H-K9LAGT by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.684743\,\lambda^2}{\lambda^2 - 0.0031354} + \frac{0.586772\,\lambda^2}{\lambda^2 - 0.0148101} + \frac{1.14804\,\lambda^2}{\lambda^2 - 116.584}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[9.03 \times 10^{-7} + 2(1.85 \times 10^{-8})\,\Delta T + 3(-2.98 \times 10^{-11})\,\Delta T^2 + \frac{4.55 \times 10^{-7} + 2(1 \times 10^{-10})\,\Delta T}{\lambda - 0.182}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$