Abstract

The Law of Reflection of a light ray incident upon a mirror (θ_in = θ_out) was first formulated by Euclid around 300 BC in his book Catoptrics; it has been a tenet of geometrical optics ever since [1]. However, it has been discussed since the 1970s, that the Law of Reflection does not necessarily hold for a physical light beam, when this is regarded as the implementation of a ray [2–5]. The violation is due to a diffractive correction to geometrical optics; it may occur for oblique incidence on any mirror provided that its reflectivity is less than 100%. We present here the first experimental demonstration of this effect in the optical domain; it may affect all kinds of optical angular metrology, e.g. in Michelson interferometers and in cantilever-based surface probe microscopies as AFM.

© 2009 IEEE