(Tanaka, Miyakawa)

Our guess seemed to be correct. We replaced two 1-inch steering mirrors to 2-inch mirrors, and we removed two steering mirrors from the current path that were used to merge the new beam path of neoLASE to the original path of FB laser to the PMC. It required the change of the beam path, so after some hard work for the realignment to PMC with the new path, especially with careful centering to the AOM hole, PMC was locked with low power. At this stage, we did not want to change the alignment anymore upstream of the AOM; we performed the fine alignment using pico motors. During the fine alignment, we did see much more stable transmitted power of PMC already.

We measured the intensity noise again, and we obtained 2-3 times better results at low frequency than the day before yesterday's result (See Fig.1, red, blue, and green lines). Current intensity noise of the neoLASE laser is almost the same as the FB laser or slightly better.

However, some sudden fluctuations sometimes exist, and they disturb the ISS lock. We need more investigation.