Using beamshifts to measure the optical conductivity of graphene

By Nathaniel Hermosa II

Dr. Nathaniel Hermosa II is a member of the Photonics Research Laboratory. The article below is a simplified version of his work published in Journal of Optics on 16 January 2016. The article can be accessed here.

When a beam of light strikes a surface, its reflection can deviate from what is predicted by the law of reflection. Light can reflect as if it is coming from above or below the surface or with a slight change in its angle of propagation (top). It can also reflect coming from the left or the right or with a slight skew in the left or the right where it is incident (bottom). These shifts are known as the Goos-Hnchen (GH) and Imbert-Federov (IF) shifts, respectively. The deviation depends on the polarization of the beam, on the shape of the beam and on the properties of the reflecting materials. Measuring the beam shift can therefore lead to the determination of such properties, including the material’s optical conductivity.

The study presents the calculation of tiny beamshifts reflected from the surface to determine graphene’s optical conductivity. All four beamshifts, spatial and angular GH and IF, appear depending on the state of polarization of the incident beam. The calculated shifts are easily detectable in experiments such as measuring the differential beamshifts using a quadrant cell.

Unlike previous methods, the proposed technique is nondestructive and does not need extra processing of data. The deviation can also instantaneously change with the material properties, making this technique dynamic.