Spatio-temporal wavefront shaping in a microwave cavity

TL;DR

This paper demonstrates that wavefront shaping in a microwave cavity using electronically tunable resonators enables diffraction-limited spatio-temporal focusing, offering new control over microwave wave propagation with broad potential applications.

Contribution

It introduces a method to achieve spatio-temporal wavefront shaping in microwave cavities using reconfigurable arrays, revealing that spatial and temporal degrees of freedom can be independently manipulated without affecting field enhancement.

Findings

Maximizing Green's function yields diffraction-limited focusing.

Changing photon dwell time does not impact field enhancement.

Wavefront shaping utilizes all available degrees of freedom.

Abstract

Controlling waves in complex media has become a major topic of interest, notably through the concepts of time reversal and wavefront shaping. Recently, it was shown that spatial light modulators can counter-intuitively focus waves both in space and time through multiple scattering media when illuminated with optical pulses. In this letter we transpose the concept to a microwave cavity using flat arrays of electronically tunable resonators. We prove that maximizing the Green's function between two antennas at a chosen time yields diffraction limited spatio-temporal focusing. Then, changing the photons' dwell time inside the cavity, we modify the relative distribution of the spatial and temporal degrees of freedom (DoF), and we demonstrate that it has no impact on the field enhancement: wavefront shaping makes use of all available DoF, irrespective of their spatial or temporal nature. Our results prove that wavefront shaping using simple electronically reconfigurable arrays of reflectors is a viable approach to the spatio-temporal control of microwaves, with potential applications in medical imaging, therapy, telecommunications, radar or sensing. They also offer new fundamental insights regarding the coupling of spatial and temporal DoF in complex media.