What's inside Virgo interferometer? Different view to the Gravitational Wave detector.

Why does it work, or sometimes does not? When the best is simply not enough? Latest detections of Gravitational Waves were accomplished by LIGO and Virgo observatories. These instruments are great result of years of efforts of scientists and engineers team. The scientific principles and ideas behind GW detectors are presented and well described in the literature, but the technical implementations are not that obvious. Some technical aspects of the solutions used in Virgo will be presented and discussed by engineer working in Virgo.