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-Hänchen and the angular Imbert-Fedorov effects are affected by the spatial degree of coherence of the incident beam, whereas, the spatial Goos-Hänchen effect does not depend on incoherence. Our data unambiguously resolve the theoretical debate in favor of one specific theory.

Figure 1

Panel 1: GS beam generation. LD: laser diode. SM: single mode. A lens (L1) is used to focus the light to a desired spot size on the ground glass (GG). The light scattered by the GG is collimated by the lens L2 covered by an amplitude filter (F). Inset: Images of two GS beams that we used for the experiment (open squares and open triangles in Fig. 2). Panel 2: Measurements for the spatial GH shift are taken in TIR configuration. LCVR: liquid-crystal variable retarder; PSD: position sensitive detector. Panel 3: Measurements for the angular GH shift are taken in external reflection.

Figure 2

Comparison of the spatial GH effect for a Gaussian beam and three GS beams. Solid squares are the data for the Gaussian beam. The solid line is the theoretical prediction for a Gaussian beam. The other points are for three GS beams with different ${\sigma }_g/{\sigma }_s$ ratios. Within our experimental precision, we do not see a decrease in the GH signal along with the ${\sigma }_g/{\sigma }_s$ ratio.

Figure 3

Angular GH shift for two GS beams. Solid and open triangles: Data are compared with solid line: theory from Ref. [20].

Figure 4

Angular IF shift for a GS beam. Solid triangles: Data are compared with solid line: theory from Ref. [20].