Brillouin Optomechanics

Optical resonators are the basis of any experiment where it is
desirable to confine light. The most basic optical resonator, a
Fabry-Perot etalon, can be as simple as a colorful layer of oil over
water, or as complicated as the parallel mirrors in the Laser
Interferometer Gravitational-Wave Observatory. For many experiments it
is important to maximize the intensity of the light confined in the
resonator. Intensity is related to the circulating power over the mode
area. Whispering gallery resonators can be ideal as they offer quality
factors over 100 billion and can confine light to a transverse mode
area smaller than a wavelength squared. Intensities that would
otherwise require pulsed lasers in free space can be achieved in
whispering gallery resonators. Using a silica microsphere WGRs, we
demonstrate a new family of optomechanics based on Brillouin
scattering. We show that stimulated Brillouin scattering can be used
as an optomechanical actuation mechanism for high frequency (11 GHz)
acoustical vibrations. Owing to ultrahigh optical and mechanical
quality factors, we are able to excite mechanical vibrations in Silica
whispering gallery resonators at microwatt input powers which allowed
for the first time access to mechanical WGM in microresonators.