Nonlocality in Ag nanocubes: dependence on the concentration and incident wavelength

Colloidal silver nanocubes systems were analyzed by the Z-scan technique. Two systems with edge length of 99 and 215 nm were obtained by the polyol method. Concentrations 0.6, 0.4 and 0.2 mg ml⁻¹ were analyzed for each particle size. Nonlinear excitation was performed with laser pulses of 26 ps, at repetition rate of 10 Hz, using wavelengths of 355, 532 and 1064 nm. The two first one wavelengths are close to surface plasmon resonance while the third one is out of resonance, for both systems. For sample featuring size of 99 nm, nonlinear absorption was observed: saturable for 355 nm and a shift from saturable to reversible for 532 nm for a specific concentration only. For 1064 nm, positive nonlinear optical refraction and saturable absorption could be observed only for sample of 215 nm. Experimental results showed that nonlinear response presents a nonlocal behavior which depends on incident wavelength. The nonlocality was affected by the concentration for 532 nm for size of 99 nm. Z-scan curves were fitted using an analytical expression for on axis far-field transmittance. (paper)