An OPO typically consists of a nonlinear crystal placed within an optical cavity. When a pump laser with sufficient intensity is directed into the crystal, it induces a nonlinear interaction that generates the signal and idler waves. The optical cavity is designed to enhance the efficiency of this process by providing feedback for the signal and idler waves, allowing them to oscillate and build up in intensity. The wavelengths of the signal and idler can be tuned by adjusting the phase-matching conditions within the crystal.
