Polarimetric technique to study (pre)biological organics in cosmic dust and planetary aerosols

Abstract

Noticeable circular polarization was measured in several dusty environments, including star forming regions and comets. These measurements have raised the possibility that circular polarization may relate to the formation (in molecular clouds) and observation (in comets) of prebiological organics, characterized by homochirality (dominance of molecules of specific handiness). We present computer simulations of light scattering by aggregates to model circular polarization from realistic particles containing homochiral molecules. Using optical constants of chlorophyll a, we study the spectral and phase angle dependencies of circular polarization. We begin our study by reproducing laboratory measurements (Sparks et al., 2009a), which found a fast change and reversal of sign for circular polarization within absorption bands. We further study how this spectral effect depends on the size and number of monomers in aggregates. We show that larger aggregates are characterized by larger values of circular polarization and that circular polarization peaks at medium (40-140• ) phase angles. We discuss at which wavelengths such a spectral feature can be expected for (pre)biological molecules other than chlorophyll. These findings may help observers to optimize spectral and geometrical parameters in the search of cosmic dust that contains prebiological organics or aerosols of biological origin in atmospheres of planets.

Thermopile detector of light ellipticity

“…The detector design is completely achiral and the chirality of the incident light is translated into the direction of current and/or the sign of d.c. voltage in the detector. Given the compactness and simplicity of the photodetectors presented here and the CMOS compatibility of the thermopile photodetector technology 41 44 , we expect that our elements can be easily integrated into various polarimetry systems and be used to provide video-rate focal-plane-array imaging of the S 3 Stokes parameter of light for identification of bio-organics 4 5 , astronomical observations 6 7 or vision in turbid media 8 9 .…”

“…Measurements of light ellipticity or the degree of circular polarization of an electromagnetic wave are highly important for the characterization of chiral molecules 1 2 , imaging of biological tissues 3 , identifying bio-organics 4 5 , studying cosmic microwave background radiation 6 7 , enhancing vision in turbid media 8 9 as well as for performing quantum cryptography and communication experiments 10 11 12 . Light ellipticity is quantified by the Stokes parameter S 3 = I RCP − I LCP , where I LCP and I RCP are the intensities of the left-circularly polarized (LCP) and right-circularly polarized (RCP) light waves in which the electric field moves along a helical trajectory, either clockwise or counterclockwise.…”

“…Monolithic detectors with the output directly proportional to the S 3 Stokes parameter would be the most compact and desirable solution for detecting and characterizing light ellipticity, especially if one thinks of polarimetric focal-plane-array imaging, for example, for identification of bio-organics 4 5 , astronomical observations 6 7 , or vision in turbid media 8 9 . Recently, the first monolithic photodetectors with voltage response directly proportional to the light ellipticity were reported in mid-infrared and terahertz spectral ranges 28 29 based on spin-galvanic and circular photogalvanic effect in semiconductors 30 31 .…”

Characterization and remote sensing of biological particles using circular polarization

“…If we suppose that mL=(n+βR/2)+i(k+βI/2) describes the optical characteristics of left-handed light, then mR=(n-βR/2)+i(k-βI/2) describes right-hand circularly polarized light. In our study we suppose that the particles contain chlorophyll a in concentration typical for cyanobacteria [11,12]. Corresponding optical constants are specified in Nagdimunov et al [12].…”

Spectral polarimetric light-scattering by particulate media: 1. Theory of spectral Vector Radiative Transfer

“…Recent experiments have reported the potential use of merging spectral and polarimetric light-scattering for optical diagnostic [14][15][16][17][18][19]. Due to the ill-posed inverse scattering problem, we propose to merge spectral (i.e.…”