BLOGS

A researcher holds the scaffolding with tiny copper foils attached. These copper pieces will be struck with lasers, heating them to thousands of degrees Fahrenheit.

Credit: Hiroshi Sawada

Topics: Applied Physics, Lasers, Materials Science, Plasma, Radiation, Thermodynamics

For the first time, researchers monitor the heat progression in laser-created plasma that occurs in only a few trillionths of a second.

A team of researchers supported by the U.S. National Science Foundation has developed a new method of tracking the ultra-fast heat progression in warm, dense matter plasmas — the type of matter created when metals are struck with high-powered lasers. Published in Nature Communications, the results of this study will help researchers better understand not only how plasma forms when metal is heated by high-powered lasers but also what's happening within the cores of giant planets and even aid in the development of fast ignition laser fusion with energy-generating potential here on Earth.

The research team aimed a high-powered laser at very thin strips of copper, which heated to 200,000 degrees Fahrenheit and momentarily shifted to a warm, dense matter plasma state before exploding. At the same time, the researchers used ultrashort-duration X-ray pulses from an X-ray free-electron laser to capture images of the copper's transformation down to a few picoseconds or trillionths of a second. By doing so, the researchers were able to observe the ultra-fast and microscopic transformation of matter.

"These findings shed new light on fundamental properties of plasmas in the warm dense matter state," says Vyacheslav Lukin, NSF program director for Plasma Physics. "The new methods to probe the plasma developed by this international team of researchers may also inform future experiments at extremely high-powered lasers, such as the NSF ZEUS Laser Facility."

Researchers track plasma creation using a novel ultra-fast laser method, National Science Foundation

Topics: Applied Physics, Atmospheric Science, Existentialism, Futurism, Lasers, Robotics, Science Fiction

"Laser" is an acronym for Light Amplification by the Stimulated Emission of Radiation. As the article alludes to, the concept existed before the actual device. We have Charles Hard Townes to thank for his work on the Maser (Microwave Amplification by the Stimulated Emission of Radiation) and the Laser. He won the Nobel Prize for his work in 1964. In a spirit of cooperation remarkable for the Cold War era, he was awarded the Nobel with two Soviet physicists, Aleksandr M. Prokhorov and Nikolay Gennadiyevich Basov. He lived from 1915 - 2015. The Doomsday Clock was only a teenager, born two years after the end of the Second World War. As it was in 2023, it is still 90 seconds to midnight. I'm not sure going "Buck Rogers" on the battlefield will dial it back from the stroke of twelve. Infrared lasers are likely going to be deployed in any future battle space, but infrared is invisible to the human eye, a weapon for which you only need a power supply and not an armory; it might appeal not only to knock drones out of the sky, but to assassins, contracted by governments who can afford such a powerful device, that will not leave a ballistic fingerprint, or depending on the laser's power: DNA evidence.

Nations around the world are rapidly developing high-energy laser weapons for military missions on land and sea, and in the air and space. Visions of swarms of small, inexpensive drones filling the skies or skimming across the waves are motivating militaries to develop and deploy laser weapons as an alternative to costly and potentially overwhelmed missile-based defenses.

Laser weapons have been a staple of science fiction since long before lasers were even invented. More recently, they have also featured prominently in some conspiracy theories. Both types of fiction highlight the need to understand how laser weapons actually work and what they are used for.

A laser uses electricity to generate photons, or light particles. The photons pass through a gain medium, a material that creates a cascade of additional photons, which rapidly increases the number of photons. All these photons are then focused into a narrow beam by a beam director.

In the decades since the first laser was unveiled in 1960, engineers have developed a variety of lasers that generate photons at different wavelengths in the electromagnetic spectrum, from infrared to ultraviolet. The high-energy laser systems that are finding military applications are based on solid-state lasers that use special crystals to convert the input electrical energy into photons. A key aspect of high-power solid-state lasers is that the photons are created in the infrared portion of the electromagnetic spectrum and so cannot be seen by the human eye.

