LIGO Document G2001920-v3

Custom polish figure for O4 ETMs

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Document type:
G - Presentations (eg Graphics)
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For test masses fabricated in the post O3 era (ops rework and A+) the strategy is to have the polish plus coating uniformity provide a surface figure that minimizes loss in case of point absorbers, yet has little impact to loss in the absence of point absorbers.

The final recommendation is to polish to a perfect sphere, then use the natural fall off of the coating, as described herein, to suppress the 7th order mode in the arm cavity.

See G2001747 for the analysis supporting and describing the ideal final surface
See T2000643 for the measurement of the expected coating plume and analysis of the expected ROC change, supported by expected stress deformation provided by LMA at C2000282

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Notes and Changes:
Coating Fall-of is found to be similar to, or better than the idealized fall-off proposed in earlier versions. We will polish to a perfect sphere, then apply the coating as analyzed in this document.

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