Saturable absorption and the changeover from saturable absorption to reverse saturable absorption of MoS2 nanoflake array films

Abstract

MoS₂ nanoflake array films on different glass substrates were fabricated by an in situ growth method. The nonlinear absorption (NLA) properties of the MoS₂ nanoflake array films were investigated by an open-aperture Z-scan technique. The MoS₂ nanoflake array films exhibited different NLA properties dependent on the input energy. In the case of lower input energy, the films exhibited saturable absorption (SA); however, if the input energy was increased, a changeover from SA to reverse saturable absorption (RSA) was observed. The interesting NLA properties of the films could be attributed to the competition between the ground-state absorption and the excited-state absorption in terms of the energy-level model of MoS₂.