The nonlinear optical properties of fluorescein-doped boric acid glass films have been investigated with sub-nanosecond laser pulses. With the use of degenerate four-wave mixing, large third-order susceptibilities of χ(3) ∼ 10−7 esu have been measured, connected to the relatively fast decay of the singlet state S1 (τ = 2.4 ± 0.6 ns). This particular system has a long-lived lowest-lying triplet state (0.1–1 s), and the transient nonlinear-optical and fluorescence properties show a marked dependence on the laser-pulse repetition rate in this time regime.
© 1992 Optical Society of America
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