Due to the presence of AOM, the length/frequency change influence GR and IR resonance in a different way. But if GR is always kept on resonance, IR detuning should have a change of 1.83e5 * cavity length correction.

In elog2611, I took a 24 hours monitor of detuning change and correction signal change. I checked the pointing loop is always kept around the good point. I used the simple above equation and compared the calculation and observed detuning change. To calibrate the observed correction to length change, the calibration method in elog2629 is used. Discrepancy between calculation and observation was found in the attached figure, but I think it is not surprising bacause the input and end mirror may have horizontal and vertical translational motion. By hitting on different position of mirror with 100um, detuning can change by few Hz.