We concluded the analysis concerning the back-scattered light introduced by the OFI. We used the data mentioned in the logbook entries: 68910 and 68926. A presentation summarizing the analysis and the results can be found on the DCC: G2300951-v1.

We first estimate the G-factor from the spctrum during the noise injections and then we used this factor to simulate the scattered light noise projections.

In Fig. 1 it is show the noise spectrum considering the OFI displacement signals during the Earthquake in New Zeland (24th April 2023 00:42:00 UTC). In green is the correct projection, where the differential motion between the SRM and the OFI is shown. The orange curve takes into account only the displacement of the OFI. 

In Fig. 2 it is show the noise spectrum considering the OFI displacement signals during a low seismic activity period (27th April 2023 12:00:00 UTC). In green is the correct projection, where the differential motion between the SRM and the OFI is shown. The orange curve takes into account only the displacement of the OFI. 

The conclusion is that for the moment the back-scattered light coming from the OFI is not limiting the sensitivity of LHO.