XTOP spans a broad portfolio of high-resolution X-ray diffraction, scattering and imaging approaches, encompassing near-field and far-field regimes as well as laboratory- and large-scale-facility-based instrumentation and applications. In particular, XTOP aims to bridge the various method groups by addressing the concepts and practical challenges they share—often across boundaries that, at first glance, appear to separate: how X-ray wavefields interact with the samples and sophisticated optics; how optics or propagation shape measurable contrast; how to model refraction, scattering, diffraction of complex samples with or without multiple-scattering effects (the forward problem); and how to achieve robust object volume reconstruction from incomplete and noisy data (the inverse problem). Increasingly, these shared challenges are accompanied by the convergence of reciprocal-space and real-space approaches.

This “bridging the gap” perspective has characterised XTOP since its start in 1992, when questions such as multiple-scattering effects / dynamical diffraction theory were central across X-ray topography and high-resolution diffraction. It remains equally relevant today as coherence-driven and hybrid near and far field strategies develop. Recent advances at modern laboratory sources and at synchrotron/XFEL facilities, with substantially increased flux and coherence, as well as new optics further accelerate this development and enable multi-contrast, multiscale (hierarchical) studies and high-throughput, in situ, operando or in vivo applications, all supported by advanced computing and AI.

In this spirit, XTOP provides a forum to identify common physical or computational principles and transferable solutions that emerge when experts from seemingly distinct method groups work together.