Cw terahertz spectrometer with high-precision frequency control

An all-fiber-based cw terahertz spectrometer, which combines distributed feedback (DFB) diode technology and precise interferometric frequency control is developed. Several solid-state samples are used to demonstrate the suitability of the system for high-resolution terahertz spectroscopy. The refractive index was determined directly from the phase shift introduced by the transparent sample, whereas the extinction coefficient was obtained from the transmitted intensity. The results for the absorption signatures of alpha-lactose monohydrate is presented. The transmission spectrum of a MgO etalon (free spectral range 100 GHz) shows regularly spaced transmission peaks and demonstrates the wide tunability of the system. Terahertz-based measurements of the area density of paper is also showed.