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Refractive Index of Fused Silica

Sellmeier equation (Malitson 1965) — phase index n and group index n_g, λ = 0.25 – 2.5 μm

Wavelength λ (μm)

Refractive index n

—

Group index n_g

—

n — phase index n_g — group index

Equations

Sellmeier (Malitson 1965):
n²(λ) = 1 + Σᵢ Bᵢ·λ² / (λ² − Cᵢ)
B₁ = 0.6961663, C₁ = 0.0684043² · B₂ = 0.4079426, C₂ = 0.1162414² · B₃ = 0.8974794, C₃ = 9.896161²

Group index: n_g(λ) = n − λ·dn/dλ = n + (λ²/n) · Σᵢ Bᵢ·Cᵢ / (λ² − Cᵢ)²

Reference implementations

n_silica.py NSilica.java n_silica_gui.py (Tkinter GUI)

# Python: print n and n_g at a wavelength
python n_silica.py 1.55      # lambda=1.5500 um   n=1.444024   n_g=1.462596

# Java
javac NSilica.java && java NSilica 1.55

# Tkinter GUI: enter wavelength, markers move on both curves
python n_silica_gui.py