I connected the laser DC modulation port to the Moku input of a spectrum analyzer. The spectrum analyzer always sees the 875Hz if it is connected to the laser, but the amount that the 875Hz shows up in the pdh error spectrum changes a bit on changing the spectrum analyzer input properties. Could the problem have something to do with impedance matching? the input impedance to the laser modulation port is 1kOhm.

We should plug the laser modulation port into a non-Moku spectrum analyzer and see if the problem persists.