L-BSL7 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{0.917474\,\lambda^2}{\lambda^2 - 0.00527701} + \frac{0.352688\,\lambda^2}{\lambda^2 - 0.0170809} + \frac{1.0558\,\lambda^2}{\lambda^2 - 104.303}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[6.37 \times 10^{-6} + 2(1.48 \times 10^{-8})\,\Delta T + 3(-4.17 \times 10^{-11})\,\Delta T^2 + \frac{4.37 \times 10^{-7} + 2(7.14 \times 10^{-10})\,\Delta T}{\lambda - 0.147}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$