Abstract
A number of spectropolarimetry measurements on leaves using white light and narrow band illumination have been reported in recent years because of interest in signatures for remote sensing of exoplanet life. Chlorophyll fluorescence occurs in white light illuminated experiments and is known to be polarised and so might contaminate surface scattering measurements. A displacing filter experiment was performed on the leaves of two common plants, Ficus benjamina and Chamaedorea elegans, to estimate the contribution of chlorophyll fluorescence in the spectropolarimetry of leaf scattering and transmission. Chlorophyll fluorescence is present as a measurable polarised component of up to 15% of scattered and transmitted light for the leaf samples. Other effects emerged which indicate that in vivo measurements on leaves are subject to the responsive nature of the leaves to changes in colour and intensity of the incident light.
Highlights
Spectropolarimetry has been used to explore linear and circular polarised scattering from a variety of algae and plant leaves to measure possible chiral scattering effects that could potentially be used to identify the presence of photosynthesis in the optical signature of exoplanets [1,2,3,4,5,6]
The original premise of this work was that chlorophyll fluorescence would have an effect on the Stokes scattering measured using narrow band light sources [3,4,5b] and broadband sources with monochromators or filters [1,2,5a,6]
Previous measurements [3,4] using narrow band illumination have consistently failed to find the ‘chiral-like’ spectral forms for circular scattering observed in white light experiments [1,2,5a,6]
Summary
Spectropolarimetry has been used to explore linear and circular polarised scattering from a variety of algae and plant leaves to measure possible chiral scattering effects that could potentially be used to identify the presence of photosynthesis in the optical signature of exoplanets [1,2,3,4,5,6]. There are a number of persistent issues amongst the current measurements including the large variety of plants and algae used by various experimenters, the lack of agreed standards, and differing techniques and apparatus to measure nominally the same set of Stokes and Mueller matrix components of the scattered or transmitted light. This short article attempts to address one aspect of the comparison of spectropolarimetric experiments with one another, namely the presence of polarised fluorescence in the scattered light from the biological sample and the effect this may have on the precise measurement of the Stokes parameters and scattering matrix coefficients.
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