Amplified Spontaneous Emission (ASE)
Since the discovery of electroluminescence from conjugated polymers they have been applied in several organic technologies, which are already competing with their inorganic counterparts such as light emitting diodes (LED), field effect transistors (FET) and solar cells (SC). Due to their charge carrier and photoluminescence properties, conjugated polymers have a high potential to become a new class of laser gain materials. Compared to their inorganic equivalents, they are cheap in production, easy in processability and have a wide tuning range. While optical pumped lasing in the solid state has been achieved, it still remains an open question if an electrically pumped organic laser can be realised. Within our research group we aim to study organic semiconductors and their photophysical behaviour systematically to make design suggestions for future molecular structures towards electrically pumped lasing. These studies will be carried out together with the synthetic chemistry group of the MPI-P.
Lasing properties of organic materials can be studied via amplified spontaneous emission (ASE). A thin film (~100 nm) of an organic material deposited on a glass substrate gets optically excited perpendicular to its surface with a stripe shape beam near the edge of the sample. The refractive index of the organic material, in general higher than its surrounding media, confines the emitted light within the waveguide structure. The photoluminescence spectra can be observed from the edge. As pump energy increases the emission spectra collapse into one single peak which is a clear indication of amplification of only one vibronic sublevel, a phenomenon which can be described with a four-level laser system. The experimental setup allows us to determine gain and loss mechanisms of organic semiconductors and will hopefully bring us a step closer towards an electrically pumped organic laser.