NikoL, RickS

First, we re-installed the transmitter module shutter (Lasermet S/N 1258) that had been repaired by Filiberto and RichardM).

Then, we proceeded to investigate the clipping that had been reported based on observation of peaks in the Pcal Rx sensor signal ASD displayed in the control room.

We found that the outer (lower) Pcal beam was WAY off center (beam to the right in the first attached photo) at the Rx module power sensor.  Since doing in-chamber alignment of the Pcal beams at all four end stations, this is the first time we have seen significant beam movement at the Rx power sensor.

Inspection of the alignment irises revealed that the Outer Beam  pointing was also significantly off (several mm left of center) on the far iris (see second attached image), with the temporary, kinematically-mounted retro-reflecting mirror in place (fourth attached image shows optical layout in Tx module).

Given that the inner beam had not moved at the Rx sensor, and that the pointing was off in the Tx sensor, it seemed that either the beamsplitter or one of the two downstream mirrors that direct the Outer Beam out of the Tx module had moved.

The attached video shows that the BS mount moves significantly, and much more than expected, in response to rocking forces applied at the top of the mirror mount.

Either there are issues with this particular mount, or this type of mount has design flaws.  Or maybe it is the way we are suing them (over-tightening?).  The third attached image shows that a piece of paper could be slid under the back of the base, indicating that the base is only contacting the breadboard one edge.    I've discussed this briefly with Stephen Appert and we plan to investigate this flaw and possible solutions with the SYS group.

We adjusted the beamsplitter to re-center the Outer Beam on the Rx power sensor aperture (see fifth image below, with both beam incident on the Rx power sensor aperture), fine-tuned the alignment onto the Far Outer Beam iris in the Tx module, then proceeded with a standard end station Pcal calibration measurement suite.  The scanned log of the measurements is in the attached .pdf file.

Current results are in good agreement (with a few hundredths of a percent) with the mean of the previous Yend measurements.