With Seiya Matsuo
We found that the beam was not perfectly aligned to the LPD used to monitor the beam power just after the laser source. This condition had probably existed since before O3GK.
We also confirmed that the LPD became saturated when the beam was fully aligned to it. To avoid this saturation, we installed a BSX11 beam splitter, with 90% reflection and 10% transmission, just before the LPD and dumped the 90% reflected beam. After this modification, the beam could be fully aligned to the LPD without saturating it. The LPD threshold in the Pcal GRD was also adjusted accordingly.
However, this work appears to have affected the beam alignment. A change in the beam alignment was observed inside the Rx module. On the other hand, the beam position on ETMY did not change significantly, so we believe that the alignment can be recovered using the picomotors.
We will correct this beam alignment the next time ETMY can be aligned.
