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Light pollution from satellite mega-constellations threaten space-based observations

Almost every image that will be taken by future space observatories in low-Earth orbit could be tainted due to light contamination from satellites. That is according to a new analysis from researchers at NASA, which stresses that light pollution from satellites orbiting Earth must be reduced to guarantee astronomical research is not affected.

The number of satellites orbiting Earth has increased from about 2000 in 2019 to 15 000 today. Many of these are part of so-called mega-constellations that provide services such as Internet coverage around the world, including in areas that were previously unable to access it. Examples of such constellations include SpaceX’s Starlink as well as Amazon’s Kuiper and Eutelsat’s OneWeb.

Many of these mega-constellations share the same space as space-based observatories such as NASA’s Hubble Space Telescope. This means that the telescopes can capture streaks of reflected light from the satellites that render the images or data completely unusable for research purposes. That is despite anti-reflective coating that is applied to some newer satellites in SpaceX’s Starlink constellation, for example.

Previous work has explored the impact of such satellites constellations on ground-based astronomy, both optical and radioastronomy. Yet their impact on telescopes in space has been overlooked.

To find out more, Alejandro Borlaff from NASA’s Ames Research Center, and colleagues simulated the view of four space-based telescopes: Hubble and the near-infrared observatory SPHEREx, which launched in 2025, as well at the European Space Agency’s proposed near-infrared ARRAKIHS mission and China’s planned Xuntian telescopes.

These observatories are, or will be placed, between 400 and 800 km from the Earth’s surface.

The authors found that if the population of mega-constellation satellites grows to the 56 000 that is projected by the end of the decade, it would contaminate about 39.6% of Hubble’s images and 96% of images from the other three telescopes.

Borlaff and colleagues predict that the average number of satellites observed per exposure would be 2.14 for Hubble, 5.64 for SPHEREx, 69 for ARRAKIHS, and 92 for Xuntian.

The authors note that one solution could be to deploy satellites at lower orbits than the telescopes operate, which would make them about four magnitudes dimmer. The downside is that emissions from these lower satellites could have implications for Earth’s ozone layer.

An ‘urgent need for dialogue’

Katherine Courtney, chair of the steering board for the Global Network on Sustainability in Space, says that without astronomy, the modern space economy “simply wouldn’t exist”.

“The space industry owes its understanding of orbital mechanics, and much of the technology development that has unlocked commercial opportunities for satellite operators, to astronomy,” she says. “The burgeoning growth of the satellite population brings many benefits to life on Earth, but the consequences for the future of astronomy must be taken into consideration.”

Courtney adds that there is now “an urgent need for greater dialogue and collaboration between astronomers and satellite operators to mitigate those impacts and find innovative ways for commercial and scientific operations to co-exist in space.”

  • Katherine Courtney, chairs the Global Network on Sustainability in Space, and Alice Gorman from Flinders University in Adelaide, Australia, appeared on a Physics World Live panel discussion about the impact of space debris that was held on 10 November. A recording of the event is available here.

Physicists use a radioactive molecule’s own electrons to probe its internal structure

Physicists have obtained the first detailed picture of the internal structure of radium monofluoride (RaF) thanks to the molecule’s own electrons, which penetrated the nucleus of the molecule and interacted with its protons and neutrons. This behaviour is known as the Bohr-Weisskopf effect, and study co-leader Shane Wilkins says that this marks the first time it has been observed in a molecule. The measurements themselves, he adds, are an important step towards testing for nuclear symmetry violation, which might explain why our universe contains much more matter than antimatter.

RaF contains the radioactive isotope 225Ra, which is not easy to make, let alone measure. Producing it requires a large accelerator facility at high temperature and high velocity, and it is only available in tiny quantities (less than a nanogram in total) for short periods (it has a nuclear half-life of around 15 days).

“This imposes significant challenges compared to the study of stable molecules, as we need extremely selective and sensitive techniques in order to elucidate the structure of molecules containing 225Ra,” says Wilkins, who performed the measurements as a member of Ronald Fernando Garcia Ruiz’s research group at the Massachusetts Institute of Technology (MIT), US.

