WFCAM optics for UK-IR telescope

Under a contract issue by the UATC, Thales Seso has designed and manufactured the Secondary and Tertiary mirrors as well as the large Filed lens of the Wide Field Camera (WFCAM) installed onto the UK infrared Telescope (UK-IRT) located in Hawaii.

The technical challenges of these mirrors were the following:

For tertiary mirror (picture here above):
• Large (Φ800mm) and aspherical (elliptical shape)
• Main difficulty is the operating mode in cryogenic conditions, i.e. down to 120°K. We had to manage more than 2mm differential dilation between mirror (Zerodur) and mount (aluminium). Appropriate flexible attachment flexures were designed by Thales Seso to solve this issue as well as qualification of specific cryogenic glue.

For Secondary mirror:
• Large (Φ550mm) and highly lightened (up to 80%)
because used at the extremity of a long and thin support
• Simultaneously aspherical and convex leading to a
Complex testing bench to get the full aperture reflected
WFE in stigmatic conditions