S-LAL12Q by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.09887\,\lambda^2}{\lambda^2 - 0.00538104} + \frac{0.6655\,\lambda^2}{\lambda^2 - 0.0186718} + \frac{1.07184\,\lambda^2}{\lambda^2 - 83.0816}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[6.77 \times 10^{-6} + 2(1.2 \times 10^{-8})\,\Delta T + 3(1.36 \times 10^{-11})\,\Delta T^2 + \frac{4.52 \times 10^{-7} + 2(4.67 \times 10^{-10})\,\Delta T}{\lambda - 0.196}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$