Vicky, Camilla. Following alog62121.
Summary. Beam bigger and better that last week, CCD moved to image the ETM but ring heater test didn't look great (photo from alog62309). The total pixel power changed with the spherical power.
We swapped the initial collimating lens from 40mm to 50mm to increase the beam size on the ETM. We used a beam splitter cube to check that the majority of the light after the wave plate was horizontally polarized. We added a 2" lens tube to the front of the Hartmann plate holder to reduce stray light.
Beam quality. Here is a photo with the CCD not saturating (25% transmission using ND06A filter). We are concerned that it doesn't look very uniform or Gaussian. When we next work on this we will take a beam scan of the outgoing beam. We will work on changing the sync frequency. Currently all at 1Hz but documentation suggests 57Hz.
CCD imaging. We dithered the ETM using awggui H1:SUS-ETMX_M0_DITHER_Y_EXC with gain 50, 0.1Hz and watched the HWS PROBE_PRISM_X/Y channels to see the beam moving. We adjusted the CCD camera position to correctly image the ETM and decided the image moved less at the furthest distance possible without moving the CCD aligning mirrors. This was hard to see and maybe with a cleaner beam we would get better results.
See attached comparing masked camera images at cold vs. hot times, for yesterday's 3 ring heaters tests on ETMX (not good), ETMY (ok), and ITMY (so good!!!). ETMX masked image looks pretty different than others. Its masked dot pattern changes visibly between cold vs hot, and in a way that also might be consistent with the (problematic) correlation between spherical power and probe pixel value. Seems like for ITMY, which is great, that cold vs hot images should look quite similar by eye.
