Three-Dimensional Second-Harmonic Generation Microscopy of Semiconductor Nanowires using Tailored Focal Fields

Abstract

Nonlinear optical (NLO) microscopy has raised much interest with its superior capabilities in high-resolution imaging of a variety of nanostructures without photodamage or labeling. Contrast in NLO microscopy relies on NLO effects, which are sensitive to the crystal structure and the physical properties of the sample at nanoscale. It turns out that the polarization of the input electromagnetic field also matters in the improvement of image contrast. In the context of NLO microscopy, it is evident that the capability to control the polarization in three dimensions at the beam focus is important. Such capability is important in the characterization and exploitation of individual nanostructures with well-known or even unexplored NLO properties. The goal of this Thesis was to perform SHG microscopy of individual vertically-aligned GaAs nanowires in three dimensions. Previously, such kind of nanowires was found to be very sensitive to the electric field component along the beam propagation axis, which can be taken advantage of when mapping the longitudinal electric field distribution of the beam. We also present a method to redistribute the longitudinal electric field of a tightly focused first-order Hermite-Gaussian (HG10) beam by spatially phase-shaping the beam. By using the presented techniques, the longitudinal electric field distribution of a spatially phase-shaped HG10 beam was verified for the first time in three dimensions.