Multi-MeV electrons from above-threshold ionization of the neon K-shell

Abstract

We present measurements of integrated electron energies produced by above-threshold ionization (ATI) of neon in a laser field with intensity exceeding 10${}^{20}$ W/cm${}^2$. We observe electrons with energy exceeding 10 MeV ejected in the laser forward direction above a threshold intensity of $2\times 10^{20}$ W/cm${}^2$. We compare to ATI models using both tunneling (ADK-PPT) and barrier suppression ionization and observe the onset of ATI at a higher threshold intensity than predicted by these models.