Optically enhanced second harmonic generation in silicon oxynitride thin films via local layer heating

TL;DR

This paper reports laser-induced enhancement of second harmonic generation in silicon nitride thin films, revealing complex behaviors influenced by local heating and material composition, with implications for nonlinear optical applications.

Contribution

It demonstrates laser-induced SHG enhancement in Si3N4 thin films and explores the complex effects of local heating and composition in silicon oxynitride films.

Findings

SHG enhancement observed in Si3N4 films due to laser irradiation

Complex SHG behavior in silicon oxynitride films linked to heating effects

Heat-induced SHG variation caused by multiphoton absorption

Abstract

Strong second harmonic generation (SHG) in silicon nitride has been extensively studied-among others, in terms of laser-induced SHG enhancement in Si3N4 waveguides. This enhancement has been ascribed to the all-optical poling induced by the coherent photogalvanic effect. Yet, an analogous process for Si3N4 thin films has not been reported. Our article reports on the observation of laser-induced 3-fold SHG enhancement in Si3N4 thin films. The observed enhancement has many features similar to all-optical poling, such as highly nonlinear power dependence, cumulative effect, or connection to the Si3N4-Si interface. However, identical experiments for low-oxygen silicon oxynitride thin films lead to complex behavior, including laser-induced SHG reduction. By a thorough experimental study, the observed results were ascribed to heat-induced SHG variation caused by multiphoton absorption. Such behavior indicates that the origin of optically-induced SHG enhancement in SiOxNy-Si structures can be a complex interplay of various phenomena.