Scientists have demonstrated what they describe as the first all-optical photonic time crystal, a material whose optical properties change in a repeating rhythm fast enough to reshape its interaction with terahertz light. In the experiment, this behavior reduced losses in coupled light-and-electron oscillations, known as plasmons, by more than 50%.
The work brings together École Polytechnique, the Collège de France and Germany’s Helmholtz-Zentrum Dresden-Rossendorf (HZDR), alongside partner laboratories. It opens a route toward new lasers and faster optical technologies, but the immediate achievement is more specific than a ready-made device for your phone or internet connection.
A crystal that repeats in time
Standard photonic crystals use repeating patterns of materials to guide, block or enhance particular wavelengths of light. Think of a carefully designed route that determines where light can travel, rather than a crystal sitting on a windowsill. The arrangement plays a role somewhat like the structures that control electrons in semiconductors.
The new system adds another way to control that journey. Instead of relying only on a fixed structure, researchers repeatedly alter the material’s optical properties while light interacts with it, on timescales comparable to the light’s own oscillation.
Those changes happen on picosecond timescales, with one picosecond equal to one trillionth of a second. The challenge was not merely making a material respond quickly, but making the change both large enough and rhythmically consistent enough to produce the sought-after behavior.
Why terahertz light matters
“The THz range represents the frontier between electronic and photonic technologies,” said Yannis Laplace, an assistant professor at École Polytechnique. This region remains less technologically developed than the frequency ranges used by more established electronic and optical systems.
At one terahertz, an electromagnetic wave oscillates one trillion times per second. That sets the scale of the task, because the material must change quickly enough to affect what the wave experiences within an oscillation. A rapidly changing field alone is not enough, because the material’s response has to keep pace.
Control over light already underpins fiber-optic connections, lasers and sensors used in chemistry and biology. The researchers’ aim is to extend those capabilities into a frequency range where generating and manipulating light still presents substantial technical hurdles.
Gold structures that trap light
The team built a “plasmonic metamaterial” using micrometer-scale gold structures above an insulating layer and an indium antimonide semiconductor. The patterned gold forms tiny cavities that confine light between the metal and semiconductor layers. Their geometry keeps the light interacting closely with the semiconductor, whose response drives the optical changes.
Inside the semiconductor, electrons move collectively in waves that interact with the trapped light. Under the applied terahertz field, changes in the electrons’ effective mass, a measure of their response within the material, alter the cavities’ resonance and optical behavior.
Driving this process required TELBE, the powerful, frequency-tunable terahertz source at HZDR’s ELBE accelerator. “TELBE’s unique ability to generate high-field, phase-stable terahertz pulses was critical,” said facility coordinator Jan-Christoph Deinert.
The result that matters beyond speed
Why focus on losses? In the photonic time crystal regime, the researchers found that amplification arising from the periodic driving partly counteracted the decay of the plasmonic oscillations. The measured reduction exceeded 50%.
A theoretical model developed by Marco Schirò and colleagues at the Collège de France reproduced the experimental observations. That agreement helped connect the measured optical changes with the physics inside the material, giving the team a way to explore what might happen under different conditions.
The 50% figure describes losses inside this driven experimental system, not a 50% cut in the electricity needed to power a future computer. Any environmental benefit would need its own testing, including the energy required to drive the material.
A path toward new lasers
The next step is to reduce losses further and strengthen amplification inside the cavities. According to the researchers’ theoretical model, changes to cavity geometry and driving conditions could bring plasmonic lasing within reach, but that remains a prediction rather than a demonstrated laser. Stronger amplification could eventually let these cavities act as light sources rather than simply responding to an incoming pulse.
The team points to possible applications in optical computing, telecommunications and new terahertz light sources, potentially including medical imaging. Those are research directions, not demonstrated improvements in processing speed, network performance or hospital equipment.
For now, the advance is a new way to control how light interacts with matter, with experimental evidence that timing can change how strongly those oscillations fade.
The study, “Plasmonic metamaterial time crystal,” was published on July 29, 2026, in Nature.
