Optical Bleaching and Deviations from Beer—Lambert's Law of Solutions Illuminated by a Ruby Laser. I. Cryptocyanine Solutions

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Abstract
The deviations from Beer—Lambert's law of solutions of cryptocyanine were measured when the solutions were illuminated by a giant ruby laser pulse. The transmission‐intensity curves show quite unambiguously that a second absorption from an excited state is needed to explain the experimental results. It is also shown that under steady state conditions it is the number of absorptions and not the detailed level scheme that governs the behavior of the system. The transmitted pulse was shown to be narrower than the incident one in an amount depending on incident intensity. Using the two absorption steady state mechanism, the change of shape could be explained and calculated. The decay rates and absorption cross sections were calculated for two models—the one which assumes absorption from an excited singlet, and the other which assumes absorption from the lowest triplet state. The blue fluorescence of cryptocyanine is explained in terms of our results. A level scheme based on the known spectrum fits with the suggested model.