An adapted optical technique reveals the temporal structure of ultrafast x-ray pulses by eliminating background light.
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Brighter red micro-LEDs could help solve full-color display stability challenge
Researchers at The University of Osaka, in collaboration with Ritsumeikan University, have demonstrated that growing europium-doped gallium nitride (Eu-doped GaN) on a semipolar crystal plane dramatically improves red light emission. The team found that this approach selectively promotes the formation of highly efficient Eu luminescent centers, resulting in red emission intensity more than 3.6 times higher than that of conventionally grown polar-plane material.
The study is published in the journal Applied Physics Letters.
Red emitters based on Eu-doped GaN are attracting attention as promising light sources for next-generation micro-LED displays because they can provide narrow-linewidth, wavelength-stable red emission based on intra-4f-shell transitions of Eu ions. This is particularly important for full-color monolithic integration with blue and green InGaN LEDs, where wavelength stability under device operation is essential.
Gravitational waves from colliding black holes may allow detection of dark matter
Dark matter is thought to make up most of the matter in the universe, but the only way it interacts with its surroundings is through gravity. If two colliding black holes spiral through a dense region of dark matter and merge, gravitational waves rippling across space and time could carry an imprint of that dark matter.
Now, physicists may be able to spot such imprints of dark matter in gravitational waves that are detected on Earth.
Researchers at MIT and in Europe have developed a method that makes predictions for what a gravitational wave should look like if it were produced by black holes that moved through dark matter, rather than empty space. They applied the technique to publicly available gravitational-wave data previously recorded by LIGO-Virgo-KAGRA (LVK), the global network of observatories that detect gravitational waves from black hole mergers and other far-off astrophysical sources.
Gravitational wave detectors can now ‘autotune’ signals to harmonize the heavens
Gravitational wave researchers working on the world’s most sensitive scientific instruments have found a way to tune their detectors using a process akin to the pitch-correction used in music production.
Scientists at the international LIGO, Virgo and KAGRA (LVK) gravitational wave observatory collaboration have employed the technique, which they call astrophysical calibration, to use gravitational-wave signals to measure the response of their incredibly sensitive instruments.
It enables them to ensure that they can clearly “hear” the sounds of colossal cosmic events like the collision of black holes, even when one gravitational wave detector is slightly out of tune. This is crucial to accurately interpret the signals and find their source location.
80 years after the Trinity nuclear test, scientists identify new molecule-trapping crystal formed in the blast
Matter behaves strangely under extreme conditions, and often, remnants of these behaviors are left behind even when conditions return to normal. The Trinity nuclear test in 1945 left behind such remnants, and now, 80 years after the explosion, researchers have identified another unique example of what happens when various materials are heated to temperatures exceeding 1,500 °C (2,730 °F) and put under pressures tens of thousands of times atmospheric pressure.
The team describes a clathrate compound never before found among nuclear-explosion products in their new study, published in the Proceedings of the National Academy of Sciences.
AI surrogate accelerates nonlinear optics simulations by orders of magnitude
Simulating the nonlinear optical physics that underlies ultrafast laser systems is computationally demanding—a practical bottleneck in settings that require rapid feedback. A study by researchers at Stanford University, University of California, Los Angeles (UCLA), and SLAC National Accelerator Laboratory introduces a deep learning surrogate that delivers orders-of-magnitude acceleration over conventional simulation methods, while maintaining high fidelity across a challenging range of pulse shapes.
The work centers on second-order nonlinear optics (χ² processes), in which light waves exchange energy inside specially engineered crystals to generate new frequencies and tailored pulse shapes. In particle accelerator facilities, these processes play a key role. At SLAC’s upgraded Linac Coherent Light Source (LCLS-II), infrared laser pulses are first to green light and then to ultraviolet (UV). The UV pulse strikes a cathode to liberate an electron bunch that is subsequently accelerated and modulated to produce intense X-ray pulses. The temporal shape of the UV pulse directly influences the properties of that electron bunch—and ultimately the quality of the X-rays available for science.
A surrogate model for the nonlinear χ² frequency conversion step at the heart of this process is reported in Advanced Photonics.
How Qing featherwork got its colors: New scans reveal multiple birds and hidden pigment layers
The kingfisher’s brilliant blue feathers were once used like paint to create works of art. The technique, known as tian-tsui, was popular during China’s Qing Dynasty. And because tian-tsui uses delicate feathers, previous scientists struggled to study them using traditional analytical techniques. So, researchers reporting in ACS Omega developed new methods of investigating these featherworks without harming them. The team found that multiple bird species and layered pigments provided a one-of-a-kind palette.
The shades of blue in kingfisher feathers are the result of a phenomenon called structural color. Rather than being created by pigment molecules, structural color is created by tiny, ordered structures in the feathers that interact with light to create the observed coloring—in this case, blue or purple. To gain insights into several featherwork pieces and the feathers that went into making them, Madeline Meier and colleagues combined different imaging and spectroscopy techniques that rely on the ways the feathers reflect and scatter light.
The team analyzed a decorative tian-tsui screen estimated to date from the late 18th to the early 19th century that features intricate scenes in a variety of colors. In one panel, analysis revealed that the blue feathers belonged to the common kingfisher, and the purple came from the black-capped kingfisher. The green feathers had different nanostructures than the blue feathers, leading the researchers to conclude that the green ones belonged to another bird entirely: the mallard duck.
Largest-ever survey of physicists puts Standard Model of cosmology under scrutiny
The largest-ever survey of physicists from around the world—released today—shows a distinct lack of consensus across many of physics’s most important questions, from the nature of black holes and dark matter, to the still-incomplete unification of Einstein’s theory of gravity with quantum mechanics.
Even the best theory of the universe’s expansion, known as the standard model of cosmology or ΛCDM (Lambda Cold Dark Matter), did not attain majority support. This surprising outcome is perhaps due to results from the Dark Energy Spectroscopic Instrument (DESI) last year, which hinted that dark energy may change over time, in opposition to the standard model’s conviction that dark energy remains constant.
But that wasn’t the only surprising outcome. The survey doesn’t seem to find much agreement anywhere.
Atoms vibrate on circular paths—with an unexpected twist
An international team of researchers, including scientists from HZDR and Fritz Haber Institute of the Max Planck Society, for the first time directly observed how angular momentum is transferred and conserved within a crystal lattice. Using intense terahertz laser pulses, the researchers were able to selectively control these processes, which unveiled a surprising effect: During the angular momentum transfer, the direction of rotation reverses—caused by the rotational symmetry of the material.
The results, published in Nature Physics, provide new insights into the foundation of magnetism and open up possibilities for tailored control of quantum materials.
Conserved quantities such as energy, momentum, and angular momentum determine the fundamental laws of nature. In a closed system, these quantities are always conserved: they cannot be created or destroyed, only transformed or transferred. While angular momentum is familiar in everyday life through rotating carousels or riding a bicycle, it plays a central role at the quantum level—for example, as the fundamental origin of magnetism.