A local company, Nova Lux is doing some interesting stuff with Vertical Cavity lasers and frequency doubling. They have created relatively high power modules using PPLN (Periodically Poled Lithium Niobate) crystals on top of a laser diode. This is getting closer to what is finally needed.
Another solution is what is being done with LEDs now. There have been lab samples demonstrated that will produce green light directly from a diode, but they are very unstable and need LN2 to operate and have a lifetime of several minutes.
that is so cool.