Based in part on the progress made in high-power industrial lasers, militaries are finding an increasing number of uses for high-energy lasers. One key advantage for high-energy laser weapons is that they provide an “infinite magazine.” Unlike traditional weapons such as guns and cannons that have a finite amount of ammunition, a high-energy laser can keep firing as long as it has electrical power.

The U.S. Army is deploying a truck-based high-energy laser to shoot down a range of targets, including drones, helicopters, mortar shells and rockets. The 50-kilowatt laser is mounted on the Stryker infantry fighting vehicle, and the Army deployed four of the systems for battlefield testing in the Middle East in February 2024.

High-energy laser weapons: A defense expert explains how they work and what they are used for, Iain Boyd, Director, Center for National Security Initiatives, and Professor of Aerospace Engineering Sciences, University of Colorado Boulder

A laser fusion power plant proposed by Longview Fusion Energy Systems would generate 1000 MWh or more of electricity. The plant would compress fusion fuel by using an indirect drive, the same approach used at the National Ignition Facility, which in December announced that it had produced ignition and gain, the first time that fusion researchers have attained those milestones.

Topics: Futurism, Lasers, Modern Physics, Nuclear Fusion

The attainment of fusion ignition and energy gain on the world’s most energetic laser late last year was indisputably a major scientific accomplishment. But the road to fusion as a viable source of energy will be a long one, if not a dead end. And if it does ultimately become a reality, most experts say that it is unlikely that a laser-driven fusion power plant will be based on the approach taken by the National Ignition Facility (NIF), where the fusion milestone occurred.

The December shot, which produced 1.5 times the 2 MJ of energy that was fired on the fusion fuel, has silenced skeptics who said that ignition could never be created by bombarding tiny capsules of deuterium–tritium fuel with lasers. (See “National Ignition Facility surpasses long-awaited fusion milestone,” Physics Today online, 13 December 2022.) “They have done something very important: demonstrating ignition and burn,” says Stephen Bodner, a retired head of the laser fusion branch at the US Naval Research Laboratory who once was a persistent critic of NIF’s approach.

And the milestone is likely to open the floodgates to new investments in the handful of startups that are pursuing inertial fusion energy (IFE). “I think you will see a proliferation of companies devoted to IFE or aspects of IFE because of this and because of investor interest,” says Todd Ditmire, a University of Texas at Austin physicist who is chief technology officer of Focused Energy, an IFE startup.

Yet despite the fanfare greeting the announcement, the fact is that the fusion energy yield from the successful shot amounted to less than 1% of the 300 MJ taken from the electricity grid to power NIF’s 192 beams. And the energy released was enough to boil about 10 tea kettles. Many experts say that economically viable fusion will require fusion reactions yielding energy gains of at least 100 times the energy deposited on the fuel capsule—two orders of magnitude greater than the NIF shot.

NIF success gives laser fusion energy a shot in the arm, David Kramer, Physics Today

On target: Water is fanned out through a specially developed nozzle, and then a laser pulse is passed through it to create a switch. (Courtesy: Adrian Buchmann)

Topics: Applied Physics, Lasers, Materials Science, Photonics, Semiconductor Technology

A laser-controlled water-based switch that operates twice as fast as existing semiconductor switches has been developed by a trio of physicists in Germany. Adrian Buchmann, Claudius Hoberg, and Fabio Novelli at Ruhr University Bochum used an ultrashort laser pulse to create a temporary metal-like state in a jet of liquid water. This altered the transmission of terahertz pulses over timescales of just tens of femtoseconds.

With the latest semiconductor-based switches approaching fundamental upper limits on how fast they can operate, researchers are searching for faster ways of switching signals. One unexpected place to look for inspiration is the curious behavior of water under extreme conditions – like those deep within ice-giant planets or created by powerful lasers.

