gamma being Einstein's coefficient A, and Omega the Rabi frequency). The formulae, containing both absorption-like and dispersion-like terms, reveal explicitly the resonant structure of the absorption spectra. At great intensities of the driving field the absorption is negative in a certain range of frequencies. The dipole-dipole interaction between the atoms is shown to modify considerably the form of this absorption spectrum. For sufficiently strong dipole-dipole interaction it exhibits dispersion-like behaviour in the vicinity of 2 Omega with a new region of negative absorption. The spectrum is asymmetric, albeit slightly. For strong dipole-dipole interaction and a weak driving field the spectrum consists of one absorption-like peak, located at omega - omega ₀= Omega ₁₂.