sheila.dwyer@LIGO.ORG - posted 09:06, Monday 06 October 2025 - last comment - 12:38, Monday 06 October 2025(87309)
SFI2 temperature with ZM fringe wrapping measurements
Camilla, Sheila
We repeated a test similar to 78125, where we changed the SFI2 temperature and measured fringe wrapping by exciting ZM2 and ZM5. The temperature of SFI2 changes the backscatter shelf amplitude seen when exciting ZM2, but not ZM5, suggesting that the source of the scattering is upstream of the isolation of SFI2.
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The attached plot shows ZM2 and ZM5 fringing measurements at LLO. The total OMC current is 50 mA.
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Here's a model of our ZM fringe wrapping measurements (the same plot as in 86836, plotted with a model that's roughly emulating Valera's measurement above. It looks like LLO has about 200pW of interferometer light reaching the filter cavity, but none of the extra scatter we see from before SFI2.
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