Tonight we performed some measurements in order to improve the assessment of arms losses and finesse.

First we tried to understand if the mutual positions of mirrors and benches could affect the DC power of the B1p, B4 and B5 PDs. Therefore we performed different tests:

1) North arm locked, West arm misaligned. Moving the SDB1 bench (bench LC open) didn't affect the power level on the PDs. The WI mirror was misaligned by ~800 urad in TY.

We performed the lock/unlocked measurement, and at least from a qualitative point of view it seemed that all the PDs see a higher power when the cavity is unlocked, as expected. Measurements start from about 19:08 UTC, as shown in figure 1.

2) West arm locked, North arm misaligned. Same as before. Measurements start from 19:33 UTC.

3) Fast unlock performed with arms locked (one at the time), and arms unlocked with only ITM aligned. They start from GPS = 1194982918 for West arm, GPS = 1194983935 for North arm.

4) Finally, we closed one at the time all the PD shutters to measure their floor level. They start from GPS = 1194984662.

Then, we relocked the ITF. The WI_PAY corrections saturated and Lucia restored the controls, so that after some attempts we could relock. Further checks are needed and Valerio is already aware of the situation.