Jennie W, Sheila
We want to do an OMC scan after unlocked today so we can estimate the mode-matching into the OMC with a hot OM2.
Set SRM, ITMX and ETMs to mis-aligned, IMC locked in guardian.
Ran DC centering loops 3 and 4 to centre on AS_A and AS_B QPDs, then ran OMC ASC to align into OMC_A and OMC_B QPDs. Waited for this to converge spots in centre of QPDs with current nominal QPD offsets.
Made sure that OMC guardian was paused then moved PZT2 slider to bottom of its range on ther OMC_Control screen and ran scan with template:
Did scan but sidebands are still on so can't do visibility measurement easily.
Ref 12-14 are today's scan measurements saved in /ligo/home/jennifer.wright/Documents/OMC_scan/2024_06_27_OMC_scan.xml.
Analysis ongoing.
See attached the spectra with identified peaks, corrected for the non-linearity of the PZT.
See also the fit to the double peak of the carrier 02 mode (can't distinguish the two peaks with the current OMC but a double peak fit still seems to work better than a single peak).
From the fitted height of the C02 and C20 we can estimate the mode-matching.
(0.11086 + 0.11086)/(0.11086 + 0.11086 + 3.13)
gives us 6.62 % mode-mismatch.
The fitted background light level when no modes are on the PDs was 9.13 e-3 mA (not quite the dark offset as labelled in the pdf) as light could still be scattering onto the DCPDs when the OMC is off-resonance.
The fitted halfwidth at half-maximum power is 0.330 MHz and the transverse mode spacing between horizontal and vertical is at most 0.195 MHz.
According to the design document (see table 20 of LIGO-T1500060-v1), this current OMC (001) has a half-width of 0.327 MHz and a transverse mode spacing between horizontal and vertical modes of 0.109 MHz.
This is consistent with the attached fit.
Analysis code is in OMCscan_nosidebands14.py and fit_two_peaks_no_sidebands14.py in /gitcommon/labutils/omc_scan/figures/2024-06-06 on the /dev branch (ie. it will not be on the workstation branch as this is the master branch).
