Progresses on the Use of Two-Photon Absorption Laser Induced Fluorescence (TALIF) Diagnostics for Measuring Absolute Atomic Densities in Plasmas and Flames

Abstract

Recent developments in plasma science and technology have opened new areas of research both for fundamental purposes (e.g., description of key physical phenomena involved in laboratory plasmas) and novel applications (material synthesis, microelectronics, thin film deposition, biomedicine, environment, flow control, to name a few). With the increasing availability of advanced optical diagnostics (fast framing imaging, gas flow visualization, emission/absorption spectroscopy, etc.), a better understanding of the physicochemical processes taking place in different electrical discharges has been achieved. In this direction, the implementation of fast (ns) and ultrafast (ps and fs) lasers has been essential for the precise determination of the electron density and temperature, the axial and radial gradients of electric fields, the gas temperature, and the absolute density of ground-state reactive atoms and molecules in non-equilibrium plasmas. For those species, the use of laser-based spectroscopy has led to their in situ quantification with high temporal and spatial resolution, with excellent sensitivity. The present review is dedicated to the advances of twophoton absorption laser induced fluorescence (TALIF) techniques for the measurement of reactive species densities (particularly atoms such as N, H and O) in a wide range of pressures in plasmas and flames. The requirements for the appropriate implementation of TALIF techniques as well as their fundamental principles are presented based on representative published works. The limitations on the density determination imposed by different factors are also discussed. These may refer to the increasing pressure of the probed medium (leading to a significant collisional quenching of excited states), and other issues originating in the high instantaneous power density of the lasers used (such as photodissociation, amplified stimulated emission, and photoionization, resulting to the saturation of the optical transition of interest).

Opportunities of Electronic and Optical Sensors in Autonomous Medical Plasma Technologies

“…(c) TALIF spectroscopy for measuring absolute atomic densities in the plasma discharge. Reproduced with permission from ref . Copyright [2021] [MDPI].…”

The temporal behavior of O atom of a nonequilibrium atmospheric pressure plasma driven by kHz nanosecond voltage pulses

“…Figure 11b Each discharge cycle can be divided into Phase Ⅰ and Phase Ⅱ. As can be seen from Figure 13a, in Phase Ⅰ, the O atoms are mainly produced by the dissociation of Reactions ( 6) and (7) and are consumed by Reactions ( 8) and (12). According to Figure 13b, in Phase Ⅱ, (10), ( 11), ( 13), ( 14) are the main consumption reactions.…”

“…[6] Studies have shown that RONS play an important role in etching organic films, surface treatments, plasma medicine, and so on. [7][8][9] Among them, atomic oxygen is a powerful oxidant and is considered essential in many plasma biomedical applications. [10] As an active diagnostic technique, two-photon laser-induced fluorescence (TALIF) enables the diagnostics of the spatially and temporally resolved absolute concentration of O atoms with minimal impact on the NAPP.…”

Absolute N-atom density measurement in an Ar/N2 micro-hollow cathode discharge jet by means of ns-two-photon absorption laser-induced fluorescence

“…Indeed, TALIF measurements are difficult in conditions where the fluorescence lifetime is shorter than the laser pulse duration. In this case, the use of picosecond or femtosecond lasers can be a better solution 27,36,37 .…”