Strong anomalous optical dispersion of graphene: complex refractive index measured by Picometrology.

We introduce spinning-disc Picometrology which is designed to measure complex refractive index of ultra-thin and size-limited sample deposited on a solid surface. Picometrology is applied to measure the refractive index of graphene on thermal oxide on silicon. The refractive index varies from ñg = 2.4-1.0i at 532 nm to ñg = 3.0-1.4i at 633 nm at room temperature. The dispersion is five times stronger than bulk graphite (2.67- 1.34i to 2.73-1.42i from 532 nm to 633 nm).