Amplified spontaneous emission from photopumped films of a conjugated polymer

By measuring the gain and loss in thin-film planar waveguides using a standard technique developed for inorganic laser materials, we show that the narrow-line emission from photopumped waveguides of the conjugated polymer poly[2-butyl-5-(2^'-ethyl-hexyl)-1,4-phenylenevinylene] results from amplification of spontaneous emission (ASE). The narrowed linewidth of the ASE spectrum is determined by gain saturation. The ASE emitted from the edge of the waveguide is polarized because the waveguide is birefringent and only allows TE modes to propogate and be amplified. We compare our results and conclusions to other reports that claim that spectral narrowing in conjugated polymers is a result of superfluorescence or excitonic interactions. The techniques presented in the paper offer a simple and useful way for evaluating conjugated polymers as materials for solid state lasers.