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|Section2= |Section3= |Section4= |Section5= |Section8= }} Barium borate is an inorganic compound, a borate of barium with a chemical formula BaB2O4 or Ba(BO2)2. It is available as a hydrate or dehydrated form, as white powder or colorless crystals. The crystals exist in the high-temperature α phase and low-temperature β phase, abbreviated as BBO; both phases are birefringent, and BBO is a common nonlinear optical material. ==Properties== Barium borate exists in two major crystalline forms, alpha and beta; the low-temperature beta phase converts into the alpha phase upon heating to 925 °C. β-Barium borate (BBO) differs from the α form by the positions of the barium ions within the crystal. Both phases are birefringent, however the α phase possesses centric symmetry and thus does not have the same nonlinear properties as the β phase. Alpha barium borate, α-BaB2O4 is an optical material with a very wide optical transmission window from about 190 nm to 3500 nm. It has good mechanical properties and is a suitable material for high-power ultraviolet polarization optics.〔(Alpha Barium Borate ). Roditi.com. Retrieved on 2012-01-15.〕 It can replace calcite, titanium dioxide or lithium niobate in Glan-Taylor prisms, Glan-Thompson prisms, walk-off beam splitters and other optical components. It has low hygroscopicity and its Mohs hardness is 4.5. Its damage threshold is 1 GW/cm2 at 1064 nm and 500 MW/cm2 at 355 nm.〔 Beta barium borate, β-BaB2O4, is a nonlinear optical material which is transparent in the range ~190–3300 nm. It can be used for Spontaneous parametric down-conversion. Its Mohs hardness is also 4.5.〔〔 Barium borate has strong negative uniaxial birefringence and can be phase-matched for type I (''ooe'') second harmonic generation from 409.6 to 3500 nm. The temperature sensitivity of the indices of refraction is low, leading to an unusually large (55 °C) temperature phase-matching bandwidth.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Barium borate」の詳細全文を読む スポンサード リンク
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