I checked the TF of the amplifier used in the ACAV loop because I did not measure that yesterday. The amplifier's TF is flat at least up to 200 kHz. The Bode plots between the loop with and without the amplifier are pretty much the same. Thus, it is ok and won't cause a problem in the loop.
The setup is similar to what I did in the previous entry, except the output of the marconi is connected with the amplifier. See blue arrow.
The TFs between the two cases have similar shape. So the amplifier will not be the limiting component. The magnitudes (in arbitrary unit) are slightly different because I did not attenuate the power by the same factor it was amplified.
The UPDH box will be modified next to see if we can increase the loop bandwidth.