Intensity dependent nonlinear absorption of pyrylium chromophores

The intensity dependence of nonlinear absorption (NLA) of a series of pyrylium chromophores was studied with femtosecond pulses in their two-photon absorption spectral region to assess their potential as optical limiters. The open z-scan technique using different excitation intensities was employed. Fifth-order effects appear above a critical value of the irradiance and consequently of the first excited singlet-state population. Reverse saturable absorption (RSA) based on two-photon(TPA) and excited-state absorption (ESA) was dominant in most cases. The third- and fifth-order NLA coefficients and high ESA cross-sections of the order of 10(-15) cm(2) are presented at 760, 790 and 840 nm. (C) 2001 Elsevier Science B.V. All rights reserved.