  Indium Sulphide (InS) single crystals are successfully grown by In flux.
Single crystal X-ray diffraction shows orthorhombic structure of Pnnm space
group. Ellipsometry measurements performed on the (010) oriented crystal
exhibit low anisotropy in the 300-1000 nm wavelength range and consequently
negligible THz emission is observed. Optical band gap of $2.09 eV$ is deduced
from linear optical measurements. Nonlinear optical properties are studied by
single beam Z-scan measurements at 800 nm, where two-photon absorption is
present. Nonlinear refractive index and absorption coefficient are estimated to
be $\eta_2$ = $2.3 10^{-11} cm^2/W$ and $\beta$= $62.4 cm/ GW$, respectively
for excitation intensity of $0.32 GW/cm^2$. The origin of nonlinearity in InS
crystal is accounted to be due to the third-order anharmonic motion of the
bound electrons.
