We report on transient laser action during the photopolymerization process in organic thin films of acrylate monomers doped with a laser dye. The emission spectrum was monitored over a period of time in the direction orthogonal to the incident laser beam which is kept at a constant intensity during the experiments. The emission spectra display the signature of laser action after a certain amount of polymerization. We have also recorded the intensity of fluorescence as well as of the amplified stimulated emission (ASE) using a photodiode. Our results confirmed that all the emission is guided by an increase of the refractive index resulting from the photopolymerization process. The spatial fluctuations in the density of the material are thought to act as micro-cavities leading to a random laser effect.
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