Enhanced coherent emission aided by an incoherent process

Enhanced emission of a coherent signal generated by the nonlinear process omega(f)+omega(b)-omega(p) has been found in an incoherently pumped four-level system. It is shown that finite (large) atomic coherence can be generated by (incoherent) pumping of the intermediate states, which removes the destructive interference effects that otherwise inhibit coherent emission of signals.