A laser-driven particle accelerator based on plasmonic nanoantennas is proposed and analyzed. The concept utilizes the enhancement and localization of the electric field by nanoantennas to maximize the acceleration gradient and to overcome potential metallic losses. The structure is optimized for accelerating relativistic particles using a femtosecond laser source operating at 800 nm and is shown to support the bandwidth of ultrashort laser pulses (up to 16 fs) while providing a high acceleration gradient potentially reaching 11.6 GV=m.

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We study theoretically various design considerations for efficient generation of second harmonic using a nonlinear substrate patterned with nano-antennas. The analysis is focused on a gap Bowtie nano-antenna array recessed in LiNbO₃ which is shown to be preferable over on surface structures due to field enhancement, field profile and linear and non-linear polarization considerations. In addition, we develop the nano-antenna counterpart of the Boyd-Klienmann model in order to analyze the impact of a Gaussian shaped fundamental beam on the generated second harmonic. Finally, we show that the dielectric properties of the substrate lead to preferable directions for the incident fundamental harmonic and the emission of the second harmonic. Our analyses lead to several design rules which can enhance second and high harmonic generation from nano-antennas arrays by several orders of magnitude.

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Dual-Vivaldi nanoantenna (DVA) arrays were designed, fabricated, and optically characterized in the infrared (IR) and visible regimes. The antenna arrays were characterized by measuring the scattered light at IR (1450-1640 nm) and visible (780 nm) spectral ranges. The radiation efficiency and the spectral response of the antennas were found to be in good agreement with numerical simulations. The results presented here demonstrate the extremely wideband nature of the DVAs and the strong impact of load at the antenna terminals on its scattering response. These properties, as well as their many degrees of freedom for design, render the DVAs excellent candidates for optical sensing applications.