The Ar+-laser-stimulated desorption of iodine molecules from an impregnated polystyrene film was investigated. The photoprocess induces a color change (from red to the transparent) and leaves in the film a marked print, which is related to the laser beam characteristics. The experimental data was fitted using a set of differential equations relating the time dependence of the film temperature and absorption coefficient. At low-power levels ( < 25 m W), the time evolution of the laser

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... power could be well matched to the experimental data. The wavelength dependence of the marking process was also studied and the relative contribution of photodissociative and photothermal processes was inferred.