Frank opened up the laser to find any burnt mark, but found nothing and put it back, and now the laser is working.
We don't know for sure yet, what's wrong with the laser. But I'll use this opportunity to work on modification of PMC servo.
The current 1064nm, 100 mW laser in our setup, NPRO lightwave 126 is broken. We are looking for a new one to replace it.
The laser stopped working when I tried to lock the cavity and saw that RCTRANSPD fluctuated a bit even after I adjust the gain setup.
So I turned the HEPA filter above the table off to see if the signal would be more stable, it was not. When I turned it back on
the laser was off. I don't think the laser and the HEPA filter are associated, but that's what happened.
The power output, as indicated on the laser driver is 8 mW. When I turned the laser off for 5 mins and turned it on.
The temperature of the crystal started from ~40 C and there was power out, then, in ~10 seconds, the temperature went up to 94 C, and the power dropped to 8 mW again.
The voltage supply for TEC went up to 4V which is the maximum V for cooling.
I switched to the 10W laser driver, the same symptom happened again, so the problem might be the head, not the driver.