Skip to main content

Reset your password

Please enter the e-mail address you used to register to reset your password

Note: The verification e-mail to change your password should arrive immediately. However, in some cases it takes longer. Don't forget to check your spam folder.

If you haven't received the e-mail in 24 hours, please contact customerservices@ioppublishing.org

Registration complete

Thank you for registering with Physics World
If you'd like to change your details at any time, please visit My account

Close
Home » Page 1115

A great day out in celebration of Maxwell’s equations

Pillars of light: this week's meeting at the Royal Society focussed on how Maxwell's equations illuminate physics (Courtesy: Tom Morris/CC BY-SA 3.0)
Pillars of light: this week’s meeting at the Royal Society focused on how Maxwell’s equations illuminate physics. (CC BY-SA 3.0 Tom Morris)

By Hamish Johnston

Earlier this week I caught the 6.30 a.m. train from Bristol to London to attend the second day of “Unifying physics and technology in light of Maxwell’s equations” at the Royal Society. It was a particularly damp and gloomy morning as I emerged from Piccadilly Circus station and tramped through St James, my sights set on the Duke of York pillar next to the Royal Society in Carlton House Terrace.

It seemed like the perfect morning to be thankful for the light described by James Clerk Maxwell’s equations, and to ponder how they have since illuminated many shadowy corners of physics.

The meeting was organized by three physicists at nearby King’s College London: biophysicist and nanotechnologist Anatoly Zayats; particle physicist John Ellis and condensed-matter physicist Roy Pike. Already, you can see the breadth of physics covered at the meeting.

(more…)

Satellite sensor unexpectedly detects waves in upper atmosphere

Atmospheric gravity waves drive winds, temperature and chemical composition in the middle and upper atmosphere, but not enough is known about those that occur at higher altitudes. Now though, an international team of researchers has unexpectedly discovered that the new “Day/Night Band” (DNB) sensor, on-board a US environmental satellite, can detect disturbances in the upper atmosphere’s nightglow caused by the waves.

“The DNB observations reveal a complex array of gravity waves in the upper atmosphere that have never before been observed globally at this spatial detail, says Steve Miller of Colorado State University, US, adding that all of the data are available thanks to the sensor’s extreme sensitivity to visible and near-infrared light.

Dark clouds

The DNB is part of the Visible Infrared Imaging Radiometer Suite (VIIRS) on the US NOAA/NASA Suomi National Polar-orbiting Partnership environmental satellite launched in October 2011. The sensor, which detects wavelengths of 505–890 nm, sits 834 km above the Earth and images the atmospheric state as it races by at about 7 km/s. When assessing their sensor’s performance, Miller and colleagues noticed clouds in images taken on nights without moonlight. They realized that the instrument could detect nightglow emissions, which in this case were reflecting off the clouds. Nightglow, also known as airglow, is due to emissions of light in the upper atmosphere from atomic oxygen, sodium and hydroxyl radicals. The emissions are strongest at about 85–95 km, around the mesopause.

Although the DNB sensor is optimized to image the nocturnal surface and lower atmosphere at extremely low levels of light, the team discovered it can pick up nightglow emissions on dark nights. These emissions are sometimes disrupted by gravity waves – disturbances to the density of the atmosphere that gravity and buoyancy act to restore – that are the main form of energy exchange between the lower and upper atmosphere.

Volcanic waves

The gravity waves alter the local temperature and density, modulating the intensity of nightglow emissions and creating rippling patterns of visible light. They may appear as alternating bright and dark bands or as complex patterns, and the team found that the DNB can image the waves with a horizontal resolution of around 0.74 km.

The team imaged gravity waves resulting from a number of phenomena, including mountains, hurricanes, thunderstorms, tropical cyclones, the jet streams of intensifying cold fronts, mesospheric bores and, in the first known spaceborne measurement of its kind, a volcano. Chile’s Calbuco volcano erupted in April 2015, sending a plume of ash into the stratosphere and making a concentric-ring gravity-wave pattern in the nightglow above.

Miller says that the volcanic eruption suggests that other seismic-related airglow signals are yet to be observed, such as “a large earthquake, which may produce an observable ‘bright-sky’ airglow response and/or gravity-wave train coupled to a tsunami front”.

Miller cautions that as their sensor was not optimized for these kinds of observations, there are a number of caveats to working with the data, but there are many more discoveries to come. “There are many wave structures that we have difficulty attributing or explaining. We anticipate that we have not observed all of the possible forms of gravity waves,” he adds.

