Three-photon-absorption-induced fluorescence and optical limiting effects in an organic compound

Three-photon-absorption-induced frequency-upconversion fluorescence emission has been observed in a solution of 2, 5-benzothiazole 3, 4-didecyloxy thiophene (BBTDOT) in tetrahydrofuran, pumped with 10-ns Q-switched 1.06-mm laser pulses. The spectral peak of the observed fluorescence emission is located in the 450–480-nm range, and the intensity dependence of the visible emission on the IR excitation obeys the cubic law. At a higher solute concentration (0.18 M/L) and moderate IR excitation intensity levels (50–200 MW/cm²), obvious optical limiting behavior has been observed as a result of three-photon absorption. The measured nonlinear absorption coeff icient and the corresponding molecular three-photon-absorption cross section are y ­ 2.7 × 1^-18 cm³/W² and σ₃= 8.8 3 10^-76 cm⁶ s², respectively.