Theory of nonlinear interactions between x rays and optical radiation in crystals

TL;DR

This paper explores how nonlinear x-ray and optical interactions in crystals depend on band structure, offering a new way to probe fundamental properties and ultrafast dynamics of crystalline materials.

Contribution

It demonstrates that nonlinear interactions reveal both valence electron details and the crystal's periodic potential, enabling advanced multi-dimensional spectroscopic techniques.

Findings

Interactions depend strongly on band structure

Potential to develop ultrafast, atomic-scale metrology methods

Distinguishes between electronic and structural contributions

Abstract

We show that the nonlinear interactions between x rays and longer wavelengths in crystals depend strongly on the band structure and related properties. Consequently, these types of interactions can be used as a powerful probe for fundamental properties of crystalline bulk materials. In contrast to previous work that highlighted that these types of nonlinear interactions can provide microscopic information on the valence electrons at the atomic scale resolution, we show that these interactions also contain information that is related to the periodic potential of the crystal. We explain how it is possible to distinguish between the two contributions. Our work indicates on the possibility for the development of novel multi-dimensional pump-probe metrology techniques that will provide spectroscopic information combined with structural information including ultrafast dynamics at the atomic scale.