The detuning measurement had some problems. The main issue is that pointing loop was not kept to be zero while these scanning.

When pointing loop is kept to be zero, either we introduce pertubation to input or end mirror yaw/pitch, the beam hitting position can change only on input mirror. Therefore, when we do this scan, we are doing a map similar to elog2615. But instead of end mirror in elog 2615, this scan is for input mirror. Attached figure 1 shows the schematic of this scanning process.

Since the PR/BS pointing loop has angular scanning range of about 200urad, which can scan a range only about 0.8mm on input mirror. After doing these scan on input/end mirrors y/p, we got detuning change, input/end mirror oplev signal, and pointing error signal as attached figure 2-5.

With position change of about 0.8mm on input mirror, the detuning change is less than 5Hz. (This is a detuning change smaller than the flat region found on filter cavity end mirror in elog2615.)