Microscope polarization calibration with nanoslits enables accurate and precise measurements of molecular orientation

Optical setups for measuring the orientation of single molecules include multiple components that can change the amplitude and/or phase of light in a polarization-dependent manner, potentially introducing errors in orientation measurements. Components such as mirrors, filters, and beam splitters have polarization-dependent coefficients of reflection and transmission that can cause systematic biases in orientation measurements. A nanoscale slit in a thin metal film can act as a broadband polarizer that mimics the polarized dipolar emission of a single molecule, and so can be used as a tool to determine the precision and accuracy of single-molecule orientation measurement methods and to help identify, quantify, and rectify sources of polarization distortion, thereby improving the accuracy of these techniques.