Differential near-field scanning optical microscopy using sensor arrays

In this paper, we introduce a new aperture-type near-field scanning optical microscopy (NSOM) imaging concept that relies on specially designed large-area (e.g., >200 nm x 200 nm) aperture geometries having sharp corners. Unlike in conventional NSOM, the spatial resolution of this near-field imaging modality is not determined by the size of the aperture, but rather by the sharpness of the corners of the large aperture. This approach significantly improves the light throughput of the near-field probe and, hence, increases the SNR. Here, we discuss the basic concepts of this near-field microscopy approach and illustrate both theoretically and experimentally how an array of detectors can be utilized to further improve the SNR of the near-field image. The results of this work are particularly relevant for imaging of biological samples at a spatial resolution of <50 nm with significantly improved image quality.