META Conference, META'12

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A polychromatic approach to far field superlensing in the visible
Geoffroy Lerosey, Fabrice Lemoult, Mathias Fink

Last modified: 2012-01-05


Conventional imaging devices such as optical lenses are limited in resolution by the so-called Rayleigh criterion to half the operating wavelength. Imaging below this resolution requires to record the evanescent waves that carry thinner spatial information of an object but decrease exponentially away from it. This can be achieved with near field scanning optical microscopy but requires a point by point scanning. The need for real time super resolution imaging has led to many proposals of superlenses or high numerical aperture lenses, whose resolutions are seriously limited by the properties of the materials available in the visible. Meanwhile, interesting sub-diffraction imaging methods based on scattering and structured monochromatic illumination have been demonstrated. Here we propose to use polychromatic light sources to beat the diffraction limit using a superlens made out of resonant plasmonic nanoparticles. We numerically prove that such a lens, combined with a femtosecond laser, could potentially focus optical waves onto 30 nm wide foci, 1/23th of a wavelength at the central wavelength of the pulse. Then we demonstrate a real time far field imaging scheme based on light pulse echo interferometry, which can image a low contrast index object with a resolution of 100 nm that could be easily improved. The concept is based on our recent proposal of resonant metalens which consists in arrays of resonators that hybridise with the free space plane waves and give rise to collective subwavelength modes that can excited from the far field.


plasmonics, subwavelength imaging, subwavelength focusing, superlens