Assembly of the optical bench in a clean room. This bench has a "diameter" of about 88 cm. It has been suspended to a suspension in April 2015.
This bench collects the laser beam at the asymmetric port of the Virgo interferometer, the one whose power will vary when a gravitational wave passes by. The beam size is reduced from 2 cm on the first big optical lens down to 300 µm on a small optical cavity called mode-cleaner cavity. The beam power is then measured on a photodiode placed on another optical bench.
Credits: Virgo Collaboration/LAPP