The laser is now back to the previous situation.

It is running with the current set to a low value of 2 A.

We will leave it as it is for now to see how stable it is.

Related logs:

Some details:

Today, I had a look at the laser (5772) again in the PSL. The laser had been switched off by the key on the front panel of the controller box since this past Friday. As I rotated the key to the ON position earlier in this morning, the temperature guard for diode A also lit up simultaneously in red as reported in 5786. Checking the diode temperature settings, I found that A was at 25 deg (c.f., nominal of 24 deg) and B was at 26 deg, the nominal value. Switching off and on the key did not turn off the LED light for diode A.

I left it with the key at the on position for a few minutes to set up a cable and oscilloscope for checking out the diagnostic signals. Then I found that both indicators for A and B became orange for some reason. No idea what had happened. Anyhow, power-cycling the controller box by the key switched off both indicators this time. So I decided to bring up the current back to a relatively low value of 2.0 A which was fine the other day (5775). As of now, it has been running at 2 A without any obvious issues for several tens of minutes.

Sidenotes (things that I learned):

Even if the temperature guard indicators light up, the laser current can be set to an arbitrary value.
The diagnositc pins for the temperature guards read +10V no matter what. I checked this when an indicator was off and in orange.
When the diode temprature are successfully controlled, the error signals are as small as 20 mV in DC.