I simulated the REFL signals demodulated at the differential frequencies of the sidebands (f2-f1), at their summed frequencies (f2+f1). I also simulated their combination as in the Double Demodulation.
I repeated the simulation for:
- Old (current) 40m
- 40m Upgrade
- AdvLIGO
I'm attaching the results to this elog entry.
The plots show how the signal varies exploring the two-dimensional space of the demodulation frequencies (differential and sum).
Both the Upgrade and the Old40m's signals look anomalous since the zero-crossing point does not change with the demodulation phases.
I suspect there's is a problem with the optickle model of the 40m. |