H-QF50A by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.113568\,\lambda^2}{\lambda^2 - 0.0529496} + \frac{1.07619\,\lambda^2}{\lambda^2 - 114.277} + \frac{1.33131\,\lambda^2}{\lambda^2 - 0.00976687}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-1.15 \times 10^{-6} + 2(1.62 \times 10^{-8})\,\Delta T + 3(-5.36 \times 10^{-11})\,\Delta T^2 + \frac{7.72 \times 10^{-7} + 2(8.65 \times 10^{-10})\,\Delta T}{\lambda - 0.235}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$