Text Size
Heisenberg's original thought experiment assumed the diffraction barrier for microscopes. This limit has been beaten by modern technology not anticipated by Heisenberg, or Einstein or anyone almost 100 years ago.


week ending 21 MAY 2010

Resonant Metalenses for Breaking the Diffraction Barrier

Fabrice Lemoult, Geoffroy Lerosey,* Julien de Rosny, and Mathias Fink

"We introduce the resonant metalens, a cluster of coupled subwavelength resonators. Dispersion allows

the conversion of subwavelength wave fields into temporal signatures while the Purcell effect permits an

efficient radiation of this information in the far field. The study of an array of resonant wires using

microwaves provides a physical understanding of the underlying mechanism. We experimentally

demonstrate imaging and focusing from the far field with resolutions far below the diffraction limit.

This concept is realizable at any frequency where subwavelength resonators can be designed.

Within all areas of wave physics it is commonly believed

that a subwavelength wave field cannot propagate in the far

field. This restriction arises from the fact that details with

physical dimensions much smaller than the wavelength are

carried by waves whose phase velocity exceeds that of light

in free space, which forbids their propagation. Such waves,

usually referred to as evanescent waves, possess an exponentially

decreasing amplitude from the surface of an

object [1].

Numerous works have been devoted to overcome this

diffraction limit, starting from the early 20th century and

the proposal by Synge of the first near field imaging

method [2]. Since this seminal work, near field microscopes

have been demonstrated from radio frequencies

up to optical wavelengths, achieving resolutions well below

the diffraction limit [38]. Fluorescence based imaging

methods have also been proposed, which allow deep

subwavelength imaging of living tissues [9]. Such concepts,

however, employ several measurements of the

same sample in order to beat the diffraction limit through

image reconstruction procedures. Finally, various new concepts

have been proposed such as far field superlens and

hyperlens [1012], demonstrating moderate subdiffraction

imaging down to a quarter of the optical wavelength.

In this Letter, we introduce the concept of resonant

metalens, a lens composed of strongly coupled subwavelength

resonators, and prove that it permits subdiffraction

imaging and focusing from the far field using a single

illumination. Our concept resides in exploiting time-coded

far field signals for spacial subwavelength resolution

[13,14]. Studying the specific case of an array of resonant

wires, we explain theoretically, prove numerically, and

demonstrate experimentally how this lens converts the

subwavelength spatial profile of an object into a temporal

signature and allows efficient propagation of this information

towards the far field.We achieve far field imaging and

focusing experiments with resolutions of, respectively,

1/80k and 1/25k, well below the diffraction limit. ..."