Absorption band saturation in the near-IR spectrum of molybdenum blue

Nonlinear absorption of a picosecond laser pulse in an aqueous solution of a partly reduced heptamolybdate and citric acid was studied. We report on t he first observations of the absorption band saturation in the near-IR spec trum of molybdenum blue and its relaxation on a picosecond time scale. A st epwise character of the intensity dependence of the absorption band saturat ion is demonstrated. Qualitative interpretation of the experimental results is based on the concept of self-defocusing in a three-level system that ex hibits two-photon transitions via an intermediate level upon high-power exc itation. (C) 2000 MAIK "Nauka/Interperiodica".