Imaging interferometric microscopy.

Imaging interferometric microscopy (IIM) is a synthetic aperture imaging approach providing resolution to the transmission medium (refractive index n) linear systems limit extending to greater, similarlambda/4n using only low-numerical-aperture (low-NA) optics. IIM uses off-axis illumination to access high spatial frequencies along with interferometric reintroduction of a zero-order reference beam on the low-NA side of the optical system. For a thin object normal to the optical axis, the frequency space limit is [(1+NA)n/lambda], while tilting the object plane allows collection of diffraction information up to the material transmission bandpass-limited spatial frequency of 2n/lambda. Tilting transforms the spatial frequencies; the algorithm to reset to the correct image frequencies is described. IIM involves combining multiple subimages; the image reconstruction procedures are discussed. A mean-square-error metric is introduced. For binary objects, sigmoidal filtering of the image provides significant resolution improvement.