The last-stage suspension of the mirrors for the gravitational wave antenna Virgo

We present the last-stage suspension for the mirrors of the gravitational wave antenna Virgo. We studied some problems encountered during the commissioning of the Virgo central interferometer (CITF) and solved them with the aim of achieving the target sensitivity of the detector in its final configuration. We measured the effect of the holder on the internal motion of the mirror, and the residual nonlinear couplings between the electromagnetic actuators and the metallic parts present on the last-stage suspension. The limits experienced on the Virgo CITF have helped us to define some important modifications to be applied to the last-stage suspension. Moreover, we present the experimental study of west input mirror internal modes after it was dismounted from the Virgo central interferometer. The results were useful to identify, in the data of the engineering run 4 of the CITF, the thermal peaks of such a mirror.