Review of Anisotropic Terahertz Material Response

TL;DR

This review discusses recent advances in anisotropic material responses in the terahertz range, highlighting their potential for developing polarization optics despite current technological limitations.

Contribution

It compiles and analyzes novel observations of linear and circular anisotropy in THz materials, emphasizing their implications for future polarization optical devices.

Findings

Macroscopically aligned carbon nanotubes exhibit extreme linear anisotropy.

Giant Faraday effects are observed in semiconductors and 2D electron systems.

Various anisotropic responses have long-term implications for THz polarization optics.

Abstract

Anisotropy is ubiquitous in solids and enhanced in low-dimensional materials. In response to an electromagnetic wave, anisotropic absorptive and refractive properties result in dichroic and birefringent optical phenomena both in the linear and nonlinear optics regimes. Such material properties have led to a diverse array of useful polarization components in the visible and near-infrared, but mature technology is non-existent in the terahertz (THz). Here, we review several novel types of anisotropic material responses observed in the THz frequency range, including both linear and circular anisotropy, which have long-term implications for the development of THz polarization optics. We start with the extreme linear anisotropy of macroscopically aligned carbon nanotubes, arising from their intrinsically anisotropic dynamic conductivity. Magnetically induced anisotropy will then be reviewed, including the giant Faraday effects observed in semiconductors, semimetals, and two-dimensional electron systems.