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\bibitem{Huebers_etal2005} Huebers, H. - W., Pavlov, S., Semenov, A., K{\"o}hler, R., Mahler, L., Tredicucci, A., et al. (2005). Terahertz quantum cascade laser as local oscillator in a heterodyne receiver. \textit{Optics Express}, \textit{13}(15), 5890--5896.

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