S-YGH52 by Ohara

$$n(\lambda) = \sqrt{3.12244 - 0.0156001\,\lambda^2 + 0.0238323\,\lambda^{-2} + 0.00072564\,\lambda^{-4} - 3.05638 \times 10^{-5}\,\lambda^{-6} + 2.08834 \times 10^{-6}\,\lambda^{-8}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.29 \times 10^{-6} + 2(1.57 \times 10^{-8})\,\Delta T + 3(4.79 \times 10^{-12})\,\Delta T^2 + \frac{6.43 \times 10^{-7} + 2(2.12 \times 10^{-10})\,\Delta T}{\lambda - 0.137}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$