Second harmonic generation by excitation of coupled two dimensional silver nanoresonantors

Abstract

Second harmonic (SH) generation enhancement from nanoantennas and nano-dimers has been observed both in near and far fields [1–3]. In a recent work we studied SH generation in gold nanowires pointing out the possibility to tailor the properties of the generated signal by proper design of the system [4]. Here we report results of calculations performed on Silver coupled 2D-nanoresonators (NR). Coupling is responsible for the formation of resonant modes that can be localized on small portions of the structure or distributed over the whole structure. Different field profiles can be obtained by varying the parameters of the input field (i.e. the wavelength). The radiation pattern of the generated SH field is obtained by considering linear scattering and the structure behaves as an antenna for the SH field. As an example we report results in figure 1 for a 4-block structure. We used a method of integration based on the Green tensor operating in the frequency regime[4], which allows to distinguish the contributions of surface and volume to the nonlinear response. We note that different configurations of the pump field lead to different SH far-field emission patterns. In particular the field at 460 nm is emitted only in the backward direction with respect to the direction of the pump field; also, the main emission lobe is centred at a different angle with respect to the case of the field of SH at 495 nm. The effect of complex structures is considered and discussed. In conclusion our calculations show that the angular emission profile of the SH field contains information about the spatial location of the pump field hot spots at different frequencies. Applications to a new class of sensors and nonlinear nano sources are discussed.