Optical time reversal from time-dependent Epsilon-Near-Zero media

TL;DR

This paper demonstrates a thin-film epsilon-near-zero material that can achieve optical time reversal, negative refraction, and phase conjugation at optical frequencies with high efficiency, enabling advanced optical applications.

Contribution

It introduces a novel ENZ thin film capable of time reversal and negative refraction at optical frequencies, overcoming previous frequency limitations.

Findings

Achieved near-unit efficiency in time-reversed beams.

Demonstrated simultaneous negative refraction and phase conjugation.

Enabled potential applications in subwavelength imaging and quantum studies.

Abstract

Materials with a spatially uniform but temporally varying optical response have applications ranging from magnetic field-free optical isolators to fundamental studies of quantum field theories. However, these effects typically become relevant only for time-variations oscillating at optical frequencies, thus presenting a significant hurdle that severely limits the realisation of such conditions. Here we present a thin-film material with a permittivity that pulsates (uniformly in space) at optical frequencies and realises a time-reversing medium of the form originally proposed by Pendry [Science 322, 71 (2008)]. We use an optically pumped, 500 nm thick film of epsilon-near-zero (ENZ) material based on Al-doped zinc oxide (AZO). An incident probe beam is both negatively refracted and time-reversed through a reflected phase-conjugated beam. As a result of the high nonlinearity and the refractive index that is close to zero, the ENZ film leads to time reversed beams (simultaneous negative refraction and phase conjugation) with near-unit efficiency and greater-than-unit internal conversion efficiency. The ENZ platform therefore presents the time-reversal features required e.g. for efficient subwavelength imaging, all-optical isolators and fundamental quantum field theory studies.