Spectrum and Polarization-Resolved Nonlinear Optical Near-Field Imaging of Plasmonic Nanoantennas

Plasmonic nanoantennas, which support surface plasmon resonances enabling the concentration of electromagnetic energy into subwavelength volumes, have emerged as versatile tools for a wide range of applications. However, achieving high-resolution near-field imaging with polarization and temporal sensitivity remains a significant challenge. In this work, we present a novel nonlinear optical microscopy technique based on degenerate four-wave mixing to enable spectrum- and polarization-resolved near-field imaging of plasmonic nanoantennas. By using a mid-infrared pump and near-infrared probe, we capture detailed spatial distributions of plasmon-enhanced near-field intensity and polarization characteristics, revealing distinct polarization patterns and frequency-dependent enhancements. Our method enables the observation of resonance-induced spectral shifts and subwavelength spatial resolution, offering valuable insights into plasmonic field behaviors, particularly in the mid-infrared range. This approach provides a powerful tool for exploring and understanding the complexities of plasmonic nanostructures, with significant potential for advancing nano-optics applications.