The nonlinear saturation absorption of nanometric metallic shell controlled by the local dielectric constant and shell thickness

The frequency-dependent nonlinear absorption coefficient of nanometric gold shell has been studied theoretically. The negative peaks of nonlinear absorption spectra always take place near the resonance frequency of localized surface plasmonm resonance (LSPR), whereas the positive peaks always take place with the wavelength longer than that of LSPR. Increasing the gold shell thickness leads to the blue shift of both negative and positive peaks. When the core dielectric constant is less than that of outer surrounding, the negative peak plays the major role in the nonlinear absorption spectrum, whereas the negative peaks fade down to be comparable with positive peaks at different frequency-bands as the core dielectric constant is greater. Furthermore, the negative peak gets intense greatly as the outer surrounding dielectric constant is increased and the nanoshell thickness gets thinner. Either saturation absorption peak or reverse saturation absorption peak can be controlled at desired frequency band of nonlinear absorption spectrum in the same nanocompsite medium. This effect provides a potential application in optical sensor and optical limiting element. Moreover, the strong saturation absorption effect is promising for a implementing of a bistable optical device.