Breaking the diffraction barrier outside of the optical near-field with bright, collimated light from nanometric apertures.

The optical diffraction limit has been the dominant barrier to achieving higher optical resolution in the fields of microscopy, photolithography, and optical data storage. We present here an approach toward imaging below the diffraction barrier. Through the exposure of photosensitive films placed a finite and known distance away from nanoscale, zero-mode apertures in thin metallic films, we show convincing, physical evidence that the propagating component of light emerging from these apertures shows a very strong degree of collimation well past the maximum extent of the near-field (lambda(0)/4n-lambda(0)/2n). Up to at least 2.5 wavelengths away from the apertures, the transmitted light exhibits subdiffraction limit irradiance patterns. These unexpected results are not explained by standard diffraction theory or nanohole-based "beaming" rationalizations. This method overcomes the diffraction barrier and makes super-resolution fluorescence imaging practical.