Progress, challenges, and opportunities of terahertz emission from liquids

Abstract

Broadband terahertz (THz) wave emission from flowing liquid targets has been demonstrated under short optical pulse excitation. Observations have been reported by using liquid THz sources, including optimal angle of incidence, preference of subpicosecond pulse excitation, and strong sideway emission. Compared with solid targets, the fluidity of liquid allows each laser pulse to interact with a fresh area, which makes it possible to use a table-top laser with a high repetition rate for excitation. Liquids with a comparable material density to solids make them promising candidates for the study of high-density plasma and bright THz sources. In this paper, we review recent progress, challenges, and opportunities of THz emission from liquids. This topic may offer new possibilities in the exploration of THz liquid photonics and may play an indispensable role in the study of laser-liquid interaction.

Plasma-based terahertz wave photonics in gas and liquid phases

“…Liquid plasmas (single color) [155] 0.02 3 1 × 10 −5 0.06 Lithium niobate crystal [150] 7.5 0.5 13.9 12…”

Enhancement of Terahertz Emission by Silver Nanoparticles in a Liquid Medium

“…In order to make more kinds of metals available for terahertz radiation and simplify the experimental system, a strategy that embeds solid metal particles into a liquid medium was employed in this work. According to previous work, the generation process takes place only at the surface of a metal target because of the much thinner penetration depths in metal of both lasers and terahertz waves [ 25 ]. Therefore, metal particles of a nanometer scale were adopted.…”

“…There are several reasons accounting for this: (1) metals have a relatively lower ionization threshold, indicating that more carriers can be created under the same laser excitation; (2) metals have free electrons both originally existing in it and excited by laser pulses; (3) metals have a higher surface tension, which leads to a smoother surface [24]. Liquid gallium was first demonstrated as a liquid metal source for terahertz wave generation because of its chemical stability, physical safety, and accessibility [25]. The melting point of gallium is 30 • C. Therefore, a high-quality liquid gallium line can be obtained using a heater-attached liquid circulating system [24].…”

Ultrafast phenomena and terahertz waves: introduction

“…One of the special sub-topics of THz technology is the generation of THz radiation by using laser fields. E et al review recent progress, challenges, and opportunities of THz emission from liquids, and their summary offers insights into the exploration of THz liquid photonics [6]. Tu et al demonstrate the enhancement of THz radiation from filament by using circularly polarized two-color laser fields [7].…”