Measurement of positive and negative Goos--Hänchen effects for metallic gratings near Wood anomalies.

Large Goos-Hänchen effects are isolated for reflection on a metallic grating. These shifts occur in the vicinity of Wood anomalies. Depending on the nature of the anomaly, these displacements are found to be either positive or, contrary to the usual GH effect, clearly negative. Those shifts, associated with forward and backward leaky surface waves, are as large as plus or minus tens of wavelengths for a classic metallic grating.