S-TIH14 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.68915\,\lambda^2}{\lambda^2 - 0.0128203} + \frac{0.290462\,\lambda^2}{\lambda^2 - 0.0618091} + \frac{2.37972\,\lambda^2}{\lambda^2 - 201.094}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-2.83 \times 10^{-6} + 2(1.27 \times 10^{-8})\,\Delta T + 3(-3.36 \times 10^{-11})\,\Delta T^2 + \frac{8.35 \times 10^{-7} + 2(1.16 \times 10^{-9})\,\Delta T}{\lambda - 0.31}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$