Multifrequency continuous wave terahertz spectroscopy for absolute thickness determination

We present a tunable multifrequency continuous wave terahertz spectrometer based on two laser diodes, photoconductive antennas, and a coherent detection scheme. The system is employed to determine the absolute thickness of samples utilizing a proposed synthetic difference frequency method to circumvent the 2 pi uncertainty known from conventional photomixing systems while preserving a high spatial resolution.