Stefan, Arnaud, Jeff, Alexa, Sheila

Yesterday we tried to test our plant inversion for each stage of the ETMX quad.  The good news is that we get the same results if we make out measurement with optical levers on or off, so we can use the same plant inversion in either case.  We had thought there was a difference based on the earlier measurements, but that was mostly due to one point with lower coherence.

The first screenshot shows a measurement we made with the slow feedback going to the top mass, made by injecting into the top mass and measuring the ALS REFL control signal.  Stefan calibrated this so that it would be flat if the plant inversion is perfect. 

The blue trace has is the original plant inversion, the green trace is just a better resolution measurement of the resonance similar to the blue. 

Stefan installed a patch filter to cancel this resonance (second screenshot attached), and we repeated the measurement (show by the red trace).  Now it is flat. 

We then switched the slow feedback to the UIMand repeated the same measurement, using the plant inversion L2L, the gain uim/tst, and the low pass blend but no high pass blend. We again found a resonance at 0.44 Hz, but need a better resolution measurement to correct it.