Banding in the derivative of a lock-in amplifier signal
It might not be so straight forward to simply take the derivative of the output from a lock-in amplifier. If you think about how a lock-in works, the final stage of a lock-in amplifier is the low-pass filter. So if you then simply take the sample-to-sample derivative, you will simply be undoing the work of the low-pass filter and getting noise. Instead, you need to decimate your time domain signal, and then take the derivative.