  In this manuscript, we report the results of optical properties of SnS thin
films, deposited on FTO coated glass substrates at room temperature by thermal
evaporation technique. In addition, the effect of film thickness on the optical
behavior of FTO/SnS is analyzed and obtained results are compared with data of
SnS films grown on glass and ITO substrates. Our study indicates that the
properties of SnS film are independent of the substrate material. Further, the
influence of the film thickness on the other optical parameters including,
linear and third order nonlinear optical constants and dispersion parameters
have also been investigated using the transmission, reflection, and absorption
spectra. It is found that the optical band gap decreases from 2.07 to 1.30 eV
with increase in SnS film thickness, whereas the refractive index increases
with increasing thickness. Additionally, the oscillator energy, and the
dispersion energy are estimated using WempleDiDomenico approach. The dispersion
energies are in the range of 7.20 to 4.59 eV, while the oscillator energies of
the thin films are in the range of 5.49 to 2.24 eV. Moreover, the nonlinear
refractive index, and optical susceptibility are calculated by using the
empirical relation of Tichy and Ticha. The volume of data suggests optical
properties of SnS thin films are strongly dependent on film thickness.
