Mixing and noise in diffusion and phonon cooled superconducting hot-electron bolometers

Experiments were conducted to test device performance as a function of device length under various operating conditions. Measurements of the spectrum of the output noise, mixer noise and conversion efficiency for phonon and diffusion cooled Nb devices of different thermal time constants are presented, and the measurement results are compared to theoretical predictions. Likewise, measurements of the device over a very broad band as well as thermometry measurements in the normal condition are presented. The results are discussed.