M. Merano

Observation of Goos-Hänchen shifts in metallic reflection

We report the first observation of the Goos-Hänchen shift of a light beam incident on a bare metal surface. This phenomenon is particularly interesting because the Goos-Hänchen shift for p polarized light in metals is negative and much bigger than the positive shift for s polarized light. The experimental result for the measured shifts as a function of the angle of incidence is in excellent agreement with theoretical predictions. In an energy-flux interpretation, our measurement shows the existence of a backward energy flow at the bare metal surface when this is excited by a p polarized beam of light.

How orbital angular momentum affects beam shifts in optical reflection

It is well known that reflection of a Gaussian light beam (TEM{sub 00}) by a planar dielectric interface leads to four beam shifts when compared to the geometrical-optics prediction. These are the spatial Goos-Haenchen (GH) shift, the angular GH shift, the spatial Imbert-Fedorov (IF) shift, and the angular IF shift. We report here, theoretically and experimentally, that endowing the beam with orbital angular momentum leads to coupling of these four shifts; this is described by a 4x4 mixing matrix.

Duality between spatial and angular shift in optical reflection

We report a unified representation of the spatial and angular Goos-Haenchen and Imbert-Fedorov shifts that occur when a light beam reflects from a plane interface. We thus reveal the dual nature of spatial and angular shifts in optical beam reflection. In the Goos-Haenchen case we show theoretically and experimentally that this unification naturally arises in the context of reflection from a lossy surface (e.g., a metal).

Brewster cross polarization

We theoretically derive the polarization-resolved intensity distribution of a TM-polarized fundamental Gaussian beam reflected by an air-glass plane interface at Brewster incidence. The reflected beam has both a dominant (TM) and a cross-polarized (TM) component, carried by a TEM(10) and a TEM(01) Hermite-Gaussian spatial mode, respectively. Remarkably, we find that the TE-mode power scales quadratically with the angular spread of the incident beam and is comparable to the TM-mode power. Experimental confirmations of the theoretical results are also presented.

Demonstration of a quasi-scalar angular Goos-Hänchen effect

We show experimentally that the angular Goos-Hänchen (GH) effect can be easily observed, also without employing its resonant enhancement at Brewster incidence. An s-polarized beam was used to decouple the polarization from the propagation dynamics of the beam. We found that, in this case, the angular GH effect can be strongly enhanced by increasing the angular aperture of the Gaussian beam. Our experiments suggest a route toward observing the angular GH effect for true scalar waves, such as acoustic waves and quantum matter waves.

Orbital angular momentum induced beam shifts

We present experiments on Orbital Angular Momentum (OAM) induced beam shifts in optical reflection. Specifically, we observe the spatial Goos-Hänchen shift in which the beam is displaced parallel to the plane of incidence and the angular Imbert-Fedorov shift which is a transverse angular deviation from the geometric optics prediction. Experimental results agree well with our theoretical predictions. Both beam shifts increase with the OAM of the beam; we have measured these for OAM indices up to 3. Moreover, the OAM couples these two shifts. Our results are significant for optical metrology since optical beams with OAM have been extensively used in both fundamental and applied research.

Observing angular deviations in specular reflection of light

We measure the direction of a TEM00 Gaussian beam reflected from an air-glass interface. We report experimental evidence of an angular deviation of the beam axis from the Reflection Law for a light ray.

Observing nonspecular reflection of a light beam

The Law of Reflection of a light ray incident upon a mirror (θin = θout) 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.

Observing Angular Deviations in the Specular Refl ection of a Light Beam

Simple diffraction does not establish the limits on lateral resolution. We can use our new knowledge of light propagation to develop ultrasensitive instruments.

Observing Nonspecular Reflection of a Light Beam

We present here the first experimental demonstration of angularly nonspecular reflection of a light beam by a planar mirror; it occurs due to a diffractive correction if the mirror reflectivity is below 100%.