To do this better:
1) Just step the analog input to the AOM (i.e. no RF switch) and measure the PMC trans output with a fast DC coupled PD. IMC should be unlocked and disable during this part. We want the PMC ringdown to be faster than 1 us.
2) Re-install a fast PD in the MC trans path without disrupting the existing MC trans QPD setup.
3) Measure IMC ringdown and fit the data to find the cavity losses.
4) Think about how to use the Isogai, et. al (2013) technique to better measure the losses, taking into account the mirror transmissions.