Lock acquisition of the Virgo gravitational wave detector

The Virgo interferometer for gravitational wave detection has concluded four months of scientific data acquisition in its final optical configuration (a power-recycled interferometer with Fabry-Perot cavities in the arms). The lock acquisition technique developed to bring and keep the Virgo detector on its working point largely proved to be very efficient and robust. In this paper we describe the variable finesse lock acquisition technique and we discuss the performance of the whole locking system.