Ultrafast terahertz monitoring of extremely high nonlinearities in semiconductors and dynamical excitons in strongly correlated materials

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Located between the near-infrared (NIR) and the microwave regions, terahertz (THz) radiation shares properties with these two spectral domains making it a unique tool for spectroscopic applications. On one hand, its moderately high photon energy covers an ideal range to interact with various elementary excitations such as phonons, excitons, and molecular vibrations, which is why THz radiation is increasingly used in academia and industry to characterize semiconductors, image bio-tissues and identify chemical agents. On the other hand, its wavelength is still long enough to enable ultrafast NIR pulses to trace its relatively slow oscillating electric field via a technique called electro-optic sampling. By comparing the time-resolved THz pulse incident on and transmitted through a sample, one can retrieve the full complex dielectric response of that material. This information can also be extracted as a function of time delay relative to a synchronized excitation pump pulse to perform ultrafast THz spectroscopy and monitor dynamical condensed-matter systems.