The Low Frequency Facility, R&D experiment of the VIRGO project

Abstract
We describe the Low Frequency Facility experiment, which aims at measuring, with an optical technique, the displacement thermal noise of suspended test masses, with an expected sensitivity of 10-18 m Hz-1/2 at about 10 Hz. The test masses are mirrors attached to a suspension, called R&D SA, which is already operational and equal to the one developed for the VIRGO interferometer. In this paper we discuss the basic principle of the experiment and the recent progress in this endeavour.