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Detection, mixing and generation of millimetre and submillimetre radiation

The project provides the physical background for developing new receiving techniques in millimetre (MM) and submillimetre (SMM) wavelength range. The phenomena used are Bloch oscillations in short-period semiconducting superlattices and non-equilibrium quasi-particle photoresponse of superconducting films. Studies performed in the framework of the project have resulted in the development of the physical background for a new terahertz receiving technique designated for radioastronomy, plasma diagnostics and remote environmental monitoring. The technique utilizes two physical phenomena: Bloch oscillations in short period semiconductor superlattices and the hot-electron bolometer effect in thin low and high temperature superconducting films. Advantages of proposed novel devices are based on both strong nonlinearity and short relaxation times inherent to these phenomena. The concept of a heterodyne receiver with a superconducting hot-electron bolometer mixer coupled to radiation by a hybrid quasioptical antenna has been developed. A laboratory demonstrator of the receiver with a niobium nitride hot-electron mixer was tested in the terahertz frequency range. It showed a performance comparable to that of Schottky diode receivers. The advantage of the hot-electron bolometer mixer is a small local oscillator power that can be, in principle, delivered by a compact low energy consumptive source, replacing presently used gas lasers. As the prototype of such a source, frequency multipliers on the basis of Esaki-Tsu semiconductor superlattices have been proposed. Harmonic multiplication by superlattices has been demonstrated up to a frequency of 2.1 THz. A linewidth of several megahertz and an output power of almost 100 microwatt make such a multiplier feasible (however, presently up to 200 GHz) as a local oscillator for the receiver with a hot-electron bolometer mixer.

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