Sensing and control in Virgo Experiment

The gravitational wave detector Virgo is presently under commissioning. A large part of the last year has been spent for control activities, such as the longitudinal locking. This work has been carried out with steps of increasing complexity: locking a simple Fabry-Perot cavity, then a Michelson interferometer with Fabry-Perot cavities in both arms, and finally recycling the light beam into the interferometer.