Relativistic absorption in plasma in an ultra strong laser field

We formulate the problem of the interaction of an ultra strong laser pulse within the framework of the quasifree state of an electron. Starting from a quantum mechanical approach the inelastic cross-section between charged particles is calculated. From this, a simple and useful approximation is obtained for the multiphoton energy transfer processes which accompany the relativistic scattering of a charged particle and an effective collision frequency is found. The amplitude of the electron oscillatory velocity vO in the radiation field is assumed to exceed the electron thermal velocity vte and vO ∼ c. Under these conditions, the absorption rate is independent of the initial distribution function and depends only on the photon flux intensity. The effective absorption coefficient is scaled as Ir, where the r-parameter is in the range of 0.5 ≤ r ≤ 0.75. Our results are compared with those of other formalisms and experimental results. (author)