Internally focused phase optical transfer function for spatial light interference microscopy

The phase optical transfer function (POTF) is a critical aspect of image formation theory for high-resolution phase imaging such as spatial light interference microscopy. However, current analytic formulae for the POTF do not match experimental results. Further, when used for deconvolution, halo artifacts still persist, and the contrast improvement is rather limited. We hypothesize that one of the reasons for this is that, during the derivation of POTF, the objective is assumed to focus at a plane outside of the sample. In this work, we have derived a new, to the best of our knowledge, POTF assuming that the objective is focused at a plane inside the sample (iPOTF), which more closely matches experimental results. When used for deconvolution, iPOTF not only leads to higher contrast of dim structures but also reduces halos compared with the traditional POTF.