Using strong electromagnetic fields to control x-ray processes

TL;DR

This paper discusses how combining intense optical lasers with tunable x-ray sources enables control over x-ray absorption processes in atoms and molecules on ultrafast timescales, revealing new possibilities in atomic and molecular physics.

Contribution

It introduces methods to reversibly control resonant x-ray absorption using strong optical fields and explores the effects of ultrafast field ionization and non-linear x-ray processes with free electron lasers.

Findings

Resonant x-ray absorption can be suppressed using optical dressing fields.

Molecular x-ray absorption can be controlled by laser-induced alignment.

Ultrafast field ionization causes irreversible changes in x-ray absorption.

Abstract

Exploration of a new ultrafast-ultrasmall frontier in atomic and molecular physics has begun. Not only is is possible to control outer-shell electron dynamics with intense ultrafast optical lasers, but now control of inner-shell processes has become possible by combining intense infrared/optical lasers with tunable sources of x-ray radiation. This marriage of strong-field laser and x-ray physics has led to the discovery of methods to control reversibly resonant x-ray absorption in atoms and molecules on ultrafast timescales. Using a strong optical dressing field, resonant x-ray absorption in atoms can be markedly suppressed, yielding an example of electromagnetically induced transparency for x rays. Resonant x-ray absorption can also be controlled in molecules using strong non-resonant, polarized laser fields to align the framework of a molecule, and therefore its unoccupied molecular orbitals to which resonant absorption occurs. At higher laser intensities, ultrafast field ionization produces an irreversible change in x-ray absorption. Finally, the advent of x-ray free electron lasers enables first exploration of non-linear x-ray processes.