We found that there was a lot of stray light on HWSX and a little bit on HWSY. Detective work and general snooping found that the beam going through the main HWS BS was hitting the rear of the BS rather than the dump behind it.
We adjusted the input alignment of the HWS beam as much as we dared, moving it away from the center of the BS closer to the top edge (in the picture shown below). More of the transmitted beam was dumped onto the beam dump behind the BS. This had the effect of reducing the scatter getting back to the Hartmann sensor by a factor of three or so. Unfortunately, should we move the beam too far across the BS surface, the concern is that the return beam from ITMX will be clipped by the beam splitter mount on transmission.
HWSX stray beam before changes to alignment on BS
The color range in this image is about 180 counts.
HWSX image after changes to alignment to BS
The color range here is about 60 counts.
HWSY stray light image
Color range is about 27 counts for HWSY.
Guide to beams on HWS BS
Input beam on HWS BS
Reflected beam from HWS BS
Beam dump behind HWS BS
Transmitted beam through BS
