Cone-shaped optical beam induced by nanohole array

Abstract

We observe an interesting optical effect of beam shaping by exploiting a laser beam incident at an arbitrary angle to a nanohole array fabricated in a dielectric aluminum oxide film. The light field with wave-vector component projected in a plane across the nanohole array exhibits omni-directional scattering process, while the light field of the wave-vector component along the elongated nanohole simply propagates toward the film–air interface where the light wave is partially retro-reflected. As a result, the optical fields with different wave vectors construct two symmetric optical beam cones about the film. We simulate the interaction process of the incident laser with nanoholes, showing excellent accordance with our experimental results. The beam shaping mechanism of nanohole array is also validated by our experimental study about scattering polarization.