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I worked on a physics project back in college (student labor is cheap) that reminds me of this.
It was called a Free Electron Laser and the boiled-down version is that you get a couple of stupidly powerful cathode “electron guns”, fire a focused stream of electrons through a bank of permanent magnets that induces a wavelength to the stream to effectively make a laser out of electrons instead of photons.
Depending on the wavelength, wherever two of these streams intersect, it causes the compounds in the point of intersection to fluoresce. Every element and compound has its own fluorescent signature, so you slap a powerful optic to focus on the point of intersection and look for the minute flashes of light. Compare those flashes of light to your known database and now you can “sniff” anything within LOS.
Damn physics is fun!