Tuning the Cerenkov second harmonic contrast from ferroelectric domain walls via anomalous dispersion

Second harmonic (SH) microscopy represents a powerful tool for the investigation of crystalline systems, such as ferroelectrics and their domain walls (DWs). Under the condition of normal dispersion, i.e., the refractive index at the SH wavelength is larger as compared to the refractive index at the fundamental wavelength, n(2 omega) > n(omega), bulk crystals will generate no SH signal. Should the bulk, however, contain DWs, an appreciable SH signal will still be detectable at the location of DWs stemming from the Cerenkov mechanism. In this work, we demonstrate both how SH signals are generated in bulk media and how the Cerenkov mechanism can be inhibited by using anomalous dispersion, i.e., n(omega) > n(2 omega). This allows us to quantitatively estimate the relative strength of the Cerenkov compared to other SH contrast mechanisms in DWs, such as the interference contrast. The results are in agreement with previous experiments based on the geometric separation of the signals. Due to the observed, strong Cerenkov contrast, such signal contributions may not be neglected in polarimetry studies of ferroelectric DWs in the future. (c) 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

Second harmonic (SH) microscopy is a powerful tool for studying crystalline systems, including ferroelectrics and their domain walls. This study demonstrates the generation of SH signals in bulk media and the inhibition of the Cerenkov mechanism using anomalous dispersion. The relative strength of the Cerenkov compared to other SH contrast mechanisms in domain walls can be quantitatively estimated.