Lasers without inversion: Raman transitions using autoionizing resonances

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Abstract
We consider laser action on a transition involving an autoionizing state ‖a〉 and an initially unpopulated state ‖f〉, the population of which builds up because of spontaneous emission and Raman processes. The autoionizing state is pumped by a coherent field. We discuss the transient amplification of the probe field on the lasing transition for a range of parameters. The coherent field on the pumping transition leads to minima in the absorption spectra if the atomic population were in the state ‖f〉. Such regions of minima can be used for obtaining gain even for long times.