Broadband Two-Photon Absorption Spectroscopy: Measuring Accurate Absolute Cross-Sections

Abstract

The properties of two-photon excitation, such as the different selection rules and superior spatial control compared with one-photon excitation, and are exploited in many different types of applications, from two-photon fluorescence microscopy to photodynamic therapy. Most prior work has emphasized the development of molecules with large two-photon absorption (2PA) cross-sections using single wavelength measurements that neglect the rich information available from broadband 2PA spectroscopy. Techniques that have been used to measure two-photon absorption spectra are often complicated by large experimental uncertainties. This thesis describes work to develop a broadband two-photon absorption method in order to provide a robust method that can accurately measure two-photon absorption spectra and absolute cross-sections, and therefore aid in the discovery of novel chromophores with large two-photon cross-sections for use in many different applications. The work presented in this thesis involves method development of the broadband two-photon absorption technique through measurements of the test compounds coumarin 153 and benzene. The broadband two-photon absorption technique simultaneously measures stimulated Raman scattering that can be used as an internal standard in the measurement of absolute two-photon absorption cross-sections. In addition, picosecond pump pulses were used in the broadband two-photon absorption method to increase the resolution of the technique. Lastly, improvements to the broad-band two-photon absorption technique were used in a preliminary study of photo-active manganese tricarbonyl complexes to demonstrate how two-photon absorption spectroscopy is helpful for understanding the non-linear photo-induced release of carbon monoxide.