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      The Photonic Nanojet is a Central Maxima in the Near Field Diffraction Pattern

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          Abstract

          In this paper, we demonstrate that the formation of photonic nanojets is the result of near-field diffraction. We show that the photonic nanojet is the central bright maxima in the field intensity distribution as a consequence of diffraction triggered by a virtual slit comprising a micro-scale dielectric surface. Details on the role of the opto-geometric environment in reshaping the photonic nanojet are provided. Based on this new understanding, we propose a new structured optical fiber end-face that produces a photonic nanojet in a wide range of environments.

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          Most cited references13

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          Direct imaging of photonic nanojets.

          We report the direct experimental observation of photonic nanojets created by single latex microspheres illuminated by a plane wave at a wavelength of 520 nm. Measurements are performed with a fast scanning confocal microscope in detection mode, where the detection pinhole defines a diffraction-limited observation volume that is scanned in three dimensions over the microsphere vicinity. From the collected stack of images, we reconstruct the full 3 dimensional photonic nanojet beam. Observations are conducted for polystyrene spheres of 1, 3 and 5 microm diameter deposited on a glass substrate, the upper medium being air or water. Experimental results are compared to calculations performed using the Mie theory. We measure nanojet sizes as small as 270 nm FWHM for a 3 microm sphere at a wavelength lambda of 520 nm. The beam keeps a subwavelength FWHM over a propagation distance of more than 3 lambda, displaying all the specificities of a photonic nanojet.
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            Optical analysis of nanoparticles via enhanced backscattering facilitated by 3-D photonic nanojets.

            We report the phenomenon of ultra-enhanced backscattering of visible light by nanoparticles facilitated by the 3-D photonic nanojet - a sub-diffraction light beam appearing at the shadow side of a plane-waveilluminated dielectric microsphere. Our rigorous numerical simulations show that backscattering intensity of nanoparticles can be enhanced up to eight orders of magnitude when locating in the nanojet. As a result, the enhanced backscattering from a nanoparticle with diameter on the order of 10 nm is well above the background signal generated by the dielectric microsphere itself. We also report that nanojet-enhanced backscattering is extremely sensitive to the size of the nanoparticle, permitting in principle resolving sub-nanometer size differences using visible light. Finally, we show how the position of a nanoparticle could be determined with subdiffractional accuracy by recording the angular distribution of the backscattered light. These properties of photonic nanojets promise to make this phenomenon a useful tool for optically detecting, differentiating, and sorting nanoparticles.
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              Photonic nanojet-enabled optical data storage.

              We show that our recently reported microwave photonic jet technique for detection of deeply subwavelength pits in a metal substrate can be extended to optical wavelengths for purposes of high-density data storage. Three-dimensional finite-difference time-domain computational solutions of Maxwell's equations are used to optimize the photonic nanojet and pit configuration to account for the Drude dispersion of an aluminum substrate in the spectral range near lambda= 400 nm. Our results show that nanojet-illuminated pits having lateral dimensions of only 50 nm x 80 nm yield a contrast ratio 27 dB greater than previously reported using a lens system for pits of similar area. Such pits are much smaller than BluRay features. The high detection contrast afforded by the photonic nanojet could potentially yield significant increases in data density and throughput relative to current commercial optical data-storage systems while retaining the basic geometry of the storage medium.
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                Author and article information

                Journal
                06 December 2017
                Article
                1712.02283
                8d0c6ddf-c468-4adc-ab1b-0f94a088bd9d

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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                physics.optics

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