September 29, 2026 by University of Glasgow edited by Gaby Clark, reviewed by Robert Egan Scientific Editor Senior Editor This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: fact-checked peer-reviewed publication trusted source proofread An international team of physicists has developed a new method for determining the precise color of laser light using an image that rotates as the laser's frequency shifts. The finding could offer a new way to ensure that lasers are 'locked' to the frequencies needed by technologies that rely on them, from GPS positioning to quantum sensors. It could also spur developments in spectroscopy, magnetometry and quantum communications. In a new paper published in the journal Optica, the University of Glasgow-led team describes how it devised a way to determine the frequency of a laser beam in a single snapshot. The team's method starts by passing two differently configured beams of laser light through a gas of rubidium atoms held in a glass cell. One beam comes from a traditional laser with a single polarization: Its electric field oscillates in a uniform direction. The other uses structured light known as a vector beam, with a ring-shaped intensity profile. Its polarization changes at each point around the ring. As the first beam travels through the rubidium atoms, its electric field aligns them, shepherding around 90% into a single quantum state. This alignment affects how the atoms respond to the polarization of the structured light from the second beam as it travels through the gas from the opposite direction. The interaction between the light and the rubidium atoms becomes stronger or weaker as the laser's frequency shifts closer to or further from the atoms' natural resonance, changing the light's polarization structure. The team visualizes this effect by separating the emerging light into different polarization components and capturing the resulting images with a digital camera. The telltale signs of how the atoms have affected the structured laser beam appear in the image as a pattern of bright 'lobes' of light around the laser's ringed shape. As the frequency changes, the lobes rotate around the ring. As the absorption of polarized light changes, they become brighter or darker. Together, these features give the team a visual indicator in a single image of how closely the laser's frequency matches the atoms' resonance or how far it has drifted. Professor Sonja Franke-Arnold of the University of Glasgow's School of Physics & Astronomy led the research. She said, "Atoms respond to light at very specific, characteristic frequencies, and this property has been exploited for a long time as an absolute frequency standard in systems that require absolute accuracy, like atomic clocks. Almost every technique for measuring frequency currently in use involves reading a single trace on a photodiode detector, providing a one-dimensional trace to which a laser is locked." The School of Physics & Astronomy's Richard Aguiar Maduro, the paper's first author, said, "In this new research, however, we probe our atoms with an image, and we watch how that image changes as the frequency changes. An image contains far more information than an individual signal, so this opens up a completely new way of determining frequencies." The connection between the laser's frequency and the image's rotation allows the team to measure how closely the frequency matches the atomic resonance of the rubidium gas. The team found that a shift of 1 megahertz in frequency produced a rotation of almost 6 degrees in the image. The technique is currently less precise than the most accurate methods of measuring frequency, which can detect changes down to the kilohertz level. However, the researchers are working to improve the system's precision beyond the sub-megahertz level demonstrated in the paper and are confident it can be fine-tuned. The technique is also sensitive to changes in magnetic fields, which could open up new sensing applications. The team says its work could help develop a new type of magnetometer that could make three-dimensional maps of magnetic fields from a single image, or create storage media for hybrid entanglement of light for use in secure quantum networks. Discover the latest in science, tech, and space with over 100,000 subscribers who rely on Phys.org for daily insights. Sign up for our free newsletter and get updates on breakthroughs, innovations, and research that matter-daily or weekly. Franke-Arnold added, "What excites us most is that we've tied together three different degrees of freedom in a light beam: its shape, its polarization and its frequency. "Normally a spatial light pattern shouldn't be affected by frequency or magnetic fields at all, but for us it does, which is a powerful correlation. These results give us a handle on a new method that hasn't been explored before, and we're excited to explore how far it will take us." The University of Glasgow's Dr. Sphinx Svensson and Craig Millar, as well as researchers from the Fraunhofer Centre for Applied Photonics, the Physikalisch-Technische Bundesanstalt and TU Braunschweig, also contributed to the research and co-authored the paper. Richard Aguiar Maduro et al, Spatio-spectral vector light created by optical activity in rubidium vapor, Optica (2026). DOI: 10.1364/optica.606117 Journal information: Optica Provided by University of Glasgow MA in English, copy editor since 2021 with experience in higher education and health content. Dedicated to trustworthy science news.

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