Large irradiance limiting induced by three-photon absorption of a symmetrical fluorene-based molecule.

Herein, three-photon absorption (3PA) effect of a symmetrical fluorene-based molecule, pumped with 38 ps Q-switched 1064 nm laser pulses, is reported. An accurate Gaussian fitting method is used to obtain the three-photon absorption cross-section. The obtained three-photon absorption cross-section, 8.54 x 10(-76) cm(6) s(2), is very high. The irradiance limiting nonlinear transmittance is as low as 2% when the incident irradiance is 120 GW/cm(2). The geometry and electronic transition of the molecule are systematically studied by AM1 and TD SCF/DFT methods.