Attosecond probing of instantaneous AC Stark shifts in helium atoms

TL;DR

This paper introduces a method using attosecond pulses to observe real-time AC Stark shifts in helium atoms, enabling sub-cycle resolution of atomic energy level changes in strong IR fields.

Contribution

It proposes a novel attosecond probing technique to measure instantaneous energy level shifts in atoms subjected to oscillating strong infrared fields.

Findings

Allows detection of atomic energy gaps with sub-laser-cycle resolution

Enables ultrafast gating for complex atomic processes

Demonstrates feasibility through numerical solutions of Schrödinger equation

Abstract

Based on numerical solutions of the time-dependent Schr\"odinger equation for either one or two active electrons, we propose a method for observing instantaneous level shifts in an oscillating strong infrared (IR) field in time, using a single tunable attosecond pulse to probe excited states of the perturbed atom. The ionization probability in the combined fields depends on both, the frequency of the attosecond pulse and the time delay between both pulses, since the IR field shifts excited energy levels into and out of resonance with the attosecond probe pulse. We show that this method (i) allows the detection of instantaneous atomic energy gaps with sub-laser-cycle time resolution and (ii) can be applied as an ultrafast gate for more complex processes such as non-sequential double-ionization.