Credit: © 2009 APS

Three-dimensional (3D) imaging can be used to visualize biological objects such as proteins, as well as to detect buried structures and defects in devices. Near-field scanning optical measurements can detect nanoscale features, and researchers have been trying to use them for 3D imaging as well. However, measurements of optical intensity alone do not produce complete 3D images, and controlling or measuring the phase of the incident or scattered light has proved to be difficult.

Now, John Schotland and colleagues at the University of Pennsylvania have proposed a method for nanoscale 3D optical imaging that does not require phase control or measurement1. The researchers introduce a strong scatterer, such as an atomic force microscope tip, into the near field of the sample, which scatters weakly by comparison. The position of the tip takes the place of the phase of the incident or scattered light beam, while being much easier to control. The inverse scattering problem can then be solved to determine the 3D structure of the sample.

The researchers demonstrate their approach numerically, and point out that it could be generalized to other imaging problems that can be represented with scattering theory.