Abstract : We present a very sensitive optical measurement of the mechanical vibrations of a micro-mirror inserted in a high finesse Fabry-Perot cavity. The micro-mirror is made of a low-loss dielectric coating deposited on a sub-millimetric sized silicon etched resonator. We have measured the thermal noise of the resonator over a wide frequency range and characterized its eigenmodes: frequency, effective mass, damping and spatial shape. They present high frequency resonances (1 MHz) and low effective masses (100 µg). Using an electrostatic force, we have tested its mechanical response and cooled the resonator using a cold damping technique.
We have also demonstrated a novel cooling mechanism, induced by the radiation pressure in a detuned cavity. Depending on the detuning, we have observed a cooling or a heating of the resonator, which can lead to an optomechanical instability at large intracavity intensity.
These cooling mechanisms, combined with passive cryogenic techniques, may lead to a sufficient cooling in order to observe the ground state of the mechanical oscillator.
We also present an experimental study of the photothermal effect and a measurement of the thermal expansion induced by the light absorbed in the dielectric layer.