Decreasing Power

[evokanivo]

I'm makings cuts and the power decreases rapidly over about a minute. For example, I cut a 4 inch circle in 1/4" MDF at 5mm/second and by the time the circle is finished, the beam no longer cuts all the way through. The beam strength decreases gradually.

The current meter shows a constant 16ish mA the whole time. I'm wondering whether 1) I burned out my laser or 2) I have insufficient cooling. The tube feels cool afterwards. I don't know whether decreasing power is consistent with a used-up tube.

I am worried that I may have burned out my tube because I was doing PPI earlier today and, although the current meter showed 10 mA, I think it could have been over 20mA for the 3 millisecond bursts that each pulse lasts.