Two-photon absorption in mesoionic compounds pumped at the visible and at the infrared

Intensity dependent transmission and laser-induced fluorescence were observed in liquid solutions of mesoionic compounds (MIC) pumped with nanosecond lasers operating at 1064, 604, and 570 nm. The results indicate that two-photon absorption (TPA) is the dominant mechanism which causes the observed behavior. The TPA cross-sections measured have values from 0.33 x 10(-20) cm(4)/GW to 0.43 x 10(-18) cm(4)/GW. (C) 2000 Elsevier Science B.V. All rights reserved.