LIGO Document E1000441-x0
- Heraeus recommends Suprasil 312 as a material that should provide figure stability through the coating and annealing process for Advanced LIGO Fold Mirrors. We have shown that Corning 7980 does not and Heraeus 3001 does provide this stability at the required level of 8nm change in sag over a 225 mm diameter for an optic of aspect ratio 6 (diameter / thickness). LMA has experience with one piece of Suprasil 312 that did change figure after coating. (out of the entire initial VIRGO effort) They suspect this may have been a polishing problem where there was some subsurface damage.
LIGO will polish a piece of Suprasil 312 that has never been coated or annealed. This piece is to be polished in the same way as a Fold mirror for Advanced LIGO: D080661-v4 AdLIGO COC FM SUBSTRATE. The piece will be supplied to CSIRO for an annealing test.
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