Low noise NbN lattice-cooled superconducting hot-electron bolometric mixers at submillimeter wavelengths

Lattice-cooled superconducting hot-electron bolometric mixers are used in a submillimeter-wave waveguide heterodyne receiver. The mixer elements are niobium nitride film with 3.5 nm thickness and $\text{∼10\hspace{0.5em}μ}$ m${}^2$ area. The local oscillator power for optimal performance is estimated to be 0.5 $\mu$ W, and the instantaneous bandwidth is 2.2 GHz. At an intermediate frequency centered at 1.4 GHz with 200 MHz bandwidth, the double sideband receiver noise temperature is 410 K at 430 GHz. The receiver has been used to detect molecular line emission in a laboratory gas cell.