Spintronic terahertz emitter

While the technology of microwave and infrared sources is quite mature and has been widely used in our daily life for decades, sources that can work well across the terahertz (THz) range are still lagging behind, which is often referred to as the "THz gap." As one of the most pioneering THz setups, terahertz time-domain spectroscopy has been a vital tool to explore the properties of materials as well as their underlying physics. The mechanism is to use an ultrafast infrared pump pulse for exciting rapidly decaying currents inside either a nonlinear or a photoconducting medium, known as a THz emitter, which produces free-space coherent THz radiation. Most recently, a novel THz emitter emerges and rises, which is based on the spin-related effects in magnetic/nonmagnetic nanofilms and can cover the full range of the THz band, named as spintronic THz emitter (STE). This perspective aims to elucidate the unique features and advantages of STE as well as its capability and potential to develop novel applications. We summarize the multidisciplinary efforts that have been made to improve the performance and function of STE, including but not limited to spintronics, optics, and electromagnetics. Distinct THz setups based on STE are reviewed, which may inspire various "real world" applications in the near future.