Design and performance of a novel vacuum-capable terahertz time-domain spectrometer

We have designed and built a vacuum-capable terahertz (THz) time-domain spectrometer which allows THz spectroscopy measurements to be made whilst avoiding interference from, for example, water vapour absorption. Using a biased semi-insulating GaAs emitter and a 1-mm-thick [110] oriented ZnTe crystal as an electro-optic detection sensor, we achieved a dynamic range of over 10¹⁰ in THz power and a useful frequency range of over 3 THz. The system is very stable with a <2% day-to-day spectral variation, and up to ten samples can be measured without the need to open the vacuum chamber. In addition, the broadband (over 30 THz) capability of the system has been demonstrated by using a 30 μm GaSe crystal as the emitter and a 20 μm ZnTe crystal as the detector. The fine absorption features of uric acid were resolved at room temperature with this spectrometer, and are also presented.