S. Dwyer, J. Kissel, J. Oberling

Given our problems yesterday with ALSX laser diode current surpassing an old threshold (see LHO aLOG 36381), I was reviewing whether we should accept the new higher threshold as the new normal. Here, I attach 20 day and 700 day (~2 year) trends of all four ALS laser diode's current (2 at each end). Also, here is the state of current values (a simple 10 sec average) vs. nominal and thresholds:
                                                                     Diff from
                                                    Current [A]      Nominal
    H1:ALS-X_LASER_HEAD_LASERDIODEPOWERNOMINAL      1.842
    H1:ALS-X_LASER_HEAD_LASERDIODEPOWERTOLERANCE    0.5 (was 0.2)
    H1:ALS-X_LASER_HEAD_LASERDIODE1POWERMONITOR     1.863            (0.021)
    H1:ALS-X_LASER_HEAD_LASERDIODE2POWERMONITOR     2.041            (0.199)

    H1:ALS-Y_LASER_HEAD_LASERDIODEPOWERNOMINAL      1.520
    H1:ALS-Y_LASER_HEAD_LASERDIODEPOWERTOLERANCE    0.2
    H1:ALS-Y_LASER_HEAD_LASERDIODE1POWERMONITOR     1.430            (0.090)
    H1:ALS-Y_LASER_HEAD_LASERDIODE2POWERMONITOR     1.588            (0.068)

As Sheila suggests, "It's not crazy that the diode current follows temperature, it's that the temperature has gone crazy over the past 20 days." However, one can see that this ALS X diode 2 current has been slowly increasing over the past 2 years, so we would have hit this threshold in a few months anyways.

For now, we'll keep the new ALS X threshold at 0.5 [A] (and leave the ALS Y threshold at 0.2 [A]).

Question: Is this OK?

The User Manual doesn't explicitly mention a limit on the diode current, but there are several mentions of a temperature controller in section 3.4 "Recommended Operation," and perhaps the most relevant is this statement in the trouble-shooting section:
    "Diagnosis: The temperature controller is not able to stabilize the diode laser temperature at the given value.
     
     Reaction: Try to increase the set temperature for the diode laser slightly using the trimmer at the front panel of the
     control electronics unit, especially if it is set below room temperature. Otherwise contact InnoLight GmbH."
Note the manual also suggests that these diodes are only under warranty for 6 months ;-).

Perhaps we should check the temperature settings on this diode? The other three diodes on site have been pretty insensitive to temperature over the past year, through and including the recent HVAC upgrade. I'll open an FRS ticket.