A far-infrared Fourier transform spectrometer with an antenna-coupled niobium bolometer

We have designed and constructed a custom far-infrared Fourier transform spectrometer using an antenna-coupled bolometer as a detector. The active element of the detector is a superconducting niobium microbridge, and the far-infrared signal is coupled to the microbridge via a planar antenna mounted on a hyperhemispherical silicon lens. The spectrometer uses a broadband blackbody source with frequency-independent optical components, and thus the system bandwidth is set by the detector antenna. We have fabricated devices with two different antenna types, the double dipole and the log spiral, and have characterized the spectral response of each. This spectrometer can utilize the fast response of the niobium bolometer to perform time-resolved far-infrared spectroscopy on nanosecond to millisecond timescales. These timescales are too fast for standard commercial bolometers and too long for a typical optical delay line.