Aritomi and Yuhang

Last week, we closed Auto-alignment (AA) loop and monitor FC_tra for half an hour. As shown in the attached figure 1, both FC_tra_GR and FC_tra_IR drifts.

With the AA loop closed, I locked FC while transmitted GR hits on different positions of Camera_tra (different alignment). As shown in the attached figure2, FC_tra_GR changes according to different positions (alignment). Therefore, although the incident beam axis aligns with the cavity axis by the AA loop, there is different cavity behavior for GR_tra for different alignment which is causing the long time drift of FC_tra. Probably the situation will be even more different for IR, which should be checked soon. For example, it is similar to the FC optical losses for IR is different for different alignment conditions.