Better predictions

Because they drive circulation patterns at high altitudes, atmospheric gravity waves also tie back to the weather and climate that we experience near the surface, so this new data could help to improve predictions of climate and climate change. Miller explains that data for the lower atmosphere – taken from surface-based sensors and satellites – are relatively good, but the information for the upper atmosphere is comparatively sparse. The DNB observations could help researchers to understand the structural details of gravity waves produced globally by a variety of mechanisms.

“As a satellite-based sensor, the DNB provides global coverage, and hence an ability to capture wave activity over remote regions and above clouds that would obscure surface-based viewing,” says Miller, explaining that these DNB measurements are unique when compared with most other existing satellite observations. The Ionosphere, Mesosphere, upper Atmosphere, and Plasmasphere (IMAP) Visible-light and Infrared spectrum Imager (VISI), on board the International Space Station, is the only other kit that can provide horizontal details of upper-atmosphere gravity waves, but its resolution is 10 km, an order of magnitude coarser than the DNB’s.

Because the DNB is slated to fly on the NOAA’s Joint Polar Satellite System (JPSS) satellites well into the next decade, it could prove useful to researchers analysing decadal-scale trends in wave activity as they attempt to improve model parameterizations. And by combining DNB observations with measurements of gravity waves in the middle atmosphere from the Advanced Infrared Sounder on NASA’s Aqua satellite or the Cross-track Infrared Sounder (CrIS) on the same JPSS satellites, researchers could study the 3D structure of the waves.

Miller and colleagues would like to develop quantitative ways to extract as much information as possible from the “challenging” DNB imagery. They also hope to collaborate with the IMAP/VISI research team and groups operating surface-based nightglow sensors, to compare information content at different spatial resolutions.

The work is reported in PNAS.

The cathedral and the cosmos

Every other year, for four nights only, the Lumiere light festival transforms the ancient cathedral city of Durham, UK, into an illuminated garden of the imagination. The 2015 Lumiere marked the fourth such transformation, and this year, for the first time, a science-themed artwork took centre stage. The World Machine – a sound-and-light show projected onto the façade of Durham Cathedral – told the story of how the universe began, and also how, over the nearly 1000 years of the cathedral’s existence, humans have worked to develop theories of cosmology. Meanwhile, below the cathedral, on the banks of the River Wear, another physics-related installation, Rainbow River, celebrated the optics work of Isaac Newton.

In the video, you’ll see The World Machine, Rainbow River and a few of the two dozen other works of art that made up the 2015 Lumiere. You’ll also hear from cosmologist Carlos Frenk, director of the Institute for Computational Cosmology at Durham University and one of the scientific consultants on The World Machine; and Richard Hornby, physicist and co-creator of Rainbow River.

The artworks in the video (in order of appearance):

Complex Meshes 2015
A “fresco of light” projected onto the arched ceiling of the nave of Durham Cathedral, it responds to the movement of the crowds of people below.
Artist: Miguel Chevalier. Music: Jacopo Baboni-Schilingi. Software: Cyrille Henry and Antoine Villeret.

The World Machine
The story of modern cosmology, projected onto the façade of Durham Cathedral.
Artist: Ross Ashton. Sound: John Del’Nero. Music: Isobel Waller-Bridge. Scientific consultants: Carlos Frenk and Richard Bower.

Garden of Light
A group of illuminated plants made of recycled materials and scattered around the cathedral grounds.
Artist: TILT.

Fogscape #03238
An artificially generated cloud of fog rises from the banks of the River Wear, creating patterns of light and shadow in the woodlands below the west front of the cathedral.
Artists: Fujiko Nakaya and Simon Corder.

Rainbow River
Created to celebrate the UNESCO International Year of Light, this work evokes Isaac Newton’s work on the optics of triangular prisms, with beams of white and coloured light reflecting off the surface of the river.
Artists: Alison Lowery and Richard Hornby.

Quantum fingerprint is impossible to replicate

A technique to authenticate the identity of electronic devices using quantum tunnelling has been developed by researchers in the UK. The idea takes a problem in quantum electronics – the extreme sensitivity of the energy levels of a quantum well to its height and breadth – and turns it into an opportunity for creating a unique “quantum fingerprint” that is impossible to forge.

