Full mechanical characterization of a cold damped mirror - art. no. 013808

We describe an experiment in which we have used a cold damping feedback mec hanism to reduce the thermal noise of a mirror around its mechanical resona nce frequency. The monitoring of the Brownian motion of the mirror allows o ne to apply an additional viscous force without any extra thermal fluctuati ons. This scheme has been experimentally implemented with the radiation pre ssure of an intensity-modulated laser beam. Large noise reductions, up to 3 0 dB, have been obtained. We have also checked the mechanical response of t he cold damped mirror, and monitored its transient evolution between the co oled regime and the room-temperature equilibrium. A simple theoretical mode l allows us to fully explain the experimental results. A possible applicati on to the active cooling of the violin modes in a gravitational-wave interf erometer is discussed.