N-LAK10 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.72878\,\lambda^2}{\lambda^2 - 0.00886015} + \frac{0.169258\,\lambda^2}{\lambda^2 - 0.0363417} + \frac{1.19387\,\lambda^2}{\lambda^2 - 82.9009}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[4.1 \times 10^{-6} + 2(1.23 \times 10^{-8})\,\Delta T + 3(-7.85 \times 10^{-12})\,\Delta T^2 + \frac{5.08 \times 10^{-7} + 2(5.76 \times 10^{-10})\,\Delta T}{\lambda - 0.205}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$