Frontend for a 2.5-THz heterodyne spectrometer without liquid cryogen

As part of a study for a second generation heterodyne spectrometer on SOFIA we are developing a 2.5-THz frontend which is implemented in a pulse-tube cooler. It consists of a quantum-cascade laser as local oscillator and a phonon-cooled NbN hot electron bolometric mixer. Frequency stabilization to below 300 kHz full width at half maximum is achieved by locking to a molecular absorption line. We will present the design and performance of the frontend and discuss the prospects for an application on board of SOFIA.