``Interaction-free'' imaging

Using the complementary wavelike and particlelike natures of photons, it is possible to make ``interaction-free'' measurements where the presence of an object can be determined with no photons being absorbed. We investigated several ``interaction-free'' imaging systems, i.e., systems that allow optical imaging of photosensitive objects with less than the classically expected amount of light being absorbed or scattered by the object. With the most promising system, we obtained high-resolution (10-μm), one-dimensional profiles of a variety of objects (human hair, glass and metal wires, and cloth fibers) by raster scanning each object through the system. We discuss possible applications and the present and future limits for interaction-free imaging.