Terahertz (THz) radiation is all around us. For example, this page emits blackbody radiation mainly in the THz region (defined here from 0.3 THz to 30 THz). However, this THz radiation or THz radiation from traditional microwave sources is usually too weak to have any measurable impact on the properties of the materials that are studied with it.
The situation drastically changed at the beginning of the 2000s: the technique of optical rectification with phase matching in crystals lacking inversion symmetry was developed. This technological breakthrough enabled the development of table-top sources of single-cycle THz pulses with field strengths exceeding 1 MV/cm. Such a field strength made it possible to engineer new dynamic states of materials by modifying their intrinsic fields in which materials exhibit properties entirely different from that of the equilibrium.
In this review, published in Physics Reports and in which the Ikerbasque Researcher from DIPC Alexey Nikitin took part, they analyze known studies dealing with the transformation, control and engineering with strong-field few-cycle THz light and outline some anticipated new results. They focus on how properties of materials can be manipulated by driving the dynamics of different excitations and how molecules and particles can be controlled in useful ways by extreme THz light. Secondly, they discuss available and proposed sources of strong-field few-cycle THz pulses and their state-of-the-art operation parameters. Finally, they review current approaches to guiding, focusing, reshaping and diagnostics of THz pulses.
As a summary of the review, we see that these new possibilities have given a better understanding of several physical and chemical processes in solids, liquids and molecules as well as the manipulation of their properties. Looking to the future, it is clear that further development of THz light sources will have a strong impact by providing the tool that enables presently unfeasible experiments.
For further information: https://doi.org/10.1016/j.physrep.2019.09.002