Optical alignment of oval graphene flakes

TL;DR

This paper investigates how linearly polarized light can exert forces and torques on oval graphene flakes, enabling their controlled optical alignment in the far-infrared spectrum through numerical and analytical methods.

Contribution

It introduces a combined numerical and analytical approach to control the optical alignment of oval graphene flakes using far-infrared light.

Findings

Oval flakes experience torque allowing rotation and orientation.

Alignment depends on wavelength, being either parallel or perpendicular.

Full control over spatial alignment is demonstrated.

Abstract

Patterned graphene, as an atomically thin layer, supports localized surface plasmon-polaritons (LSPPs) at mid-infrared or far-infrared frequencies. This provides a pronounced optical force/torque in addition to large optical cross sections and will make it an ideal candidate for optical manipulation. Here, we study the optical force and torque exerted by a linearly polarized plane wave on circular and oval graphene flakes. Whereas the torque vanishes for circular flakes, the finite torque allows rotating and orienting oval flakes relative to the electric field polarization. Depending on the wavelength, the alignment is either perpendicular or parallel. In our contribution, we rely on full-wave numerical simulation but also on an analytical model that treats the graphene flakes in dipole approximation. The presented results reveal a good level of control on the spatial alignment of graphene flakes subjected to far-infrared illumination.