Shot-noise-limited X-ray powder diffraction from organic crystals with laser-driven femtosecond X-ray source.

Laser-driven X-ray sources are increasingly used to investigate the transient behaviour of optically excited materials. While their application to thin films and powders of radiation-hard samples has been extensively explored, their use for radiation-sensitive materials such as organic and protein crystals remains limited. A key challenge is the low signal-to-noise (S/N) ratio, caused by the inherently low flux of these sources and additional non-Poissonian noise arising from temporal fluctuations. Improving noise suppression and enhancing the S/N ratio are therefore critical steps toward extending the applicability of these sources to more demanding systems. We demonstrate shot-noise-limited X-ray powder diffraction from 4-phenylazophenol, representing an organic crystal, using a laser-driven plasma X-ray source. These results highlight the potential of such sources for future studies of transient structural dynamics in photo-excited organic crystals.