Visualization of ferroelectric domains in boracite using emission of terahertz radiation

TL;DR

This paper demonstrates the visualization of ferroelectric domains in boracite using terahertz radiation emitted by femtosecond laser pulses, revealing domain structures and polarization states.

Contribution

It introduces a novel method for imaging ferroelectric domains in boracite via terahertz emission analysis, combining nonlinear optics and domain visualization.

Findings

Terahertz radiation is generated by optical rectification in boracite.

Ferroelectric domains are visualized through polarization analysis of emitted terahertz waves.

Domain walls and polarization vectors are mapped over a large crystal area.

Abstract

We report on the emission of terahertz radiation by irradiation of femtosecond laser pulses in non-centrosymmetric paraelectric and ferroelectric phases of Co$_3$B$_7$O$_{13}$I boracite. The Generation of the terahertz waves in both phases is caused by optical rectification via a second-order nonlinear optical effect. In the ferroelectric phase, we successfully visualized ferroelectric domains by analyzing the polarization state of the terahertz wave radiated from the crystal. In a large area of the crystal ($\sim$ 500 $\times$ 500 $\mu$m$^2$), the observed polarization vector of the radiated terahertz wave was tilted from directions of spontaneous polarization, i.e., [100]$_{\rm cub}$, [010]$_{\rm cub}$, and [001]$_{\rm cub}$ in cubic setting, which can be explained by the presence of a ferroelectric 90$^\circ$ domain wall of the (101)$_{\rm cub}$ plane.