Neciah Dorh

Fluorescent emission enhancement by aluminium nanoantenna arrays in the near UV

In this paper, we demonstrate fluorescence enhancement of a laser dye, using aluminium nanoantenna arrays designed for the near UV range. A series of nanorod arrays were fabricated by focused ion beam milling then spin-coated with a dye with an intrinsic quantum yield (QY) in the range 0.5 to 0.6. Scanning confocal photoluminescence measurements of the arrays show up to 1.9× enhancement of the fluorescence signal compared to the reference on glass. The observed near UV fluorescence enhancement is affected by the relatively high intrinsic QY of the dye and coupling to an array mode. FDTD modelling predicts strong dependence of the emission on angle, with maximum emission at high angles with respect to normal. The model predicts that using a lens with a numerical aperture of 0.9 would lead to an enhancement of up to ~6×.

Polarization and mutual coupling effects in aluminum nanoantenna arrays

This paper uses finite-difference time-domain modeling to study the impact of varying the polarization of the point source(s) on both a single aluminum dipole nanoantenna and a 2×2 array. Starting with the single dipole nanoantenna, this paper demonstrates the strong dependence of power enhancement and resonance on the polarization of the source by alternating between orthogonal polarization states. With each element of the array excited by a single point source, the resonance, power enhancement, and far-field radiation patterns are observed as the polarization of each source is rotated, in varying combinations. The results demonstrate that a unique far-field radiation pattern is produced for each polarization combination, which may lead to applications in subdiffraction limit imaging and quantum optics.

Purcell enhancement and focusing effects in plasmonic nanoantenna arrays

This paper presents measured fluorescence results for PMMA dye-coated 5×5 gold plasmonic nanoantenna arrays. We use numerical electromagnetic modeling to show how array size and element spacing can be used to control emitted beam shape and compare this with experimental data. The Friis formula from RF antenna theory is used to calculate the intensity enhancement produced by the array. A figure of merit is then developed, which accounts for the very small mode volume from which the array emission is occurring.

Nanoantenna arrays combining enhancement and beam control for fluorescence-based sensing applications

This paper presents measured fluorescence enhancement results for ∼250×250 element aluminum nanoantenna arrays fabricated using electron beam lithography. The arrays have been designed to use diffractive coupling to enhance and control the direction of fluorescent emission. Highly directional emission is obtained at the designed angles with beam widths simulated to be in the range of 4-6°. Angle-resolved spectroscopy measurements of dye-coated nanoantenna arrays were in good agreement with finite difference time domain modeling. Critically, these results were obtained for near UV wavelengths (∼360  nm), which is relevant to a number of biosensing applications.