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How dual-comb spectroscopy works and why it could reshape precision sensing

Spectroscopy has many applications, ranging from fundamental tests of quantum electrodynamics and investigations of molecular structure to environmental sensing, biomedical diagnostics and industrial monitoring. A highly promising spectroscopic instrument that has the potential to transform the field has emerged over the years: the dual-comb spectrometer, which relies on the interference of two mode-locked ultrafast lasers that produce broad frequency combs composed of evenly spaced narrow spectral lines.

A frequency comb is a spectrum of phase-coherent sharp laser lines that are evenly spaced. Such combs based on femtosecond mode-locked lasers, as pioneered at the Max-Planck Institute of Quantum Optics in the 1990s, have revolutionized measurements of frequency and time. In frequency metrology, a laser comb acts as a ruler in frequency space that conveniently links microwave and optical frequencies, and/or measures a large separation between two optical frequencies.

In the past two decades, frequency combs have found new applications. One of them is dual-comb spectroscopy. Dual-comb spectroscopy addresses the challenge of combining wide spectral coverage with high resolution and accuracy by using two optical frequency combs with slightly different repetition frequencies to map optical spectra directly into the radio-frequency domain. The method relies on time-domain interferometry and avoids mechanical scanning, enabling precise, rapid, and broadband measurements. Dual-comb spectroscopy has been implemented across the electromagnetic spectrum, from the terahertz to the visible range, with ongoing efforts towards the ultraviolet range.

Hidden brain circuit could explain how movement errors sharpen new skills

While humans are acquiring new skills that entail performing coordinated movements, such as walking, playing an instrument or skateboarding, their brains are known to continuously detect mistakes and correct movements over time. This gradual acquisition of task-specific movements is known as motor learning.

Past neuroscience studies suggest that a brain region known as the cerebellum plays a central role in motor learning. The cerebellum is a structure at the back of the brain that contributes to coordination, balancing the timing of voluntary actions and the execution of precise movements.

This brain structure hosts a type of nerve cell known as Purkinje cells (PCs), which receive input information via climbing fibers (CFs), nerve fibers that originate from a lower region in the brainstem. Neuroscientists have hypothesized that climbing fibers also carry signals that instruct the brain to adapt to movements based on earlier mistakes.

Mercury’s water ice may have been deposited by a larger, slower impactor than previously thought—in only one day

The source of the significant water ice deposits hidden in Mercury’s polar regions has been a topic of debate among researchers. A new study, published in the Journal of Geophysical Research: Planets, suggests that these deposits were accumulated in only one Mercurian day (176 Earth days) by a large impactor, such as a comet or asteroid. While previous studies have suggested a similar scenario, this is the first study to fully model the impact. Furthermore, these new models suggest that the impactor may have been larger and slower than previously suggested.

Being the closest planet to the sun, Mercury sees daytime temperatures of up to 430°C (806°F). On top of that, Mercury doesn’t have a true atmosphere. Instead, it has an ultra-thin, tenuous layer of gas, called an exosphere, in which gases are constantly blown into space and then replenished by the solar wind. While these aspects of Mercury should make water retention extremely difficult, both Earth-based and orbital observations have found reflective areas that indicate the presence of water ice hidden in permanently shadowed regions (PSRs) near Mercury’s north and south poles.

Scientists have suggested several potential sources of the ice found in PSRs. Some hypotheses include steady delivery by micrometeoroids, solar wind, or a single large, volatile-rich impact. Some studies have found that the ice appears to be relatively pure and “young” (at only a few 100 million years). These findings suggest a rapid, episodic delivery rather than slow accumulation, according to more recent studies.

Low-power, flexible radio-frequency transistors break 100 GHz barrier

Over the past decades, electronics engineers worldwide have been trying to develop devices that could enable even faster communications between devices, all while consuming less energy. To meet the demands of the sixth generation (6G) of wireless communication technology, these devices should operate at frequencies above 100 gigahertz (GHz).

So far, developing flexible electronic components that can operate at these high frequencies while consuming little power has proved challenging. One promising approach for fabricating these devices entails the use of carbon nanotubes (CNTs), extremely thin and cylindrical structures with advantageous electrical and thermal properties.

Researchers at Peking University and Stanford University recently developed new flexible and low-power CNT-based transistors that operate at frequencies above 100 GHz. These transistors, presented in a paper published in Nature Electronics, could potentially help to speed up communications between future smartphones, sensors, wearable devices, and other flexible devices.