Molecular dynamics simulations suggest water enters a metallic state at pressures of 300 GPa and temperatures of 7000 K. While such conditions do not occur on Earth, it is possible that this state contributes to the magnetic fields of Uranus and Neptune. To study this effect closer to home, recent experiments have used powerful, ultrashort laser pulses to trigger photo-ionization in water-based solutions – creating fleeting, metal-like states.

Water-based switch outpaces semiconductor devices, described in APL Photonics.

National Ignition Facility operators inspect a final optics assembly during a routine maintenance period in August. Photo credit: Lawrence Livermore National Laboratory

Topics: Alternate Energy, Applied Physics, Climate Change, Energy, Global Warming, Lasers, Nuclear Fusion

After the heady, breathtaking coverage of pop science journalism, I dove into the grim world inhabited by the Bulletin of the Atomic Scientists on their take on the first-ever fusion reaction. I can say that I wasn’t surprised. With all this publicity, it will probably get the Nobel Prize nomination (my guess). Cool Trekkie trivia: the National Ignition Facility was the backdrop for the Enterprise's warp core for Into Darkness.

*****

This week’s headlines have been full of reports about a “major breakthrough” in nuclear fusion technology that, many of those reports misleadingly suggested, augurs a future of abundant clean energy produced by fusion nuclear power plants. To be sure, many of those reports lightly hedged their enthusiasm by noting that (as The Guardian put it) “major hurdles” to a fusion-powered world remain.

Indeed, they do.

The fusion achievement that the US Energy Department announced this week is scientifically significant, but the significance does not relate primarily to electricity generation. Researchers at Lawrence Livermore National Laboratory’s National Ignition Facility, or NIF, focused the facility’s 192 lasers on a target containing a small capsule of deuterium–tritium fuel, compressing it and inducing what is known as ignition. In a written press release, the Energy Department described the achievement this way: “On December 5, a team at LLNL’s National Ignition Facility (NIF) conducted the first controlled fusion experiment in history to reach this [fusion ignition] milestone, also known as scientific energy breakeven, meaning it produced more energy from fusion than the laser energy used to drive it. This historic, first-of-its-kind achievement will provide the unprecedented capability to support [the National Nuclear Security Administration’s] Stockpile Stewardship Program and will provide invaluable insights into the prospects of clean fusion energy, which would be a game-changer for efforts to achieve President Biden’s goal of a net-zero carbon economy.”

Because of how the Energy Department presented the breakthrough in a news conference headlined by Energy Secretary Jennifer Granholm, news coverage has largely glossed over its implications for monitoring the country’s nuclear weapons stockpile. Instead, even many serious news outlets focused on the possibility of carbon-free, fusion-powered electricity generation—even though the NIF achievement has, at best, a distant and tangential connection to power production.

To get a balanced view of what the NIF breakthrough does and does not mean, I (John Mecklin) spoke this week with Bob Rosner, a physicist at the University of Chicago and a former director of the Argonne National Laboratory who has been a longtime member of the Bulletin’s Science and Security Board. The interview has been lightly edited and condensed for readability.

See their chat at the link below.

The Energy Department’s fusion breakthrough: It’s not really about generating electricity, John Mecklin, The Bulletin of the Atomic Scientists, Editor-in-Chief

Credit: sakkmesterke/ Getty Images

Topics: Lasers, Modern Physics, Quantum Computer, Quantum Mechanics

Physicists have devised a mind-bending error-correction technique that could dramatically boost the performance of quantum computers.

When the ancient Incas wanted to archive tax and census records, they used a device made up of a number of strings called a quipu, which encoded the data in knots. Fast-forward several hundred years, and physicists are on their way to developing a far more sophisticated modern equivalent. Their “quipu” is a new phase of matter created within a quantum computer, their strings are atoms, and the knots are generated by patterns of laser pulses that effectively open up [a] second dimension of time.

