Polarization Control with Plasmonic Antenna Tips: A Universal Approach to Optical Nanocrystallography and Vector-Field Imaging

• DOI: 10.1021/acs.nanolett.8b00108
• Publication Date: 2018-03-23T20:59:02Z
• Authors: Kyoung-Duck Park; Markus B. Raschke
• Keywords: 0301 basic medicine; RAMAN-SCATTERING; Tip-enhanced second-harmonic generation; domain boundary; SYMMETRY; WSE2; FOS: Physical sciences; 535; 02 engineering and technology; YMnO3; optical nanocrystallography; 03 medical and health sciences; ROOM-TEMPERATURE; LIGHT; vector-field control; 2ND-HARMONIC GENERATION; SINGLE-MOLECULE; MoS2; 0210 nano-technology; Physics - Optics; Optics (physics.optics)

Controlling the propagation and polarization vectors in linear and nonlinear optical spectroscopy enables to probe the anisotropy of optical responses providing structural symmetry selective contrast in optical imaging. Here we present a novel tilted antenna-tip approach to control the optical vector-field by breaking the axial symmetry of the nano-probe in tip-enhanced near-field microscopy. This gives rise to a localized plasmonic antenna effect with significantly enhanced optical field vectors with control of both \textit{in-plane} and \textit{out-of-plane} components. We use the resulting vector-field specificity in the symmetry selective nonlinear optical response of second-harmonic generation (SHG) for a generalized approach to optical nano-crystallography and -imaging. In tip-enhanced SHG imaging of monolayer MoS$_2$ films and single-crystalline ferroelectric YMnO$_3$, we reveal nano-crystallographic details of domain boundaries and domain topology with enhanced sensitivity and nanoscale spatial resolution. The approach is applicable to any anisotropic linear and nonlinear optical response, and provides for optical nano-crystallographic imaging of molecular or quantum materials.