[Eleonora, Matteo]

Today we did good progress on the dithering.

We gave up on measuring the sensing matrix and we tried to close the loops by simply feeding back each demodulated signal to "its" mirror. 

This seemed to work surprisingly well. (See pic 1-2). The transmitted power increased and became quite stable as well as the lock.

I tried to move one by one the BS, the INPUT mirror and the END mirror when dithering is engaged and the loops seem able to move the cavity mirrors to recover the good alignment. (See pic 3, 4, 5)

From the last two plots we can also check the level of coupling of our error signals, and possibly improve the driving.

The main problem I see is that the error signals are not oscillating around zero but they have an offset and the dithering lines are still well visible in transmission. It shouldn't be like this but I'm not sure about the reason.

Currently the corrector filter is a simple pole at 0.001 Hz. Maybe we should move it to zero. I will also try to put a offset in the loops and see if it can improve the transmission and reduce the dithering line in transmission.

Even if the transmitted power is very stable because we were mostly affected by pitch misalignment, I also tried to close the loops in yaw. They seem not to work well. The error signal is always around zero, so it is not easy to tell the difference when I close the loops, but when tried to misalign the BS in yaw they didn't recover. I didn't spend much time to investigate the problem but I will do it soon.

Since the error signals get crazy if the cavity unlocks I decided it was safer to stop the lock for the night. The cavity kept the lock for more than 5 hours (best record ever) and the lock was stopped on purpose before I go to sleep. It will be good to implement some kind of guardian that will open the dithering loops when the cavity unlocks.

Some details:

- The gain of the input and end loops are respectively -1 and -0.5.

- I reduced the amplitude of both dithering lines from 10000 to 5000 counts.