IMAGE CHARACTERIZATION IN THE SUB-DIFFRACTION-LIMITED REGIME

A shot-noise-limited image profiling technique is developed whereby th e images of special classes of objects that fall substantially below t he conventionally defined diffraction limit can be characterized with respect to their shape, size, orientation, and reflectance. This is ac complished via the point-by-point subtraction of a point-source refere nce profile from the unknown object profile, the resulting difference profile providing a ''fingerprint'' of the unknown object. Computer si mulations of this process have been Validated by experiments conducted with 8-channel and 64-channel profiting instruments. The latter instr ument performs hundreds of profile scans per second: autocentering, do wnloading, and integrating the scans so as to provide shot-noise-limit ed profiles in near-real time. Experiments conducted to date have demo nstrated the characterization of objects subtending angles as small as 0.07 lambda/D, where lambda is the dominant wavelength of radiation a nd D is the diametric aperture of the optical instrument used to achie ve that resolution. It is predicted that an instrument similar to the 64-channel system, when used in conjunction with a l-m telescope in an exoatmospheric environment, will make it possible to characterize obj ects that are significantly less than a meter in size from distances i n excess of 10,000 km. Meanwhile, its application to microscopy likely will make possible the in vivo study of viruses. (C) 1997 Society of Photo-Optical Instrumentation Engineers.