Explaining A Plasmon Version of Young's Experiment.

When light strikes a metallic array of subwavelength apertures surface plasmons may be created. An electromagnetic phenomenon like light itself, the plasmons propagate in the plane of the metal but with a wavelength smaller, sometimes appreciably smaller, than the illuminating light. Just as light can couple to surface plasmons, these plasmons propagating between apertures can also be reconstituted as light. The overall effect is that “large” light can pass through tiny holes.

If now the number of openings is limited to two, then one has the makings of a plasmonic version of the famous Young's experiment, the early nineteenth-century experiment in which light falling on two slits in a baffle produced an interference pattern---revealing the wave nature of light. A number of experiments have now been performed on exactly this version of Young's experiment. At the Frontiers in Optics meeting C.H. Gan of the University of North Carolina (Charlotte) reports on some new theoretical predictions relating to the coherence properties of light transmitted through the slits.

His detailed simulations, done with collaborators G. Gbur of UNC Charlotte and T.D. Visser of the Free University of Amsterdam, show how surface plasmons traveling between the apertures result in a correlation of the light fields emitted from the apertures. Gan (chgan@uncc.edu) shows how this effect can be tuned (such as by varying the size or spacing of the slits) to achieve varying degrees of spatial coherence (that is, the amount by which the waves are “in step”) of the emergent reconstituted light waves. This tunability in turn has the potential to be exploited in new forms of coherence-relating imaging, such as 'variable coherence scattering microscopy.