Tunability of nonlinear optical properties of amorphous Cu–Al–O films induced by thermal oxidation

Abstract

A series of Cu–Al–O thin films with excellent nonlinear absorption properties were prepared by magnetron sputtering at room temperature. An absorption peak at around 440 nm was observed in the as-deposited thin films, with CuAlO2 as the main phase. After thermal oxidation at 400 °C, the surface roughness of the films decreased, the absorption peak was blue-shifted, with the optical band gap increased. Open aperture Z-scan measurements revealed that the as-deposited samples had strong saturable absorption and reached the maximum nonlinear absorption coefficient (β) of −6.29 × 10−5 cm/W. The nonlinear optical conversion from saturable absorption to reverse saturable absorption was observed in as-annealed samples with β values up to 2.592 × 10−5 cm/W. In addition, the time-domain finite-difference simulation results were basically consistent with those of the experimental results.