The team chose RaF despite these difficulties because theory predicts that it is particularly sensitive to small nuclear effects that break the symmetries of nature. “This is because, unlike most atomic nuclei, the radium atom’s nucleus is octupole deformed, which basically means it has a pear shape,” explains the study’s other co-leader, Silviu-Marian Udrescu.

Electrons inside the nucleus

In their study, which is detailed in Science, the MIT team and colleagues at CERN, the University of Manchester, UK and KU Leuven in the Netherlands focused on RaF’s hyperfine structure. This structure arises from interactions between nuclear and electron spins, and studying it can reveal valuable clues about the nucleus. For example, the nuclear magnetic dipole moment can provide information on how protons and neutrons are distributed inside the nucleus.

In most experiments, physicists treat electron-nucleus interactions as taking place at (relatively) long ranges. With RaF, that’s not the case. Udrescu describes the radium atom’s electrons as being “squeezed” within the molecule, which increases the probability that they will interact with, and penetrate, the radium nucleus. This behaviour manifests itself as a slight shift in the energy levels of the radium atom’s electrons, and the team’s precision measurements – combined with state-of-the-art molecular structure calculations – confirm that this is indeed what happens.

“We see a clear breakdown of this [long-range interactions] picture because the electrons spend a significant amount of time within the nucleus itself due to the special properties of this radium molecule,” Wilkins explains. “The electrons thus act as highly sensitive probes to study phenomena inside the nucleus.”

Searching for violations of fundamental symmetries

According to Udrescu, the team’s work “lays the foundations for future experiments that use this molecule to investigate nuclear symmetry violation and test the validity of theories that go beyond the Standard Model of particle physics.” In this model, each of the matter particles we see around us – from baryons like protons to leptons such as electrons – should have a corresponding antiparticle that is identical in every way apart from its charge and magnetic properties (which are reversed).

The problem is that the Standard Model predicts that the Big Bang that formed our universe nearly 14 billion years ago should have generated equal amounts of antimatter and matter – yet measurements and observations made today reveal an almost entirely matter-based universe. Subtler differences between matter particles and their antimatter counterparts might explain why the former prevailed, so by searching for these differences, physicists hope to explain antimatter-matter asymmetry.

Wilkins says the team’s work will be important for future such searches in species like RaF. Indeed, Wilkins, who is now at Michigan State University’s Facility for Rare Isotope Beams (FRIB), is building a new setup to cool and slow beams of radioactive molecules to enable higher-precision spectroscopy of species relevant to nuclear structure, fundamental symmetries and astrophysics. His long-term goal, together with other members of the RaX collaboration (which includes FRIB and the MIT team as well as researchers at Harvard University and the California Institute of Technology), is to implement advanced laser-based techniques using radium-containing molecules.

Quantum-scale thermodynamics offers a tighter definition of entropy

A new, microscopic formulation of the second law of thermodynamics for coherently driven quantum systems has been proposed by researchers in Switzerland and Germany. The researchers applied their formulation to several canonical quantum systems, such as a three-level maser. They believe the result provides a tighter definition of entropy in such systems, and could form a basis for further exploration.

In any physical process, the first law of thermodynamics says that the total energy must always be conserved, with some converted to useful work and the remainder dissipated as heat. The second law of thermodynamics says that, in any allowed process, the total amount of heat (the entropy) must always increase.

“I like to think of work being mediated by degrees of freedom that we control and heat being mediated by degrees of freedom that we cannot control,” explains theoretical physicist Patrick Potts of the University of Basel in Switzerland. “In the macroscopic scenario, for example, work would be performed by some piston – we can move it.” The heat, meanwhile, goes into modes such as phonons generated by friction.

Murky at small scales

This distinction, however, becomes murky at small scales: “Once you go microscopic everything’s microscopic, so it becomes much more difficult to say ‘what is it that that you control – where is the work mediated – and what is it that you cannot control?’,” says Potts.

Potts and colleagues in Basel and at RWTH Aachen University in Germany examined the case of optical cavities driven by laser light, systems that can do work: “If you think of a laser as being able to promote a system from a ground state to an excited state, that’s very important to what’s being done in quantum computers, for example,” says Potts. “If you rotate a qubit, you’re doing exactly that.”

