Tomographic reconstruction of weak, replicated index structures embedded in a volume

Measurements of weak, embedded index structures are important for material characterization of photopolymers, glass and other optical materials as well as for characterization of fabricated structures such as waveguides. We demonstrate an optical diffraction tomography system capable of measuring deeply-buried, weak, fabricated index structures written in a homogeneous volume. High-fidelity cross sections of these weak index structures are constructed by replicating the structure to be measured to form a diffraction grating. The coherent addition of scattering from each of these objects increases the sensitivity of the imaging system. Measurements are made in the far field, without the use of lenses, eliminating phase aberration errors through thick volumes.