[Shimoda, Stefan, Nakano
We found the source of this timing signal coupling noise. That was the offset circuit just before the AOM driver which injects the offset to a VCO for bringing the operation point to the center frequency of the AOM.
After some investigation, we found that the noise has gone after disconnecting between the AOM driver and the offset circuit. Also we found that the noise appear when we re-connected those and disconnected the input of offset circuit. In this situation, the offset circuit connected only with +/-18V power supply. So the offset circuit coupled with the timing signal via power supply, and that shake the laser frequency.
We added some bypath capacitor to remove the noise, but somehow does not work well. The output of the circuit has 0.3mVrms oscillation at timing signal frequencies which corresponds to 4-5kHzrms frequency oscillation (the double path AOM efficiency is roughly 15MHz/V). Actually it is consistent with the result from the PZT control signal. It has 3.8mVrms peak at 960Hz and it shakes the laser frequency 3.8* 1.4MHz/V = 5.32 kHzrms
we will continue to hunting it tomorrow