LASF32 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.84091\,\lambda^2}{\lambda^2 - 0.0120091} + \frac{0.293073\,\lambda^2}{\lambda^2 - 0.0560734} + \frac{2.01292\,\lambda^2}{\lambda^2 - 152.279}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[6.21 \times 10^{-7} + 2(8.93 \times 10^{-9})\,\Delta T + 3(-1.82 \times 10^{-11})\,\Delta T^2 + \frac{8.61 \times 10^{-7} + 2(1.26 \times 10^{-9})\,\Delta T}{\lambda - 0.273}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$