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Entry  Mon Feb 11 19:53:59 2019, gautam, Summary, Loss Measurement, Loss measurement setup DQcheck.pdfinitialData.pdf
    Reply  Tue Feb 12 18:00:32 2019, gautam, Summary, Loss Measurement, Loss measurement setup 
       Reply  Tue Feb 12 22:59:17 2019, gautam, Summary, Loss Measurement, Y arm loss segmented.pdfconsolidated.pdf
          Reply  Wed Feb 13 02:28:58 2019, gautam, Summary, Loss Measurement, Y arm loss systUnc.pdf
             Reply  Thu Feb 14 21:29:24 2019, gautam, Summary, Loss Measurement, Inferred Y arm loss  modelPerturb.pdfposterior_modelParams.pdfposterior_Loss.pdf
                Reply  Sun Feb 17 17:35:04 2019, gautam, Summary, Loss Measurement, Inferred X arm loss  DQcheck_XARM.pdfconsolidated.pdfposterior_modelParams_XARM.pdfposterior_Loss_XARM.pdf
Message ID: 14463     Entry time: Sun Feb 17 17:35:04 2019     In reply to: 14454
Author: gautam 
Type: Summary 
Category: Loss Measurement 
Subject: Inferred X arm loss  

Summary:

To complete the story before moving on to ALS, I decided to measure the X arm loss. It is estimated to be 20 +/- 5 ppm. This is surprising to say the least, so I'm skeptical - the camera image of the ETMX spot when locked almost certainly looks brighter than in Oct 2016, but I don't have numerical proof. But I don't see any obvious red flags in the data quality/analysis yet. If true, this suggests that the "cleaning" of the Yarm optics actually did more harm than good, and if that's true, we should attempt to identify where in the procedure the problem lies - was it in my usage of non-optical grade solvents?

Details:

  1. Unlike the Y arm, the ratio \kappa = 1.006 \pm 0.002 is quite unambiguously greater than 1, which is already indicative of the loss being lower than for the Y arm. This is reliably repeatable over 15 datapoints at least.
  2. Attachment #1 shows the spectrum of the single-bounce off ITMX beam and compares it to ITMY - there is clearly a difference, and my intuition is to suspect some scatter / clipping, but I confirmed that on the AS table, in air, there is no clipping. So maybe it's something in vacuum? But I'm not sure how to explain its absence for the ITMX reflection. I didn't check the Michelson alignment since I misaligned ITMY before locking the XARM - so maybe there's a small shift in the axis of the X arm reflection relative to the Yarm because of the BS alignment. The other possibility is clipping at the BS?
  3. Attachment #2 shows the filtered time series for a short segment of the measurement. The X arm ASS is mostly well behaved, but the main thing preventing me from getting more statistics in is the familiar ETMX glitching problem, which while doesn't directly break the lock causes large swings in TRX. Given the recent experience with ETMY satellite box, I'm leaning towards blaming flaky electronics for this. If this weren't a problem, I'd run a spatial scan of ETMX, but I'm not going to attack this problem today.
  4. Attachments #3 and #4 show the posterior distributions for model parameters and loss respectively. 
  5. Data quality checks done so far (suggestions welcome):
    • Confirmed that there is no fringing from other ITM (in this case ITMY) / PRM / SRM / ETM in the single-bounce off ITMX config, by first macroscopically misaligning all these optics (the spots could be seen to move on the AS port PD, until they vanished, at some point presumably getting clipped in-vac), and then moving the optics around in PIT/YAW and looking for any effect in the fast time-series using NDScope.
    • Checked for slow drifts in locked / misaligned states - looks okay.
    • Checked centering on PDA520 using both o'scope plateau method and IR viewer - I believe the beam to be well centered.

Provisional conclusions:

  1. The actual act of venting / pumping down doesn't have nearly as large an effect on the round-trip loss as does working in chamber - the IX and EX chambers have not been opened since the 2016 vent.
  2. The solvent marks visible with the green flashlight on ETMY possibly signals the larger loss for the Y arm. 
Attachment 1: DQcheck_XARM.pdf  67 kB  | Hide | Hide all
DQcheck_XARM.pdf
Attachment 2: consolidated.pdf  208 kB  | Hide | Hide all
consolidated.pdf
Attachment 3: posterior_modelParams_XARM.pdf  966 kB  | Hide | Hide all
posterior_modelParams_XARM.pdf
Attachment 4: posterior_Loss_XARM.pdf  15 kB  | Hide | Hide all
posterior_Loss_XARM.pdf
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