[Matt, Jason O, Maik F (remote)]
We wanted to see the run hours on the PSL systems at both sites to check on the health of everything (and as an easy kickoff on the FCA review of the detector itself....see slide 10 of G2610464). The chillers we swap out regularly to get refurbished so we have no concerns there, but the PSL laser diode lifetimes are the point of interest here.
LLO
LLO finished the O4 upgrade of the PSL circa November 2022.
LLO appear in very good shape. The run hours LLO have are:
AMP1: 30,427 hours
AMP2: 30,399 hours
From Maik "The diodes have the standard specifications of 20,000h but the vendor typically says that they will do more than 30,000h which you proved !"!
The diode currents for the laser diodes at LLO has not been changed from its initial set points at install.
Note: The laser diode current has to be changed as the laser diodes start to die to maintain the same output power from the diode itself and retain the thermal lens profile of the crystals inside the amplifier.
LHO
LHO finished their O4 upgrade of the PSL circa February 2022.
LHO are in a bit more of a concerning shape than LLO. The run hours LHO have are:
Amp1: 38,512
Amp2: 38,365
More concerningly from LHO's point of view, LHO HAVE had to start adjusting their laser diode currents to maintain output form their laser diodes. From Jason "We’ve been able to keep output power good by increasing the injection currents, but our PMC reflected power has more than doubled since install (~12 W -> ~28 W). I can’t get it lower with injection current increases, further increases only increase PMC Refl; at this point we’d have to redo the mode matching to the PMC to restore our original power available to the IFO"
Summary
Both sites laser diodes are beyond the manufacturers specifications for runtime.
LHO have around a year of extra runtime on their laser diodes and the LHO diodes have started to degrade in terms of performance.
Each site does have a complete set of spare diode boxes that can be swapped in. LLO's have hours on them as they are part of the T&T lab setup, but LHO's should still be brand new (other than burn in time). However we do need to starting thinking/planning about refurbishing (or buying new), laser diodes for the PSL system. So at this point in time both sites should be fine for the IR1 run (however laser diodes typically degrade at a non-linear rate and so LHO will have to keep an eye on their performance and make a judgment call on if they think they need to swap theirs at some stage). However for O5 (or even the upgrades/commissioning before them), both sites are going to have to swap out to fresh laser diodes.
