function y=nAlO(lambda)
% refractive index of MgO lambda in um

% 
x=lambda;
% extrordinary
ne = sqrt( 1 + 1.5039759*x^2/(x^2-0.0740288^2) + 0.55069141*x^2/(x^2-0.1216529^2) + 6.5927379*x^2/(x^2-20.072248^2) );
% ordinary
no = sqrt( 1 + 1.4313493*x^2/(x^2-0.0726631^2) + 0.65054713*x^2/(x^2-0.1193242^2) + 5.3414021*x^2/(x^2-18.028251^2) );
y = (ne+no)/2;