The light interacts with the cavity and makes an arbitrary number of bounces before leaking out. This emergent light is traditionally treated as heat in quantum simulations. However, it can still be partially coherent – if the cavity is empty, it can be just as coherent as the incoming light and can do just as much work.

In 2020, quantum optician Alexia Auffèves of Université Grenoble Alpes in France and colleagues noted that the coherent component of the light exiting a cavity could potentially do work. In the new study, the researchers embedded this in a consistent thermodynamic framework. They studied several examples and formulated physically consistent laws of thermodynamics.

In particular, they looked at the three-level maser, which is a canonical example of a quantum heat engine. However, it has generally been modelled semi-classically by assuming that the cavity contains a macroscopic electromagnetic field.

Work vanishes

“The old description will tell you that you put energy into this macroscopic field and that is work,” says Potts, “But once you describe the cavity quantum mechanically using the old framework then – poof! – the work is gone…Putting energy into the light field is no longer considered work, and whatever leaves the cavity is considered heat.”

The researchers new thermodynamic treatment allows them to treat the cavity quantum mechanically and to parametrize the minimum degree of entropy in the radiation that emerges – how much radiation must be converted to uncontrolled degrees of freedom that can do no useful work and how much can remain coherent.

The researchers are now applying their formalism to study thermodynamic uncertainty relations as an extension of the traditional second law of thermodynamics. “It’s actually a trade-off between three things – not just efficiency and power, but fluctuations also play a role,” says Potts. “So the more fluctuations you allow for, the higher you can get the efficiency and the power at the same time. These three things are very interesting to look at with this new formalism because these thermodynamic uncertainty relations hold for classical systems, but not for quantum systems.”

“This [work] fits very well into a question that has been heavily discussed for a long time in the quantum thermodynamics community, which is how to properly define work and how to  properly define useful resources,” says quantum theorist Federico Cerisola of the UK’s University of Exeter. “In particular, they very convincingly argue that, in the particular family of experiments they’re describing, there are resources that have been ignored in the past when using more standard approaches that can still be used for something useful.”

Cerisola says that, in his view, the logical next step is to propose a system – ideally one that can be implemented experimentally – in which radiation that would traditionally have been considered waste actually does useful work.

The research is described in Physical Review Letters.  

Bring gravity back down to Earth: from giraffes and tree snakes to ‘squishy’ space–time

When I was five years old, my family moved into a 1930s semi-detached house with a long strip of garden. At the end of the garden was a miniature orchard of eight apple trees the previous owners had planted – and it was there that I, much like another significantly more famous physicist, learned an important lesson about gravity.

As I read in the shade of the trees, an apple would sometimes fall with a satisfying thunk into the soft grass beside me. Less satisfyingly, they sometimes landed on my legs, or even my head – and the big cooking apples really hurt. I soon took to sitting on old wooden pallets crudely wedged among the higher branches. It was not comfortable, but at least I could return indoors without bruises.

The effects of gravity become common sense so early in life that we rarely stop to think about them past childhood. In his new book Crush: Close Encounters with Gravity, James Riordon has decided to take us back to the basics of this most fundamental of forces. Indeed, he explores an impressively wide range of topics – from why we dream of falling and why giraffes should not exist (but do), to how black holes form and the existence of “Planet 9”.

Riordon, a physicist turned science writer, makes for a deeply engaging author. He is not afraid to put himself into the story, introducing difficult concepts through personal experience and explaining them with the help of everything including the kitchen sink, which in his hands becomes an analogue for a black hole.

Gravity as a subject can easily be both too familiar and too challenging. In Riordon’s words, “Things with mass attract each other. That’s really all there is to Newtonian gravity.” While Albert Einstein’s theory of general relativity, by contrast, is so intricate that it takes years of university-level study to truly master. Riordon avoids both pitfalls: he manages to make the simple fascinating again, and the complex understandable.

He provides captivating insights into how gravity has shaped the animal kingdom, a perspective I had never much considered. Did you know that tree snakes have their hearts positioned closer to their heads than their land-based cousins? I certainly didn’t. The higher placement ensures a steady blood flow to the brain, even when the snake is climbing vertically. It is one of many examples that make you look again at the natural world with fresh eyes.

