Strongly confined, low-threshold laser modes in organic semiconductor microgoblets.

We investigate lasing from high-Q, polymeric goblet-type microcavities covered by an organic semiconductor gain layer. We analyze the optical modes in the high-Q cavities using finite element simulations and present a numerical method to determine the cutoff thickness of the gain layer above which the whispering gallery modes are strongly confined in this layer. Fabricated devices show reduced lasing thresholds for increasing gain layer thicknesses, which can be explained by a higher filling factor of the optical modes in the gain layer. Furthermore, reduced lasing threshold is accompanied by a red-shift of the laser emission.