Participants : Marc, Yuhang

We locked the SHG and connect only DDS3 to its power supply. The peaks are still present on the SHG error signal.

We checked each output channel of this DDS3 with the spectrum analyzer :

     No peaks present from CH0 nor CH1 (Fig1).

     CH2 exhibits a peak at 21.957 kHz (Fig2) at exact same frequency as the peak on SHG error spectrum ! (note that the peak freauency changed with respect to yesterday measurement. Also we checked that it changes by few hundred Hz within ~10mn)

     As the CH2 output is connected to a splitter, we also checked the splitter second output which also exhibits a similar peak (Fig3).

    We disconnected all outputs from DDS3 but the peaks are still present on the SHG error signal (Fig4).

Remind that we added an amplifier to each channel of DDS3 which could mean that the problem does not arise from the amplifier itself. Only difference between these channels output is that CH0,1 and 3 have attenuators at their output but not CH2.

     We removed attenuator from CH0 and a peak at around 20 kHz appeared (fig5).

We then tested DDS2 (as it has only 1 amplifier).

SHG ERR signal exhibits peak at 17.4kHz (Fig6)

    CH1 (amplifier, no attenuator at its output) : only harmonic visible in Fig7

     DDCH0 ( no amplifier, no attenuator) : clear peaks in Fig8

The conclusion seems to be that the amplifier is not the culprit.