A study recently published in the journal Nanophotonics reveals that by rapidly modulating the refractive index – which is the ratio of the speed of electromagnetic radiation in a medium compared to its speed in a vacuum – it’s possible to produce photonic time crystals (PTCs) in the near-visible part of the spectrum.
The study’s authors suggest that the ability to sustain PTCs in the optical domain could have profound implications for the science of light, enabling truly disruptive applications in the future.
A PTC is only stable if the refractive index can be made to rise and fall in line with a single cycle of electromagnetic waves at the frequency concerned so, unsurprisingly, PTCs have thus far been observed at the lowest-frequency end of the electromagnetic spectrum: with radio waves.
In this new study, lead author Mordechai Segev of the Technion-Israel Institute of Technology, Haifa, Israel, with collaborators Vladimir Shalaev and Alexndra Boltasseva from Purdue University, Indiana, USA, and their teams, sent extremely short (5-6 femtosecond) pulses of laser light at a wavelength of 800 nanometers through transparent conductive oxide materials.
This caused a rapid shift in refractive index that was explored using a probe laser beam at a slightly longer (near infrared) wavelength. The probe beam was rapidly red-shifted (that is, its wavelength increased) and then blue-shifted (wavelength decreased) as the material’s refractive index relaxed back to its normal value.
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