Riordon’s treatment of gravity in Einstein’s abstract space–time is equally impressive, perhaps unsurprisingly, as his previous books include Very Easy Relativity and Relatively Easy Relativity. Riordon takes a careful, patient approach – though I have never before heard general relativity reduced to “space–time is squishy”. But why not? The phrase sticks and gives us a handhold as we scale the complications of the theory. For those who want to extend the challenge, a mathematical background to the theory is provided in an appendix, and every chapter is well referenced and accompanied with suggestions for further reading.

If anything, I found myself wanting more examples of gravity as experienced by humans and animals on Earth, as opposed to in the context of the astronomical realm. I found these down-to-earth chapters the most fascinating: they formed a bridge between the vast and the local, reminding us that the same force that governs the orbits of galaxies also brings an apple to the ground. This may be a reaction only felt by astronomers like me, who already spend their days looking upward. I can easily see how the balance Riordon chose is necessary for someone without that background, and Einstein’s gravity does require galactic scales to appreciate, after all.

Crush is a generally uncomplicated and pleasurable read. The anecdotes can sometimes be a little long-winded and there are parts of the book that are not without challenge. But it is pitched perfectly for the curious general reader and even for those dipping their toes into popular science for the first time. I can imagine an enthusiastic A-level student devouring it; it is exactly the kind of book I would have loved at that age. Even if some of it would have gone over my head, Riordon’s enthusiasm and gift for storytelling would have kept me more than interested, as I sat up on that pallet in my favourite apple tree.

I left that house, and that tree, a long time ago, but just a few miles down the road from where I live now stands another, far more famous apple tree. In the garden of Woolsthorpe Manor near Grantham, Newton is said to have watched an apple fall. From that small event, he began to ask the questions that reshaped his and our understanding of the universe. Whether or not the story is true hardly matters – Newton was constantly inspired by the natural world, so it isn’t improbable, and that apple tree remains a potent symbol of curiosity and insight.

“[Newton] could tell us that an apple falls, and how quickly it will do it. As for the question of why it falls, that took Einstein to answer,” writes Riordon. Crush is a crisp and fresh tour through a continuum from orchards to observatories, showing that every planetary orbit, pulse of starlight and even every apple fall is part of the same wondrous story.

  • 2025 MIT Press 288pp £27hb

Ice XXI appears in a diamond anvil cell

A new phase of water ice, dubbed ice XXI, has been discovered by researchers working at the European XFEL and PETRA III facilities. The ice, which exists at room temperature and is structurally distinct from all previously observed phases of ice, was produced by rapidly compressing water to high pressures of 2 GPa. The finding could shed light on how different ice phases form at high pressures, including on icy moons and planets.

On Earth, ice can take many forms, and its properties depend strongly on its structure. The main type of naturally-occurring ice is hexagonal ice (Ih), so-called because the water molecules arrange themselves in a hexagonal lattice (this is the reason why snowflakes have six-fold symmetry). However, under certain conditions – usually involving very high pressures and low temperatures – ice can take on other structures. Indeed, 20 different forms of ice have been identified so far, denoted by roman numerals (ice I, II, III and so on up to ice XX).

Pressures of up to 2 GPa allow ice to form even at room temperature

Researchers from the Korea Research Institute of Standards and Science (KRISS) have now produced a 21st form of ice by applying pressures of up to two gigapascals. Such high pressures are roughly 20 000 times higher than normal air pressure at sea level, and they allow ice to form even at room temperature – albeit only within a device known as a dynamic diamond anvil cell (dDAC) that is capable of producing such extremely high pressures.

“In this special pressure cell, samples are squeezed between the tips of two opposing diamond anvils and can be compressed along a predefined pressure pathway,” explains Cornelius Strohm, a member of the DESY HIBEF team that set up the experiment using the High Energy Density (HED) instrument at the European XFEL.

Much more tightly packed molecules

The structure of ice XXI is different from all previously observed phases of ice because its molecules are much more tightly packed. This gives it the largest unit cell volume of all currently known types of ice, says KRISS scientist Geun Woo Lee. It is also metastable, meaning that it can exist even though another form of ice (in this case ice VI) would be more stable under the conditions in the experiment.

