The Interferometer As An Optical Mixer: A Novel Approach To Far Infrared Spectroscopy

In Tokamaks, the Electron Cyclotron Emission (ECE) radiation frequency spans from 80 GHz up to 1 THz for high magnetic field (Bt>5 T) and higher harmonics (n>2). This frequency ranges between Microwaves and Far Infrared (FIR), moulding an intrinsically hybrid nature for ECE diagnostics(1). Signal detection is carried out in two surprisingly different ways: electronics and optics. The two detection methods, beyond the chief external differences, are conceptually the same. The dualism often reflects the mindset of the laboratory performing the measurement. In this paper we discuss a different approach to an integrated instrument. A traditional quasi‐optical interferometer is the first down‐conversion stage with intrinsic broad band capability. Its output signal can then be analysed with a radio‐style detection, in the amenable kHz frequency range.