Sound amplification by stimulated emission of radiation the axes of the mirrors, it is possible for photons to repeat multiple reflections and force more and more photons to follow them producing an avalanche effect. The number of photons of this coherent laser beam increases and competes the number of photons perished due to losses. The basic necessary condition for the generation of a laser radiation is the population inversion, which can be achieved either by exciting atoms and inducing percussion or by external radiation absorption. A SASER device mimics this procedure using a source-pump to induce a sound beam of phonons. This sound beam propagates not in
Raman amplification Raman amplification Raman amplification is based on the stimulated Raman scattering (SRS) phenomenon, when a lower frequency 'signal' photon induces the inelastic scattering of a higher-frequency 'pump' photon in an optical medium in the nonlinear regime. As a result of this, another 'signal' photon is produced, with the surplus energy resonantly passed to the vibrational states of the medium. This process, as with other stimulated emission processes, allows all-optical amplification. Optical fiber is today mostly used as the nonlinear medium for SRS, for telecom purposes; in this case it is characterized by a resonance frequency downshift of ~11 THz (corresponding