S-BSM10 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{0.945443\,\lambda^2}{\lambda^2 - 0.0157264} + \frac{0.643237\,\lambda^2}{\lambda^2 - 0.00161924} + \frac{1.17753\,\lambda^2}{\lambda^2 - 121.362}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.16 \times 10^{-6} + 2(1.34 \times 10^{-8})\,\Delta T + 3(-3.75 \times 10^{-11})\,\Delta T^2 + \frac{4.33 \times 10^{-7} + 2(3.86 \times 10^{-10})\,\Delta T}{\lambda - 0.213}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$