KAGRA Logbook

MIF (General)

masayuki.nakano - 1:56 Friday 09 November 2018 (6920)

Xarm alignment

[Enomoto, Izumi, Akutsu, Michimura, Nakano]

What we did

- First, PR3, ITMX, ETMX were brought back to the best position of yesterday.
- Second, the flash appears, and I tried to increase the green transmitted power by using the POP-POM pico motor and the PR3. But it does not work well, and the TMSX GR PD signal goes up to only ~400 counts.
- Then, bring back the PR3 to the first position and lock the cavity. And I found the beam position on the ITMX and the ETMX were not good from the Tcam image. I brought those position to the center. At this time, I mainly moved the ETMX by 7 um in yaw and pitch. After those mirrors alignment, the trans power went up to ~750 counts, which is the comparable value as the yesterday's best.
- To find the IR flash, the PR2, the IMMT1, the IMMT2 were aligned by using yesterday's oplev value as the reference. Afterward, the PR2 was excited in pitch and we find the IR flash.
- After cavity alignment, we went to the Xend to align the TMSX table for IR. By using the green laser, the IR path was aligned. At the same time, the Green path was also aligned. However, the IR flash cannot be found in the camera immediately. So, we moved the camera around, and then the IR flash was found. But we could not find the TEM00 but we saw the higher-order Laguale Gaussian mode. We are not sure, but we afraid that the mode match to the arm cavity is very bad.

Memo

- The PR2 oplev were centered, after the cavity alignment.
- The TMSX IR PD gain was changed to 50 dB

Comments to this report:

tomotada.akutsu - 2:45 Friday 09 November 2018 (6921)

Figs 1 and 2: taken at the flange of TMSX. You can see an image of the ETMX (pink colored).
Fig 3 is the 2nd mirror of BRT; the bright green spot was observed when the cavity was locked to green. The spot was found lower than the horizontal center of the mirror.
In Fig 4, you can find the green spot on the 1st mirror is also lowered.
FIg 5: when the iris left on the BRT bread board closed, the green spot seemed lowered again.

So the TMSX is located higher now?

Images attached to this comment

koji.nagano - 9:36 Friday 09 November 2018 (6922)

Hi Akutsu-san,
Maybe it is not a main topic of this thread but could you find the ghost beam (i.e. AR-side reflection of ETMX) when the arm cavity was resonating?

tomotada.akutsu - 21:22 Saturday 10 November 2018 (6949)

Nagano-kun, thank you for remembering the topic; during the work, I found the ghost beam-like spot in the next (-Y direction) of the main green beam when the cavity is locked to green. Actually I think it would be an important thing to be confirmed from several viewpoints, and I took some pictures of them... so I will take time to estimate the separation of them and the angle and like to confirm/compare the number with the designed wedge angle.