Optics of material media

To clarify how light interacts with matter, we'll begin with a brief review of the properties of its basic constituents, atoms 1.1 . Atoms are sometimes grouped into molecules, whose structure we will discuss 1.2 . A group of atoms and molecules can emit, absorb or modify the light that passes through it, with characteristics that depend on the specific features of each component. But these characteristics dominate the optical properties of the medium only if the concentration is low, as in a gas under low pressure. In condensed media such as liquids and solids, optical properties are linked to very strong interactions between neighboring atoms, and require special treatment 1.3 .