The excitation processes of the low energy isomeric level in nucleus 229Th by optical photons are investigated for different values of relations between energies of nuclear transition and photons. The role of the atomic shell, which "works" as electron bridge, is considered. The cross-sections of the resonance nuclear excitation by laser beam (the narrow line) and by special lamp (the wide line) are calculated. The possibilities of experimental researches are discussed.

The effect of fluorescence saturation under laser pulsed excitation appears as a non-linear response of emission signal versus intensity of excitation. The saturation becomes important when the rate of molecular excitation exceeds the rate of their deactivation. Typically the effect is noticeable when excitation photon flux (p) exceeds 1023... 1024 cm2s'. We present the theory offluorescence saturation under laser pulsed excitation for both quasi-stationary and non-stationary cases, as well as the experimental study on fluorescence saturation for of organic dyes in aqueous and ethanol solutions and in polymer film.

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