Visible Light Superlens

Conceptual drawing of nanoparticle-based metamaterial solid immersion lens (Source: Bangor Univ. / Fudan Univ.)

Conceptual drawing of nanoparticle-based metamaterial solid immersion lens (Source: Bangor Univ. / Fudan Univ.)

Nanobeads are all around us- and are, some might argue, used too frequently in every­thing from sun-screen to white paint, but a new ground-breaking appli­cation is revealing hidden worlds. A new concept is using new solid 3D superlenses to break through the scale of things previously visible through a micro­scope. Illustrating the strength of the new superlens, Zengbo Wang at Bangor University and Limin Wu at Fudan Uni­versity describe seeing for the first time, the actual information on the surface of a Blue Ray DVD. That shiny surface is not as smooth as we think. Current micro­scopes cannot see the grooves containing the data, but now even the data itself is revealed.

The team created minute droplet-like lens structures on the surface to be examined. These act as an addi­tional lens to magnify the surface features previously invisible to a normal lens. Made of millions of nano­beads, the spheres break up the light beam. Each bead refracts the light, acting as individual torch-like minute beam. It is the very small size of each beam of light which illu­minate the surface, extending the resolving ability of the micro­scope to record-breaking levels. The new super­lens adds fivefold magnification on top of existing micro­scopes.

Extending the limit of the classical micro­scope’s reso­lution has been the Holy Grail of micro­scopy for over a century. Physical laws of light make it impossible to view objects smaller than 200 nm using a normal micro­scope alone. However, superlenses have been the new goal since the turn of the millen­nium, with various labs and teams resear­ching different models and materials. “We’ve used high-index titanium dioxide nano­particles as the building element of the lens. These nano­particles are able to bend light to a higher degree than water. To explain, when putting a spoon into a cup of this material, if it were possible, you’d see a larger bend where you spoon enters the material than you would looking at the same spoon in a glass of water,” Wang says. “Each sphere bends the light to a high magni­tude and splits the light beam, creating millions of indi­vidual beams of light. It is these tiny light beams which enable us to view previously unseen detail.”

Wang believes that the results will be easily repli­cable and that other labs will soon be adopting the techno­logy and using it for themselves. The advan­tages of the techno­logy is that the material, titanium dioxide, is cheap and readily available, and rather than buying a new micro­scope, the lenses are applied to the material to be viewed, rather than to the micro­scope. “We have already viewed details to a far greater level than was pr­eviously possible. The next challenge is to adapt the techno­logy for use in biology and medicine. This would not require the current use of a combi­nation of dyes and stains and laser light- which change the samples being viewed. The new lens will be used to see germs and viruses not previously visible,” Wang says. (Source: Bangor Univ.)

Reference: W. Fan et al.: Three-dimensional all-dielectric metamaterial solid immersion lens for subwavelength imaging at visible frequencies, Sci. Adv. 2, e1600901 (2016); DOI: 10.1126/sciadv.1600901

Links: School of Electronic Engineering, Bangor University, Wales, UK • Dept. of Materials Science (Li-Min Wu), Fudan University, China

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