I measured the slope of the error signal vs RF voltage, the result is plotted below
To increase the overall gain of the PMC loop, one thing we can do is changing the slope of the error signal.
This will increase the gain on the optical path of the loop.
So I measured the slope of the error signal, this information will allow me to know how much
gain I would get from each RF setting. The slope increases as the RF voltage increases, until V_RF ~ 8 V.
The error signal does not change at all when V_RF on the slider is between 8 to 10 [Max] V, and
there is no saturation in the signal.
Note: I use the oscilloscope to measure the slope around the center of the error signal, by
measureing dt and dV to get dV/dt around the center, (this can be converted to dV/dHz by the sideband)
but the result has large deviation, so I measure the pk-pk in stead, and divide that by the
cavity FWHM = 3.8 MHz which corresponds to the peak-peak of the signal. to get the average slope.
It will be lower than the actual value
but I'll keep it for now.