Thanks all for the great workshop! A couple talks showed 60Hz line noise in the US based IFOs. Where does line noise enter the strain data capture? For example, does it come in ADCs of the detector? I can quickly reason about how seismic activity creates noise in the strain time series by moving the mirrors, but I can’t figure out how line noise would change the length of the path of the lasers.
@kevinjos Thank you! That’s a great question.
I’m not really an expert, but my impression is that there are a number of paths where the 60 Hz signal can couple to the strain channel.
The laser and control systems are all powered. So it is easy for me to believe that the 60 Hz signal could leak into the intensity of the laser or maybe the control systems. As you say, the ADCs are a possible entry point as well.
The mirrors are actuated by electronics. Initial LIGO had small magnets with coils on the back of the mirrors - I think Advanced LIGO uses and electro-static actuator. Either way, I could imagine that an EM signal could propagate in from nearby electronics and push the on the actuator. Since this would push directly on the mirrors, it would by-pass all of our noise cancellation systems, so I could imaging this being a very sensitive coupling.
I suspect their are other possible paths as well. The bottom line is that the whole instrument uses a lot of electronics, so there are likely many possible couplings.