function n=nSiO2(lambda)
%n=nSiO2(lambda) lambda in um
%lambda from 0.6 to 1.6
%n=1.48891 -0.07862*lambda + 0.05411*lambda^2  -0.01418*lambda^3;  % my
% lamda 0.21 to 3.71 um
n = sqrt( 1 + 0.6961663*lambda^2/(lambda^2-0.0684043^2) + 0.4079426*lambda^2/(lambda^2-0.1162414^2) + 0.8974794*lambda^2/(lambda^2-9.896161^2));