Maybe he’s sponsored by Big Eye-Patch.
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…and he also destroyed the $500 laser at the end of the video, when he tried to increase its output.
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There is some good (but very technical) information here:
What it boils down to is, you point a laser at a non-linear crystal (we semi-jokingly call them "magic crystals) and some of the original laser energy gets converted to a shorter wavelength through generation of harmonic frequencies that escape the crystal at a different angle than the original laser (which continues through the crystal). That’s important because, if the harmonic frequencies remained on-axis with the original laser (also called the fundamental), then it would be very difficult to separate them, even with very good filters. Technically, these crystals generate multiple harmonics (2nd, 3rd, 4th, etc) but each harmonic is of much lower power than the previous one, with efficiencies of 0.2% down to 0.05% for each harmonic. So the 2nd harmonic is faint compared to the fundamental, the 3rd harmonic is very faint compared to the 2nd, and the 4th harmonic is so tiny as to be functionally nonexistent unless your fundamental is hugely powerful.
Green and blue laser pointers are often made by generating the second harmonic from a laser diode. Green lasers use a 1064 nm IR laser diode, run it through a nonlinear crystal, physically block the fundamental, and emit the 532 nm 2nd harmonic.
Particular crystals only work with particular wavelengths. You have to tune the incoming angle of the laser to it’s wavelength and the crystal, and you have to be able to pick off the harmonic you want on the other side of the crystal. The angles of the emitted harmonics are often close to the fundamental, so it can be tough to get a clean beam. It’s tricky stuff!
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