BK7G18 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.26539\,\lambda^2}{\lambda^2 - 0.00813104} + \frac{0.0144191\,\lambda^2}{\lambda^2 - 0.0543303} + \frac{1.00323\,\lambda^2}{\lambda^2 - 102.821}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.52 \times 10^{-6} + 2(1.37 \times 10^{-8})\,\Delta T + 3(-1.26 \times 10^{-11})\,\Delta T^2 + \frac{4.36 \times 10^{-7} + 2(4.17 \times 10^{-10})\,\Delta T}{\lambda - 0.194}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$