Investigation of liquid lines as terahertz emitters under ultrashort optical excitation

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.