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16 April 2008 Lower limit of the lasing threshold in an organic microcavity
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The application of organic materials as solid state lasers critically relies on a low lasing threshold. We investigate the characteristics of emission from an organic vertical cavity surface emitting laser. The microcavity studied here consists of two highly reflective distributed Bragg reflectors enclosing a wedge-shaped active layer of Alq3:DCM. Lasing of the DCM molecules is induced via two different pump regimes, either exciting Alq3 at a wavelength of 400 nm or pumping directly into the absorption band of DCM at 532 nm. By a variation of the pump beam position with respect to the microcavity surface, we demonstrate a continuous wavelength tuning in the organic microcavities in a range of 55 nm. The continuously variable cavity thickness allows us to study the thickness dependence of the input-output characteristics in a single sample. These data are obtained at a certain emission wavelength, λ, close to the maximum of the gain spectrum, for a number of cavity thicknesses, which correspond to different multiples of λ/2. For a decreasing thickness of the active layer, one-dimensional optical confinement is expected to result in an increased spontaneous emission factor. On the other hand, the loss rate through the mirrors increases with decreasing thickness resulting in a minimum threshold value for an active layer thickness of approximately 3/2 λ. This lower threshold limit is set by nonradiative losses as well as residual absorption.
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Bernd Schütte, Hannes Gothe, Markas Sudzius, Vadim G. Lyssenko, Susanne I. Hintschich, Hartmut Fröb, and Karl Leo "Lower limit of the lasing threshold in an organic microcavity", Proc. SPIE 6999, Organic Optoelectronics and Photonics III, 699930 (16 April 2008);

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