How to Build a Laser Death Ray
Mid Infrared Light
Mid infrared light is emitted as thermal radiation by jet engines and automobile motors and other machinery that gets burning hot while it works. Military heat seaking missiles home in on the mid infrared glow of their targets. There is a window from 3 to 4 microns in air that is fairly transparent to mid infrared light.|
Most materials that are transparent to visible light are opaque to mid infrared. You would need to use special materials for lenses and windows for a mid infrared death ray. Mid infrared light has an attenuation length in water of less than a millimeter.
The United States miltary has built a few chemical laser heat rays that emit light in the mid infrared. These have been deuterium fluoride chemical lasers, lasing at 3.8 microns. With large beam pointer mirrors, they can track and explode in flight missiles, artillery shells, and mortar shells. One such laser was tested against a satellite (to "test American satellites for vulnerability," with strenuous claims that the U.S.A. is not developing antisatellite weapons). Apparently, not much happened to the satellite (at least, not that they told us).
The long wavelength of mid infrared means that shorter wavelength light is more desirable when long range death rays are needed, due to the diffraction limit for focusing light. For this reason, mid infrared should be avoided for space applications.