“This rapid compression of water allows it to remain liquid up to higher pressures, where it should have already crystallized to ice VI,” explains Lee. “Ice VI is an especially intriguing phase, thought to be present in the interior of icy moons such as Titan and Ganymede. Its highly distorted structure may allow complex transition pathways that lead to metastable ice phases.”

Ice XXI has a body-centred tetragonal crystal structure

To study how the new ice sample formed, the researchers rapidly compressed and decompressed it over 1000 times in the diamond anvil cell while imaging it every microsecond using the European XFEL, which produces megahertz frequency X-ray pulses at extremely high rates. They found that the liquid water crystallizes into different structures depending on how supercompressed it is.

The KRISS team then used the P02.2 beamline at PETRA III to determine that the ice XXI has a body-centred tetragonal crystal structure with a large unit cell (a = b = 20.197 Å and c = 7.891 Å) at approximately 1.6 GPa. This unit cell contains 152 water molecules, resulting in a density of 1.413 g cm−3.

The experiments were far from easy, recalls Lee. Upon crystallization, Ice XXI grows upwards (that is, in the vertical direction), which makes it difficult to precisely analyse its crystal structure. “The difficulty for us is to keep it stable for a long enough period to make precise structural measurements in single crystal diffraction study,” he says.

The multiple pathways of ice crystallization unearthed in this work, which is detailed in Nature Materials, imply that many more ice phases may exist. Lee says it is therefore important to analyse the mechanism behind the formation of these phases. “This could, for example, help us better understand the formation and evolution of these phases on icy moons or planets,” he tells Physics World.

Studying the role of the quantum environment in attosecond science

Attosecond science is undoubtedly one of the fastest growing branches of physics today.

Its popularity was demonstrated by the award of the 2023 Nobel Prize in Physics to Anne L’Huillier, Paul Corkum and Ferenc Krausz for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter.

One of the most important processes in this field is dephasing. This happens when an electron loses its phase coherence because of interactions with its surroundings.

This loss of coherence can obscure the fine details of electron dynamics, making it harder to capture precise snapshots of these rapid processes.

The most common way to model this process in light-matter interactions is by using the relaxation time approximation. This approach greatly simplifies the picture as it avoids the need to model every single particle in the system.

Its use is fine for dilute gases, but it doesn’t work as well with intense lasers and denser materials, such as solids, because it greatly overestimates ionisation.

This is a significant problem as ionisation is the first step in many processes such as electron acceleration and high-harmonic generation.

To address this problem, a team led by researchers from the University of Ottawa have developed a new method to correct for this problem.

By introducing a heat bath into the model they were able to represent the many-body environment that interacts with electrons, without significantly increasing the complexity.

This new approach should enable the identification of new effects in attosecond science or wherever strong electromagnetic fields interact with matter.

Read the full article

Strong field physics in open quantum systems – IOPscience

N. Boroumand et al, 2025 Rep. Prog. Phys. 88 070501

 

Characterising quantum many-body states

Describing the non-classical properties of a complex many-body system (such as entanglement or coherence) is an important part of quantum technologies.

An ideal tool for this task would work well with large systems, be easily computable and easily measurable. Unfortunately, such a tool for every situation does not yet exist.

With this goal in mind a team of researchers – Marcin Płodzień and Maciej Lewenstein (ICFO, Barcelona, Spain) and Jan Chwedeńczuk (University of Warsaw, Poland) – began work on a special type of quantum state used in quantum computing – graph states.

These states can be visualised as graphs or networks where each vertex represents a qubit, and each edge represents an interaction between pairs of qubits.

The team studied four different shapes of graph states using new mathematical tools they developed. They found that one of these in particular, the Turán graph, could be very useful in quantum metrology.

Their method is (relatively) straightforward and does not require many assumptions. This means that it could be applied to any shape of graph beyond the four studied here.

The results will be useful in various quantum technologies wherever precise knowledge of many-body quantum correlations is necessary.

Read the full article

Many-body quantum resources of graph states – IOPscience

M. Płodzień et al, 2025 Rep. Prog. Phys. 88 077601

 

Extra carbon in the atmosphere may disrupt radio communications

Higher levels of carbon dioxide (CO2) in the Earth’s atmosphere could harm radio communications by enhancing a disruptive effect in the ionosphere. According to researchers at Kyushu University, Japan, who modelled the effect numerically for the first time, this little-known consequence of climate change could have significant impacts on shortwave radio systems such as those employed in broadcasting, air traffic control and navigation.

