Today we keep investigating on the beam astigmatism. As a first thing we realign all the optics on the bench and measured the beam in different position. There results will be posted in a dedicated entry by Yuefan which has also calculated the astigamism expected at 300 m on the basis of the measuremts done on the bench. (Very small).

Then we sent the beam in the pipe and open the first windows between the BS and NM2. The change in the shape when the windows is open is shown in this video.

After that we let the beam propagate for about 30 m in the corridor and move the small telescope mirror in order to have the beam as collimated as possible. We succeded in finding a position allowing to have a beam which remains pretty small (2-3 cm) up to the end of the tunnel.

After the small telescope tuning, the beam (both with closed and open window) looks different on the 290 target. Here there is another viedo who recorded the beam during the closure of the BS-NM2 windows. The beam with open widows looks still very astigmatic while with the close window is seems aftected by diffused light and very difficult to judge.

[I have the impression than after opening the windows for the first time it becames somehow dirtier and once we close it again, it affects the beam more than it was doing before.]

Some preliminary conclusions:

1) Tuning the 2"  telescope mirror position have a great impact on the beam shape at 290 m.

2) The windows seem to have a great impact on the beam shape at 290 m.

3) The beam seems well collimated and not significantly astigmatic when it propagates in the corridor.