A straightforward way of fabricating nanometer-scale convex lenses developed by researchers at Pohang University of Science and Technology (Pohang, Korea), Sungkyunkwan University (Suwon, Korea) and Columbia University (New York, NY) has led them to demonstrate near-field magnification and imaging of objects that are otherwise too small and close together to resolve because they are beyond Abbe’s diffraction limit. The imaging takes place without resorting to surface-plasmon excitation.
Monomers of calix[4]hydroquinone are dissolved in water and acetone; the resulting crystals are heated at 40°C and form plano-convex lenses with diameters of 50 nm to 3 µm. When, for example, a 250-nm-period grating is viewed through a 1.5-µm-diameter lens resting on the grating, with the image field obtained by a 100× microscope objective with a 0.9 numerical aperture, the grating surrounding the nanolens cannot be seen (because it’s smaller than the diffraction limit), but the grating magnified by the nanolens is easily seen. The near-field image is formed by secondary surface waves that arise from the convex surface of the nanolens. Experimental observations of light paths through the lens indicated an actual focal point much nearer the lens than the theoretical far-field focal point. Contact Kwang S. Kim at [email protected].