S-BSL7R by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.25482\,\lambda^2}{\lambda^2 - 0.0080568} + \frac{0.0151112\,\lambda^2}{\lambda^2 - 0.0529921} + \frac{1.01494\,\lambda^2}{\lambda^2 - 103.373}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.57 \times 10^{-6} + 2(1.52 \times 10^{-8})\,\Delta T + 3(-1.46 \times 10^{-11})\,\Delta T^2 + \frac{4.19 \times 10^{-7} + 2(3.97 \times 10^{-10})\,\Delta T}{\lambda - 0.207}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$