Free-space coherent broadband terahertz time-domain spectroscopy

This paper reports on a free-space broadband terahertz (THz) spectroscopy t echnique with frequency ranging from 30 GHz to over 40 THz. A historical re view is given on the development of THz spectroscopy and its unique feature s. We focus on a time-domain detection technique using free-space electro-o ptic sampling. This broadband THz spectroscopy technique opens the door to many interesting applications. We present some recent developments in appli cations of THz spectroscopy, including characterization of the optical prop erties of materials, study of the dynamics of phonon and photocarriers and THz imaging. This THz time-domain technique continues to attract interest i n both fundamental research and real-world applications.