With Kozu-kun.
As the oplev was out of range, we checked the position of the beam on the QPDs.
- QDP No. 31 is in the path of the lens and measures length.
- QDD No. 44 aims to measure tilt.
- The full QPD is 10 mm × 10 mm.
- On the tilt sensing QPD, the beam was 3 mm to the left of the centre and 1 mm below it.
- It might not be relevant information but we still report that QPD board No. 44 has its two green LEDs on whereas QDP board No. 31 has only one on.
During the process of measuring the position of the beam on the length sensing QDP we noticed that the beam was not reaching any of the two QPDs anymore. Then we noticed that the beam was indeed coming out from the wiewport but was not reaching the first optic of the system, which is a folding mirror. Instead, the beam reached the mirror holder but missed the mirror by a small distance. Initially we thought the mirror holder was loose and we had accidentally moved it, but tapping and poking the holder with a finger proved it was robustly fixed. Therefore, likely, the optic moved. Unfortunatelly, because of lack of communication the folding mirror was moved in tip and tilt and we will have to recover the alignment once the suspension is recovered.