NikoL, RickS

Following up on the work we did at Yend last week (see this Link), Niko inspected the beam positions at the input aperture of the Rx sensor at Yend yesterday after completing calibration measurements at Xend.

He found that the Outer (lower) beam had again drifted to the right (see attached photo), this time by a few millimeters.  This likely did NOT impact the calibration because it did not appear to be clipping at the Rx sensor aperture.

Given that it was near the end of the Tuesday maintenance period, we did not have much time to improvise a potential fix.  But we end up trying a kind of "flying buttress" approach.  We used a second ThorLabs base and some 5-minute epoxy we found in the toolbox (it was WAY beyond its expiration date of 1/21/2013, but it was unopened, so we gave iit a try) - see second attached photo.  If this epoxy actually hardens, it should help stabilize the post holder.   If this is the source of the alignment drifts, this may help.

We also tightened the set screw that holds the 1" diameter beamsplitter in place in the Newport U100 mount.  Slight tightening of the set screw resulted in the beam at the Rx module moving by more than the 1" diameter of the power sensor aperture.  This might indicate that the optic was not seated properly to begin with.  Maybe this is the real source of the alignment woes at Yend. We did not want to risk removing and re-seating it yesterday, but may try that in the future if this problem persists.

We carefully aligned both beams to the center of the Rx power sensor aperture before leaving the end station (see last attached photo).