Resonances in the collision-induced spectrum of six-wave mixing susceptibility: Generation of subharmonics

Resonances of the six-wave mixing susceptibility chi((5))(omega(1), omega(1 ), omega(1), -omega(2), -omega(2)) at frequency 3 omega(1) - 2 omega(2) of a system of two-level atoms dissipating through the spontaneous emission an d collisions and driven by a weak bichromatic external field of frequencies ol and wt in a finite Q cavity are analyzed. It is shown that the atomic c ollisions not only induce the usual Bloembergen resonances but that they al so play a major role in enhancing the transitions among the higher-order dr essed states, thereby bringing out some of the quantum resonances that are suppressed in the absence of collisions. The important contribution of coll isions in this higher-order nonlinear process is the generation of the subh armonic resonances at +/-1/2 times the hyperfine splitting of the first and the second excited manifolds. (C) 2000 Optical Society of America.