ETMY ring heaters were turned on to 0.5W for an hour at 12:42 PDT (gps 1302032546 to 1302036042).
Attached is an image of the result. You can persuade yourself we are seeing something, but it's not clear.
Strangely, after 13020338593 when the ITMY was aligned, we got a very different image (which looked much nicer): see BUT DON'T TRUST second attachment. But the Spherical Power also changed dramatically. We are unsure why ITMY alignment would be effect the HWS so times after this are not ring heater related.
In the past, when aligning the probe beam for the ITM HWS, we found that there was a small reflection from the ETM optic. It's possible there is something similar going on here - the ETM probe beam might be getting all the way to the ITM and reflecting back.
We were wondering if we were getting confused by ALS being unshuttered in the second image in Camilla's alog. Looking at the spherical power, if we choose a show time before the jump at t+27 mins in the attachment here we get the lumpy Hartmann image, if we choose a time afterwards we see the nice clean circular gradients. Weirdly, this time is not correlated with ALS being unshuttered (t+37 mins), but with ITMY being aligned. Could the ETMY Hartmann be somehow sensitive to ITMY?
Edit: according the Aidan's comment posted at the same time as mine: the answer to this question is yes :-)
We want to work really hard to avoid any secondary reflections from the ITM. I haven't analyzed the spurious ETMY HWS signal from the perspective of a stray return beam from ITMY. However, we've aligned all ETMs multiple times and have only ever seen issues on H1-ETMY (consistently) and never on any other installations. It would be curious if that configuration somehow consistently aligned to yield a secondary beam from the ITM while none of the other installations ever did.
Unless there is there something unusual in the spectal reflectance of the H1-Y arm optics at the HWS wavelength?
I didn't get a chance to work on the alignment of ETMY HWS today since ITMY was out of commission, but I did take another ring heater test. First attachment shows the spherical power, ring heater power, as well as the ITMY oplevs.
I looked at the contours between the two time cursors, where I suspect the effect of the ring heater dominates over the ITMY drift, the result is shown in the second attachment. It looks pretty well aligned to me.
I was curious about the ITMY ghost beam, so I looked at the gradients when ITMY got a big kick about 4 hours before the ring heater test (I think this was when the ISI tripped), between the two t cursors in the third attachment. The result is the 4th attachment, I'm not sure if this tells us anything reliable about the ghost beam, since I'm not sure how well the ITM was between those two times.