“While increasing CO2 levels in the atmosphere warm the Earth’s surface, they actually cool the ionosphere,” explains study leader Huixin Liu of Kyushu’s Faculty of Science. “This cooling doesn’t mean it is all good: it decreases the air density in the ionosphere and accelerates wind circulation. These changes affect the orbits and lifespan of satellites and space debris and also disrupt radio communications through localized small-scale plasma irregularities.”

The sporadic E-layer

One such irregularity is a dense but transient layer of metal ions that forms between 90‒120 km above the Earth’s surface. This sporadic E-layer (Es), as it is known, is roughly 1‒5 km thick and can stretch from tens to hundreds of kilometres in the horizontal direction. Its density is highest during the day, and it peaks around the time of the summer solstice.

The formation of the Es is hard to predict, and the mechanisms behind it are not fully understood. However, the prevailing “wind shear” theory suggests that vertical shears in horizontal winds, combined with the Earth’s magnetic field, cause metallic ions such as Fe+, Na+ and Ca+ to converge in the ionospheric dynamo region and form thin layers of enhanced ionization. The ions themselves largely come from metals in meteoroids that enter the Earth’s atmosphere and disintegrate at altitudes of around 80‒100 km.

Effects of increasing CO2 concentrations

While previous research has shown that increases in CO2 trigger atmospheric changes on a global scale, relatively little is known about how these increases affect smaller-scale ionospheric phenomena like the Es. In the new work, which is published in Geophysical Research Letters, Liu and colleagues used a whole-atmosphere model to simulate the upper atmosphere at two different CO2 concentrations: 315 ppm and 667 ppm.

“The 315 ppm represents the CO2 concentration in 1958, the year in which recordings started at the Mauna Loa observatory, Hawaii,” Liu explains. “The 667 ppm represents the projected CO2 concentration for the year 2100, based on a conservative assumption that the increase in CO2 is constant at a rate of around 2.5 ppm/year since 1958.”

The researchers then evaluated how these different CO2 levels influence a phenomenon known as vertical ion convergence (VIC) which, according to the wind shear theory, drives the Es. The simulations revealed that the higher the atmospheric CO2 levels, the greater the VIC at altitudes of 100–120 km. “What is more, this increase is accompanied by the VIC hotspots shifting downwards by approximately 5 km,” says Liu. “The VIC patterns also change dramatically during the day and these diurnal variability patterns continue into the night.”

According to the researchers, the physical mechanism underlying these changes depends on two factors. The first is reduced collisions between metallic ions and the neutral atmosphere as a direct result of cooling in the ionosphere. The second is changes in the zonal wind shear, which are likely caused by long-term trends in atmosphere tides.

“These results are exciting because they show that the impacts of CO2 increase can extend all the way from Earth’s surface to altitudes at which HF and VHF radio waves propagate and communications satellites orbit,” Liu tells Physics World. “This may be good news for ham radio amateurs, as you will likely receive more signals from faraway countries more often. For radio communications, however, especially at HF and VHF frequencies employed for aviation, ships and rescue operations, it means more noise and frequent disruption in communication and hence safety. The telecommunications industry might therefore need to adjust their frequencies or facility design in the future.”

Phase-changing material generates vivid tunable colours

A toy gecko featuring a flexible layer of the thermally tunable colour coating
Switchable camouflage A toy gecko featuring a flexible layer of the thermally tunable colour coating appears greenish blue at room temperature (left); upon heating (right), its body changes to a dark magenta colour. (Courtesy: Aritra Biswa)

Structural colours – created using nanostructures that scatter and reflect specific wavelengths of light – offer a non-toxic, fade-resistant and environmentally friendly alternative to chemical dyes. Large-scale production of structural colour-based materials, however, has been hindered by fabrication challenges and a lack of effective tuning mechanisms.

In a step towards commercial viability, a team at the University of Central Florida has used vanadium dioxide (VO2) – a material with temperature-sensitive optical and structural properties – to generate tunable structural colour on both rigid and flexible surfaces, without requiring complex nanofabrication.

