The laser tripped this afternoon because the flow rate through the heads went to zero or fell
below its trip point.  As noted in this alog
the flow rates took a dive over the weekend and did not return to their previous values.  Upon restarting the
crystal chiller, the flow rates were stuck around 0.3 lpm.  Since all four heads were affected, the pressure
regulator in that part of the cooling circuit was exercised as the bypass valve was varied.  At some point the
flow rates returned to ~0.5 lpm, so we suspect that there's a problem with the regulator.  Beyond a certain point,
the pressure did not increase as the regulator was steadily being closed.  The same is true for the regulator in
the amplifier circuit.

    The laser has been restarted but the flow rates will have to be monitored.


  Jason / Peter