S-NPH53 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.85485\,\lambda^2}{\lambda^2 - 0.0134621} + \frac{0.396194\,\lambda^2}{\lambda^2 - 0.0631945} + \frac{2.43512\,\lambda^2}{\lambda^2 - 170.865}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-4.85 \times 10^{-6} + 2(9.27 \times 10^{-9})\,\Delta T + 3(-2.86 \times 10^{-11})\,\Delta T^2 + \frac{9.57 \times 10^{-7} + 2(1.4 \times 10^{-9})\,\Delta T}{\lambda - 0.304}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$