The properties of dichroism in the nonlinear absorption response of silver nanoprism arrays are experimentally investigated by the z-scan technique. Open aperture z-scan measurements are performed with a picosecond laser at a low repetition rate to excite the third-order electronic component of the optical nonlinearity for different linear polarization directions of the incident beam. A strong saturable absorber behavior is observed for all the linear polarization orientations and a continuous, sinusoidal modulation of the nonlinear absorption coefficient (up to about 30% of its absolute value) is demonstrated as a function of the polarization angle. The dichroic nonlinear absorption of the samples is explained by taking into account the polarization-dependent local electric-field distribution in the nanoprism arrays, as demonstrated by finite elements method electrodynamic simulations. These findings make silver nanoprism arrays an ideal platform for the development of nanophotonic devices with fast, strong and tunable nonlinear optical responses.
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