[Eleonora, Matteo B.]

We have measured the rampeuto PZT output noise by connecting the PZT output to the spectrum analyzer. It is about 2 uV/sqrt(Hz) at low frequency and it starts to decrease above 5 kHz, as can be seen from pic 1 (blue curve) 

We also observed with the oscilloscope that there is an offset of -10mV. (pic 2).

In order to reduce the rampeauto output noise, following the advice of Pierre, we have disconnected the ramp input (which normaly is not used for suspended cavities). (pic 3) 

The output noise has been reduced by a factor 3 and now  it is about 800 nV/sqrt(Hz),  below 5 kHz.  (see pic. 1 and 4)

In pic 5,  we have compared the rampeauto noise (actuation noise)  with the free running laser noise and found that it becomes dominant above 2 kHz.

For the conversion to Hz we used a piezo gain of 2 MHz/V, as measeured in entry  #859.

The next step is to re-measure the phase noise, as done in entry #863, with this new configuration.