After POP table realignment, I checked OLTF of MICH and PRCL because we replaced BS.
Figure 1 and 2 shows OLTF of MICH and PRCL, respectively.
Both gain are slightly larger than before but acceptable level.

Also, I measured spectra of MICH error, PRCL error, and POP90 signals but no timeto summarize it.
So, I will post it tomorrow.

Attached figure shows the spectra of POP90, MICH error, and PRCL error signals at several timing.
Blue and black lines show the spectra on July 31 and Aug 1 during PRFPMI_RF_LOCKED state (before POP work).
Brown and red lines show the spectra yesterday with and without ISS.

As you can see, PRCL and POP90 signals becomes worse after POP work, while MICH has no significant difference
Also, a part of noise enhancement could be reduced by engaging ISS.
Since we also had the work for laser power increase on Aug. 2, we need to carefully check what work caused the problems.

I checked ISS spectrum (fig1).
As yu can see, current laser intensiy noise after IMC is larger than before.
However, PSL power up doesn't seem the cause because ISS spectrum on Aug. 2 was quiet.
Also, we can see the noise excess even when there is no IFO controls, so it is unlikely due to the PRFPMI control.
Did POP alignment work affect IMC output?

I guess Miyakawa-kun did something in the PSL room for the stray light mitigation on the GR laser body?? in the last week in parallel with your POP works?

I checked spectra of fiber laser outputs before and after PSL power up.
Figuire 1 shows the power spectrum of fber outputs every one hour before (lower graph) and after (upper graph) PSL laser power increase.
Though absolute fluctuation when fibser output is around 6W is smaller, the intensity noise varies time by time.
So, it is very likely that intensity noise was there even before power up (and also POP table realignment).

Then, I also compared current intensity noise with the one during O3GK.
Figure 2 shows the spectrum of fiber output and IMC output.
Figure 2 also show the coherence between laser output and IMC output.
As you can see, intensity noise during O3GK is much smaller than current one, and coherence between IMC output and laser output is low.

So, it is better to check the laser and recover the stbility during O3GK.

[Uchiyama, Ushiba]

Today, we found that wedge direction of a newly installed 2-inch BS was not good (sorry for my stupid mistake), and flipped it.
Due to this change, alignment of downstream was slightly changed, so we realigned them.
After this change, beam size on POP WFS QPDs seemed fine.