Abstract
The authors present organic semiconductor distributed feedback lasers based on thin films of the conjugated polymer poly[9,9-dioctylfluorene-co-9,9-di(4-methoxy-phenyl)fluorene] and employing an improved resonator design. In order to combine the advantages of first- and second-order distributed feedback resonators, the authors utilize a mixed-order grating design: A second-order Bragg scattering region that provides efficient vertical outcoupling of the laser radiation is surrounded by first-order scattering regions that give rise to strong feedback. By optimizing the film thickness to obtain laser oscillation at the polymer maximum gain wavelength, a very low laser threshold of
45
pJ
∕
pulse
(
≈
36
nJ
∕
cm
2
)
was realized with this resonator concept.