TAFD30 by Hoya

$$n(\lambda) = \sqrt{3.4419 - 0.0141752\,\lambda^2 + 0.034351\,\lambda^{-2} + 0.00117523\,\lambda^{-4} - 3.90103 \times 10^{-5}\,\lambda^{-6} + 3.74171 \times 10^{-6}\,\lambda^{-8}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.21 \times 10^{-6} + 2(9.96 \times 10^{-9})\,\Delta T + 3(-3.19 \times 10^{-11})\,\Delta T^2 + \frac{8.4 \times 10^{-7} + 2(2.81 \times 10^{-10})\,\Delta T}{\lambda - 0.184}\right] \Delta T = T - T_0, \quad T_0 = 23\,°\text{C}$$