S-BSL7 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.1515\,\lambda^2}{\lambda^2 - 0.0105984} + \frac{0.118584\,\lambda^2}{\lambda^2 - -0.0118225} + \frac{1.26301\,\lambda^2}{\lambda^2 - 129.618}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.7 \times 10^{-6} + 2(1.43 \times 10^{-8})\,\Delta T + 3(-4.27 \times 10^{-11})\,\Delta T^2 + \frac{4.08 \times 10^{-7} + 2(6.74 \times 10^{-10})\,\Delta T}{\lambda - 0.201}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$