Fig. 3. Schematic representation of the optical absorption for regimes of low and high pump intensities. The left exhibits plasma ground-state bleaching (third-order nonlinearity) related to saturable absorption. The right displays three-photon absorption (fifth-order nonlinearity) related to reverse saturable absorption. S0 and S1 are the ground state and first singlet state, respectively. hν is the pump light energy. The dashed line is the virtual states.
