Cascaded optical parametric oscillation

This work considers a cascaded optical parametric oscillator (OPO) in which photons at frequency are generated from a not-resonated pump field at frequency 4/spl omega/ by means of the two cascading down-conversion processes, the fields at frequencies 2/spl omega/ and /spl omega/ being resonated in the same cavity. It is shown that a self-pulsing instability as a result of the competition between the two parametric processes appears close to the OPO threshold, leading to self Q-switching for the down-converted field.