Optical limiting in the red–NIR range with soluble two-photon absorbing molecules

Two-photon absorbing chromophores were designed and investigated for optical power limitation based on multiphoton absorption processes. These molecules combine very large two-photon absorption cross-sections (with typical σ2p maximum values of 3 × 10−20 cm4 GW−1 at 735 nm) and large excited-state cross-sections (with typical maximum σe values of 5 × 10−16 cm2) in the red–NIR region, as shown by two-photon-excited fluorescence and pump–probe Kerr ellipsometry experiments. Numerical simulations demonstrate that these chromophores show a strongly nonlinear absorption behavior suitable for optical limiting of ns pulses (with threshold values down to 1.5 × 10−2 J cm−2 for 0.55 ns pulses).