About Time: Observation of Time-Reflection at Optical Frequencies

Ohad Segal; Noa Konforty; Oded Schiller; Maxwell J. Tolchin; Tony Yasniger; Michael Birk; Alexander Palatnik; Soham Saha; Pavel Sidorenko; Jon-Paul Maria; Yonatan Plotnik; Mordechai Segev

arXiv · 2605.15632

About Time: Observation of Time-Reflection at Optical Frequencies

Ohad Segal·Noa Konforty·Oded Schiller·Maxwell J. Tolchin·Tony Yasniger·Michael Birk·Alexander Palatnik·Soham Saha·Pavel Sidorenko·Jon-Paul Maria·Yonatan Plotnik·Mordechai Segev

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Abstract

Time-reflection occurs when a wave is propagating in a medium undergoing a large and abrupt change in its properties: the original wave splits into a time-refracted wave and a time-reflected wave, each displaying different features. The time-refracted wave continues along its original course but experiences a frequency shift, whereas the time-reflected wave is propagating backwards in space with a reversed phase, also with a shifted frequency. These phenomena are fundamental to any wave system, but the most interesting are electromagnetic (EM) waves, specifically at optical frequencies, where they can couple to light-matter interactions. However, time-reflection of EM waves was thus far observed only at RF frequencies, never at optical frequencies. This is because time-reflection requires an order-unity variation of the refractive index occurring faster than a single wave cycle, and conventional optical nonlinearities are either too weak or too slow by orders of magnitude. Here, we present the first observation of time-reflection at optical frequencies. We induce an order-unity refractive-index change with sub-cycle duration, observe the time-reflection, and study its fundamental properties. These results provide an experimental pathway to experimenting with time-interfaces, generating photonic time-crystals and exploring new regimes of light-matter interaction in time-varying media.

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Ohad Segal, Noa Konforty, Oded Schiller, Maxwell J. Tolchin, Tony Yasniger, Michael Birk, Alexander Palatnik, Soham Saha, Pavel Sidorenko, Jon-Paul Maria, Yonatan Plotnik, Mordechai Segev. 2026-05-15. About Time: Observation of Time-Reflection at Optical Frequencies. https://arxiv.org/abs/2605.15632

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