Scientists experimenting with some of the most fundamental laws of physics have found further evidence of what they call photonic time crystals (PTCs): materials in which the speed at which light travels (the refractive index) vibrates very quickly.
We already know a lot more about it Photonic Crystals, where a repeating pattern in a material produces a shift in refractive index over a region of space; You can recognize this by the shimmering of insect wings or precious minerals. PTCs also introduce the element of change over time.
Here, researchers aimed lasers at two materials known as transparent conducting oxidesthat allow light to pass through and conduct electricity at the same time. They used the lasers to rapidly change the index of refraction for periods of less than 10 femtoseconds (that’s 10 billionths of a second).
Researchers observed significant shifts in light frequency and in light relaxation time (the time it takes for the refractive index to return to normal), depending on the thickness of the material and the rate at which the refractive index has changed.
“Electrons excited to high energy in crystals generally take more than ten times as long to return to their ground state, and many researchers thought that the ultrafast relaxation we observe here would be impossible.” says Physicist Mordechai Segev from the Technion-Israel Institute of Technology.
“We don’t yet understand exactly how it happens.”
If the high-level physics here aren’t already making your head hurt, there’s more than one type of photonics time crystal. The research here is separate from photonic time crystals can manipulate light for various advanced purposes.
So far, these types of PTCs have only been observed in use radio waves, which have much lower frequencies than light waves – the faster the waves pass, the higher the frequency. The stability of PTCs depends on the index of refraction rising and falling within a single electromagnetic wave cycle.
This is much more difficult in the superfast range of light waves, which is what makes these experiments so interesting. The researchers didn’t quite succeed in observing PTCs in the visible light spectrumbut they came close.
As Segev says, it’s not exactly clear why this is happening or how it might ultimately be used, but we’re talking about breaking new ground in physics — a “new chapter in physics.” science of light“, according to Vladimir Shalaev, an electrical engineer at Purdue University in the USA.
“Our findings … pave the way for observing photonic time crystals at optical frequencies and many other phenomena involving time boundaries.” write the researchers in their published work.
The research was published in nanophotonics.
