REALVIEW_1.9_LIGHTWEIGHT by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.99085\,\lambda^2}{\lambda^2 - 0.0148094} + \frac{0.502624\,\lambda^2}{\lambda^2 - 0.0648963} + \frac{2.89672\,\lambda^2}{\lambda^2 - 201.494}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-5 \times 10^{-6} + 2(8.92 \times 10^{-9})\,\Delta T + 3(-2.05 \times 10^{-11})\,\Delta T^2 + \frac{1.17 \times 10^{-6} + 2(1.79 \times 10^{-9})\,\Delta T}{\lambda - 0.301}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$