We experimentally demonstrate the high-sensitivity optical monitoring of a micro-mechanical resonator and its cooling by active control. Coating a low-loss mirror upon the resonator, we have built an optomechanical sensor based on a very high-finesse cavity (30 000). We have measured the thermal noise of the resonator with a quantum-limited sensitivity at the 10 −19 m/ √ Hz level, and cooled the resonator down to 5 K by a cold-damping technique. Applications of our setup range from quantum optics experiments to the experimental demonstration of the quantum ground state of a macroscopic mechanical resonator.

Reducing thermal noise from optical coatings is crucial to reaching the required sensitivity in next generation interferometric gravitational-wave detectors. Here we show that adding TiO 2 to Ta 2 O 5 in Ta 2 O 5 /SiO 2 coatings reduces the internal friction and in addition present data confirming it reduces thermal noise. We also show that TiO 2 -doped Ta 2 O 5 /SiO 2 coatings are close to satisfying the optical absorption requirements of second generation gravitational-wave detectors.

Abstract. In this paper, we describe in detail the BMV (Biréfringence Magnétique du Vide) experiment, a novel apparatus to study the propagation of light in a transverse magnetic field. It is based on a very high finesse Fabry-Perot cavity and on pulsed magnets specially designed for this purpose. We justify our technical choices and we present the current status and perspectives. PACS. PACS-key discribing text of that key -PACS-key discribing text of that key