Study On Two-Photon Absorption And Two-Photon Pumped Fluorescence Of Organic Dyes

Two-photon absorption (TPA) is a third-order nonlinear optical process,in which a molecule (atom) of a medium in ground state simultaneously absorbs two photons, and then transits to an excited state. Molecules with large two-photon cross sections have attracted considerable attention due to a number of potential applications such as upconverted lasers, optical limiting, stabilization, three-dimensional optical data storage, three-dimensional microfabrication, and two-photon induced fluorescence microscopy. In recent years, great progress has been achieved in this field, and plenty of new organic dyes with excellent TPA and two-phonton induced fluorescence properties have been synthesized. However, there are still many problems need to be solved before organic TPA materials can practically be applied in above-mentioned areas.TPA cross section depends on the pump wavelength intensely, in order to find the most suitable pump wavelength and also to investigate the influence of solvent environment on the TPA properties, the TPA spectra of a typical TPA molecule trans-4- [p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium iodide (abbreviated as ASPI) in two different solvents ( benzyl alcohol, dimethyl formamide (DMF)) with different polarities are studied. It is found that the peak values of the TPA spectra are much larger than the TPA cross sections measured at 1064nm, and there are some blue shifts between the peak positions of the TPA spectra and the twice of their one-photon absorption peaks, the shifts are about 28nm for DMF and 34nm for benzyl alcohol. With the increasing of the polarity of the solvents, the peak values of the TPA spectra decrease, meanwhile, there is about 30nm blue shift of their peak positions.The optical-physics properties of a newly synthesized organic molecule are studied in this article. This molecule shows a large stokes shift. By the measurement of single-photon induced fluorescence and the lift time under different excited wavelength, we find the excited molecule transit to the ground state through the same energy level finally. The molecule also shows a strong two-photon induced fluorescence when excited from 800nm to 1000nm.