Optical Parametric Amplification (OPA)
After separation of the signal photons from the OPG outputs, the remaining idler photons pass through a nonlinear optical crystal collinearly with the photons of the same wavelength as the pump, and the stronger output of the same wavelength as the signal and idler is 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.
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