Terbium gallium garnet

{{Short description|Synthetic garnet}}

{{Infobox mineral

| name = Terbium gallium garnet

| category = Synthetic mineral

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| formula = Tb₃Ga₅O₁₂

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| refractive = 1.95

| opticalprop = Faraday rotator material

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| other = Paramagnetic material

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Terbium gallium garnet (TGG) is a kind of synthetic garnet, with the chemical composition {{chem2|Tb3Ga5O12|auto=1}}.{{cite web|title=Terbium Gallium Garnet - TGG|url=http://www.northropgrumman.com/BusinessVentures/SYNOPTICS/Products/SpecialtyCrystals/Documents/pageDocs/TGG.pdf|publisher=Northrop Grumman|year=2011|access-date=2014-07-14|archive-date=2016-04-18|archive-url=https://web.archive.org/web/20160418061032/http://www.northropgrumman.com/BusinessVentures/SYNOPTICS/Products/SpecialtyCrystals/Documents/pageDocs/TGG.pdf|url-status=dead}} This is a Faraday rotator material with excellent transparency properties and is very resistant to laser damage. TGG can be used in optical isolators for laser systems, in optical circulators for fiber optic systems, in optical modulators, and in current and magnetic field sensors.

TGG has a high Verdet constant which results in the Faraday effect. The Verdet constant increases substantially as the mineral approaches cryogenic temperatures.{{cite journal|author1=Hassaan Majeed |author2=Amrozia Shaheen |author3=Muhammad Sabieh Anwar |name-list-style=amp |title=Complete Stokes polarimetry of magneto-optical Faraday effect in a terbium gallium garnet crystal at cryogenic temperatures|journal=Optics Express |url=http://www.opticsinfobase.org/oe/viewmedia.cfm?URI=oe-21-21-25148|publisher=Optics InfoBase|doi=10.1364/OE.21.025148|year=2013|volume=21 |issue=21 |pages=25148–58 |pmid=24150356 |bibcode=2013OExpr..2125148M|doi-access=free }} The highest Verdet constants are found in terbium doped dense flint glasses or in crystals of TGG. The Faraday effect is chromatic (i.e. it depends on wavelength) and therefore the Verdet constant is quite a strong function of wavelength. At 632 nm, the Verdet constant for TGG is reported to be {{val|-131|u=rad/(T·m)}}, whereas at 1064 nm it falls to {{val|-38|u=rad/(T·m)}}.{{cite journal |last1=Vojna |first1=David |last2=Slezák |first2=Ondřej |last3=Lucianetti |first3=Antonio |last4=Mocek |first4=Tomáš |title=Verdet Constant of Magneto-Active Materials Developed for High-Power Faraday Devices |journal=Applied Sciences |date=2019 |volume=9 |issue=15 |page=3160 |doi=10.3390/app9153160 |doi-access=free }}{{cite journal |last1=Vojna |first1=David |last2=Duda |first2=Martin |last3=Yasuhara |first3=Ryo |last4=Slezák |first4=Ondřej |last5=Schlichting |first5=Wolfgang |last6=Stevens |first6=Kevin |last7=Chen |first7=Hengjun |last8=Lucianetti |first8=Antonio |last9=Mocek |first9=Tomáš |title=Verdet constant of potassium terbium fluoride crystal as a function of wavelength and temperature |journal=Opt. Lett. |date=2020 |volume=45 |issue=7 |pages=1683–1686 |doi=10.1364/ol.387911 |pmid=32235973 |bibcode=2020OptL...45.1683V |s2cid=213599420 |url=https://www.osapublishing.org/ol/fulltext.cfm?uri=ol-45-7-1683&id=429076}} This behavior means that the devices manufactured with a certain degree of rotation at one wavelength, will produce much less rotation at longer wavelengths. Many Faraday rotators and isolators are adjustable by varying the degree to which the amount of the Faraday rotator material is inserted into the magnetic field of the device. In this way, the device can be tuned for use with a range of lasers within the design range of the device.{{cite web|title=Optical Isolator Tutorial (Page 1 of 2)|url=http://www.skphotonics.com/pdf/la_pdf/Isolator.pdf|publisher=SeongKyeong Photonics / Thorlabs|access-date=2014-07-15|archive-date=2017-08-29|archive-url=https://web.archive.org/web/20170829094929/http://www.skphotonics.com/pdf/la_pdf/Isolator.pdf|url-status=dead}}