Low- and high-order nonlinear optical properties of Ag 2 S quantum dot thin films

Abstract

Thin films containing small-sized quantum dots (QDs) and nanoparticles have shown strong optical nonlinearities caused by the confinement effect. Here, we report the study of third-order optical nonlinearities of silver sulfide (Ag 2 S) QD thin films using 800 and 400 nm, 30 fs pulses. The absorption spectrometry and transmission electron microscopy are used to characterize the synthesized 80 and 500 nm Ag 2 S QD films. The giant enhancement of nonlinearities is observed up to three to six orders of magnitude larger compared to those for the bulk and liquid Ag 2 S samples. We also demonstrate the efficient high-order harmonic generation in the plasmas produced during ablation of the Ag 2 S QD thin films. The analysis of the dynamics of the QD-containing plasma spreading allowed optimization of the delay between the heating and the driving pulses for an enhancement of harmonics conversion efficiency.