Young's Double-slit Experiment in the Nanoworld

DESCRIPTION:

Fig. 1. Illustration of the Young's double-slit experiment.

In Young's original experiment (see Fig. 1), sunlight passes first through a single slit, next through two thin subwavelength vertical slits, and is then viewed on a rear screen. When either slit is covered, a single peak is observed on the screen from the light passing through the other slit. But when both slits are open, instead of the sum of these two individual peaks that would be expected if light were made of particles, a pattern of light and dark fringes is observed. The animation shows an electromagnetic wave scattering by subwavelength two slits in a metal film at the incident wavelength, which is far from the resonance (see Fig. 2A). However, in case of nanostructural films composed of a nobel metal at some incident wavelength metal becomes transparent and interference picture on the detection screen is lost (see Fig. 2C).

At the plasmon resonance wavelength conductive electrons in metal films are excited in phase and produce a secondary electromagnetic field, which adds to the incident field and results in a total transmission of the incident light through the structure practically with very small losses. Further decrease of the thickness of a metal and correct adjustment of the incident wavelength results in complete transparency of the structure.

Figure 2. Young's double-slit experiment in macro- (left panel) and nano-worlds (right panel). At the plasmon resonance wavelength metal nanostructures become transparent and the interference pattern from two subwavelength slits is different.

Simulations supporting presented animations are exact numerical solution of Maxwell equations on a grid, where metal is considered within a Drude model.

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FOR TEACHERS:

This simulation is appropriate for high school and college level courses. It can be incorporated into general electrodynamics courses to illustrate the concepts of surface waves and plasmon resonances, but can serve also in the general study of wave phenomena in the nano domain.