Abnormal Spatial Shifts in Graphene Measured via the
Beam Displacement Amplification Technique: Implications for Sensors
Based on the Goos–Hänchen Effect
The
Goos–Hänchen (GH) shift and Imbert–Fedorov
(IF) shift caused by light–matter and spin–orbit interactions
can reveal the intrinsic properties of nanomaterials. We propose a
beam displacement amplification technique (BDAT) that can break the
optical diffraction limit in beam displacement measurements. The displacement
resolution of the BDAT is 4 nm, and the detection size is 5 μm,
which is very suitable for the displacement measurement of mechanically
exfoliated two-dimensional (2D) materials with a thickness on the
scale of nanometers. With the help of the BDAT, we measured the GH
shift and IF shift of graphene with different thicknesses. We found
that the s-polarized light has a strong absorption effect in graphene
with a thickness of approximately 15 nm, causing abnormal GH and IF
shifts. This abnormal GH shift combined with the BDAT can be applied
to detect changes in the refractive index, with a sensitivity of up
to 9.5 × 10–8 per reflective index unit. The
BDAT holds promise as the most widespread means of displacement measurement,
uncovering the properties of 2D materials and enhancing their application
potential.