Inverse bremsstrahlung absorption in strong radiation fields during binary collisions: 'straight-line path' approximation

Considers the relationship between the impact, Born and 'straight-line path' approximations and the overlap of the regions of applicability. Particular emphasis is given to a perturbative fully classical model of the electron motion. It is shown that the perturbative fully quantum-mechanical approach (Born approximation) leads to a formally similar result. The impact approximation is shown to exist as an asymptotic limit. These results are used...