Nonlinear scattering, absorption, and refraction processes in the colloidal suspensions of Bi_2S_3 and CuS nanoparticles and their combined effects for broadband optical limiting

We report the nonlinear absorption, nonlinear scattering, nonlinear refraction, and optical limiting effects in two semiconductor suspensions formed by nanowires of Bi2S3 and nanometer-sized hollow spheres of CuS with nanosecond incident lasers when the incident photon energy (2.33 eV) is above the bandgap. The nonlinear scattering and nonlinear absorption processes were regarded as the mechanisms of the optical limiting effects. With the large positive nonlinear refractive index of those suspensions given by our Z-scan studies, we believed that the nonlinear variation of the refractive index mismatch is one of the reasonable origins of nonlinear scattering. Then, based on the combined effects of nonlinear scattering and absorption, the broadband optical limiting effects in those suspensions were observed. Two Bi2S3 nanowires with different morphologies have similar optical limiting properties.