Near-field optical imaging with a non-evanescently excited high-brightness light source of sub-wavelength dimensions

Abstract

NEAR-field optics involves scanning a spot of light, of dimensions smaller than a wavelength, across the surface of a sample at a distance small enough (a few hundred ångströms) that far-field diffraction effects do not occur1,2. In principle this method should generate an image with a resolution determined principally by the dimensions of the spot of light and not limited by the wavelength³. Although near-field imaging was first proposed in 1928^4,5, efficient implementations that overcome the problem of large evanescent losses in passing light through a sub-wavelength aperture have not been previously realized. Here we present a technique that creates a point of sub-wavelength light without associated evanescent losses in its excitation while achieving the advantage of the exponential increase in intensity that occurs within the near-field³. The sub-wavelength light source is provided by a micropipette coated with a metal and filled with a fluorescent dye embedded in a plastic matrix. The instrument we describe combines the potential for near-field microscopy with the characteristics of a conventional far-field light microscope. Images with overlapping resolutions can be obtained having magnifications that range from a few hundred with the conventional microscope to magnifications, in the near-field mode, of tens of thousands that are of the order normally associated with scanning electron microscopy. Such imaging with light can be achieved even with fluorescence, under ambient conditions and without the destructive sample preparation and beam damage that is characteristic of electron microscopy.