I was shown one of these built in minutes from found components at Noisebridge in SF a few years back, an old TV flyback transformer, a couple of resistors and

I was shown one of these built in minutes from found components at Noisebridge in SF a few years back, an old TV flyback transformer, a couple of resistors and caps and a pair of straight edges almost parallel for the spark gap (the lasing exits parallel to the edges) - you can detect it with a sheet of paper (because of the dyes embedded in it)