S-BSM36 by Ohara

$$n(\lambda) = \sqrt{2.65467 - 0.0128194\,\lambda^2 + 0.0151972\,\lambda^{-2} + 0.000504208\,\lambda^{-4} - 3.49956 \times 10^{-5}\,\lambda^{-6} + 2.04927 \times 10^{-6}\,\lambda^{-8}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-7.36 \times 10^{-7} + 2(1.43 \times 10^{-8})\,\Delta T + 3(-2.88 \times 10^{-12})\,\Delta T^2 + \frac{5.38 \times 10^{-7} + 2(1.11 \times 10^{-9})\,\Delta T}{\lambda - 0.119}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$