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Output characteristics of organic distributed feedback lasers with varying grating heights

: Döring, S.; Rabe, T.; Stumpe, J.


Applied Physics Letters 104 (2014), Nr.26, Art. 263302
ISSN: 0003-6951 (Print)
ISSN: 1077-3118
ISSN: 1931-9401 (online)
Fraunhofer IAP ()

In this study, we examine the influence of the corrugation height of surface relief gratings on the output characteristics of organic distributed feedback (DFB) lasers. A series of surface relief gratings with a constant corrugation period (410 nm) and variable corrugation heights ranging from 20 and 80 nm are fabricated by the illumination of a new developed photosensitive azobenzene containing material with an interference pattern. A blend of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo{2,1′,3}-thiadiazol)] and poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] is used as organic laser active material which is deposited by spin-coating onto the grating array. The investigation of the laser output characteristics reveals an increase of the slope efficiency by a factor of 4 from 0.8% to 3.7% due to an increase of the grating height. The laser threshold decreases only slightly from 8.5 μJ/cm2 to 6.0 μJ/cm2 with increasing corrugation height. We interpret this as a result of the change of coupling between light mode and grating. The study helps to relate this to loss mechanisms of the DFB lasing process. This enables a further optimization of the DFB laser design.