Investigation of two-photon-induced-fluorescence from semiconducting polythiophenes

Among the many laser spectroscopy techniques that have revolutionized the 21 century optical spectroscopy research, two-photon spectroscopy is certainly one of the most important experimental techniques. Through this thesis research, the femto-second laser induced two-photon-fluorescence was studied from three fluorescent and soluble polythiophenes. The polymer solutions at various concentrations were excited with 800 nm pulses from a mode-locked femto-second laser. The conjugated polymers were also well characterized using one-photon optical spectroscopy. The size distribution of the polymers at different concentration was studied using dynamic light scattering method. Two-photon-absorption cross sections were calculated. For two-photon-absorption cross section measurement the fluorescence signals from these polythiophenes were compared with Rhodamine 6G. The calculated absorption cross-section is higher than those of other reported soluble polythiophenes. This opens up the possibility of the using these polymers in different nonlinear optical device and in multiphoton imaging.