Second-Harmonic Generation from Dendritic Fractal Structures

Nanostructured conductive surfaces have been exploited for a variety of applications in photonics and optical sensing due to the broad spectral tunability of the localized surface plasmon resonances and the subsequent electromagnetic field confinement in the vicinity of the structures. Herein, we report on the second-order nonlinear optical properties of dendritic fractal structures with specific geometries that were optimized to yield resonances at both the fundamental and the second-harmonic wavelengths. Using a femtosecond excitation at 800 nm, second-harmonic generation microscopy experiments were conducted on a series of gold fractal dendritic structures with and without center of inversion. The polarized second-harmonic maps reveal the local character of the second-harmonic generation (SHG) emission and even structures with center of inversion show SHG activity in the periphery of the core dendron where non-centrosymmetric features are forming the higher fractal generations. The experiments were correlated using finite-difference time-domain electromagnetic time modelling performed at both the fundamental and second-harmonic wavelengths.