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

TF measurements were saved and will be attached later as soon as I have access one of the workstations.