Information-rich interferometric point-spread function for type-B 4Pi localization microscopy

The 3D location of light emitters provides essential information in many biological, chemical and physical systems. 4Pi single-molecule localization microscopy (SMLM) being one of the state-of-the-art techniques provides exceptional precision in the axial direction; however, the lateral precision degrades significantly when the emitter is displaced several wavelengths away from the mutual focal plane. Here we propose a hybrid system employing type-B 4Pi microscope and engineered point-spread function (PSF), the resultant interferometric PSF is optimized against the Cramer-Rao metric, yielding the richest information regarding the emitter's 3D locations. It outperforms conventional 4Pi SMLM with a larger axial range and compares advantageously to the non-interferometric PSFs with doubled photon efficiency and better precision in all directions.