So what about non-linear optics and optical frequency doubling? https://en.wikipedia.org/wiki/Second-harmonic_generation https://en.wikipedia.org/wiki/Second-h

So what about non-linear optics and optical frequency doubling? https://en.wikipedia.org/wiki/Second-harmonic_generation https://en.wikipedia.org/wiki/Second-harmonic_generation It was just an option on my MSc in LASERs but I thought it was cool (with the potential to be very warm). Although my frequency has been halved and I've been working in software for decades