camilla.compton@LIGO.ORG - posted 10:43, Thursday 08 October 2026 - last comment - 05:39, Friday 09 October 2026(92245)
WIP Table of Buildups before and after BS swap, with and without arms.
Sheila, Louis, Elenna, Camilla. Follow on from 92167.
Louis made this Googledoc. It incudes a table of Powers before and after BS swap, with and without arms. It shows that we now have a higher ratio of powers on POP ports with the arms that without the arms that we used to have in O4.
There’s still work done on this and finding better comparism times, but see attached table for arms vs no arms ratios.
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Focusing only on measurements from O4 till now (ignoring everything before 2023) and only on POPAIR B:
- The observed power ratios RF18 / LF and RF90 / LF in each configuration don't actually show any change from O4 till now. For PRMI, RF18 / LF ~ 10 and RF90 / LF ~ 8–9. For DRMI, RF18 / LF ~ 17. For DRMI with antiresonant arms, RF90 / LF ~ 2.5. (The single measurement of DRMI without arms has RF90 / LF ~ 2.0.)
- For PRMI, switching from no arms to antiresonant arms should raise both the carrier power and the 9 MHz power by a factor of 2.2, theoretically (91738). It seems hard to explain the observed factor of 4 just due to a change in the cavity configuration, rather than something like POP path clipping.
I ignored the 2019 and 2020 measurements, which aren't consistent with the later ones, including having very different ratios of RF90 / RF18 (some configuration/electronics change?).