Single-pulse time-resolved terahertz spectroscopy of sub-millisecond time dynamics

Slow motion movies are not only fascinating to watch, they also allow us to see intricate details of the mechanical dynamics of complex phenomena. If the images in each frame are replaced by terahertz (THz) waves, such movies can monitor low-energy resonances and reveal fast structural or chemical transitions. Here, we combine THz spectroscopy as a non-invasive optical probe with a real-time monitoring technique to resolve non-reproducible phenomena at 50k frames per second. The concept, based on dispersive Fourier transform spectroscopy to achieve unprecedented acquisition speed of THz spectroscopy data, is demonstrated by monitoring sub-millisecond dynamics of hot carriers injected in silicon by successive resonant pulses as a saturation density is established. We anticipate that our experimental configuration will play a crucial role in revealing fast irreversible physical and chemical processes at THz frequencies with microsecond resolution to enable new applications in fundamental research as well as in industry, notably as a rapid supply chain monitoring system in high-volume manufacturing.