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.
For a larger picture click here (postscript file, size 47KB) or click here (jpeg file, size 38KB).

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.

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