WP# 6379

Peter, Kiwamu,

As a part of the PSL ISS/mystery noise study, we swapped a mirror to reduce the light power going to the ISS box during the maintenance period today. This is a temporary configuration and we will decided on the final configuration based on the results we get out of this configuration.

Since the ISS box is not used for stabilizing the intensity, we don't expect any impacts on H1 noise or stability performance.

[M32 swapped, HWP rotated]

We swapped mirror M32 with an window, W1-PW-1025-1064-UV-45P without pulling out the entire mount. This decreased the light power coming into the ISS to 4 mW (measured by a Vega) as expected from presumably 400 mW. We rotated the half wave plate in the box to maximize the transmission and therefore we think PDB is now sensing much higher P-polarizing light than S-pol. Checking the reflection of the polarizing BS, we didn't visually see any light on a laser card which is good. After the swap, the power on PDB was measured to be 2 mW as expected due to a 50/50 BS in the box. After the fine alignment, PDB had a DC output of about 5 V. We also confirmed that the ADC was not saturating. We placed a Kenteck beam dump behind M32 to capture the large transmission.

We had a difficulty aligning the beam back to the center of PDB due to the narrow space and view. We spent an hour trying to get back to good alignment. During this process, we touched M32 and the steering mirror right in front of PDB. Once fine alignment was established, we re-centered the light on the QPD in the box by touching the steering mirror in front of it. Also, we removed an optical filter labeled "NG5 2mm". This had been attached to the entrance hole of the ISS box in the inside.

The attached are pictures showing the optical layout after today's activity. You can see M32 and the newly installed Kenteck beam dump.