ABSTRACT
When electromagnetic waves enter a gas or plasma, a number of different phenomena can occur, and these can be classified in the four ways shown in figure 2.1: reflection, transmission, refraction and scattering. The degree to which each phenomenon occurs depends on the parameters that characterize the gas or plasma together with the properties of the incident laser light, such as its wavelength, spectral structure, pulse length and intensity. In laser-aided measurements, the changes in the laser radiation due to the gas or plasma are measured quantitatively. Information about the gas or plasma then is obtained using known relationships between the induced changes in the laser radiation and the plasma parameters. In order to make high-quality measurements, it is necessary to use a laser that has properties that produce effects that are large enough to measure. The quality of any particular measurement usually is determined by the suitability of the laser source.
