Free-space coherent broadband terahertz time-domain spectroscopy

This paper reports on a free-space broadband terahertz (THz) spectroscopy technique with frequency ranging from 30 GHz to over 40 THz. A historical review is given on the development of THz spectroscopy and its unique features. We focus on a time-domain detection technique using free-space electro-optic sampling. This broadband THz spectroscopy technique opens the door to many interesting applications. We present some recent developments in applications of THz spectroscopy, including characterization of the optical properties of materials, study of the dynamics of phonon and photocarriers and THz imaging. This THz time-domain technique continues to attract interest in both fundamental research and real-world applications.