Light and Matter

Abstract

In this and the following chapter, we will discuss basic phenomena occurring when matter is exposed to light. While here we will be concerned with various actions of matter on light, the opposite effect will be discussed in Chap. 3. Matter can act on electromagnetic radiation in manifold ways. In Fig. 2.1, a typical situation is shown, where a light beam is incident on a slice of matter. In principle, three effects exist which may interfere with its undisturbed propagation:

• reflection and refraction,

• absorption,

• scattering.

Reflection and refraction are strongly related to each other by Fresnel’s laws. Therefore, these two effects will be addressed in the same section. In Fig. 2.1, refraction is accounted for by a displacement of the transmitted beam. In medical laser applications, however, refraction plays a significant role only when irradiating transparent media like corneal tissue. In opaque media, usually, the effect of refraction is difficult to measure due to absorption and scattering.