$\mu$-Raman Investigations of Periodically-Poled X-Cut Thin-Film Lithium Niobate for Integrated Optics

In this study, Raman micro-spectroscopy is utilized as an imaging technique for the analysis of periodically-poled x-cut thin-film lithium niobate (TFLN) samples. These materials are very promising candidates for high performance integrated nonlinear and quantum optical applications. Analyzing the different peak intensities and frequency shifts of the lithium niobate (LN) phonon modes by
$\mu$
-Raman spectroscopy (
$\mu \text{RS}$
) allows to map and visualize the domain polarity and domain wall (DW) contrasts with high precision. Notably, these signatures are similar to the ones found for bulk LN, but exhibit larger frequency shifts in TFLN, which hints towards larger strain fields and built-in electric fields in these samples.
$\mu \text{RS}$
thus not only serves as a powerful imaging technique, but equally provides in-situ analytical fingerprints in order to both differentiate domains from DWs, and to provide a structure-sensitive mimic for optimizing TFLN poling processes.