Brillouin Lasing with a CaF_2 Whispering Gallery Mode Resonator
  Stimulated Brillouin scattering with both pump and Stokes beams in resonance with whispering gallery modes of an ultra high Q CaF_2 resonator is demonstrated for the first time. The resonator is pumped with 1064 nm light and has a Brillouin lasing threshold of 3.5 microwatt. Potential applications include optical generation of microwaves and sensitive gyros. 
Ivan S. Grudinin, Andrey B. Matsko, and Lute Maleki