Kenji NUMATA, Giuseppe Bertolotto BIANC, Atushi SEKIYA, Naoko OHISHI, Sigemi OTSUKA, Keita KAWABE, Kimio TSUBONO

The thermal noise of the mirrors is thought to limit the sensitivity of interferometric gravitational wave detectors at observation band. According to the fluctuation-dissipation theorem, the quality factor of the mirrors must be high in order to suppress the thermal noise. For example the required quality factor of the mirrors of the TAMA300 is 2x10^7. The lower limit of the thermal noise of the mirrors is derived from intrinsic quality factor of its material. Therefore it is significant to know intrinsic quality factor. However the measured quality factor of the sample is degraded by the loss of the support system, such as wire friction. It remains uncertain what the intrinsic loss in such low loss material is. To measure intrinsic quality factor directly, we proposed a new measurement method. In this method, the samples are supported by two small ruby balls. If the contact points are at its nodes of its vibration modes, losses due to this support system should be very small. Measured quality factor in our preliminary experiment reached 1x10^8 for silicon sample at room temperature. This indicates availability of this system to measure high quality factor. We will present this novel method and the measured quality factors.