Complex refractive index measurement for atomic-layer materials via surface plasmon resonance holographic microscopy

The optical characterization of atomic-layer materials is significant for the clarification of fundamental physical properties of newly emerging nanomaterials. Here we propose to utilize the surface plasmon resonance (SPR) holographic microscopy to measure the complex refractive index (RI) of atomic-layer materials (i.e., graphene). We unambiguously determine the complex RI of single-layer graphene and few-layer graphene by fitting the measured reflection phase shift difference with theoretical values under the five-layer SPR model. The measurement results of the graphene layer grown by chemical vapor deposition at the visible range agree with the previous reports. Our method offers a cost-effective and robust avenue to characterize the complex RI of atomic-layer materials with distinct optical absorption, particularly the two-dimensional materials.