J. Kissel

In order to begin exploring the systematic discrepancy between model and measurement below ~30 [Hz] in the IFO's sensing function (see, e.g. LHO aLOG 24709), we've taken PCAL2DARM and DARMOLGTF transfer functions at the normal amplitude and at half amplitude. Sadly, the IFO lost lock during the last few (low frequency) data points of the last half amplitude DARMOLGTF, but I think we have enough data to make a comparison. 

Premiliminary message: there's no obvious, unexpected difference between normal and half amplitude. Coherence is less, so the data points are a little more scattered, but no surprise there.

One thing of note, while watching the DARM ASD during the measurement, there are no signs of higher harmonics in the PCAL excitation, but once the DARM OLGTF (as driven by the ESD and subsequent upper stages) reaches ~20 Hz, one can clearly see a second harmonic in the ASD meaching along right behind the fundamental excitation frequency. To give a feel, during the normal amplitude drive, once the excitation hit ~15 [Hz], the second harmonic's amplitude was roughly 3.5 orders of mangitude below the fundamental (but still clearly visible thanks to the discrepancy between the 10 and 30 [Hz] sensitivity). Recall that the linearization for ETMY is *not* on in the IFO's lowest noise state. The EY bias voltage remains -380 [V] (with an effective bias voltage from charge of ~ -20 [V]; see LHO aLOG 24547).

We leave the IFO down for the PCAL team to explore PCALX problems (see LHO aLOG 24726), and so Betsy can grab this week's charge measurements on ETMY.

Analysis of the data to come later, but the files live here:
/ligo/svncommon/CalSVN/aligocalibration/trunk/Runs/PostO1/H1/Measurements/DARMOLGTFs/
2016-01-08_H1_DARM_OLGTF_7to1200Hz.xml
2016-01-08_H1_DARM_OLGTF_7to1200Hz_halfamp.xml

/ligo/svncommon/CalSVN/aligocalibration/trunk/Runs/PostO1/H1/Measurements/PCAL
2016-01-08_PCALY2DARMTF_7to1200Hz.xml
2016-01-08_PCALY2DARMTF_7to1200Hz_halfamp.xml