A team led by Hiromi Okamoto at the Institute for Molecular Science in Okazaki, Japan, have found another way to coax photons through tiny holes – paradoxically, by obscuring the hole with a gold disc.
We report an anomalous light transmission phenomenon for a nanoaperture on an opaque screen when the aperture is covered with an opaque cap. In conventional optics, light transmission must decrease when the aperture is capped. However, we found that light transmission is enhanced when the nanodisk is in close proximity to the aperture at a wavelength close to the plasmon resonance. This effect even occurs when the disk is larger than the aperture.
Transparent windows are opened in optically thick metallic films perforated with subwavelength holes by adsorbing a thin layer of molecules at the surface. Counterintuitively, transmission occurs at wavelengths at which the molecular layer absorbs strongly (in this case at 700 nm), as revealed by transmission spectra of the hole array without (black curve) and with adsorbed molecules (red).