I'd love to stick a mirror under the thing at a 45° angle & see how the beam looks while it punches a hole through the wall, the tree outside, the warehouse next door & the traffic jam a few miles away. I wouldn't want to be responsible for the mess though..
The idea reminds me of the movie 'The Explorers' where they created a computer generated sphere that could penetrate through anything, so they squeezed an old 'tilt-a'whirl' inside it and flew it up into space to meet aliens fixed on Earth TV.
Uhm, before to start a war ..... cutting capability of a laser against specific materials, depends from a lot of things, not just density and reflection property ..... and one of the more important one is the thermal resistance of the material (or, better said, thermal conductivity, that we use more frequently and that is simply the inverse of thermal resistance).
Let me give you a simple example: aluminium have a density of approximatively 2400 Kg/m^3 and a thermal conductivity around 250, and lead, if i recall correctly, have a density of something more than 11300Kg/m^3 and a thermal resistance around 35 ..... also if lead is more than 5 times dense than aluminium, is much more easy to cut it, with a low power laser, than aluminium, cause it "draw away" less heat from the line of cut than aluminium, so the material will melt much easily and quickly in the line of cut (and this regardless the melting temperatures).
With the same principle example, supposing that you want to cut a material with a thermal resistance of 0 (thing that is impossible in the practical way, cause 0 thermal resistance means infinite thermal conductivity, and this does not exist in the reality ), you will NEVER reach to cut it, regardless how much power you pump in the laser ..... simply cause 0 thermal resistance means that all the piece of material go at the same temperature with no delay of time when you heat any part of it ..... you can pump 100Kw of power in it, and melt it all together, but never cut it.
So, when you try to cut with a laser a material with a very low thermal resistance, you need to use high powers and high speeds for reduce times, otherwise the metal around the cutting line draws away too much heat and "cook" badly, instead to just cut ..... where instead, with a material with a high thermal resistance, you can use lower powers and go slow, and still get a decent cutting line.
Ofcourse then there are other factors, as mass, melting point, reflectivity, and so on, but one of the more important (and that, usually, none keep in consideration), is thermal conductivity .
EDIT: @danefex: you can't try that, CO2 beams easily punch a hole in the mirror in almost no time (except if you use a quarter-wave polished heavy copper or gold mirror )
Hehe I'm surprised it's reflectable at all... I didn't even think it was possible anyways because I assume there isn't a beam with a laser like this being focused at pinpoint range for cutting. I'm guessing if it were fired into open air also (however possible) it'd look like a strobe light/flash because of how quickly the light (un)diverges over a short distance. Just a guess though..if it is a beam, then look out balloons! :beer: