Fig. 2

Experiment geometry and sample design. a An optical system focuses the incoming beam (red lines) onto the sample. Downstream, a 2D pixelated detector records the scattered radiation (red cone). b Enlarged view of the sample and the scattering geometry. The sample bears a suitably tailored, continuously varying grating with local periodicity p(ξ, η) and local orientation angle φ(ξ, η), where ξ and η are the coordinates in the sample plane. Incident light is diffracted away from the undeflected beam (q = 0) with a momentum transfer of ±q(p, φ) according to the local grating parameters. We design the grating such that it maps an enlarged image of the incident illumination, centered around ±(x₀, y₀) in the detector plane at distance z_det.