The secure exchange of electronic information is a cornerstone of modern society and security technology must be improved continuously to stay one step ahead of criminals and hackers. Password encryption is known to be vulnerable to cyber-attack. Where possible, it is far more secure to store data on hardware that has an identifying mark or feature that is random and therefore impossible to clone – a hi-tech version of a key. These marking systems are called physically unclonable functions (PUFs), and several have already been developed using the laws of classical physics. For example, the speckle pattern produced when a laser is incident on a surface is invariant, so the same surface will produce the same speckle pattern repeatedly; and yet it is impossible even for the manufacturer to produce another surface that will produce the same pattern. Other examples of such PUFs are modes in silicon ring oscillators and states of static random-access memories.

Forging ahead

As computers become more powerful, there is a real danger that criminals will find ways to reproduce the signature of such a device. In 2013, for example, Jean-Pierre Seifert and colleagues at the Technical University of Berlin produced a physical clone of a “unique” static random-access memory that, when tested, demonstrated identical responses to the original.

“Quantum devices all behave slightly differently, and that’s a big problem” 
Robert Young, Lancaster University






In the new research, experimental physicist Robert Young of Lancaster University has made his mark by exploiting a problem facing quantum technologists. Making practical quantum devices is very difficult because their performance is extremely sensitive to tiny imperfections introduced during manufacturing – imperfections that are much smaller than state-of-the-art manufacturing tolerances. “In a lab environment, on a one-off basis, [quantum devices] work fantastically well,” explains Young. “But when you want to make millions [of them], they all behave slightly differently, and that’s a big problem.” The researchers realized that this shortcoming is also a potential opportunity to create a device that is impossible to duplicate.

To exploit this opportunity, the researchers used resonant tunnelling diodes (RTDs) – quantum wells formed by sandwiching a layer of a conductor between two insulating gaps. The current through the diode depends on whether or not the potential difference across it is in resonance with the potential of one of the electronic energy levels in the well. The positions of these energy levels are sensitive to the atomic-scale variations of the atoms in the four interfaces on either side of the two barriers. These variations cannot be controlled using existing technology. The researchers manufactured 26 RTDs, all of which supposedly had identical specifications. However, when the researchers tested the voltage at which the peak current occurred and the maximum current through the diode at this peak, there was no overlap between the diodes.

Commercially sensitive

Straightforward circuitry exists for picking out a single resonant peak, says Young, so this technology could be commercialized by using multiple quantum wells, each with a different resonant peak. “This is standard semiconductor technology,” says Young. “You can make devices that are less than a micron squared, so you can easily make huge arrays of these identities.” The researchers have patented the technology, and they are currently looking at ways to exploit it in practice. Young describes the details as “commercially sensitive”, but he says that “these physically unclonable functions are already in use in many different markets, and all we’ve done is made one which is better – we think – than any that’s been made before”.

Jean-Pierre Seifert is intrigued. “All the PUFs so far presented that are manufacturable are clonable, either mathematically or physically,” he says. This one, he feels, is not clonable with available technology. However, he does have two concerns about the technology. Conceptually, he wonders whether the device truly relies on quantum mechanics as, although tunnelling is a quantum phenomenon, the positions of the resonances, though difficult to calculate, are still deterministic. More practically, he questions Young’s claim to be using standard semiconductor technology because, in the laboratory, the researchers grew the device by molecular beam epitaxy on an indium-phosphide substrate. “The question is whether a similar device can be manufactured in a standard CMOS process,” he says.

The research is published in Scientific Reports.

A dark day for dinosaurs

On average, 91 people are killed by asteroids each year. This number – taken from a 2010 report published by the US National Academy of Science – might seem alarmingly high, especially since we know of only a few such deaths in recorded history. But in fact it is simply a consequence of statistics: the average value takes into account deaths from enormous collisions that happen only rarely, but could potentially cause massive destruction. For example, it is generally thought that, roughly 66 million years ago, the impact of an object at least 10 km in diameter produced effects that led to the extinction of around three-quarters of life on Earth, including the majority of the world’s dinosaurs.

Many questions remain unanswered about the sequence of events that produced this cataclysm. In her book Dark Matter and the Dinosaurs, theoretical physicist Lisa Randall focuses on a novel one: how did the dinosaur-killing asteroid end up on its collision course with Earth in the first place? It has been suggested that the impactor was a comet nudged from an innocuous orbit in the Oort Cloud at the outermost reaches of the solar system. But if that is the case, Randall asks, what did the nudging?

