The goal of the activity was to swap the ML with the spare previously brought in the laser lab atrium 51579.
We starting by measuring the TF of the PZT and thermal loops on the installed ML. We then switched off the fiber amplifier and measured the power at the output of the ML fiber (470 mW) and of the pickoff for the amplifier (132 mW).
We turned on the ML spare and checked the coupling on the fiber but we did not find the expected 83%. We obtained at the best 50%. We connected this fiber to the one going to the LB (410 mW at the output of the fiber, 940 mW output ML) and we switched on the fiber amplifier and we had to wait a bit for the amplifier to stabilize and when we locked the PMC we found out a quite large misalignment, so that we had 0.6 V od transmission when locked instead of 0.91 V. We measured the new PZT and thermal transfer functions and found they had a similar behaviour (to be confirmed by deeper analysis).
Because of the poor PMC transmission we decided to swap again to the old master laser. However, when plugging again the fiber there was no light at the output, probably due to a misalignment of the collimator. We struggled to inject again light into the fiber and we never recovered the 470 mW. We measured in fact 160 mW at max.
Given this issue we decided to use the spare ML. Nevertheless we didn't manage to find again the same coupling. We realized that a fiber (the 15 m long with metallic jacket) was burnt. We then installed the fiber that had been used for ALS and was fixed below the floating floor. We obtained around 200 mW at the output of the fiber on the LB with 2A driving current. We then turned on the fiber amplifier and we relocked everything. We checked that we have no peak due to the noise eater when leaving the lab and that the green sources had correctly switched on again.
More details will be given tomorrow.
We should add a box to protect the new ML from air flux, which has been made today from the mechanicians (thanks).