Participants: Matteo Tacca, Eleonora

Today we installed the 2" telescope mirror in the BS chamber. The infrared and green beams have been superposed. They impinge the first telescope mirror and are reflected on the second one (PR suspended mirror). Beams are both hitting the PR mirror almost in the center. We observed that the green beam is slightly elliptical (also before hitting the first telescope mirror)

Then we tried to send the beams back on the BS mirror but we didn't manage to move the yaw of the PR mirror enough to do that.

We spent some time investigating this issue.

Some remarks:

1) The PR mirror is very sensitive to pich motion: few turns of the pitch picomotors screw are enough to remarkably change the vertical angle of the beam.

2) The yaw picomotor screw works fine as we can observe the relative slide to move (in both directions) when turning the screw.

3) We checked that the mirror is free to move and it not touching the earthquake stops

4) It was possible to observe the pitch motion using the error signal of the optical lever. The displacement is big enough to make it sweep the all the signal range  (from -5V  to +5V). Assuming a calibration of 2.2e-4 rad/V this means that the yaw motion achievable is al least larger than 2.2e-3 rad. 

5) Another critical point is the intermidiate mass. During the mirror istallation we noticed that one side of it was almost touching the magnet holder plate. We cannot rule out the possibility that the yaw motion is limited by this.