We used the new prism protection shield on the PUM prisms during the welding of the ETMy monolithic in Dec and again this last week.  We used the shield during the welding steps but not always during the lower power annealing steps, as was assumed by the users.  We think the shield caused more stray beams from the welding laser than when we weld without it.  We found more stray beam damage to curtains and garb than in any previous welding session, all of which we tried to mitigate.  Possibly we could consider making the shield out of a different material than copper.

We also found that one of the prism glue joints suffered some heating, and subsequent charring, at the exterior of the prism when the shield was not in place during annealing.  This occurred on only 1 prism.  The other prism had the shield in place for all of the welding (as is standard) and for the annealing in Jan which is why we didn't see the charring.  (We did not observe any stress fractures in the glass as was seem in the ETMx PUM!)  So, the new shield has the following:

PRO
Prism joint is better isolated from heating/burning during welding.

CON
Shield causes more CO2 beam reflections which are difficult to manage.

Below are some pictures of the shield and the prism charring when the shield was not in place.  Note, we had to cut a half circle view hole on each side of the prism for better visibility of the horn welding.  Also, as shown in the pictures, it was difficult to get the shield positioned against the optic.