Initial inspections of the fossil record (which Randall describes in detail) reveal some evidence to suggest that large impacts tend to occur in groups separated by around 35 million years. Although this periodicity has not been clearly established, could it provide a clue to the nature of the dislodging force?

After ruling out the possibility that the gravitational influence of an invisible companion star of our Sun might be responsible, Randall considers the motion of our solar system through the Milky Way galaxy. As it orbits the galactic centre, the solar system also oscillates through the plane that contains most of the galaxy’s stars. If there was a thin, dense region of matter contained within this stellar plane, then our orbit would periodically take us through regions of space with a density greater than the average. In that case, the additional gravitational interactions that take place during that period could be responsible for nudging Oort Cloud objects towards the Sun.

At first sight, this idea is hard to justify, as we have no observational evidence for such dense patches of space. But if these regions were made of dark matter – the invisible substance that makes up around 85% of the mass in the universe – then an absence of observational evidence is exactly what we would expect. This is an intriguing idea, because it is now widely accepted that dark matter has helped to create the cosmic scaffold on which the large-scale structure of the universe was built.

The story is that these dark-matter particles were created in the Big Bang and, through gravitational interactions, began to concentrate in the very first moments of the life of the universe. The resulting clumps acted as seeds that attracted (again via gravity) the stable atoms that began to form once the temperature of the universe had fallen sufficiently. As the universe expanded, gravity magnified these irregularities in the matter distribution, finally producing the pattern of galaxies we see today.

Unfortunately for Randall’s dinosaur-killing story, the cold and essentially collisionless dark matter described above does not behave in the same way as conventional matter. In particular, it could not be distributed in the galactic plane as a thin, dense disc capable of triggering a comet’s fatal trajectory through gravitational attraction, because galaxy-formation models fail to predict the existence of an overdense region within the plane of the galaxy.

This leads Randall to introduce a more hypothetical variety of dinosaur-killing dark matter, via the radical concept of a whole new “dark sector” in which partially interacting dark matter interacts with itself through the new force of “dark electromagnetism” to which ordinary matter is oblivious. Such self-interactions might allow this new class of dark matter to lose energy and slow down enough to form a disc within the galaxy.

There is little doubt that a massive impact 66 million years ago was, at least in part, responsible for the demise of the dinosaurs. The nature of the impactor remains unknown, but if it was indeed a comet dislodged from the Oort Cloud, then Randall’s book provides an entertaining and radical explanation of the events leading up to their ultimate extinction. However, the partially interacting dark-matter model that spawned this explanation is, as Randall concedes, “speculative”, with little experimental evidence to support it. Many of the observations that provided the original motivation for creating the model have now been questioned, while some reported discrepancies between observations and the results of dark-matter simulations have since been resolved. And as Randall herself states, “If there is a conventional explanation for an observation, it is almost always the right one. Radical departures should be accepted only when they explain phenomena that older ideas fail to accommodate. In only very rare instances are new ideas truly necessary to explain observations.”

Perhaps I am more comfortable with established ideas, aligning myself with the majority of scientists who are (in Randall’s opinion) a “conservative lot”. But you may wish to read this entertaining book before making up your own mind. After all, to misquote Robert Frost, “We dance round in a ring and suppose, but nature sits in the middle and knows”.

Forthcoming data from the Large Hadron Collider at CERN and the European Space Agency’s Gaia mission – which is designed to produce a 3D map of the Milky Way with unprecedented accuracy – may well cast some light on the properties of dark matter in our galaxy and the universe at large. In doing so, there is a chance that we could come closer to discovering what was ultimately responsible for the demise of the dinosaurs.

  • Ecco Press £19.80/$29.99hb 432pp

All-optical technique shines a light on electronic band structure

A new technique for measuring the electronic band structure of solid materials has been unveiled by physicists in Canada. The new method does not require the sample to be placed in a vacuum chamber and can also probe the bulk of a sample – something that some other techniques cannot do. The team believes that its new method could be particularly useful for studying matter under extreme conditions, including samples under extremely high pressure in a diamond anvil.

Angle-resolved photoemission spectroscopy (ARPES) is an important laser-based method for studying the electronic band structure of solid materials. Photons with enough energy to eject electrons from a material are fired at a sample and the energy and momenta of the emitted electrons are then measured. This information reveals the structure of the electronic bands in terms of the energy and momentum of the electrons within them.

