We characterize a heterodyne receiver based on a surface-plasmon waveguide quantum cascade laser (QCL) emitting at as a local oscillator, and an hot electron bolometer as a mixer. We find that the envelope of the far-field pattern of the QCL is diffraction-limited and superimposed onto interference fringes, which are similar to those found in narrow double-metal waveguide QCLs. Compared to the latter, a more directional beam allows for better coupling of the radiation power to the mixer. We obtain a receiver noise temperature of when the mixer is at , which, to our knowledge, is the highest sensitivity reported at frequencies beyond .
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