P-SK60 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.4079\,\lambda^2}{\lambda^2 - 0.00784382} + \frac{0.143381\,\lambda^2}{\lambda^2 - 0.0287769} + \frac{1.16514\,\lambda^2}{\lambda^2 - 105.373}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.41 \times 10^{-6} + 2(9.52 \times 10^{-9})\,\Delta T + 3(-8.08 \times 10^{-12})\,\Delta T^2 + \frac{4.72 \times 10^{-7} + 2(6.22 \times 10^{-10})\,\Delta T}{\lambda - 0.193}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$