[Nagano, Nakano]

From today, we started to prepare the beam separated from main pass.

Aim
The aim of this work is preparing the beam bypassing PMC which does not exist yet.
Unfortunately, PMC delivery is delayed and will be delivered in the beginning of Aug. (still under discussion).
In the current setup, the beam does not go to IMC when the PMC is not locked.
This means that when we work on PMC, such as PMC locking and so on, we cannot do works after the IMC, such as IMMT work.
This could lead to the delay of the total schedule.
To avoid this delay, we should prepare the beam bypassing PMC.
This allows us to do works related with PMC and the works after IMC parallelly.

What we did today
We considered where the bypassing beam should be picked off and decided to use the beam reflected by the PBS of the first Faraday isolator.
(The beam is planed to inserted again just before the EOM for IMC.)
Since we used the PBS to adjust the beam power incident to IMC and we cannot use the PBS for this purpose any more if we use the PBS for the bypassing beam, we installed a new PBS in the end of PSL at first.
Then, we installed some mirrors to align the bypassing beam and half-wave plate and PBS to adjust the bypassing beam power.
Finally, we measured the beam profile of the bypassing beam as shown in the figure.
(Zero point is set as the position of the second new installed mirror, we named it ME.)
This beam will be mode-matched to the mode of IMC with a few lenses.

Next steps
Calculate mode matching and install a few lenses for the mode match.
Align the beam and confirm that we can lock IMC using this bypassing beam.