Terahertz wave generation and detection using liquid water

Water, especially liquid water, strongly absorbs terahertz (THz) waves. Generating or detecting THz waves with liquid water has long been thought impossible. Some recent literatures have reported the successful radiation of THz waves from liquid water, which brings new opportunities for the development of THz-related devices based on liquid media. However, the radiation mechanism has not been well elucidated, and the generation efficiency needs to be further improved. We experimentally show that the application of liquid water lines instead of liquid films as THz radiation sources can effectively enhance THz signals. Generally, the generation and detection of THz waves are considered to be "reversible" physical processes. In view of this, we realized the coherent detection of THz waves for the first time based on plasma in liquid water, filling the gap in the field of coherent detection of THz waves in liquid media. Meanwhile, the THz Kerr effect technique for THz-driven liquid water, as a novel tool, is expected to help explore the low-frequency molecular dynamics associated with hydrogen bonding in liquid water.