H-ZK50 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.434311\,\lambda^2}{\lambda^2 - -0.00192253} + \frac{1.1056\,\lambda^2}{\lambda^2 - 0.0147271} + \frac{0.988776\,\lambda^2}{\lambda^2 - 110.412}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.24 \times 10^{-6} + 2(1.77 \times 10^{-8})\,\Delta T + 3(-2.57 \times 10^{-11})\,\Delta T^2 + \frac{5.34 \times 10^{-7} + 2(1.22 \times 10^{-10})\,\Delta T}{\lambda - 0.194}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$