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Sellmeier EquationIn optics, the Sellmeier equation is an empirical relationship between refractive index n and wavelength λ for a particular transparent medium. The usual form of the equation for glasses is: -
n^2(\lambda) = 1 + \frac{B_1 \lambda^2 }{ \lambda^2 - C_1} + \frac{B_2 \lambda^2 }{ \lambda^2 - C_2} + \frac{B_3 \lambda^2 }{ \lambda^2 - C_3} where B1,2,3 and C1,2,3 are experimentally determined Sellmeier coefficients. These coefficients are usually quoted for λ measured in micrometres. The equation is used to determine the dispersion of light in a refracting medium. A different form of the equation is sometimes used for certain types of materials, e.g. crystals. As an example, the coefficients for a common borosilicate crown glass known as BK7 are shown below: | Coefficient | Value | | B1 | 1.03961212 | | B2 | 2.31792344x10-1 | | B3 | 1.01046945 | | C1 | 6.00069867x10-3 | | C2 | 2.00179144x10-2 | | C3 | 1.03560653x102 | Using these in the above equation produces the following plot for refractive index versus wavelength: .
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