% sellmeier equation which is wavelength depended.
%n(lambda)=sqrt(1+B1*lambda^2/(lambda^2-C1)+B2*lambda^2/(lambda^2-C2)+B3*lambda^2/(lambda^2-C3))
close all
clear all
% set coefficients
B1=0.6961663;
B2=0.4079426;
B3=0.8974794;
C1=0.0684043; % unit of 米m
C2=0.1162414; % unit of 米m
C3=9.896161; % unit of 米m
% set variables
syms lambda
n=sqrt(1+B1.*lambda.^2./(lambda.^2-C1^2)+B2.*lambda.^2./(lambda.^2-C2^2)+B3*lambda.^2./(lambda.^2-C3^2));
diff(n);
y=diff(n);
yy=diff(n,lambda,2);
lambda=0.5:0.1:1.6; %unit of 米m
% equation
n=sqrt(1+B1.*lambda.^2./(lambda.^2-C1^2)+B2.*lambda.^2./(lambda.^2-C2^2)+B3*lambda.^2./(lambda.^2-C3^2));
y=diff(n);
ng=n(2:end)-lambda(2:1:end).*y;
yy=diff('lambda',2);
% figures
figure(1)
plot(lambda,n)
axis([0.5 1.6 1.44 1.49])
xlabel('Wavelength (米m)')
ylabel('n')
%%%%%%%%%
figure(2)
plot(lambda(2:end),ng)
axis([0.5 1.6 1.44 1.49])
xlabel('Wavelength (米m)')
ylabel('ng')
figure(3)
plot(lambda(4:end),yy)
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