We report on the laser modes in optically pumped solid-state lasers using a
n electroluminescent organic semiconductor as the active medium. Mechanical
ly flexible distributed-feedback lasers are fabricated by depositing a thin
film of an active material onto a nano-patterned polyester substrate eithe
r via spin-coating of a soluble ladder-type poly(p-phenylene) or via vacuum
co-sublimation of small organic molecules. The different surface texture r
esulting from the fabrication process causes different feedback mechanisms.
In both lasers higher lateral modes give rise to a broadening of the laser
spectra at higher pumping levels.