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

位于近红外（NIR）和微波区域之间，太赫兹（THz）辐射具有这两个光谱域的特性，使其成为光谱应用的独特工具。一方面，其较高的光子能量覆盖了与各种基本激发（如声子，激子和分子振动）相互作用的理想范围，这就是为什么太赫兹辐射越来越多地用于学术界和工业中表征半导体，成像生物组织和识别化学剂。另一方面，它的波长仍然足够长，可以使超快的近红外脉冲通过一种称为电光采样的技术来跟踪其相对缓慢的振荡电场。通过比较入射和透射于样品上的时间分辨太赫兹脉冲，可以获得该材料的完整复介电响应。该信息也可以作为相对于同步激励泵脉冲的时间延迟的函数来提取，以执行超快太赫兹光谱和监测动态凝聚态物质系统。

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.