Raman scattering process: A photon with shorter wavelength from a "pump" laser loses portion of its energy for being scattered by silica molecules and is converted to a 'signal' photon of longer wavelength (labelled as Raman signal) together with a "phonon." Sum of the energies of the signal photon and the phonon equals to the energy of the pump photon. Signal photons inside the whispering-gallery-mode resonator are then coherently amplified leading to Raman laser.
J. Zhu, B. Peng, S.K. Ozdemir, L. Yang