aLIGO LHO Logbook

H1 IOO

stefan.ballmer@LIGO.ORG - posted 12:11, Tuesday 01 October 2013 - last comment - 07:49, Wednesday 02 October 2013(7934)

Faraday isolation ratio measurement

(Kiwamu, Paul, Stefan)
This morning we found the back-reflection from the PRM, leaking through the Faraday, back on the PSL table.
We measured the following powers:
- direct beam, sampled by ~30% BS: 339mWatt
- return beam, sampled by the same ~30% BS: 37.0uWatt
- as reference, we also measured the power on the REFL beam on ISCT1, just after the periscope: 6.94mWatt

Faraday isolation ratio: 37.0uW/339mW, minus other losses (IMC visibility, PRM reflectivity)

Comments related to this report

kiwamu.izumi@LIGO.ORG - 07:43, Wednesday 02 October 2013 (7954)

Link

Some more small information regarding to this measurement:

We left these two temporary beam splitters in the main beam path just in case somebody wants to return to this measurement in some near future.
When we obtained the returning beam at the PSL, we took this opportunity to realign the REFL path on ISCT1. The beam is aligned such that it hits the center of almost every optics, Length RFPD and BBPD.
The reason why we didn't get the returning beam the other day (see alog 7926) was simply because of a big misalignment in PRM which we noticed after we came out from the PSL. It was not difficult find it once the PRM was coarsely aligned back to the nominal point.
We used a hand-held type power meter, Ophir Vega, for this power measurement.

kiwamu.izumi@LIGO.ORG - 07:49, Wednesday 02 October 2013 (7955)

Link

The "good" alignment in PRM is :

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