that's super exciting! precisely cutting 220μm-thick steel sheet without warping it is an ability not to be underestimated, particularly when you can cut it to literally any shape you want to an x-y precision of 10μm, subject to i guess a minimum corner radius. 220μm ÷ 300 passes suggests you were vaporizing about 700nm of steel per pass, which seems pretty plausible; it's faster than the w&m levsha results but not that much

how efficient is this? heat of vaporization of iron is 354 kilojoules per mole, which works out to 6.3 kilojoules per gram, plus another 3 kilojoules per gram or so to reach the boiling point. if i estimate your cut width as 100μm and the cut length as 60mm (600ms at 100mm/s, 18 frames at 30fps), that's about 1.3 mm³ of iron, about 10 mg, which should require about 90 joules to vaporize it. this is about 500 milliwatts over 3 minutes, which is a lot less than 14.4 watts, so probably most of the heat is being lost to things like reflection and conduction; maybe most of the focus spot isn't getting hot enough and only the center is actually boiling (though the sparks suggest that some of the iron is being ejected in liquid form)

i suspect it could become a lot more practical with automatic focus