Polarization pattern

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Above: reflecting water surface.
Below: water surface photographed with polarization filter

A polarization pattern is an optical phenomenon that results in a pattern that is characterized by differently polarized light compared to the rest of the environment. The pattern can usually be seen when a polarizing filter is used.

Pattern generation

Rayleigh scattering
Observation of the Haidinger tuft in the sky at sunset

Day sky

The sun is a light source that produces unpolarized light. By Rayleigh scattering mainly of blue light, little red, results in part-polarized in the atmosphere sky blue . The polarized part hits an observer at a right angle to the incident sunlight. The polarization pattern of the daytime sky describes a very wide, narrow circular band with the position of the sun in the center . Usually this band is only partially present as a circular arc in the firmament. It is completely present, but hardly recognizable and extends over the entire horizon when the sun is exactly at its zenith and the observer assumes an elevated position. At sunrise and sunset, the polarization pattern shown in the sky consists of a semicircular band, the highest point of which runs through the zenith. Before sunrise or in polar winter , the polarization pattern consists of a circular arc band that is smaller than a semicircle. With practice it can be perceived as a Haidinger tuft even without aids when the sky is clear during sunrise or sunset.

Bodies of water

Water surfaces reflect light preferentially to its plane of vibration. Areas with moist and dry areas make this surface quality recognizable by means of a conspicuous polarization pattern with appropriate lighting. They are the only natural surfaces that show a clear polarization pattern.

The same applies to anthropogenic reflective surfaces such as asphalt streets or shop windows.

plants

Some flowers attract insects through polarization patterns.

arthropod

Fangschreckenkrebs Gonodactylus smithii

The cuticle of some arthropods can reflect light from different levels of vibration in different ways. Rose beetles and other scarab beetles are known to be highly light-reflective. However, they only reflect circularly polarized light on the left and thus generate a special polarization pattern. Not only bugs (especially borer ) or other insects can produce polarization pattern, but also cancers (eg. As mantis shrimp ).

The strikingly colored butterfly wings can also produce polarization patterns, which, however, are usually not created by the scales, but rather by the cuticle below. However, the transparent scales of the knightly butterfly (like swallowtail ) reflect polarization patterns.

Mantis shrimp come in a myriad of colors, with iridescent patterns on their body surfaces and particularly on their antennae and telson .

Technical production

Polarized light and polarization patterns can be generated by different techniques, e.g. B. by means of polarization filter. An LCD monitor emits linearly polarized light.

Pattern recognition

Human eye

The human eye cannot differentiate between different vibration levels of polarized light when viewed directly.

If an observer stares at a polarization pattern for a few seconds and then changes the posture of the head a little without changing the direction of his gaze, with some practice a diffuse yellow or blue appearance can be perceived. This ability has been known since 1844 by Wilhelm Ritter von Haidinger under the term "Haidinger tufts". Observers describe the Haidinger tuft as a diffuse, yellowish shape, which is constricted in the middle and is cut vertically by a corresponding bluish-violet shape in the middle (similar to a four-leaf clover). The appearance is very inconspicuous, which is why a plain background without distracting patterns is recommended for observation. The two perceptible colors (bluish-purple and yellow) are complementary colors. Depending on the observation situation, it can be different for one and the same viewer whether he sees the yellow or the bluish arm of the tuft as a continuous stripe.

The Haidinger tuft is not a direct optical event, but rather arises like an afterimage during the processing of optical perception. It cannot therefore be reproduced photographically. If the observer waits long enough for the appearance to fade and then averts his gaze to an unpolarized source, a negative afterimage will briefly appear, with the former yellow arm now blue and vice versa.

Polarizing filters in different orientations in front of an LCD monitor that emits polarized light

Tools

When looking through a polarization filter, polarized light can be identified by turning it on the basis of the reduced light transmission and thus allows a polarization pattern to be searched. However, with this method, a pattern that is largely uniformly polarized is more recognizable than patterns that are composed of differently polarized light. For the photographic representation by means of polarization filters, it applies that only uniformly polarized patterns can be represented.

It should be noted that the display using polarizing filters always involves a reduction in light and therefore affects the darker areas in comparison without polarizing filters. With a polarizing filter it is hardly possible to take a holistic picture of patterns of different polarization, except by analyzing individual images. A photographically successful representation of the sky polarization pattern is not known. In contrast to photographic capture using polarization filters, physiological perception often allows complex pattern recognition.

It is speculated that the Vikings used it as a sunstone ( sólsteinn ) as a navigation aid . This method reaches its limits in high fog.

arthropod

insects

In contrast to the human eye, most insects can perceive polarized light, which they use to determine the position of the sun or the moon when the sky is overcast, to find areas of water, flowers or conspecifics that display a polarization pattern.

The first proof of the differential perception of polarized light by insects was achieved in bees through studies by Karl von Frisch .

Desert ants orientate themselves on the polarization pattern of the sky in their often extensive search for prey.

