{"id":579,"date":"2012-11-22T08:33:03","date_gmt":"2012-11-21T19:33:03","guid":{"rendered":"https:\/\/blog.waikato.ac.nz\/physicsstop\/2012\/11\/22\/seeing_circular_polarization\/"},"modified":"2012-11-22T08:33:03","modified_gmt":"2012-11-21T19:33:03","slug":"seeing-circular-polarization","status":"publish","type":"post","link":"https:\/\/blog.waikato.ac.nz\/physicsstop\/2012\/11\/22\/seeing-circular-polarization\/","title":{"rendered":"Seeing circular polarization"},"content":{"rendered":"

Physicsworld<\/a> magazine is doing a ‘special feature’ this month on animal superheroes – those with rather unusual physical abilities.<\/p>\n

The best of the lot (in my subjective opinion) is the featured-on-the-cover mantis shrimp. Not because of its ‘dactyl clubs’ that can produce a force of 700 N, but because of its eyesight.<\/p>\n

The mantis shrimp can see circularly polarized light <\/a>– something that no other animal is known to do. Polarization describes how the electric and magnetic fields in the light wave are oriented. For example, a horizontally-travelling light wave (say in the x- direction) might have its electric field pointing in the z-direction (vertically) and the magnetic field in the negative y direction. In an electromagnetic wave, the electric field, magnetic field and direction of travel are all mutually perpendicular. We could call that a vertical, plane polarization.<\/p>\n

In circular polarization<\/a>, the electric field moves in a corkscrew-like shape as the wave travels. The corkscrew can spiral one of two ways – hence there are two distinct polarizations which we call left-handed and right-handed. The mantis shrimp can distinguish between the two. It does this by using its own version of a quarter-wave plate – made of a birefringent material – one that has a different refractive index in different directions. That converts a circular polarization to a linear polarization, which it detects via more conventional methods. (There are several animals that can ‘see’ linear polarization – bees are a famous example. There are plenty that don’t distinguish one  polarization from another at all, such as humans.)<\/p>\n

The mysterious question is why? Bees use linear polarization to assist navigation (light from the sky is linearly polarized), but what use is distinguishing left-handed and right-handed circular polarizations to a shrimp? There’s a cool research question for someone’s PhD thesis.<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Physicsworld magazine is doing a ‘special feature’ this month on animal superheroes – those with rather unusual physical abilities. The best of the lot (in my subjective opinion) is the featured-on-the-cover mantis shrimp. Not because of its ‘dactyl clubs’ that can produce a force of 700 N, but because of its eyesight. The mantis shrimp […]<\/p>\n","protected":false},"author":20,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[16,13,6,20],"yoast_head":"\nSeeing circular polarization : Physics Stop<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/blog.waikato.ac.nz\/physicsstop\/2012\/11\/22\/seeing-circular-polarization\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Seeing circular polarization : Physics Stop\" \/>\n<meta property=\"og:description\" content=\"Physicsworld magazine is doing a ‘special feature’ this month on animal superheroes – those with rather unusual physical abilities. 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