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

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.