Optimal control of strong-field ionization with time-dependent density-functional theory

TL;DR

This paper demonstrates how combining quantum optimal control theory with time-dependent density-functional theory can generate femtosecond laser pulses that significantly enhance ionization yields in many-electron systems, with potential for further improvements.

Contribution

The study introduces a method to optimize laser pulses for ionization using OCT combined with TDDFT, comparing different approximations and highlighting the importance of correlation effects.

Findings

TDDFT pulses achieve up to 50% ionization yield in H2.

Single-frequency pulses reach 5-15% yield unless tuned to a Fano resonance.

Exact system optimization yields over 80% ionization, surpassing TDDFT approximations.

Abstract

We show that quantum optimal control theory (OCT) and time-dependent density-functional theory (TDDFT) can be combined to provide realistic femtosecond laser pulses for an enhanced ionization yield in many-electron systems. Using the H$_2$-molecule as a test case, the optimized laser pulse from the numerically exact scheme is compared to pulses obtained from OCT+TDDFT within the TD exact-exchange (TDEXX) and the TD local-density approximation (TDLDA). We find that the TDDFT-pulses produces an ionization yield of up to 50% when applied to the exact system. In comparison, pulses with a single frequency but the same fluence typically reach to yields around 5-15%, unless the frequency is carefully tuned into a Fano-type resonance that leads to $\sim 30%$ yield. On the other hand, optimization within the exact system alone leads to yields higher than 80%, demonstrating that correlation effects beyond the TDEXX and TDLDA can give rise to even more efficient ionization mechanisms.