Terahertz Mach-Zehnder interferometer based on a hollow-core metallic ridge waveguide

While terahertz time-domain spectroscopy directly measures amplitude and phase of pulsed terahertz electric fields, the use of more compact terahertz continuous wave sources requires interferometric measurement techniques to obtain phase information. Since constructive and destructive interference are governed by the relative phase of the superimposing fields the phase information can be retrieved from the amplitude modulation signal at the output of the interferometer. Here, we present phase-sensitive measurements of terahertz electric fields in a Mach-Zehnder interferometer that is integrated in a hollow-core metallic ridge waveguide. With lactose in one of the interferometer arms, we measured the modulated amplitude spectrum of the interferometer output signal which carries information about the dielectric properties of the investigated lactose. We explain the measured transmission spectra and the observed dielectric resonances by analytic and numerical means and further confirmed the results by a spectroscopic reference measurement of lactose in a conventional waveguide.