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Science. 2007 Feb 23;315(5815):1120-2.

Focusing beyond the diffraction limit with far-field time reversal.

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  • 1Laboratoire Ondes et Acoustique, Ecole Sup√©rieure de Physique et de Chimie Industrielles, Universit√© Paris VII, Centre National de la Recherche Scientifique, UMR 7587, 10 rue Vauquelin, 75005 Paris, France.


We present an approach for subwavelength focusing of microwaves using both a time-reversal mirror placed in the far field and a random distribution of scatterers placed in the near field of the focusing point. The far-field time-reversal mirror is used to build the time-reversed wave field, which interacts with the random medium to regenerate not only the propagating waves but also the evanescent waves required to refocus below the diffraction limit. Focal spots as small as one-thirtieth of a wavelength are described. We present one example of an application to telecommunications, which shows enhancement of the information transmission rate by a factor of 3.

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