Laser assisted positronium formation in positron collision with Rydberg hydrogen*

We investigate the formation of positronium (Ps) in the presence of a linearly polarized infrared laser field, via the collision of positrons with Rydberg hydrogen atoms ${\rm H}(n_H)$ where $n_H$ is the principal quantum number. We are using classical trajectory Monte Carlo method (CTMC) which is justified for $n_H \geq 3$. The hydrogen in excited states has an effective dipole moment which in the presence of a laser field leads to a dipolar focusing [1]. Due to this effect, the Ps formation cross-section is enhanced substantially as compared to the zero-field case. The degree of this enhancement is controlled by the positron velocity, laser frequency and the laser-field amplitude. The final-state distribution in Ps is much broader than in the zero-field case.

[1] H.B. Ambalampitiya, M.K. Matfunjwa and I. I. Fabrikant, J. Phys. B: At. Mol. Opt. Phys. 57, 10LT01 (2024)