SYMMETRY-BREAKING OF THE 2-LEVEL ATOMIC RESPONSE DUE TO FIELD-DEPENDENT RELAXATION

We show that the dependence of the relaxation rates on the frequencies of the dressed transitions breaks in general the emission-absorption symmetry of the atomic response. This leads to nonzero resonant refrac tion index, frequency shift of the driving field maximal absorption, u nexpected population inversions both in the dressed and bare states, a nd a modification of the Mellow spectrum for sufficiently intense fiel ds.