How to Build a Laser Death Ray

Near Ultraviolet Light

The near ultraviolet part of the spectrum is made up of frequencies just a bit shorter than what we can see. It is typically divided up into three bands
UV-C0.2 to 0.29 microns
UV-B0.29 to 0.32 microns
UV-A0.32 to 0.40 microns
UV-A light can pass though air and window glass. UV-B light is mostly absorbed by the ozone layer, but can propagate through ozone-free air and some can get through the ozone layer to earth. It cannot penetrate window glass, but can go through quartz. UV-C is completely blocked by the ozone layer, but can go some distance through ozone free air (the attenuation length graph below seems to consider attenuation data due to the ozone layer). It also cannot go through window glass, but can pass through quartz. The lower wavelength limit for the near ultraviolet is set by the opacity of the air. At 0.2 microns and below, air rapidly absorbs all light, entering the range of vacuum ultraviolet.

Water is somewhat transparent to near ultraviolet, particularly at the longer wavelengths.

Near ultraviolet light has a number of health effects. It damages the skin and eye, causing sunburn, skin cancer, and cataracts. On the other hand, UV-B at wavelengths from 0.27 to 0.29 microns is necessary for producing vitamin D, a hormone that is needed for calcium regulation in the body. Exposure to ultraviolet radiation is often sought out by the appearance conscious because it produces tanned skin.

The near ultraviolet will have a few issues to overcome in oder to use it as a death ray in air. It scatters more than visible light, meaning the beam attenuates faster. The short wavelength allows multi-photon absorption and ionization to occur more effeciently than visible and near infrared, meaning high powered beams will also be absorbed faster and may produce visible beams due to glowing ionized air. Many parts of this spectrum will be blocked by ozone, making them useless for space to ground bombardment. On the other hand, the short wavelength allows near ultraviolet to focus better than visible or near infrared light in vacuum, or if adequate adaptive optics can be made. This could make near ultraviolet a useful frequency for combat in outer space if shorter wavelengths are not available.

There are no high powered lasers that currently operate in the near ultraviolet. In the past, there had been some speculation about using excimer lasers, which do emit near ultraviolet beams, as death rays, but these seem not to have panned out.

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