Just watched a talk on this topic from last December: https://media.ccc.de/v/39c3-of-boot-vectors-and-double-glitc...
I'm more interested in the 3D printed platform made to to hold up the chip and the fact that this seemed to be done in a garage. I thought anything laser related would require much more precision but the article has pretty much everything ordered online.
Previously discussed: https://news.ycombinator.com/item?id=42708682
The GaN hemt would make sense for a second board iteration where you drive the 75V straight through the diode with a very short (variable) pulse like in this EPC reference design:
https://epc-co.com/epc/products/evaluation-boards/epc9172
That way the 1.4 Ohm resistor doesn't eat like 60-80% of the energy (40amps drop around 60V for an instant 240W in the resistor vs the foward voltage of the diode which is like 1.5V or so for the 60W peak).