Triply-eclipsing triple star system discovered with TESS

Using NASA’s Transiting Exoplanet Survey Satellite (TESS), astronomers have discovered a triply-eclipsing star system. The newfound system, designated TIC 295741342, consists of two sun-like stars in an eclipsing binary and a giant tertiary companion, which orbits the binary. The finding was reported in a paper published May 19 on the arXiv pre-print server.

Astrophysicists strike black gold with treasure trove of gravitational wave detections

Researchers from the University of Glasgow’s Institute for Gravitational Research are celebrating the publication of a vast new treasure trove of gravitational wave detections, hailed as a milestone marking the coming of age of gravitational astronomy.

The Gravitational Wave Transient Catalogue-5.0, or GWTC-5, is released online, with corresponding scientific papers submitted to Astrophysical Journal and Astrophysical Journal Letters.

This latest update details a total of 161 new signals from colliding black holes detected between April 2024 and the end of January 2025 by the gravitational wave detectors LIGO in the United States, Virgo in Italy, and KAGRA in Japan, known as the LVK collaboration. The publication brings the total number of gravitational wave signals detected to date to 390.

Researchers capture inception of hydrogen-uranium reaction for the first time

When hydrogen gas interacts with uranium metal, the combination creates a chemically reactive powder and a runaway reaction that is difficult to stop. The result can impact the safety and lifespan of technology critical for fusion energy, hydrogen storage and nuclear fuels.

In a recent study published in npj Materials Degradation, researchers from Lawrence Livermore National Laboratory (LLNL) observed and characterized the beginning stages of hydrogen-uranium corrosion for the first time. The result will lead to more predictive and physically grounded models for how uranium components degrade.

Imagine the hydrogen-uranium interaction like a geyser. Much like surface water seeping through cracks to make its way underground, hydrogen dissolves and diffuses into the uranium metal. This happens silently and invisibly until it becomes too much hydrogen for the uranium to hold. The two materials combine to form a new compound called uranium hydride, which takes up significantly more volume than the original uranium metal.

Single-step 8-9x expansion reveals nanoscale centrioles without electron microscopy

In a study published in ACS Nano, researchers from National Taiwan University report a new expansion microscopy strategy termed high-fold homogeneous expansion microscopy (hiHomoExM), capable of achieving approximately 8–9× isotropic expansion in a single expansion step while preserving delicate ultrastructural organization.

Expansion microscopy works by embedding biological samples within a swellable polymer hydrogel. Following chemical processing, the hydrogel expands uniformly in water, physically separating biomolecules and effectively increasing the spatial resolution achievable by conventional light microscopes.

“To achieve nanoscale imaging faithfully, both high expansion and homogeneous specimen preservation are essential,” explains the research team. “Nonuniform expansion can distort ultrastructural information and limit biological interpretation.”

Surface design transforms thermal management and enables frictionless systems

A research team led by Professor Steven Wang, Associate Vice President (Resources Planning) and Associate Professor in the Department of Mechanical Engineering and School of Energy and Environment, has designed a revolutionary capillary structure that can trigger the Leidenfrost effect, offering a practical solution for the temperature-regulated Leidenfrost effect without requiring complex surface engineering.

The study, titled “Capillary Leidenfrost Effect”, was recently published in the journal Nature Physics.

The Leidenfrost effect is a physical phenomenon discovered in 1756. It occurs when a liquid droplet touches a surface much hotter than its boiling point, forming a vapor layer that makes it levitate and hover, slowing down evaporation. A simple example is water on a very hot pan: the drops sizzle and disappear quickly, but once it reaches the Leidenfrost point, they bead up, skate and dance around on a steam barrier, and last much longer before evaporating. This effect is ubiquitous in a wide range of laboratory and industrial applications.

Imaginary-time technique speeds X-ray scattering simulations by 50-fold for extreme matter

Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) have developed a new procedure, enabling them to speed up elaborate computer simulations that analyze matter under extreme conditions. In particular, this work improves the evaluation of experiments at large-scale research facilities like the European XFEL—and should facilitate substantial progress, among others, in fusion research and laboratory astrophysics.

The team presented the results in the journal npj Computational Materials.

Sometimes, matter is present in extreme states—such as in stars or in the interior of gas giants where enormous pressures and temperatures prevail. Such conditions can also be produced in the lab, in laser fusion experiments, for instance. In order to understand precisely what happens, researchers use X-ray scattering—as at the European XFEL near Hamburg.

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