lamda=780 * 10^-9;
d=17 * 10^-6;
theta_r=0 * pi/180;
theta_s=[];
dn=[];

 efficiency_s=100%
for m=1:5
    theta_s(m)=theta_r+acos(m/(m+1/2));
    dn(m)=1/d*(m+1/2)*lamda*(cos(theta_r)*cos(theta_s(m)))^.5;
end;


% efficiency_p=100%
%for m=1:5
%    theta_s(m)=theta_r+acos((m-1/2)/m);
%    dn(m)=1/d*m*lamda*(cos(theta1)*cos(theta2(m)))^.5;
%end;

theta_s *180/pi
dn