Liquid Lasers Challenge Fiber Lasers as the Basis of Future High-Energy Weapons
takyon writes:
Liquid Lasers Challenge Fiber Lasers as the Basis of Future High-Energy Weapons
Despite a lot of progress in recent years, practical laser weapons that can shoot down planes or missiles are still a ways off. But a new liquid laser may be bringing that day closer.
Much of the effort in recent years has focused on high-power fiber lasers. These lasers usually[sic] specially doped coils of optical fibers to amplify a laser beam, and were in originally developed for industrial cutting and welding. Initially, fiber laser were dark horses in the Pentagon's effort to develop electrically powered solid-state laser weapons that began two decades ago. However, by 2013 the Navy was testing a 30-kilowatt fiber laser on a ship. Since then, their ability to deliver high-energy beams of excellent optical quality has earned fiber lasers the leading role in the current field trials of laser weapons in the 50- to 100-kilowatt class. But now aerospace giant Boeing has teamed with General Atomics-a defense contractor also known for research in nuclear fusion-to challenge fiber lasers in achieving the 250-kilowatt threshold that some believe will be essential for future generations of laser weapons. Higher laser powers would be needed for nuclear missile defense.
The challenging technology was developed to control crucial issues with high energy solid-state lasers: size, weight and power, and the problem of dissipating waste heat that could disrupt laser operation and beam quality. General Atomics "had a couple of completely new ideas, including a liquid laser. They were considered completely crazy at the time, but DARPA funded us," said company vice president Mike Perry in a 2016 interview. 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. A crucial trick was ensuring that the cooling liquid has a refractive index exactly the same as that of the solid laser material. A perfect match of the liquid and solid could avoid any refraction or reflection at the boundary between them. Avoiding reflection or refraction in the the cooling liquid also required making the fluid flow smoothly through the channels to prevent turbulence.
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