Plasma Diagnosctics

Chapter 1

Qing Xiong

Abstract

1. Introduction

3

Advanced Optical Diagnostics of

Atmospheric-pressure plasma has been employed in various applications including bio-medicine, environmental pollution control, material processing. Diagnostic characterization of plasma sources is critical and indispensable for plasma control and achieving optimized treatment efficiency. In this chapter we will introduce several advanced optical techniques to visualize the detailed physical-

and-chemical properties of atmospheric-pressure discharges. Non-invasive approaches of optical emission spectroscopy (OES), schlieren or shadowgraph, invasive methods of active laser spectroscopy including laser-induced fluorescence (LIF), laser or broadband absorption, cavity ring-down spectroscopy (CRDS), and laser scattering are illustrated. Basic plasma parameters of gas temperature, electron density and temperature, electric field strength, and reactive chemical gaseous species (O, H, N, OH, NO, O3, etc.) are able to be monitored. Comparisons and comments of these approaches are provided depending on diagnostic purposes.

Atmospheric pressure plasmas attract intensely interests because of non-need of

Plasma parameters mainly are the gas temperature Tg, electron density ne and temperature Te. The three are important physical factors directly influencing the

costly vacuum requirement and enabling in-line processing. Prospective novel applications have emerged over recent years, e.g., plasma bio-medicine, material synthesis, pollutant degradation, chemical conversion. However, with increase of gas pressure, plasmas tend to become constricted, unstable, and non-uniform. Miniaturization of discharge volume with non-equilibrium kinetic property are typically characterized by atmospheric pressure plasmas. And in many cases they are of strong gradients in space and in time as well, e.g., the so-called microplasmas. Much higher diagnostic requirements are put forward to atmospheric pressure plasmas with high time-and-space resolution. Not only the traditional optical emission spectroscopy (OES) accessing emitting species, but also advanced active diagnostics particularly the laser-aided techniques probing plasma parameters (Tg, ne,Te) and reactive plasma species, are the topics discussed in this chapter.

Keywords: advanced optical techniques, plasma parameters, active laser spectroscopy, LIF, absorption spectroscopy

2. Diagnostics of basic plasma parameters

Atmospheric Pressure Plasma

#### Chapter 1
