Progress Made in Near‐Field Imaging with Light from a Sharp Tip

R esearchers are striving to image objects optically at smaller and smaller scales. For example, they'd like to determine the chemical identity of individual molecules and examine the optical properties of semiconductor nanostructures. The required resolution is finer than that allowed by diffraction, which sets a lower limit of half the wavelength of light (hundreds of nanometers for visible light). But much higher resolution can be achieved by viewing objects at distances closer than the wavelength of light. Such near‐field imaging has been hotly pursued since the early 1990s, when researchers demonstrated its promise for imaging single molecules (see PHYSICS Today. May 1994, page 17 and November 1997, page 67). As Dieter Pohl (University of Basel) puts it, “Imagine the potential of microscopy that combines the resolving power of an electron microscope with the enormous spectral resolving power of light.”