The times they are A'Changin…

The THz field, so vividly represented at the IRMMW-THz 2016 conference in Copenhagen, emerged as a consequence of new developments in both laser technology and materials science approximately 30 years ago. In science, research fields rarely arise as result of a singular event in space and time, but rather as a result of several things leading to a revived interest in specific areas of science. The same with the THz field, which in some sense revived and revolutionized the field of far-infrared spectroscopy by introducing new experimental techniques that were simpler, much more sensitive, and provided the possibility of obtaining both time and spectral resolution. So, the revived THz-field arising in the mid-1980's was the result of a gradual evolution of science and technologies. Revolution is perhaps a more fitting expression when it comes to the scientific experiments enabled by the new THz techniques. For nearly 100 years, since the beginning of the 20th century atomic and molecular structure has been in focus of most scientific experimentation. Structures are observed and studied using frequency resolved techniques whereby resonances representing specific atomic and molecular structures are observed. However, with the advent of time-resolved spectroscopic techniques in general and THz sources in particular, much emphasis is nowadays put on dynamics, the transformation of one (or more) structure into a new and different structure. Such processes are mediated by the relatively weak intermolecular interactions and thus, perfectly suited to the frequency and time-resolution of the new THz sources that emerged. The talk will present a personal account of the early THz-field from a scientist who witnessed the rebirth of the field in the mid-1980's and worked in the THz field for 10 years until the end of the 1990's. Focus will be on the concept of intermolecular interactions and how THz spectroscopy has helped us toward a better understanding of dynamical processes in nature.