Development of a Frequency Tunable Green Laser Source for Advanced Virgo+ Gravitational Waves Detector

After one year of data taking, the observing run three (O3), we are preparing for an improved version of the system, named the Advanced Virgo plus. One of the major upgrades will be the installation of the signal recycling mirror to form an additional optical cavity and improve the sensitivity of the interferometer. This also requires a change in the lock acquisition strategy. In particular, the arms will be locked at the beginning with lasers at a different wavelength from the main one. Such a strategy has already been implemented and tested in LIGO and KAGRA, and in this paper we will present how it has been conceived in Virgo.