Photodecomposition of dyes in a polymer matrix under lasing conditions

An experimental study was made of the optical bleaching of organic dyes in liquid and solid (polymer) media during lasing. The results were analyzed by introducing a photostabilization coefficient defined as the ratio of the rates of photodecomposition of the dye molecules in the presence and absence of lasing. Theoretical calculations indicated that the photostabilization coefficient was directly proportional to the stimulated transition cross section at the lasing frequency and to the photon lifetime in the resonator. At the threshold value of the pump power density in the range 0.2–0.5 MW/cm² the photostabilization coefficient reached 2–5, in good agreement with the experimental values of liquid dye solutions. In the case of polymer active media (in contrast to liquid dye solutions) the experimental values of the photostabilization coefficient were systematically lower than those found by calculation, which was due to the absence of stabilization of the population inversion during lasing. An analysis was made of the possible reasons for this effect. The most probable reason was the spectral inhomogeneity of the vibronic transitions in the dyes embedded in a polymer matrix.