camilla.compton@LIGO.ORG - posted 13:24, Tuesday 29 November 2022 - last comment - 09:34, Wednesday 30 November 2022(66077)
Slow ITM dither to check HWS calibration.
Mitchell, Dan, Camilla.
Repeating Aidan's 52513, we put a very slow 0.005Hz +/-10urad dither on H1:SUS-ITM{X,Y}_M0_OPTICALIGN_{P,Y}_EXCMON using awggui.
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PIT on ITMX and Y injected from 1353788533 to 1353789462.
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YAW on ITMX and Y injected from 1353789578 to 1353790528.
At 11:20am, we tried a 0.2Hz but the HWS code only calculates at 1Hz so this was too fast.
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Processed the data from this test (see attached plots) to estimate the magnification according to how it was done in the above mentioned ALOG (I think). Results show quite a bit of astigmatism in both the ETM and ITM HWS, but there is roughly the same amount in each. The current set magnifications for both is the default value of 17.5. The origins for each Hartmann may not be correct which could explain why these results look strange? Summary: HWS-ITMX: Magnification x: 15.7 Magnification y: 12.0 Ratio x/y: 1.31 Ratio y/x: 0.76 HWS-ITMY: Magnification x: 12.9 Magnification y: 17.8 Ratio x/y: 0.72 Ratio y/x: 1.38
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Have followed up and applied quadratic fits to the ITMX/ITMY ring heater test done a month ago. In these tests only the ring heaters were left on for a period of 5 hours, the deformation seen by the HWS should be approximately quadratic and the same in x/y assuming no astigmatism in the hartmann optics. The results are summarized in the attached images. ITMX Quadratic fits: x slice: -1.54e9*x**2 + 4.14e5*x + 3.42e4 y slice: -1.49e9*x**2 + 1.27e6*x + 3.31e4 quad x / quad y : 1.03 quad y / quad x : 0.97 ITMY Quadratic fits: x slice: -1.86e9*x**2 + 2.85e5*x + 6.29e4 y slice: -1.68e9*x**2 + 1.39e5*x + 6.04e4 quad x / quad y : 1.11 quad y / quad x : 0.90 Avg quad ITMX / Avg. quad ITMY: = 1.52/1.77 = 0.86 Avg quad ITMY / Avg. quad ITMX: = 1.77/1.52 = 1.16 These results seem more reasonable, and imply only a 3-10% astigmatism in the magnification in the ITMX/IMTY HWS (if the ratio of the quadratic terms in the fits is the correct metric).
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For future reference, I will attach the python scripts used to process the Hartmann magnification measurement/calibration and to perform the quadratic fit to the ringheater test. In each script you will only need to modify the specified GPS times and which HWS to use, and the rest will be processed automatically.
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Data from another much longer ring heater test from April 2022 shows similar behaviour in HWS-ITMY (data from ITMX was bad due to misalignment). ITMY Quadratic fits: x slice: -1.43e9*x**2 + 1.39e5*x + 4.11e4 y slice: -1.28e9*x**2 + 7.78e5*x + 3.89e4 quad x / quad y : 1.12 quad y / quad x : 0.90
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The magnification of the HWS images can also be estimated directly from the shape of the shadows in the intensity distribution. Measurements of the ITMY intensity distribution earlier this year are close to what is predicted with magnifcation of 17x. A closer look at this is definitely recommended.
Analysis of the uniformity of the Ring Heaters is given in: https://dcc.ligo.org/LIGO-T1000727. There is some small astigmatism predicted. The document quotes it in absolute Zernike values - annoyingly the spherical power component is not also given (might be possible to back it out).