S. Muusse, C. Compton

0920 QCL unit failure summary:

We were beam profiling the laser and I had the profiler ~8” from the laser head, with a steering mirror to steer onto the scanner. Laser was at 1A. I blocked and unblocked the beam but as it was unblocked there was a beep and there laser controller turned off with message “LD output voltage protection was tripped”.

I then turned controller off and back on again with power down to 0.5A and it would not turn on.

Camilla then came into the lab, we turned off and unplugged controller. It was turned on again, would not turn on. Remembering LLO's issues, on the Temperature Protection screen we eased the +-5 deg requirement to +-6. Laser then appeared to turn on with “laser current reading 0.500 A” and “laser voltage reading 10.440V”, temperature 25deg. However no beam was coming from the laser.

We then turned off and on laser. Again appeared on but no beam, slowly turned up current from 0.5A towards 1A, at 0.84A controller beeped with “LD output voltage protection was tripped” message again.

QCL Unit q-parameter dependance on laser temperature:

Unit failure happened while profiling the laser to check if the q-parameter of the QCL has a temperature dependence. This profiling was done largely at a 23mm offset with one point near the waist. However, there was not an opportunity to take more measurements around the waist in this new data because of the failure which may cause some inaccuracies in the fitted q. I used a non linear fit where M2=1. This is consistent with the fitting by Matt. His measurements were completed at 20 deg but after advisement from thorlabs we have increased operating temperature to 25 deg. 

With the new q factors there is slightly better agreement between the fitted q-parameter for L2 and the model.

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