Electron-ion recombination has been a subject of thorough studies in plasma physics and astrophysics for last 70 years. From the theoretical point of view the process under consideration is the inverse of photoionization. Direct experimental observation of the spontaneous recombination was extremely difficult due to its small cross section. The situation has changed when the usage of merged electron and ion beams in the storage rings enabled performance of very precise measurements and it was possible to perform successful experiments on radiative recombination.
The rate of recombination can be significantly enhanced by the presence of an external electromagnetic field. This process is called stimulated radiative recombination or laser-induced radiative recombination or finally laser-assisted recombination. Qualitatively the enhancement of the electron-ion recombination in laser fields can be explained with the help of the following classical picture. Namely, during one laser field period electrons are accelerated and decelerated by the field. It appears that at the stage of deceleration there are much more favorable conditions for recombination and hence a respective recombination rate is increased.
Electron-atom collision in the presence of a strong laser field are of importance in applied physics, e.g. laser heating of plasma and high power gas lasers but also due to their relevance to fundamental collision theory and in astrophysics. On the one hand, the laser-assisted electron-atom collisions permit the experimental observation of multiphoton processes at relatively moderate laser field intensities while, on the other hand, from theoretical point of view, they require non-perturbative techniques for treating the laser-matter interaction. The laser field introduces new parameters such as laser photon energy, intensity, polarization and mode structure, which may influence the collision and cause new effects, for example new resonances or the off-shell effects, that would be unobservable in the absence of the laser field. From theoretical point of view a laser photon plays the role of an 'ideal third body', since it has no internal structure and each photon delivers the same well-defined amount of energy and momentum.