Surface science

ARPES has been used extensively by physicists to study a wide range of materials including semiconductors and superconductors – but the technique has some important limitations. Measurements must be done in an ultra-high vacuum (UHV) because the emitted electrons are scattered and absorbed by air. Also, ARPES only probes a thin layer of material near the surface of the sample because the electrons cannot escape from deeper in the bulk.

Now, Paul Corkum and colleagues at the University of Ottawa, the Institut National de la Recherche Scientifique and the National Research Council of Canada have developed a new all-optical technique for studying the band structure of solids that overcomes these problems.

The technique involves exposing a sample to intense pulses of laser light, but with a photon energy much lower than that required to eject an electron from the material. There is a very large electric field associated with such a pulse, which causes an electron to quantum-mechanically tunnel from the top of the valence band to the bottom of the conduction band, thus creating a hole in the conduction band. The electron and hole are then driven by the electric field to high momenta in opposite directions. The electric field itself oscillates, and when the field direction switches, the electron and hole both reverse direction and are reunited. At this point, the electron and hole recombine, giving off a photon that can escape the material and be detected. The energy of the photon is equal to the energy gap between the valence and conduction band at the point of recombination.

To measure the momentum of the electron at recombination, Corkum and colleagues fire a much dimmer pulse from a different-coloured laser light at the sample, at the same time as the intense pulse. By measuring the intensity of the emitted light as a function of the phase between the light in the two laser pulses, the team can work out the momentum of the electron that recombined to produce the emitted photon.

Chemical processes

The electron–hole recombination process occurs very quickly, and this combined with the use of very short laser pulses means that the technique could be used to study changes in band structure over very short timescales.

Corkum says that the technique could prove particularly useful for studying materials under great pressure in a diamond anvil, because diamond is transparent to the laser light used to make the measurements. The method could be used to look at how the band structure of a material changes during catalysis and other chemical processes that cannot be studied in UHV. The study of materials in very high magnetic fields, which would deflect ARPES electrons, should also be possible.

The technique is described in Physical Review Letters.

Radiation blasts render Earth's twin inhospitable to life

Radioactive? Kepler-438b is regularly irradiated by huge flares of radiation from its host star. (Courtesy: Mark A Garlick/University of Warwick)

By Tushna Commissariat

In the past decade or two, exoplanetary research has been booming as NASA’s Kepler telescope and its cohorts have found nearly 2000 exoplanets and 5000 promising candidates. Unsurprisingly, we have been searching long and hard for those planets that could be habitable or are as similar in shape, size and proximity to the host star as the Earth is to the Sun. Indeed, in January this year Kepler scientists announced that they had found the most Earth-like planet to date – Kepler-438b – orbiting within the habitable zone of its host star, the red dwarf Kepler-438, which lies about 470 light-years from Earth.

The planet, which is slightly bigger than our own, was found to be rocky, and, thanks to its location, rather temperate, meaning that it could have flowing water on it – two key factors that astronomers look for when accessing a planet’s habitability. Unfortunately, David Armstrong of the University of Warwick in the UK and colleagues have now found that Earth’s twin is regularly bathed in vast quantities of radiation from its star – a real dampener when it comes to the formation of life as we known it.

(more…)

Revealing the hidden connection between pi and Bohr’s hydrogen model

A nearly 400 year-old formula for pi has been spotted in a quantum-mechanics formula for the energy states of the hydrogen atom, according to researchers in the US. Derived by English mathematician John Wallis in 1655, the original formula calculates pi as the product of an infinite series of ratios – it has now emerged from a solution of physicist Niels Bohr’s early 20th-century hydrogen-atom model, which most budding physicists learn.

University of Rochester physicist Carl Hagen was designing homework problems for his graduate quantum-mechanics class when a particular exercise for the hydrogen atom intrigued him. It posed a twist on the Bohr model of hydrogen, which approximates the atom as an electron orbiting a point-like positive nucleus in circles. The Bohr model, while not an accurate description of an atom, is often close enough to the real thing in many situations. It is especially so when teaching physics, because it is one of the few systems that can be solved analytically by Schrödinger’s equation – that is, it can be solved exactly, rather than making approximations or using a computer program.

Varying homework

But instead of solving the Bohr-model problem, Hagen applied the “variational principle” – a technique usually reserved for approximating quantum-mechanical systems that cannot be solved analytically with the Schrödinger equation. The technique involves making an educated guess of the hydrogen’s wavefunction and then optimizing that guess. Hagen found that as the atom’s orbital angular momentum increased, the allowed energies of the predicted atom approached and gradually equalled the analytically found hydrogen energies. Indeed, Hagen noticed that the error of the variational approach was about 15% for the ground state of hydrogen, 10% for the first excited state, and kept decreasing as the excited states grew larger. This was unusual, because the variational approach normally works best for approximations of the lowest energy levels.

