Observation of nonspecular effects for Gaussian Schell-model light beams

We investigate experimentally the role of spatial coherence on optical beam shifts. This topic has been the subject of recent theoretical debate. We consider Gaussian Schell-model beams, with different spatial degrees of coherence, reflected at an air-glass interface. We prove that the angular Goos-H"anchen and the angular Imbert-Fedorov effects are affected by the spatial degree of coherence of the incident beam, whereas the spatial Goos-H"anchen effect does not depend on incoherence. Our data unambiguously resolve the theoretical debate in favour of one specific theory.