N-SF19 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.52005\,\lambda^2}{\lambda^2 - 0.0109614} + \frac{0.175739\,\lambda^2}{\lambda^2 - 0.0593248} + \frac{1.43623\,\lambda^2}{\lambda^2 - 126.795}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.32 \times 10^{-6} + 2(1.22 \times 10^{-8})\,\Delta T + 3(-1.36 \times 10^{-11})\,\Delta T^2 + \frac{7.64 \times 10^{-7} + 2(1.09 \times 10^{-9})\,\Delta T}{\lambda - 0.279}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$