Silica as a key material for advanced gravitational wave detectors

The thermal noise coupling with the displacement of the mirrors of a gravitational wave interferometric detector is a limit to its sensitivity in a range of frequencies from about 10 Hz to few hundreds of Hz; fused silica proved to be a very suitable material to reduce this source of noise for the first generation of detectors. The future advanced detectors are planning to make use of fused silica mirrors and suspending elements in a monolithic arrangement: in these conditions, the main contribution to the thermal noise will come from the amorphous multilayered coating deposited on the mirrors. This paper is focused on the multiple advantages provided by the use of fused silica material in a present day interferometric detector; a new suspension for measurements of the acoustic attenuation in fused silica is presented together with the loss angle dependance on frequency and aspect ratio. Furthermore we report on the status of the art of the research activity on fused silica wires production and characterization and coating thermal noise accomplished by the Firenze–Urbino Virgo group.