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Nonlinear Absorption Spectroscopy of Organic Dyes
Eric W. Van Stryland, David J. Hagan, Olga V. Przhonska, Seth R. Marder, Scott Webster and Lazaro A. Padilha

We perform nonlinear spectroscopic measurements on organics materials with the aim of building a database of nonlinear optical parameters to aid in investigating and developing new experimental techniques and theories. Through years of collaboration, our groups have developed several experimental techniques and apparatus’ which have been precursors to developing a true nonlinear optical spectrophotometer needed to understand complex photophysical and photochemical processes. With these techniques, including: open- and closed-aperture Z-scan; white-light continuum (WLC) Z-scan; one- and two-photon fluorescence; emission and excitation anisotropy; direct luminescence lifetime measurements; and femtosecond-pump WLC-probe spectroscopy, we have investigated many unique classes of organic dyes with nonlinear responses due to two and three-photon absorption, excited-state absorption induced by one and multi-photon absorption, and combinations of these processes. By performing both experiment and modeling, including quantum chemical calculations, determining both frequency degenerate and non-degenerate spectra along with their associated temporal dynamics, the responsible physical mechanisms can be determined. Additionally, we are studying the nonlinear refraction of these materials and the observed nonlinear responses, both absorptive and refractive, which mirror those observed in bulk semiconductors with relatively minor differences). This allows us to apply our experience and previously developed theories of modeling semiconductors to organics. Working in collaboration with optical scientists, physicists, materials scientists, and chemists has greatly increased our progress towards predictive structure-property relations in organics.

Keywords: Nonlinear optics, absorption, refraction, organics, Z-scan, white-light continuum, structure-property relations.

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