Inhibition of Atomic Ionization in Strong Laser Fields

Abstract

When an atom interacts with an intense laser pulse which generates electric fields comparable to the atomic (Coulombic) field, high order processes become dominant as for example multiphoton ionization(1) and above threshold ionization(2). In some particular circumstances however, coherence phenomena may be at the origin of a substantial inhibition of ionization and lead to the stabilization of the atom. In this contribution, we analyze in detail a physical mechanism which is responsible for strong suppression of ionization(3). We show that the intense field excitation of the atom may generate a new kind of spatially extended wave packet through virtual transitions from the initial state via high-lying Rydberg and continuum states to a coherent superposition of Rydberg states with a small initial overlap with the nucleus. Conventional atomic wave packets(4) are created by direct short pulse excitation of overlapping Rydberg states from a compact initial source which ensures a large initial overlap with the nucleus and a substantial ionization. By contrast, our wave packet stems from extended high-lying states which are accessed virtually through Raman coupling rather than directly through short pulse excitation from compact low-lying states.