Coherent low-frequency effects in three-level media with asymmetric optical transitions

An asymmetry of the spectral characteristics of optical transitions influences strongly the nature of a coherent nonlinear interaction between a broad-band three-level absorber and a series of ultrashort pulses. It is predicted that the absorption of the field will be reduced substantially in a three-level medium with asymmetric 1–3, 2–3 transitions. It is shown that the strong asymmetry results in coherent bleaching of the medium even in the absence of a resonance between the low-frequency 1–2 transition and the pulse repetition frequency (also under the action of high-power single ultrashort pulses). There is a range of parameters where a resonant dependence of the absorbed power on the pulse repetition frequency is observed and this dependence is enhanced appreciably by increasing the asymmetry.