Refractive index: Difference between revisions

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For [[visible light]] most [[transparency and translucency|transparent]] media have refractive indices between 1 and 2. A few examples are given in the adjacent table. These values are measured at the yellow doublet [[D2 line|D-line]] of [[sodium]], with a wavelength of 589 [[nanometers]], as is conventionally done.<ref name="FBI">{{cite web |title= Forensic Science Communications, Glass Refractive Index Determination |url= https://www.fbi.gov/about-us/lab/forensic-science-communications/fsc/jan2005/index.htm/standards/2005standards9.htm |url-status= dead |archive-url= https://web.archive.org/web/20140910195815/http://www.fbi.gov/about-us/lab/forensic-science-communications/fsc/jan2005/index.htm/standards/2005standards9.htm |archive-date= 2014-09-10 |access-date= 2014-09-08 |publisher= FBI Laboratory Services}}</ref> Gases at atmospheric pressure have refractive indices close to 1 because of their low density. The refractive index of water is approximately 1.33 at room temperature. Almost all solids and liquids have refractive indices above 1.3, with [[aerogel]] as the clear exception. Aerogel is a very low density solid that can be produced with refractive index in the range from 1.002 to 1.265.<ref>{{cite conference |last1= Tabata |first1= M. |date= 2005 |conference= IEEE Nuclear Science Symposium Conference Record |title= Development of Silica Aerogel with Any Density |volume= 2 |pages= 816–818 |url= http://www.ppl.phys.chiba-u.jp/~makoto/publication/N14-191.pdf |display-authors= 1 |url-status= dead |archive-url= https://web.archive.org/web/20130518075319/http://www.ppl.phys.chiba-u.jp/~makoto/publication/N14-191.pdf |archive-date= 2013-05-18 |doi= 10.1109/NSSMIC.2005.1596380 |isbn= 978-0-7803-9221-2 |s2cid= 18187536 |last2= Tabata |first2= M. |last3= Adachi |first3= I. |last4= Fukushima |first4= T. |last5= Kawai |first5= H. |last6= Kishimoto |first6= H. |last7= Kuratani |first7= A. |last8= Nakayama |first8= H. |last9= Nishida |first9= S. |last10= Noguchi |first10= T. |last11= Okudaira |first11= K. |last12= Tajima |first12= Y. |last13= Yano |first13= H. |last14= Yokogawa |first14= H. |last15= Yoshida |first15= H. }}</ref> [[Moissanite]] lies at the other end of the range with a refractive index as high as 2.65. Most plastics have refractive indices in the range from 1.3 to 1.7, but some [[high-refractive-index polymer]]s can have values as high as 1.76.<ref>{{cite web |last1= Sadayori |first1= Naoki |last2= Hotta |first2= Yuji |date= 2004 |title= Polycarbodiimide having high index of refraction and production method thereof |url= https://patents.google.com/patent/US20040158021 |id= US patent 2004/0158021 A1 |publisher= US Patent Office |via= Google Patents}}</ref>

For [[infrared]] light refractive indices can be considerably higher. [[Germanium]] is transparent in the wavelength region from {{val|2|to|14|u=µm}} and has a refractive index of about 4.<ref>Tosi, Jeffrey L., article on [http://www.photonics.com/EDU/Handbook.aspx?AID=25495 Common Infrared Optical Materials] in the Photonics Handbook, accessed on 2014-09-10</ref> A type of new materials termed "[[topological insulators]]", was recently found which have high refractive index of up to 6 in the near to mid infrared frequency range. Moreover, topological insulators are transparent when they have nanoscale thickness. These properties are potentially important for applications in infrared optics.<ref>{{Cite journal|last1=Yue|first1=Zengji|last2=Cai|first2=Boyuan|last3=Wang|first3=Lan|last4=Wang|first4=Xiaolin|last5=Gu|first5=Min|date=2016-03-01|title=Intrinsically core-shell plasmonic dielectric nanostructures with ultrahigh refractive index|journal=Science Advances|language=en|volume=2|issue=3|pages=e1501536|doi=10.1126/sciadv.1501536|issn=2375-2548|pmc=4820380|pmid=27051869|bibcode=2016SciA....2E1536Y}}</ref>