Microscopic study of resonant third-harmonic generation from amorphous silicon nanodisk arrays

A detailed microscopic study of third-harmonic generation (THG) from two-dimensional arrays of sub-wavelength spaced amorphous silicon nanodisks is reported. The arrays are designed to support broadband, minimally angle-sensitive resonances for the fundamental excitation wavelength in the 1500 nm region. This results in resonantly enhanced visible THG in the green spectral range with similar to 500-fold enhancement on-resonance, compared to the un-patterned a-Si thin-film. THG multispectral microscopic imaging reveals individual nanodisks with enhanced non-linear signal on-resonance. For increasing pump intensities, spatially dependent saturation effects are observed for the first time, to the best of our knowledge, in such dielectric nanostructure arrays with THG images showing a reversal of contrast. (C) 2018 Optical Society of America