Non-Lorentzian laser lineshapes in intense field-atom interaction

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Abstract
The effect of a cut off of the Lorentzian laser lineshape (as predicted by the phase-diffusion model of ideal laser theory) on the laser-atom interaction is investigated. The damping terms in the averaged density matrix equation of the atom, arising from the finite laser bandwidth are shown to be multiplied by a detuning-dependent cut-off. For detunings of the laser well within the Lorentzian part of the spectrum, the authors recover the previously derived results, while these damping terms are seen to drop out for detuning larger than the cut-off. Within their model, therefore, a laser with a lineshape falling faster than a Lorentzian, and for large detunings, appears monochromatic to the atom. In particular, the authors obtain qualitative agreement with recent experiments in which the reversed peak asymmetry in the doublet of double optical resonance persists only within a certain range of detuning from resonance.