Decoherence phenomenon in X-ray diffraction and scattering from rough multilayers

High-resolution X-ray diffractometry was used to study the diffuse scattering from a series of rough multilayers. Reciprocal-space maps were obtained around the small- and wide-angle Bragg reflections using SR from the VEPP-3 storage ring. The data obtained reveal well-known quasi-Bragg diffuse-scattering sheets caused by conformal behavior of interfacial roughness as well as amplification of diffuse scattering when the incoming or outgoing angle is nearly equal to the Bragg angle (incoming and outgoing Bragg scattering) and when incoming and outgoing angles are nearly equal (quasi-specular diffuse scattering). The observed domination in intensity of the incoming Bragg features over outgoing ones, which demonstrates the breakdown of the reciprocity principle, is shown to reflect the decay rate of the coherent X-ray field through the diffuse-scattering channel, which becomes predominant as the spatial coherence of the incident X-ray beam increases. This diffuse-scattering behavior can be considered as a decoherence phenomenon inherent to open quantum systems.