Yesterday the reference cavity could not stay locked for more than half an hour. Today I tried to improve the alignment to make the lock more stable. I doubled the transmitted power (from 45mW to 90mW on the monitor PD) by mainly chainging the alignemnt in Pitch.

The cavity stayed locked for 2.5 hrs but then the lock broke again for no apparent reason and despite the quiet at work today.

During the time it was locked, the arm lock was also good and stable. After re-aligning ETMY and ITMY I obtained 9000 cts at the REFL monitor PD for over 2hrs.

While the arm was lockedthe WFS sensing matrix. Like yesterday, I kep obtaining an almost degenerate YAW matrix. The Pitch matrix was better and the integrator in the ARM_POS_PIT and ARM_ANG_PIT loops appaeared to be stable.

Before continuing with the work on the WFS we have to understand why the reference cavity has become so unstable.