From Umweg Peaks to Analyzer-Based Imaging: Four Decades of High-Resolution X-Ray Diffraction

High-resolution X-ray diffraction has transformed from a precise technique for determining lattice constants into a multifaceted platform for imaging strains, flaws, and phase changes across a wide array of materials. Expanding upon the foundational research of Kotsis and Alexandropoulos [1] and later investigations on Umweg peaks and asymmetric Bragg reflections, the discipline has established a thorough dynamical framework that supports contemporary synchrotron optics. Significant innovations encompass the utilization of asymmetrically cut crystals to regulate angular acceptance, triple-axis diffractometry for dispersion-free measurements, and rocking-curve imaging for real-space strain mapping with sub-arcsecond precision. Recent advancements in analyzer-based phase-contrast imaging and coherent diffraction techniques have expanded these ideas to the non-destructive viewing of interior structures in semiconductor nanostructures, diamond and sapphire crystals, and protein crystals. This paper outlines the historical evolution of dynamical diffraction theory, analyzes the instrumental advancements facilitating ultra-high-resolution measurements, and emphasizes emerging trends in analyzer-based imaging and operando characterization. The synthesis highlights the essential role of crystallographic principles in fostering technological advancement, providing a framework for future inquiry and a comprehensive backdrop for physics instruction.