[Sheila, Kiwamu]

This morning, we switched the simulated laser from the 532nm to 1064 nm one to make the alignment work more reliable. After that, we managed to finish all the necessary work for installing the 90/10 BS in POP. We are done.

Some pictures are available in Resourcespace (https://ligoimages.mit.edu/?c=1483).

(Installation of a 1064 nm laser)

The difficulties we had yesterday were due to the use of a green laser (see alog 12507) although green light is usually more convenient than IR since it is visible and therefore easy to handle. In addition to it, a concern we had is that insertion of the 90/10 BS in the path may further reduce the power of the green light and consequently may make it difficult for us to find the HR reflected light which had been an issue yesterday and in the past. To asses this power reduction issue, we temporarily inserted the BS to see how dim the beam would become. The BS reflected seemingly more than 50 % of the green light and therefore it was far from transparent. We decided to switch the laser to a 1064 nm one.

(Alignment work)

We changed the injection path such that the IR laser bypasses PR2 as PR2 has an extremely low transmissivity for 1064 nm. We placed the fiber launcher at the east side on the table and placed a temporary steering mirror in front of the 1st picomotorized mirror (M1). In this way, the simulated beam skipped PR2 and the 3" mirror behind PR2 and joined the real path before M1. This worked really well. We could obtain decent alignment after approximately half an hour of alignment work on the fiber launcher and temporary steering mirror. We checked the centering on the QPDs by looking at MEDM screens and confirmed that both QPD A and B were well centered.

(Insertion of BS and more alignment)

We placed the BS and its associated V-black glasses according to the drawing (D0901094). Then the misalignment caused by the insertion of the BS was compensated by steering the two picomotorized mirrors (i.e. M1 and M2) by hand. This also went very smooth. We could get back to the good alignment within half an hour or so. We checked the alignment once again with the MEDM screen and confirmed that both QPDs are well centered. To wrap up the mission, we then took out the temporary steering mirror and fiber launcher out of the HAM3 chamber. We are done.