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\bibitem{Ekstroem_etal1997} Ekstr{\"o}m, H., Kollberg, E., Yagoubov, P., Gol{\textquoteright}tsman, G., Gershenzon, E., \& Yngvesson, S. (1997). Phonon cooled ultra thin NbN hot electron bolometer mixers at 620 GHz. In \textit{Proc. 8$^{th}$ Int. Symp. Space Terahertz Technol.} (pp. 29--35).

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