STIMULATED-EMISSION AND LASING IN SOLID FILMS OF CONJUGATED POLYMERS - ULTRAFAST PHOTOPHYSICS AND PHOTON CONFINEMENT VIA SCATTERING

Two major hurdles to producing solid-state polymer laser diodes are id entified: the presence of a photoinduced absorption (PA) which inhibit s the stimulated emission (SE) necessary for lasing; and the difficult y with making emitted light in an excited polymer travel farther than the gain length. The first of these difficulties is addressed utilizin g femtosecond spectroscopic experiments on a new conjugated polymer, p oly(2-butyl-5-(2'-ethyl-hexyl)-1,4-phenylene vinylene) (BuEH-PPV). The 60 ps SE decay time of BuEH-PPV is nearly an order of magnitude longe r than that of other conjugated polymers, and is limited only by a dyn amic blue-shift of the PA. Long SE times in polymer films open the pos sibility for addressing the second difficulty by producing lasing usin g multiple scattering. Above a critical excitation threshold, addition of TiO2 nanoparticles to solutions and dilute blend films of thoxy,5- (2'-ethyl-hexyloxy)1,4-phenylene-vinylene) (MEH-PPV) confines the emit ted photons in the excited film until gain exceeds loss. With this tec hnique, lasing is observed in a solid-state polymer for the first time . The combination of new materials with persistent SE like BuEH-PPV an d lasing by photon confinement should open major new avenues in the pr oduction of polymer laser diodes.