ABSTRACT

When an optical wave is incident in a medium, the incoming photons scatter, producing a phonon by exciting molecular vibrations, and a “Stokes” photon with a smaller frequency, so that as usual the total energy is conserved. The wavenumber decreases of the Stokes wave relatively to the pump wave has been determined for various vitreous bulk samples. The use of more unusual dopants may make it possible to vary the wavenumber shift and/or the gain, for various applications. Brillouin scattering is similar to Raman scattering, but the corresponding phonons are “acoustical” instead of “optical,” as they are related to lattice vibrations. If the chromatic dispersion of the fiber is positive, there exist critical pulse shapes and powers for which the pulse shape remains unchanged along the fiber or oscillates. Stimulated Brillouin scattering has been used for obtaining CW lasers with various cavity mirrors configurations.