How to Build a Laser Death Ray
Vacuum and Extreme Ultraviolet Light
While the other wavelength class pages have graphs of the attenuation how well that light passes through air and water, those graphs are missing from this page for the simple fact that light in the vacuum ultraviolet and extreme ultraviolet part of the spectrum does not propagate through either medium. In fact, it is pretty much instantly absorbed by any matter. Hence the name "vacuum" ultraviolet - it only propagates in vacuum.
Vacuum ultraviolet, or VUV, light has a maximum wavelength of 200 nanometers. Extreme ultraviolet, or EUV, light has a shortest wavelength around 1 to 2 nanometers. The border between VUV and EUV is nebulous. The border between EUV and soft x-rays is similarly fuzzy.
VUV and EUV is difficult to work with. It cannot be focused with lenses, nor can it pass through windows. Thus, you cannot isolate the lasing element from the environment. It cannot be reflected by normal mirrors - it is absorbed at the surface. You can get reflection at grazing angles. It is possible, but difficult and expensive, to make grazing incidence mirrors for vacuum ultraviolet light. Some special dielectric mirrors allow normal incidence reflection of VUV and EUV light, but the reflectivity of modern EUV mirrors is fairly poor - no better than 70% of the light is reflected.
The short wavelength of vacuum and extreme ultraviolet makes it useful for space combat, if you can focus it.