{'fraction_non_alphanumeric': 0.034408602150537634, 'fraction_numerical': 0.03655913978494624, 'mean_word_length': 4.8924050632911396, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Large third-order nonlinear susceptibility from a gold metasurface far off the plasmonic resonance

A large third-order nonlinear susceptibility was measured at 1500 nm from a self-assembled metasurface composed of a 2D superlattice of ligand-capped gold nanospheres. A self-defocusing nonlinear refractive index (n2=−1.05×10−10  cm2 W−1) and a nonlinear absorption coefficient (α2=3.00×10−6  cm W−1) were determined using the Z-scan technique with 70 fs pulses at 1 kHz. The nonlinearity response time was measured to be 1.42 ps using an Optical Kerr Gate configuration. The large n2 value is four orders of magnitude larger, in modulus, than in the silica glass substrate at 1500 nm. We show the nonlinear enhancement depends on the morphology of the metasurface and is due to collective near-neighbor coupling between the nanospheres. The physical origin of the gold nonlinearity in the short-wave infrared region is discussed.