Researchers from the Swiss Federal Institute of Technology (EPFL) have announced the first ultrafast laser delivering 1.05 nanojoules of energy in extremely short pulses as short as 147 femtoseconds integrated onto a photonic chip.

The research team behind the accomplishment said that successfully scaling down ultrafast lasers of this magnitude from large tabletop models to microchip integration could enable extremely advanced sensing technologies, improve medical imaging, and potentially enable next-generation atomic clocks for yet-to-be-developed communication and navigation applications.

Ultrafast Lasers on a Microchip Scale Have Remained an Elusive Photonics ‘Holy Grail’

In a statement announcing the breakthrough, team leader and EPFL Professor Tobias J. Kippenberg explained that ultrafast lasers emit extremely short pulses of light energy lasting only a few hundred femtoseconds, which are quadrillionths of a second. Although the development of this category of lasers has enabled ultraprecise micromachining, atomic clocks, and advanced eye surgery, the team notes that the “bulky” technology has been limited to optical laser tables.

On the other end of the spectrum, engineers have built extremely small photonic chips that channel light in a similar way to how traditional microprocessors channel electricity to perform calculations. Some photonic chip designs are already widely used in the communications industry. However, integrating the ultrafast laser technology at the power levels demonstrated by the research team into a smaller chip has remained particularly elusive.

“For more than twenty years, a high-pulse-energy femtosecond laser on chip was widely regarded as a holy grail of integrated photonics,” Professor Kippenberg explained.

“Overlooked, Surprisingly Elegant Technology” Could Enable Futuristic Technologies

To find the nexus between size, speed, and power that could enable a true high-energy, ultrafast laser on a chip, the EPFL team opted to turn away from traditional laser designs and instead took advantage of what they termed a “largely overlooked” design: a Mamyshev oscillator.

Unlike some designs, this oscillator uses a nonlinear waveguide placed between the two optical filters in the laser cavity, each of which allows a different color of the spectrum to pass through. When a strong light pulse travels through the installed waveguide, the beam broadens into a wider range of colors.

The team notes that this effect allows part of the light pulse to pass through both filters and remain in circulation. However, they also note that “weak light” does not broaden enough when impacting the waveguide and is ‘rejected.’

Zheru Qiu, a co-lead author of the paper, said that beyond speed and power, their chip has commercial potential due to its material simplicity.

“This design is especially attractive because it does not require any component that is difficult to make on this erbium-doped silicon nitride chip,” Qiu explained.

Another advantage to the team’s design is its resistance to nonlinear interaction. Put simply, when waveguides squeeze light into tiny spaces, that same light interacts strongly with itself.

The resulting nonlinear interactions can degrade the performance of traditional photonic chip designs. However, Qiu said that a laser with a Mamyshev oscillator is “well suited to the tight confinement of light in photonic chips.”

“Our result shows that it is not only possible, but that it can be achieved with a surprisingly elegant architecture that the integrated-photonics community had overlooked,” Qiu explained of their revolutionary architecture. 

Integrated Chips Could Replace Large, Expensive Laboratory Lasers

When discussing the versatility of their ultrafast laser on a chip, the researchers noted that the prototype’s 42-cm-long laser cavity can be folded down to a size smaller than a matchhead. For comparison, they noted that 42 centimeters is “far smaller than optical fiber-based lasers.”

For potential commercial applications, the team said their chips can be manufactured “at-scale,” with an excess of 1,000 individual laser cavities per chip. Although currently in the demonstration phase, the team suggested that a fully realized commercial-grade ultrafast laser-on-a-chip could provide engineers with a critical microengineering tool they have lacked.

“With kilowatt-level peak powers, the chip can drive demanding applications that have long depended on large, expensive laboratory lasers,” says Qiu.

The researchers suggested their chip could impact several technologies, such as advanced sensing and medical imaging, and potentially pave the way for futuristic technologies based on ultraprecise atomic clocks.

The study “High-pulse-energy integrated mode-locked laser using a Mamyshev oscillator” was published in Nature.

Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.

An international team of astronomers has uncovered what they are calling the clearest evidence yet for dying white dwarf stars as the origin of a class of mysterious cosmic signals called long-period radio transients.

