A homodyne quadrature interferometer for the study of thermal noise in solids in non-equilibrium steady states

Non equilibrium thermal noise is expected to be a limiting factor in the future generation of gravitational waves interferometers. Nevertheless is still a marginally investigated phenomenon and its understanding would strongly improve the design of future interferometers. In collaboration with the VIRGO experiment, a homodyne interferometric readout was realized using the quadrature technique in order to be sensible to displacements longer than one laser-source wavelength. The interferometer was designed and characterized, reaching a ~3e-15 m/vHz at 1400 Hz sensitivity, enough to measure the mean-square excitations of an oscillator’s acoustic modes induced by thermal noise in non-equilibrium conditions.