Hidden formula

Hagen turned to his colleague, mathematics professor Tamar Friedmann, who found that they could derive Wallis’s infinite product from the ratio of the approximate energies to the exact energies. Friedmann points out how unexpected it is that a centuries-old math formula, derived under completely different motivations, has been lurking in a basic quantum-mechanics problem. Wallis’s original 1655 infinite-series formula, published in his book Arithmetica infinitorum, predates Newton’s invention of calculus, and arose when he was trying to relate the area of a square to the circle inscribed within it.

“Wallis couldn’t have possibly known [the trend] would show up in the hydrogen atom because no-one knew about the hydrogen atom then,” Friedmann says. She adds that, while the formula could have been found ever since Bohr developed his model in 1913, the pair were the first to spot it, probably thanks to their interdisciplinary experience. Their findings suggest that more mathematical formulae could lie in wait in other seemingly well-studied systems.

Universal pi?

“I’m not surprised that pi is in there. Pi is everywhere,” says Drew Milsom, a physicist at the University of Arizona. While the most obvious appearance of pi is the ratio of a circle’s circumference to its diameter, Milsom cites another example in probability studies – known as “Buffon’s needle problem” – that finds that the probability of a falling matchstick landing between two lines is related to pi. What is more surprising, Milsom says, is that Hagen and Friedmann decided to use the variational principle and actually recognized the Wallis formula, which is obscure to most physicists.

It is ultimately unsurprising that the pi formula emerged from the quantum solution because, as Friedmann herself points out, “mathematical formulae come up in physics all the time”. She adds that finding the link “is a manifestation of the ultimate connection between math and physics”, but whether there exists some deeper, fundamental correlation between the two remains unknown.

“Once you see it, it’s clear and beautiful and you can understand it, even if you weren’t able to derive it,” says Friedmann, adding that it could now even be taught to undergraduates. “Physical problems inspire questions in mathematics and vice versa,” Friedmann says. “Mathematics is the language that describes physics. Learning one helps enrich the other.”

The research is described in the Journal of Mathematical Physics.

Is there life on Mars?

In this November episode of the Physics World podcast, astrobiologist Lewis Dartnell addresses these big questions in a conversation with journalist James Dacey. Dartnell’s own research is concerned with examining the micro-organisms that can survive in some of the most extreme conditions here on Earth. By studying the physiology and survival tactics of these so-called extremophiles, astrobiologists hope to gain an understanding of the type of life that could survive in a place like the Martian surface – and where to look for these hardy little creatures on alien worlds.

Dartnell was speaking ahead of a public lecture he gave in London about the possibilities of life beyond the Earth. As well as discussing what we already know about the Martian surface, Dartnell talked about the new possibilities that will come with ExoMars, a mission by the European Space Agency (ESA) set for launch in 2018. Dartnell is working on the design of a Raman-spectroscopy instrument for that mission that will help examine the mineralogy of Mars and identify potential signs of life inside Martian rocks.

The talk was held in an underground tunnel near King’s Cross Station – a venue that resembles the kind of provisional habitat that humans would have to create should we attempt to live on Mars. Watch some highlights from that talk, along with reaction from the audience, in the video above. In addition, the November issue of Physics World is a special issue about extremes in physics, including a feature about how physicists are helping to uncover some of the mysteries of extremophiles on Earth. It includes more about Lewis’ favourite little critter: Deinococcus radiodurrans. Find out how to access that issue here.

Making noise in the quietest room in the Netherlands

Wiggling electrons: an undulator at one of FELIX’s free-electron lasers.

By Tim Wogan in Nijmegen, the Netherlands

Tucked away near the German border is the Dutch city of Nijmegen and Radboud University, which has a treasure trove of fantastical physics facilities. I was in town for a two-day, whistle-stop tour of the university that included the the opening of the FELIX facility. FELIX stands for “free-electron laser for infrared experiments laboratory”. It is a  cavernous chamber housing four free-electron lasers that together can generate high-intensity, tunable radiation with wavelengths anywhere between 3–1500 μm. Something, I was told, that is possible nowhere else in the world.

(more…)

Copyright © 2026 by IOP Publishing Ltd and individual contributors