Butterflies (e.g. Papilio ) find flowers with polarization patterns, sometimes in moonlight.

Water bugs ( Notonecta glauca ) flying around in sunlight also find water surfaces due to their polarization properties.

Mantis shrimp

Many mantis shrimp can perceive and differentiate polarized light, including circularly polarized light.

Mantis shrimp can use the perception of the sky polarization pattern to orientate themselves in their habitat.

Mantis shrimp have a complex social behavior that is particularly evident in territorial disputes: They react promptly to intruders, but mostly communicate with pennant-like appendages on their heads, so that deadly territorial fights do not occur. These vehemently moving appendages, antennas and the telson reflect particularly well polarized light, which the crabs can clearly recognize and use for intra-species signal exchange.

Individual evidence

  1. ↑ Polarized scattered light from the sky . Retrieved March 7, 2013.
  2. ↑ a b c Gábor Horváth et al .: Does reflection polarization by plants influence color perception in insects? Polarimetric measurements applied to a polarization-sensitive model retina of Papilio butterflies . In: J. Experimental Biology . 205, Nov. 1, 2002, pp. 3281-3298. Retrieved March 7, 2013.
  3. ↑ Ramón Hegedüs, Győző Szélb, Gábor Horváth: Imaging polarimetry of the circularly polarizing cuticle of scarab beetles (Coleoptera: Rutelidae, Cetoniidae) . In: Vision Research . 46, No. 17, September 2006, pp. 2786-2797. doi : 10.1016 / j.visres.2006.02.007 . PMID 16564066 .
  4. ↑ Structural origin of circularly polarized iridescence in jeweled beetles ( Engl. ) Retrieved October 17, 2013.
  5. ↑ a b c d e Justin Marshall et al: Behavioral evidence for polarization vision in stomatopods reveals a potential channel for communication . In: Current Biology . 9, No. 14, July 15, 1999, pp. 755-758. doi : 10.1016 / S0960-9822 (99) 80336-4 .
  6. ↑ Jonathan M. Douglas et al .: Light habitats and the role of polarized iridescence in the sensory ecology of neotropical nymphalid butterflies (Lepidoptera: Nymphalidae) . In: The Journal of Experimental Biology . 210, May 1, 2007, pp. 788-799. doi : 10.1242 / jeb.02713 .
  7. ↑ Doekele G. Stavenga et al: Glass scales on the wing of the swordtail butterfly Graphium sarpedon act as thin film polarizing reflectors . In: The Journal of Experimental Biology . 215, No. 4, February 15, 2012, pp. 657-662. doi : 10.1242 / jeb.066902 .
  8. ↑ Doekele G. Stavenga, Marco A. Giraldo, Hein L. Leertouwer: Butterfly wing colors: glass scales of Graphium sarpedon cause polarized iridescence and enhance blue / green pigment coloration of the wing membrane . In: Journal of Experimental Biology . 213, No. Pt 10, 2010, pp. 1731-1739. PMID 20435824 .
  9. ^ Physical Models of Haidinger's Brush. ( November 29, 2010 memento on the Internet Archive ) By Maxwell B. Fairbairn (page 248).
  10. ↑ Navigation: Vikings could have used sunstones. At: Spiegel.de. February 7, 2007.
  11. ↑ Gábor Horváth, György Kriska, Péter Malik, Bruce Robertson: Polarized light pollution: a new kind of ecological photopollution . In: Frontiers in Ecology and the Environment . 7, 2009, pp. 317-325.
  12. ↑ Peter Duelli: Orientation of polarization pattern in the desert ant Cataglyphis bicolor Fabr: Formicidae, Hymenoptera. Diss., University of Zurich, 1974.
  13. ↑ Bruno Carlo Lanfranconi: Compass orientation according to the rotating sky pattern in the desert ant Cataglyphis bicolor . Diss. Ed .: University of Zurich. 1982.
  14. ↑ Karl Fent: Polarized skylight orientation in the desert ant Cataglyphis . In: Journal of Comparative Physiology A . 158, No. 2, 1986, pp. 145-150. doi : 10.1007 / BF01338557 .
  15. ↑ Almut Kelber, Christel Thunell, Kentaro Arikawa: Polarization-dependent color vision in Papilio butterflies . In: The Journal of Experimental Biology . 204, July 15, 2001, pp. 2469-2480. Retrieved March 7, 2013.
  16. ^ Rüdiger Wehner : Polarization vision - a uniform sensory capacity? . In: The Journal of Experimental Biology . 204, July 15, 2001, pp. 2589-2596. PMID 11511675 .
  17. ↑ Tsyr-Huei Chiou, Sonja Kleinlogel, Tom Cronin, Roy Caldwell, Birte Loeffler, Afsheen Siddiqi, Alan Goldizen, Justin Marshal: Circular Polarization Vision in a Stomatopod Crustacean . In: Current Biology . March 18, 2008, p. 429. doi : 10.1016 / j.cub.2008.02.066 .