Enhanced Light Confinement in a Near-Field Optical Probe with a Triangular Aperture

We present a probe concept for scanning near-field optical microscopy combining the excellent background suppression of aperture probes with the superior light confinement of apertureless probes. A triangular aperture at the tip of a tetrahedral waveguide (full taper angle ∼90°) shows a strong field enhancement at only one rim when illuminated with light of suitable polarization. Compared to a circular aperture of equivalent size, the resolution capability is doubled without loss of brightness. For a ∼60  nm sized triangular aperture, we measured an optical resolution <40  nm and a transmission of ∼10^-4.