This afternoon the goal of the shift was to excite mirror mounts resonances by activating the picomotors on the SDB1 bench, and checking the effect on the spectrum of the dark fringe beam.

Since when the interferometer is locked on B1, activating picomotors produces as side effect to unlock the interferometer, a different configuration was tried. The ITF was locked at dark fringe using B1p_PD1 (which receives 10 times more power than PD2), the differential angular loops were engaged is this configuration, and the OMC1 was locked manually.

At GPS 1188311026, we excite the mount SDB1_Mmot2 by performing one step with the TX picomotor. This actually induced some peaks visible both in the spectrum of B1p_DC and B1s2_DC (see attached figure). These peaks are located at 275-292 Hz, 307 Hz, 318 Hz, 343-354 Hz, 370 Hz.

Unfortunately, this was the only excitation we could make, because we never managed to lock again the ITF in a robust way, presumably because of the large microseismic noise.

It should be possible and instructive to perform more excitations on other mounts of SDB1 during a period of quiet weather.