Here at ET we occasionally delve into topics for no particular reason beyond curiosity. In this case, that’s lasers. At the consumer level, we’re surrounded by products that rely on lasers — optical media, barcode scanners, fiber optics, and printers are all common — but for this article, we decided to scale up a bit. There are a couple contenders for the world’s biggest laser, and they’re all involved in some really cool science.
Honorable Mention: Large Hadron Collider
The Large Hadron Collider isn’t technically a laser, but it’s very much the physically largest particle beam — and I’m including it here because not only is it an intangible high-energy beam, there is some (literally!) very cool laser science happening at the LHC facility. CERN’s ALPHA experiment actually uses X-ray lasers to cool antimatter down to just a shiver above absolute zero.
ALPHA scientists use the instrument’s reaction chamber to trap antihydrogen in a magnetic bottle. Then they tune the laser so that its beam is just out of phase with the antihydrogen’s energy states, a little like someone “stealing your bounce” when you’re on a trampoline. The momentum of the photons in the laser slows the antihydrogen, and because heat is a form of molecular motion, that slowing has a cooling effect. Researchers were able to cool the antihydrogen to 0.012K.
While the ALPHA experiment is doing laser cooling, the aptly named ZEUS three-petawatt laser at the University of Michigan is colliding with an electron beam to study extreme plasmas. ZEUS is the most powerful laser in the United States. It’s actually designed to punch above its weight: while ZEUS doesn’t deliver this much raw power, its design simulates a laser that is roughly a million times more powerful than what it says on the tin. This allows a petawatt-class laser to simulate a zetawatt beam.
Once it’s fully powered up, the laser will be directed into a vacuum chamber and focused on its gaseous target, where it will begin to deliver ultrashort pulses of light. Then, an electron beam is directed at the same target, such that the laser and the electron beams intersect within the volume of gas. All that energy ionizes the gas into plasma, and because of the geometry, the intersecting beams simulate a much more powerful zetawatt-class laser. In fact, the Z in zetawatt is where Zeus got its name: the “Zetawatt Equivalent Ultrashort pulse laser System.”
Extreme Light Infrastructure – Nuclear Physics (ELI-NP)
It’s a leap from three to ten petawatts, but the ambitious Extreme Light Infrastructure (ELI) project in Europe has fired up their flagship ELI-NP, a dual ten-petawatt IR laser. ELI-NP puts forth a coherent beam of infrared light at 820nm, with a planned diameter up to fifty centimeters, which — guys — that’s like a foot-and-a-half-wide ten-petawatt heat ray. I know we joke about a Death Star, but this thing is the real deal. It has exquisitely fine targeting capabilities. Within the reaction chamber, that 50cm beam can focus on an area of a single square millimeter. That 1022 W/cm2 intensity is an appreciable fraction of Earth’s total solar gain, focused on a tiny little dot.
ELI-NP was built to study extremely high-energy physics, like how heavy metals are formed by supernovae. But it’s also engaged in more practical research, such as proton therapy for cancer, or new ways to handle radioactive waste.
The only reason it’s not a closer tie for first place is that ELI-NP is incomplete, and running badly behind schedule. The facility’s has faced scandal over its choice of director and its gamma source was delayed for multiple years. A new contract with Lyncean Technologies in California is set to deliver a gamma source in 2023.
Center for Relativistic Laser Science (CoReLS)
The breakout winner is a gigantic four-petawatt titanium-sapphire laser named CoReLs, which is located in South Korea. Ever since UMich achieved a 1022 W/cm2 output in 2004, physicists have been trying to push it one notch higher, and they’ve finally realized the dream. While four petawatts is definitely a smaller raw power output, CoReLS uses physical optics to confine the beam into a tiny area. Because it’s so tightly focused, the photons that strike this laser’s micron-sized target actually outnumber those that strike ELI-NP’s square millimeter, even though ELI-NP can output more photons. In April of this year, a team of researchers achieved an intensity of 1023 W/cm2, which is roughly equivalent to focusing the entire output of the Sun on a space the size of a small office desk. Except that they focused it on an area of about a square micron, which is smaller than an E. coli. Pew pew.
To get the 28cm beam focused down, the laser uses extremely fine glass optics and parabolic mirrors. CoReLS originally used Pyrex in its optical compression gratings, but there is so much heat coming off the beam that even Pyrex couldn’t disperse it evenly enough, leading to distortions in the wavefront and fluctuations in the beam. In the end researchers had to use straight fused silica, the same stuff that the shuttle windows are made of.
(Author’s note: Upstate New Yorkers might chuckle at this. Pyrex is made by Corning, which is the same company that makes tableware called Corelle. Serendipity?)
The goal of CoReLS is to study what happens in the most extreme conditions we know of, where interactions are dominated by relativistic effects. One thread of research is strong field quantum electrodynamics. The intensity of this laser allows physicists to do real-life experiments on wibbly-wobbly quantum stuff that has been purely theoretical until now.
While these almost indescribably powerful lasers are doing their work, other projects continue to push the boundaries of human understanding by creating more and more powerful instruments. Several other ultra-high-energy laser facilities are planned or under construction, including one at Apollon (France), the EP-OPAL project at the University of Rochester (USA), and China’s 100-petawatt Source of Extreme Light. If you like giant lasers, watch this space: as challengers move up in the ranks, we’ll update our roster.
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