Recent studies have revealed faster oscillations in the refractive index than can be explained by current theory.
Research recently published in journals nanophotonics have shown that photonic time crystals (PTCs) can be produced in the near-visible part of the spectrum by rapidly modulating the refractive index (the ratio of the speed of electromagnetic radiation in a medium compared to its speed in vacuum). did.
The authors of this study suggest that the ability to maintain PTCs in the optical domain has profound implications for the science of light and could enable truly disruptive applications in the future.
PTC is a material whose refractive index rises and falls rapidly over time, making it a photonic crystal whose refractive index oscillates periodically in space, causing, for example, the iridescence of precious minerals or insect wings. are equivalent.
A PTC is stable only if the index of refraction can rise and fall with one cycle of the electromagnetic wave at the frequency of interest. Not surprisingly, then, PTC has traditionally been observed at the lowest frequency end of the electromagnetic spectrum. By radio waves.
The new study is led by lead author Mordechai Segev of the Technion-Israel Institute of Technology in Haifa, Israel, and co-authors Vladimir Shalayev and Alexandra Bortaseva of Purdue University in Indiana, USA, and their team. It also sent very short (5-6 femtosecond) pulses. Laser light with a wavelength of 800 nanometers is transmitted through a transparent conductive oxide material.
This causes a rapid change in the refractive index, which was investigated using a slightly longer (near-infrared) wavelength probe laser beam. The probe beam was rapidly red-shifted (i.e., wavelength increased) and blue-shifted (wavelength decreased) as the material’s refractive index returned to its normal value.
The time taken for each of these refractive index changes was very short, less than 10 femtoseconds. Therefore, it was within one cycle required to form a stable PTC.
“Electrons excited to high energies in a crystal generally take 10 times longer to relax and return to the ground state. Many researchers believe that the ultrafast relaxation observed here is not possible. “I thought so,” Segev said. “We still don’t understand exactly how that happens.”
Co-author Sharaev added that the ability to sustain PTC in the optical domain, as demonstrated here, “opens a new chapter in the science of light and enables truly disruptive applications.” It suggests that it is deaf. But as much as physicists in the 1960s knew about the potential applications of lasers, we know as little about what these might be.
Reference: “Time refractive optics with single cycle modulation” Eran Lustig, Ohad Segal, Soham Saha, Eliyahu Bordo, Sarah N. Chowdhury, Yonatan Sharabi, Avner Fleischer, Alexandra Voltasseva, Oren Cohen, Vladimir M. Shalaev, Mordechai Segev Author, May 31, 2023 nanophotonics.
DOI: 10.1515/nanoph-2023-0126
This study was funded by the German Research Foundation.