Physicists at the University of Colorado Boulder have demonstrated a new kind of vacuum ultraviolet laser that is 100 to 1,000 times more efficient than existing technologies of its kind.
The researchers say the device could one day allow scientists to observe phenomena currently out of reach for even the most powerful microscopes—such as following fuel molecules in real time as they undergo combustion, spotting incredibly small defects in nanoelectronics and more.
The new laser might also allow for practical, ultraprecise nuclear clocks that rely on an energy transition in the nuclei of thorium atoms. These long sought-after devices could, theoretically, allow researchers to robustly track time with unprecedented precision.
The group is led by physicists Henry Kapteyn and Margaret Murnane, fellows of JILA, a joint research institute between CU Boulder and the U.S. National Institute of Standards and Technology (NIST). Jeremy Thurston, who earned his doctorate in physics from CU Boulder in 2024, spearheaded work on the new laser.
“Scientists have been working toward vacuum ultraviolet lasers for decades,” said Kapteyn, a professor in the Department of Physics . “We think we might have finally found a great route that can be scaled in power, and that is compact in size—two essential requirements for challenging applications.”
The team will present its preliminary findings at sessions on March 17 and March 19 at the American Physical Society’s Global Physics Summit in Denver Colorado.
All light comes in very small waves, not unlike the peaks and troughs in the ocean close to shore. The waves in visible light, for example, measure roughly 380 to 750 nanometers from crest to crest. That’s equal to several millionths of an inch.
Scientists have long strived to make better lasers that push those wavelengths shorter and shorter.
For decades, however, scientists have struggled to design lasers that shoot out bright beams of light in a region of the spectrum known as the vacuum ultraviolet (VUV)—where wavelengths reach about 100 to 200 nanometers across, many times smaller than the width of a human hair.
Murnane and Kapteyn’s laser is small enough to fit on top of an ordinary desk, and the researchers hope to make it even smaller and more efficient.
“Shorter wavelengths matter because you can use them to make higher resolution microscopes,” said Murnane, a distinguished professor of physics. “If a chemical reaction is happening, you can see what molecules are there—to see, for example, how they ablate the tiles on a space capsule as it reenters the atmosphere.”
Murnane, Kapteyn and their students are no stranger to powerful lasers.
The researchers and their colleagues previously pioneered the design of tabletop X-ray lasers . These machines emit beams of light that oscillate more than a billion billion times per second.
Laser scientists, however, haven’t had much luck breaking into the vacuum ultraviolet, a region in between X-rays and visible light. All kinds of matter, from solids to atoms and organic molecules, interact strongly with vacuum ultraviolet light.
“Basically, everything absorbs light at this range, which is why vacuum ultraviolet is so interesting and why it’s so difficult to engineer,” Kapteyn said.
To get around those challenges, Kapteyn and Murnane’s group started with ordinary beams of red and blue laser light.
The team combined those beams in a special kind of chamber called an “anti-resonant hollow core fiber.”
The fiber is a bit like the fiberoptic cables that move internet data to and from your house. But this chamber is made of a single hollow tube circled by seven smaller tubes. (The researchers compare it to the barrel of a revolver).
Laser light passes through the central tube, and, in the process, slams into atoms of xenon gas. Those atoms absorb the light and spit it back out, transforming the visible light into vacuum ultraviolet light.
“To our knowledge, no other approach, either at big or small facilities, has the VUV power levels, tuning ranges and coherence that our new approach has shown,” Murnane said.
That could come in handy. Murnane added that many technologies today are increasingly depending on nanoelectronics, or incredibly small devices. They include the semiconductors in the computer chips in your phone, laptop and more.
The team’s laser could help engineers optimize these devices—spotting tiny defects, for example, that could make them less efficient.
In their presentation, the researchers will also highlight how that approach could also make robust and portable nuclear-referenced atomic clocks a reality.
Murnane explained that if you hit a cloud of thorium atoms with the laser tuned to just the right wavelength, the atoms will begin to fluctuate in energy—much like flicking the pendulum in a grandfather clock will get it swinging.
Scientists could track that kind of ticking to help people navigate the globe and through space without GPS, or even search for planets beyond Earth’s solar system.
In a separate effort, researchers led by physicist Jun Ye at JILA and NIST have made major strides in developing such a clock .
Murnane added that thorium atoms “tick” only when exposed to light with a wavelength of exactly 148.3821 nanometers—within the realm of vacuum ultraviolet light.
Currently, scientists generate that light using lasers that often take up entire rooms. Murnane and Kapteyn think they can achieve the exact same feat using their new laser, which would be cheaper and easier to deploy.
The team still has a lot of work to do. The researchers are experimenting with ways to make their vacuum ultraviolet laser many times smaller without making it less efficient—an engineering challenge.
“There are a lot of applications that we would like to use VUV light for, but there haven’t been any lasers that were practical,” Murnane said. “Now, there’s a huge block of the spectrum that’s being opened up where light is super sensitive to exquisite details of atoms, molecules and materials.”