Raman Amplifier

https://www.optical-sintai.com/products/raman-amplifier/

Raman amplification is based upon stimulated Raman scattering in which the photon induces inelastic scattering of the pump photon in the non-linear regime of the medium.
This scattering generates another photon with lower frequency (and energy) while the energetic difference (and therefore the frequency difference) is passed to the vibration states of the medium.
Raman Amplifier FAQs