Thermally-induced nonlinear optical properties of silver nano-films near surface plasmon resonance

Abstract Silver nano-films with thicknesses of 5, 10 and 50 nm were grown using e-beam evaporation on glass substrates at room temperature in order to investigate their thermal nonlinear optical properties near surface plasmon resonance. The nonlinear response was verified using single beam z-scan setup in the cw regime. At 5 and 10 nm thickness, the films showed plasmonic resonance at 488 and 518 nm, respectively. The 50 nm films illustrated normal bulk behavior. Optical nonlinearities were stimulated at three different wavelengths, namely, 405, 532 and, 650 nm. Self-focusing and saturable absorption behavior was observed and compared at these wavelengths. The highest response was obtained at 532 nm close to the plasmonic wavelengths in both films. This behavior is related to the ultimate concentration of the optical power and hence, the temperature, to the nanometer range resulting in a large index change within a predicted time scale of sub-picoseconds. This outcome could pave the way for ultrafast thermal nonlinearity in nanomaterials. A discussion of this behavior and its consequence is presented.