Free-carrier absorption and optical limiting in the suspensions of CuS and Cu 2 O hollow spheres

In order to reveal the optical limiting mechanisms of semiconductor hollow spheres, the nonlinear optical properties of CuS and Cu 2 O hollow spheres were investigated via the fluence-dependent transmittance and the nonlinear scattering measurements. The CuS and Cu 2 O hollow spheres have similar morphologies and different types of optical band-gap. The experimental results show that the optical limiting performance of CuS is better than that of Cu 2 O, although the nonlinear scattering of Cu 2 O is stronger than that of CuS. Free-carrier absorption based on the delocalized carriers (holes) in CuS is believed to play an important role in the optical limiting effects. The merits of the structure of semiconductor hollow spheres used for optical limiting were discussed.