K. Tanaka, Akutsu on Dec 19, 2018

Viewport window for the transmitting light beams

Prepared a  very high quality viewport window for the transmitting beams from EXT to the optical table. The window (Fig 1) was categorized "Cat.B", which was produced with identical specification as that of Cat. A at different timing. Today the window was combined into a viewport adapter (Fig 2). According to my memo, the window was originally ordered for "the first planned" iKAGRA, and unfortunately the coating specification for green light was not defined for the window. as in 2014 July, I did not think that a bKAGRA TMS would be still partly set up in air. We just left the combined viewport witout installing; once the window is installed, the beam paths would be changed due to the thickness and the wedge of the window, so we wait  for the next day, considering the time sharing for interferometer commissioning.

The arrow marking at the side of the window (Fig 3) is explained as  "Marking: an arrow on the OD at the thickest point of the wedge pointing to S1." in the cost estimation sheet, where there are also descriptions that "Wedge: 0.75deg (+-0.05deg) on S2". The adaper was such deisgned that the no-wedge side S1 should come to vacuum side, while the wedged side "S2" should air. On the combined viewport window unit, I indicated the wedge side with a marking by a magic pen (Fig 4); you can see it in the right-hand side in Fig 4.

Installed an oplev viewport

We installed an oplev viewport #0042 to EXT (Fig 5). Shamefully I found that the mirror for the oplev was not installed but only the mirror holder was installed in the chamber; I thought it has been... Anyway, probably we don't need the oplev now. (or, we might be able to use the backside of a stirring mirror which can be seen from the installed viewport).