Editing Dichroism

{{Short description|Phenomenon where the material is splitting two or more beams of different colours}}
{{Redirect|Dichroic|the filter|dichroic filter|the glass|dichroic glass}}
[[Image:Dichroicclose.jpg|thumb|right|[[lampworking|Lampworked]] [[dichroic glass]] bead]]
In [[optics]], a '''dichroic''' material is either one which causes [[visible light]] to be split up into distinct beams of different [[wavelength]]s ([[colour]]s) (not to be confused with [[Dispersion (optics)|dispersion]]), or one in which light rays having different [[Polarization (waves)|polarizations]] are absorbed by different amounts.<ref>{{cite book |title=University Physics |edition=6th |author=F. W. Sears |author2=M. W. Zemansky |author3=H. D. Young |publisher=Addison-Wesley |year=1982 |isbn=0-201-07199-1}}</ref>

==In beam splitters==
{{Main|Beam splitter}}
The original meaning of ''dichroic'', from the [[Greek language|Greek]] ''dikhroos'', two-coloured, refers to any optical device which can split a beam of light into two beams with differing wavelengths. Such devices include [[mirror]]s and [[dichroic filter|filter]]s, usually treated with [[optical coating]]s, which are designed to reflect light over a certain range of wavelengths and transmit light which is outside that range. An example is the [[dichroic prism]], used in some [[camcorder]]s, which uses several coatings to split light into red, green and blue components for recording on separate [[charge-coupled device|CCD arrays]], however it is now more common to have a [[Bayer filter]] to filter individual pixels on a single CCD array. This kind of dichroic device does not usually depend on the polarization of the light. The term ''dichromatic'' is also used in this sense.

==With polarized light==
{{Main|Linear dichroism|Circular dichroism}}
The second meaning of ''dichroic'' refers to the property of a material, in which light in different polarization states traveling through it experiences a different [[absorption (optics)|absorption]] coefficient; this is also known as '''diattenuation.''' When the polarization states in question are right and left-handed [[circular polarization]], it is then known as [[Circular dichroism|circular dichroism (CD)]]. Most materials exhibiting CD are [[chiral]],<ref name="Rodger2014">{{cite book|author=Alison Rodger|title=Encyclopedia of Analytical Chemistry|chapter=Circular Dichroism and Linear Dichroism |year=2014|publisher=[[John Wiley & Sons, Ltd]]|isbn=978-0-470-02731-8 |pages=1–34|doi=10.1002/9780470027318.a5402.pub2}}</ref> although non-chiral materials showing CD have been recently observed.<ref>{{cite journal | title = Angular momentum-induced circular dichroism in non-chiral nanostructures | author = X. Zambrana-Puyalto | journal = Nature Communications | year = 2014 | volume = 5 | page = 4922 | doi = 10.1038/ncomms5922| pmid = 25215603 | arxiv = 1404.0440 | bibcode = 2014NatCo...5.4922Z | s2cid = 2135734 | doi-access = free }}</ref> Since the left- and right-handed circular polarizations represent two [[spin angular momentum of light|spin angular momentum]] (SAM) states, in this case for a photon, this dichroism can also be thought of as spin angular momentum dichroism and could be modelled using [[quantum mechanics]].

In some [[crystal]]s,{{which|date=August 2016}}, such as [[tourmaline]], the strength of the dichroic effect varies strongly with the wavelength of the light, making them appear to have different colours when viewed with light having differing polarizations.{{dubious|date=July 2014}} This is more generally referred to as [[pleochroism]],<ref name="Schumann2009">{{cite book |author=Walter Schumann |title=Gemstones of the World |url=https://books.google.com/books?id=V9PqVxpxeiEC&pg=PA49 |year=2009 |publisher=[[Sterling Publishing Company, Inc.]] |isbn=978-1-4027-6829-3 |pages=49–}}</ref> and the technique can be used in [[mineralogy]] to identify [[mineral]]s. In some materials, such as [[herapathite]] (iodoquinine sulfate) or [[Polaroid (polarizer)|Polaroid]] sheets, the effect is not strongly dependent on wavelength.

===In liquid crystals===
Dichroism, in the second meaning above, occurs in [[liquid crystals]] due to either the [[optical anisotropy]] of the molecular structure or the presence of impurities or the presence of '''dichroic dyes'''. The latter is also called a ''[[guest–host effect]]''.<ref>{{cite book | title = Flat Panel Displays: Advanced Organic Materials | author = Stephen M. Kelly | publisher = [[Royal Society of Chemistry]] | year = 2000 | isbn = 0-85404-567-8 | page = 110 | url = https://books.google.com/books?id=LMW0gofBH7sC&q=%22guest+host+effect%22&pg=PA110}}</ref>

==See also==
* [[Birefringence]]
* [[Dichromatism]]
* [[Lycurgus Cup]]
* [[Pleochroism]]

==References==
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[[Category:Polarization (waves)]]