The beam position on the test masses is estimated from the a2l gains from the last minimization (method explained in alog 22426)
The gains values before and after the mimization are attached in a2l_gains_1151366417.mat.
The corresponding beam positions are reported in each suspension base in the Fig.1 attached. We can see that the beam is not more off-centered than previously.
However, we can observe that the beam hits the ITM and ETM in differents vertical places now in each cavity, suggesting an increase of the beam tilts in PIT with respect to the optical axes (HARD PIT).
That is what I tried to represent with the projection in Fig. 2, where you can imagine the cavities facing you: the figure axis orientation is the ETMs coordinates orientation.
The YAW tilts are reduced in both cavities. But their directions were opposite before the a2l minimization whereas now both cavity axes have a negative YAW tilt (in the ETM coordinates).
I don't know when the script was run for the last time before that, but it could give an indication that the beam is now more tilted in HARD PIT at 40W, and it enters the cavities from the lower area of the ITMs.
Arm | Before a2l | After a2l |
X |
D pit = 1.3 mm D yaw = 9.4 mm |
D pit = 7.8 mm D yaw = 2.4 mm |
Y |
D pit = 2.3 mm D yaw = 6.5 mm |
D pit = 8.0 mm D yaw = 6.3 mm |