Existence of continuous-wave threshold for organic semiconductor lasers

Abstract

We develop a model that predicts two threshold pump intensities in optically pumped organic semiconductor lasers (OSLs); one for pulsed lasing, ${I}_{PS}$, and another for continuous-wave (CW) lasing, ${I}_{CW}$. The theory predicts a decrease in ${I}_{CW}$ from 32 kW/cm${}^{2}$, or well above the damage threshold, to 2.2 kW/cm${}^{2}$, for a laser employing 4-(dicyanomethylene)-2-methyl-6-julolidyl-9-enyl-4H-pyran--doped tris(8-hydroxyquinoline) aluminum if the triplets can be effectively removed from the emissive guest. Based on this analysis, we demonstrate that the lasing duration can be extended to nearly 100 \ensuremath{\mu}s, ultimately limited by degradation of the lasing medium when a ``triplet manager'' molecule, 9,10-di(naphtha-2-yl)anthracene, is blended into the gain region of an otherwise conventional distributed feedback OSL. The triplet manager facilitates radiative singlet transfer while suppressing nonradiative triplet transfer to the emitter molecule, thus reducing the triplet-induced losses. Our theory conclusively shows that these lasers have entered the CW lasing regime.