Research Article

# Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction

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Science  21 Oct 2011:
Vol. 334, Issue 6054, pp. 333-337
DOI: 10.1126/science.1210713

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• RE: Generalized Laws of Reflection and Refraction
• Timothy Davis, Honorary Professor, School of Physics, University of Melbourne

In this article the authors make misleading statements regarding a generalization of Snell's law of refraction and inadequately reference a considerable body of work done previously on this topic. Their device, which they claim demonstrates anomalous refraction, is nothing more than a diffracting phase grating, well known in optics, that preferentially diffracts into the -1 order and suppresses the +1 diffraction order. Their equation (2) and in particular equation (6) is the diffraction equation, known for well over 100 years and usually taught in undergraduate physics. However, they misleadingly call this a generalisation of refraction rather than use the commonly accepted term "diffraction equation".

There is clear evidence of diffraction in their data that was not mentioned at all in their article. If you look closely at the red curve in Figure 3c, 11 micron period, you will see the 0-th order peak (the straight-through beam) at 0 degrees (which they call ordinary refraction), then the -1 diffraction order at about -48 degrees (which they call anomalous refraction) and if you look closely at the high resolution image of Fig. 3 you will see evidence of the +1 diffraction order at +48 degrees - a small peak which would be clearer in the original data but which is just discernible in this graphic. This peak appears in the data for the other grating periods and exactly follows the change in angle of the -1 diffraction order, as expected from the diff...

Competing Interests: None declared.