Optical parametric amplifier

An optical parametric amplifier, abbreviated OPA, is a laser light source that emits the light of variable wavelengths by an optical parametric amplification process. This light emission is based on the non-linear optical principle. The photon of an incident laser pulse (pump) is divided into two photons, the sum energy of which is equivalent to the energy of the photon of the pump, by a non-linear optical crystal. Ordinary light and extraordinary light are generated; the ordinary light is called the signal and the other extraordinary is called the idler. The wavelengths of the two generated laser pulses, the signal and the idler, are determined by the phase matching condition, which is changed by the angle between the incident pump laser ray and the axes of the crystal. The wavelengths of the signal and the idler lights can, therefore, be tuned by changing the phase matching condition. This process is called optical parametric generation, or OPG. After separation of the signal light from the OPG outputs, the remaining idler passes through a non-linear optical crystal collinearly with the light of the same wavelength as the pump, and the stronger output of the same wavelength as the signal and idler are acquired as the output of the OPA. These wavelength-variable outputs are efficiently used in many spectroscopic methods. As an example of OPA, the incident pump pulse is the 800 nm (12500 cm^-1) output of a Ti:sapphire laser, and the two outputs, signal and idler, are in the near-infrared region, the sum of the wavenumber of which is equal to 12500 cm^-1.