Ultrafast two-photon absorption in organic molecules: Quantitative spectroscopy and applications

This dissertation explores quantitative two-photon absorption spectroscopy to relate molecular structure with optical properties of organic chromophores.;The dissertation describes an advanced fluorescence-based technique for reliable measurements of the two-photon spectra and cross sections. To facilitate the measurements it establishes a set of reference compounds measured with a 15% absolute accuracy covering a broad range of excitation and fluorescence wavelengths.;The dissertation shows that in many cases the few-essential-levels model can be successfully applied for the description and interpretation of two-photon absorption spectra and cross sections, at least for the low-energy transitions.;The dissertation presents examples of applications of two-photon absorption for volumetric optical storage and cancer tumor detection. It describes the basic principles of the two-photon absorption-based optical memory and limitations imposed on two-photon sensitivity of photochromic materials by a necessity of fast access to the data. It also proposes a novel technique for sensitive detection of cancer cells by using two-photon excitation of near-IR fluorescence of a commercial dye and discusses the mechanisms responsible for differentiation between the normal and the cancer cells.;The methods described in this dissertation can be applied to understanding the relations between structure and two-photon absorption strength of individual transitions of organic and biological chromophores, which can be used for design of new materials, maximally adapted for particular applications.