Radiative Recombination in strong laser field

A theoretical treatment of the laser-assisted radiative recombination (LARR) is presented in which the low-frequency (LF) assumption is exploited. The merit of the proposed LF approximation is twofold. First, the LF approximation considerably simplifies the calculations of the transition rates, whereas the results obtained within this approximation are only slightly different from those obtained without resorting to it. Second, the LF approximation gives more insight into the physical picture of the process, which may be viewed as a two-step process. In the first step, the free electron propagates toward the ion, and its motion is described classically with motion changes ascribed mainly to the action of the laser field; in the second step, the free electron recombines with the ion instantaneously at a given value of the laser field phase phi. Since the instant of recombination is not observed, the instantaneous result is averaged over the laser field phase in order to obtain observable quantities. Finally, the LARR rate is calculated for a plasma in the conditions when electronelectron collisions are dominant and a Maxwellian electron distribution function is appropriate. The basic features of the spectra are explained in a simple way thanks to the simple picture offered by the LF approximation.