function n=nSi(lambda)
%n=nSi(lambda) lambda in um
%lambda from 0.6 to 1.6
n=sqrt(1 + 10.6684293*lambda^2/(lambda^2-0.301516485^2) + 0.003043475*lambda^2/(lambda^2-1.13475115^2) + 1.54133408*lambda^2/(lambda^2-1104.0^2) );