Theoretical and experimental studies of three-photon-induced excited-state absorption

Abstract

We theoretically and experimentally study excited-state absorption (ESA) induced by three-photon absorption (3PA) under the excitation of ultrafast laser pulses. Based on five-level rate-equation theory, we obtain an analytical expression for the effective four-photon absorption coefficient that originates from both singlet-singlet (S-S) and triplet-triplet (T-T) ESA. We validate that the T-T ESA could be justifiably neglected in the femtosecond regime. Experimentally, we verify it in acetone solution of 2,4,5-trimethoxychalcone by performing femtosecond Z-scan measurements; at low excitation intensity, only 3PA is determined; and under the excitation of high intensity, however, we observe the concurrence of 3PA and 3PA-induced S-S ESA processes.