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

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 threefold 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. Following a thorough experimental study, including the effects of repetition rate or pulse length, the observed results were ascribed to heat-induced SHG variation. In addition to revealing a new mechanism of laser-induced SHG variation, our results also provide a means to identify this mechanism.

SUBMITTER: Lukes J 

PROVIDER: S-EPMC10227052 | biostudies-literature | 2023 May

REPOSITORIES: biostudies-literature