Characterization of vine, Vitis vinifera, leaves by Mueller polarimetric microscopy

In this work, we present the study of vine leaves, Vitis vinifera, performed by imaging polarimetry in the visible (at the wavelength of 530 nm). The purpose is to demonstrate, on a case study example, the high potential of imaging polarimetry and of polarimetric microscopy, in particular, for the characterization of vegetal tissues. The analysis of the Mueller matrix image of the sample provided by the polarimetric microscope by means of a matrix decomposition protocol yields a series of observables that are directly related to the fundamental physical properties that characterize the sample. Birefringence and dichroism are related to the structural properties of the medium and can be advantageously used as non-chemical, non-contact, non-destructive and non-toxic markers to highlight the presence of specific structures in the probed sample. Polarimetric images may also be used to enhance the contrast of the measured images. Specifically, we use the polarimetric properties and the depolarization indices to unveil the presence of structures such as raphides, some of them invisible under nonpolarized light, and to investigate their properties.