LITHOSIL-Q by Schott

$$n(\lambda) = \sqrt{1 + \frac{0.670711\,\lambda^2}{\lambda^2 - 0.00449192} + \frac{0.433323\,\lambda^2}{\lambda^2 - 0.0132813} + \frac{0.877379\,\lambda^2}{\lambda^2 - 95.89}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.06 \times 10^{-5} + 2(2.51 \times 10^{-8})\,\Delta T + 3(-2.47 \times 10^{-11})\,\Delta T^2 + \frac{3.12 \times 10^{-7} + 2(4.22 \times 10^{-10})\,\Delta T}{\lambda - 0.16}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$