AEROSPACE ENGINEER EUGEN SÄNGER hypothesized in the 1950s that if matter could be completely converted into light particles (called photons), the photons themselves could be a power source to thrust a rocket to intergalactic speeds. While he assumed a photon rocket could only ever be the stuff of science fiction, the seed of his idea has only continued to take root. To create the ultimate laser, a number of research teams are pursuing technology that could maintain coherent gamma rays, the most energetic form of light in our universe.

If we could produce coherent gamma rays just as an ordinary laser produces coherent rays of visual light, the technology could unlock interstellar travel—as well as blow missiles out of the sky and revolutionize cancer treatment. While the gamma ray laser (also known as a "graser") is still conceptual, it's considered one of the most important problems in physics.

Invisible to our eyes, gamma rays burst from supernova explosions as well as the hottest and most energy dense objects in the cosmos, like pulsars, those highly magnetized neutron stars that emit pulses of radiation. Gamma rays travel through the vacuum of space at the speed of light, with wavelengths so minuscule that they can pass through the space within the atoms of a detector. With the smallest wavelengths and the fastest frequency, gamma rays fall on one extreme end of the electromagnetic spectrum.

NASA, Public domain, via Wikimedia Commons Invisible to our eyes, gamma rays fall on an extreme end of the electromagnetic spectrum. They have the shortest wavelengths and the highest frequency of any form of light.

Visionaries have been trying to push laser technology into the farthest reaches of the electromagnetic spectrum since the invention of the first laser in 1961. Along the way, scientists have learned how to stabilize gamma rays into a coherent beam, a necessary step toward developing any laser technology.

A TRADITIONAL LASER excites electrons in a gas,…

Manasee Wagh

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