We have collected some data with SR aligned both this Tuesday and last Tuesday which is an opportunity to look again at how the 1/f^{2/3} depends on SR aligment

Figure 1 shows for reference a noise budget in standard condition with SR misaligned

Figure 2 is last week on Feb 4 with SR aligned. To match the observed noise curve I have increased the level of 1/f^{2/3} noise by a factor 1.6 compared to the SR misaligned case. This is in addition to the 1.38 change in level due to change in optical gain.

Figure 3 is today on Feb 11 with SR aligned. Again to match the observed noise curve the 1/f^{2/3} noise level is increased by a factor 1.6 compared to the SR misaligned case. In this case the SSFS noise is slightly lower as the EOM passive RF filtering was put in place this morning https://logbook.virgo-gw.eu/virgo/?r=66176

This is a similar conclusion from measurements from November 2024 https://logbook.virgo-gw.eu/virgo/?r=65488, but this time the frequency noise has been lower, likely thanks to the BS TX being in full bandwidth, good weather and the additional reduction due to the EOM RF filtering. And the measured factor remains comparable to the 1.7 factor that can be estimated from SR recycling gain for HOM.

/users/mwas/detchar/toySensitivity_20250211/toySensitivity.m