Exploiting disorder for perfect focusing

Abstract

Optical microscopy and manipulation methods rely on the ability to focus light to a small volume. However, in inhomogeneous media such as biological tissue, light is scattered out of the focusing beam. Disordered scattering is thought to fundamentally limit the resolution and penetration depth of optical methods1,2,3. Here we demonstrate, in an optical experiment, that scattering can be used to improve, rather than deteriorate, the sharpness of the focus. The resulting focus is even sharper than that in a transparent medium. By using scattering in the medium behind a lens, light was focused to a spot ten times smaller than the diffraction limit of that lens. Our method is the optical equivalent of highly successful methods for improving the resolution and communication bandwidth of ultrasound, radio waves and microwaves4,5,6. Our results, obtained using spatial wavefront shaping, apply to all coherent methods for focusing through scattering matter, including phase conjugation7 and time-reversal4.

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Figure 1: Schematic of the experiment.
Figure 2: Measured intensity distribution in the focal plane at 200±3 mm from the glass lens.
Figure 3: Focal width w, relative to the diffraction limit of the glass lens (w0 = 62 µm, dashed line), as a function of the distance f2 between the scattering sample and the focal plane.
Figure 4: Intensity profile of the focus at y = 0 (solid curve) and speckle correlation function (dashed curve).

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Acknowledgements

The authors thank W.L. Vos and E.G. van Putten for support and discussions. This work is part of the research programme of the Stichting voor Fundamenteel Onderzoek der Materie (FOM), which is financially supported by the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO). A.P.M. is supported by a VIDI grant from NWO.

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I.M.V., A.L. and A.P.M. designed the experiments, analysed the data, developed the theory and wrote the paper. I.M.V. performed the experiments.

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Correspondence to A. P. Mosk.

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The authors declare no competing financial interests.

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Vellekoop, I., Lagendijk, A. & Mosk, A. Exploiting disorder for perfect focusing. Nature Photon 4, 320–322 (2010). https://doi.org/10.1038/nphoton.2010.3

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