The research, led by University of Sydney PhD student Kovi Rose, potentially offers researchers a ‘Rosetta Stone’ capable of deciphering and categorizing other such signals.

“For the first time, we have pinpointed the origin of these signals, confirming the source to be a ‘cataclysmic variable’, or an accreting white dwarf star,” Rose explained in an email to The Debrief.

The team behind the discovery, including the astronomers at CSIRO’s ASKAP radio telescope, said that identifying the origin of these transient cosmic signals that come from a few remote regions of the Milky Way galaxy could also offer researchers a “natural laboratory” to study the extreme physics that occur in such environments.

Mysterious Cosmic Signals “Have Puzzled Astronomers for Years”

According to the same email, long-period radio transients were initially thought to be slow-spinning neutron stars, known as pulsars, emitting periodic energy bursts. However, the team notes that mathematical models suggest that slow-rotating neutron stars cannot generate enough energy to produce the mysterious cosmic signals.

“Long-period radio transients have puzzled astronomers for years,” Mr. Rose explained. “We’ve only found about a dozen, and their origins have been unclear.”

Hoping to solve the mystery, the University of Sydney-led team aimed their instruments at a region of space and discovered a small, dense star called a white dwarf. However, unlike our solitary Sun, this white dwarf is part of a binary star system, named ASKAP J1745−5051, with a much larger but less dense red dwarf as its companion.

After several scans with ASKAP, the team discovered that the smaller white dwarf, about the size of Earth but with a mass closer to the Sun’s, was shedding or accreting material onto the larger but less dense red dwarf star. As the material heats up, it releases X-rays.

The team also detected periodic bursts of radio signals from the binary system. Although these regular emissions are tied to the system’s orbital motion, the researchers found that the bursts of X-rays and radio signals didn’t peak at the same time. According to Mr. Rose, this lack of synchronicity “tells us they’re being produced in different regions of the system.”

Analysis Reveals Long-Period Radio Transient Match

A closer analysis suggested that, due to the proximity of the two stars, which orbit each other in just one hour, their interacting magnetic fields were producing regular radio-wave bursts, which the team clocked at 1.4-hour intervals.

Professor Murphy, Head of School at the University of Sydney School of Physics and Chief Investigator at the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), said that similar objects have previously been linked to binary star systems, “but this is the first one where we can clearly see both stars and the accretion process in action.”

When the team compared the emissions from the binary system with those of previously detected long-period radio transients, the data were a clear match. According to Rose, this comparison proved definitively that this elusive category of mysterious cosmic signals “comes from a white dwarf actively pulling material from a companion star.”

Natural Laboratories for Exploring Extreme Plasma Physics

Although the team’s findings do not rule out other causes of these mysterious cosmic signals, they said their discovery “strengthens an alternative explanation” that at least some are caused by binary star systems involving white dwarfs.

“The system is also only the second known long-period radio transient to emit regular X-rays – and the first where the cause of the regularity has been confirmed,” they explained.

When discussing the potential impact of their findings on future research, the team noted that ASKAP J1745-5051 could provide astronomers “a reference point” for understanding other long-period radio transients that have remained uncharacterized.

Mr. Rose said that the system could help researchers determine whether other long-period transients are more like pulsars or like white dwarf systems, “acting like a stellar Rosetta stone,” referencing the famous stone tablet that helped modern researchers decipher Egyptian hieroglyphs. He also noted that the system offers researchers a unique opportunity to study extreme plasma physics and magnetic-field interactions “under conditions that cannot be replicated on Earth.”

“These systems are natural laboratories,” Mr Rose said. “They allow us to test our understanding of how matter behaves in strong magnetic fields and under intense gravitational forces.”

In the future, the University of Sydney-led team said they are planning future observations of the system with a combination of optical, radio, and X-ray telescopes “to better understand how these emissions are generated” and to determine whether similar mechanisms found in this system can explain the full population of long-period radio transients spotted to date.

“Each new discovery is helping us piece together the bigger picture,” Mr Rose explained. “We’re only just beginning to understand this new class of cosmic events.”

The findings are published in the journal Nature Astronomy.

 Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.