ABSTRACT
In principle, the optical parametric oscillator can consist simply of a nonlinear optical crystal and two mirrors forming a Fabry-Perot cavity. Given the basic oscillator configuration in the form of a nonlinear optical crystal in a Fabry-Perot cavity, the oscillation threshold condition can be obtained by applying the proper boundary conditions. For parametric oscillators in general, the oscillation threshold condition is simply that the total round-trip gain over the interaction length is equal to the loss, just as in ordinary lasers. There are two basic types of optical parametric oscillator: the singly-resonant oscillator in which only the signal wave is resonated while the idler wave is lost from the cavity on each passage, and the doubly-resonant oscillator in which both the signal and idler waves are resonated. The practical efficiency of an optical parametric oscillator is often limited by the optical damage, however.
