For decades, physicists have been fascinated by the idea of controlling light not just in space, but in time. Now, a team led by Yannis Laplace at the Irradiated Solids Laboratory (LSI) has achieved a breakthrough: the first experimental demonstration of a temporal photonic crystal. Their results, published in Nature, open the door to new ways of shaping light and could lead to exotic lasers and detectors operating in the terahertz range.
So, in physics the so-called “crystal”: system with periodic structure. Electrons and photons interact in a controlled way with structures whose properties are determined by their atomic lattices, which can be periodic (solids). Scientists took this concept and applied it to photonic crystals, structures that manipulate only light by alternating materials with different indices of refraction. These crystals with spatial patterns are the basis of technologies ranging from optical fibers to high-tech sensors.
But what if the crystal’s properties could change over time? That’s the radical idea behind photonic time crystals. Until now, they existed only in theory or in electrical circuit analogs.
Laplace’s team, working with collaborators at the Collège de France, Helmholtz-Zentrum Dresden-Rossendorf, Thales’ Albert Fert Laboratory, and LPICM, built a device that operates in the terahertz (THz) range, where light oscillates a trillion times per second.
The device consists of gold crenelated structures at the micrometer scale, an insulating layer beneath, and a semiconductor layer made of indium and antimony.
These layers form cavities that trap photons. When hit with terahertz laser pulses, the material’s optical properties, especially its reflectivity, were modulated strongly and rapidly, on the picosecond scale (a trillionth of a second).
Achieving modulation that is both strong and ultrafast was “an experimental feat,” the team noted.
The key lies in the semiconductor layer. Laser pulses excite surface plasmons, collective waves of electrons. As their effective mass oscillates, the material’s optical properties alternate, creating the temporal crystal effect.
This dynamic modulation hints at new phenomena, including photon amplification inside the cavities. Researchers have already seen early signs and hope to observe a plasmonic laser effect soon.
Temporal photonic crystals could revolutionize:
Light sources in the terahertz range; Detectors for advanced sensing; Optical devices that exploit symmetry-breaking and time-dependent modulation.
By shaping light in time as well as space, scientists are entering a new frontier of photonics, one where abstract theory transforms into tangible technology.
