The role of Coulomb singularity and Coulomb focusing in radiative recombination and related processes

Coulomb focusing has been shown to strongly enhance the laser-assisted radiative recombination process [1,2]. Since the radiation occurs at close approach of the radiating particle to the Coulomb center, the Coulomb singularity also plays a crucial role. In this report we use the semiclassical Kramers' theory [3] to calculate the laser-assisted radiative recombination of an electron with a proton and demonstrate the importance of these two effects. Radiative recombination is the last stage of high-order harmonic generation (HHG), therefore we also apply the same approach to the HHG and show that the Coulomb focusing and the Coulomb singularity play an important role  in this process leading to enhancement of the photon yield.