MP-BACD15 by Hoya

$$n(\lambda) = \sqrt{2.59092 - 0.0125948\,\lambda^2 + 0.015202\,\lambda^{-2} + 0.000299998\,\lambda^{-4} - 1.13155 \times 10^{-5}\,\lambda^{-6} + 9.15464 \times 10^{-7}\,\lambda^{-8}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[4.93 \times 10^{-6} + 2(8.9 \times 10^{-9})\,\Delta T + 3(-1.03 \times 10^{-11})\,\Delta T^2 + \frac{4.28 \times 10^{-7} + 2(4.67 \times 10^{-10})\,\Delta T}{\lambda - -0.223}\right] \Delta T = T - T_0, \quad T_0 = 23\,°\text{C}$$