Self-absorption and light amplification in perylimide dyes-doped poly(methyl-methacrylate)

Optical properties of poly(methyl-methacrylate) (PMMA) doped with perylimide molecules are studied. The self-absorption of perylimide BASF 339 (red) and KF 241 (yellow) is investigated by measuring the emission spectrum in the sample as a function of the distance traveled by the emitted light, after being excited with a continuous laser. The effect of this phenomenon on the shape of the emission spectrum and consequently on the wavelength tunability range is found to be important. The optical gain coefficient is measured using a simple set-up based on only one exciting laser beam, and the detection of a single-pass amplified light emitted along the length of an optically excited sample. The presence of stimulated emission is determined by the exponential increase of the photoluminescence output intensity, when only the length of the excited region is varied. Under moderate pumping intensities, a net laser gain of 53 cm−1 and 36 cm−1 is measured for yellow KF 241 and red BASF 339, respectively. The increase of the emission spectra as the length of the excited region of the sample is increased is found to be wavelength dependent.