The Pentagon began developing work on electrically powered solid-state laser weapons two decades ago. By 2013 the Navy was testing a 30-kilowatt fiber laser on a ship. Then focus shifted to fiber lasers in the 50- to 100-kilowatt class. Now aerospace giant Boeing has teamed with General Atomics to build lasers achieving the 250-kilowatt threshold needed to defend against nuclear missiles, reports IEEE Spectrum.

The design of high-energy solid-state lasers entails a tradeoff between size, weight and power, and the problem of dissipating heat. General Atomics had the idea of developing a liquid laser, considered crazy at the time, but DARPA funded it. Liquid lasers are similar to solid-state lasers but they use a cooling liquid that flows through channels integrated into the solid-state laser material. The trick was achieving a perfect match in the refractive index between the liquid and the solid material. more “Boeing, General Atomics to Advance Work on Liquid Lasers”