jason.oberling@LIGO.ORG - posted 12:40, Tuesday 25 April 2017 - last comment - 11:04, Tuesday 02 May 2017(35776)
ITMy Optical Lever Laser Swapped, Yet Again (WP 6591)
As I noted here, the oplev laser SN 191 was found to be running very warm; this in turn made it very difficult to eliminate glitches. In light of this, as per WP 6591, this morning I re-installed laser SN 189-1 into the ITMy oplev. The laser will need a few hours to come to thermal equilibrium, then I can assess whether or not further tweaks to the laser output power are needed to obtain glitch-free operation. I will leave WP 6591 open until the laser is operating glitch-free.
SUM counts for this laser have been very low; ~2.8k versus the ~30k the last time this laser was used (March 2017). Today I pulled the laser out of the cooler and tested it in the Pcal lab and found the output power to be very low; at the setting being used I measured 0.11 mW versus the 2.35 mW I measured before I installed the laser. By tweaking the lens alignment (lens that couples light from the laser diode into the internal 1m fiber) I was able to increase the output power to ~0.2 mW. There is clearly something not quite right with this laser, my suspicion being either a gross misalignment of the coupling assembly (which takes longer than a maintenance period to correct) or something is going bad with the laser diode. Knowing the history of these lasers, both are equally probably in my opinion.
Unfortunately there is not a spare currently ready for install. In light of this, since the laser is currently working, I reinstalled SN 189-1 into the ITMy optical lever so at least we have a functional ITMy oplev. Once I get a spare ready for install this laser will be swapped out at the earliest opportunity. I have closed WP 6591.