jason.oberling@LIGO.ORG - posted 12:14, Tuesday 11 April 2017 - last comment - 11:35, Tuesday 18 April 2017(35470)
ITMy Optical Lever Laser Swapped, Again (WP 6565)
This morning I swapped the ITMy oplev laser, per LHO WP 6565. This was in response to this alog from K. Venkateswara and J. Kissel, indicating an ~0.44 Hz feature on the ITMy oplev (that showed up after the laser swap on March 7th) was possibly due to an issue with the laser and causing range issues. The old laser SN was 189-1, the new laser SN is 191. This laser will need a few hours to come to thermal equilibrium, once that is done I will assess whether or not the laser needs a power tweak for glitch-free operation; I will leave WP 6565 open until this is complete.
Went out today to tweak the power of this laser, as it is still glitching, and found the interior of the box to be very warm. This is highly unusual. I also found the exterior mounted box that holds the DC/DC converter that powers the laser to be very warm as well. My suspicion is that something, likely the laser, is drawing more current than it should. I checked the other oplev lasers in the LVEA and none of them were running warm like this. The quickest fix at this point is to swap in another laser. Unfortunately the only laser currently ready for swap in is SN 189-1, which happens to be the laser I just removed from the ITMy oplev due to concerns over an ~0.44 Hz feature that might be from the laser. Doing a quick spectrum of the new ITMy oplev laser SUM, pitch, and yaw signals after install on 4/11/2017 (attachment 1) and this morning (attachment 2) shows that the laser is currently very noisy compared to just after install (likely due to the increased operating temperature), but also still shows a feature at ~0.44Hz. As this ~0.44Hz feature is still there with this new laser, the feature is likely either from the the electronics of the ITMy oplev (QPD, whitening chassis) or is something real that the oplev is only a witness for. Assuming laser SN 189-1 checks out in the lab, I will re-install SN 189-1 into the ITMy oplev at the next available opportunity.