The displacement spectra and corresponding RMS of the PR2 and PR3 lengths were measured overnight, and the results are shown in the attached figure.
These suspensions were in the lock acquisition state with the BF length damping.

The displacement RMS above 0.1 Hz for both suspensions was around 0.1 µm.
PR3 had larger noise at lower frequencies, resulting in a higher total RMS for PR3 compared to PR2.

The motivation for this work is to avoid degradation of the DARM sensitivity when the micro-seismic activity is high, as observed in O4a, likely due to larger PRCL causing scattering noise.
However, this measurement was performed on a very quiet night.
Therefore, we will measure these spectra again in the near future when the micro-seismic motion is high and compare it to the data from O4a.