N-LAF36 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.85744\,\lambda^2}{\lambda^2 - 0.00982397} + \frac{0.294099\,\lambda^2}{\lambda^2 - 0.0384309} + \frac{1.16615\,\lambda^2}{\lambda^2 - 89.3985}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[8.72 \times 10^{-6} + 2(1.12 \times 10^{-8})\,\Delta T + 3(-1.38 \times 10^{-11})\,\Delta T^2 + \frac{7.81 \times 10^{-7} + 2(9.48 \times 10^{-10})\,\Delta T}{\lambda - 0.212}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$