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\bibitem{Huebers_etal2005} H{\"u}bers, H. W., Pavlov, S. G., Semenov, A. D., Tredicucci, A., K{\"o}hler, R., Mahler, L., et al. (2005). Investigation of a 2.5 THz quantum cascade laser as local oscillator. In \textit{Proc. 16$^{th}$ Int. Symp. Space Terahertz Technol.} (18). G{\"o}teborg, Sweden.

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