Introduction to Matter Radiation Interaction

The main phenomena associated to the interaction between radiation and matter relevant for synchrotron radiation studies, i.e. absorption and scattering, are introduced and described. First a classical approach is used in which the radiation is described as an electromagnetic wave and the matter as a macroscopic system characterized by its optical constants; then the optical constants are calculated using the microscopic classical Lorentz model, describing the matter as a set of damped oscillators. A more accurate description is achieved using the semiclassical approach, describing the matter as a quantum system and the radiation as a perturbation which induces transition between the quantum state of the matter. Then, using the full quantum approach in which the radiation field is described as a set of photons, the complete expressions of the absorption and scattering cross section are calculated. In particular for the scattering cross section, relativistic effects associated with the spin are also taken into accounts.