Gain enhancement of multistage parametric intracavity frequency conversion

Multistage intracavity frequency conversion in optical parametric oscillators (OPOs) can generate new frequencies efficiently over a large dynamic range of pump intensity. These frequencies can be either higher or lower than the pump frequency. High efficiency is correlated with steady states exhibiting nearly complete pump depletion (CPD). Placing a second OPO crystal with high small-signal gain in the cavity does not affect the steady states with CPD, if the pump is depleted and the idler out-coupled before these fields reach the high-gain crystal. However, the high-gain crystal promotes rapid saturation, and hence higher time-averaged efficiency, in Q-switched devices. Numerical modeling of injection-seeded Q-switched devices in three spatial dimensions suggests that excellent beam quality at high peak power is obtainable. However, instabilities can occur in this modeling, and it is not known if these numerical instabilities entail instabilities in the physical devices.