S-TIH23 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.73986\,\lambda^2}{\lambda^2 - 0.0129441} + \frac{0.313895\,\lambda^2}{\lambda^2 - 0.0612117} + \frac{2.31093\,\lambda^2}{\lambda^2 - 197.42}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-3.78 \times 10^{-6} + 2(1.09 \times 10^{-8})\,\Delta T + 3(-3.66 \times 10^{-11})\,\Delta T^2 + \frac{8.62 \times 10^{-7} + 2(1.13 \times 10^{-9})\,\Delta T}{\lambda - 0.309}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$