Flat liquid jet as a highly efficient source of terahertz radiation

Abstract

Polar liquids are strong absorbers of electromagnetic waves in the terahertz range, therefore, historically such liquids have not been considered as good candidates for terahertz sources. However, flowing liquid medium has explicit advantages, such as a higher damage threshold compared to solid-state sources and more efficient ionization process compared to gases. Here we report systematic study of efficient generation of terahertz radiation in flat liquid jets under sub-picosecond single-color optical excitation. We demonstrate how medium parameters such as molecular density, ionization energy and linear absorption contribute to the terahertz emission from the flat liquid jets. Our simulation and experimental measurements reveal that the terahertz energy has quasi-quadratic dependence on the optical excitation pulse energy. Moreover, the optimal pump pulse duration, which depends on the thickness of the jet is theoretically predicted and experimentally confirmed. The obtained optical-to-terahertz energy conversion efficiency is more than 0.05%. It is comparable to the commonly used optical rectification in most of electro-optical crystals and two-color air filamentation. These results, significantly advancing prior research, can be successfully applied to create a new alternative source of terahertz radiation.

Double-pump technique – one step closer towards efficient liquid-based THz sources

“…Figure 2(b) demonstrates the THz waves energy dependence on the temporal delay ∆τ between two pump pulses typical for the series of our experiments on THz generation in water jet of 100 and 270 µm thickness. Figure 2(b) shows that the maximum enhancement value corresponds to the optimal duration for a certain jet thickness [9]. Moreover, using a thicker jet we get weaker THz signal due to the linear THz absorption in water medium.…”

“…The phenomenon of the generation of THz radiation in liquid media has been rather fully considered in works [6,8]. The single-color excitation of acetone jet in the recent paper [9] gave an optical-to-terahertz conversion efficiency value comparable to the case of two-color laser filamentation in atmospheric air. Moreover, the authors of [10] have successfully modified the experimental setup replacing the flat liquid jets by liquid columns, thus, increasing THz generation efficiency by an order of magnitude.…”

Laser‐Driven Strong‐Field Terahertz Sources

“…[149] A theoretical parametric study as a function of the driving laser wavelength, from the near to the far infrared, [150] as well as an experimental one up to 2.6 µm, [151] confirms that the use of long wavelength short pulses, above critical power, results in energetic THz pulses. One way is to limit the propagation effects by confining the liquid in space, like in the case of water films [154] or water lines. [148] The THz radiation generated by a two-color plasma filament has a conical emission pattern, a feature characteristic especially for long filaments.…”

Giant Enhancement of THz Wave Emission under Double-Pulse Excitation of Thin Water Flow

“…Considering the damage issue in solid samples, liquids can be an ideal target for plasma-based THz wave emission since it can be refreshed continuously during experiments. Indeed, experiments with a water film [25][26][27][28][29] or a line [30] and other liquids such as deionized-water, alcohols, acetone, dichloroethane, or carbon disulfide [31] have been carried out. It is also reported that THz wave emission can be induced in association with X-ray emission from thin water flow and its intensity is enhanced under double-pulse excitation [32].…”