Abstract-Preference of subpicosecond laser pulses for terahertz wave generation from liquids

Qi Jin,  Yiwen E,  Shenghan Gao,  Xi-Cheng Zhang,

https://www.spiedigitallibrary.org/journals/advanced-photonics/volume-2/issue-01/015001/Preference-of-subpicosecond-laser-pulses-for-terahertz-wave-generation-from/10.1117/1.AP.2.1.015001.full

Terahertz (THz) wave generation from laser-induced air plasma generally requires a short temporal laser pulse. In contrast, it was observed that THz radiation from ionized liquid water prefers a longer pulse, wherein the mechanism remains unclear. We attribute the preference for longer pulse duration to the process of ionization and plasma formation in water, which is supported by a numerical simulation result showing that the highest electron density is achieved with a subpicosecond pulse. The explanation is further verified by the coincidence of our experimental result and simulation when the thickness of the water is varied. Other liquids are also tested to assure the preference for such a pulse is not exclusive to water.

Abstract-Investigation of liquid lines as terahertz emitters under ultrashort optical excitation

Qi Jin, Yiwen E, Shenghan Gao, Xi-Cheng Zhang

https://arxiv.org/abs/1902.07150

Recently, there has been growing interest in terahertz (THz) wave generation from liquids under optical excitation. Here, we propose and demonstrate the use of liquid lines in place of liquid films as THz emitters to boost THz signals. The geometry of the emitter eliminates the total internal reflection at the flat liquid-air interface. In addition, we observe that the polarity of the liquid has a significant influence on the THz wave generation. Alpha-pinene, a nonpolar liquid, offers much stronger THz radiation than water does. Besides paving the way to develop intense liquid THz sources, our work indicates that THz waves could be a tool for the further study of laser-liquid interaction.