KAGRA Logbook

MIF (General)

yoichi.aso - 18:16 Monday 17 January 2022 (19489)

REFL beam clipping by a steering mirror

Ushiba, Nishino, Yasui, Yano, Tamaki, Aso

Today, we wanted to construct a beam path for the REFL beam to the PDs.
However, we found that the REFL beam coming out of the Faraday was clipped by STM2, as shown in the first page of the attached PDF.

In order to slove this problem, we decided to move STM2 a bit. We also rotated the mirror mount by 90 degree as shown in the second page of the PDF.

Before doing this work, put several irises in the beam path to preserve the beam path. We put irises after MC, before IMMT1, after IMMT2 and at the POP table.

When moving STM2, we put a metal bar pushed against the pillar of STM2. This bar is set to be parallel with the mirror surface. By moving the STM2 pillar along this bar, we can preserve the beam spot position on STM2.

After STM2 was moved, we adjusted the orientation of STM2 to put the beam through the irises.
We also checked the beam spots inside the Faraday and found no beam clipping.

By doing the above, we were able to see small flashes of IR in the X-arm.

Images attached to this report

19489_1642410959_2022-01-17 14.51.30.jpg

Non-image files attached to this report

STM2 clipping.pdf

Comments to this report:

takafumi.ushiba - 19:15 Monday 17 January 2022 (19490)

After seeing the flash, I tweeked IMMT1 and IMMT2 manually to maximize the amount of TEM00 flash.
However, I cannot find the good alignment.

I'm not sure why but one possible reason is alignment falls into local maximum.
So, I decided to scan the alignment of IMMT1 and IMMT2 until tomorrow.
So, please do not use IMC, IMMT1, IMMT2, PR2, PR3, ITMX, and ETMX tonight.

yoichi.aso - 6:24 Wednesday 19 January 2022 (19497)

On Jan. 18th, we tried to recover the alignment of the IR X-arm after moving STM2.

Just moving IMMT1 and IMMT2 did not yield a good alignment. So we checked the beam positions on PR2 and PR3 to find that they are off centered by a few cm.

We did the same iterative alignment process as before, i.e. centering PR3 with IMMT2 while making the REFL beam go through the Faraday with PR2.

After this work, we confirmed that PR3 is well centered and PR2 is nearly centered (maybe 2mm off centered ?).

We will scan IMMT2 and PR2 to find IR resonances later. (We forgot to remove the target plate on PR2. So we need to remove it first).

A tip:
When trying to align the reflected beam back through the Faraday, dithering ITMX at 2Hz helped a lot. This way, we can always find which beam is the reflected beam from ITMX (it moves up and down at 2Hz).

takafumi.ushiba - 8:52 Wednesday 19 January 2022 (19499)

After the work, we found the cap of the IR viewer switch went away somewhere and we couldn't find it yesterday.
So currently IR viewer switch has no cap.
Sorry for incovenience.