An all-cryogenic THz transmission spectrometer

This article describes a THz transmission spectrometer for the spectral range of 2–65 cm−1 (100 GHz to 2 THz) with a spectral resolution of at least 1.8 cm−1 (50 GHz) where the source, sample, and detector are all fully contained in a cryogenic environment. Cyclotron emission from a two-dimensional electron gas (2DEG) heated with an electrical current serves as a magnetic-field tunable source. The spectrometer is demonstrated at 4.2 K by measuring the resonant cyclotron absorption of a second 2DEG. Unique aspects of the spectrometer are that (1) an ultrabroadband detector is used, and (2) the emitter is run quasicontinuously with a chopping frequency of only 1 Hz. Since optical coupling to room temperature components is not necessary, this technique is compatible with ultralow temperature (sub-100 mK) operation.