Laser properties of luminescent conducting polymers in open resonators

We have investigated the lasing properties of several luminescent conducting polymers, i.e. DOO-PPV and the bi-substituted polyacetylenes PDPA-nBu, and PHJPA, dissolved in various polar and non-polar solvents. PP V polymers emit with high quantum efficiencies in broad emission bands centered in the orange/red region of the spectrum, depending on the solvent, and the PDPA polymers emit in the blue/green region. Our tested laser resonators include polymer solutions excited with 100 ps pulses from a regeneratively amplified mode-locked Nd: YAG laser. We obtain pulsed, low- threshold (uJ-level) laser operation with repetition rate of up to 1 kHz. Resulting mainly from recent refinements in material quality, the DOO-PPV laser characteristics appear to be significantly improved compared to laser results reported originally in the literature. The dependencies of threshold pump energy and output versus input power characteristics on material parameters (type of solvent, polymer concentration) are investigated for a fixed optical gain length. The results are compared with the standard Rhodamine 590 organic dye system used in the same wavelength regions. We have observed that the well known phenomenon of "concentration quenching" in dye molecules does not happen in polymers. Spectral narrowing in PDPA-nBu solution, emitting near 500 nm, is also obtained for the first time.