AURIGA: the sensitivity
|Resonant bar gravitational wave
detectors are extremely sensitive detectors of tidal or quadrupolar
forces. Usually, the sensitivity of all gravitational wave detectors is
described by referring the detector noise in terms of the quantity they
are designed to measure, i.e. the equivalent amplitude of the
gravitational wave, which is a strain. The power spectral density of this
equivalent strain noise referred at the input of the detector is generally
called Shh: it is a function of frequency and its dimensions
are Hz-1. A sample of the AURIGA Shh is shown in fig.1.
The shape of the Shh depends crucially by the noise sources of the AURIGA detector, namely the thermal brownian noise of the mechanical resonators (i.e. the bar and the resonant transducer) and the back-action and additive noises of the transducer-amplifier readout. The back action noise is the component of the noise generated by the readout that acts on the mechanical resonators; its effect is similar to an heating of the bar and transducer oscillators above their thermodynamical temperatures.