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Entry  Thu Oct 3 02:43:34 2013, rana, jenne, Summary, LSC, PRMI: comparison of 1f and 3f signals w/ calibration REFL_signals_CalLinesLinedUp.pdf
    Reply  Mon Oct 7 18:39:29 2013, Jenne, Summary, LSC, PRMI: REFL11 beam realigned 
Message ID: 9191     Entry time: Thu Oct 3 02:43:34 2013     Reply to this: 9218
Author: rana, jenne 
Type: Summary 
Category: LSC 
Subject: PRMI: comparison of 1f and 3f signals w/ calibration 

The attached plot shows the spectra of all the REFL signals with the PRMI SB lock.

We excited the ITMY_LSC with 3000 counts. We used the Masayuki calibration of ITMY (5 nm / count * (1/f^2)) to estimate this peak in the REFL spectra.

To correctly scale the REFL spectra we account for the fact that the DTT BW was "0.187 Hz" and we turn off the "Bin" radio box before measuring the peak height with the cursor.

Since the ITMY motion is 3000 * 5e-9 / (580.1 Hz)^2 = 44.6 pm_peak, we want the DTT spectrum of the REFL spectra to report that too.

i.e. to convert from peak height to meters_peak, we use this formula:

meters_peak = peak_height * sqrt(BW) * sqrt(2)

I *think* that since the line shows up in multiple bins of the PSD, we should probably integrate a ~0.5 Hz band around the peak, but not sure. Need to check calibration by examining the time series, but this is pretty close.

Mystery: why are the REFL_I 3f signals nearly as good in SNR as the 1f signals? The modelling shows that the optical gain should be ~30-100x less. Can it be that our 1f electronics are that bad?

Bonus: notice how we have cleverly used the comb of bounce frequencies around the calibration line to determine that REFL11 is clipping!

Attachment 1: REFL_signals_CalLinesLinedUp.pdf  95 kB  Uploaded Thu Oct 3 03:44:14 2013  | Hide | Hide all
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