Influence of the orientation of liquid crystalline poly(9,9-dioctylfluorene) on its lasing properties in a planar microcavity

We present a study of optically pumped laser emission from a microcavity containing an oriented layer of the liquid crystalline conjugated polymer poly(9,9-dioctylfluorene) [PFO]. The birefrigence of the oriented polymer results in the definition of two cavity modes with electric vectors polarised perpendicular and parallel to the alignment direction. At high excitation density, the emission intensity from the cavity mode polarised parallel to the orientation direction increases rapidly compared to the orthogonal polarised mode and its linewidth narrows from 8 to 2 nm. We identify the parallel-polarised emission as laser action with a threshold excitation density of 7.8 x 10E19cm-3.