Impact of the apex of an elongated dielectric tip upon its light absorption properties

Abstract

This paper discusses the impact of the hemispherical ending of a conical dielectric tip on its optical absorption capabilities. We show that the bottleneck for light coupling via the apex is its ability to resonantly interact with the incident light, which is only possible for apex radii commensurate with the wavelength. Once light has been fed into the apex, however, the fundamental guided mode of the dielectric tip is excited independently from the apex size. The existence and propagation of the fundamental mode from the apex into the shank are supported experimentally by the observation of periodic ripples close to the apex of a silicon tip irradiated with high-fluence green laser pulses. The periodicity and attenuation of these ripples along the tip axis are in excellent agreement with the theoretical properties of the fundamental guided mode.