LIGO Document T2000643-v1

Characterizing the figure change after coating of PEN-ITM02 at LMA

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T - Technical notes
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For test masses fabricated in the post O3 era (ops rework and A+) the polishing and coating strategy is to have the substrate polished with a figure that is the inverse of the coating uniformity, so that the final shape of the HR surface is ideal. We will also incorporate a custom figure in order to suppress 7th order mode degeneracy in the arm cavities. See G2001747

These data are one piece of the calculation. Pen-ITM02 was measured before and after coating at LMA. The substrate was not annealed before coating. The substrate is HOQ-310, see Q1300005 and C0900072, so slightly different than aLIGO ETMs in an unknown way. Since LMA uses a flat transmission sphere, there are many fringes in the data. The best data for our purposes are taken when the temperature is stable, and the tilt is as similar as possible in the before and after coating measurements.

The metropro data are provided (.dat) along with a radial profile (.xlsx) for the difference file (Final) and estimated uniformity (Final_minus_stress)with the stress being provided in C2000282

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