Max Born is the director of the Institute for Nonlinear Optics and Short pulse Spectroscopy.

Mixing laser- and x-ray-beams
Two light beams from flashlights will not be influenced by each other when they cross. This is different for very intense laser pulses which meet in a suitable “nonlinear material” – here, beams can be deflected and new beams of different color can be created in a process called wave-mixing. The observation of such wave-mixing phenomena allows researchers to draw conclusions about electronic transitions within the nonlinear material which are otherwise invisible. Researchers from MBI and DESY have now observed how an x-ray beam interacts with a laser beam, paving a route to atom-selective studies of ultrafast processes in the future. Credit: Anne Riemann, Forschungsverbund Berlin e.V.

Unless the beams meet within a suitable material, real laser beams do not interact with each other. Waves can give rise to beams with different colors and directions.

Wave-mixing processes between different light beams are one of the cornerstones of the field. In this process, energy and momentum can be exchanged, giving rise to additional laser beams emerging from the interaction zone in different directions. These effects can be used to design and realize new laser light sources.

Understanding the nature of the material in which the wave mixing process occurs is provided by the analysis of the emerging light beams in wave mixing phenomena. Researchers can understand the electronic structure of a specimen and how light can interact with it by using wave-mixing based spectroscopy. These approaches have not been used outside of the visible range.

A team of researchers from Max Born Institute, Berlin, and DESY, Hamburg, have observed a new kind of wave mixing process. They were able to see how the X-ray photon and the soft X-rays could be combined in a single crystal of LiF.

They were able to map out the process's efficiency when changing the X-rays' color, because they observed it for the first time. When the process involves an inner-shell electron from a lithium atom being promoted into a state where this electron is tightly bound to the vacancy it left behind, the mixing signals are not visible. An otherwise forbidden transition of an inner-shell electron contributes to the wave mixing process.

The researchers got a detailed picture of where the excited electron travels in its short lifetime, only if it is in the vicinity of the hole.

Due to the ability of X-rays to excite inner shell electrons at the different atomic species in a material, the demonstrated approach allows researchers to track electrons moving around in molecule or solid after they have been stimulated by an ultrafast laser pulse. electrons moving towards different atoms are crucial steps in photochemical reactions or applications such as light harvesting, e.g., via photovoltaics or direct solar fuel generation.

Many different atoms of the periodic table can be excited by X-ray lasers as our wave-mixing spectroscopy approach can be scaled to much higher photon energies. Daniel Schick, researcher at MBI, says that it will be possible to track the presence of electrons at many different atoms of a more complex material.

Science Advances published the research.

More information: Horst Rottke et al, Probing electron and hole colocalization by resonant four-wave mixing spectroscopy in the extreme ultraviolet, Science Advances (2022). DOI: 10.1126/sciadv.abn5127. Journal information: Science Advances Provided by Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) Citation: Mixing laser beams and X-ray beams (2022, May 20) retrieved 20 May 2022 from This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.