With the previous optical lever setup, I couldn't recouple a pitch to longitudinal coupling. I suspect that might be due to a misplacement of the len QPD. Therefore, I adjusted the position of the LEN QPD again according to the signal output while one of the pure pitch mode is excited. I tweaked the position but couldn't remove the TM pitch oscillation from the LEN QPD signal. I believe this is because the beam is not centered vertically. I will try to implement the correction in the diagonalization matrix for that later but the coupling ratio between all degrees of freedom is very small already.
I redid calibration for both QPDs. See attachment for the calibration curves. Distance parameters are available at 7751. The rotational angle for the transformation for tilt sensing OPLEV is 2° while that for length sensing OPLEV is 2.2°. The beam spot at the optic is estimated to be horizontally off-centered by 1.3 cm torward the +T side, and vertically by an unknown value (also close to 1 cm).
The current OL2EUL matrix is
TILT_PIT | TILT_YAW | LEN_PIT | LEN_YAW | |
L |
0.00117035902 |
0.0402812829 | -3.06589521 | 0.13032171 |
P | 2.06114698 | -0.103151637 | 1.2651721 | -0.0537785503 |
Y | 0.0900276168 | 3.09856022 | 0 | 0 |
TF measurements were saved and will be attached later as soon as I have access one of the workstations.