LAF50 by Hoya

$$n(\lambda) = \sqrt{2.51961 - 0.0121426\,\lambda^2 + 0.0166059\,\lambda^{-2} + 0.000334192\,\lambda^{-4} + 2.63135 \times 10^{-7}\,\lambda^{-6} + 6.78123 \times 10^{-7}\,\lambda^{-8}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.51 \times 10^{-6} + 2(9.19 \times 10^{-9})\,\Delta T + 3(-1.8 \times 10^{-11})\,\Delta T^2 + \frac{6.38 \times 10^{-7} + 2(8.25 \times 10^{-10})\,\Delta T}{\lambda - 0.135}\right] \Delta T = T - T_0, \quad T_0 = 23\,°\text{C}$$