Intensity favored switching of nonlinear optical absorption mechanism in silver nanoparticles under nanosecond pulsed laser excitation

摘要

Silver nanoparticles were prepared by pulsed laser ablation technique using a second harmonic wavelength (532 nm) ofQ switched Nd:YAG laser of 7 ns pulse width and 10 Hz repetition rates. Formation of Ag NPs was confirmed fromcharacteristic surface Plasmon resonance induced absorption (～418 nm). Spherical shape morphology and crystallinenature of structure were revealed from SEM and TEM analysis. Nonlinear optical studies were conducted by z scananalysis with the same laser system used for ablation. A switching of nonlinear absorption (saturable absorption toreverse saturable absorption) in Ag NPs were observed when on axis input intensity increased from 0.27 GW/cm~2 to0.83 GW/cm~2 and it could be attributed to interplay of different nonlinear absorption mechanisms, that is stronglydepends on the intensity of the excitation source. Self-defocusing nature of the sample was revealed from the closedaperture z scan analysis.