  Two-dimensional materials such as MoS2 have attracted much attention in
recent years due to their fascinating optoelectronic properties. Dielectric
property of MoS2 is desired for the optoelectronic application. In this paper,
terahertz (THz) time-domain spectroscopy and ellipsometry technology are
employed to investigate the dielectric response of MoS2 crystal in THz and
visible region. The real and imaginary parts of the complex dielectric constant
of MoS2 crystal are found to follow a Drude model in THz region, which is due
to the intrinsic carrier absorption. In visible region, the general trend of
the complex dielectric constant is found to be described with a Lorentz model,
while two remarkable peaks are observed at 1.85 and 2.03 eV, which have been
attributed to the splitting arising from the combined effect of interlayer
coupling and spin-orbit coupling. This work affords the fundamental dielectric
data for the future optoelectronic applications with MoS2.
