New synthesized fluorophores with large MPE cross-sections have been reported in the course of research directed toward enhancing optical limiting absorption. We have established a collaboration with Dr. J. Perry and Dr. Seth Marder, organic chemists of Jet Propulsion Lab (JPL), to explore design and prediction capabilities for new and promising fluorophores with large MPE cross-sections. Our preliminary data show that four of the ten compounds synthesized by the JPL group have effective two photon cross sections exceeding 1000 GM. Note that most common fluorophores have cross-sections on the order of 10 GM.

A recent emphasis of the lab has been the use of three photon excitation (3PE) microscopy to access normally <300 nm excited native indoleamine fluorescence. Red light 3PE alleviates the need for deep UV optics and their associated aberrations and low transmissivities. Nonlinear excitation is also intrinsically localized to the focal plane and thus is potentially less invasive than single photon techniques. Using this method we have imaged serotonin-containing secretory granules in RBL-2H3 cells (Maiti, 1997), which are viable and release upon stimulation. The feasibility of these experiments was first suggested by our measured 3PE monoamine cross-sections shown below:

For more MPE cross-section measurements and measurement techniques see:

C. Xu, J. Guild, W.W. Webb and W. Denk. Opt. Lett., 20: 2372, 1995.

C. Xu and W.W. Webb. J. Opt. Soc. Am. B, 13:481, 1996.

C. Xu, W.R. Zipfel, J.B. Shear, R.M. Williams and W.W. Webb. Proc. Nat. Acad. Sci, 93:10763, 1996.

C. Xu, R.M. Williams, W.R. Zipfel and W.W. Webb. Bioimaging, 4:198, 1996.

S. Maiti, J.B. Shear, R.M. Williams, W. R. Zipfel and W.W. Webb. Science, 275:530, 1997.