Steady state photoisomer accumulation in the absorber jet of the passively mode-locked femtosecond dye laser

In continuous were passively mode-locked dye lasers a steady state distribution of two isomers of the saturable absorber dye can be established. We report the first intracavity transmission measurement and estimation of the amount of the photoisomer of DODCI in the femtosecond CPM ring laser. Comparison with a simple model based on rate equations allows to estimate the quantum yield of a photo-back reaction. The obtained dependence of the photoisomer concentration on the laser wavelength and pulse energy can be used in theories describing the generation process for adequate estimation of its part in the modelocking regime.