Quantitative differential phase measurement and imaging in transparent and turbid media by optical coherence tomography

Differential phase-contrast optical coherence tomography allows one to measure the path-length differences of two transversally separated beams in the nanometer range. We calculate these path-length differences ti-om the phase functions of the interferometric signals. Pure phase objects consisting of chromium layers containing steps of approximately 100-200-nm height were imaged. Phase differences can be measured with a precision of +/-2 degrees, corresponding to a path-difference resolution of 2-3 nm. To investigate the influence of scattering, we imaged the phase objects through scattering layers with increasing scattering coefficients. The limit of phase imaging through these layers was at approximately 8-9 mean free path lengths thick (single pass). (C) 2001 Optical Society of America.