[Eleonora, Matteo, Raffaele]

On 29/11 dIthering was implemented also in Yaw, with the same scheme used for pitch.

Dithering lines are injected on INPUT and END mirrors at a frequency of 16.5 Hz and 17.5 Hz respectively. Each error signal obtained from transmitted power demodulation is filtered with a simple integrator and fed back to its own mirror.

From the time taken by the loop to recover the alignemnt after misalignig a mirror on purpose, the UGF seems smaller 50 mHz. I tried to measure openloop TF with a swep sine injection at very low frequency but coherence was not good, no matter the excitation amplitude.

Note that with the current filter configuration (simple integrator) the UGF of dithering is limited by the interaction with the damping loops. See attached simulation. We discussed the possibiliy to shape the filter to avod the instabilty. Anyway since damping UGF is quite high ~1 Hz. in the present configuration the sum of the two loops is stable. Another possibility would be to go back to DC controlled optical lever and add the dithering DC correction to the set point of this loop. I think this is what is done in Virgo.