P-SK58A by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.31678\,\lambda^2}{\lambda^2 - 0.00720717} + \frac{0.171155\,\lambda^2}{\lambda^2 - 0.024566} + \frac{1.12501\,\lambda^2}{\lambda^2 - 102.74}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.16 \times 10^{-6} + 2(1.23 \times 10^{-8})\,\Delta T + 3(-1.08 \times 10^{-11})\,\Delta T^2 + \frac{4.41 \times 10^{-7} + 2(3.2 \times 10^{-10})\,\Delta T}{\lambda - 0.176}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$