The laser shut off last night around 6 pm. It looks like this was due to low water flow through laser head 4. PSL_TRIP_1 shows this shutdown. Channel HEAD4FLOW drops to 0.45 lpm and the interlock trips at this point. The time scale for this plot is 20 seconds.

I turned the laser back on but before I could leave the laser room it shut off again for the same reason. PSL_TRIP_2 shows the trip, as the flow through head 4 drops and trips the interlock. I'm not sure what the threshold here is but it must be around 0.45 lpm. I turned the laser back and and increased the flow through the crystal chiller from 17.6 lpm to 18.2 lpm to try and give some more head room for the flow sensor, but it did not have much of an effect. The flow sensors have always had some erratic behavior, as you can see in the 2 week plot attached. LLO found the filters in their laser heads were quite dirty, so maybe we are starting to see the effect of particle buildup.