Broadband saturable absorption and optical limiting in graphene-polymer composites

Nonlinear optical properties of a graphene-polyvinyl alcohol composite are studied using an irradiance-scan setup. The measurements are carried out at 785 nm and 1064 nm in the nanosecond and picoseconds temporal regimes, respectively. It is shown that the output fluence readily clamps with increasing input and graphene concentration due to nonlinear absorption and scattering. Furthermore, the nonlinear transmission demonstrates weak saturable absorption followed by strong optical limiting. The nonlinear coefficients βeff and Isat calculated via numerical fitting show that βeff depends on the graphene content and increases significantly in nanosecond regime due to high degree of thermally induced nonlinear scattering.