  As properties of mono- to few layers of exfoliated van der Waals
heterostructures are heavily dependent on their thicknesses, accurate thickness
measurement becomes imperative in their study. Commonly used atomic force
microscopy and Raman spectroscopy techniques may be invasive and produce
inconclusive results. Alternatively, spectroscopic ellipsometry is limited by
tens-of-microns lateral resolution and/or low data acquisition rates,
inhibiting its utilization for micro-scale exfoliated flakes. In this work, we
demonstrate a Fourier imaging spectroscopic micro-ellipsometer with sub-5
microns lateral resolution along with fast data acquisition rate and present
angstrom-level accurate and consistent thickness mapping on mono-, bi- and
trilayers of graphene, hexagonal boron nitride and transition metal
dichalcogenide (MoS2, WS2, MoSe2, WSe2) flakes. We show that the optical
microscope integrated ellipsometer can also map minute thickness variations
over a micro-scale flake. In addition, our system addresses the pertinent issue
of identifying monolayer thick hBN.
