We misaligned the NI mirror and we aligned the PR mirror to have the simple PR reflection on B2. Then, we analyzed the coherence between the transmission of the IMC and the beams acquired on the two B2 photodiodes. We discovered that the time trends of these signals were slightly different (figure 1) and that there was a lack of coherence between 1 and 10 Hz. We checked the path of the B2 beam on the bench and we found that the beam was a bit misaligned on camera and photodiodes. We optimized the path of the beam on the bench slightly moving the PR mirror recovering the alignment on the camera. Finally, we re-centered the photodiodes acting on SIB2_M4/M5/M6. At the end of the intervention, the time trends of the IMC transmission and the B2 signals were almost the same (figure 3) and the coherence improved (figure 4).
It is likely that the B2 quadrants are misaligned too. We will realign it next week or as soon as it is needed.