Plasma reflectivity behavior under strong subpicosecond excitation of liquids

E Ponomareva,A N Tcypkin,A Ismagilov,S Putilin

doi:10.1063/5.0070963

Abstract

Emerging laser plasma-based technologies require new knowledge on the optical pump optimization and underlying physics of laser–matter interaction. Plasma in liquid jets is still largely unexplored, although this configuration is actively used as a part of optical devices. Hereby, in this work, we report on the reflectivity-based approach to study the optical properties of the induced plasma and quasi-free electron temporal dynamics. The single-shot experiments provide plasma characteristics relative to the laser pump parameters. A strong angular dependence of the plasma absorptivity, which affects rigorously the reflectivity curve, is demonstrated. Furthermore, twofold higher plasma reflectivity in ethanol is revealed and explained through the theoretical model of ultrashort laser pulse interaction with a thin dielectric surface layer. Finally, the time-resolved fundamental and third harmonic reflection measurements and associated analytical study provide the new insight into the electron density dynamics in the case of optical breakdown in water and ethanol. We believe that these findings are of particular significance for the development of highly efficient plasma-based x rays and THz radiation sources.

Highlights

Laser-induced plasmas play a pivotal role in modern physics, having both fundamental and applied significance and particular interest for industrial companies
We reveal a twofold higher plasma reflectivity in the ethanol compared to water, which is further interpreted through the differences in collision relaxation time
To elucidate the experimental curves obtained in the singleshot experiments, we use a theoretical model of the ultrashort pulse unidirectional propagation in the dielectric medium to estimate the reflectivity induced by a change in the free electron density

Summary

Introduction

Laser-induced plasmas play a pivotal role in modern physics, having both fundamental and applied significance and particular interest for industrial companies. Irradiation of solid materials by strong laser pulses is actively used for various types of thin film deposition. Another versatile technique is laser-induced breakdown spectroscopy (LIBS) used in geochemistry, environmental studies, and even remote applications, being an effective elemental analysis technique.. A plasma excited by a pulsed laser system is an emission source covering various spectral ranges. Plasma-based terahertz (THz) radiation sources are being actively developed; they are among the most efficient ones, making it possible to reach the optical-to-THz conversion efficiency values of the order of few percent.. Laser plasma is capable of sustaining these high power fields, leading to the development of the whole range of high-intensity optical elements. The plasma-based accelerators allow obtaining very short electron bunches and large accelerating gradients. On the other hand, laser plasma is capable of sustaining these high power fields, leading to the development of the whole range of high-intensity optical elements.

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