An attempt to measure the amount of misalignment that is currently present  in the PSL-to-IMC coupling.

First I centered the direct reflection from the IMC onto the WFS A and WFS B sensors.  There was about 30% reduction in the RIN.  See attached png and xml files: IMC_jitter_centering.*

Next, I  injected an excitation in to the PSL_PZT pitch and yaw  at 7.33 Hz .  I then took a PSD of the IM4_TRANS_SUM signal to measure the power fluctuations in at 7.33 Hz and 14.66 Hz (P1f and P2f) respectively. 

Attached files show these peaks in the IM4_TRANS_SUM spectra.  Attached also are the xml files which have the data and an excel file which has the computation of the amount of misalignment.

In summary: 

       1)  Pitch misalignment is 0.6% of the IMC cavity beam divergence

       2) Yaw misaligment is 1.2% of the IMC cavity beam divergence.

An attempt to see how the misalignment could have arisen:

I  tried to vary several offsets to see whether this coupling from jitter to RIN could be changed.  The ones I tried are

a) Common mode offset in the MC servo board: To see if a length offset is causing this H1:IMC-REFL_SERVO_COMOFS

b) Slow offset in the MC servo board H1:IMC-REFL_SERVO_SLOWOFS

c) Slow out offset in the MC servo board H1:IMC-REFL_SERVO_SLOWOUTOFS

d) DOF1 to DOF3 offsets in both both pitch and yaw in the MC WFS servo loops.

None of these by themselves had a significant impact on the jitter to RIN coupling.  More investigation required.

And now for those nay sayers :-)  Things I did not do!! 

1)  I returned all offsets to where they were.

2) The MC2 spot is centered and the IM4_TRANS spot has not moved from before to after my WFS centering => output beam has not shifted

3) The WFS outputs were not off loaded: the IMC alignment slider values have remained the same

4) No other Pico motors other than that of IMC WFS A and IMC WFS B were touched.

So in essence if something broke, its not coz of me!!  :-p