Abstract

Instead of stimulated emission from a population inversion, Brillouin and Raman lasers use stimulated scattering from optically-excited phonons as the light amplification mechanism - optical phonons in the case of Raman scattering, and acoustic phonons for Brillouin. The interaction of optical pump, the phonons and the wavelength-shifted output beam relies on the strength of the third-order Raman or Brillouin nonlinearity of the material. These fundamental differences yield a source of laser power that has distinctive characteristics in the way the beams spatiotemporally develop as well as their spectral content. For example, stimulated scattering lasers are generally efficient generators of beams in their lowest-order spatial mode and therefore with very high beam quality. Meanwhile, recent research is also showing both Raman and Brillouin lasers are excellent at producing ultra-narrow linewidths. The lasers also have the major benefit of being capable of providing output wavelengths anywhere across the spectrum, aided by the fact the Stokes shift can be cascaded, but constrained by the wavelength of the pump source.

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