Runout correction for Optical Diffraction Tomography by numerical refocusing

In the Optical Diffraction Tomography (ODT) the set of measurements for rotated object is performed. For each angular object position complex scattered field is measured. From this set of measurements internal three dimensional structure can be recovered only when rotation is performed accurately. This includes accurate rotation step and accurate object positioning at rotation center. In our system we apply accurate angular step motor and rotation error is relatively small. Therefore the main source of error in ODT is related to inaccurate object positioning at rotation center. When the object is rotated with runout error defocused fields are measured giving inaccurate tomographic reconstruction. The error is especially important for structures of size of several micrometers and we aim to characterize such kind of structures.

In this paper we propose technique of solving this error. We present five autofocusing methods for determination of the optimal focus position in the modified tomographic reconstruction algorithm. The validity of proposed correction method is confirmed by experimental studies carried out on two kinds of optical microtips.