Abstract
Optically excited organic semiconductor distributed feedback (DFB) lasers enable efficient lasing in the visible spectrum. Here, we report on the rapid and parallel fabrication of DFB lasers via transferring a nanograting structure from a flexible mold onto an unstructured film of the organic gain material. This geometrically well-defined structure allows for a systematic investigation of the laser threshold behavior. The laser thresholds for these devices show a strong dependence on the pump spot diameter. This experimental finding is in good qualitative agreement with calculations based on coupled-wave theory. With further investigations on various DFB laser geometries prepared by different routes and based on different organic gain materials, we found that these findings are quite general. This is important for the comparison of threshold values of various devices characterized under different excitation areas.
Highlights
Since the first demonstration of lasing with organic semiconductors as gain material more than 15 years ago this material class has attracted a lot of attention [1, 2]
We demonstrate nanograting transfer as a novel fabrication method to fabricate organic semiconductor distributed feedback (DFB) lasers based on the small molecule tris(8-hydroxyquinoline) aluminum (Alq3) and the laser dye 4-dicyanmethylene-2-methyl-6-(p-dimethylaminostyryl)4H-pyran (DCM)
By further investigations on various DFB laser configurations fabricated through thermal evaporation, spin coating and horizontal dipping, we found the laser threshold fluences for all the devices decreased for increasing pump spot diameters and decreased insignificantly above a certain value between 3.0 × 10−4 cm2 and 1.0 × 10−3 cm2, depending on the type of materials and the DFB laser configurations
Summary
Since the first demonstration of lasing with organic semiconductors as gain material more than 15 years ago this material class has attracted a lot of attention [1, 2]. The DFB laser fabricated via nanograting transfer supplies a simple geometry on the unstructured active layer We used this device to investigate experimentally and theoretically the dependence of lasing threshold on the excitation area. By further investigations on various DFB laser configurations fabricated through thermal evaporation, spin coating and horizontal dipping, we found the laser threshold fluences for all the devices decreased for increasing pump spot diameters and decreased insignificantly above a certain value between 3.0 × 10−4 cm and 1.0 × 10−3 cm, depending on the type of materials and the DFB laser configurations This is important for the comparison of threshold values of various devices characterized under different excitation areas
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