Enhanced Light Transmission Through Nano-Apertures with Dielectric Filling and Its Implications for Biomedical Applications
Huizhong Xu, Department of Physics, St. John’s College of Liberal Arts and Sciences
The study of optical nano-materials has attracted great attention in the past decade or so for both its significance in basic science and huge potential in applications ranging from biomedical engineering to information technology. Among the various types of optical nano-materials, nanometer-sized apertures are particularly interesting for their potential of being used as novel biomedical devices. Using both analytical and numerical methods to study transmission of light through dielectric-filled subwavelength apertures in a real metal, we have found that a propagating mode can in principle exist inside a waveguide of arbitrary small size if a particular relationship between the dielectric constants of the cladding and filling materials at the incident frequency is satisfied. Practical transmission through a subwavelength aperture of finite depth can be enhanced when the depth is such that Fabry-Pérot-like resonances are excited. For 810 nm light incident on a silicon-filled 50-nm-diameter aperture in a 200-nm-thick gold film, we found that a normalized near-field intensity ratio of 1.6 at the exit can be achieved. This resonantly enhanced transmission phenomenon can be utilized to make devices capable of imaging cellular samples at a resolution way beyond what is currently available. Different choices of filling materials enable such a device to operate at different wavelength and thus offer a wide variety of applications ranging from rapid DNA sequencing to studying biochemical processes in a single cell at the single molecule resolution.