Optical Parametric Oscillator (OPO): A laser-pumped crystal with nonlinear optical properties inside of an optical resonator in which the output generates coherent light whose output can be tuned continuously over a variety of infrared and visible wavelengths. The OPO generates a short wavelength component called the signal and a longer wavelength component called the idler. Conservation of energy dictates that the sum of the photon energy of the signal and that of the idler equals the original pump photon energy.
