Intrinsic cascade-free intramode scattering Brillouin laser

The cascade operation of Brillouin lasers (BLs) is an identified obstacle to single-frequency power scaling and further compression of the fundamental linewidth. In this study, we reveal the relationship between the maximum cascade order and system parameters, starting from the phase-matching conditions of the Stokes cascade. The second Stokes is suppressed for modes that fall away the Brillouin gain linewidth (ΓB), which is heightened for Brillouin gain media with high sound velocity, large refractive index, and narrow linewidth. Diamond, with its extremely high product of speed of sound and refractive index, satisfies these requirements and is found to achieve cascade-free intramode scattering (TEM00) without manipulating cavity mode structures. This study elucidates a route to single-frequency, narrow-linewidth BLs via Brillouin material selection.