Figure 1, this results in a large coupling of laser frequency noise, as shown by the ~50% coherence with LSC_PRCL which is an out-of-loop sensing of frequency noise. That coupling is fluctuating in time, the noise floor moves down at the same time as the line at 3345Hz (SSFS line) in B1 moves down in amplitude.
Figure 2, it also visible in the live noise budget, the quantum (shot) noise of the SSFS (laser frequency) sensing is at the same level as the DARM (B1_DC) shot noise.
