How to block the next Covid in mid-air

I found this more interesting for light production and a new led driven method. [1] The premise of using far UVC ( see lead / lede [2]) to kill off pathogens is also interesting.

[1] So if you shoot a 444 nm blue laser into an appropriate crystal, you get exactly 222 nm far-UVC light back

[2] In January 2024, I wrote a big piece on a relatively new, and very promising, approach to fighting respiratory diseases like Covid, tuberculosis, and flus. It’s called “far-UVC,” a type of ultraviolet light, at wavelengths of roughly 200 to 235 nanometers, that can kill the vast majority of airborne pathogens it targets, without damaging human skin or eyes the way longer-wavelength UV does.