Paper NS+TR-TuM5
Optical Energy Density Inside Metallic Nano-Apertures
Tuesday, November 10, 2009, 9:20 am, Room L
We use numerical methods and calculate the optical energy density inside a sub-micron sized hole surrounded by metallic cladding as light wave travels through it. Such information is important in the use of Zero-Mode-Waveguides (ZMWs) [1], where the diameter of the apertures is less than the wavelength of the light. In ZMWs, it has been postulated the evanescent wave inside the aperture defines the illumination volume, which is a function of the illumination wavelength and the aperture cut-off wavelength, which is in-turn a function of the aperture-diameter. Although the cut-off wavelength of a circular hole in an infinitely thin perfect conductor is a monotonically increasing function of the hole diameter [2], we see from our calculation result that, inside apertures surrounded by aluminum cladding, optical energy density increases until it reaches a peak as aperture diameter increases, and then levels off as aperture becomes more transmitting. This result suggests that, in order to achieve the best signal-to-noise ratio in fluorescent single-molecule experiments involving ZMWs, there is an optimal aperture diameter for each wavelength and application. [1] Levene et al, “Zero-Mode Waveguides for Single-Molecule Analysis at High Concentrations, Science, Vol 299, 2003.
[2] Jackson, J. D., Classical Electrodynamics, 1998.