Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas.

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Plasma-liquid interactions: A review and roadmap

The energy balance at substrate surfaces during plasma processing

This tutorial presents a guided tour of laser feedback interferometry, from its origin and early development through its implementation to a slew of sensing applications, including displacement, distance, velocity, flow, refractive index, and laser linewidth measurement Along the way, we provide a step-by-step derivation of the basic rate equations for a laser experiencing optical feedback starting from the standard Lang and Kobayashi model and detail their subsequent reduction in steady state to the excess-phase equation We construct a simple framework for interferometric sensing applications built around the laser under optical feedback and illustrate how this results in a series of straightforward models for many signals arising in laser feedback interferometry Finally, we indicate promising directions for future work that harnesses the self-mixing effect for sensing applications

Laser feedback interferometry: a tutorial on the self-mixing effect for coherent sensing

An apparatus for producing light includes a chamber and an ignition source that ionizes a gas within the chamber. The apparatus also includes at least one laser that provides energy to the ionized gas within the chamber to produce a high brightness light. The laser can provide a substantially continuous amount of energy to the ionized gas to generate a substantially continuous high brightness light.

Laser-driven light source

M Mitchner and Charles H Kruger Jr Chichester: J Wiley 1973 pp 518 price £13.95 Sandy Brown of MIT and his publishers (Wiley) have been encouraged by the enormous success of Basic Data of Plasma Physics to embark upon the Wiley Series in plasma physics which has now reached the dozen mark. In Partially Ionized Gases the Stanford authors, Mitchner and Kruger, deal with the theory of real plasma properties in a clear and comprehensive manner.

https://iopscience.iop.org/article/10.1088/0031-9112/26/1/026/pdf

Partially Ionized Gases

We present free-bound Biberman factors (12,000, 13,500 and 14,500 K) for the wavelength range of 250–320 nm and 380–800 nm. These values were determined by measuring the absolute continuum intensity of a thermal argon plasma in a cascade arc (2mm dia) for a pressure range of 2–6×105 Pa and a current range of 20–60 A. The continuum emission is corrected for free-free contributions. Two highly accurate experimental reference values of the free-bound factors were used to check the electron density. Agreement with experiments in the u.v. is good. Comparison with theoretical values also shows good agreement below 430 nm. Above this wavelength, theory predicts an edge structure which is not apparent in the available experimental values. The agreement between our results and recent experimental values (for which the electron density was obtained with two-wavelength interferometry) is good. The influence of non-equilibrium has been found to be negligible. We conclude that absolute continuum measurements are well suited to determine electron densities (visible spectroscopy) and electron temperatures (u.v. spectroscopy) by using the known free-bound Biberman factors. Prediction of the absolute intensity as a function of wavelength is possible within 10%.

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The continuum emission of an arc plasma

The parameters and transport properties of a wall stabilized argon arc (40-200 A) at atmospheric pressure with diameters of 5 and 8 mm are studied by spectroscopy and interferometry. The plasma is assumed to be partial local thermal equilibrium and this assumption is verified with the aid of a collisional-radiative model. The departures from Saha-equilibrium of the argon neutral ground state are found to be associated with particle diffusion and the escape of recombination radiation. The measurement of the total excitation rate, from the ground level, including direct ionization, of neutral argon is in reasonable agreement with the literature value

/pdf/an-investigation-of-non-equilibrium-effects-in-thermal-argon-40tu7673b0.pdf

An investigation of non-equilibrium effects in thermal argon plasmas

The authors have determined the characteristic quantities (the electron temperature and the electron density) of an argon plasma in a cascade arc (diameter of 2 and 4 mm) for a pressure range of 1*105-8*105 Pa and a current range of 20-70 A. The absolute continuum intensity was also determined in the wavelength ranges from 250-320 nm and 380-800 nm for pressures of 2, 4 and 6 bar and 20, 40 and 60 A in the case of a 2 mm arc. The plasma is close to local thermal equilibrium (LTE). Using the mentioned quantities, prediction of the absolute intensity as a function of the wavelength is possible from 140 nm to the infrared within 10%. The use of the arc as a light source in photon induced chemical vapour deposition, spectroscopic ellipsometry and infrared absorption spectroscopy is discussed.

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Characteristic quantities of a cascade arc used as a light source for spectroscopic techniques

A description of the deposition process for the production of amorphous carbon coatings, based on decomposition of hydrocarbons in a new type of plasma reactor, is presented. In this reactor the dissociation and ionization of the original, carbon containing material takes place follo- wing injection in the thermal high density plasma of a cascaded arc. This plasma is close to local thermal equilibrium (LTE). The hot seeded arc plasma is cooled by allowing it to expand supersonically into a large va- cuum system. In the expansion high particle velocities are attained, ensu- ring that the plasma composition does not change substantially before the substrate is reached. At the substrate an amorphous carbon film is deposi- ted with rates up to 200 ds, which are measured with in-situ ellipsome- try. The quality of this film, determined by parameters like refractive index, hardness, absorption coefficient in the infrared spectral region, resistance against oxidation, adhesion to the substrate and internal stress, is strongly dependent on the plasma parameters. These parameters can be controlled easily so the intensity and conditions of the particle flux impinging on the substrate can be influenced. Plasma parameters such as electron density, temperatures as well as drift velocities have been measured.

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Expanding plasma used for plasma deposition

The energy balance for electrons and heavy particles constituting a plasma in partial local thermodynamic equilibrium is derived. The formulation of the energy balance used allows for evaluation of the source terms without knowledge of the particle and radiation transport situation, since most of the contributions that arise from that situation (diffusion, local capture of radiation, etc.) are taken into account in the nonequilibrium term. The small correction for the contribution of the loss of excited states, which is slightly overestimated in this approach, can usually be neglected. The overpopulation factor, which can often be evaluated from measurements of the pressure, electron density, and temperature, becomes one of the most important plasma parameters; in the energy balance it accounts for most of the phenomena which may be difficult to evaluate otherwise. As an illustration, some rate coefficients are given for an argon plasma, and the evolution of the several terms of the electron energy equation in a flowing cascaded arc is discussed. >

/pdf/the-energy-balance-of-a-plasma-in-partial-local-nne7wmshzk.pdf

CJ Timmermans

Papers

The continuum emission of an arc plasma

An investigation of non-equilibrium effects in thermal argon plasmas

Characteristic quantities of a cascade arc used as a light source for spectroscopic techniques

Expanding plasma used for plasma deposition

The energy balance of a plasma in partial local thermodynamic equilibrium