Optical near-field imaging and nanostructuring by means of laser ablation

Abstract

In this review we consider the development of optical near-field imaging and nanostructuring by means of laser ablation since its early stages around the turn of the century. The interaction of short, intense laser pulses with nanoparticles on a surface leads to laterally tightly confined, strongly enhanced electromagnetic fields below and around the nano-objects, which can easily give rise to nanoablation. This effect can be exploited for structuring substrate surfaces on a length scale well below the diffraction limit, one to two orders smaller than the incident laser wavelength. We report on structure formation by the optical near field of both dielectric and metallic nano-objects, the latter allowing even stronger and more localized enhancement of the electromagnetic field due to the excitation of plasmon modes. Structuring with this method enables one to nanopattern large areas in a one-step parallel process with just one laser pulse irradiation, and in the course of time various improvements have been added to this technique, so that also more complex and even arbitrary structures can be produced by means of nanoablation. The near-field patterns generated on the surface can be read out with high resolution techniques like scanning electron microscopy and atomic force microscopy and provide thus a valuable tool—in conjunction with numerical calculations like finite difference time domain (FDTD) simulations—for a deeper understanding of the optical and plasmonic properties of nanostructures and their applications.