Differential phase contrast in optical coherence tomography

We report on a modification of optical coherence tomography. (OCT) that all ows one to measure small phase differences between beams traversing adjacen t areas of a specimen. The sample beam of a polarization-sensitive low-cohe rence interferometer is split by a Wollaston prism into two components that traverse the object along closely spaced paths. After reflection at the va rious sample surfaces, the beams are recombined at the Wollaston prism. Any phase difference encountered between the two beams is converted into a cha nge of polarization state of the recombined beam. This change is measured, and the resulting signals are converted to differential phase-contrast OCT images. The first images obtained from simple test objects allowed us to de termine path-difference gradients with a resolution of the order of 5 x 10( -5). (C) 1999 Optical Society of America.