On the gate valve unit to be installed in-between the PR3 and PRM chambers, I replaced an originally-installed glass window with a new (but purchased in the last year) viewport window with anti-reflection coating: JGW-D2214401. (Category L)

The screws were tightened in 5 Nm with a torqu wrench.

Looking at the peformance now, this viewport window would not be suitable for our purpose..., as this is a broadbandly AR window. For example, for the similar case, I used a very high quality coated window; see wiki, and klog5701. Hmm...