Optimizing the localization precision in coherent scattering microscopy using structured light

We employ the concept of quantum Fisher information to optimize the focused excitation fields in coherent scattering microscopy. Our optimization goal is to achieve the best possible localization precision for small scatterers located above a glass coverslip, while keeping the intensity of the total incoming excitation fields fixed. For small numerical aperture (NA) values, the optimal fields have linear or circular polarization, and the excitation beam can be well approximated by a Gaussian one. For larger NA values, the optimal beam acquires radial polarization. We show that the high localization precision can be attributed to high field strengths at the scatterer position, and correspondingly a large number of scattered and detected photons. Finally, we evaluate the performance of the optimized beams in interferometric scattering microscopy (iscat), and further optimize these fields for iscat localization using the concept of Fisher information.