After the installation of the hardware for phase noise suppression the activities continued in the first part of this week:

1) New setpoint for the squeezer MAIN-PLL

The AOM dedicated to the fiber signal going to the squeezer operates at 100 MHz unlike the previous setup where the phase camera AOM was used ( 80 MHz) . We have therefore reset the squeezer main PLL with a frequency offset of 100 MHz. This is done by changing the PLL-LO frequency from 80 MHz to 100 MHz (see figure 1). To close the PLL loop we had to change the initial set point of the main laser peltir from 25780 to 25760. This last value was put in the squeezer automation configuration file (leaving the old one commented).

2)Characterization of the fiber  phase noise

The purpose of this activity is to monitor the phase noise acquired by the light propagating in the fiber  from Inj to DetLab (L=54m). First we set the parameters of the DDS#8 (see fig. 3 of #66789) in the following way

CH2-FIX frequency=99.99998566 MHz, amplitude (measured) 4.9 dBm

CH3-FIX frequency=199.99997132 MHz, amplitude (measured) 4.3 dBm

CH4-FIX frequency=199.99997132 MHz, amplitude (measured) 4.5 dBm

A 10 dB RF attenuator was inserted at the output of CH2 and the resulting signal was used as input to a customized amplifier (fig. 4 of #66789). Then the amplifier output (about 29 dBm) is used to drive the  AOM in the fiber box at 100 MHz.

After these operations we measured the RF powers of the PD1,2 at 200 MHz after the double pass in the AOM (fig. 4 of #66789) photodiodes which result

RF power -PD1: -4 dBm

RF power -PD2: -7 dBm

The reasn of this amplitude difference is not clear and needs to be investigated.

To estimate the in-phase noise acquired by the fiber we use the scheme in figure 2  but this requires re-starting some processes and will be done when possible.