Sellmeier Calculator
Compute refractive index from Sellmeier coefficients for common optical materials. Includes Fresnel reflectance and Abbe number.
The Sellmeier equation models how the refractive index of an optical material varies with wavelength — a relationship known as dispersion. Given the three-term Sellmeier coefficients B₁, B₂, B₃, C₁, C₂, C₃ for a material, this tool computes the refractive index n(λ) at any specified wavelength, the resulting Fresnel surface reflectance, and the Abbe number Vd (a dispersion metric used in achromatic doublet design). Built-in presets include BK7, N-SF11, fused silica, CaF₂, and sapphire. Use this tool to verify material data, plan achromat pairs, or check whether a substrate is suitable at a target wavelength.
Input
Refractive Index — N-BK7
n
at 632.8 nm
n²
Fresnel Reflectance (Normal Incidence)
R per surface
((n−1)/(n+1))²
Two-surface T
(1−R)²
Dispersion (Visible)
nᵈ (587.56 nm)
n_F (486.13 nm)
n_C (656.27 nm)
n_F − n_C
principal dispersion
Abbe number Vᵈ
(nᵈ−1)/(n_F−n_C)
Abridged Optics — Sellmeier Calculator v1.0n²(λ) = 1 + Σ Bᵢλ²/(λ²−Cᵢ) · R = ((n−1)/(n+1))² · Vd = (nd−1)/(nF−nC)