Scientists have successfully generated photonic time crystals (PTCs) in the spectrum close to visible light, posing the possibility for sweeping changes in optical science applications. This significant advancement broadens the previously known spectrum of PTCs, which had only been identified within radio waves.
Recent research has disclosed refractive index oscillations that exceed the speed accounted for by existing theoretical frameworks.
A paper newly published in the scientific journal Nanophotonics establishes that the rapid modulation of the refractive index—the measure of how quickly electromagnetic radiation travels through a medium relative to its speed in a vacuum—enables the creation of PTCs in the part of the spectrum near visible light.
The authors of the research propose that sustaining PTCs within the realm of optical wavelengths could lead to transformative consequences for light science, paving the way for unprecedented future applications.
PTCs are materials where the refractive index undergoes rapid temporal oscillations. These are the time-based counterparts to photonic crystals, which exhibit periodic spatial oscillations in their refractive index, responsible for phenomena like the iridescence observed in certain minerals and insect wings.
The experimental methodology for measuring time-refraction was conducted in a single-cycle regime. Credit is attributed to Eran Lustig and colleagues.
A PTC remains stable only if its refractive index can oscillate in synchrony with a single electromagnetic wave cycle at the concerned frequency. Until now, PTCs have predominantly been discovered at the lowest-frequency ranges of the electromagnetic spectrum, particularly within radio waves.
In this groundbreaking study, the principal author Mordechai Segev, from the Technion-Israel Institute of Technology in Haifa, Israel, along with co-researchers Vladimir Shalaev and Alexandra Boltasseva from Purdue University, Indiana, USA, dispatched extremely brief laser pulses (ranging between 5-6 femtoseconds) of 800-nanometer wavelength through transparent conductive oxide materials.
These extremely brief pulses induced a swift change in the refractive index, examined through a probe laser beam with a slightly longer wavelength in the near-infrared range. The probe beam’s wavelength rapidly elongated (red-shifted) and subsequently contracted (blue-shifted) as the material’s refractive index reverted to its standard value.
The duration required for each refractive index alteration was exceedingly brief—less than 10 femtoseconds—hence meeting the single-cycle condition essential for stable PTC formation.
“Generally, electrons energized to high levels in crystals take more than a tenfold longer duration to revert to their basal states, leading many in the field to presume that such rapid relaxation, as we observed, would be infeasible,” stated Segev. “The exact mechanisms remain unclear.”
Co-author Shalaev additionally remarked that sustaining PTCs in the optical range, as demonstrated in this study, will “inaugurate a novel era in light science and facilitate profoundly innovative applications,” although the specifics of what those might be remain as uncertain as the potential applications of lasers were to physicists in the 1960s.
Reference: “Time-refraction optics with single cycle modulation” authored by Eran Lustig, Ohad Segal, Soham Saha, Eliyahu Bordo, Sarah N. Chowdhury, Yonatan Sharabi, Avner Fleischer, Alexandra Boltasseva, Oren Cohen, Vladimir M. Shalaev, and Mordechai Segev, published on 31 May 2023, in Nanophotonics.
DOI: 10.1515/nanoph-2023-0126
The study received financial support from the German Research Foundation.
Table of Contents
Frequently Asked Questions (FAQs) about Photonic Time Crystals
What are Photonic Time Crystals?
Photonic Time Crystals (PTCs) are materials where the refractive index undergoes rapid temporal oscillations. They can be considered the temporal equivalent of photonic crystals, which exhibit periodic spatial oscillations in their refractive index.
Who conducted this research and where was it published?
The research was led by Mordechai Segev of the Technion-Israel Institute of Technology, with collaborators from Purdue University, Indiana, USA. The study was published in the scientific journal Nanophotonics on May 31, 2023.
What is the significance of generating Photonic Time Crystals in the near-visible spectrum?
Generating PTCs in the near-visible spectrum broadens the known applications and characteristics of these materials. Until this study, PTCs had only been observed in radio waves. This opens up the possibility of transformative advances in optical science and various future applications.
What challenges to current theories does this research present?
The research disclosed refractive index oscillations that occur at a speed faster than what current theories can account for. This raises questions about existing theoretical frameworks related to the behavior of electromagnetic waves in various media.
What was the experimental setup for the research?
Extremely short pulses of laser light (5-6 femtoseconds) at a wavelength of 800 nanometers were sent through transparent conductive oxide materials. A probe laser beam at a slightly longer wavelength in the near-infrared range was used to study the rapid shifts in the refractive index.
What future applications could this breakthrough lead to?
While specific applications are still unclear, the ability to sustain PTCs in the optical domain could pave the way for groundbreaking technological advances in light science.
Who funded the research?
The study received financial support from the German Research Foundation.
Are there any unresolved questions left by the study?
Yes, the mechanisms behind the ultra-fast relaxation of energized electrons back to their basal states in crystals remain unclear. The study opens up further avenues for research to understand these phenomena.
What is the refractive index and why is it important in this study?
The refractive index is the measure of how quickly electromagnetic radiation travels through a medium relative to its speed in a vacuum. The rapid modulation of the refractive index enabled the creation of PTCs in the near-visible spectrum in this study.
More about Photonic Time Crystals
- [Original Research Article in Nanophotonics](https://doi.org/10.1515/nanoph-
