[Kiwamu, Katrin]
As reported earlier an oscillation around 7kHz is an the PDH error signal. The lower spectrum show that there is a peak from 6-7kHz.
This peak is somehow dependent on the modulation frequency. This means the peak can be shifted to a higher frequency when the modulation frequency is increased (see for comparsion f_mod=279kHz).
If the power supply for the green PD is switched of the peak vanishes. The same happens if the LO is switched of.

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