High-speed frequency-domain terahertz coherence tomography

High-speed frequency-domain terahertz (THz) coherence tomography is demonstrated using frequency sweeping of continuous-wave THz radiation and beam steering. THz frequency sweeping with a kHz sweep rate and a THz sweep range is implemented using THz photomixing in which an optical beat source consists of a wavelength-swept laser and a distributed feedback laser diode. During the frequency sweep, frequency-domain THz interferograms are measured using the coherent homodyne detection employing signal averaging for noise reduction, which are used as axial scan data via fast Fourier transform. Axial scan data for 100×100 points can be acquired in 100 s while scanning a transverse range of 100×100 mm² using a THz beam scanner comprised of a two-dimensional galvanometer scanner and a telecentric f-θ lens.