Cavity optomechanics in gallium phosphide microdisks

We demonstrate gallium phosphide (GaP) microdisk optical cavities with intrinsic quality factors >2.8 x 10(5) and mode volumes <10(lambda/n)(3), and study their nonlinear and optomechanical properties. For optical intensities up to 8.0 x 10(4) intracavity photons, we observe optical loss in the microcavity to decrease with increasing intensity, indicating that saturable absorption sites are present in the GaP material, and that two-photon absorption is not significant. We observe optomechanical coupling between optical modes of the microdisk around 1.5 mu m and several mechanical resonances, and measure an optical spring effect consistent with a theoretically predicted optomechanical coupling rate g(0)/2 pi similar to 30 kHz for the fundamental mechanical radial breathing mode at 488 MHz.