Hugo F. Schouten

Phase singularities of the coherence functions in Young's interference pattern

We analyze the coherence properties of a partially coherent field emerging from two pinholes in an opaque screen and show that the spectral degree of coherence possesses phase singularities on certain surfaces in the region of superposition. To our knowledge, this is the first illustration of the singular behavior of the spectral degree of coherence, and the results extend the field of singular optics to the study of phase singularities of correlation functions.

Achieving superresolution in near-field optical data readout systems using surface plasmons

The effects of surface plasmons and enhanced transmission on the readout contrast in a superresolving near-field optical data system are studied numerically using an exact Green’s tensor formulation. It is shown that plasmon effects can both help and hinder such a readout system, and the system geometry must be chosen carefully to produce optimal effects. Under certain conditions, the system can have a readout contrast approaching 50% and a resolution of at least λ∕3.

Creation and annihilation of phase singularities near a sub-wavelength slit

The anomalously-high transmission of light through subwavelength apertures is a phenomenon which has been observed in numerous experiments, but whose theoretical explanation is incomplete. In this article we present a numerical analysis of the power fl ow (characterized by the Poynting vector)of the electromagnetic fi eld near a sub-wavelength sized slit in a thin metal plate, and demonstrate that the enhanced transmission is accompanied by the annihilation of phase singularities in the power fl ow near the slit.

Optical vortices near sub-wavelength structures

In this paper the phase singularities of the electromagnetic field near a sub-wavelength slit are studied. These phase singularities, such as optical vortices, are found in regular patterns, which can be created or annihilated under the conservation of certain topological quantities, when a parameter such as the slit width is changed. The connection between the phase singularities and the light transmission though the slit is considered.

Plasmon switching: Observation of dynamic surface plasmon steering by selective mode excitation in a sub-wavelength slit

We report a plasmon steering method that enables us to dynamically control the direction of surface plasmons generated by a two-mode slit in a thin metal film. By varying the phase between different coherent beams that are incident on the slit, individual waveguide modes are excited. Different linear combinations of the two modes lead to different diffracted fields at the exit of the slit. As a result, the direction in which surface plasmons are launched can be controlled. Experiments confirm that it is possible to distribute an approximately constant surface plasmon intensity in any desired proportion over the two launching directions. We also find that the anti-symmetric mode generates surface plasmons more efficiently than the fundamental symmetric mode.

Enhancement of spatial coherence by surface plasmons

We report on a method to generate a stationary interference pattern from two independent optical sources, each illuminating a single slit in Youngs interference experiment. The pattern arises as a result of the action of surface plasmons traveling between subwavelength slits milled in a metal film. The visibility of the interference pattern can be manipulated by tuning the wavelength of one of the optical sources.

The Pancharatnam-Berry phase for non-cyclic polarization changes

We present a novel setup that allows the observation of the geometric phase that accompanies polarization changes in monochromatic light beams for which the initial and final states are different (so-called non-cyclic changes). This Pancharatnam-Berry phase can depend in a linear or in a nonlinear fashion on the orientation of the optical elements, and sometimes the dependence is singular. Experimental results that confirm these three types of behavior are presented. The observed singular behavior may be applied in the design of optical switches.

New effects in Young’s interference experiment with partially coherent light

We analyze the coherence properties of a partially coherent optical field emerging from two pinholes in a plane opaque screen. We show that at certain pairs of points in the region of superposition the light is fully coherent, regardless of the state of coherence of the light at the pinholes. In particular, this result also holds if each pinhole is illuminated by a different laser.

The diffraction of light by narrow slits in plates of different materials

We analyse the diffraction of light incident on a sub-wavelength slit in a thin plate. It is found that plates with different material properties, such as conductivity and thickness, show a fundamentally different behaviour of the field near the slit. Depending on the material properties, the light transmission can either be enhanced or frustrated. A correspondence between the handedness of optical vortices and the transmission behaviour is demonstrated.

Correlation singularities in partially coherent electromagnetic beams

We demonstrate that coherence vortices, singularities of the correlation function, generally occur in partially coherent electromagnetic beams. In successive cross sections of Gaussian Schell-model beams, their locus is found to be a closed string. These coherence singularities have implications for both interference experiments and correlation of intensity fluctuation measurements performed with such beams.