CREATION OF POPULATION-INVERSION BY FANO INTERFERENCE IN 3-LEVEL CASCADE-TYPE SYSTEM

We demonstrate how Fano interference produces a large population inver sion in a three-level cascade-type system involving an autoionizing st ate. We show that when an intense monochromatic field driving the lowe r transition of the atom by a two-photon resonant interaction creates a pair of dressed states which then are coupled by a second coherent f ield to ionization continuum and an autoionizing state, the Fano inter ference prevents the photoionization from the upper dressed state wher eas the second state is quickly exhausted, thus making possible the co herent generation of short-wavelength light free of phase-matching con dition. We discuss the incoherent processes which can destroy the Fano interference.