Polarization-Controlled Raman Microscopy and Nanoscopy.

Polarization imaging reveals unique characteristics of samples, such as molecular symmetry, orientation, or intermolecular interactions. Polarization techniques extend the ability of conventional spectroscopy to enable the characterization and identification of molecular species. In the early days of spectroscopy, it was considered that a set of polarizers placed in the illumination and the detection paths was enough to enable polarization analysis. However, with the development of new microscope imaging techniques, such as high-resolution microscopy, nonlinear spectroscopic imaging, and near-field microscopy, the inevitable polarization changes caused by external optical components needs to be discussed. In this Perspective, we present some of the hot topics that are specific to high-spatial-resolution microscopy and introduce recent related work in the field. Among the many spectroscopic techniques available, we focus in particular on Raman spectroscopy because Raman tensors are widely used in pure and applied sciences to study the symmetry of matter.