Near-field terahertz imaging of ferroelectric domains in barium titanate

Abstract

We report on results of a near-field imaging experiment with broadband terahertz pulses applied to a BaTiO3 multidomain single crystal. Data with a spatial resolution below 15 µm were collected by our scanning time-domain terahertz imaging setup. We performed the scanning by an asymmetric skewed sapphire probe metallised from two sides ended with a 60 µm × 140 µm facet. The imaging scans were performed with various angles of the polarisation of the probing field with respect to the direction of the domain walls in order to identify the orientations with optimal sensitivity. The raw experimental data were prewhitened and processed by the singular value decomposition. In this way, independent components belonging to experimental features (polarisation, noise and external perturbations) were found. The spatial resolution of the sensing probe was found significantly higher than that allowed by the outer dimensions of the probe end facet. This result was also confirmed by electromagnetic-field simulations.