Regensburg 2010 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 54: Photonic Crystals: Theory
HL 54.3: Vortrag
Donnerstag, 25. März 2010, 14:30–14:45, H13
Transport Theory of Diffusive Random Lasers — •Regine Frank1,2, Andreas Lubatsch1, and Johann Kroha1 — 1Physikalisches Institut, Universität Bonn, 53115 Bonn, Germany — 2Present address: KIT Karlsruhe, Germany
Despite substantial investigations mostly for low dimensional systems, the physics of homogeneously disordered random lasers bears intriguing, open problems. The conditions for transport and localization and, in particular, the origin of confined spacial regions from which laser radiation is emitted (“lasing spots”) as well as the dependence of their size on the pump rate, have remained poorly understood. We present a semi-analytic transport theory for light propagating diffusively, in a random, lasing medium, including self-interference (“Cooperon”) corrections [1]. The diffusion coefficient is strongly renormalized by the non-linear gain rate. The latter is obtained from the local laser rate equations which, in turn, are controlled by loss channels due to diffusion and surface losses. In the stationary lasing state, the volume gain is compensated by surface losses. We solve the resulting surface boundary condition problem to obtain an analytical equation for the average lasing spot size. The full spatial intensity profile of lasing spots is obtained numerically in dependence of the pump rate. We show that the lasing spot size is closely related to the requirement of causality within a coherent lasing mode. The results are in qualitative agreement with experimental findings.
[1] R. Frank. A. Lubatsch, J. Kroha, J. Optics A 11, 114012 (2009).