Spectral measurements of THz radiation emitted from intrinsic Josephson junction stacksV.P. Koshelets, N.V. Kinev, A.B. Ermakov, F. Rudau, R. Wieland, D. Koelle, R. Kleiner and H.B. WangEPJ Web Conf., 195 (2018) 05013DOI: https://doi.org/10.1051/epjconf/201819505013