Metal-free scanning optical microscopy with a fractal fiber probe.

Scanning Near-field Optical Microscopy (SNOM) is the leading instrument used to image optical fields on the nanometer scale. A metal-coating is typically applied to SNOM probes to define a subwavelength aperture and minimize optical leakage, but the presence of such coatings in the near field of the sample can often cause a substantial change in the sample emission properties. For the first time, the authors demonstrate near-field imaging on a metal substrate with a metal-free probe made from a novel structured optical fiber, designed to maximize optical throughput and potentially remove the need for the metal.