Putting a superlens to work

Researchers from Max Planck Institute for Biochemistry in Martinsried, Germany, and the University of Texas at Austin have imaged objects far smaller than the illumination wavelength by combining scanning near-field optical microscopy (SNOM) with a superlens — a thin slab of a material that, at specific wavelengths, allows imaging below the conventional optics diffraction limit of half a wavelength.

The technique could be useful in a number of areas. “One new possible application could be the imaging of biological objects in their natural environment, separated from the probing tip by the superlens,” said team member and institute nanophotonics group head Rainer Hillenbrand.

That separation is an advantage because, in scattering SNOM, a metallic tip is brought into close contact with a specimen. The tip creates near-field scattering and allows imaging below the diffraction limit. The probe, however, can damage delicate specimens, and the technique can scan only the surface.

As detailed in the Sept. 15 issue of Science, the group used a 440-nm-thick layer of silicon carbide to create a superlens at wavelengths close to 11 μm. They sandwiched it between two 220-nm silicon dioxide layers, constructed a gold film with holes from 1200-nm down to 540-nm diameter and placed the film against one oxide layer. They scanned a probe tip across the other oxide layer and scattered light at 10.84 μm off the superlens. They imaged holes on the far side, 880 nm distant, down to a 540-nm size, 1/20 of the source wavelength.

Hillenbrand foresees a number of applications, such as probing living cells, dependent upon finding or constructing the appropriate superlensing materials.