The secret sauce is in component selection and tuning. Opengeiger uses the BPW34 diode because it is relatively common and has a large surface area, but also because it has a very low capacitance ...
Here at Hackaday we’ve covered a bunch of DIY laser diode projects. And for good reason, they are just cool. We’ve seen people add lasers to their 3D printers, stick one in a milling machine ...