Optical limiting and dynamical two-photon absorption of organic compounds for a nanosecond pulse

Abstract

The nonlinear absorption and propagation of nanosecond laser pulses in a strong two-photon absorption (TPA) organic medium (4,4'-bis(diphenylamino) stilbene (BDPAS)) are studied by solving coupled rate equations and field intensity equations. Hybrid density functional theory is used to calculate the electronic structures and the static TPA properties of the compound. Ab initio calculations show that this molecular system should be described by a three-level model in the visible light regime. Special attention has been paid to its optical limiting behaviour and dynamical TPA cross section. Our numerical results show that the BDPAS molecular medium exhibits a strong optical limiting behaviour. For rather short pulses, the dynamical TPA cross section is almost a linearly increasing function of the pulse width. For longer pulses, the dynamical TPA cross section is largely enhanced because of the two-step TPA. The performance of optical limiting strongly depends on the pulse width, the thickness and the concentration of the absorber.