Dynamics of a lasing atom in hot plasma

We study theoretically the dynamics of lasing atoms in a very hot plasma capillary, which produce coherent X-ray radiation. The atoms which participate in the lasing action are treated as a dilute gas, embedded in the plasma, whose electrons play the dominant role in inducing relaxations and decoherences. The active atom interacting with the electron reservoir in thermal equilibrium is described by a general Hamiltonian. In analogy with a radiation reservoir, by eliminating the degrees of freedom of the electron reservoir, the evolution rates of the Master Equation, i.e. the transition rates for the populations and dephasing rates for coherences, are calculated. It is demonstrated, by going beyond the dipole approximation, that the contribution of the adiabatic dephasing rate is significant compared to that of the non-adiabatic rate, in contrast to the case of a radiation reservoir. We also study other dephasing mechanisms, e.g. the motion of the lasing atom's center of mass, and the role of other atomic levels.