S-TIM22 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.44222\,\lambda^2}{\lambda^2 - 0.0104249} + \frac{0.194432\,\lambda^2}{\lambda^2 - 0.0550235} + \frac{1.74092\,\lambda^2}{\lambda^2 - 169.711}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-1.42 \times 10^{-6} + 2(1.44 \times 10^{-8})\,\Delta T + 3(-3.73 \times 10^{-11})\,\Delta T^2 + \frac{7.64 \times 10^{-7} + 2(8.16 \times 10^{-10})\,\Delta T}{\lambda - 0.281}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$