Enhancement of Terahertz Emission by Silver Nanoparticles in a Liquid Medium.

Due to higher molecular density, lower ionization potential, and a better self-healing property compared with gases, liquid targets have been used for laser-induced terahertz generation for many years. In this work, a liquid target used for terahertz radiation is embedded with silver nanoparticles (Ag NPs), which makes the material have both the fluidity of liquids and conductivity of metals. Meanwhile, the experimental setup is easier to implement than that of liquid metals. Polyvinyl alcohol (PVA) is used as a stabilizing agent to avoid precipitation formation. It is observed that the power of 0.5 THz radiation from the Ag NP suspension is five times stronger than that from liquid water in identical experimental conditions. In addition, the reusability of the material is investigated using multiple excitations. UV-visible spectroscopy and TEM imaging are carried out to analyze the target material after each excitation. As a result, quasispherical Ag NP suspensions show good reusability for several excitations and only a decrease in particle concentration is observed. By contrast, the chain-like Ag NP suspension shows poor stability due to PVA damage caused by intense laser pulses, so it cannot be used in a recyclable manner.