Time-Performance Of Multi-Photon Absorption Induced Fluorescence Of C₂₂H₂₂N₄O

In the 21st century, with the development of high peak power and ultra-shot-pulses lasers, multi-photon absorption induced fluorescence technique has become an important tool for the investigation of physical properties of materials. Especially materials with strong two-photon absorption(TPA) are currently attracting considerable attention in the chemistry, photonics and biology communities because of their potential applications in optical power limiting, up-converted lasering, three-dimensional data-storage, nondestructive imaging and photo-dynamic therapy. However, due to very low absorption rates, two- and three-photon absorption cross sections are difficult to measure directly using absorption technique. The development of two- and three-absorption technology is confined.In this thesis, firstly, several methods used for two - photon absorption (TPA) cross section measurements were introduced and the properties of each method were analyzed in detail. Secondly, we provide a two-level model to depict the one-, two-and three-photon fluorescent process and with it to calculate the one-, two-and three-photon fluorescence intensity dependence of the incident excitation intensity and time. We study the fluorescence intensity when excitation light's time distribution are square pulse,Gaussian pulse and sech pulse. We find that the influence of excitation light's time distribution on the two- and three- photon fluorescence peak intensity is larger than the one-photon fluorescence peak intensity. Two-level model can account for the behavior of saturation fluorescence. The model also provides a method for determining one-,two-and three-photon absorption cross sections. To determine the absorption cross sections, the present method does not require fluorescence quantum efficiency and collection efficiency of the measurement system, which are need in some other methods. Finally, we obtain one,two-and three- photon absorption cross-section of C22H22N4O and two-photon absorption cross-section of C22H19F3N4O.