This isn’t quite as incomprehensible as it first appears. The new phase is one of many within a family of so-called topological phases, which were first identified in the 1980s. These materials display order not on the basis of how their constituents are arranged—like the regular spacing of atoms in a crystal—but on their dynamic motions and interactions. Creating a new topological phase—that is, a new “phase of matter”—is as simple as applying novel combinations of electromagnetic fields and laser pulses to bring order or “symmetry” to the motions and states of a substance’s atoms. Such symmetries can exist in time rather than space, for example in induced repetitive motions. Time symmetries can be difficult to see directly but can be revealed mathematically by imagining the real-world material as a lower-dimensional projection from a hypothetical higher-dimensional space, similar to how a two-dimensional hologram is a lower-dimensional projection of a three-dimensional object. In the case of this newly created phase, which manifests in a strand of ions (electrically charged atoms), its symmetries can be discerned by considering it as a material that exists in higher-dimensional reality with two-time dimensions.

“It is very exciting to see this unusual phase of matter realized in an actual experiment, especially because the mathematical description is based on a theoretical ‘extra’ time dimension,” says team member Philipp Dumitrescu, who was at the Flatiron Institute in New York City when the experiments were carried out. A paper describing the work was published in Nature on July 20.

Opening a portal to an extra time dimension—even just a theoretical one—sounds thrilling, but it was not the physicists’ original plan. “We were very much motivated to see what new types of phases could be created,” says study co-author Andrew Potter, a quantum physicist at the University of British Columbia. Only after envisioning their proposed new phase did the team members realize it could help protect data being processed in quantum computers from errors.

New Phase of Matter Opens Portal to Extra Time Dimension, Zeeya Merali, Scientific American

Artist's representation of the circular phonons. (Courtesy: Nadja Haji and Peter Baum, University Konstanz)

Topics: Applied Physics, Lasers, Magnetism, Materials Science, Phonons

When a magnetic material is bombarded with short pulses of laser light, it loses its magnetism within femtoseconds (10^–15 seconds). The spin, or angular momentum, of the electrons in the material, thus disappears almost instantly. Yet all that angular momentum cannot simply be lost. It must be conserved – somewhere.

Thanks to new ultrafast electron diffraction experiments, researchers at the University of Konstanz in Germany have now found that this “lost” angular momentum is in fact transferred from the electrons to vibrations of the material’s crystal lattice within a few hundred femtoseconds. The finding could have important implications for magnetic data storage and for developments in spintronics, a technology that exploits electron spins to process information without using much power.

In a ferromagnetic material, magnetism occurs because the magnetic moments of the material’s constituent atoms align parallel to each other. The atoms and their electrons then act as elementary electromagnets, and the magnetic fields are produced mainly by the spin of the electrons.

Because an ultrashort laser pulse can rapidly destroy this alignment, some scientists have proposed using such pulses as an off switch for magnetization, thereby enabling ultra-rapid data processing at frequencies approaching those of light. Understanding this ultrafast demagnetization process is thus crucial for developing such applications as well as for better understanding the foundations of magnetism.

Researchers find ‘lost’ angular momentum, Isabelle Dumé, Physics World

Image source: CERN - accelerating science

Topics: CERN, Condensed Matter Physics, Entanglement, Lasers, Quantum Mechanics

Much of modern experimental physics relies on a counterintuitive principle: Under the right circumstances, zapping matter with a laser doesn’t inject energy into the system; rather, it sucks the energy out. By cooling the system to a fraction of a degree above absolute zero, one can observe quantum effects that are otherwise invisible.

Laser cooling works like a charm, but only when a system’s ladder of quantum states is just right. Atoms of alkali metals and a few other elements are ideal. Molecules, with their multitudes of energy levels, pose a much greater challenge. And fundamental particles such as protons, which lack internal states altogether, can’t be laser-cooled at all.

Nevertheless, there’s a lot of interest in experimenting on protons at low temperature—in particular, precisely testing how their mass, magnetic moment, and other properties compare with those of antiprotons. Toward that end, the Baryon Antibaryon Symmetry Experiment (BASE) collaboration has now demonstrated a method for using a cloud of laser-cooled beryllium ions to sympathetically cool a single proton, even when the proton and ions are too distant to directly interact.

