In relationship with the Paolo‘s entry <a a href="https://logbook.virgo-gw.eu/virgo/?r=19237" class="urlcopy" target="_parent" >Horizon drift Vs arm asymmetry</a>, to evaluate the current situation of the Etalon effect in our input mirrors I repeated part of the analysis presented in the entry <a a href="https://logbook.virgo-gw.eu/virgo/?r=18390" class="urlcopy" target="_parent" >Etalon, mirror characterization and end benches alignment: the revenge</a>.

In the first figure the usual mirror temperatures (red symbols, evaluated if the OMC is locked) and the power transmitted at the arms terminals (black symbols, evaluated only in science mode) are reported. Are evident the large temperature oscillations due to the in and around tower commissioning interventions occurred after the VSR1 completion. These oscillations could be the responsible of the large horizon variation underlined by Paolo.

In addition, in the second figure the relative power variation measured (black symbols) at the end of the arms is compared to the expected value (red symbols) computed through the double cavity model. As underlined in the entry <a a href="https://logbook.virgo-gw.eu/virgo/?r=18390" class="urlcopy" target="_parent" >Etalon, mirror characterization and end benches alignment: the revenge</a>, the realignment of the end benches performed during the run restored the agreement betwen the measurement and the model. According to the second figure, after 2.5 months the end benches should be again misaligned, expecially the NE.