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The nonlinear photonic behavior of a quasi-hexagonally close packed monolayer composed of gold nanospheres on glass substrate was studied using Z-scan with femtosecond laser pulses (70fs, 1kHz) in two regimes: on-resonance (~800nm) [1] and off-resonance (1500nm) [2]. The gold metasurface were prepared by self-assembly [3]. The third order nonlinear optical response of the gold metasurface revealed enhanced optical nonlinearities for both on and off-resonance. The values of n2 = -7.9x10-13 (-1.05x10-14) m2W-1 at 800nm(1500nm) was inferred for the nonlinear refractive index from closed aperture Z-scan, and 2 -0.9x10-6 (3x10-8) mW-1 at 800nm (1500nm) was inferred for nonlinear absorption from the open aperture data.
Time resolved measurements using a Kerr gate setup showed an off-resonance ~2ps response time. We also studied the nonlinear response of the metasurface as a function of wavelength/linear refractive index, and observed that Miller's rule is not valid in this case.
The large n2 value is four orders-of-magnitude larger, in modulus, than in silica glass at 1500 nm. The role of the metasurface arrangement as well as the origin of the gold nonlinearity in the short-wave infrared region is discussed.
[1] J. Fontana, M. Maldonado, N. Charipar, S. A. Trammell, R. Nita, J. Naciri, A. Pique, B. R. Ratna, and A. S. L.
Gomes, “Linear and nonlinear optical characterization of self-assembled, large-area gold nanosphere metasurfaces
with sub-nanometer gaps,” Opt. Express 24(24), 27360-27370 (2016).
[2] L. S. Menezes, L. H. Acioli, M. Maldonado, J. Naciri, N. Charipar, J. Fontana, D. Rativa, C. B. de Araujo and A. S. L.
Gomes,
Large third-order nonlinear susceptibility from a gold metasurface far-off the plasmonic ressonance, TO be submitted.
[3] J. Fontana, J. Naciri, R. Rendell, and B. R. Ratna, “Macroscopic self- assembly and optical characterization of
nanoparticle-ligand metamaterials,” Adv. Opt. Mater. 1(1), 100-106 (2013).
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