Image characterization in the sub-diffraction-limited regime

A shot-noise-limited image profiling technique is developed whereby the images of special classes of objects that fall substantially below the conventionally defined diffraction limit can be characterized with respect to their shape, size, orientation, and reflectance. This is accomplished via the point-by-point subtraction of a point-source reference profile from the unknown object profile, the resulting difference profile providing a `fingerprint' of the unknown object. Computer simulations of this process have been validated by experiments conducted with 8-channel and 64- channel profiling instruments. The latter instrument performs hundreds of profile scans per second: autocentering, downloading, and integrating the scans so as to provide shot-noise-limited profiles in near-real time. Experiments conducted to date have demonstrated the characterization of objects subtending angles as small as 0.07 (lambda) /D, where (lambda) is the dominant wavelength of radiation and D is the diametric aperture of the optical instrument used to achieve that resolution. It is predicted that an instrument similar to the 64-channel system, when used in conjunction with a 1-m telescope in an exoatmospheric environment, will make it possible to characterize objects that are significantly less than a meter in size from distances in excess of 10,000 km. Meanwhile, its application in microscopy likely will make possible the in vivo study of viruses.