All-Optical Domain Inversion in LiNbO₃ Crystals by Visible Continuous-Wave Laser Irradiation

LiNbO₃ is a distinguished multifunctional material where ferroelectric domain engineering is of paramount importance. This degree of freedom of the spontaneous polarization remarkably enhances the applicability of LiNbO₃, for instance, in photonics. In this work, we report the first method for all-optical domain inversion of LiNbO₃ crystals using continuous-wave visible light. While we focus mainly on iron-doped LiNbO₃, the applicability of the method is also showcased in undoped congruent LiNbO₃. The technique is simple, cheap, and readily accessible. It relies on ubiquitous elements: a light source with low/moderate intensity, basic optics, and a conductive surrounding medium, e.g., water. Light-induced domain inversion is unequivocally demonstrated and characterized by combination of several experimental techniques: selective chemical etching, surface topography profilometry, pyroelectric trapping of charged microparticles, scanning electron microscopy, and 3D Čerenkov microscopy. The influence of light intensity, exposure time, laser spot size, and surrounding medium is thoroughly studied. To explain all-optical domain inversion, we propose a novel physical mechanism based on an anomalous interplay between the bulk photovoltaic effect and external electrostatic screening. Overall, our all-optical method offers straightforward implementation of LiNbO₃ ferroelectric domain engineering, potentially sparking new research endeavors aimed at novel optoelectronic applications of photovoltaic LiNbO₃ platforms.