Unveiling optical in-plane anisotropy of 2D materials from oblique incidence of light

Abstract

In this work, we present a theoretical study of the dispersion of linearly polarized light between two dielectric media separated by an anisotropic two-dimensional (2D) material under oblique incidence. Assuming that the 2D material is a conducting sheet of negligible thickness, generalized Fresnel coefficients are derived as a function of usual quantities (e.g. refraction indexes and scattering angles) and the anisotropic in-plane optical conductivity of the interstitial 2D material. In particular, we analyzed the modifications due to the 2D material of two classical optical phenomena: the Brewster effect and the total internal reflection. As an application, our general findings are particularized for uniaxially strained graphene. Effects of a uniaxial strain on the Brewster angle and the reflectance (under total internal reflection) are evaluated as a function of the magnitude and direction of strain.

Effect of Uniform Strain on Graphene Surface Plasmon Excitations

“…Applying the boundary condition from Eq. ( 9), the field coefficients in the medium 1 can be related with the field coefficients of the medium 2 as follows [21,28,35,36],…”

“…Usually surface plasmon can be excited via evanescent waves using the Kretschmann configuration, Once, surface plasmon is excited in the Kretschmann configuration, a sharp minimum is observed in the refection coefficient versus incident angle (or wavelength) curve. Recently [28], a theoretical study of the dispersion of linearly polarized light between two dielectric media separated by an anisotropic graphene under oblique incidence has been reported considering the unstrained high frequency optical conductivity (equal to e 2 /4ħ for ħω>2Ef where Ef is the Fermi energy), the optical response of graphene is limited by the fine-structure constant α ≈ 1/137, which describes the coupling between light and relativistic electrons in quantum electrodynamics.…”

Atomically Thin, Optically Isotropic Films with 3D Nanotopography

“… 11 − 13 A primary bottleneck is the appalling angular performance, originating from a fundamental limitation on 2D materials; as a consequence of their atomic thinness, these materials interact only with in-plane polarized light, resulting in negligible out-of-plane responses (i.e., they exhibit strong anisotropy). 23 − 25 Being able to generate out-of-plane optical responses is a key challenge for engineering light–matter interactions in the angular domain.…”

“…Compact and tunable optical components are essential building blocks in flat optics for a wide range of applications that require small optical form factors such as lensless imaging, − beam steering devices, − and optical computation with stackable diffractive plates. − Recently, atomically thin materials have emerged as a next-generation platform − due to their ultimate dimensionality, architectural flexibility, , diversified library, − and exotic optical properties. , However, 2D material-based flat optics is at an early stage of development, limited to specific optical configurations such as normal incidence with small numerical apertures. − A primary bottleneck is the appalling angular performance, originating from a fundamental limitation on 2D materials; as a consequence of their atomic thinness, these materials interact only with in-plane polarized light, resulting in negligible out-of-plane responses (i.e., they exhibit strong anisotropy). − Being able to generate out-of-plane optical responses is a key challenge for engineering light–matter interactions in the angular domain.…”