[Chiaki, Haoyu, Marc, Matteo]

We rotated RBS1 to have the HR side on the input beam. Then, we realigned the IR beam on the camera and PD in transmission of this optic. 

We checked the beam profile far after RBS1 reflection and could still see not perfect round shape.

We installed a pick-off mirror between LNS1 and LNS2 and could see also some non-perfect round shape of the beam (see fig1 far from the optic). We actually suspect some clipping on the right side of the beam (in fig1) more than astigmatism.

We also checked before LNS1 and had some similar conclusion even though we did not had good picture of the beam.

It is a bit tricky to check the beam between the 2 mirrors of the periscope but it seems that even if the beam is a bit low on the top mirror, there is no clipping there. It would mean that the clipping could come from the in-vacuum optics.

A good check could be to lock the GR beam and check from the GR camera if we see similar clipping. If yes, the culprit is on the common path of GR/IR. Otherwise, it might be due to something around the in-vacuum dichroic.

Also, discussing with Ushiba-san, a possible explanation for the clipping could be the cooling of X end that may affect the beam path after the mirror as the mirror is moved vertically during cooling.