Abstract
Dielectric nanoparticles offer low optical losses and access to both electric and magnetic Mie resonances. This enables unidirectional scattering along the incident axis of light, owing to the interference between these two resonances. Here we theoretically and experimentally demonstrate that an asymmetric dimer of dielectric nanoparticles can provide unidirectional forward scattering with high efficiency. Theoretical analyses reveal that the dimer configuration can satisfy the first Kerker condition at the resonant peaks of electric and magnetic dipolar modes, therefore showing highly efficient directional forward scattering. The unidirectional forward scattering with high efficiency is confirmed in our experiments using a silicon nanodisk dimer on a transparent substrate. This study will boost the realization of practical applications using low-loss and efficient subwavelength all-dielectric nanoantennas.
Highlights
Controlling visible light with nanoparticles smaller than the wavelength has been subject of high interest in many applications; for instance, improving the efficiency of solar cells,[1] increasing the sensitivity of optical sensors[2,3] and realizing optical nanocircuits.[4]
We revealed that highly efficient unidirectional forward scattering can be obtained using dimers of asymmetric silicon nanoparticles
Theoretical and numerical analyses of the spherical dimer showed that this configuration is capable of scattering light to the forward direction selectively with high efficiency by fulfilling the first Kerker condition between the electric dipolar resonance excited in one particle and the magnetic in the other
Summary
Controlling visible light with nanoparticles smaller than the wavelength has been subject of high interest in many applications; for instance, improving the efficiency of solar cells,[1] increasing the sensitivity of optical sensors[2,3] and realizing optical nanocircuits.[4] Plasmonic nanoparticles made of noble metals have been demonstrated as a potential building block for nanoantennas able to control electromagnetic waves even below the diffraction limit.[5,6] Coherent oscillations of free electrons in metallic nanoparticles, called localized surface plasmon resonances, are capable of confining the electric field into a subwavelength area, while at the same time resonantly enhancing scattering into the far field. Substantial energy losses are inevitable, especially at visible light wavelengths, because of the presence of free electrons and their ohmic losses. This drawback has hampered the realization of the aforementioned applications using metallic plasmonic nanoparticles[7] and stimulated the study of high-refractive-index dielectric nanoparticles as an alternative. Dimers or oligomers of silicon nanostructures have been revealed to enhance and confine the electromagnetic field into the small gap, and to increase the scattering efficiency, without appreciable heat generation.[8,9,10,11,12,13,14,15,16] These dielectric nanoantennas can be exploited, for example, by spectroscopic techniques such as fluorescence microscopy or surface enhance Raman scattering, where undesired heat could disturb the response of the sample.[17]
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