Continuous wave terahertz spectroscopy based on photomixing offers the attractive feature of detecting both amplitude and phase of the terahertz radiation. Experimentally, it is challenging to achieve sufficient accuracy at a high data acquisition rate. We use two fiber stretchers as fast phase modulators in a symmetric setup. Compared to a mechanical delay stage, the fiber stretchers are rather fast (), which enables us to record a spectrum up to 1.8 THz with a step size of 1 GHz in only 10 min. We achieve a stability of the optical path difference of around 10 μm and use low-doped Si as an example to demonstrate the performance of our spectrometer.
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