To build a laser, you would need at least three energy levels, and ideally four, with particular constraints in the transition probabilties so that you can crea

To build a laser, you would need at least three energy levels, and ideally four, with particular constraints in the transition probabilties so that you can create population inversion. And you would need to pump it with a higher-energy (shorter wavelength) laser. Perhaps doable with a free electron laser, but probably not with traditional lasers, due to the energies involved. But, yeah, not sure what the use would be. Maybe a form of lidar that allowed measuring speed of objects to extreme precision, by measuring the dopler shift of reflected light? (Assuming light at such a short wavelength is reflected sufficiently, which it probably wouldn't be). If there happened to be one atom/matrix that could be tuned to the transition energy of another atom's fission transition energy, then you could use it to burn nuclear material / waste. But you could just do that with the pump laser directly. I suppose you could maybe pump such a laser with a very high temperature plasma (like fusion temperatures hot), rather than with a free electron laser. Then maybe it might make more sense.