Two-photon fluorescence of Coumarin 30 excited by optimally shaped pulses.

We optimized the two-photon fluorescence (TPF) of a Coumarin 30 dye by using a feedback-controlled femtosecond pulse shaping technique. For optimization we implemented an evolutionary algorithm with a liquid crystal phase-only pulse shaper in a folded 4f setup. The optimization procedure applied to the second harmonic generation, and TPF noticeably improved the output signals and demonstrated good convergence. In addition, signal ratios involving TPF and second harmonic generation (SHG) were successfully optimized. The correlation between TPF and SHG was studied, and it was found to decrease when the pulse shape was close to the optimum. These experimental results are of interest for potential applications of coherent control to complex molecular systems as well as in biomedical imaging.