I got permission a long time ago to have this calc around, so I am putting it here, but the links are dead so it will have to be redone. As such the page stats it will affect will be subject to change.
"i.imgur.com/O25mDFu.png
Value for Military-grade modern steel violent fragmentation is 1000 j/cc
Judging by the fact the door is about twice as high as some relatively tall guards, I would say that it's about 4 meters in height or so.
312 / 376 = 0.829787234
0.829787234 * 4 = 3.31914894 meters
14 / 376 = 0.0372340426
0.0372340426 * 4 = 0.14893617 meters
Calculating as volume of cylinder
Plugging our values in we get about 1288700 cm^3
1000 * 1288700 = 1288700000 or 0.31 tons of TNT equivalent
It looked like a melting laser though. If you can prove that it's a heat based/melting weapon then that would bring it closer to 9420229469 joules or 2.25 tons of TNT equivalent"