I'm going to work on the X arm to measure the arm cavity finesse.
The idea is to measure the cavity transfer function to estimate the frequency of its cavity pole. That should be a more accurate measurement than that based on the cavity decay time.
I'm starting now and I'm going to inject a swept sine excitation on the OMC_ISS_EXC input cable laying on the floor nearby the AP table (see pic).
In orderf to do that I disconnected the cable from the OMC breakout box laying on the floor. I'm going to plug the cable back in as soon as I'm done.
Since I need to measure the transfer function between TRX and MC_TRANS_DC I picked off the beam going to RFAM PD to send it to a PDA255 photodiode (cannibalized from the AbsL's PLL) which I installed on the PSL table.
I centerd the beam on the PD and I was able to see the injected signal.
I think I'm ready to measure the transfer function.
Except for the RFAM PD everything is as before.
I'm gonna go grab dinner and I should be back to keep working on that in about one hour.
Back from dinner. Taking measurements.