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 pa rticles and the external laser held is microscopically described by a Green 's function approach on the one- and two-particle level. Particularly for t he (1s --> 2p) transition of hydrogen the influence of the particle density , laser intensity and detuning on the polarization dynamics is discussed. T reating the collision integral with the Lipavsky ansatz allows to determine the relaxation times T-1 and T-2 for the inversion and the polarization. T hese relaxation times vary from the ps scale (in the low-density case) to t he fs region (at high densities). Considering the pulse duration in compari son with the relaxation times, the Markovian limit is valid for moderate an d high densities, whereas the low-density case requires a non-Markovian com putation.