Connection between the Dielectric and the Ballistic Treatment of Collisional Absorption

In this work two important models of treating collisional absorption in a laser driven plasma are compared, the dielectric and the ballistic model. We will see that there exists a remarkable connection between these basic approaches which could give a hint how to overcome the inherent limitations. The approximations made in the models are not identical and lead to different advantages and disadvantages. We notice that the dieletric model is able to handle screening in a selfconsistent manner, but is limited to first order in the electron-ion interaction. The ballistic model calculates the electronion collision exactly in each order of the interaction, but has to introduce a cut-off to incorporate screening effects. This means in the context of kinetic theory that the electron-ion correlation has to be calculated either in random phase or in ladder approximation, or, in other words, the linearized Lenard-Balescu or Boltzmann collision term has to be used.