I replaced thorlabs PD55A for ACAV_RCTRANSPD with PD36A, ACAV TF now looks reasonable.
From a quick look, ACAV pole is 57.4 kHz (previous result, 54kHz), RCAV pole is 39.7 kHz (previous result, 38kHz).
1)result for RCAV TF, with RCAV's PD55A for RCAV_RCTRANSPD
2) For ACAV, I used PD36A to measured ACAV_RCTRANSPD, and its TF.
However, when the spotsize is too small, the result looks weird (like yesterday,) so I moved the new
PD where the spot is not too small and measured the TF again to get the reasonable result.
For the original PD55A for ACAV_RCTRANSPD, I also tried moving it for various spotsizes,
the results are still bad (look like that from yesterday), so I decided to go with the new PD.
3) As Frank suggested that I can use the 120 MHz PD for beat, to measure the TF, I also tried that.
The beam from ACAV was blocked while I measure RCAV TF, and vice versa, the results are quite similar for
both RCAV and ACAV, here I show only the result from RCAV.
I'm not sure if this means the spotsize on 120MHz PD for beat is too small or not. This might worth checking out.