COHERENT EFFECTS THROUGH THE CONTINUUM - TRANSPARENCY, POPULATION TRAPPING AND AMPLIFICATION WITHOUT INVERSION THROUGH AUTOIONIZING RESONANCES

We show how coherent interactions with an autoionizing state may lead to transparency, stabilization and amplification without inversion. Th ese effects arise due to the inherent asymmetry of an autoionizing sta te, and reflect the possibility of complete destructive interference o f two alternative paths for ionization and for photon absorption. We s how how these coherent features can be exploited to generate short-wav elength radiation, in particular that they lead to enhanced third-harm onic generation, which compares favorably with that in an intermediate two-photon resonance system. Numerical calculations are presented for a specific autoionizing state in atomic Ca.