Enhanced Second Harmonic Generation From Noncentrosymmetric Nanohole Arrays in a Gold Film

A subwavelength aperture array in a gold film is fabricated for the purpose of second harmonic generation (SHG). The sunglass aperture shape is chosen to have an apex to increase the local field; however, unlike past research on double-hole structures, the inversion symmetry of the structure is intentionally broken to enhance the SHG. A systematic study of the influence of array periodicity and aperture shape is provided. The conditions for maximum SHG are discussed in terms of local field enhancement, excitation of the localized surface plasmon resonances, and the influence of array periodicity. Fully vectorial finite-difference electromagnetic calculations provide the effective index of the aperture modes, as well as the surface electric field to quantify the discussion. Both the sunglass and double-hole structures are promising for future implementation with less-expensive optical lithography since it is mainly composed of two holes; yet they produce sharp apexes for enhanced local field and thereby enhanced nonlinear light-matter interaction.