Ways to use linien as purely a lock in amplifier for Double resonance optical pumping spectrum spectroscopy

[SoraUmika]

Hi,
I was wondering if there is a way to use Linien as purely a lock-in amplifier. I am doing two-photon absorption and the first laser is locked to sat.spec using conventional dithering techniques. For the second laser, I am scanning it using a second red pitaya and measuring the absorption profile of the 2nd photon from the first laser's beam on a different cell. Since this first laser beam is being modulated, then I should be able to demodulate it even if the 2nd laser is not being modulated as I scan through the frequency.

For reference, I am only using the GUI version of Linien for now

I have attempted to set the output modulation frequency of the red pitaya (which is not getting output anywhere) to my actual external modulation frequency that I have somewhere else. Then I assumed Linien does its own thing to demodulate based on the modulation frequency, this does produce an error signal but the error signal would be inverted alternatively which I'm not sure how to fix.

[bleykauf]

Thank your for writing up this issue.

This is currently not possible and I do not see an easy way to do this without significant changes to the program. The main issue that I see is that modulation/demodulation requires a static phase relation between the the modulation frequency and the signal to be demodulated. Currently, there is no way to phase-lock an external modulation signal for the purpose of demodulation.

What you could do, is modulate and demodulate with a hardware mixer and use Linien purely as a PID controller. Maybe https://github.com/lneuhaus/pyrpl is more useful for this kind of setup? Personally I have no experience with this package, but colleagues of mine built some useful stuff with that.

In case you do want to go ahead and implement this into Linien I would highly appreciate it as it definitely does fall into the scope of problems Linien tries to solve but I will not work on this myself.