Selection rules impose geometrical constraints on the interactions of light and matter. In
particular, an emitter with a well-defined orientation will emit photons of a characteristic
polarization and wavevector distribution, even as viewed in the far field. Knowledge of these
distributions can be leveraged to enhance a number of state-of-the-art microscopy techniques. In
the first part of the talk I will discuss such an approach to single-molecule localization
microscopy, relevant for single-molecule tracking and super-resolution imaging. It is known that
constricted rotational diffusion of single fluorophores can result in localization inaccuracies up to
an order of magnitude worse than the precision of such methods [1,2]. We recently
demonstrated that by employing a metamaterial polarization converter we can filter the collected
light based on its symmetry, ensuring localization accuracy [3]. In the second part of the talk I
will describe the application of related ideas to magnetic imaging by optical readout of dense
ensembles of nitrogen-vacancy (NV) centers in diamond. An NV in such an ensemble points
along one of four crystal axes, with each of the four NV orientation classes sensitive to a
different projection of the magnetic field. By modulating NV photoluminescence at the Fourier
plane of the microscope we enable vector magnetic imaging in cases where it would otherwise
fail, e.g. at low applied fields [4].

[1] J. Engelhardt, J. Keller, P. Hoyer, M. Reuss, T. Staudt, and S. W. Hell, Molecular orientation affects localization accuracy in superresolution far-field fluorescence microscopy, Nano Letters 11, 209 (2010).
[2] M. P. Backlund*, M. D. Lew*, A. S. Backer, S. J. Sahl, G. Grover, A. Agrawal, R. Piestun, and W. E. Moerner, Simultaneous, accurate measurement of the 3D position and orientation of single molecules, Proceedings of the National Academy of Sciences 109 , 19087 (2012).
[3] M. P. Backlund, A. Arbabi, P. N. Petrov, E. Arbabi, S. Saurabh, A. Faraon, and W. E. Moerner, Removing orientation-induced localization biases in single-molecule microscopy using a broadband metasurface mask, Nature Photonics 10 , 459 (2016).
[4] M. P. Backlund, P. Kehayias, and R. L. Walsworth, Diamond-Based Magnetic Imaging with Fourier Optical Processing, Physical Review Applied 8 , 054003 (2017).