  We report a determination of the complex in-plane dielectric function of
monolayers of four transition metal dichalcogenides: MoS2, MoSe2, WS2 and WSe2,
for photon energies from 1.5 - 3 eV. The results were obtained from reflection
spectra using a Kramers-Kronig constrained variational analysis. From the
dielectric functions, we obtain the absolute absorbance of the monolayers. We
also provide a comparison of the dielectric function for the monolayers with
the corresponding bulk materials.
