Polarized X-rays from table-top free-electron-driven van der Waals crystals

Abstract

Polarized X-rays are essential for polarization-sensitive techniques such as X-ray absorption near-edge structure (XANES) spectroscopy, magnetic microscopy, and fluorescence imaging. These techniques are crucial in the study of molecular and material dynamics, which are in turn central to driving the global transition to clean energy and sustainability through research in photovoltaics, catalysis and optoelectronics. Currently, polarized X-rays with tunable polarization and photon energy are available only in large facilities like synchrotrons. Here, we theoretically predict and experimentally demonstrate the generation of linearly polarized X-rays from free electron-driven van der Waals crystals, without the need for additional optical stages like polarizers. We show that precise, real-time control over the polarization can be achieved by simply re-orienting the van der Waals crystal. Furthermore, we show that a high degree of polarization can be achieved across all polarization angles - from perpendicular to in-plane - with intensities exceeding 10^9 photons s^(-1) sr^(-1) mA^(-1). Using our findings, we present a scheme for table-top XANES, achieving performance comparable to that of synchrotron facilities. In the process, we develop a new methodology for performing XANES using high-quality polarized X-rays with larger spectral linewidths, named ORIXANES (Orientation-controlled XANES). Our findings pave the way to greater accessibility and smaller carbon footprint for advanced X-ray modalities.