Optical parametric amplifier

Summary

An optical parametric amplifier is a device in which a strong pump wave amplifies a weak signal wave in a medium with second-order nonlinear susceptibility. A third wave, the idler, is created at the difference frequency $\omega_i = \omega_p - \omega_s$. The medium only mediates the exchange of energy and stores none, which is why the process is called parametric. Because the signal frequency can be tuned continuously, it is a common source of tunable short pulses.