A) Terahertz spectroscopy

The terahertz (THz) frequency band is part of the electromagnetic spectrum and extends from about 100 GHz to 100 THz. Although many important electronic and molecular properties become visible in this band, it was hard to reach for a long time because of the lack of sensitive techniques.

Fig 1: Illustration of the electromagnetic spectrum. The wavelength of THz radiation is about 1 mm.

Today, time-resolved THz techniques allow for spectroscopy in this band. They distinguish from most other optical techniques by the fact that the electric field of the radiation is detected. In contrast, in the optical part of the spectrum, only time-averaged light intensities can be measured. The time-resolved detection of the THz fields yields both, amplitude and phase information. This is advantageous when the charge carrier's response to a THz pulse is probed. The observed THz response of the carriers can be directly connected to their motion and allows for the extraction of the desired transport parameters.

Fig 2: Time-resolved THz pulse. The signal is proportional to the electric field.