Imaging linear and circular polarization features in leaves with complete Mueller matrix polarimetry

TL;DR

This study employs Mueller matrix polarimetry to visualize and analyze linear and circular polarization features in leaves, revealing spatial variations linked to leaf structure and chloroplast orientation, with implications for remote sensing of vegetation health.

Contribution

It introduces a comprehensive Mueller matrix polarimetry approach to map polarization in leaves, highlighting distinct features near veins and advancing understanding of polarization signals in vegetation.

Findings

Distinct polarization features near leaf veins identified

Circular polarization signals show negative bands close to veins

Results consistent across multiple independent measurements

Abstract

Spectropolarimetry of intact plant leaves allows to probe the molecular architecture of vegetation photosynthesis in a non-invasive and non-destructive way and, as such, can offer a wealth of physiological information. In addition to the molecular signals due to the photosynthetic machinery, the cell structure and its arrangement within a leaf can create and modify polarization signals. Using Mueller matrix polarimetry with rotating retarder modulation, we have visualized spatial variations in polarization in transmission around the chlorophyll a absorbance band from 650 nm to 710 nm. We show linear and circular polarization measurements of maple leaves and cultivated maize leaves and discuss the corresponding Mueller matrices and the Mueller matrix decompositions, which show distinct features in diattenuation, polarizance, retardance and depolarization. Importantly, while normal leaf tissue shows a typical split signal with both a negative and a positive peak in the induced fractional circular polarization and circular dichroism, the signals close to the veins only display a negative band. The results are similar to the negative band as reported earlier for single macrodomains. We discuss the possible role of the chloroplast orientation around the veins as a cause of this phenomenon. Systematic artefacts are ruled out as three independent measurements by different instruments gave similar results. These results provide better insight into circular polarization measurements on whole leaves and options for vegetation remote sensing using circular polarization.