Interaction of Very Intense Radiation Fields with Atomic Systems

In this paper a theory is developed which permits one to treat radiation processes involving a large number of photons in first- or second-order perturbation theory. The theory is applied to the interaction of an atomic electron with a very intense linearly polarized laser beam. It is found under certain approximations that induced radiation will occur at all harmonics nω₀ of the fundamental laser frequency ω₀. The intensity distribution of this radiation is symmetric about the axis of polarization of the primary beam and is peaked at an angle of about 45^∘{} with respect to direction of propagation of the secondary radiation and the polarization of the incident radiation for the first few modes. This angle markedly shifts toward 0^∘{} for increasing n (higher harmonics). The transition probabilities are high enough to make the effect readily observable.