lunedì 27 agosto 2007

Explaining a 21st Century Version of Young's Experiment


Science Daily — When light strikes a metallic array of tiny openings, smaller than the wavelength of the light itself, interesting entities known as plasmons may be created. An electromagnetic phenomenon like light itself, the plasmons are waves of electrons that move on the surface of a material like ripples on a pond, but they can oscillate back and forth at the frequency of the incoming light. Like water ripples on a pond surface, plasmons travel in the plane of the metal but with a wavelength smaller, sometimes considerably smaller, than the original light.
Just as light can interact with plasmons, these plasmons traveling between the openings, or "apertures," can be reconstituted as light at the apertures. The overall effect is that "large" light can pass through tiny holes.
Scientists are now running experiments to find how the plasmons appear and reform into light by passing light through apertures in various ways. One way is to do the plasmon version of a common high school physics lab experiment: passing waves through two slits, and watching how they interact on the other side. In a high school lab, the waves would be made of water; in the latest experiments, physicists examined the intermediary step in which the plasmons are created near the aperture, pass through, and then reform into a light wave on the other side. This kind of test results in interference patterns from which the coherence altering influence of surface plasmons can be deduced.
C.H. Gan of the University of North Carolina (UNC), Charlotte will report on some new theoretical predictions about the coherence properties of light transmitted through the slits. The theoretical predictions were done by computer simulations of the plasmons' action. The detailed simulations, done with collaborators Greg 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 shows how this effect can be tuned (such as by varying the size or spacing of the slits). This tunability in turn has the potential to be exploited in new, potentially high-resolution, high-quality forms of coherence-related imaging.
Paper FTuS3, "Surface Plasmons in Young's Experiment Modulate the Spatial Coherence of Light"
Note: This story has been adapted from a news release issued by Optical Society of America.

Fausto Intilla

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