Experimental optomechanics with silicon micromirrors

We experimentally demonstrate the high-sensitivity optical monitoring of moving micromirrors, made of low-loss dielectric coatings upon silicon resonators of various shapes and sizes. The very high optical finesses obtained (\mathcal{F}\simeq 30\,000 ) have allowed us to measure the thermal noise of the micromirrors at room temperature with a shot-noise limited sensitivity at the 10^{-19}\,{\rm m}/\sqrt{\rm Hz} level and to completely characterize their mechanical behavior, in excellent agreement with the results of a finite-element computation. Applications of such optomechanical systems range from quantum optics experiments to the experimental demonstration of the quantum ground state of a macroscopic mechanical resonator.