This measurement was done on 20210622. 

I measured the CCFC locking accuracy with the new beam spot (Fig 1). CCFC calibration amplitude is 166mVpp and CCFC filter is gain of 1000 and LPF of 30Hz. CC2 mass feedback gain is 2.7.

Compared with old beam spot, the locking accuracy without CCFC is smaller. The locking accuracy with CCFC is similar to before because it is limited by high frequency noise.

Then I measured FDS with CCFC (Fig 2). The squeezing degradation parameters are as follows. Here are some points of this result.

• Because of improved reflection mode matching, the propagation loss is lower than before and squeezing level is 2.4dB. The propagation loss is 49%, which is consistent with 36% of propagation loss in PRL paper plus 20% pick off (0.64*0.8=0.51).
• In addition to the 100Hz bump, there is a large bump around 50Hz. This bump should be related to the new beam spot because this bump was not present in the old beam spot.
• The detuning fluctuation is ~20Hz with new beam spot. I think it is better to use the old beam spot for CCFC FDS measurement due to the bump around 50Hz and larger detuning fluctuation.

sqz_dB = 10.8;                    % generated squeezing

L_rt = 120e-6;                    % FC losses

L_inj = 0.32;                     % Injection losses  

L_ro = 0.25;                      % Readout losses (propagation loss is 49%) 

A0 = 0.06;                        % Squeezer/filter cavity mode mismatch

C0 = 0.02;                        % Squeezer/local oscillator mode mismatch

ERR_L =   1e-12;                  % Lock accuracy (m)

ERR_csi = 30e-3;                  % Phase noise (rad)