Ambiguity-free spectral-domain optical coherence tomography for determining the layer thicknesses in fluttering foils in real time

When imaging thick or axially moving samples with spectral-domain optical coherence tomography, mirror terms overlapping with the signals of interest can cause ambiguities. These ambiguities complicate the analysis of the imaged structures and are especially troublesome for processes in which sample parameters have to be monitored in a fully automated way and in real time. In this study we focus on a purely hardware-based approach to overcome this problem. The method is based on shifting and shaping the sensitivity profile by spatially separating the two interferometer beams on the diffraction grating in the spectrometer. The usefulness of the approach, including its robustness against axial sample movements, is demonstrated for a multi-layered plastic foil structure. The proposed method neither requires additional data post-processing nor a significant increase in cost or complexity of the experimental design. It is therefore well suited for in-line quality control purposes.

► We study in depth a purely hardware-based approach to overcome the mirror terms problem in SD-OCT. ► The method is suitable for an in-line determination of foil thicknesses in the production process. ► The approach does not require specific hard- or software changes with respect to standard SD-OCT.