The properties of an atomic system immersed in dense plasmas are strongly modified by the interactive plasma environment. For instance, the emission spectrum originating from bound-bound and bound-free transitions is shifted and broadened due to collisions between the emitter system and the plasma particles. These modifications are known as pressure broadening and shift of spectral lines for bound-bound transitions and ionization potential depression for bound-free transitions. However, recent experimental observations on these modifications cannot be explained by those simple analytical models which have been widely used so far. A systematically derived self-consistent quantum mechanical many-body theory is indispensable.
In this thesis work the optical properties in dense plasmas, such as the transition rates, the ionization potential depression, and the optical spectra, are investigated within a quantum-statistical approach. The dynamical structure factors are introduced to account for the detailed spatial and temporal correlations and fluctuations of the plasma environment. The plasma spectral line profile is derived by means of a quantum master equation approach, which coincides in the quantum mechanical region with the spectral line profile calculated via the thermodynamic Green's function technique. In the quasi-classical region of highly excited Rydberg states, the transition rates are found to be more reasonably explained by a coherent quasi-classical wave packet description. As another important result, a general expression for the ionization potential depression in plasmas is obtained. This expression takes into account the dynamical ionic structure factor and is valid in a wide density and temperature range. Using this new theory, recent experimental results performed in warm dense matter can be explained.