Coating chambers in the ELT Technical Facility at Paranal Observatory

These two coating chambers inside the Extremely Large Telescope (ELT)’s Technical Facility at ESO’s Paranal Observatory are used to give a shiny new finish to the hundreds of mirror segments that will make up the ELT’s primary mirror. They were produced by AGC Europe. The reflective coating is made up of 1.7 grams of silver, with additional layers of nickel chromium and silicon nitride to improve adhesion to the mirror blank and protect the silver from tarnishing. Overall, the coating on each segment is around 120 nanometres thick, or about one thousand times thinner than a human hair. The machine on the foreground to the left is used to check the segments prior to coating; if imperfections are detected, the segment is washed manually before the coating is applied.