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

Differential phase-contrast optical coherence tomography allows one to meas ure the path-length differences of two transversally separated beams in the nanometer range. We calculate these path-length differences ti-om the phas e functions of the interferometric signals. Pure phase objects consisting o f 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 th e influence of scattering, we imaged the phase objects through scattering l ayers with increasing scattering coefficients. The limit of phase imaging t hrough these layers was at approximately 8-9 mean free path lengths thick ( single pass). (C) 2001 Optical Society of America.