Twofold improvement in axial resolution of Optical Coherence Tomography by four pass sample probing

摘要

In this contribution a proof of concept for the alternate way of twofold increasing the axial resolution of Optical Coherence Tomography systems is shown. On the contrary to expanding the bandwidth of the light source, the number of passes of light between sample and the Michelson interferometer is increased. In two simplified novel configurations of Spectral OCT devices designed for this research, the interferometer is equipped with polarization controlling elements in order to force light to pass the distance from the beam splitter to the sample four times: during the first pass the initial linear polarization of the probing beam is converted to the perpendicular one and on return to the interferometer deflected by the polarization sensitive beam splitter towards the additional mirror reflecting it back to the sample. After the second pass the state of polarization is changed again and restored to the initial one in order to interfere with the reference beam. As a result in both set-ups optical paths difference between both arms of the Michelson interferometer is twofold longer comparing to the standard system. This results in two times smaller axial calibration coefficient and finally twofold increase of an effective axial resolution for the same coherence length of the light source. In the paper the experimental evidences are given and limitations of the method discussed.