KAGRA Logbook

Report of the work on Feb 8.

First thing we did in the morning was to measure the transmittance of the OSTM
using the external beam. The mirror was supposed to be a 99% reflective mirror
for the P polarization with AOI of 45 deg, while what I ordered was a 99.998%
reflective mirror for the S polarization with AOI of 3 deg (+/- 10 deg).

Luckily the transmittance turned out to be as high as 97% for the S polarization
beam at 45 deg. The difference will make extra 2% losses in the GW channel but
it also gives more power for the AS RF.

Another concern was the AR. With injecting the 25 mW beam, however, the AR beam
could not be found. This means the AR must be lower than 1% if the minimum possible
light power one can see on a sensor card is ca 10 uW.

At around 3pm, the beam from the main interferometer came to the OMM/OMC area.
The commissioning team people, namely Nakano-kun, Enomoto-kun, and Sugimoto-kun
came to the area as well.

As was found by Nakano-kun earlier the week, the beam was off-centered at the
OMMT1. The gap was about 3cm. After Nakano-kun tried the fine tuning of the SRC
alignment, it became 1-2cm. Though the gap was a bit bigger than what could be
explained from possible errors, we concluded that this would be the final position
of the beam from the main interferometer. We then moved the OMMT1 to make the
beam centering.

At the end of the day, the OMMT1/2/OSTM were successfully aligned and we saw
a resonance at the DCPDs.

S.Otabe, R.Nakashima, and K.Somiya