Bloch Equations in Dense Plasmas

In this paper we discuss pulsed laser excitation, which is nearly resonant with an atomic transition in a partially ionized plasma. The dynamics of particles and the external laser field is microscopicaily described by a Greenʹs function approach on the one- and two-particle level. Particularly for the (1s - 2p) transition of hydrogen the influence of the particle density, laser intensity and detuning on the polarization dynamics is discussed. Treating the collision integral with the Lipavsky ansatz allows to determine the relaxation times T1 and T2 for the inversion and the polarization. These relaxation times vary from the ps scale (in the low-density case) to the fs region (at high densities). Considering the pulse duration in comparison with the relaxation times, the Markovian limit is valid for moderate and high densities, whereas the low-density case requires a non-Markovian computation.