Two-Color X-Ray Coherent Diffraction Imaging of Helium Nanodroplets
Abstract
Two-color X-ray imaging with Free Electron Laser pulses offers a powerful approach for probing ultrafast structural dynamics in nanoscale systems, combining (near-)atomic spatial resolution with femtosecond temporal precision. The first X-ray pulse captures the object's initial state, while the time-delayed second pulse records its subsequent evolution. A key challenge lies in disentangling the two views simultaneously recorded by the same detector. We demonstrate the realization of this approach on structurally varying nanoscale particles using two X-ray pulses of different photon energies, 1 and 1.2~keV. Sub-micrometer helium nanodroplets generated in vacuum are irradiated by the two X-ray pulses separated in time by up to 750 femtoseconds. Taking advantage of the high energy sensitivity of the imaging detector, we separate the overlapping images by analyzing individual pixel counts and applying pattern recognition. The helium nanodroplets' spherical shape allows us to cross-validate this approach by fitting the radial scattering profiles with Mie solutions for a bichromatic field. The excellent agreement between the two methods, particularly in the sparsely illuminated outer regions of the diffraction images where fine structural information is encoded, highlights the quality of this approach and its potential for future advanced X-ray movie techniques.
Cite
@article{arxiv.2508.19991,
title = {Two-Color X-Ray Coherent Diffraction Imaging of Helium Nanodroplets},
author = {Linos Hecht and Yevheniy Ovcharenko and Asbjørn Ø. Lægdsmand and Björn Bastian and Thomas M. Baumann and Alessandro Colombo and Subhendu De and Alberto De Fanis and Simon Dold and Thomas Fennel and Robert Hartmann and Katharina Kolatzki and Sivarama Krishnan and Björn Kruse and Aaron C. Laforge and Bruno Langbehn and Suddhasattwa Mandal and Tommaso Mazza and Cristian Medina and Christian Peltz and Thomas Pfeifer and Björn Senfftleben and Keshav Sishodia and Frank Stienkemeier and Rico Mayro P. Tanyag and Paul Tümmler and Sergey Usenko and Andreas Heidenreich and Michael Meyer and Daniela Rupp and Marcel Mudrich},
journal= {arXiv preprint arXiv:2508.19991},
year = {2025}
}