What I did

• Ringdown and doppler measurements @room temp.
• Open loop TF measurement of PDH locking loop

Results

The obtained data are still in USB and floppy disk...
But the UGF of TF was about 3.1 kHz and phase margin was much larger than 30 deg.
Therefore, the lock seems to be stable one.

Next

• Cooling down to 10 K

I am planning to cool down the cavity to 10 K which is the designed temperature for the ET-LF.
And then monitor the finess in order to estimate the optical loss at 10 K.