Focusing characteristics of polarized second-harmonic emission at non-Ising polar domain walls

Abstract

Non-Ising polar domain walls have recently emerged as individual two-dimensional materials exhibiting localized nonlinear optical emission. The analysis of this emitted light often requires focusing with high apertures. As a result, the vectorial properties of light come into play. This study provides an analytic treatment of the vector light fields’ effect on the polarized second-harmonic emission (SHG) arising at polar domain walls. While confined optical fields are expected to alter the SHG polarization response, we identify extrinsic and intrinsic properties capable of canceling focusing effects. We determine a precise combination of the fundamental wave polarization and orientation of the domain walls at which focusing effects are negligible. Furthermore, the perimeter defined by the domain walls intrinsic optical parameters below which focusing effects are negligible is extracted from a systematic focus-dependent analysis. Our study provides the necessary methodology and precautions to probe the internal structure of non-Ising domain walls with confined optical fields, and it can be extended to explore newly discovered ferroelectric topologic nanostructures.