Offset-apertured near-field scanning optical microscope probes

Near-field scanning optical microscope (NSOM) probe designs consisting of a subwavelength aperture offset of either a metallic or metal-coated dielectric cantilevered tip are investigated using finite-difference time-domain calculations. The offset aperture and metal-coated dielectric tip couple surface plasmons that illuminate the tip apex, which results in a single-lobed probing optical spot having a full-width half maximum (FWHM) similar to the apex diameter. Since the surface plasmons converge at the apex, an offset-apertured probe promises significantly higher throughput light intensities than an apertured NSOM having a comparable spot FWHM.