Multi-photon excitation fluorescence emission

Several articles and reviews on different aspects of multi-photon excitation of biomolecule system are available. For example, Birch [11] consideraticms concentrate mainly on the impact of multi-photon techniques to the time-resolved fluorescence spectroscopy. Lakowicz and Gryczynski [12] have discussed examples of three-photon excited fluorescence. Rehms and Callis studied the two-photon excited fluorescence emission of aromatic amino acids [13]. Kierdasz et al analyzed emission spectra of Tyrosine- and Tryptophan-containing proteins using one-photon (270-3 10 nm) and two-photon (565-6 10 nm) excitation [14]. 

This chapter is devoted to describe the impact of metallic nanosphere to the multi-photon excitation fluorescence of Tryptophan, and little further consideration to multi-photon absorption process will be given, as the reader can find several studies in [11-14]. In section II, the nonlinear light-matter interaction in composite materials is discussed through the mechanism of nonlinear susceptibilities. In section III, experimental results of fluorescence induced by multi-photon absorption in Tryptophan are reported and analyzed. Section IV described the main results of this chapter, which is the effect of metallic nanoparticles on the fluorescent emission of the Tryptophan excited by a multi-photon process. Influence of nanoparticle concentration on the Tryptophan-silver colloids is observed and discussed based coi a nonlinear generalization of the Maxwell Garnett model, introduced in section II. The main conclusion of the chapter is given in secticHi IV. 

Fluorescence emission is just one, but probably the most convenient, of several methods available for observing multi-photon absorption. In a multi-photon excited fluorescence process, the fluorescence intensity Iji does not increase linearly with increasing of the excitation intensity, lac- Instead, Iji and la are related by... 

The laser combustion diagnostics techniques discussed so far utilized resonant processes, whether it be single- or multi-photon excitation, fluorescence or stimulated emission. We will now consider non-resonant processes of Raman nature. Because of its msensitivity to quenching (the lifetime of the virtual state is lO s), Raman spectroscopy is of considerable interest for quantitative measurements on combustion processes. Further, important flame species such as O2, N2 and H2 that do not exhibit IR transitions (Sect. 4.2.2) can be readily studied with the Raman technique. However, because of the inherent weakness of the Raman scattering process (Sect. 4.3) only non-luminous (non-sooting) flames can be studied. 

The total fluorescence intensity saturated around a few hundreds of mJ/cm2 which corresponds to the irradiation condition where the new plasma-like emission was observed. Above this value fluorescence intensity decreased, which is accompanied with the recovery of the relative intensity of excimer emissions. This means that a quite efficient deactivation channel of excitation intensity opens in this energy range, and the contribution of Si -Si annihilation is depressed. This suggests that fragmentation reactions to diatomic radicals are not induced by the annihilation process. Multi-photon absorption processes via the Si states and chemical intermediates should be involved, although no direct experimental result has as yet been obtained. 

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