Elliptically polarized terahertz radiation from a chiral oxide

TL;DR

This paper demonstrates a simple method to control the polarization state of terahertz radiation generated from a chiral oxide, enabling elliptic and nearly linear polarization by adjusting the incident laser polarization.

Contribution

It introduces a novel approach to manipulate terahertz polarization using a chiral oxide and explains the underlying mechanisms involving velocity mismatch and optical activity.

Findings

Terahertz radiation from Bi12GeO20 is elliptically polarized with ellipticity ~0.37.

The polarization ellipticity can be tuned to nearly zero by changing incident laser polarization.

The polarization control is due to velocity mismatch and optical activity effects.

Abstract

Polarization control of terahertz wave is a challenging subject in terahertz science and technology. Here, we report a simple method to control polarization state of the terahertz wave in terahertz generation process. At room temperature, terahertz radiation from a noncentrosymmetric and chiral oxide, sillenite Bi$_{12}$GeO$_{20}$, is observed by the irradiation of linearly polarized femtosecond laser pulses at 800 nm. The polarization state of the emitted terahertz wave is found to be elliptic with an ellipticity of $\sim$0.37$\pm$0.10. Furthermore, the ellipticity was altered to a nearly zero ($\sim$0.01$\pm$0.01) by changing the polarization of the incident linearly polarized femtosecond laser pulses. Such a terahertz radiation characteristic is attributable to variation of the polarization state of the emitted terahertz waves, which is induced by retardation due to the velocity mismatch between the incident femtosecond laser pulse and generated terahertz wave and by the polarization tilting due to the optical activity at 800 nm.