A superconducting circuit is a cooling teleporter, Johanna L. Miller, Physics Today

In their experiments, the researchers used ultrathin crystals consisting of a single layer of atoms. These sheets were sandwiched between two layers of mirror-like materials. The whole structure acts as a cage for light and is called a microcavity.

Topics: Applied Physics, Bose-Einstein Condensate, Lasers, Nanotechnology, Optics

Physicists have taken a step towards realizing the smallest-ever solid-state laser by generating an exotic quantum state known as a Bose-Einstein condensate (BEC) in quasiparticles consisting of both matter and light. Although the effect has so far only been observed at ultracold temperatures in atomically thin crystals of molybdenum diselenide (MoSe₂), it might also be produced at room temperature in other materials.

When particles are cooled down to temperatures just above absolute zero, they form a BEC – a state of matter in which all the particles occupy the same quantum state and act in unison, like a superfluid. A BEC made up of tens of thousands of particles behaves as if it were just one giant quantum particle.

An international team of researchers led by Carlos Anton-Solanas and Christian Schneider from the University of Oldenburg, Germany; Sven Höfling of the University of Würzburg, Germany; Sefaattin Tongay at Arizona State University, US; and Alexey Kavokin of Westlake University in China, has now generated a BEC from quasiparticles known as exciton-polaritons in atomically thin crystals. These quasiparticles form when excited electrons in solids couple strongly with photons.

“Devices that can control these novel light-matter states hold the promise of a technological leap in comparison with current electronic circuits,” explains Anton-Solanas, who is in the quantum materials group at Oldenburg’s Institute of Physics. “Such optoelectronic circuits, which operate using light instead of electric current, could be better and faster at processing information than today’s processors.”

Anton-Solanas, Schneider, and colleagues studied crystals of MoSe₂ that were just a single atomic layer thick. MoSe₂belongs to a family of materials known as transition-metal dichalcogenides (TMDCs). In their bulk form, these materials act as indirect band-gap semiconductors. Still, when scaled down to a monolayer thickness, they behave as direct band-gap semiconductors, capable of efficiently absorbing and emitting light.

In their experiments, the researchers assembled sheets of MoSe₂ less than a nanometer thick and sandwiched them between alternating layers of silicon dioxide and titanium dioxide (SiO₂/TiO₂), which reflect light like a mirror. The resulting structure is known as a microcavity and acts as a cage for light. “It’s like trapping the light-emitting material in a room filled with mirrors and mirrors only,” Tongay tells Physics World. “The light gets reflected these mirrors and is absorbed by the material back and forth.”

Exotic quantum state could make smallest-ever laser, Isabelle Dumé, Physics World

Lasers are used to create an indestructible optical fiber out of plasma.

Credit: Intense Laser-Matter Interactions Lab, University of Maryland

Topics: Lasers, Optics, Plasma, Research, Star Trek, Star Wars

In science fiction, firing powerful lasers looks easy — the Death Star can just send destructive power hurtling through space as a tight beam. But in reality, once a powerful laser has been fired, care must be taken to ensure it doesn’t get spread too thin.

If you’ve ever pointed a flashlight at a wall, you’ve observed an example of the diffusion of light. The farther you are from the wall, the more the beam spreads, resulting in a larger and dimmer spot of light. Lasers generally expand much more slowly than the beams from flashlights, but the effect of diffusion is important when the laser travels a long way or must maintain a high intensity.

Whether your goal is to achieve galactic domination or, more realistically, to accelerate electrons to incredible speeds for physics research, you’ll want as tight and powerful a beam as possible to maximize the intensity.

In their experiments, researchers can use devices called waveguides, like the optical fibers that might be carrying the internet throughout your neighborhood, to transport lasers while keeping them contained to narrow beams.

Plasma guides maintain focus of lasers, National Science Foundation Public Affairs