S-TIH11 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.72677\,\lambda^2}{\lambda^2 - 0.012937} + \frac{0.324569\,\lambda^2}{\lambda^2 - 0.0618255} + \frac{2.65817\,\lambda^2}{\lambda^2 - 221.905}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-3.76 \times 10^{-6} + 2(1.17 \times 10^{-8})\,\Delta T + 3(-3.59 \times 10^{-11})\,\Delta T^2 + \frac{8.88 \times 10^{-7} + 2(1.27 \times 10^{-9})\,\Delta T}{\lambda - 0.308}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$