Abstract: Nonlinear absorption of yellow (587 nm) laser light by a liquid crystal material has been investigated using dual-pulse (`excite/probe') measurement techniques. Two separate absorption phenomena were observed; these were identified as two-photon absorption from the ground state, and single-photon absorption from an excited state whose lifetime exceeded 10 ns. Strong blue fluorescence was emitted by the material following excitation. Measurements of the spectrum of this fluorescence identify its source as the S$-1$/ to S$-0$/ transition. Lifetime and energy level evidence suggest that the S$-1$/ state may also be responsible for the excited state absorption. Estimates of the absorption cross-sections $sigma$-ex$//$sigma$-gr$/ exceeds 3 $MUL 10$+5$/, which suggests that the excited state absorption may be exploited to produce very strong nonlinear effects. !10
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