Marc, Michael, and Yuhang

When we lock filter cavity with GR, IR detuning has change related to alignment. When GR automatic alignment (AA) and pointing loop is closed, IR detuning change can be stabilized.The filter cavity pointing loop is working mainly to fix the injection beam on end mirror. AA works to align filter cavity to the incident beam.

To check how detuning change for different alignment condition, we can change the pointing. By pointing the incident beam to different positions on end mirror and keeping AA loop closed, we can get AOM frequency for each point on end mirror when BAB is on resonance. The change of position on end mirror gives us a dependence of detuning as end mirror beam hitting point. In this way, we call it a detuning map for end mirror.

The changed parameters are not only beam hitting position on end mirror, the other changed parameters are input/end mirror angles and cavity length. A typical change for input angle is 40urad, end angle is 10urad and cavity length is 0.2um. Since the optical axis of filter cavity is almost the same for GR and IR, the GR AA should work also for IR. In addition, GR length control should also work for IR. Therefore, the map we get should just depend on beam hitting position of end mirror. The corresponding map is attached.