Control of concerted back-to-back double ionization dynamics in helium

Area of Science:

• Atomic, Molecular, and Optical Physics
• Quantum Chemistry
• Computational Physics

Background:

• Double ionization (DI) in helium, while seemingly simple, reveals complex electron dynamics.
• Standard DI models predict front-to-back electron ejection, but controlling back-to-back ejection remains a challenge.

Purpose of the Study:

• To optimize external laser fields for achieving back-to-back double ionization in helium.
• To explore and validate control mechanisms for this non-trivial DI pathway.

Main Methods:

• Utilized a (1+1)-dimensional model for simulating helium DI.
• Employed four distinct control strategies: short-time control, derivative-free optimization, Krotov method, and classical equations of motion control.
• Performed quasi-classical calculations to verify the underlying mechanism.

Main Results:

• All four control methods successfully generated laser fields that predominantly induce back-to-back DI.
• Identified a consistent two-step mechanism across all successful control procedures.
• Confirmed the classical nature of the dominant DI mechanism through quasi-classical simulations.

Conclusions:

• Achieved controlled back-to-back double ionization in helium using optimized laser fields.
• The identified two-step mechanism involves initial same-direction displacement followed by field-off electron repulsion and nuclear attraction.
• The study highlights the potential for precise control over electron dynamics in atomic systems.