PT Unknown AU Gerecht, E Musante, CF Yngvesson, KS Waldman, J Gol'tsman, GN Yagoubov, PA Voronov, BM Gershenzon, EM TI Optical coupling and conversion gain for NbN HEB mixer at THz frequencies SE Proc. 4-th Int. Semicond. Device Research Symp. PY 1997 BP 47 EP 50 DE NbN HEB mixers ER