Abstract
Effects of humidity on nonlinear transmission properties due to saturable absorption were investigated using eosin-Y-doped polyvinyl alcohol (PVA) films which had been exposed to a highly humid atmosphere. In a pump-probe measurement, a transmitted probe signal changed in every shot of the pump-pulse irradiation, and tended to approach a steady characteristic. Simultaneous measurements of the transmitted probe power and the phosphorescent lifetime showed that these phenomena stem from the phosphorescent lifetime being lengthened by the successive pump irradiations. This increase in lifetime was found to have originated from reduction of a nonradiative decay rate of an excited state of the dyes. The recurrent pump irradiations are believed to remove moisture, which has strengthened the nonradiative decay rate, from the PVA films.
