Interferometric synthetic aperture microscopy (ISAM)

The trade–off between transverse resolution and depth–of–field, and the mitigation of optical aberrations, are long–standing problems in optical imaging. The deleterious impact of these problems on three–dimensional tomography increases with numerical aperture (NA), and so they represent a significant impediment for real–time cellular resolution tomography over the typical imaging depths achieved with OCT. With optical coherence microscopy (OCM), which utilizes higher–NA optics than OCT, the depth–of–field is severely reduced, and it has been postulated that aberrations play a major role in reducing the useful imaging depth in OCM. Even at lower transverse resolution, both these phenomena produce artifacts that degrade the imaging of fine tissue structures. Early approaches to the limited depth–of–field problem in time–domain OCT utilized dynamic focusing. In spectral–domain OCT, this focus–shifting approach to data acquisition leads to long acquisition times and large datasets. Adaptive optics (AO) has been utilized to correct optical aberrations, in particular for retinal OCT, but in addition to requiring elaborate and expensive setups, the real–time optimization requirements at the time of imaging, and the correction of spatially varying effects of aberrations throughout an imaged volume, remain as significant challenges. This chapter presents computed imaging solutions for the reconstruction of sample structure when imaging with ideal and aberrated Gaussian beams.