Senior author Debashis Chanda and colleagues created their structural colour platform by stacking a thin layer of VO2 on top of a thick, reflective layer of aluminium to form a tunable thin-film cavity. At specific combinations of VO2 grain size and layer thickness this structure strongly absorbs certain frequency bands of visible light, producing the appearance of vivid colours.

The key enabler of this approach is the fact that at a critical transition temperature, VO2 reversibly switches from insulator to metal, accompanied by a change in its crystalline structure. This phase change alters the interference conditions in the thin-film cavity, varying the reflectance spectra and changing the perceived colour. Controlling the thickness of the VO2 layer enables the generation of a wide range of structural colours.

The bilayer structures are grown via a combination of magnetron sputtering and electron-beam deposition, techniques compatible with large-scale production. By adjusting the growth parameters during fabrication, the researchers could broaden the colour palette and control the temperature at which the phase transition occurs. To expand the available colour range further, they added a third ultrathin layer of high-refractive index titanium dioxide on top of the bilayer.

The researchers describe a range of applications for their flexible coloration platform, including a colour-tunable maple leaf pattern, a thermal sensing label on a coffee cup and tunable structural coloration on flexible fabrics. They also demonstrated its use on complex shapes, such as a toy gecko with a flexible tunable colour coating and an embedded heater.

“These preliminary demonstrations validate the feasibility of developing thermally responsive sensors, reconfigurable displays and dynamic colouration devices, paving the way for innovative solutions across fields such as wearable electronic, cosmetics, smart textiles and defence technologies,” the team concludes.

The research is described in Proceedings of the National Academy of Sciences.

Semiconductor laser pioneer Susumu Noda wins 2026 Rank Prize for Optoelectronics

Susumu Noda of Kyoto University has won the 2026 Rank Prize for Optoelectronics for the development of the Photonic Crystal Surface Emitting Laser (PCSEL). For more than 25 years, Noda developed this new form of laser, which has potential applications in high-precision manufacturing as well as in LIDAR technologies.

Following the development of the laser in 1960, in more recent decades optical fibre lasers and semiconductor lasers have become competing technologies.

A semiconductor laser works by pumping an electrical current into a region where an n-doped (excess of electrons) and a p-doped (excess of “holes”) semiconductor material meet, causing electrons and holes to combine and release photons.

Semiconductors have several advantages in terms of their compactness, high “wallplug” efficiency, and ruggedness, but lack in other areas such as having a low brightness and functionality.

This means that conventional semiconductor lasers required external optical and mechanical elements to improve their performance, which results in large and impractical systems.

‘A great honour’

In the late 1990s, Noda began working on a new type of semiconductor laser that could challenge the performance of optical fibre lasers. These so-called PCSELs employ a photonic crystal layer  in between the semiconductor layers. Photonic crystals are nanostructured materials in which a periodic variation of the dielectric constant — formed, for example, by a lattice of holes — creates a photonic band-gap.

Noda and his research made a series of breakthrough in the technology such as demonstrating control of polarization and beam shape by tailoring the phonic crystal structure and expansion into blue–violet wavelengths.

The resulting PCSELs emit a high-quality, symmetric beam with narrow divergence and boast high brightness and high functionality while maintaining the benefits of conventional semiconductor lasers. In 2013, 0.2 W PCSELs became available and a few years later Watt-class PCSEL lasers became operational.

Noda says that it is “a great honour and a surprise” to receive the prize. “I am extremely happy to know that more than 25 years of research on photonic-crystal surface-emitting lasers has been recognized in this way,” he adds. “I do hope to continue to further develop the research and its social implementation.”

Susumu Noda received his BSc and then PhD in electronics from Kyoto University in 1982 and 1991, respectively. From 1984 he also worked at Mitsubishi Electric Corporation, before joining Kyoto University in 1988 where he is currently based.

Founded in 1972 by the British industrialist and philanthropist Lord J Arthur Rank, the Rank Prize is awarded biennially in nutrition and optoelectronics. The 2026 Rank Prize for Optoelectronics, which has a cash award of £100 000, will be awarded formally at an event held in June.

Copyright © 2026 by IOP Publishing Ltd and individual contributors