The new Advanced Virgo interferometer laser beam injection system was switched on Friday, September 26th 2014 at EGO, the European Gravitational Observatory.
The big interferometers, built to detect gravitational waves for the first time, almost one century after Einstein announced their existence in 1916, are being improved.
On the Earth, there are only four such giant interferometers, with arms up to 4km long: Virgo, near Pisa; GEO600, near Hannover; and the two LIGO interferometers, in Louisiana and Washington State.
By autumn 2015, all of them will have been upgraded to enhance their sensitivity by a factor of 10. The scientists working there will be able to listen to gravitational wave sources 10 times further away, reaching a horizon of hundreds of millions of light years. The detection rate is expected to be of the order of tens of signals per year of observation.
The new Virgo laser beam injection system includes several perfectly seismically-isolated in-air and in-vacuum optical benches, together with a 140m-long resonating triangular optical cavity.
The laser system, the wavelength of which is 1064nm, is composed of solid state lasers, providing up to 45W. The laser frequency is pre-stabilized down to 1Hz RMS, thanks to optical cavities. All of the injection system optics are qualified to withstand a maximum laser power of up to 200W, which is the power foreseen in later stages of Advanced Virgo operation.
The switching on took place in the presence of former Italian Minister for Education and Research, Maria Chiara Carrozza, and regional and local authorities.
From now on it will be possible to feed the 3km Virgo arms with an ultra-high-quality laser beam. The fully upgraded interferometer will be operational one year from now.
The EGO director, Federico Ferrini, with due optimism, said: “in September 2015 I bet there will be an even more important event: the switch-on of full Advanced Virgo. It will be the beginning of the final hunt for gravitational waves!”
Gravitational wave astronomy will give a much more complete view of the universe. It will be possible to study the inside of supernovae, the interactions of neutron stars and black holes, and to go back to the first moments after the Big Bang, detecting the cosmological background of gravitational waves.
The EGO observatory and Virgo, were designed and built by the Centre National de la Recherche Scientifique (France) and the Istituto Nazionale di Fisica Nucleare (Italy), who were subsequently joined by institutions from the Netherlands, Poland and Hungary.