Diagnostics of reactive species in atmospheric pressure non-thermal plasmas

Atmospheric pressure non-thermal plasmas play a major role in the novel and emerging field of, more generally, plasma health care, not least because they make expensive and size limited vacuum equipment dispensable. In contrast to plasmas in equilibrium, low temperature atmospheric pressure plasmas operate far away from LTE (local thermal equilibrium), with the ion temperature and the electron temperature differing by orders of magnitude. The processes are driven by electrons, while the heavy particles remain at low temperature. Despite their low gas temperature, non-equilibrium plasmas show the same effective plasma chemistry as plasmas in equilibrium. Because the neutrals remain relatively cold, these plasmas do not cause thermal damage to surfaces they may come in contact with. This characteristic provides the possibility of using these plasmas for low-temperature plasma chemistry and for treatment of heat-sensitive materials including biological surfaces and living tissues. Plasmas can be produced by discharges in air, in noble gases or in any desired mixture in order to produce a ‘chemical cocktail’ of atoms, ions and molecules for biomedical applications. Under certain conditions, heat, charged particles and metastable molecules and atoms produced by plasmas may play important roles in the interaction between plasma and biological systems. In practical, the ‘dose’, or the amount of time over which the plasma is applied, depends on the plasma composition and the purpose. The delivery of bactericidal plasma species for example must be appropriately weighed and timed, highlighting the critical need to understand the identities of key plasma species and their critical concentrations that induce bacterial inactivation with little toxicology consequence. The quantitative measure of plasma generated reactive species is the precondition for its bio-medical applications. One of the main causes for the currently limited fundamental insight in the physics of these plasmas is that only few diagnostics are applicable. The most popular diagnostic tool for investigating low temperature atmospheric plasma properties is without question optical emission spectroscopy (OES) as it is a noninvasive and rather straightforward diagnostic tool. However, most of the produced reactive species occupy the respective metastable and ground states, whose density lies five to six orders of magnitudes higher than the density of excited states, and does not give optical emission. The traditional optical emission spectrum gives direct access only to excited particles, and conclusions on the ground state (or metastable) density require rather complex models of approximate character. Another difficulty is to single out one particular plasma species in APPs (in fact any low-temperature plasma). Such plasmas tend to produce a cocktail of several reactive species with little opportunity to enable their individual production alone. In this case, advanced laser spectroscopy diagnostic techniques are desirable. The laser spectroscopy methods provide another important and attractive way to study the fundamental mechanisms of low-temperature plasmas. In an attempt to shed light on which species of APPs are definitely important and which are definitely minor players, absorption spectroscopy (AS) and laser induced fluorescence spectroscopy (LIF) are employed in this dissertation, which give direct access to the ground state (and metastable) populations. In order to control APPs efficiently and further improve its applications, It is mandatory to have the accurate knowledge of the radical densities, its spatial distribution, production mechanism and plasma features like electron temperature, gas temperature, etc. On topic of this, three plasma sources with potential application have been selected as the target. Several advanced non-intrusive diagnostics are utilized to characterize the plasma sources.