P-BK7 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.18319\,\lambda^2}{\lambda^2 - 0.00722142} + \frac{0.0871756\,\lambda^2}{\lambda^2 - 0.0268217} + \frac{1.03134\,\lambda^2}{\lambda^2 - 101.702}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[5.96 \times 10^{-6} + 2(1.36 \times 10^{-8})\,\Delta T + 3(1.04 \times 10^{-12})\,\Delta T^2 + \frac{5 \times 10^{-7} + 2(6.97 \times 10^{-10})\,\Delta T}{\lambda - 0.125}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$