This photo shows some of the innards of the Centre for Advanced Laser Applications. This is the Laser Beam Delivery (LBD) system, an underground maze of mirrors and shafts that distributes the beam emitted by the ATLAS laser to the various experimental workstations. Here we see the CALA team installing one of the large mirrors used to redirect the beam – a 30-kg block of quartz glass that has been polished on the reflecting facet.
The experiments demand extreme precision, and the reflective surface must be almost perfectly flat (to a tolerance of a few nanometers!). Once that is achieved, the surface is coated with a thin film of a specially developed material, which is one of the few that can withstand the stresses imposed by the high-intensity laser beam. This surface film is designed to be highly reflective in the infrared region; in visible light it has a blue shimmer and looks almost transparent. Installation of the mirror requires extreme care, as the tiniest scratches or flecks can have a negative impact on the experiments.