Why could the world’s most powerful lasers unlock secrets of the cosmos? – 12/23/2023 – Science

Inside a University of Michigan research laboratory, a bright green light fills a giant vacuum chamber. It’s the size of two tennis courts. The walls are protected by 60cm of concrete to prevent radiation leakage, and staff wear masks and hairnets to ensure delicate electronics are not affected.

This is Zeus, which will soon be the most powerful laser in the USA — and now appears for its first official experiments.

Unlike the continuous lasers that scan your barcodes in stores, Zeus is a pulsed laser, firing in bursts of a few billionths of a second. Each pulse will be capable of reaching a peak power of three petawatts — which is equivalent to a thousand times the electricity consumption of the entire world. A laser capable of such extremely compressed energy will help researchers study the quantum laws that underpin reality, for example, or recreate the conditions of extreme astrophysics in space.

But Zeus isn’t the only massive laser that could unlock new discoveries in the coming years — there are a number of other high-powered lasers at facilities from Europe to Asia hot on its heels.

The field as a whole “is really growing,” says Karl Krushelnick, director of the Gérard Mourou Center for Ultrafast Optical Science at the University of Michigan. “People are pushing the boundaries of technology.”

In the UK, a laser called the Vulcan 20-20 will become the most powerful in the world when it is completed in 2029. It will produce a beam billions of times brighter than the most intense sunlight. This single pulse will produce six times more energy than is produced worldwide — but it will last less than a trillionth of a second, with its target measuring just a few micrometers (or 0.001 of a millimeter). Like Zeus, Vulcan 20-20 will welcome scientists from around the world to carry out experiments that could expand our understanding of the cosmos, nuclear fusion and even create previously unknown matter.

The 20-petawatt Vulcan 20-20 is an £85 million ($106 million) upgrade to the existing Vulcan at the Central Laser Facility (CLF) in Harwell, UK — which is being dismantled.

Currently the size of two Olympic swimming pools, its one meter wide mirrors weigh 1.5 tonnes each. Thick white wires snake out of the laser’s opening as the device bends around the room. Considered cutting-edge technology when it was first built at the Rutherford Appleton Laboratory in 1997, the new laser will be 100 times brighter.

The “impressive thing is not just the power, but the intensity of the laser,” says Rob Clarke, leader of CLF’s experimental science group. To understand this intensity, imagine 500 million million standard 40W light bulbs.

Now “compress that light into something around a tenth the size of a human hair,” he says. “The result of this is a very, very intense light source, and that’s what creates all the fun plasma things, like huge electric and magnetic fields, and particle acceleration.”

Vulcan 20-20 will allow scientists to conduct astrophysical research in the laboratory — recreating the conditions of distant galaxies to analyze the inner workings of stars or gas clouds, or how matter might behave when exposed to specific temperatures and densities.

The field of study is driven by the desire to investigate the cosmos, explains Alex Robinson, the lead theoretical plasma physicist at CLF. Astrophysical research is generally “observational,” he says. “You’re pointing some kind of telescope and you see a lot of things. But the question arises of what’s really going on.” The hope is that carrying out experiments with a laser of such power will, for the first time, allow for “really rigorous tests of whether certain theories could work or not.”

Among the mysteries expected to be investigated at Oxford are the origins of magnetic fields, which surround most substantial objects in the Universe, such as stars and planets. “Why are these magnetic fields there? It’s not exactly obvious,” says Robinson, and no observations can really go back and test why they first appeared.

One such testing method could involve fusing matter to create shock waves and adding manufactured turbulence, such as caused by molecular clouds, planets and dust, to see if this “could give rise to magnetic fields.”

Other experiments will explore the origins of cosmic rays (high-energy particles that can travel at nearly the speed of light), how jets (sprays of particles that shoot from high-energy collisions) are formed, and the structure inside giant planets.

Researchers will also use the Vulcan 20-20 laser to investigate the formation of new materials. A form of boron nitride, a material harder than diamond, has been found to be potentially metastable – created under conditions of very high pressure and intensity manufactured in the laboratory, which can subsequently survive at ambient temperatures.

“And then the question is, what other materials could you make in the same way?” Robinson says. “Would they have fantastic electronic or optical properties? I don’t know. But at least there’s a piece there telling us there’s something worth exploring.”

Achieving fusion

Nuclear fusion is also on the list of areas where ultra-high power lasers. In July, researchers at the National Ignition Facility at Lawrence Livermore National Laboratory in California used lasers to achieve a net gain in energy for the second time.

Following the center’s original breakthrough last December, this year’s experiment has created a higher energy yield than the first, again raising hopes that clean energy can replace our existing energy sources. (Fusion reactions do not release greenhouse gases or radioactive waste.)

Fusion has also been one of the main areas of study at the Extreme Light Infrastructure for Nuclear Physics (ELI-NP) center in Măgurele, Romania—which with a strength of 10 petawatts holds the title of the most powerful laser in the world (Mourou, its director and namesake of the University of Michigan facility said its creation is “on par with a lunar landing, where failure is not an option”).

Last year, the Romanian laser operator began partnering with private companies to develop technology that could power the world’s first commercial fusion plants. Using the “Chirped Pulse Amplification” technique that earned Mourou and Donna Strickland the Nobel Prize in Physics in 2018, laser pulses will be stretched, reducing their maximum power, before being amplified and compressed again.

This “pretty much changed laser development entirely,” says Clarke, allowing much higher intensities to be achieved at low power.

Their research into the physical processes of this interaction is expected to be published within three years, before the first commercial fusion plants are built in the 2030s.

Is bigger better?

Physicists are quite keen to emphasize the collaborative nature of the field — but the size remains a point to brag about. According to Chang Hee Nam, director of the Center for Relativistic Laser Science (CoReLS) in South Korea and professor at the Gwangju Institute of Science and Technology, the center’s laser currently “holds the record for the highest intensity laser” in the world, reaching 10^23 W/sq cm —or an intensity as powerful as all the light on Earth focused to just over a micrometer, or less than one-fiftieth the diameter of a human hair.

South Korean scientists are using the technology to explore, among other things, proton therapy – a cancer treatment that targets positively charged beams at patients’ tumors.

Research that could produce new medical applications, along with testing centuries-old ideas about the state of the Universe, has been well explored on CoReLS’ four-petawatt machine — but the team isn’t stopping there. Nam says that “we are now pushing to have a higher petawatt laser; we are preparing some proposals for a 25 petawatt laser beam.” If ordered within the next six years, as he hopes, it will outperform the as-yet-unbuilt Vulcan 20-20.

Still, Vulcan’s Clarke says power and intensity aren’t everything. The most important metric now is “what can you do with it? What science are you pursuing? What will you get out of it?”

These lasers, and the researchers who work on them, care about one thing above all else, he says. “It’s about building it right and using it right.”