The nonlinear optical properties of N,N-diphenyl-7-$LB@2-(4- pyridinyl) ethenyl$RB@-9,9-di-n-decylfluoren-2-amine $LB@AF- 50$RB have been investigated. The nonlinear absorption of a saturated solution of this material in acetone was investigated with 430 femtosecond pulses at 790 nm. From these results, the two-photon absorption cross-section was determined to be 25 $MUL 10$+$MIN@50$/ cm$+4$/sec/photon molecule. This number is in agreement (within a factor of 2) with theoretical calculations. Nonlinear absorption and optical limiting measurements were also made using a Nd:YAG pumped dye laser with 4.3 ns pulses at 694 nm. These results suggest inherent differences in the performance of two-photon absorbing materials in these two different geometries.
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