Development of phonon cooled hot-electron-bolometers (HEB) for applications in THz radioastronomy

Heterodyne detection of weak THz signals can be obtained with ultrathin superconducting microbridge bolometers where frequency mixing is achieved by rapid relaxation of hot electrons in resistive hot spots. These devices do not suffer from the superconducting band gap limit of conventional SIS mixers. Phonon cooled HEBs from NbN allow mixing with IF bandwidths up to several GHz. We discuss NbN thin film optimization and present characterization methods which allow to investigate the phonon cooling path.