Review on VUV to MIR absorption spectroscopy of atmospheric pressure plasma jets

Abstract

Absorption spectroscopy (AS) represents a reliable method for the characterization of cold atmospheric pressure plasma jets. The method's simplicity stands out in comparison to competing diagnostic techniques. AS is an in situ, non-invasive technique giving absolute densities, free of calibration procedures, which other diagnostics, such as laser-induced fluorescence or optical emission spectroscopy, have to rely on. Ground state densities can be determined without the knowledge of the influence of collisional quenching. Therefore, absolute densities determined by absorption spectroscopy can be taken as calibration for other methods. In this paper, fundamentals of absorption spectroscopy are presented as an entrance to the topic. In the second part of the manuscript, a review of AS performed on cold atmospheric pressure plasma jets, as they are used e.g. in the field of plasma medicine, is presented. The focus is set on special techniques overcoming not only the drawback of spectrally overlapping absorbing species, but also the line-of-sight densities that AS usually provides or the necessity of sufficiently long absorption lengths. Where references are not available for measurements on cold atmospheric pressure plasma jets, other plasma sources including low-pressure plasmas are taken as an example to give suggestions for possible approaches. The final part is a table summarizing examples of absorption spectroscopic measurements on cold atmospheric pressure plasma jets. With this, the paper provides a 'best practice' guideline and gives a compendium of works by groups performing absorption spectroscopy on cold atmospheric pressure plasma jets.

Electron characterization in weakly ionized collisional plasmas: from principles to techniques

“…Thus, external radiation sources, such as lasers and microwaves, should be used to derive the information of ground state species. For neutrals or ions, LIF [131][132][133], two-photon absorption LIF (TALIF) [134], and optical absorption spectroscopy [135] have been widely used, and laser Thomson scattering and interferometry are well established and feasible as diagnostic techniques for free electrons.…”

Highly Sensitive, Calibration-Free WM-DAS Method for Recovering Absorbance—Part I: Theoretical Analysis

“…In the past several decades, the tunable diode laser absorption spectroscopy (TDLAS) has played a growing role in the diagnostic of combustion and plasmas, as well as in some industrial applications [1][2][3][4][5][6][7][8][9]. As the key parameter in TDLAS, the absorbance contains the information of both gas properties (temperature, pressure, concentration, velocity, etc.)…”

Detection of HO2in an atmospheric pressure plasma jet using optical feedback cavity-enhanced absorption spectroscopy

“…Due to their small size and high density gradients in space and time, these jets, however, are difficult to diagnose quantitatively. Absorption spectroscopy has become a popular method for characterizing the fluxes of species generated by these plasma sources [15]. To achieve space-resolved densities from the line-of-sight integrated densities, Abel inversion is most commonly used, which leads to a local density as a function of distance from the centre [16].…”