N-KZFS5 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.47461\,\lambda^2}{\lambda^2 - 0.00986144} + \frac{0.193584\,\lambda^2}{\lambda^2 - 0.0445478} + \frac{1.2659\,\lambda^2}{\lambda^2 - 106.436}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[4.54 \times 10^{-6} + 2(1.19 \times 10^{-8})\,\Delta T + 3(2.93 \times 10^{-12})\,\Delta T^2 + \frac{6.89 \times 10^{-7} + 2(8.6 \times 10^{-10})\,\Delta T}{\lambda - 0.23}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$