Two-photon absorption spectrum of silver nanoparticles

We have investigated the spectral dispersion of real and imaginary parts of third-order nonlinear optical susceptibility of silver nanospherical particles in the aqueous solution using Z-scan and antiresonant ring interferometric nonlinear spectroscopic (ARINS) techniques by femtosecond pulses from the modelocked Ti:Sapphire laser over the spectral range of 720-820 nm. The observed characteristic of imaginary part shows a peak at similar to 766 nm which coincides with the peak of spectral dispersion of real part induced thermally. The observed peak in the dispersion of nonlinear absorption coefficient at similar to 766 nm is attributed to the two-photon absorption. This two-photon resonance peak is attributed to l =2 plasmon (quadrupolar mode) arising from the phase retardation effects in the spherical nanoparticles present in our polydispersed sample with their diameters (80 +/- 20 nm) beyond the quasi-static limit. (C) 2012 Elsevier B.V. All rights reserved.