The knowledge of material transport properties at finite frequencies is of basic importance in many fields of researches spanning from condensed matter physics and material science, to industrial applications. In particular, measurements of the optical properties of materials in the terahertz (THz) and sub-THz spectral region of the electromagnetic spectrum (1 THz= 33 cm-1= 300 microns), a spectral range located between the microwaves (<10 GHz) and the infrared (>20 THz), provide very useful information about high-frequency resistive and inductive properties of metals and dielectrics. However, a complete THz material characterization is far from to be well established. This is due, in particular, to the lack of stable, wideband and powerful THz sources.
In this talk I will discuss useful physical mechanisms for the production of THz radiation whose associated electric field spans from 10 KV/cm to several MV/cm. As this radiation can be used for the investigation of materials in linear (low-field) and unlinear (high-field) regime, here I will present several examples of applications in condensed matter physics and material science.