N-SF57HTultra by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.87544\,\lambda^2}{\lambda^2 - 0.014175} + \frac{0.373757\,\lambda^2}{\lambda^2 - 0.064051} + \frac{2.30002\,\lambda^2}{\lambda^2 - 177.39}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-4.51 \times 10^{-6} + 2(8.73 \times 10^{-9})\,\Delta T + 3(-1.64 \times 10^{-11})\,\Delta T^2 + \frac{1.07 \times 10^{-6} + 2(1.57 \times 10^{-9})\,\Delta T}{\lambda - 0.295}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$