Editing Circular polarization (section)

==In nature==
[[File:Cetonia-aurata.jpg|thumb|right|The [[Cetonia aurata|rose chafer]]'s external surface reflects almost exclusively left-circularly polarized light.]]

Only a few mechanisms in nature are known to systematically produce circularly polarized [[light]]. In 1911, [[Albert A. Michelson|Albert Abraham Michelson]] discovered that light reflected from the golden scarab beetle ''[[Chrysina resplendens]]'' is preferentially left-polarized. Since then, circular polarization has been measured in several other [[Scarabaeidae|scarab beetles]] such as ''[[Chrysina gloriosa]]'',<ref>{{Cite journal|url=https://www.science.org/doi/10.1126/science.1172051|title=Structural Origin of Circularly Polarized Iridescence in Jeweled Beetles|first1=Mohan|last1=Srinivasarao|first2=Jung Ok|last2=Park|first3=Matija|last3=Crne|first4=Vivek|last4=Sharma|date=July 24, 2009|journal=Science|volume=325|issue=5939|pages=449–451|via=science.sciencemag.org|doi=10.1126/science.1172051|pmid=19628862|bibcode=2009Sci...325..449S|s2cid=206519071|url-access=subscription}}</ref> as well as some [[crustacean]]s such as the [[mantis shrimp]]. In these cases, the underlying mechanism is the molecular-level helicity of the [[chitin]]ous [[cuticle]].<ref name="Hegedüs">{{cite journal |title=Imaging polarimetry of the circularly polarizing cuticle of scarab beetles (Coleoptera: Rutelidae, Cetoniidae) |author1=Hegedüs, Ramón |author2=Győző Szélb |author3=Gábor Horváth |doi=10.1016/j.visres.2006.02.007 |journal=Vision Research |volume=46 |issue=17 |date=September 2006 |pages=2786–2797 |pmid=16564066 |s2cid=14974820 |doi-access=free }}</ref>

The [[bioluminescence]] of the [[larva]]e of [[firefly|fireflie]]s is also circularly polarized, as reported in 1980 for the species ''[[Photuris|Photuris lucicrescens]]'' and ''[[Photuris versicolor]]''. For fireflies, it is more difficult to find a microscopic explanation for the polarization, because the left and right lanterns of the larvae were found to emit polarized light of opposite senses. The authors suggest that the light begins with a [[linear polarization]] due to inhomogeneities inside aligned [[photocyte]]s, and it picks up circular polarization while passing through linearly [[Birefringence|birefringent]] tissue.<ref>{{cite journal |title=Circular polarization observed in bioluminescence |author1=Wynberg, Hans |author2=Meijer, E.W. |author3=Hummelen, J.C. |author4=Dekkers, H.P.J.M. |author5=Schippers, P.H. |author6=Carlson, A.D. |url=http://keur.eldoc.ub.rug.nl/FILES/wetenschappers/10/29/29.pdf |journal=Nature |volume=286 |issue=5773 |pages=641–642 |date=7 August 1980 |doi=10.1038/286641a0 |bibcode=1980Natur.286..641W |s2cid=4324467 |url-status=dead |archive-url=https://web.archive.org/web/20110724164914/http://keur.eldoc.ub.rug.nl/FILES/wetenschappers/10/29/29.pdf |archive-date=24 July 2011 }}</ref>

Circular polarization has been detected in light reflected from leaves and photosynthetic microbes.<ref name="b966">{{cite journal | last1=Sparks | first1=William B. | last2=Hough | first2=James | last3=Germer | first3=Thomas A. | last4=Chen | first4=Feng | last5=DasSarma | first5=Shiladitya | last6=DasSarma | first6=Priya | last7=Robb | first7=Frank T. | last8=Manset | first8=Nadine | last9=Kolokolova | first9=Ludmilla | last10=Reid | first10=Neill | last11=Macchetto | first11=F. Duccio | last12=Martin | first12=William | title=Detection of circular polarization in light scattered from photosynthetic microbes | journal=Proceedings of the National Academy of Sciences | volume=106 | issue=19 | date=2009-05-12 | issn=0027-8424 | pmid=19416893 | pmc=2674403 | doi=10.1073/pnas.0810215106 | pages=7816–7821| doi-access=free | arxiv=0904.4646 | bibcode=2009PNAS..106.7816S }}</ref>

Water-air interfaces provide another source of circular polarization. Sunlight that gets scattered back up towards the surface is linearly polarized. If this light is then [[total internal reflection|totally internally reflected]] back down, its vertical component undergoes a phase shift. To an underwater observer looking up, the faint light outside [[Snell's window]] therefore is (partially) circularly polarized.<ref>{{cite book |title=Polarized Light in Animal Vision: Polarization Patterns in Nature |author1=Horváth, Gábor |author2=Dezsö Varjú |year=2003 |publisher=Springer |isbn=978-3-540-40457-6 |pages=100–103}}</ref>

Weaker sources of circular polarization in nature include multiple scattering by linear polarizers{{dubious|date=June 2021}}, as in the circular polarization of starlight, and selective absorption by [[circular dichroism|circularly dichroic]] media.

Radio emission from pulsars can be strongly circularly polarized.<ref>{{cite journal|doi=10.1111/j.1365-2966.2005.09681.x |title=On the origin of the circular polarization in radio pulsars |date=2005 |last1=Gogoberidze |first1=G. |last2=Machabeli |first2=G. Z. |journal=Monthly Notices of the Royal Astronomical Society |volume=364 |issue=4 |pages=1363–1366 |doi-access=free |arxiv=astro-ph/0510116 |bibcode=2005MNRAS.364.1363G }}</ref>

Two species of [[mantis shrimp]] have been reported to be able to detect circular polarized light.<ref>{{cite journal|author1=Tsyr-Huei Chiou |author2=Sonja Kleinlogel |author3=Tom Cronin |author4=Roy Caldwell |author5=Birte Loeffler |author6=Afsheen Siddiqi |author7=Alan Goldizen |author8=Justin Marshall |title=Circular polarization vision in a stomatopod crustacean |journal=[[Current Biology]] |year=2008 |volume=18 |issue=6 |pages=429–34 |doi=10.1016/j.cub.2008.02.066 |pmid=18356053|s2cid=6925705 |doi-access=free |bibcode=2008CBio...18..429C }}</ref><ref name="Kleinlogel et al.">{{cite journal |author1=Sonja Kleinlogel |author2=Andrew White |title=The secret world of shrimps: polarisation vision at its best |journal=[[PLoS ONE]] |year=2008 |doi=10.1371/journal.pone.0002190 |volume=3 |issue=5 |pages=e2190 |pmid=18478095 |pmc=2377063 |bibcode=2008PLoSO...3.2190K|arxiv = 0804.2162 |doi-access=free }}</ref>