Manipulating light using nanostructures

This dissertation describes progress made towards the control of emission direction and polarization from a single emitter using a sharp gold-coated atomic force microscope tip. When a metallic tip is scanned in the emitter near-field, the probe acts as a secondary emitter such that the superposition of electromagnetic fields from these two emitters modifies the emission polarization and pattern in the far-field.;The physical mechanism underlying this ability to manipulate the emission polarization and direction is studied in detail using a unique data acquisition technique and finite-difference time domain (FDTD) simulations. This technique enables us to reveal how the polarization of emitted photons from a quantum dot (QD) is modified as a gold-coated tip is scanned laterally and vertically in its proximity, and the FDTD simulations are used to calculate the angular emission pattern. The simulated emission pattern at the back-focal plane enables us to identify how the direction of emitted photons is altered as the gold tip is scanned in the proximity of a dipole emitter.;This dissertation also highlights a novel back-focal imaging technique correlated with the vertically oscillating probe. By pulsing the continuous-wave laser at various phases of tip oscillation and using the near-field interaction of the tip-sample, the exact tip-sample distance can be identified. Tip-induced modification of the angular emission pattern from an individual quantum dot is experimentally demonstrated.;This work also includes the study of the emission properties of GaN nanowires. A hyper-spectral imaging technique combined with spectral center of mass (SCOM) analysis helps us to identify the spectral inhomogeneity within a nanowire. The spectral information within a diffraction-limited spot of a nanowire provides the insight regarding the distribution of mid-gap defect states within a nanowire.